JP2007290329A - Light receiving element, light emitting device, optical head, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light head equipped with a light detecting which highly accurately detecting the light quantity of the light head. <P>SOLUTION: The light head is equipped with a light-emitting element and the light detecting element detecting the light output from the light-emitting element. The light detecting element is so constituted of a transistor as to operate in an OFF region, and can take out only light current with no drain current of the light detecting element flowing, enabling highly accurate light detection to be executed efficiently. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light receiving element, a light emitting device, an optical head, and an image forming apparatus using the optical head.

  In recent years, image forming apparatuses such as fax machines and printers have been rapidly reduced in size and cost, and researches are being carried out for downsizing and cost reduction of elements constituting the apparatus.

  Examples of the image forming method of the image forming apparatus include a thermal recording method in which an image is formed by heat transfer using heat of a heating resistor, an ink jet method in which minute ink particles are applied to a printed matter, a method using light, and the like. It is done. Among these, the image forming apparatus using light charges the photoconductor by irradiating the photoconductor with light, and forms an image by transferring the toner adhering to the photoconductor to the print target such as recording paper by static electricity. ing. The light irradiated onto the photosensitive member is controlled by an exposure device called an optical head. The optical head includes a light source and a circuit for controlling driving of the light source, and a laser device or a light emitting diode is mainly used as the light source.

  In order to configure the optical head in a space-saving manner, it is necessary to reduce the size of the light source and the circuit that controls the driving of the light source. With the widespread use of thin film transistors, it is possible to easily reduce the size of the drive control circuit. On the other hand, downsizing of a laser device or a light-emitting diode as a light source is technically complicated. When this is performed, it is difficult to avoid an increase in manufacturing cost.

  An optical head using an electroluminescent element typified by an organic electroluminescent element or an inorganic electroluminescent element as a light source of the optical head as a means for reducing the size of the light source while suppressing an increase in manufacturing cost Has been proposed. Electroluminescence is a light emission (luminescence) phenomenon obtained by applying an electric field to a light emitter. Organic electroluminescent devices inject electrons and holes by applying a potential difference to the organic light-emitting layer that composes the devices, and use the energy generated by the combination of electrons and holes for the light emission phenomenon of organic molecules. It is a light emitting device to obtain. One inorganic electroluminescent element is obtained by replacing the light emitting layer constituting the element with an inorganic substance, and the light emission principle is the same as that of organic electroluminescent.

  The basic structure of an organic electroluminescent element or an inorganic electroluminescent element is a simple structure in which an organic or inorganic layer is sandwiched between an anode and a cathode. Forming electrodes and organic layers or inorganic layers into a thin film can be easily performed by processing techniques such as chemical vapor deposition, sputtering, and spin coating, so laser devices and light-emitting diodes can be used. As compared with the case of downsizing, the increase in manufacturing cost can be suppressed.

  Among electroluminescent elements, there are Patent Document 1 and Patent Document 2 as examples in which an organic electroluminescent element is used as a light source of an optical head. Patent Document 1 describes a light emitting / detecting element, and Patent Document 2 describes a configuration of an optical head on the basis of a pixel. The light emitting part of both patent documents is a laminated body composed of a light emitting layer composed of an organic electroluminescent element, a light detecting element used for light amount correction, and a thin film transistor serving as a circuit for controlling driving of the light emitting layer. Have the same configuration. Both of these patent documents are forms of outputting light from the drive control circuit side, and such an output form of light is called bottom emission.

JP 2002-144634 A JP 2002-178560 A

  The optical heads in Patent Document 1 and Patent Document 2 are composed of a laminate composed of layers of several kinds of materials, as shown in a schematic diagram of the structure in FIG. In this optical head, a base coat layer 101 is provided on a glass substrate 100 to form a drive circuit and an electroluminescent element serving as a light source and a drive circuit thereof. A light detection element is formed on a part of the base coat layer 101. 120 is disposed. Next, an interlayer insulating film 103 made of a silicon oxide film or the like is formed on the stacked body. In this state, a voltage is applied between the anode 111 and the cathode 113, and a potential difference is applied to the light emitting layer 112 to emit light.

  By the way, the thin film transistor that constitutes the photodetecting element faces the anode 111 of the electroluminescent element through the interlayer insulating film 103. However, the influence of the potential of the anode 111 is considerably affected. The thin film transistor operates as a gate electrode. However, since the drain current of this thin film transistor is as large as about 100 times the photocurrent generated by photoelectric conversion, it is extremely difficult to detect a minute photocurrent when the drain current is flowing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical head including a photodetecting element capable of detecting the light quantity of the optical head with high accuracy.
It is another object of the present invention to provide a light receiving element and a light emitting device that can perform highly accurate light detection.

The present invention is an optical head comprising a light emitting element and a light detecting element for detecting light output from the light emitting element, wherein the light detecting element is constituted by a transistor and operates in an OFF region. It is structured.
With this configuration, since only the photocurrent can be taken out in a state where the drain current of the photodetection element does not flow, it becomes possible to perform photodetection efficiently and accurately.

According to the present invention, in the above-described optical head, an electroluminescent element as a light source formed so that a light emitting layer is sandwiched between the first electrode and the second electrode, and output from the electroluminescent element And a photodetecting element having a photoelectric conversion layer for detecting light, and the photodetecting element has a first electrode positioned on the photodetecting element side of the electroluminescent element as a gate electrode. Including those that are thin film transistors.
With this configuration, the first electrode of the electroluminescent element acts as the gate electrode of the thin film transistor that constitutes the light detection element, and the thin film transistor can be operated in the OFF state by adjusting the gate potential. Become.

According to the present invention, in the above optical head, the first electrode located on the photodetecting element side of the electroluminescent element covers the entire photoelectric conversion portion of the photodetecting element via an insulating film. Includes configured ones.
With this configuration, the gate electric field generated by the first electrode can be applied to the entire photoelectric conversion unit, and controllability can be improved.

According to the present invention, in the optical head, the thin film transistor includes a thin film transistor in which a doping concentration of a channel region is adjusted so that a threshold voltage is 0 V or less.
With this configuration, the threshold voltage can be adjusted very efficiently only by adjusting the doping concentration in the semiconductor layer such as the polycrystalline silicon layer that constitutes the channel region, and the thin film transistor that constitutes the photodetecting element is turned off. It becomes possible to operate.

According to the present invention, in the above optical head, the thin film transistor is connected to a drive circuit for a light detection element through a level shift circuit.
With this configuration, the gate potential can be used while being shifted from the potential of the first electrode of the electroluminescent element, which makes it possible to operate the thin film transistor constituting the photodetecting element in the OFF state. .

According to the present invention, in the optical head, the level shift circuit is a transistor switch network connected between a gate and a drain of the thin film transistor.
With this configuration, the gate potential can be used by shifting the potential of the first electrode of the electroluminescent element by a desired potential, thereby operating the thin film transistor constituting the photodetecting element in the OFF state. Is possible.

According to the present invention, in the above optical head, the level shift circuit is a circuit integrated on a substrate on which the light emitting element is formed.
With this configuration, a voltage drop due to wiring routing can be reduced, and a light amount correction circuit having a small size and a high operation speed can be configured, and an optical head with high controllability can be provided.

  According to the present invention, in the optical head, one photodetecting element is arranged for one light emitting region. The optical head is configured by arranging a plurality of light emitting areas in a row. By arranging one light detection element corresponding to one light emitting area, it becomes possible to simultaneously measure the light output from the plurality of light emitting areas, and measure the light quantity of the entire optical head. It can be performed at high speed.

  In addition, the present invention includes the optical head using an organic electroluminescent element as a light source. Since the organic electroluminescent element can obtain high luminance with low power, it is possible to provide an optical head excellent in terms of power consumption.

  In addition, the present invention includes the optical head using an inorganic electroluminescent element as a light source. Inorganic electroluminescent elements can be manufactured by screen printing, so there are few defects during production, and no equipment such as a clean room is required, so that the mass production is high. Therefore, it is possible to provide an optical head that is excellent in manufacturing cost.

  Further, the present invention includes the optical head in which a detection element for correcting the amount of light is arranged. If a light detection element for the purpose of light quantity correction is arranged, an electrical signal suitable for light quantity correction can be fed back from the light detection element to the electroluminescent element, so that the light quantity is appropriately controlled. Is possible.

  In addition, the present invention includes the optical head in which a light detecting element for correcting the light emission time is arranged. If a light detection element for the purpose of correcting the light emission time is arranged, an electrical signal suitable for correction of the light emission time can be fed back from the light detection element to the electroluminescent element. It becomes possible to control appropriately.

