JP2007033572A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance lighting efficiency, in a display device in which a lighting section is arranged on a front face. <P>SOLUTION: The lighting section 14 is arranged on the front face of a display section 10 constituted of with a reflective liquid crystal display device and so on. The lighting section 14 has light-emitting elements 52 which emit lights with respective colors of R, G, B. Consequently, the transmittance of light, passing through color filters 44 with the respective colors of R, G and B, is heightened, and the efficiency of energy is increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device having an illumination unit that illuminates a display unit on an observation side.

  Conventionally, a liquid crystal display (LCD) has been widely used as a typical flat panel display. This liquid crystal display device includes a passive type and an active matrix type, and an active matrix type in which each pixel has an individual pixel electrode and voltage supply to the pixel electrode is controlled by an individual pixel circuit is mainly used. It has become.

  Liquid crystal display devices include a transmissive type, a transflective type, and a reflective type. The transmissive type usually has a backlight and performs display by modulating light from the backlight with liquid crystal. In the reflection type, light incident from the observation side is reflected by the reflection layer below the liquid crystal layer and returned to the observation side. For this reason, the reflected and emitted light is modulated by the liquid crystal layer. The transflective type is a combination of both a transmissive type and a reflective type.

  The transmissive type can display a sufficient contrast in a dark place by the light of the backlight, but there is a problem that the display is difficult to see in a bright environment such as outdoors. On the other hand, the reflection type has a problem that it can display sufficiently under the condition of strong external light, but the display cannot be seen in a dark place. The transflective type can be adapted to both environments, but usually has both a transmissive region and a reflective region for each pixel, and thus has a problem that display efficiency is not so good in either environment.

  There has also been proposed a display device in which a reflection type liquid crystal display device is provided with a front light (light on the observation side) to make the display easy to see even in a dark environment (see Patent Documents 1 and 2). According to this, it is possible to perform sufficient display using the front light in a dark environment and the outside light in a bright environment, and always using almost all of the pixels.

JP-A-5-325586 JP 2003-255375 A

  However, in the above prior art, a transparent acrylic plate having a triangular groove formed on the surface is used as the front light, and light is introduced into the acrylic plate from the side so that the light is inclined to the inclined surface of the triangular groove. Reflected towards the liquid crystal display. However, since a part of the light introduced into the acrylic plate leaks not only to the liquid crystal display unit side but also to the observation side, there is a problem that the contrast in the liquid crystal display is lowered.

  The present invention controls the voltage applied to the display element to modulate the light incident from the observation side based on the optical characteristics of the display layer and reflect and emit the light to the observation side of the display unit. An illumination unit that is partially provided and irradiates light toward the display unit, and irradiates the display unit with either or both of external light incident from the observation side and light from the illumination unit, A display device that radiates reflected light from a display unit to an observation side, wherein the illumination unit irradiates light having a peak at at least one specific wavelength toward the display unit.

  The at least one specific wavelength is preferably at least one wavelength of R (red), G (green), and B (blue).

  Further, it is preferable that the illuminating unit irradiates the display unit with light having three peaks of RGB.

  The heights of the three RGB peaks are preferably substantially the same.

  Further, it is preferable that the illumination unit includes a plurality of light emitting units arranged in a plan view so that each light emitting unit emits light of one of RGB colors.

  In the illuminating unit, it is preferable that light emitting units of RGB colors are arranged in a predetermined repeating pattern with periodicity.

  In addition, it is preferable that the reflected light from the display unit has a peak in at least one specific color, and the specific color is substantially the same as the light from the illumination unit.

  Moreover, it is preferable that the said illumination part contains an organic EL element.

  The display unit is preferably a liquid crystal display unit.

  According to the present invention, the illumination unit emits light of a specific color. Accordingly, by accepting light of the same color as the display color, the light use efficiency in the display portion can be increased. Therefore, utilization efficiency can be increased for the light from the illumination unit, and power saving can be achieved. A full color display is possible by setting the display colors to three colors of RGB.

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

  FIG. 1 is a diagram illustrating a conceptual configuration of a display device according to an embodiment.

  First, an illumination unit 14 is formed on the display unit 10 via a transparent adhesive layer 12. In the present embodiment, the display unit is an active matrix reflective liquid crystal display device.

  The display unit 10 includes a pixel substrate 20, a counter substrate 24 disposed to face the pixel substrate 20, and a liquid crystal layer 22 sealed between the pixel substrate 20 and the counter substrate 24.

