JPH0522217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device, and more particularly to a matrix liquid crystal display device having a display section and a photodetector for each pixel.

In recent years, there has been active development of matrix liquid crystal display devices using thin film transistors as switch elements using amorphous silicon or polycrystalline silicon as semiconductor films. Furthermore, attempts have been made to provide a photodetector for each pixel to provide a photographing function or an optical writing function using a light pen.

Figure 1 is an equivalent circuit diagram of a conventional matrix liquid crystal display device in which each pixel is equipped with a photodetector.
A MOS transistor, 2 a capacitance for storing an image signal for a frame period, and 3 a liquid crystal cell. One electrode 4 of the liquid crystal cell has a potential common to all pixels. The photodetector of each pixel is composed of a switch 5 using a MOS transistor for extracting a detection signal to the outside, and a diode 6 for generating photovoltaic force. To display an image on this display device, an X-line scanning signal generator 7
X ₁ line is in ON state, i.e. on this line
Turn on all MOS transistors. In this state, the video signal of each pixel is sequentially written as Y ₁ , Y ₂ ... Yn to each pixel along the X ₁ line by the Y line scanner 8, and then the gate of the X ₁ line is turned off.
If so, the video signal held in the capacitance 2 continues to be applied to the liquid crystal cell 3 until the next rewriting is performed. The same operation is then repeated on the X ₁ to X _o lines. Next, to perform photodetection, for the X line, the photocurrent generated in the diode 6 when the MOS transistor 5 is ON is detected via the _S1 line in the same way as for image display. If the S line scanning circuit 9 repeatedly scans from S ₁ to _{S o} , one line's worth of image signals can be detected, and by repeating this from X ₁ to X _o , one screen's worth of image signals can be detected. In the above manner, the first
Although the matrix liquid crystal display device shown in the figure can display images and take pictures, it has the following drawbacks. That is, (1) since light detection and display are performed within the same pixel, the area required for wiring and light detection increases, and the brightness of the display decreases.

(2) Since the structure is complex, high manufacturing yields cannot be expected.

The purpose of the present invention is to eliminate the drawbacks of the conventional art and provide a display circuit and a photodetection circuit on separate substrates, thereby (1) providing a bright display that prevents a reduction in display area; and (2) improving the panel structure. This is an improvement in manufacturing yield due to simplification.

The present invention will be described in detail with reference to the drawings. Second
The figure is a cross-sectional view of a unit pixel in one embodiment of the present invention, and the third figure shows an equivalent circuit of a substrate provided with a MOS transistor for driving the liquid crystal shown by 11 in FIG. Figure 4 is the second
FIG. 2 is a diagram showing an equivalent circuit of a substrate provided with a photodetector element indicated by 12 in the figure. In FIG. 1, 11 is a substrate made of a transparent insulator such as glass, and on top of 11 is a gate electrode 13, a gate insulating film 14, and a semiconductor film 1 made of amorphous or polycrystalline silicon.
5, the first from the source electrode 16 and the drain electrode 17
A thin film transistor is formed, and a first transparent electrode 18 for driving the liquid crystal is connected to the drain electrode 17. When the semiconductor film 15 is amorphous silicon, the gate electrode 13 is preferably an opaque conductive film such as aluminum in order to avoid leakage current of the transistor due to light irradiation. Further, it is desirable that the thickness of the amorphous silicon film is 2 μm or more. MOS transistor and liquid crystal drive electrode 18
Above, a color filter 19 consisting of the three primary colors of red, green, and blue is provided for each pixel, making it possible to display color pixels. A substrate 2 facing the substrate 1 is also made of a transparent insulator such as glass, and on the substrate 12, like the substrate 11, a gate electrode 2 is provided.
0, a second thin film transistor consisting of a gate insulating film 21, a semiconductor film 22, a source electrode 23, and a drain electrode 24 is formed, and the drain electrode 24
A diode, which is a Pin type or Pn type photodetecting element, is connected to the diode 25, and the diode 25 is connected to a ground electrode 27 via an n ⁺ type automic junction layer 26. The second transparent electrode 27 is connected to ground, and also drives the liquid crystal layer between it and the first transparent electrode 18. In FIG. 2, capacitance is omitted for simplicity of explanation.