  According to the present invention, in the optical head, the light detection element is formed of the same layer as a thin film transistor serving as a drive circuit for the electroluminescent element. By forming the thin film transistor and the photodetecting element from the same layer using a processing method such as etching, the manufacturing process of the optical head can be simplified and the cost required for manufacturing can be reduced. In particular, the process of forming a polycrystalline silicon layer on a glass substrate goes through a high-temperature process, but it is possible to obtain highly controllable and highly reliable characteristics by a single adjustment.

The present invention also provides an image forming apparatus including the above-described optical head. By mounting an optical head having a uniform light emission distribution, an image forming apparatus excellent in terms of durability and image quality can be obtained.
Here, the first electrode formed on the light detection element side of the electroluminescent element is usually an anode, and is made of a light-transmitting electrode material.

  In addition, the light receiving element of the present invention is configured by a transistor and configured to operate in the OFF region.

  The light receiving element of the present invention is a light receiving element composed of a thin film transistor having at least a gate, a source, and a drain, and controls the potential applied to the gate so that no current flows through the drain. The element is in an active state.

  Moreover, the light-emitting device of this invention is equipped with the said light receiving element.

  In the configuration of the optical head of the present invention, the thin film transistor that constitutes the photodetecting element is operated in the OFF region, so that a photocurrent that is a minute current can be efficiently detected, and highly accurate and reliable light quantity detection can be performed. It becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a configuration of an optical head provided in an exposure unit of the image forming apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a top view of the main part thereof, and shows electroluminescence as a light source. It is sectional drawing of the cent element 110 and its periphery, and the relationship of the vertical arrangement | positioning of each layer which comprises the photon detection element 120 is shown. The optical head is configured such that the threshold voltage is higher than the potential of the first electrode by adjusting the impurity concentration of the channel layer 121i of the thin film transistor (TFT) that constitutes the photodetecting element 120. The light detection element 120 is configured to operate in the OFF region. As shown in FIG. 2, the electroluminescent element 110 is stacked on the upper layer of the thin film transistor constituting the photodetecting element 120 formed on the substrate, and is located on the photodetecting element 120 side of the electroluminescent element 110. Since the anode as the first electrode 111 is formed so as to cover the entire photoelectric conversion part of the light detection element 120, the first electrode of the electroluminescent element faces the whole photoelectric conversion part of the light detection element. The light detection element 120 is adjusted so that the threshold voltage of the light detection element becomes higher than the potential of the first electrode 111, and the light detection element 120 is configured to operate in the OFF region. To do.

  With this configuration, since only the photocurrent can be taken out in a state where the drain current of the photodetection element does not flow, it is possible to efficiently and highly accurately perform photodetection.

  In addition, since the first electrode is configured to cover the entire photoelectric conversion portion of the photodetecting element, the first electrode effectively acts as the gate electrode of the photodetecting element and has a stable potential. Control of the channel characteristics of the light detection element is ensured by the potential of the electrodes, and an optical head having stable light emission characteristics can be provided. In addition, a cathode serving as the second electrode 115 provided to face the first electrode with the light emitting layer interposed therebetween is formed on the upper layer side.

Further, this optical head, the outer edge of the island region 121 of the polycrystalline silicon constituting the element region of the photodetector element 120 is formed such that the outside of the light emission region A _LE of the electroluminescent element. Thus, here namely the island region 121 of the light detecting element 120 result in the formation of the step, formed to the outer edge of the element region A _R is the outside of the light emission region A _LE of the electroluminescent element, There is no step in the region corresponding to the light emitting region of the electroluminescent element, and the base of the light emitting layer forms a flat surface. Therefore, in the light emitting region that is the effective region of the optical head, the light emitting layer of the optical head is Uniformly formed.

As shown in FIG. 1, the optical head of the present embodiment sequentially includes a photodetecting element 120 and an electroluminescent element 110 on a glass substrate 100 on which a base coat layer 101 for planarization is formed. A thin film transistor as a switching transistor 130 for driving the electroluminescent element while correcting the driving current or the driving time according to the output of the light detecting element 120 and a chip IC connected to the thin film transistor The drive circuit (140) is mounted. The photodetector element 120 is the source region 121S by doping the desired concentration at a channel region formed of the island region A _R of polycrystalline silicon layer formed on the base coat layer 101 surface of a strip-shaped i layer, a drain A source made of a polycrystalline silicon layer formed through a through hole so as to penetrate the first insulating film 122 and the second insulating film 123 made of a silicon oxide film formed in the region 121D and over the region 121D. And drain electrodes 125S and 125D. Further, an electroluminescent element 110 is formed on the upper layer through a silicon nitride film as a protective layer 124, and ITO (indium tin oxide) 111 serving as an anode, a protective film 124, a light emitting layer 112, a cathode Each layer is formed in the order of 113.

On the other hand, each layer constituting the photodetecting element 120 is formed in the same manufacturing process as the selection transistor 130 as a driving transistor. In other words, the source regions 132S and 132D are formed in the same process as the semiconductor island of the photodetecting element across the channel region 131C, the source / drain electrodes 134S and 134D that are in contact therewith are stacked, and the gate electrode 133 and the selection transistor The thin film transistor is configured.
Each of these layers is formed through a usual semiconductor process such as formation of a semiconductor thin film by a CVD method, patterning by photolithography, impurity ion implantation, and formation of an insulating film.

  Here, the glass substrate 100 is a single plate of colorless and transparent glass. Examples of the glass substrate 100 include transparent or translucent soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz glass, and other inorganic oxide glasses, inorganic fluorides Inorganic glass such as glass can be used.

Other materials can be used as the glass substrate 100, for example, transparent or translucent polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polyether sulfone, polyvinyl fluoride, polypropylene, polyethylene, polyacrylate, amorphous polyolefin. Polymer films using polymer materials such as fluororesin polysiloxane and polysilane, or transparent or translucent chalcogenoid glasses such as As ₂ S ₃ , As ₄₀ S ₁₀ , S ₄₀ Ge ₁₀ , ZnO, Nb _When extracting light emitted from a material such as ₂ O, Ta ₂ O ₅ , SiO, Si ₃ N ₄ , HfO ₂ , TiO _2, or other metal oxides and nitrides, or a light emitting region without passing through a substrate For opaque silicon, germanium, silicon carbide, gallium A laminated substrate obtained by laminating a plurality of substrate materials, which can be appropriately selected from semiconductor materials such as silicon and gallium nitride, or the above-mentioned transparent substrate materials containing pigments, metal materials whose surfaces are insulated, etc. Can also be used.

  On the surface of the substrate such as the glass substrate 100 or inside the substrate, a circuit composed of a resistor, a capacitor, an inductor, a diode, a transistor and the like for driving the electroluminescent device 110 is integrated as described later. Also good.

  Further, depending on the application, a material that transmits only a specific wavelength, a material that converts light into a specific wavelength having a light-light conversion function, or the like may be used. The substrate is preferably insulative, but is not particularly limited, and may have conductivity depending on a range or use that does not hinder driving of the electroluminescent element 110.

A base coat layer 101 is formed on the glass substrate 100. The base coat layer 101 is composed of, for example, a first layer made of SiN and a _second layer made of SiO ₂ . Each layer of SiN and SiO ₂ can be formed by vapor deposition or the like, but is preferably formed by sputtering.

On the base coat layer 101, the selection transistor 130 of the electroluminescent element 110 and the light detection element 120 are formed using a polycrystalline silicon layer formed in the same process. The driving circuit for the electroluminescent element 110 is composed of circuit elements such as a resistor, a capacitor, an inductor, a diode, and a transistor. In consideration of downsizing of the optical head, it is desirable to use a thin film transistor. In the first embodiment, the light detection element 120 is positioned between the electroluminescent element 110 including the light emitting layer 112 and the glass substrate 100 that is the light output surface as is apparent from FIG. element region _{a R} of the detecting element 110 is larger than the light emission region _{a LE.} Further, since the light emission region A _LE exists inside the light detection element 120, a material that does not transmit light cannot be used for the light detection element 120. Therefore, in order not to disturb the light output from the light emitting layer 112, the photodetecting element 120 must be made of a transparent material. As a material of the photodetecting element 120 having transparency, it is desirable to select, for example, polycrystalline silicon.

In Embodiment 1, after forming a uniform semiconductor layer over the base coat layer 101, the selection transistor 130 and the photodetector element 120 are formed from the same layer by etching the semiconductor layer. . The process of forming the selection transistor 130 and the metal layer of the photodetecting element 120 independent from each other in the form of islands from the same metal layer is advantageous in reducing the number of manufacturing steps and the manufacturing cost. Note in the photodetector element 120, the element region A _R for receiving the light output from the light emission region A _LE is the surface of the polycrystalline silicon or amorphous silicon that is configured in an island shape having a light-detecting element 120.