  The pixel substrate 20 has a glass substrate 30. On the glass substrate 30, a TFT layer 32 including a TFT having, for example, low-temperature polysilicon as an active layer is formed, and a plurality of pixel electrodes 34 are arranged in a matrix thereon.

  The TFT layer 32 has a pixel circuit for controlling the voltage supply to each pixel electrode 34, various wirings for supplying a data voltage, a gate voltage, and the like to the pixel circuit. The pixel electrode 34 is formed of a transparent electrode such as ITO, for example, and a reflective film 36 such as aluminum is formed on the back surface (between the TFT layer 32). Note that the reflective film 36 may be omitted by forming the pixel electrode 34 from a metal such as aluminum.

  The counter substrate 24 disposed opposite to the pixel substrate 20 via the liquid crystal layer 22 has a glass substrate 40, a color filter 44 provided on the entire surface on the liquid crystal layer 22 side, and a common electrode 42 covering the color filter 44. . The color filter 44 is provided for each pixel and transmits only one of RGB light. Therefore, the color filter 44 limits the display color of the pixels. The color filter 44 is provided corresponding to each pixel, and a black matrix 46 is disposed in the gap between the pixels.

  Note that an alignment film is formed on the surface of the pixel electrode 34, the common electrode 42, etc. in contact with the liquid crystal layer 22, but is omitted in FIG.

  Further, by controlling the potential of each pixel electrode 34 individually, it is possible to apply a different potential for each pixel to the liquid crystal between each pixel electrode 34 and the common electrode 42 and change its optical characteristics to perform display. .

  In particular, the display unit 10 reflects light incident from the counter substrate 24 side by providing a reflective film 36 below the pixel electrode 34 or by causing the pixel electrode 34 to function as a reflective film. Therefore, the reflected light modulated by the liquid crystal of each pixel is obtained on the counter substrate 24 side. An electrophoretic display or the like can also be used as the display unit 10.

  An illumination unit 14 is disposed above the display unit 10 via a transparent adhesive layer 12. The illumination unit 14 includes a glass substrate 50, a light emitting element 52 partially formed on the upper surface thereof, and a counter substrate 54 that faces the glass substrate 50 and seals a space where the light emitting element 52 exists. Yes. Then, the display unit 10 is irradiated with light from the light emitting element 52.

  The transparent adhesive layer 12 is made of UV resin, visible light curable UV resin, or the like, and bonds the glass substrate 40 in the display unit 10 and the glass substrate 50 in the illumination unit 14.

  The structure of the light emitting element 52 will be described based on the plan view of FIG. 2 and the cross-sectional view of FIG. In this example, the light emitting element 52 is formed in an island shape on the glass substrate 50. A rectangular anode 60 made of a transparent conductive material such as ITO is provided on the glass substrate 50, and an insulating film 62 such as acrylic resin is provided to cover the periphery of the anode 60. The anode 60 and the insulating film 62 are formed by a normal patterning process.

  Next, the organic EL layer 64 is formed on the anode 60 (the peripheral portion is on the insulating film 62). The organic EL layer 64 includes a hole transport layer, an organic light emitting layer, and an electron transport layer, and is formed by sequentially depositing using one mask. A cathode 66 made of a metal such as aluminum or chromium is formed on the organic EL layer 64.

  With such a configuration, when a predetermined voltage is applied between the anode 60 and the cathode 66, a current flows through the organic EL layer 64, and light emission occurs. Since the cathode 66 is made of metal, the light traveling upward (observation side) from the organic EL layer 64 is reflected by the cathode 66 and directed toward the display unit 10. Further, only the portion of the anode 60 that is not covered with the insulating film 62 acts as an electrode.

  Here, each light emitting element 52 may emit light similarly. Therefore, the anodes 60 of the light emitting elements 52 are connected to each other by the wiring 60a, and the cathodes 66 are connected to each other by the wiring 66a. Accordingly, when the display unit 10 is irradiated with light by the illumination unit 14, the light emitting element 52 can emit light by applying a predetermined voltage between the anode 60 and the cathode 66.

  In particular, in the present embodiment, the organic EL layer 64 emits light in RGB colors. That is, the organic EL layer 64 emits light with different colors, for example, by using different chemical substances for the dopant of the organic light emitting layer. In this example, each light emitting element 52 is set to one of RGB colors so that the whole is white.

  In addition, the wavelength of each color of RGB is not strictly determined, and the wavelength may be in a certain range. That is, you may utilize the light of a wavelength different from each color of RGB currently utilized normally.

