JP2004006339A - EL panel dimming method and EL panel - Google Patents

Abstract

An object of the present invention is to effectively reduce the brightness of a bright spot defective pixel.
An active layer (semiconductor layer) 40a of a second TFT 40 of a pixel is selectively irradiated with a UV laser. As a result, the crystallinity of the active layer 40a is deteriorated, and electrical cutting can be performed. As a result, the pixel can be dimmed without adverse effects. Further, by targeting the active layer 40a below the gate electrode 40c, the laser can be reflected by the gate electrode 40c, and more efficient laser irradiation can be performed.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to repairing defective pixels of an EL (electroluminescence) panel.
[0002]
[Prior art]
Conventionally, an EL display panel is known as one of the flat display panels. This EL display panel is self-luminous unlike a liquid crystal display panel (LCD), and is expected to spread as a bright and easy-to-see flat display panel. In particular, organic EL elements can be driven at a lower voltage than inorganic EL elements, and are expected to be widely used in various displays.
[0003]
The organic EL display is configured by arranging a large number of organic EL elements as pixels in a matrix. Further, as a driving method of the organic EL element, there are a passive method and an active method as in the case of the LCD, and it is considered that the active matrix method is preferable as in the case of the LCD. That is, the active matrix method in which a switching element is provided for each pixel and the switching element is controlled to control the display of each pixel is higher than the passive method in which no switching element is provided for each pixel. This is preferable because a fine screen can be realized.
[0004]
In the case of an LCD, one switching element (TFT) is used and is directly connected to a pixel electrode. In the case of an organic EL panel, two TFTs and one capacitor are used. FIG. 5 shows a configuration example of a pixel circuit in an organic EL panel using a thin film transistor (TFT). The organic EL panel is configured by arranging such pixels in a matrix.
[0005]
The gate of the first TFT 10 which is an n-channel thin film transistor selected by the gate line is connected to the gate line extending in the row direction. The drain of the first TFT 10 is connected to a data line DL extending in the column direction, and the other end of the data line DL is connected to a storage capacitor CS whose other end is connected to a capacitor line SL which is a low-voltage power supply. The connection point between the source of the first TFT 10 and the storage capacitor CS is connected to the gate of the second TFT 40 which is a p-channel thin film transistor. The source of the second TFT 40 is connected to the power supply line VL, and the drain is connected to the organic EL element EL. The other end of the organic EL element EL is connected to a cathode power supply CV.
[0006]
Therefore, when the gate line GL is at the H level, the first TFT 10 is turned on, and the data on the data line DL at that time is held in the holding capacitor CS. Then, the current of the second TFT 40 is controlled according to the data (potential) maintained in the storage capacitor CS, and the current flows through the organic EL element EL according to the current of the second TFT 40 to emit light.
[0007]
Then, when the first TFT 10 is on, a video signal corresponding to the pixel is supplied to the data line DL. Accordingly, the storage capacitor CS is charged in accordance with the video signal supplied to the data line DL, whereby the corresponding current flows through the second TFT 40, and the luminance control of the organic EL element EL is performed. That is, by controlling the gate potential of the second TFT 40 and controlling the current flowing through the organic EL element, gradation display of each pixel is performed.
[0008]
In such an organic EL panel, a defect may occur in the first TFT 10 or the second TFT 40 provided for each pixel. In the case of a defect in which the TFT is fixed so as to turn off the current to the organic EL element, the pixel only becomes a dark spot, and even if there is one dark spot among the bright spots, it is visible. This is not a problem. On the other hand, in the case of a defect in which the current to the organic EL element is always on, the pixel becomes a bright spot. If even one pixel has a bright spot while surrounding pixels are displaying black, the bright spot is visually recognized by an observer, which causes a problem. Therefore, for a defective pixel that becomes a bright spot, a process of dimming the dark pixel (darkening) is conventionally performed.
[0009]
That is, an organic EL panel having a predetermined number of dark spots has no problem as a product, and a significant improvement in yield can be achieved by dimming bright spots.