On the selection transistor 130 and the photodetecting element 120 for applying an electric field to the light emitting layer 112 of the electroluminescent element 110, the first insulating layer 122 and the second insulating layer 123 made of this silicon oxide film are protected. The layer 124 acts as a gate insulating film between the layer 111 and the ITO 111 serving as the anode of the electroluminescent element, and the drop width from the ITO potential is determined by the voltage drop due to the film thickness. The first insulating layer 122, the second insulating layer 123, and the protective layer 124 constituting the gate insulating film 3 are made of, for example, SiO _{2 and} are formed by vapor deposition, sputtering, or the like.

  A gate electrode 133 is formed on the surface of the first insulating layer 122 as a gate insulating film directly above the select transistor 130. For example, Cr is used as the material of the gate electrode 133. The gate electrode 133 is formed by vapor deposition, sputtering, or the like.

  A second insulating layer 123 is formed on the substrate surface on which the gate electrode 133 is formed. The second insulating layer 123 is formed over the entire surface of the stacked body that has been formed so far. The second insulating layer 123 is made of, for example, SiN or the like, and is formed by a vapor deposition method, a sputtering method, or the like.

  On the second insulating layer, a drain electrode 125D as a light detection element output electrode, a source electrode 125S as a light detection element ground electrode, a source electrode 134S, and a drain electrode 134D are formed. The drain electrode 125D as the light detection element output electrode and the source electrode 125S as the light detection element ground electrode are connected to the source / drain regions 121S and 121D of the light detection element 120, and an electric signal output from the light detection element 120. Transmission and grounding of the light detection element 120. The source electrode 134S and the drain electrode 134D are connected to the source / drain regions 132S and 132D of the selection transistor 130, and the gate electrode 133 described above is applied with a predetermined potential difference between the source electrode 134S and the drain electrode 134D. By applying a predetermined potential, the selection transistor 130 has a function as a switching element, and operates as a circuit for driving the electroluminescent element 110 as a light emitting element. For example, a metal such as Cr is used as the material of the drain electrode 125D as the light detection element output electrode, the source electrode 125S as the light detection element ground electrode, the source electrode 134S, and the drain electrode 134D. As shown in FIG. 1, the drain electrode 125 </ b> D as the light detection element output electrode and the light detection element ground electrode pass through the first insulating film 122 and the second insulating layer 123 and are connected to the end of the light detection element 120. Similarly, the source electrode 134S and the drain electrode 134D penetrate the first insulating film 122 and the second insulating layer 123 and are connected to the end portion of the selection transistor 130. Therefore, prior to the formation of the drain electrode 125D as the light detection element output electrode, the source electrode 125S as the light detection element ground electrode, the source electrode 134S, and the drain electrode 134D, the first insulating film 122 and the second insulating layer 123 are formed. On the other hand, the drain electrode 125D as the light detection element output electrode and the source electrode 125S as the light detection element ground electrode and the through hole for connecting the light detection element 120, the source electrode 134S and the drain electrode 134D, and the selection transistor 130 are connected. It is necessary to provide a through hole for this purpose. The through holes are formed on the surface of the photodetecting element 120 and the surface of the selection transistor 130, that is, the contact surface between the photodetecting element 120 and the drain electrode 125D serving as the photodetecting element output electrode and the source electrode 125S serving as the photodetecting element ground electrode. 130 and has a depth until the contact surface of the source electrode 134S and the drain electrode 134D is exposed, and is provided by etching or the like directly above the ends of the photodetecting element 120 and the selection transistor 130. For the etching, a halogen-based etching gas is used. Etching gas is introduced and patterned by photolithography while the surface is covered with a resist pattern having openings. (Through holes are opened in the first insulating film 122 and the second insulating layer 123.) At this time, an etching gas that does not cause a chemical reaction with the materials constituting the light detection element 120 and the selection transistor 130 is selected. To do. Processing to expose the contact surface between the source electrode 125S as the photodetection element output electrode and the source electrode 125S as the photodetection element ground electrode and the photodetection element 120 and the contact surface between the source electrode 134S and the drain electrode 134D and the selection transistor 130 is completed. After that, the drain electrode 125D as the light detection element output electrode, the source electrode 125S as the light detection element ground electrode, the source electrode 134S, and the drain electrode 134D are formed. The source electrode 134S and the drain electrode 134D are formed by forming a metal layer serving as a sensor electrode on the surface of the second insulating layer 123, the surface of the through hole and the both sensor electrodes, the surface of the light detection element 120, and the contact surface of the selection transistor 130. After the uniform formation on the surface, the metal layer is etched using a resist pattern formed by photolithography as a mask, and the uniform metal layer is used as a drain electrode 125D as a light detection element output electrode, and the light detection element grounding. It is obtained by dividing the source electrode 125S, the source electrode 134S, and the drain electrode 134D as electrodes.

  After the drain electrode 125D as the light detection element output electrode, the source electrode 125S as the light detection element ground electrode, the source electrode 134S, and the drain electrode 134D are formed, the protective film 124 is formed. The protective film 124 is made of, for example, SiN and is formed by vapor deposition, sputtering, or the like.

An anode 111 is formed on the protective film 124. The anode 111 is made of, for example, ITO (indium tin oxide). As the constituent material of the anode 111, IZO (zinc-doped indium oxide), ATO (Sb-doped SnO ₂ ), AZO (Al-doped ZnO), ZnO, SnO ₂ , In ₂ O _{3 and the} like are used in addition to ITO. be able to. As shown in FIG. 1, the anode 111 is formed on the surface of the protective film 124 that is directly above the photodetecting element 120. As shown in FIG. 1, the anode 111 penetrates the protective film 124 and is connected to the end of the drain electrode 134D. Therefore, before forming the anode 111, it is necessary to provide a through hole for connecting the anode 111 and the drain electrode 134D to the protective film 124. This through hole has a depth until the surface of the drain electrode 134D, that is, the contact surface between the drain electrode 134D and the anode 111 is exposed, and is provided directly above the end of the drain electrode 134D by etching or the like. It is done. After this etching process is performed, a layer of the anode 111 is formed. The anode 111 can be formed by vapor deposition or the like, but is preferably formed by sputtering. In the first embodiment, ITO is used as the anode 111.

After the anode 111 is formed, a silicon nitride film 114 as a pixel restricting portion is formed. As a material of the silicon nitride film 114 as the pixel restricting portion, a material having high insulating properties, strong against dielectric breakdown, good film forming properties and high patterning properties is desirable. In the first embodiment, silicon nitride or aluminum nitride is used as a material constituting the silicon nitride film 114 as the pixel restricting portion. A silicon nitride film 114 serving as a pixel restricting portion is provided between a light emitting layer 112 and an anode 111, which will be described later, and insulates the light emitting layer 112 outside the light emitting area _ALE from the anode 111. The place where light is emitted is regulated. Therefore, the region of the light emitting layer 112 that overlaps the silicon nitride film 114 serving as the pixel restricting portion is a non-light emitting region, and the region that does not overlap the silicon nitride film 114 serving as the pixel restricting portion is the light emitting region A _LE . Silicon nitride film as the pixel restricting portion 114 restricts so that the light emission region _{A LE} of the light emitting layer 112 is smaller than the element region _{A R} of the light-detecting element 120, and the light emission region _{A LE} photodetection element 120 configured to be placed inside the element region a _R.