  Thus, the use efficiency of the emitted light can be increased by setting the light emission colors of the light emitting element 52 to the RGB colors. In other words, the wavelength of the display unit 10 is limited by the color filter 44. As shown in FIG. 4, each color filter 44 has a broad spectral characteristic but has a peak, and the transmittance is wavelength-dependent. Therefore, as shown in FIG. 4, when white light passes through the color filter 44, the light passing therethrough is a very small percentage of the total power and the utilization efficiency is low.

  On the other hand, when the light emitting element 52 emits light of each color of RGB and the peak is approximately coincident with the peak of the color filter 44, the light of the same color as the color filter 44 can be transmitted efficiently. Therefore, even when all the light of each RGB color is incident on the color filter 44, a utilization factor of about 30% can be secured, and RGB with higher color purity can be realized. When white light having a broad spectrum at each wavelength of visible light is used, only a limited wavelength is transmitted through the color filter 44, so that the utilization rate is 30% and high color purity is obtained. Not far away. Therefore, energy efficiency can be improved by using each color of RGB for the light emitting element 52 as in this embodiment.

  FIG. 4 shows the use of this light. The white light has a broad spectrum in the entire visible light, and passes through the color filter 44 and becomes light having a peak in the wavelength of each RGB color. That is, light having a peak at R is obtained by the R color filter 44, light having a peak at G is obtained by the G color filter 44, and light having a peak at G is obtained by the B color filter 44. White light includes light that is difficult to transmit through any of the RGB color filters 44, which leads to a reduction in efficiency. On the other hand, in the light emission of each color of RGB in the light emitting element 52 shown by a broken line, light (RGB) having a specific wavelength is emitted. Among these lights, those of the same color are transmitted through the color filter 44 with little attenuation. Therefore, the efficiency can be increased by using light of each color of RGB.

  In order to further increase the efficiency, light from the R light emitting element 52 is applied to the pixel having the R color filter 44, light from the R light emitting element 52 is applied to the pixel having the G color filter 44, and B color. The pixel having the filter 44 may be irradiated with light from the R light emitting element 52. Therefore, it is preferable to provide a light emitting element 52 corresponding to the color of each pixel and irradiate each pixel with light of the same color.

  In this case, it is preferable to reliably irradiate the corresponding pixels with the light emitted from each light emitting element 52. Therefore, it is preferable to configure the light emitting element 52 as shown in FIG.

  In this example, the light emitting element 52 has a step forming layer 58 formed on the glass substrate 50. For example, a photosensitive acrylic resin is used for the step forming layer 58. An anode 60 made of a transparent conductive material such as ITO or IZO is formed on the step forming layer 58, and an organic EL layer 64 covers the top of the anode 60 and the upper and side surfaces of the step forming layer 58 and the anode 60. It is formed. The organic EL layer 64 includes a hole transport layer, an organic light emitting layer, and an electron transport layer as in the case described above. In particular, the mountain-shaped organic EL layer 64 can be formed by covering the entire step forming layer 58 and the anode 60 by forming the hole transport layer positioned on the anode 60 side relatively thick. The organic EL layer 64 is formed by sequentially depositing a hole transport layer, an organic light emitting layer, and an electron transport layer using one mask.

  Note that the organic EL layer 64 emits light in one of RGB by each pixel. A cathode 66 made of a metal such as aluminum or chromium is formed so as to cover the organic EL layer 64.

  In such a configuration, a current easily flows in a portion corresponding to the anode 60 and the cathode 66, and the organic EL layer 64 in this portion emits light. The anode 60 and the step forming layer 58 are transparent, and the light directed downward in the drawing is directed to the display unit 10 as it is. On the other hand, light directed from the organic EL layer 64 in the other direction is reflected by the cathode 66, condensed downward, and irradiated to the corresponding pixel of the display unit 10.

  Thus, in the configuration of FIG. 5, the directivity of the light from the light emitting element 52 is controlled so as to go to the corresponding pixel of the display unit 10. Thereby, the color filter 44 of each pixel of the display unit 10 is irradiated with the same color light. Therefore, the attenuation here can be made very small, and the energy efficiency can be improved.

  Here, in the liquid crystal display device, RGB pixels are not systematically arranged but systematically arranged. For example, in the stripe type, pixels of the same color are arranged in the column direction. In this case, the light emitting elements 52 are provided in a row shape in the column direction, and are distributed to the RGB colors, whereby each pixel can be irradiated with light of the same color.

  In the above example, an organic EL element is used as the light emitting element 52. However, the light emitting element 52 is not limited to this, and may be an inorganic EL that emits light with RGB light.

