JP2008083109A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid a decrease in display quality due to specular reflection by wiring while making a display device adaptive to light pen input, and also to make the display device cope with semi-transmission. <P>SOLUTION: An optical sensor 10 is disposed in each pixel and detects light from a spot light source (light pen 60). An array substrate 2 having driving transistors of respective pixels formed on a back light (rear light source) 7 emitting backlight and an opposite substrate 3 where color filters are formed are stacked in this order, and optical sensors 10 are formed on the array substrate 2. In the optical sensor 10, the backlight is not intercepted. Further, in the optical sensor 10, an exposure condition is so set that the difference between the white pixel rate of a background part and the white pixel rate of a light irradiated part irradiated with light from a light pen 60 is ≥30%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device such as a liquid crystal display device, and more particularly to a display device with a built-in reading function in which a photosensor is built in a pixel.

  For example, a liquid crystal display device, which is one type of flat display device, has features such as light weight, thinness, and low power consumption, and is therefore applied to various fields such as OA equipment, information terminals, watches, and televisions. In particular, a liquid crystal display device using a thin film transistor element (TFT element) is excellent in responsiveness, and thus is used as a display device in many electronic devices such as a mobile phone, a television, and a computer.

  In recent years, applications of flat display devices tend to expand more and more. For example, display devices with an input function using a light pen input and display devices with an image capturing function have been developed. If the user can input directly on the screen of the display device, the user interface can be greatly improved.

  As a display device having the above-described input function or image reading function, for example, as disclosed in Patent Document 1, each pixel includes a photosensor element, and each photosensor element detects light input from the screen. Such a display device is known. In Patent Document 1, at least one display element is provided corresponding to each of the display elements formed near the intersections of the signal lines and the scanning lines arranged in rows and columns, and each of the display elements is designated. A display device including a photoelectric conversion unit that receives incident light in a range and converts it into an electrical signal is disclosed. In the display device, light reflected by an image reading object (for example, a paper surface) is reflected on an array substrate. The sensor (photoelectric conversion unit) receives the light and reads the image.

For example, in a liquid crystal display device, the drive circuit that was previously an external component is integrated on a main surface of a light-transmitting substrate (glass substrate) by integrating thin film transistors (TFTs), thereby reducing the total cost. Technology to make it develop. Therefore, if this technology is applied to create a photo sensor element on a glass substrate and a reading function can be built at the same time as the driving circuit, the total cost of the liquid crystal display device having an input function is reduced. It is expected that added value can be improved.
JP 2004-93894 A

  By the way, in a display device that detects light input from a screen by an optical sensor, an array substrate on which a drive circuit is built is disposed on the front surface, and a counter substrate on which a color filter is formed is disposed on the back surface side. The optical sensor is formed on the array substrate. This is because it is necessary to form a light shielding layer in the lower part of the optical sensor in order to shield the backlight light. Conventionally, when backlight light is directly input to an optical sensor, it is considered that the detection of the incident light by the optical sensor is hindered, and the above structure is employed. When the array substrate is placed on the front surface and a photosensor is built here, the gate electrode and wiring electrode of the photodiode that constitutes the photosensor function as a light shielding layer, and the backlight is not irradiated to the photodiode. .

  However, in the case of adopting the above structure, since the photodiode and the wiring of the driving circuit (thin film transistor) are formed on the array substrate disposed on the front surface of the liquid crystal layer, glare is caused by the mirror reflection of the metal, and the display quality is improved. There is a problem of serious damage. Further, the structure in which the array substrate is disposed on the front surface of the liquid crystal layer has a problem that a transflective configuration cannot be adopted. In the case of a transflective liquid crystal display device, it is necessary to form a reflective electrode corresponding to the reflective region. However, when the reflective electrode is formed on the array substrate arranged in front of the liquid crystal layer, this portion is shielded from light. This is because the display cannot be performed.

  The present invention has been proposed in view of such a conventional situation, and can cope with optical pen input, while avoiding deterioration in display quality due to mirror reflection of wiring, and can also cope with semi-transmission. An object is to provide a simple display device.

  In order to achieve the above-described object, a display device according to the present invention is a display device in which a photosensor is disposed in each pixel, and light from a point light source is detected by the photosensor, and is irradiated with backlight light. An array substrate on which a driving transistor for each pixel is formed on a back light source and a counter substrate on which a color filter is formed are stacked in this order, and the photosensor is formed on the array substrate and irradiated from the back light source. The backlight light to be emitted is not shielded.