Next, the operation will be explained.

MOS transistor 28 on the substrate 11
(Figure 3) is turned on by the gate signal of the X1 line, which is the first _X line electrode, and is turned on by the gate signal of the first Y line electrode.
Capacitance 29 for video signal from Y ₁ line
, and voltage continues to be applied to the liquid crystal cell 30 even after the gate is turned off. 31 is an X line scanning circuit, and 32 is a Y line scanning circuit. Substrate 12
The upper MOS transistor 33 (Fig. 4) is also turned on by the gate signal of the SX1 line, which is the second X line electrode, and transfers the photocurrent generated by the diode 34, which is the photodetecting element, to the S1 line, which is the second line electrode. It can then be detected. 35 is an SX line scanning circuit, and 36 is an S line scanning circuit. When performing light detection, light is incident from the substrate 11 side and detected by the substrate 2, thereby detecting the filter layer 1.
Since color-modulated light is detected in step 9, color images can also be detected.

As explained above, in the present invention, by separately forming a photodetection array and a liquid crystal drive array using thin film transistors on two upper and lower substrates,
We have realized a liquid crystal display panel that has a bright display with a large aperture ratio for each pixel, has a high manufacturing yield due to the simplified structure of each substrate, and is capable of displaying in color, photographing, and writing. In Figure 2, it appears that the photodetector diode occupies a large area of the liquid crystal display, but this is because the shape of the diode has been made large for the sake of ease of explanation; in reality, the photodetector diode is sufficiently small compared to the pixel area. A diode is also sufficient for photodetection. For other transistors and wiring sections, the influence can be ignored by using the same wiring pattern and transistors on the substrate 11 and the substrate 12. Regarding the type of liquid crystal, a field effect type, twisted nematic type, guest host type, etc. are used. It is clear that the display panel can be constructed by using filters, reflectors, etc. as necessary.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional embodiment, FIG. 2 is a cross-sectional diagram of an embodiment of the present invention, and FIGS. 3 and 4 are diagrams each showing an equivalent circuit of the embodiment of the present invention. 1...transistor, 2...capacitance,
3...Liquid crystal cell, 4...Common electrode, 5...Transistor, 6...Diode, 7, 8, 9...Scanning circuit, 11, 12...Substrate, 13...Gate, 1
4... Insulating film, 15... Semiconductor film, 16, 17...
...Electrode, 18...First transparent electrode, 19...Filter, 20...Gate, 21...Insulating film, 22...
... semiconductor film, 23, 24 ... electrode, 25 ... diode, 26 ... electrode, 27 ... second transparent electrode,
28...Transistor, 29...Capacitance, 30...Liquid crystal cell, 31, 32...Scanning circuit, 33...Transistor, 34...Diode, 35, 36...Scanning circuit.

Claims (1)

[Claims] 1. A plurality of first X line electrodes and a plurality of first Y line electrodes are formed in a lattice shape on one substrate, and at each intersection of the first X line electrode and the first Y line electrode. A first thin film transistor and a first transparent electrode are formed, a plurality of second X line electrodes and a plurality of second Y line electrodes are formed in a lattice shape on the other substrate, and the
A second thin film transistor, a photodetection element, and a second transparent electrode are formed at each intersection of the 2X line electrode and the second Y line electrode, and the one substrate and the other substrate are spaced apart from each other. A liquid crystal panel in which a pixel is constituted by the first transparent electrode and the second transparent electrode, which are arranged so that they face each other, a liquid crystal is sealed in the interval, and the liquid crystal is sandwiched between the first transparent electrode and the second transparent electrode, wherein a line is connected to the first X-line electrode. A gate signal is sequentially supplied to turn on the first thin film transistor on the first X line electrode, an image signal is supplied to the first Y line electrode, and the image signal is applied to the liquid crystal of the pixel via the first thin film transistor. The image signal is supplied to perform a display operation, and the second thin film transistor on the second X-line electrode is turned on by supplying a gate signal line-sequentially to the second X-line electrode, and the second thin-film transistor on the second X-line electrode is turned on. A matrix liquid crystal display device, characterized in that a photocurrent of is detected through the second thin film transistor and the second Y line electrode.