[0010]
Here, the darkening can be performed by disconnecting the wiring leading to the pixel. That is, as in the case of the LCD, it is conceivable that the wiring between the second TFT 40 and the power supply line or the pixel electrode is cut by a visible light YAG laser or the like.
[0011]
As a result, the bright spot can be turned into a dark spot, and the problem in the entire display can be solved.
[0012]
[Problems to be solved by the invention]
However, when the dark spot processing is performed by the visible light YAG laser, the cathode may be damaged and the display of other pixels may be affected. That is, in the case of an active matrix type organic EL panel, a TFT is formed on a glass substrate, an ITO anode is formed above the TFT, and a hole transport layer, an organic light emitting layer, an electron transport layer, and the like are formed thereon. An organic layer is laminated, on which a metal cathode is formed. As described above, a part of the organic layer and the cathode exist above the TFT. In particular, the cathode is formed as a common electrode over almost the entire surface of the panel.
[0013]
Therefore, when the wiring of the TFT is cut by the visible light YAG laser, the laser reaches the cathode, and the cathode suffers damage such as ablation. Accordingly, the cathode has a configuration in which a hole is formed in that portion. In addition, the ablation may alter the quality of the cathode and affect the display of peripheral pixels. Further, the cutting by the laser is to evaporate and fly away a substance present therein, and the side surface of the organic layer of the organic EL element is directly exposed to the space above the cathode. Therefore, deterioration of the organic layer due to intrusion of moisture, oxygen, or the like from the exposed portion is likely to progress, and there is a possibility that defective pixels may spread.
[0014]
In addition, when the wiring is cut by ablation, the wiring material (usually a metal) that has blown off once adheres to another wiring portion, which may cause a short circuit.
[0015]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for dimming an organic EL panel in which defective pixels can be dimmed effectively.
[0016]
[Means for Solving the Problems]
The present invention is a method for dimming defective pixels in an EL panel having an EL light emitting element and a thin film transistor for controlling a current to the EL light emitting element for each pixel arranged in a matrix, wherein the thin film transistor is formed. The method is characterized in that at least a portion of the semiconductor layer to be irradiated is selectively irradiated with a laser to increase the resistance value of the semiconductor layer in that region, thereby dimming the pixel.
[0017]
As described above, according to the present invention, the process of dimming the pixel can be performed by irradiating the semiconductor layer with the laser. In particular, in this treatment, the crystal structure of the semiconductor layer is microscopically broken to increase resistance and thereby electrically cut. Accordingly, the defective pixel can be dimmed basically without damaging other parts, so that a suitable dimming process can be performed.
[0018]
Further, it is preferable that a portion where the metal layer is disposed above the semiconductor layer is irradiated with laser from below, and the laser irradiated by the metal layer is reflected. As a result, the reflected laser is also applied to the semiconductor layer, so that efficient irradiation can be performed, and the laser does not reach the upper portion and adversely affect the portion.
[0019]
In addition, the thin film transistor has a configuration in which a semiconductor layer is provided over a glass substrate, and a gate electrode is provided thereover via a gate insulating film, and the semiconductor layer is irradiated with a laser through the glass substrate, It is preferable to reflect the laser beam emitted from the gate electrode. As a result, the irradiation of the laser to other portions is prevented, and the occurrence of adverse effects on other portions can be reliably prevented.
[0020]
Preferably, said laser is a UV laser. For example, the semiconductor layer can be electrically cut by a laser having a wavelength of about 308 or 355 nm without adversely affecting a metal.
[0021]
Further, the EL display panel according to the present invention is characterized in that defective pixels are dimmed by the method for dimming the EL panel.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
In the present embodiment, a laser beam is irradiated from below the gate electrode, and the laser beam causes micro ablation in the semiconductor layer made of polysilicon existing below the gate electrode of the TFT, thereby forming a semiconductor layer. The TFT is fixed off by deteriorating the crystallinity and increasing the resistance. In particular, since the laser is reflected by the gate electrode, the semiconductor layer is effectively irradiated with the laser, and there is no adverse effect of the laser on the upper layer of the gate electrode.