  In the display device of the present invention, the array substrate is disposed on the back side, and the counter substrate is disposed on the front side. Therefore, the optical sensors and driving circuits (thin film transistors) formed on the array substrate are not directly recognized, and glare due to specular reflection is eliminated. In particular, the counter substrate on which the color filter is formed has a black matrix formed at the boundary between the pixels, and the wiring is concealed by the black matrix of the counter substrate disposed on the front surface. Quality does not deteriorate. In addition, since the array substrate is disposed on the back side, even if a reflective electrode is formed on the array substrate, display is not hindered, and transflective display can be supported.

  On the other hand, in the display device of the present invention, the array substrate on which the photosensor is formed is disposed on the back side (directly above the back light source), and the backlight light from the back light source is light from the structure of the photo sensor formed. The sensor will be irradiated directly. Until now, it has been considered that irradiation of backlight light to an optical sensor hinders detection of original incident light in the optical sensor. However, as a result of repeated studies by the present inventors, exposure of the optical sensor is performed. It was found that by setting the conditions appropriately, the S / N ratio between the detection light incident from a point light source such as an optical penlight and the backlight light from the back light source is secured. Therefore, in the display device of the present invention, the backlight light emitted from the back light source is not shielded by the optical sensor, but the S / N ratio is ensured by the detection light (signal S) and the backlight light (noise N). Therefore, the detection light is accurately detected.

  Further, in the display device of the present invention, the light receiving portion of the photosensor is always irradiated with the backlight light from the back light source, and a photocurrent flows. This is advantageous in terms of the reliability of the device (light sensor). This is because all photosensors experience a nearly uniform bias history. In the configuration in which the light sensor blocks the backlight light as in the conventional display device with an input function, a photocurrent is always generated in the light sensor irradiated with strong light from the front side, whereas the light is generated. No photocurrent is generated in a photosensor that is not irradiated with light, and the bias history of the photosensor is biased. As a result, sensitivity unevenness occurs in the reading sensitivity, and proper reading may not be performed.

  According to the present invention, light input from a pen (light from a point light source) can be detected with certainty, and deterioration in display quality due to specular reflection of wiring can be avoided. It is possible to provide a display device that can handle display.

  Hereinafter, a display device (here, a liquid crystal display device) to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 shows an example of a liquid crystal display device to which the present invention is applied. In the liquid crystal display device 1, a liquid crystal cell is formed by a pair of light-transmitting insulating substrates, and a liquid crystal material is sealed in a gap between them to form a liquid crystal layer. Specifically, a liquid crystal layer 4 is sealed between the array substrate 2 and the counter substrate 3.

  The array substrate 2 uses, for example, a light-transmissive insulating substrate made of glass or the like as a support substrate. On the light-transmissive insulating substrate, scanning lines arranged substantially parallel to each other at equal intervals, or substantially orthogonal to these scanning lines. Signal lines arranged in layers, an interlayer insulating film (transparent insulating film) that is interposed between the scanning lines and the signal lines to electrically insulate them, and a switching element disposed near the intersection of the scanning lines and the signal lines Drive transistors (thin film transistors: TFTs) are formed.

  In the array substrate 2, pixel electrodes 22 electrically connected to the switching elements through through holes formed in the interlayer insulating film 21 are arranged in a matrix. The pixel electrode 22 is formed as a transparent electrode. In the present embodiment, a part of the pixel electrode 22 is used as a reflective electrode 23 to form a transflective liquid crystal display device. In addition to the interlayer insulating film 21, switching elements such as signal lines, scanning lines, and thin film transistors are disposed between the light-transmissive insulating substrate of the array substrate 2 and the pixel electrode 22, as described above. In FIG. 1, these illustrations are omitted. Furthermore, an alignment film is provided on almost the entire surface of the array substrate 2 on which the pixel electrodes 22 are provided, but this is also omitted here.

  On the other hand, the counter substrate 3 also has a light transmissive insulating substrate made of glass or the like as a support substrate, and a color filter layer 31 is formed on the surface on the liquid crystal layer 4 side corresponding to each pixel. In addition, a transparent counter electrode (not shown) made of a transparent conductive material such as ITO is formed on the entire surface so as to cover the surface. The color filter layer 31 is a resin layer colored in colors with pigments or dyes, and is configured by combining filter layers of R, G, and B colors, for example. Although not shown, a so-called black matrix layer is formed at the pixel boundary portion of each color filter layer 31 for the purpose of improving the contrast.