After the silicon nitride film 114 as the pixel restricting portion is formed, the light emitting layer 112 is formed. The light emitting layer 112 is formed of an inorganic light emitting material, or a high molecular weight or low molecular weight organic light emitting material described in detail below. As the inorganic light emitting material for forming the light emitting layer 112, titanium / potassium phosphate, barium / boron oxide, lithium / boron oxide, or the like can be used. As the polymer organic light emitting material constituting the light emitting layer 112, a material having fluorescence or phosphorescence characteristics in the visible region and good film forming property is desirable. For example, polymers such as polyparaphenylene vinylene (PPV) and polyfluorene are used. A light emitting material or the like can be used. In addition to Alq ₃ and Be-benzoquinolinol (BeBq ₂ ), low molecular organic light emitting materials constituting the light emitting layer 112 include 2,5-bis (5,7-di-t-pentyl-2). -Benzoxazolyl) -1,3,4-thiadiazole, 4,4'-bis (5,7-benzyl-2-benzoxazolyl) stilbene, 4,4'-bis [5,7-di- (2-Methyl-2-butyl) -2-benzoxazolyl] stilbene, 2,5-bis (5,7-di-t-benzyl-2-benzoxazolyl) thiophine, 2,5-bis ( [5-α, α-dimethylbenzyl] -2-benzoxazolyl) thiophene, 2,5-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl]- 3,4-diphenylthiophene, 2,5-bis (5-methyl-2 -Benzoxazolyl) thiophene, 4,4'-bis (2-benzoxazolyl) biphenyl, 5-methyl-2- [2- [4- (5-methyl-2-benzoxazolyl) phenyl] Benzoxazoles such as vinyl] benzoxazolyl, 2- [2- (4-chlorophenyl) vinyl] naphtho [1,2-d] oxazole, 2,2 ′-(p-phenylenedivinylene) -bisbenzothiazole Such as benzothiazole, 2- [2- [4- (2-benzimidazolyl) phenyl] vinyl] benzimidazole, 2- [2- (4-carboxyphenyl) vinyl] benzimidazole, etc. Whitening agent, tris (8-quinolinol) aluminum, bis (8-quinolinol) magnesium, bis (benzo [f] -8-quino Nor) zinc, bis (2-methyl-8-quinolinolate) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8- Quinolinol) gallium, bis (5-chloro-8-quinolinol) calcium, poly [zinc-bis (8-hydroxy-5-quinolinyl) methane] and other 8-hydroxyquinoline metal complexes and dilithium ependridione Metal chelated oxinoid compounds, 1,4-bis (2-methylstyryl) benzene, 1,4- (3-methylstyryl) benzene, 1,4-bis (4-methylstyryl) benzene, distyrylbenzene, 1 , 4-Bis (2-ethylstyryl) benzene, 1,4-bis (3-ethyl) Styryl) benzene, 1,4-bis (2-methylstyryl) 2-methylbenzene and other styrylbenzene compounds, 2,5-bis (4-methylstyryl) pyrazine, 2,5-bis (4-ethylstyryl) ) Pyrazine, 2,5-bis [2- (1-naphthyl) vinyl] pyrazine, 2,5-bis (4-methoxystyryl) pyrazine, 2,5-bis [2- (4-biphenyl) vinyl] pyrazine, Distil pyrazine derivatives such as 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine, naphthalimide derivatives, perylene derivatives, oxadiazole derivatives, aldazine derivatives, cyclopentadiene derivatives, styrylamine Derivatives, coumarin derivatives, aromatic dimethylidin derivatives and the like are used. Furthermore, anthracene, salicylate, pyrene, coronene and the like are also used. Alternatively, a phosphorescent material such as fac-tris (2-phenylpyridine) iridium can be used. The light emitting layer 112 made of a high molecular weight material or a low molecular weight material can be obtained by forming a layer in which a material is dissolved in a solvent such as toluene or xylene by spin coating and volatilizing the solvent in the solution. .

  In Embodiment 1, the light-emitting layer 112 is described as a single layer for convenience, but the light-emitting layer 112 is sequentially formed from the anode 111 side with the hole transport layer / electron blocking layer / the above-described organic light-emitting material layer (both The light-emitting layer 112 may have a two-layer structure of an electron transport layer / organic light-emitting material layer (both not shown) in order from the cathode 113 side, or may be positive in order from the anode 111 side. 2 layer structure of hole transport layer / organic light emitting material layer (both not shown), or hole injection layer / hole transport layer / electron blocking layer / organic light emitting material layer / hole blocking layer / A seven-layer structure (both not shown) such as an electron transport layer / electron injection layer may be used. Alternatively, the light emitting layer 112 may have a single layer structure made of only the organic light emitting material described above. As described above, the light-emitting layer 112 in Embodiment Mode 1 includes a case where the light-emitting layer 112 has a multilayer structure including functional layers such as a hole transport layer, an electron block layer, and an electron transport layer. The same applies to other embodiments described later.

The hole transport layer in the functional layer described above preferably has a high hole mobility, is transparent and has good film-forming properties, and besides TPD, porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine, titanium phthalocyanine oxide, etc. Or 1,1-bis {4- (di-P-tolylamino) phenyl} cyclohexane, 4,4 ′,
4 ″ -trimethyltriphenylamine, N, N, N ′, N′-tetrakis (P-tolyl) -P-phenylenediamine, 1- (N, N-di-P-tolylamino) naphthalene, 4,4 ′
-Bis (dimethylamino) -2-2'-dimethyltriphenylmethane, N, N, N ', N'
Aromatic compounds such as tetraphenyl-4,4′-diaminobiphenyl, N, N′-diphenyl-N, N′-di-m-tolyl-4,4′-diaminobiphenyl, N-phenylcarbazole Tertiary amines, stilbene compounds such as 4-di-P-tolylaminostilbene, 4- (di-P-tolylamino) -4 ′-[4- (di-P-tolylamino) styryl] stilbene,
Triazole derivatives, oxazizazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, annealed amine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, Fluorenone derivatives, hydrazone derivatives, silazane derivatives, polysilane aniline copolymers, polymer oligomers, styrylamine compounds, aromatic dimethylidin compounds, poly-3,4 ethylene dioxythiophene (PEDOT) ), Organic materials such as polythiophene derivatives such as tetradihexylfluorenylbiphenyl (TFB) or poly-3-methylthiophene (PMeT) are used. Further, a polymer-dispersed hole transport layer in which an organic material for a low-molecular hole transport layer is dispersed in a polymer such as polycarbonate is also used. There is also a _{MoO 3, V 2 O 5,} WO 3, TiO 2, SiO, also be an inorganic oxide such as MgO. These hole transport materials can also be used as an electron block material.

  Examples of the electron transport layer in the functional layer described above include oxadiazole derivatives such as 1,3-bis (4-tert-butylphenyl-1,3,4-oxadiazolyl) phenylene (OXD-7), and anthraquinodimethane derivatives. , Diphenylquinone derivatives, polymer materials composed of silole derivatives, bis (2-methyl-8-quinolinolate)-(para-phenylphenolate) aluminum (BAlq), bathopproin (BCP), and the like are used. Moreover, the material which can comprise these electron carrying layers can also be used as a hole block material.

  After the light emitting layer 112 is formed, the cathode 113 is formed. The cathode 113 can be obtained, for example, by forming a layer of metal such as Al by vapor deposition or the like. As the cathode 113 of the organic electroluminescent element 110, a metal or alloy having a low work function, for example, a metal such as Ag, Al, In, Mg, Ti, a Mg alloy such as Mg-Ag alloy, Mg-In alloy, An Al alloy such as an Al—Li alloy, an Al—Sr alloy, an Al—Ba alloy, or the like is used. Alternatively, a first electrode layer in contact with a metal such as Ba, Ca, Mg, Li, or Cs, or an organic material layer made of a fluoride or oxide of these metals such as LiF or CaO, and Ag formed thereon It is also possible to use a laminated structure of a metal made of a second electrode made of a metal material such as Al, Mg, or In.

  The optical head of the first embodiment as shown in FIG. 1 employs a method of outputting light from the selection transistor 130 side of the organic electroluminescent element, and the structure of such an organic electroluminescent element is as follows. This is called bottom emission. Since the bottom emission structure extracts light from the glass substrate 100 side, the light detection element 120 needs to be made of a highly transparent material, for example, polycrystalline silicon (polysilicon), as described above. The photo-detecting element 120 made of polycrystalline silicon has a problem that the photocurrent generation capability is lower than that made of amorphous silicon, but for example, a capacitor (not shown) is made organic. The problem can be solved by providing a processing circuit that is provided in the vicinity of the electroluminescent element 110 and stores a charge based on the current output from the photodetecting element 120 in a capacitor for a predetermined period of time and then performs voltage conversion. it can. In the case of the bottom emission structure, since the electrode (anode) on the side from which light is extracted can be easily made transparent, there is an advantage that manufacture is simplified.

  FIG. 2 is a configuration plan view showing the configuration in the vicinity of the light detection element of the optical head in the first embodiment of the present invention.

As shown in FIG. 2, the optical head according to the first embodiment is configured by arranging a plurality of electroluminescent elements 110 in the main scanning direction (direction of element rows), and includes one light emitting area (light emitting area). A light detection element 120 is arranged corresponding to (A _LE ). By setting it as such a structure, the light-emission light quantity of each organic electroluminescent element 110 can be measured independently with the photon detection element 120. FIG. That is, it becomes possible to measure the light quantity of the plurality of organic electroluminescent elements 110 at the same time, and the measurement time can be greatly shortened.