[0024]
As a laser at this time, an ultraviolet (UV) laser such as a 355 nm YAG laser or a 308 nm excimer laser is preferable. That is, if the wavelength is longer than this, if the semiconductor layer is to be deteriorated, the gate electrode also undergoes ablation, and if the wavelength is shorter than this, it becomes difficult to transmit through the glass substrate.
[0025]
FIG. 1 illustrates a configuration of a pixel. Here, on the element substrate, the TFTs 10 and 40, the capacitor CS, and the organic EL element EL shown in FIG. 5 are formed for one pixel. In this figure, only the second TFT 40 and the organic EL element EL are shown. .
[0026]
In the figure, the element substrate has a second TFT 40 formed on a glass substrate 30. The configuration of the second TFT 40 and the organic EL element EL is shown. As described above, the second TFT 40 is formed on the glass substrate 30, and the second TFT 40 has the active layer (semiconductor layer) 40a formed of polysilicon. Both ends of the active layer 40a are a source region and a drain region where impurities are doped, and a central portion sandwiched between these is a channel region. A gate electrode 40c is formed above the channel region via a gate insulating film 40b made of a silicon-based insulating film such as silicon oxide. The gate insulating film 40b and the gate electrode 40c are covered with the interlayer insulating film 34. On both sides of the gate electrode 40c, source electrodes 40d connected to the source region and the drain region through the contact holes of the interlayer insulating film 34, A drain electrode 40e is formed. The upper ends of the source electrode 40d and the drain electrode 40e are located on the surface of the interlayer insulating film 34.
[0027]
On the surface of the interlayer insulating film 34, a metal wiring or the like connecting the drain electrode 40e and the power supply line VL is arranged. Further, a first planarizing film 36 is formed to cover the interlayer insulating film 34.
[0028]
A transparent electrode 50 made of ITO is formed on the upper surface of the first flattening film 36, and one end of the transparent electrode 50 is connected to the source electrode 40d of the second TFT 40 via the contact hole of the first flattening film 36. .
[0029]
The transparent electrode 50 constitutes the anode of the organic EL device, and a metal cathode 58 is formed on the transparent electrode 50 via a hole transport layer 52, an organic light emitting layer 54, and an electron transport layer 56. Have been. Note that a second planarizing film 60 is disposed around and on the side of the transparent electrode 50. The organic light emitting layer 54 is larger than the transparent electrode 50 in order to cope with a displacement during the formation, but extends to the second flattening film 60 so as to be present only in the pixel region. are doing. On the other hand, the hole transport layer 52 and the electron transport layer 56 other than the organic light emitting layer 54 are formed to extend over the entire surface. However, the electron transport layer 56 may include a light-emitting material such as Alq3, and the electron transport layer 56 is often limited to only the light-emitting portion similarly to the organic light-emitting layer 54.
[0030]
Note that this figure shows a so-called bottom emission type organic EL element in which an organic layer is provided on the transparent electrode 50 and light is emitted through the substrate. However, the present invention is not limited to such a bottom emission type, but can also be applied to a top emission type. In the top emission type, an electrode (usually a cathode) disposed above the organic layer is made transparent or translucent, and light is emitted from above the organic layer. Further, as an organic EL panel, there is a white EL type in which a white light is emitted as an organic light emitting layer, a color filter is provided for each pixel, and color display is performed. The present invention can be applied to such a type of organic EL panel. In addition, as the organic light emitting layer that emits white light, an organic light emitting layer in which an orange light emitting layer and a blue light emitting layer are stacked, and the light emitted from both layers is combined to make white can be adopted. Also in this white EL type, both a bottom emission type and a top emission type can be adopted.
[0031]
In such an organic EL panel, as for a short-wavelength laser for selectively irradiating a short-wavelength laser from below the glass substrate 30 toward the gate electrode 40c, a YAG laser having a wavelength of 355 nm or a 308 nm Excimer laser is suitable. As a result, the active layer 40a in the channel region below the gate electrode 40c undergoes micro-ablation, and the crystallinity is destroyed, thereby increasing the resistance value. Therefore, the TFT 40 is electrically disconnected. Therefore, the pixel is dimmed. In particular, since the laser is reflected by the gate electrode 40c, other portions are not irradiated, and only the active layer 40a can be electrically disconnected.