  As described above, the light emitting element 52 does not have to be provided corresponding to each pixel, but moire is generated when the pitch is deviated from the pitch of the pixel. Therefore, both pitches are the same or the other pitch. It is preferable that the integer multiple of.

  In such an embodiment, the display unit 10 performs display as a normal liquid crystal display device. On the other hand, the illumination unit 14 is turned on when the illuminance of outside light is small, and a predetermined voltage is applied between the anode 60 and the cathode 66. As a result, a current flows through the organic EL layer 64 and light emission occurs in the organic EL layer 64. The anode 60 is transparent and goes to the display unit 10 as it is.

“Configuration of Display Unit”
FIG. 6 is a part of a planar configuration on the pixel substrate side of the display unit (active matrix type total reflection LCD) 10 according to the present embodiment, and FIG. 7 is a schematic cross-section at a position along the line AA in FIG. The configuration is shown. In an active matrix LCD, a plurality of pixels are provided in a matrix in a display area, and here, a TFT 110 is provided as a switch element for each pixel.

  The TFT 110 has an active layer 220, and a drain region 220d, a channel region 220c, and a source region 220s are formed by the active layer 220. A gate insulating film 130 is formed so as to cover the active layer 220, and a gate electrode 132 is formed on the gate insulating film 130 at a position that is above the channel region 220 c. Then, an interlayer insulating film 134 is formed so as to cover the gate insulating film 130 and the gate electrode 132. A data line 136 is disposed on the interlayer insulating film 134, and the data line 136 is connected to the drain region 220 d through a contact penetrating the interlayer insulating film 134. In addition, a contact hole is formed in the interlayer insulating film 134 and the planarization insulating film 138 on the source region 220s, and a part of the pixel electrode 150 extends and is electrically connected thereto.

  The TFT 110 is formed for each pixel, for example, on the pixel substrate 100 side, and pixel electrodes 150 formed in individual patterns are connected to the TFT 110, respectively. An alignment film 160 is formed on the surface of the pixel substrate 100 so as to cover the pixel electrode 150. Further, the counter substrate 200 is disposed to face the pixel substrate 100 with the liquid crystal layer 300 interposed therebetween.

  A transparent substrate such as glass is used for the pixel substrate 100 and the counter substrate 200, and in the case of a color type, a color filter 210 is formed on the pixel substrate 100 and the counter substrate 200 side. A common electrode 250 made of a conductive material is formed. As the transparent conductive material of the common electrode 250, IZO (Indium Zinc Oxide), ITO, or the like is employed. In the active matrix type, the common electrode 250 is formed as a common electrode for each pixel. An alignment film 260 made of polyimide or the like is formed on the common electrode 250.

  In the present embodiment, an electrode structure is adopted in which the electrical characteristics of the liquid crystal layer 300 on the pixel substrate 100 side are aligned with the counter substrate 200 side configured as described above. Specifically, as shown in FIG. 6, a material having a work function similar to that of the common electrode 250, i.e., IZO or ITO, is not provided directly below the alignment film on the pixel substrate 100, instead of the conventional reflective metal electrode. Thus, the pixel electrode 150 made of the same transparent conductive material as the common electrode 250 is formed. In order to obtain a reflective LCD, a reflective layer 144 that reflects incident light from the counter substrate 200 side is formed below the pixel electrode 150.

  The material used for the pixel electrode 150 is the same as the material of the common electrode 250, so that the electrode having the same work function is disposed with respect to the liquid crystal layer 300 through the alignment films 160 and 260. Therefore, the liquid crystal layer 300 can be AC driven with very good symmetry by the pixel electrode 150 and the common electrode 250. However, the pixel electrode 150 and the common electrode 250 may be approximated as long as the liquid crystal layer 300 can be driven with good symmetry even if their work functions are not completely the same. For example, if the difference between the work functions of both electrodes is about 0.5 eV or less, even if the liquid crystal drive frequency is CFF (critical flicker frequency) or less, high quality display without flickering or liquid crystal burn-in is possible. Is possible.

  As the pixel electrode 150 and the common electrode 250 that satisfy such conditions, for example, the pixel electrode 150 has IZO (work function 4.7 eV to 5.2 eV), and the common electrode 250 has ITO (work function 4.7 eV to 5.0 eV). ), Or vice versa, and materials may be selected in consideration of process characteristics such as transmittance and patterning accuracy, manufacturing cost, and the like.