In FIG. 2, the photodetecting element 120, the drain electrode 125 </ b> D as the photodetecting element output electrode, the source electrode 125 </ b> S as the photodetecting element ground electrode, the light emitting area A _LE , the element area A _R , and the ITO serving as the anode of the light emitting layer 112. (indium tin oxide) 111, interrelationship of the contact hole _{H D} and the drain electrode 134D are shown. The light detection element 120 is connected to a drain electrode 125D as a light detection element output electrode and a source electrode 125S as a light detection element ground electrode. The drain electrode 125D as the light detection element output electrode is an electrode that transmits an electric signal output from the light detection element 120 for light correction to a correction circuit (not shown). A feedback signal generated by the correction circuit is determined based on the electrical signal, and processing necessary for light correction is performed based on the feedback signal. In the first embodiment, the light emission amount of each electroluminescent element 110 is corrected based on this feedback signal, and the current value for driving each electroluminescent element 110 is controlled by a driver circuit (not shown). Yes. As described above, in Embodiment 1, the amount of emitted light is controlled based on the output of the light detection element 120, but so-called PWM control is performed to control the driving time of each electroluminescent element 110 based on the feedback signal. You may comprise as follows.

  The source electrode 125S as the light detection element ground electrode is an electrode for grounding the light detection element 120. ITO (indium tin oxide) 111 which is an anode of the electroluminescent element 110 as a light emitting element is connected to the drain electrode 134D of the selection transistor 130, and the electroluminescent element 110 is connected via the drain electrode 134D. It is controlled by the selection transistor 130.

As shown in FIG. 1 and FIG. 2, the optical head of the first embodiment is arranged with photodetecting elements 120 formed of island-shaped polycrystalline silicon (polysilicon) arranged in a row in the main scanning direction. each organic electroluminescent device 110 having a light emission region a _{LE is} limited large element region a _R than the light emission region a _LE at the bottom of the light-emitting layer 112 by the silicon nitride film 114 serving as a pixel restricting portion It can be seen that the light detection element 120 is arranged. By making the element region A _R (island-like portion of polycrystalline silicon formed in an island shape) of the light detection element 120 larger than the light emission region A _LE, a local change in the layer thickness of the light-emitting layer 112 is suppressed. Thus, the bias of the current flowing through the light emitting layer 112 can be suppressed. Therefore, it is possible to manufacture an optical head that achieves a uniform light emission distribution and improved lifetime.

Furthermore, since the element region A _R of the light-detecting element 120 configured in an island shape to be mounted on the optical head of the first embodiment larger than the light emitting area or the light emission region A _LE, the output light from the light-emitting layer It can be efficiently converted into an electrical signal used for light correction.

  Next, a light amount correction circuit used in the optical head of the present invention will be described. As shown in an equivalent circuit in FIG. 3, the light amount correction circuit is formed by being integrated on the glass substrate 100 described above so as to be connected to the driving IC 150 having a charge amplifier and the input terminal of the driving IC 150. The correction circuit unit C includes the switching transistor 130, the photodetection element 120, and the capacitor 140 that is connected in parallel to the photodetection element and charges the output current of the photodetection element. Composed. Although not shown in the cross-sectional view of FIG. 1, the capacitor 140 is a conductive film formed in the same process so as to be connected to the source electrode 134S and the drain electrode 134D of the photodetecting element. It is formed by sandwiching the second insulating films 122 and 123.

Here, the photodetection element is photoelectrically converted in the polycrystalline silicon layer 121i by the light from the electroluminescent element, and the current flowing from the source region to the drain region is taken out as a photocurrent. Is detected. However, as described above, the ITO electrode 111 that is the anode of the electroluminescent element 110 is used as a gate electrode, and an electric field is applied to the polycrystalline silicon layer 121i that is the channel region of the photodetecting element by the potential of the gate electrode. As a result, the drain current _ID flows. Since the drain current _ID is added to the photoelectric conversion current, the photoelectric conversion current output from the drain electrode 125D as a sensor output to the correction circuit unit C (see FIG. 3) is converted into the actual photoelectric conversion current. The current _ID is added. For this reason, there exists a problem that the light quantity detection accuracy falls. The result of measuring the relationship between the gate voltage Vg and the drain current ID is shown by a solid line in FIG. As is apparent from this figure, it is desirable to use the thin film transistor in a region where the drain current is 0, that is, a region where the transistor operation is turned off (OFF region).

Desirably, the thin film transistor can be used in the OFF region by making the gate potential shift in the minus direction as shown by the broken line in FIG. 4, and the dark current can be almost eliminated.
Further, the channel is controlled by the gate electric field when the entire polycrystalline silicon layer 121i, which is the channel region of the thin film transistor that constitutes the photodetecting element, is completely covered with the ITO electrode that is the anode of the electroluminescent element. It is more effective.
In the present invention, since it is extremely important to detect the output of the light detection element with high accuracy, it is important to detect the thin film transistor constituting the light detection element in the OFF state.
In addition, the state in which the entire polycrystalline silicon layer that becomes the channel region 121i of the thin film transistor that constitutes the photodetecting element is completely covered with the ITO electrode that is the anode of the electroluminescent element controls the channel by the gate electric field. It is more effective.

The output of the photodetecting element is obtained by taking out a current charged in the capacitor 140 for a desired number of lighting times by switching the selection transistor 130 as shown in the timing charts of FIGS. Highly accurate light quantity detection is possible. Here, FIG. 5A is a diagram showing the state of charge, FIG. 5B is a diagram showing the operation of the selection transistor, and FIG. 5C is a diagram showing the lighting timing of the electroluminescent element. 5D is a diagram showing the potential of the capacitive element 140, FIG. 5E is a diagram showing the output voltage of the operational amplifier, FIG. 5F is a diagram showing the data read operation, and FIG. ) Is a diagram showing a light amount detection signal.
In addition, since it is very important to detect the output of the light detection element with high accuracy, it is important to detect the thin film transistor constituting the light detection element in an OFF state. Therefore, a desired detection accuracy can be obtained by adjusting the gate potential of the light detection element.

First, the selection transistor 130 is turned on, and the capacitor 140 is charged with the initial voltage V _ref (S1: reset step).
When the selection transistor 130 is turned off, the charge charged in the capacitor element 140 is reduced by the photocurrent flowing through the light detection element 120 (S2: lighting step).
In this state, the switching transistor 153 of the charge amplifier 150 is turned off, and the charge amplifier is in a measurable state (S3: measurement start step).
Then, the selection transistor 130 is turned on, and the charge lost in the capacitor element 140 is supplied from the capacitor element 152 of the charge amplifier. As a result, the output voltage V _r0 of the operational amplifier of the charge amplifier 150 increases. Even during this period, the photocurrent of the photodetection element flows and _Vr0 rises, but the influence is almost negligible because it is a very short current (S4: charge transfer step).
Then, the selection transistor 130 is turned off and V _r0 is determined. This voltage is taken in by the AD converter, the photometric operation is finished, and the output D0 of the AD converter is determined (S5: read step).

As a modification of the first embodiment of the present invention, as shown in FIG. 6, a light shielding film 104 made of a chromium thin film is formed on the back surface side of the glass substrate, and the second light emitting area A _LE1 is defined by this opening. is doing. By forming the second light emitting region _ALE1 smaller than the opening of the silicon nitride film 114 as the pixel defining portion described in the first embodiment, a step portion of the light emitting layer caused by the silicon nitride film 114 is formed. It can be excluded from the light emission region, and the light emitting layer can be made more uniform. Other configurations are the same as those in the first embodiment.

In the optical head, the anode as the first electrode 111 of the electroluminescent element may be formed so as to have the same width as the channel region 121i.
With this configuration, the gate electric field is applied with high efficiency, and the light emitting layer itself of the electroluminescent element is formed on a flat surface. It can be avoided. At this time, since the light emitting region does not become a light emitting region on the source / drain region, the light emitting region and the light emitting region can be substantially matched, and a fine line light emitting region can be obtained. Therefore, it is possible to avoid crosstalk when the pitch is increased due to miniaturization. Thus, since a small exposure spot (line) can be obtained in the sub-scanning direction, it is effective for multi-value reproduction based on area modulation.
The exposure head and the photoconductor move relative to each other in the sub-scanning direction, and the exposure area changes with this relative movement. Considering only from the aspect of area modulation, it is ideal that the exposure spot shape is a single line having no width in the sub-scanning direction. However, the light emission luminance in this case must be infinite. That is, in this case, since the light emitting area in the sub-scanning direction becomes small, the light emitting area becomes small, and the exposure condition becomes strict in terms of energy, so it is necessary to increase the luminance.