  In the liquid crystal display device 1 having the above-described configuration, polarizing plates 5 and 6 are provided outside the array substrate 2 and the counter substrate 3, respectively, and a backlight (back light source) 7 disposed on the back side is used as a light source. As shown in FIG. The array substrate 2 and the counter substrate 3 are arranged in such a manner that the array substrate 2 is on the back side and the counter substrate 3 is on the front side. Therefore, in the liquid crystal display device 1 of this embodiment, the backlight 7, the polarizing plate 5, the array substrate 2, the liquid crystal layer 4, the counter substrate 3, and the polarizing plate 6 are arranged in this order from the back side.

  The above is the basic configuration of the liquid crystal display device 1, but the liquid crystal display device 1 of the present embodiment is configured as a light pen input panel in which coordinate input or the like is performed using a light pen as a point light source, An optical sensor 10 for detecting pen light is installed on the array substrate 2 for each pixel.

  The optical sensor 10 is directly formed on the array substrate 2 and is formed at the same time as these thin film transistors using, for example, a low-temperature polysilicon technique, for example, similarly to the thin film transistors constituting the drive circuit on the array substrate 2.

  FIG. 2 shows a configuration example of the optical sensor 10 formed on the array substrate 2, and here shows a configuration of a PIN diode used as the optical sensor 10.

  In the array substrate 2, a polycrystalline semiconductor layer (polysilicon layer) 11 is formed on a glass substrate 24 via an undercoat layer 25, and the polycrystalline semiconductor layer 11 is used as a channel layer. Here, the purpose of the undercoat layer 25 is to block the surface of the glass substrate 24 by scratching or scratching the surface, to prevent the impurities contained in the glass substrate 24 from diffusing into the polycrystalline semiconductor layer 11. Is formed. The undercoat layer 25 is formed by forming a silicon oxide film, a silicon nitride film, or the like. For example, a planarization layer made of a fluidized resin that is fluidized by heat treatment, and a covering layer that prevents diffusion of impurities. It is also possible to have a laminated structure consisting of Alternatively, when the glass substrate 24 is excellent in planarization and contains a small amount of impurities, the undercoat layer 25 can be omitted.

  The polycrystalline semiconductor layer 11 formed on the undercoat layer 25 is annealed with amorphous silicon (a-Si) formed by, for example, a plasma CVD method, and then polycrystallineized by laser irradiation or the like. Is formed. The polycrystalline semiconductor layer 11 is separated into islands by etching and arranged in a matrix corresponding to each pixel.

In the polycrystalline semiconductor layer 11 on the undercoat layer 25, ap ⁺ region 11a, ap ⁻ region 11b, an n ⁻ region 11c, and an n ⁺ region 11d are formed. Thus, p ⁺ / p ⁻ / n ^A diode is configured by forming ⁻ / n ⁺ in the horizontal direction.

Note that the PIN diode (photosensor 10) may be configured without the n ⁻ region 11c. Instead of forming each region in the lateral direction and forming a PIN diode as shown in FIG. A PIN diode may be configured by laminating these regions in the vertical direction. Also in the PIN diode, a first metal (gate electrode) 14 and a second metal 15 are formed on the polycrystalline semiconductor layer 11 via a first insulating layer 12 and a second insulating layer 13.

  Next, a circuit configuration in the liquid crystal display device 1 will be described. As shown in FIG. 3, the drive circuit of the liquid crystal display device 1 includes a circuit unit formed on the array substrate 2 and a circuit unit formed on the semiconductor substrate 40.

  Here, on the array substrate 2, a signal line and a scanning line, as well as the pixel array section 41 in which the above-described pixel electrode and thin film transistor are formed corresponding to each pixel, and an exposure time control circuit (which controls the exposure time) 42, a signal line drive circuit 43 that drives the signal lines, a scan line drive circuit 44 that drives the scan lines, and a detection and output circuit 45 that captures and outputs an image. It has been. Each circuit on the array substrate 2 is formed by, for example, a polysilicon TFT. Among these circuits, for example, the signal line drive circuit 43 includes a D / A conversion circuit that converts digital image data into an analog voltage suitable for driving the display element. A known D / A conversion circuit can be used as the D / A conversion circuit of the signal line driver circuit 43.

  On the other hand, a logic IC 46 that performs display control and image capture control is mounted on the semiconductor substrate 40. The circuit unit on the array substrate 2 and the circuit unit on the semiconductor substrate 40 transmit and receive various signals via, for example, a flexible printed circuit board (FPC).