  As the reflective layer 144, a material excellent in reflective properties such as Al, Ag, and alloys thereof (Al—Nd alloy in this embodiment) is used at least on the surface side (liquid crystal layer side). The reflective layer 144 may be a single layer of a metal material such as Al, but a refractory metal layer such as Mo may be provided as a base layer in contact with the planarization insulating film 138. When such a base layer is formed, the adhesion between the reflective layer 144 and the planarization insulating film 138 is improved, so that the reliability of the element can be improved. In the configuration of FIG. 6, an inclined surface having a desired angle is formed in each pixel region of the planarization insulating film 138, and the reflective layer 144 is laminated so as to cover the planarization insulating film 138. A similar slope is formed on the surface of the layer 144. If such an inclined surface is formed at an optimum angle and position, it is possible to collect and emit external light for each pixel. For example, it is possible to improve the display brightness at the front position of the display. is there. Of course, such an inclined surface does not necessarily exist.

In the present embodiment, a protective film 146 is formed between the reflective layer 144 and the pixel electrode 150 so as to cover the reflective layer 144. For example, acrylic resin or SiO ₂ is used for the protective film 146. The protective film 146 is a film for protecting the reflective layer 144, and is used in particular for the light etching that exposes the active layer 220 on the bottom surface of the contact hole for connecting the active layer 220 of the TFT 110 and the pixel electrode 150. A function of protecting the reflective surface of the reflective layer 144 from an etching solution or the like.

The protective film 146 only needs to have a function of protecting the reflective layer 144 from the etching process and maintaining good reflection characteristics, and the material thereof is not limited to the resin or SiO ₂ , Moreover, the film thickness should just have a grade which can exhibit this protective function. Further, from the viewpoint of flattening the formation surface of the pixel electrode 150 formed on the upper layer of the protective film 146, it is preferable to employ a material having a flattening function on the upper surface such as the acrylic resin. Further, the film thickness and material of the protective film 146 are selected so as to have an optimum thickness and refractive index, so that the protective film 146 can be used as, for example, an optical buffer layer having a color compensation function, a reflectance improvement function, and the like. Is possible.

  Note that it is preferable to scatter reflected light to some extent by forming irregularities in the reflective layer 144. By forming appropriate irregularities on the surface of the planarization insulating film 138 below the reflective layer 144 and forming the reflective layer 144 thereon, the irregularities can be easily formed in the reflective layer 144.

It is a figure which shows the structure of this embodiment. It is a top view which shows the structural example of an illumination part. It is sectional drawing which shows the structure of an illumination part. It is a figure which shows the light emission state of a light emitting element. It is a figure which shows the other structural example of a light emitting element. It is a top view which shows the structure of total reflection LCD. It is AA sectional drawing in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Display part, 12 Transparent adhesive layer, 14 Illumination part, 20 Pixel substrate, 22 Liquid crystal layer, 24, 54 Opposite substrate, 30, 50 Glass substrate, 32 TFT layer, 34 Pixel electrode, 36 Reflective film, 40 Glass substrate, 42 common electrode, 44 color filter, 52 light emitting element, 58 step forming layer, 60 anode, 60a, 66a wiring, 62 insulating film, 64 organic EL layer, 66 cathode.

Claims (9)

By controlling the voltage applied to the display element, the display unit that modulates the light incident from the observation side based on the optical characteristics of the display layer and reflects and emits the light,
An illumination unit that is partially provided on the observation side of the display unit and irradiates light toward the display unit;
Including
A display device that irradiates the display unit with either or both external light incident from the observation side and light from the illumination unit, and radiates reflected light from the display unit to the observation side,
The illumination unit is
A display device characterized by irradiating light having a peak at at least one specific wavelength toward a display portion. The display device according to claim 1,
The display device, wherein the at least one specific wavelength is at least one wavelength of R (red), G (green), and B (blue). The display device according to claim 2,
The illumination unit is
A display device that irradiates light having peaks in three of RGB toward a display portion. The display device according to claim 3,
The display device characterized in that the three peaks of RGB have substantially the same height. In the display device according to any one of claims 2 to 4,
The illumination unit is
A display device comprising: a plurality of light emitting portions arranged separately from each other in a plane, wherein each light emitting portion emits light of one of RGB colors. The display device according to claim 5,
The illumination unit is
A display device characterized in that light emission portions of RGB colors are arranged in a predetermined repeating pattern with periodicity. In the display device according to any one of claims 1 to 6,
The reflected light from the display unit has a peak in at least one specific color, and the specific color is substantially the same as the light from the illumination unit. In the display device according to any one of claims 1 to 7,
The illumination device includes an organic EL element. In the display device according to any one of claims 1 to 8,
The display unit is a liquid crystal display unit.

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