JPH07113723B2 - Liquid crystal display - Google Patents

Description

The present invention relates to an active liquid crystal display device using a thin film transistor having a semiconductor layer of amorphous silicon as a switch element.

"Prior Art" In an active liquid crystal display device, transparent substrates 11 and 12 such as glass are provided in close proximity to each other as shown in FIG. 1, and a spacer 13 is interposed at a peripheral portion thereof. 1
A liquid crystal 14 is enclosed between the two. A plurality of display electrodes 15 are formed on the inner surface of one transparent substrate 11, thin film transistors 16 are formed as switching elements in contact with the respective display electrodes 15, and the drains of the thin film transistors 16 are connected to the display electrodes 15. These plural display electrodes 15
A transparent common electrode 17 on the inner surface of the other transparent substrate 12 facing the
Are formed.

The display electrodes 15 are, for example, pixel electrodes, and as shown in FIG. 2, square ones are arranged on the transparent substrate 11 in rows and columns, that is, in a matrix form. Gate bus 18
And a source bus (data line) 19 is formed along and adjacent to each column array of the display electrodes 15. A thin film transistor 16 is provided at the intersection of each gate bus 18 and source bus 19, a gate of each thin film transistor 16 is connected to the gate bus 18 at an intersection position of both buses, and each source is connected to a source bus 19 respectively. The drain is connected to the display electrode 15.

Each of the gate bus 18 and the source bus 19 is selected and a voltage is applied between them, and only the thin film transistor 16 to which the voltage is applied becomes conductive, and a display connected to the drain of the conductive thin film transistor 16 is displayed. A charge is accumulated in the electrode 15 and a voltage is applied only to the liquid crystal 14 between the display electrode 15 and the common electrode 17, whereby only the display electrode 15 part becomes transparent or light-shielded, and selective. Is displayed. The display can be erased by discharging the charges accumulated in the display electrode 15.

As shown in FIG. 3, the thin film transistor 16 has a transparent substrate 11
The pixel electrode 15 and the source bus are formed on the transparent conductive film such as ITO, the semiconductor layer 21 of amorphous silicon is formed over the pixel electrode 15 and the source bus 19, and the semiconductor layer 21 is nitrided. A gate insulating film 22 such as silicon is formed. A gate electrode 23 is formed on the gate insulating film 22 so as to partially overlap the pixel electrode 15 and the source bus 19 via the semiconductor layer 21. In this way, the pixel electrode 15 and the source bus 19 that face the gate electrode 23 respectively form the drain electrode 15a and the source electrode 19a, and these electrodes 15a and 19a, the semiconductor layer 21, and the gate insulating film 2 are formed.
2. The gate electrode 23 constitutes the thin film transistor 16.

"Problems to be Solved by the Invention" In a conventional liquid crystal display device of this type, the contrast changes according to the temperature change, that is, the contrast decreases as the temperature rises as shown in FIG.

When the illuminance on the display surface changes, the contrast also changes as shown in FIG.

Further, in the case of a color liquid crystal display device, the chromaticity changes as the illuminance on the display surface changes, as shown in FIG.

An object of the present invention is to provide a liquid crystal display device capable of preventing display characteristics from changing regardless of changes in operating conditions such as ambient temperature and illuminance.

[Means for Solving Problems] A pixel electrode and a source electrode are formed on a transparent substrate, an amorphous silicon semiconductor layer is formed on the transparent substrate between the pixel electrode and the source electrode, and the semiconductor layer is formed on the semiconductor layer. In an active liquid crystal display device in which a thin film transistor in which a gate insulating film is formed and a gate electrode is formed on the gate insulating film is used as a switching element, it is formed on the transparent substrate at the same time with the same material as the pixel electrode. A pair of electrodes, an amorphous silicon layer that covers these electrodes and is made of the same material as the semiconductor layer at the same time, and a pair of electrodes that covers the amorphous silicon layer and is made of the same material as the gate insulating film at the same time It consists of an insulating film and a light-shielding layer that covers the insulating film and is formed of the same material as the gate electrode at the same time. A temperature sensor, a pair of electrodes made of the same material as the pixel electrodes and formed on the transparent substrate at the same time, and an amorphous silicon layer formed of the same material as the semiconductor layer at the same time and covering the electrodes. An illuminance sensor formed of an insulating film that covers the amorphous silicon layer and is made of the same material as the gate insulating film at the same time, and is formed on a surface of the transparent substrate opposite to the temperature sensor and the illuminance sensor. A light-shielding layer that shields each of the temperature sensor and the illuminance sensor is provided.

[Embodiment] FIG. 7 shows an example in which the present invention is applied to a monochrome liquid crystal display device. The video signal from the input terminal 31 is input to the data terminal of the shift register 32 and the clock generation circuit 33. The clock generation circuit 33 generates a clock synchronized with the pixel period of the input video signal, and the shift register 32 is shifted by this clock. Further, this clock is counted by the pixel counter 34, and a clock having a horizontal cycle is created. The output clock of the pixel counter 34 is counted by the horizontal counter 35 to generate a clock having a vertical cycle, and this clock is supplied to the data input terminal of the gate shift register 36.
The shift control is performed by the output clock of. The parallel outputs of the shift register 36 are driven by the gate drive circuit 37, respectively, corresponding to the gate bus 18 (FIG. 2) of the active liquid crystal display element 38. On the other hand, the video signal serial-parallel converted by the shift register 32 is latched by the latch circuit 39 by the output clock of the pixel counter 34, and the output of the latch circuit 39 is passed through the source drive circuit 41 to the source bus 19 of the liquid crystal display element 38 (see FIG. 2). ) Corresponding ones are respectively driven. The operating voltage of the source drive circuit 41 is applied from the power supply 42.