  FIG. 4 is a block diagram showing a part of the pixel array section 41 in detail. Each pixel includes a pixel TFT 51, a liquid crystal capacitor C1 and an auxiliary capacitor C2 connected to one end of the pixel TFT 51, and a photosensor 10 for capturing an image. The photosensor 10 for capturing an image has a different size for each pixel. The pixels have colors such as red, green, and blue, and at least one photosensor 10 is provided corresponding to each of the three pixels. Each optical sensor 10 receives an incident light in a specified range and converts it into an electrical signal, a charge storage unit that accumulates charges according to the electrical signal converted by the imaging unit, and Switching between an imaging result storage unit that temporarily stores a signal corresponding to the charge accumulated in the charge accumulation unit and whether to output a signal stored in the imaging result storage unit according to the logic of the control signal line It has an output switching unit to be controlled, and a mechanism that can vary the amount of charge accumulated in the charge accumulation unit called imaging exposure time and precharge voltage according to the illuminance of ambient light.

  The optical sensor 10 is directly formed on the array substrate 2 as described above, and data acquired from the optical sensor 10 is processed by the logic IC 46 on the semiconductor substrate 40. The logic IC 46 can calculate the average gradation, sets the exposure conditions such as the precharge voltage and the exposure time, and sends the corresponding control signal to the exposure time control for controlling the exposure time on the glass substrate 1. Transmit to circuit 42.

  In the liquid crystal display device 1 (optical pen input panel) having the above configuration, incident light such as pen light or external light is subjected to image processing and coordinate detection is performed, so that the exposure time and the imaging signal amplification amount are not set appropriately. And a sufficient S / N ratio cannot be obtained. The S / N ratio is the ratio of signal to noise. In the light pen input panel, the signal is the gradation value of the incident light of the light pen, and the noise is the gradation value of the portion where the light of the light pen is not incident. It is. Image processing accuracy improves as the S / N ratio increases.

  Here, when the arrangement of the array substrate 2 and the counter substrate 3 is considered, for example, as shown in FIG. 5A, when the array substrate 2 is arranged on the front surface and the counter substrate 3 is arranged on the back surface side, the backlight from the backlight 7 is displayed. The light is shielded by the first metal 14 and the second metal 15, and the photosensitive portion (PIN diode) of the photosensor 10 formed on the array substrate 2 is not irradiated with the backlight. Therefore, as shown in FIG. 5B, the background that becomes noise is only the external light incident from the front surface, the background level (noise level) is suppressed low, and the background from the light pen 60 is reduced. The S / N ratio can be increased. However, if the array substrate 2 is disposed on the front surface and the counter substrate 3 is disposed on the rear surface side, the wiring on the array substrate 2 is mirror-reflected and the display quality is greatly impaired. Further, there is a restriction that the configuration of the transflective liquid crystal display device cannot be adopted.

  On the other hand, in the case of the above-described liquid crystal display device 1 according to the embodiment of the present invention, as shown in FIG. 6A, the array substrate 2 is arranged on the back side and the counter substrate 3 is arranged on the front side. Then, the backlight light from the backlight 7 is applied to the optical sensor 10, and the background level increases as shown in FIG. 6B. This is because, as a result of the backlight light irradiation, the amount of the outside light and the backlight light combined is the background (noise).

  The increase in the background is disadvantageous for increasing the S / N ratio. However, as a result of repeated investigations by the present inventors, for example, in the case of light pen input, the signal is relatively strong, so the conclusion that it can be sufficiently detected by setting the exposure conditions appropriately has been reached. .

  The photosensor 10 provided corresponding to each pixel outputs a value of “white” or “black”. If the light applied to the optical sensor 10 is strong, it is “white”, and if the light is weak, it is “black”. When light of the same intensity is irradiated, the proportion of the optical sensor 10 that outputs “white” increases as the exposure time increases. That is, for light of the same intensity, the ratio (white pixel ratio) of the optical sensor 10 that outputs “white” can be adjusted by adjusting the exposure time.

  FIG. 7 shows the relationship between the exposure time and the white pixel ratio in the background portion (portion irradiated only with external light and backlight light), and the exposure time and white in the pen irradiation portion (portion irradiated with light from the optical pen). This shows the relationship between the proportions of painters. Therefore, FIG. 7 shows responsiveness to the exposure time in the background portion and the pen irradiation portion, and the white pixel ratio corresponds to the gradation.