(Embodiment 2)
Next, FIG. 7 of the present invention is a cross-sectional view in the case where the optical head has a top emission structure. In contrast to the bottom emission structure, the top emission structure is a type in which light output from the light emitting layer 112 is output to the cathode side above the light emitting layer 112. In the configuration of FIG. 3, a reflective layer 105 made of metal is provided on the glass substrate 100, and the light output is on the cathode side.

  When this structure is adopted, as shown in the figure, among the light generated in the light emitting layer 112 of the organic electroluminescent element 110, the light (not shown) is emitted by the light emitted in the direction opposite to the light detecting element 120. (See 28Y to 28K in FIG. 9 described later). On the other hand, the light generated in the light emitting layer 112 is also emitted in the direction opposite to the direction used for exposure, that is, the light detection element 120 side, and this light is received by the light detection element 120.

  When the top emission structure is adopted, it is not necessary for the light used for exposure to pass through the photodetecting element 120. Therefore, the photodetecting element 120 does not need to dare to use highly transparent polycrystalline silicon, and has a high photocurrent generation capability. The photodetecting element 120 may be composed of amorphous silicon (amorphous silicon).

  Now, in order to implement the top emission structure, the cathode needs to be made of a transparent metal material, which is technically difficult. Therefore, as shown in FIG. 7, a very thin metal layer (thin film cathode) 113a such as Al or Ag and a transparent electrode 113b such as ITO are stacked and used as a cathode. Since the metal layer 113a is very thin, it is possible to realize a cathode with a light-transmitting property. The top emission structure requires a larger number of manufacturing steps than the bottom emission structure, and thus the manufacturing cost increases. However, an optical head with good light emission efficiency can be configured.

  The configuration and operation of the electroluminescent element 110 and the photodetecting element 120 constituting the optical head have been described above in detail. In the first embodiment, the light emitting element (electroluminescent element) row in the optical head has been described as one row. However, it may be configured in a plurality of rows so as to substantially increase the amount of emitted light.

  Of course, the above-described structures of the electroluminescent element 110 and the light detecting element 120 can be applied two-dimensionally to a display device.

As a modification of the second embodiment of the present invention, as shown in FIG. 8, a light shielding film 106 made of a chrome thin film is formed on the back surface side of the glass substrate, and the second light emitting area A _LE1 is defined by this opening. is doing. By forming the second light emitting region _ALE1 smaller than the opening of the silicon nitride film 114 as the pixel defining portion described in the first embodiment, a step portion of the light emitting layer caused by the silicon nitride film 114 is formed. It can be excluded from the light emission region, and the light emitting layer can be made more uniform. Other configurations are the same as those in the first embodiment.

(Embodiment 3)
FIG. 9 is a diagram showing a configuration of an image forming apparatus 21 using the optical head of the present invention. In FIG. 9, the image forming apparatus 21 arranges development stations for four colors, a yellow developing station 22Y, a magenta developing station 22M, a cyan developing station 22C, and a black developing station 22K, in a vertical stepwise manner. Is provided with a paper feed tray 24 in which the recording paper 23 is accommodated, and a recording paper transport serving as a transport path for the recording paper 23 supplied from the paper feed tray 24 at locations corresponding to the developing stations 22Y to 22K. The path 25 is arranged in the vertical direction from the top to the bottom.

  The developing stations 22Y to 22K form yellow, magenta, cyan, and black toner images in order from the upstream side of the recording paper conveyance path 25. The yellow developing station 22Y includes a photoconductor 28Y and a magenta developing station 22M. The photosensitive member 28M and the cyan developing station 22C include the photosensitive member 28C, the black developing station 22K includes the photosensitive member 28K, and each developing station 22Y to 22K includes a series of electrophotographic systems such as a developing sleeve and a charger (not shown). The member which implement | achieves the image development process in is included.

  Further, exposure devices 33Y, 33M, 33C, and 33K for exposing the surfaces of the photoreceptors 28Y to 28K to form electrostatic latent images are disposed below the developing stations 22Y to 22K. The optical head shown in the first embodiment is mounted on the exposure apparatuses 33Y, 33M, 33C, and 33K.

  The developing stations 22Y to 22K are different in the color of the filled developer, but the configuration is the same regardless of the developing color. Therefore, the developing stations are excluded unless particularly necessary to simplify the following description. 22, the photosensitive member 28, and the exposure device 33 will be described without specifying specific colors.

  FIG. 10 is a configuration diagram showing the periphery of the developing station 22 in the image forming apparatus 21 according to the second embodiment of the present invention. In FIG. 10, the developing station 22 is filled with a developer 26 that is a mixture of carrier and toner. Reference numerals 27a and 27b denote stirring paddles for stirring the developer 26. The toner in the developer 26 is charged to a predetermined potential by friction with the carrier by the rotation of the stirring paddles 27a and 27b, and the interior of the developing station 22 is also charged. By circulating, the toner and the carrier are sufficiently stirred and mixed. The photoreceptor 28 is rotated in the direction D3 by a driving source (not shown). A charger 29 charges the surface of the photoreceptor 28 to a predetermined potential. 30 is a developing sleeve, and 31 is a thinning blade. The developing sleeve 30 has a mag roll 32 having a plurality of magnetic poles formed therein. The layer thickness of the developer 26 supplied to the surface of the developing sleeve 30 is regulated by the thinning blade 31 and the developing sleeve 30 is rotated in a direction D4 by a driving source (not shown). The developer 26 is supplied to the surface of the developing sleeve 30 by the action, and an electrostatic latent image formed on the photoconductor 28 is developed by an exposure device to be described later, and the developer 26 that has not been transferred to the photoconductor 28 is developed in the developing station. 22 is collected inside.

  Reference numeral 33 denotes the exposure apparatus already described. The image forming apparatus 21 to which the exposure apparatus 33 equipped with the optical head according to the first embodiment is applied has a long product life because the exposure apparatus 33 can stably form a latent image over a long period of time as described above. Since the exposure apparatus 33 equipped with the optical head of Embodiment 1 can obtain an electrostatic latent image of a desired shape over a long period of time, it can always form a high-quality image.

  The exposure apparatus 33 in the second embodiment is a linear arrangement of organic electroluminescent elements with a resolution of 600 dpi (dot / inch). For the photoreceptor 28 charged to a predetermined potential by the charger 29, An electrostatic latent image of maximum A4 size is formed by selectively turning on / off the organic electroluminescent element according to the image data. Only the toner of the developer 26 supplied to the surface of the developing sleeve 30 adheres to the electrostatic latent image portion, and the electrostatic latent image is visualized.

  A transfer roller 36 is provided at a position facing the recording paper conveyance path 25 with respect to the photoreceptor 28, and is rotated in the direction D5 by a driving source (not shown). A predetermined transfer bias is applied to the transfer roller 36, and the toner image formed on the photoconductor 28 is transferred to the recording paper conveyed through the recording paper conveyance path 25.

  Subsequently, returning to FIG. 9, the description will be continued.

  As described above, the image forming apparatus 21 according to the second embodiment is a tandem type color image forming apparatus in which a plurality of developing stations 22Y to 22K are arranged in a stepwise manner in the vertical direction, and is equivalent to a color inkjet printer. It aims at the size of. Since a plurality of units are arranged in the developing stations 22Y to 22K, in order to reduce the size of the image forming apparatus 21, the developing stations 22Y to 22K themselves are reduced in size and are arranged around the developing stations 22Y to 22K. It is necessary to reduce the members involved in the image process and to reduce the arrangement pitch of the developing stations 22Y to 22K as much as possible.

  In consideration of user convenience when installing the image forming apparatus 21 on the desktop in an office or the like, in particular, accessibility to the recording paper 23 at the time of paper feeding or paper ejection, from the bottom surface of the image forming apparatus 21 to the paper feed port 65. The height is preferably 250 mm or less. In order to realize this, it is necessary to suppress the height of the entire developing stations 22Y to 22K to about 100 mm in the entire configuration of the image forming apparatus 21.

  However, the existing LED head, for example, has a thickness of about 15 mm, and if it is disposed between the developing stations 22Y to 22K, it is difficult to achieve the target. According to the examination results of the present inventors, when the thickness of the exposure device 33 is 7 mm or less, the height of the entire development station is 100 mm or less even if the exposure devices 33Y to 33K are arranged in the gaps between the development stations 22Y to 22K. It is possible to suppress.

  A toner bottle 37 stores yellow, magenta, cyan, and black toners. A toner transport pipe (not shown) is provided from the toner bottle 37 to each of the developing stations 22Y to 22K, and supplies toner to each of the developing stations 22Y to 22K.

  A paper feed roller 38 is rotated in the direction D1 by controlling an electromagnetic clutch (not shown), and feeds the recording paper 23 loaded in the paper feeding tray 24 to the recording paper transport path 25.