[0032]
As the laser, a pulse laser is usually used, but continuous light may be used. The irradiation amount depends on the type of the glass substrate, the material of the organic layer, other layers, and the like, but can be determined experimentally as an amount that can surely make a dark spot and does not significantly damage the gate electrode 40c. It is suitable.
[0033]
That is, as shown in FIG. 2, a test panel is prepared (S11), the irradiation amount is changed, and a plurality of pixels are irradiated with a laser (S12). Then, the result of the laser irradiation test is evaluated (S13). That is, it is evaluated whether or not the dark spot is surely performed. The laser intensity is set so that at least the cathode is not damaged. Then, a condition under which the dark spot can be surely determined is determined (S14). For example, a change in the amount of light emission according to pulse irradiation may be measured to determine an appropriate amount of laser irradiation.
[0034]
When the condition is determined in this way, the condition is adopted to perform the process of darkening the bright spot defective pixel of the actually manufactured organic EL panel (S15).
[0035]
As described above, according to the present embodiment, the process of dimming the pixel can be performed by irradiating the laser to the active layer 40a below the gate electrode 40c. In particular, in this treatment, the crystal structure of the semiconductor layer is microscopically broken to increase resistance and thereby electrically cut. Accordingly, the defective pixel can be dimmed basically without damaging other parts, so that a suitable dimming process can be performed.
[0036]
Here, FIG. 3 shows a plan configuration of one pixel of the organic EL panel. The gate line GL extends in the horizontal direction, and the gate 2 of the first TFT 10 is connected to the gate line GL. The first TFT 10 is of a double gate type in which two gates 2 are provided. The active layer 6 of the first TFT 10 is formed of a semiconductor layer of polysilicon, and one end (source) is connected to the data line DL. The other end of the active layer 6 is connected to the lower electrode of the capacitor CS or also serves as the lower electrode. The active layer 6 is a channel region below the gate 2 of the first TFT 10, a region between the two gates 2 is a drain and a source, and a region connected to the lower electrode of the capacitor CS is a source. .
[0037]
An upper electrode (substantially the same layer as the gate electrode) is disposed opposite to the lower electrode of the capacitor CS made of the semiconductor layer via a silicon oxide film, and the lower electrode, the dielectric, and the upper electrode form the capacitor CS. Is formed. The upper electrode of the capacitor CS is connected to a capacitor line SL maintained at a low potential.
[0038]
Therefore, when the gate line GL becomes H level, the first TFT 10 is turned on, and the voltage of the data line DL is written (charged) to the capacitor CS.
[0039]
The lower electrode of the capacitor CS is connected to the gate 25 of the second TFT 40 via a contact. The second TFT 40 is composed of two second TFTs 40-1 and 40-2 connected in parallel, both ends being a source and the center being a drain. That is, the second TFT 40 has the active layer 16 made of a semiconductor layer, and the sources 16s-1 and 16s-2 at both ends of the active layer 16 are connected to the power supply line VL via the contact. The lower part of the gate 25 is the channels 16c-1 and 16c-2, and the central part is the drains 16d-1 and 16d-2.
[0040]
The drains 16d-1 and 16d-2 are connected to the organic EL element EL via the contact and the wiring 41. That is, the drains 16d-1 and 16d-2 of the second TFTs 40-1 and 40-2 in FIG. 3 are connected to the anode 50 of the organic EL element.
[0041]
In such a pixel, the active layer (semiconductor layer) 16 below the gate electrode 25 may be irradiated with a laser to cut the second TFT 40. In this case, the second TFT 40 includes two second TFTs 40-1 and 40-2, and irradiates the laser to the channel regions 16c-1 and 16c-2 of the active layer 16 of the second TFTs 40-1 and 40-2. Is electrically disconnected.
[0042]
Note that, in the above example, the semiconductor layer below the gate electrode is irradiated with a laser to perform electrical cutting, but any other location may be used as long as the semiconductor layer is below the metal layer. For example, it is also preferable to irradiate a laser to a source region and a drain region below the source electrode and the drain region and to electrically cut this portion.