  As is apparent from FIG. 7, it can be seen that the response is sensitive under the exposure condition where the white pixel ratio in the background portion is around 10%. That is, under the exposure condition where the white pixel ratio in the background portion is around 10%, the white pixel ratio greatly changes due to a slight change in the amount of light. Therefore, if the exposure condition is set so that the white pixel ratio in the background portion is around 10%, the S / N ratio (difference) between the pen irradiation portion and the background portion can be increased, and the signal from the light pen The background (external light and backlight light) can be distinguished.

  As the exposure condition, what percentage of the white pixel ratio in the background portion is appropriate depends on the sizing (sensitivity design) of the optical sensor 10, but the white pixel ratio in the pen irradiation portion and the background portion is different. It is preferable to choose to maximize the difference. For example, FIG. 7 shows the white pixel ratio of the pen irradiation portion to the background portion. When the white pixel ratio of the background portion is about 10%, the white pixel ratio of the pen irradiation portion to the background portion is also maximized. Specifically, the difference between the white pixel ratio in the background portion irradiated with backlight and external light and the white pixel ratio in the light irradiation portion irradiated with light from the light pen as a point light source is 30% or more. It is preferable to set so. By setting the exposure condition, a sufficient S / N ratio can be ensured, and a signal from the optical pen can be detected.

  In the background portion, the background level varies due to variations in external light, backlight light, and the like. In such a case, the exposure condition may be set so that the average value of the background level is taken and the white pixel ratio of the background portion becomes a predetermined value. Alternatively, it is possible to set the exposure condition using other statistical information such as a median value for the background level.

  As described above, in the liquid crystal display device 1 of the present embodiment, the wiring of the optical sensor 10 and the drive circuit (thin film transistor) formed on the array substrate 2 is not directly visible, and glare due to specular reflection, etc. It is possible to eliminate the deterioration of the display quality due to. Further, since the array substrate 2 is arranged on the back side, even if a reflective electrode is formed on the array substrate 2, display is not hindered, and it is possible to cope with transflective display.

  Furthermore, in the liquid crystal display device 1 of the present embodiment, the S / N ratio between the detection light (signal S) and the backlight light (noise N) can be ensured. For example, the detection light from the optical pen can be accurately obtained. It is possible to detect. Further, in the liquid crystal display device 1 of the present embodiment, since the backlight light from the back light source is always radiated to the optical sensor 10, all the optical sensors 10 experience a substantially uniform bias history, and the device (optical sensor 10). ) Reliability can be improved.

It is a schematic sectional drawing which shows an example of the liquid crystal display device to which this invention is applied. It is a principal part schematic sectional drawing which shows the structural example of an optical sensor. It is a schematic diagram which shows the circuit structure of a liquid crystal display device. It is a figure which shows the circuit structural example of the pixel which comprises a pixel array part. (A) is a figure which shows schematic structure of the liquid crystal display device which has arrange | positioned the array board | substrate to the front side, (b) is a figure which shows the signal strength (gradation) in an optical sensor. (A) is a figure which shows schematic structure of the liquid crystal display device which has arrange | positioned the array board | substrate on the back side, (b) is a figure which shows the signal strength (gradation) in an optical sensor. It is a characteristic view which shows the relationship between the exposure time in a background part and a pen irradiation part, and a white pixel ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 2 Array substrate, 3 Opposite substrate, 4 Liquid crystal layer, 5,6 Polarizing plate, 7 Backlight, 10 Optical sensor, 11 Polycrystalline semiconductor layer, 14 1st metal, 15 2nd metal, 22 Pixel electrode , 23 Reflective electrode, 31 Color filter layer, 40 Semiconductor substrate, 41 Pixel array section, 42 Exposure time control circuit, 43 Signal line drive circuit, 44 Scan line drive circuit, 45 Detection and output circuit, 46 Logic IC

Claims (3)

A photo sensor is disposed in each pixel, and the display device detects light from a point light source by the photo sensor,
The array substrate in which the drive transistor of each pixel is formed on the back light source that irradiates the backlight and the counter substrate in which the color filter is formed are stacked in this order,
The optical sensor is formed on an array substrate, and backlight light emitted from the back light source is not shielded.   In the optical sensor, the exposure condition is set so that a difference between a white pixel ratio in a background portion irradiated with backlight light and a white pixel ratio in a light irradiation portion irradiated with light from the point light source is 30% or more. The display device according to claim 1, wherein the display device is set.   The display device according to claim 2, further comprising an optical sensor adjustment unit that adjusts an exposure condition of the optical sensor, wherein the white pixel ratio in the background portion is controlled by the optical sensor adjustment unit.

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