  A registration paper 39 and a pair of pinch rollers 40 are provided as a nip conveyance means on the inlet side in the recording paper conveyance path 25 positioned between the paper supply roller 38 and the transfer portion of the most upstream yellow developing station 22Y. The registration roller 39 and the pinch roller 40 pair temporarily stop the recording paper 23 conveyed by the paper supply roller 38 and convey it in the direction of the yellow developing station 22Y at a predetermined timing. This temporary stop restricts the leading edge of the recording paper 23 in parallel with the axial direction of the registration roller 39 and pinch roller 40 pair, thereby preventing the recording paper 23 from skewing.

  Reference numeral 41 denotes a recording paper passage detection sensor. The recording paper passage detection sensor 41 is constituted by a reflective sensor (photo reflector), and detects the leading edge and the trailing edge of the recording paper 23 based on the presence or absence of reflected light.

  When the rotation of the registration roller 39 is started (the power transmission is controlled by an electromagnetic clutch (not shown) and the rotation is turned ON / OFF), the recording paper 23 is conveyed along the recording paper conveyance path 25 in the direction of the yellow developing station 22Y. However, starting from the rotation start timing of the registration roller 39, the writing timing of the electrostatic latent images by the exposure devices 33Y to 33K disposed in the vicinity of the developing stations 22Y to 22K is independently controlled.

  A fixing device 43 is provided as a nip conveying means on the outlet side in the recording paper conveyance path 25 located further downstream of the most downstream black developing station 22K. The fixing device 43 includes a heating roller 44 and a pressure roller 45. The heating roller 44 is a multi-layered roller composed of a heating belt, a rubber roller, and a core material (both not shown) in order from the surface. Among them, the heat generating belt is a belt having a three-layer structure, and is composed of a release layer, a silicon rubber layer, and a base material layer (both not shown) from the side closer to the surface. The release layer is made of a fluororesin having a thickness of about 20 to 30 micrometers and imparts release properties to the heating roller 44. The silicon rubber layer is made of silicon rubber having a thickness of about 170 micrometers and gives the pressure roller 45 appropriate elasticity. The base material layer is made of a magnetic material that is an alloy of iron, nickel, chromium, or the like.

  A back core 26 includes an exciting coil. Inside the back core 46, an excitation coil in which a predetermined number of copper wires (not shown) whose surfaces are insulated is bundled in the direction of the rotation axis of the heating roller 44, and at both ends of the heating roller 44, the heating roller It circulates along the circumferential direction of 44. When an alternating current of about 30 kHz is applied to the exciting coil from an exciting circuit (not shown) that is a semi-resonant inverter, a magnetic flux is generated in a magnetic path constituted by the back core 46 and the base layer of the heating roller 44. Due to this magnetic flux, an eddy current is formed in the base material layer of the heat generating belt of the heating roller 44 and the base material layer generates heat. The heat generated in the base material layer is transmitted to the release layer through the silicon rubber layer, and the surface of the heating roller 44 generates heat.

  Reference numeral 47 denotes a temperature sensor for detecting the temperature of the heating roller 44. The temperature sensor 47 is a ceramic semiconductor obtained by sintering at a high temperature using a metal oxide as a main raw material, and it is possible to measure the temperature of a contacted object by applying a change in load resistance according to the temperature. it can. The output of the temperature sensor 47 is input to a control device (not shown). The control device controls the power output to the exciting coil inside the back core 46 based on the output of the temperature sensor 47, and the surface temperature of the heating roller 44 is about 170 °. Control to be C.

  When the recording paper 23 on which the toner image is formed is passed through the nip formed by the heating roller 44 and the pressure roller 45 that are controlled in temperature, the toner image on the recording paper 23 is connected to the heating roller 44. The toner image is fixed on the recording paper 23 by being heated and pressurized by the pressure roller 45.

  A recording paper trailing edge detection sensor 48 monitors the discharge state of the recording paper 23. Reference numeral 52 denotes a toner image detection sensor. The toner image detection sensor 52 is a reflective sensor unit that uses an electroluminescent element (both visible light) as a plurality of light emitting elements having different emission spectra and a single light receiving element (light detecting element). The image density is detected by utilizing the fact that the absorption spectrum differs depending on the image color between the background and the image forming portion. Further, since the toner image detection sensor 52 can detect not only the image density but also the image forming position, in the image forming apparatus 21 in the first embodiment, two toner image detection sensors 52 are provided in the width direction of the image forming apparatus 21 to perform recording. The image formation timing is controlled based on the detection position of the image displacement amount detection pattern formed on the paper 23.

  53 is a recording paper transport drum. The recording paper transport drum 53 is a metal roller whose surface is covered with rubber having a thickness of about 200 micrometers, and the recording paper 23 after fixing is transported along the recording paper transport drum 53 in the direction D2. At this time, the recording sheet 23 is cooled by the recording sheet conveying drum 53 and is bent and conveyed in the direction opposite to the image forming surface. As a result, curling that occurs when a high density image is formed on the entire surface of the recording paper can be greatly reduced. Thereafter, the recording paper 23 is conveyed in the direction D6 by the kicking roller 55 and discharged to the paper discharge tray 59.

  Reference numeral 54 denotes a face-down paper discharge unit. The face-down paper discharge unit 54 is configured to be rotatable about the support member 56. When the face-down paper discharge unit 54 is opened, the recording paper 23 is discharged in the direction D7. In the closed state, the face-down paper discharge unit 54 is formed with ribs 57 along the transport path on the back surface so as to guide the transport of the recording paper 23 together with the recording paper transport drum 53.

  Reference numeral 58 denotes a drive source. In the first embodiment, a stepping motor is employed. By the drive source 58, peripheral portions of the developing stations 22Y to 22K including the paper feed roller 38, the registration roller 39, the pinch roller 40, the photoconductors (28Y to 28K), and the transfer rollers (36Y to 36K), the fixing device 43, The recording paper transport drum 53 and the kicking roller 55 are driven.

  A controller 61 receives image data from a computer (not shown) via an external network and develops and generates printable image data.

  Reference numeral 62 denotes an engine control unit. The engine control unit 62 controls the hardware and mechanism of the image forming apparatus 21, forms a color image on the recording paper 23 based on the image data transferred from the controller 61, and performs overall control of the image forming apparatus 21. Yes.

  63 is a power supply unit. The power supply unit 63 supplies power of a predetermined voltage to the exposure apparatuses 33Y to 33K, the drive source 58, the controller 61, and the engine control unit 62, and supplies power to the heating roller 44 of the fixing device 43. The power supply unit also includes a so-called high-voltage power supply system such as charging of the surface of the photosensitive member 28, a developing bias applied to the developing sleeve (see reference numeral 30 in FIG. 7), a transfer bias applied to the transfer roller 36, and the like. .

  The power supply unit 63 includes a power supply monitoring unit 64 so that at least the power supply voltage supplied to the engine control unit 62 can be monitored. This monitor signal is detected by the engine control unit 62 to detect a drop in power supply voltage that occurs when the power switch is turned off or a power failure occurs.

  In the above description, the case where the present invention is applied to a color image forming apparatus has been described. However, the present invention can also be applied to a single color image forming apparatus such as black. When applied to a color image forming apparatus, the development colors are not limited to four colors of yellow, magenta, cyan and black.

  Since the image forming apparatus 21 of the present invention is equipped with exposure apparatuses 33Y to 33K having a uniform light emission distribution and excellent durability, the image forming apparatus 21 is excellent in image quality and durability.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described.
In the first embodiment, the threshold voltage of the thin film transistor constituting the light detection element is adjusted by the impurity concentration of the channel region. However, in this embodiment, the light detection element is not adjusted. A voltage source is connected between the gate and the drain as shown in FIG. 11A, and the gate potential is maintained at such a potential that the thin film transistor is always in the OFF region. . This voltage source can also be constituted by a voltage source using a capacitor, for example, as shown in an equivalent circuit in FIG.
As described above, in this embodiment, as shown in FIGS. 11A and 11B, the transistor switch network 190 is connected and the level shift circuit is configured, so that the gate potential is always set to this level. The potential is maintained such that the thin film transistor is in the OFF region.

Next, the level shift operation by the electric circuit will be described with reference to FIG. 11B and FIG.
The voltage source circuit 190 shown in FIG. 11B includes a transistor 1904 connected to the voltage source + Vb, a transistor 1903 connected to VITO, a transistor 1902 connected to Vp, and a capacitor 1901 holding a voltage. It comprises.
This circuit operates in response to the signal B. When the signal B is at a high potential, the transistors 1904 and 1902 are turned on, + Vb is applied to the capacitor 1901, and the capacitor 1901 is charged. Next, when the signal B changes to a low potential, the transistors 1904 and 1902 are turned off and the transistor 1903 is turned on. At that time, the capacitor 1901 becomes a voltage source connected to VITO. Next, when the signal A becomes a high potential, the capacitor 1901 is connected to the sensor, gives a potential difference between the source and drain of the sensor, and shifts the gate potential of the thin film transistor 120 to a desired value.