[0043]
Also, the first TFT 10 can be cut in the same manner. Further, it is also preferable to irradiate a laser to a connection contact portion between the data line DL and the semiconductor layer of the first TFT 10 to separate the first TFT 10 from the data line DL.
[0044]
The absorption of laser light in the semiconductor layer has wavelength dependence, and the light near 300 nm absorbs several tens times or more with respect to light of 500 nm or more. In other words, the transmission of light near 300 nm is relatively small. Therefore, the use of light of a short wavelength such as around 300 nm reduces the damage to the cathode and enables electrical disconnection.
[0045]
In the case of a YAG laser having a wavelength of 355 nm, the reflectance differs depending on the metal. For example, the reflectance of aluminum is about 99%, and that of chromium is about 50%. Therefore, it is preferable to irradiate a laser to a lower semiconductor layer such as the data line DL usually formed of aluminum, but it is not necessarily limited to this. That is, although the gate electrodes of the first TFT 10 and the second TFT 40 are usually formed of chromium, it has been experimentally found that the semiconductor layer below the chromium can be sufficiently electrically disconnected. Basically, the metal easily reflects the short-wavelength laser as described above, and can be used for electrically cutting a semiconductor layer below an electrode or wiring such as molybdenum.
[0046]
In the above-described processing, the light emission amount may be equal to or smaller than a predetermined value without performing even a complete darkening process. Therefore, as shown in FIG. To increase the resistance.
[0047]
The above description has dealt with only the organic EL panel. However, the method of the present invention can be applied to an inorganic EL panel of a fluorescent display (Vacuum Fluorescence Display) or another display device having the same TFT or the like. Can be applied to
[0048]
【The invention's effect】
As described above, according to the present invention, the process of dimming the pixel can be performed by irradiating the semiconductor layer with the laser. In particular, in this treatment, the crystal structure of the semiconductor layer is microscopically broken to increase resistance and thereby electrically cut. Accordingly, the defective pixel can be dimmed basically without damaging other parts, so that a suitable dimming process can be performed.
[0049]
In addition, the thin film transistor has a configuration in which a semiconductor layer is provided over a glass substrate, and a gate electrode is provided thereover via a gate insulating film, and the semiconductor layer is irradiated with a laser through the glass substrate, It is preferable that the laser beam emitted from the gate electrode is reflected, whereby the laser beam can be prevented from being irradiated on other portions, and the adverse effect on other portions can be reliably prevented.
[0050]
The laser is preferably a UV laser, which allows the semiconductor layer to be electrically cut without adversely affecting the metal.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a pixel.
FIG. 2 is a flowchart illustrating an example of laser irradiation amount setting.
FIG. 3 is a diagram illustrating a planar configuration of a pixel.
FIG. 4 is a diagram showing a laser irradiation part.
FIG. 5 is a diagram illustrating a configuration example of a pixel circuit in an organic EL panel.
[Explanation of symbols]
10 First TFT, 40 Second TFT, 50 Anode.

Claims (5)

A method for dimming defective pixels in an EL panel having an EL light emitting element and a thin film transistor controlling a current to the EL light emitting element for each pixel arranged in a matrix,
A method for dimming an EL panel, comprising selectively irradiating at least a part of a semiconductor layer constituting the thin film transistor with a laser to increase a resistance value of the semiconductor layer in the region and dimming the pixel. The method for reducing the brightness of an EL panel according to claim 1,
A method for dimming an EL panel, comprising: irradiating a laser from below onto a portion where a metal layer is disposed above the semiconductor layer, and reflecting the laser radiated by the metal layer. The method for reducing the brightness of an EL panel according to claim 1,
The thin film transistor has a configuration in which a semiconductor layer is provided over a glass substrate, and a gate electrode is provided thereover with a gate insulating film interposed therebetween. A method for reducing the light intensity of an EL panel, which comprises reflecting the laser irradiated by the method. A method for dimming an EL panel according to any one of claims 1 to 3,
A method for dimming an EL panel, wherein the laser is a UV laser. 5. An EL panel, wherein defective pixels are dimmed by the method of dimming an EL panel according to claim 1.

Images