As shown in FIG. 11 (b) (FIG. 11 (b) is a diagram showing a main part of FIG. 11 (a)), the transistor switch network 190 is gated with respect to the thin film transistor 120 constituting the photodetecting element. The first transistor TrA is connected to each other and the drains to each other, and the second transistor TrB is connected to the drain via a capacitor Bc. Note that the gate of the second transistor TrB is commonly connected to the gate of the thin film transistor 120 constituting the first transistor TrA and the photodetecting element.
By sequentially applying the signal voltages A and B to the first and second transistors TrA and TrB and turning them on and off, the gate potential of the thin film transistor 120 is shifted to a desired value.

The potential of each transistor at this time is shown in FIG. 12A shows the on / off potential of the thin film transistor for switching, FIG. 12B shows the potential V _ITO of the anode 111 of the electroluminescent element, and FIG. 12C shows the photodetecting element and level. The gate potential of the first transistor TrA constituting the shift circuit, FIG. 12D shows the gate potential of the second transistor TrB, and FIG. 12E shows the output current to the capacitor Vc of the photodetection circuit. In the present invention, when the anode, that is, the ITO potential is positive, the transistor to which the signal B is connected is turned OFF, and after the BC and the power supply line are disconnected, the transistor to which the signal A is connected is turned ON. Therefore, it is possible to easily drive in the OFF region always by the voltage accumulated in the BC.

  As apparent from the output current to the capacitor Vc of the photodetection circuit shown in FIG. 12 (e), the gate level of the thin film transistor as the photodetection element is set by the level shift circuit using the transistor switch circuit network of this embodiment. It can be seen that by shifting to 0 V or less, this thin film transistor can be used in the OFF region, and an output current with no variation can be obtained stably.

  As described above, the gate potential is shifted from the potential of the first electrode of the electroluminescent element by a desired potential so that the thin film transistor operates in the region shown by the broken line in FIG. This thin film transistor constituting the element can always be operated in the OFF state.

  In the first embodiment, the light detection element (light receiving element) is formed of a transistor and is configured to operate in the OFF region. The composite of the light emitting element and the light detecting element (light receiving element) can be regarded as a single light emitting device. In this case, the light detecting element (light receiving element) of the light emitting device is constituted by a transistor and operates in the OFF region. Is configured to do.

  The optical head applied to the image forming apparatus has been described above as an example. However, the light receiving element and the light emitting unit according to the present invention are substantially the same for a display device such as a display and an image sensor mounted on an image reading device. It is possible to apply in an aspect.

  The light receiving element, light emitting device, optical head, and image forming apparatus of the present invention can be applied to a copying machine, a printer, a multifunction printer, a facsimile, a display device, and the like.

Sectional drawing of the electroluminescent element 110 which comprises the optical head of Embodiment 1 of this invention, and its periphery Plane configuration explanatory diagram showing a configuration in the vicinity of the light detection element of the optical head described in the first embodiment of the present invention. 1 is an equivalent circuit diagram of a light amount detection circuit of an optical head described in the first embodiment of the present invention. The figure which shows the characteristic of the photon detection element of the optical head described in Embodiment 1 of this invention The figure which shows the light quantity detection flow of the optical head as described in Embodiment 1 of this invention. Sectional drawing which shows the modification of the optical head as described in Embodiment 1 of this invention. Sectional drawing at the time of comprising the optical head of Embodiment 2 of this invention with a top emission structure Sectional drawing which shows the modification of the optical head as described in Embodiment 2 of this invention. Configuration of an image forming apparatus 21 using the optical head of the present invention Configuration diagram showing the periphery of the developing station 22 in the image forming apparatus 21 according to the third embodiment of the present invention. FIG. 7 is an equivalent circuit diagram showing a main part of the light amount detection circuit of the optical head according to the fourth embodiment of the present invention. FIG. 7 is a time chart showing the operating characteristics of the light amount detection circuit of the optical head according to the fourth embodiment of the present invention. Schematic diagram regarding the configuration of a conventional optical head

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Glass substrate 101 Overcoat layer 110 Electroluminescent element 111 Anode 112 Light emitting layer 113 Cathode 114 Pixel control part 120 Photodetection element 121 Polycrystalline silicon layer 121S, D Source / drain region 121i Channel region 122 First insulating layer 123 Second insulating layer 124 Protective layer 125S, D source / drain electrode 130 Drive transistor 131 Active layer 132S, D source / drain region 133 Gate electrode 134S, D source / drain electrode 21 Image forming apparatus 22 Development station 22Y Development station 22M Development Station 22C developing station 22K developing station 23 recording paper 24 paper feed tray 25 recording paper transport path 26 developer 27a stirring paddle 27b stirring paddle 28 photoconductor 28Y photoconductor 2 8M photosensitive member 28C photosensitive member 28K photosensitive member 29 charger 30 developing sleeve 31 thinning blade 32 mag roll 33 exposure device 33Y exposure device 33M exposure device 33C exposure device 33K exposure device 36 transfer roller 37 toner bottle 38 paper feed roller 39 registration roller 39 40 Pinch roller 41 Recording paper passage detection sensor 43 Fixing device 44 Heating roller 45 Pressure roller 46 Back core 47 Temperature sensor 48 Recording paper trailing edge detection sensor 52 Toner image detection sensor 53 Recording paper conveyance drum 54 Face down discharge section 55 Kicking out Roller 56 Support member 57 Rib 58 Drive source 59 Paper discharge tray 61 Controller 62 Engine control unit 63 Power supply unit 64 Power supply monitoring unit 65 Paper feed port

Claims (18)

An optical head comprising a light emitting element and a light detecting element for detecting light output from the light emitting element,
The optical detection element is an optical head configured by a transistor and configured to operate in an OFF region. The optical head according to claim 1, wherein
An electroluminescent element as a light source formed so as to sandwich a light emitting layer between a first electrode and a second electrode, and a photoelectric conversion layer for detecting light output from the electroluminescent element The light detection element is stacked and arranged.
The optical detection element is an optical head which is a thin film transistor having a gate electrode as a first electrode located on the optical detection element side of the electroluminescent element. The optical head according to claim 2,
An optical head configured such that a first electrode of the electroluminescent element located on the light detection element side covers the entire photoelectric conversion portion of the light detection element via an insulating film. The optical head according to claim 2,
The thin film transistor is an optical head in which the doping concentration of the channel region is adjusted so that the threshold voltage is 0 V or less. The optical head according to claim 2,
The thin film transistor is an optical head connected to a drive circuit for a light detection element via a level shift circuit. The optical head according to claim 5, wherein
The level shift circuit is an optical head which is a transistor switch network connected between the gate and drain of the thin film transistor. The optical head according to claim 5, wherein
The level shift circuit is an optical head which is a circuit integrated on a substrate on which the light emitting element is formed. The optical head according to any one of claims 1 to 7,
An optical head in which one photodetecting element is arranged for each light emitting region of the electroluminescent element. The optical head according to any one of claims 1 to 8,
The optical head is an organic electroluminescent device using an organic semiconductor layer as a light emitting layer. The optical head according to any one of claims 1 to 8,
The electroluminescent element is an optical head which is an inorganic electroluminescent element using an inorganic semiconductor layer as a light emitting layer. The optical head according to any one of claims 1 to 10,
An optical head comprising light amount correction means for correcting the light amount of the electroluminescent element based on the output of the light detection element. The optical head according to claim 10, comprising:
The light quantity correction means is an optical head comprising light emission time correction means for correcting the light emission time of the electroluminescent element. The optical head according to any one of claims 1 to 12,
The photodetecting element is an optical head composed of the same semiconductor layer as the thin film transistor that constitutes the driving circuit of the light source. The optical head according to claim 1,
An optical head configured by arranging a plurality of electroluminescent elements on the same substrate, and laminating and arranging photodetecting elements corresponding to each electroluminescent element.   An image forming apparatus using the optical head according to claim 1 as an exposure unit for image formation.   A light receiving element that is configured by a transistor and configured to operate in an OFF region.   A light receiving element comprising a thin film transistor having at least a gate, a source, and a drain, wherein a state in which a current does not flow to the drain by operating a potential applied to the gate is set to an active state of the light receiving element. A light emitting device comprising the light receiving element according to claim 16.

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