This liquid crystal display element is of a transmissive type, and as shown in FIG. 8, the liquid crystal display element 38 is attached to the casing 42 so as to close the opening of the display device casing 42, and is arranged in the casing 42. Light from the light source for backlight 43 is incident on the back surface of the liquid crystal display element 38. The brightness of the light emitted from the light source 43 is a dimmer.
Controlled by 44.

In the present invention, as shown in FIGS. 7 and 8, the liquid crystal display element 38 is a temperature sensor that outputs a signal according to the ambient temperature.
45 is made of amorphous silicon on the surface of the liquid crystal display element 38 on which the thin film transistor 16 is formed. For example, as shown in FIG. 9 and FIG. 10, comb-tooth electrodes 46 and 47 meshed with each other are formed on the substrate 11 at the same time as the pixel electrode 15 and the source bus 19 by the same material. An amorphous silicon layer 48 is formed simultaneously with the semiconductor layer 21 so as to cover 46 and 47. An insulating film 49 is formed on the amorphous silicon layer 48 at the same time as the gate insulating film 22. Further, if necessary, light shielding layers 51 and 52 are formed on the surface of the insulating film 49 and the surface of the substrate 11 facing the temperature sensor 45, respectively. The light shielding layer 51 can be formed simultaneously with the gate electrode 23.

On the surface of the substrate 11 on which the thin film transistor 16 is formed, an illuminance sensor 54 that outputs a signal according to the illuminance of the external light 53 incident on the liquid crystal display element 38 is formed of amorphous silicon. The illuminance sensor 54 has a structure similar to that of the temperature sensor 45. That is, the comb-teeth electrodes 55 and 56 are formed on the substrate 11 so as to mesh with each other, and the amorphous silicon layer 57 is formed so as to cover these electrodes 55 and 56. The illuminance sensor 54 is obtained by forming the insulating film 58 on the amorphous silicon layer 57. A light shielding layer 59 is formed on the surface of the substrate 11 facing the illuminance sensor 54.

As shown in FIG. 7, the power source 42 is output according to the output of the temperature sensor 45.
Is controlled, that is, the power supply voltage of the drive transistor of the source drive circuit 41 is controlled. The specific resistance of amorphous silicon changes by 1.5 digits when the temperature changes by 1 digit, and the resistance value decreases as the temperature rises. When the ambient temperature rises, the effective voltage applied to the pixel electrode 15 drops, the contrast drops, and the brightness also drops, but the power supply 42 is controlled by the output of the temperature sensor 45, and the The source drive signal amplitude is made large, and the ON level of the liquid crystal is kept almost constant.

The illuminance sensor 54 outputs an output according to the illuminance of the external light 53, that is, the amorphous silicon has photoconductivity and the illuminance is 1
When the digit changes, the resistivity of amorphous silicon changes by one digit, and the resistance value decreases as the illuminance increases. The output of the illuminance sensor 54 controls the dimmer 44 by the control unit 61,
When the illuminance of the extraneous light 53 increases, the illuminance of the emitted light of the backlight light source 43 increases. As shown in FIG. 8, the controller 61 outputs the output of the illuminance sensor 54 to the amplifier 62 as necessary.
The amplified output is added to the reference value from the reference power source 64 by the adder 63, and the dimmer 44 is controlled by the added output.

FIG. 11 shows an example in which the present invention is applied to a color liquid crystal display device. The color video signal from the input terminal 31 is the chroma circuit 65.
Thus, the red color signal R, the green color signal G, and the blue color signal B are separated into respective color signals and a synchronizing signal. These three color signals are amplified by the variable gain amplifier circuits 66R, 66G, 66B, respectively, and input to the signal inverting circuit 68 through the pedestal level adjusting circuit 67. The signal inversion circuit 68 outputs a red signal R, a green signal G, a blue signal B, and inverted color signals obtained by respectively inverting the levels of these signals. These six color signals are input to the AC video signal circuit 69, and the red signal R, the green signal G, the blue signal B, and the three inverted color signals are alternately taken out for each field, and the RGB switching circuit 7
Entered in 1. The RGB switching circuit 71 matches each of the three color signals with the color array of the active color liquid crystal display element 38 and supplies it to the source drive circuit 41. The source drive circuit 41 selects signals V ₁ , V ₂ and V ₃ that match each color arrangement of the color liquid crystal panel 38 and supplies them to the source bus.

On the other hand, the sync signal separated by the chroma circuit 65 is input to the sync control circuit 72. The synchronization control circuit 72 supplies the field signal to the AC video signal circuit 69 in synchronization with the input vertical synchronization signal, supplies the horizontal signal synchronized with the horizontal synchronization signal to the RGB switch circuit 71, and connects the pixel terminal The synchronized clock signal is supplied to the source drive circuit 41, and the clock signal synchronized with the horizontal sync signal is further supplied to the gate drive circuit 37.
Supply to. The gate drive circuit 37 selectively drives the gate bus of the liquid crystal display element 38 for each line.

In this example, the thin film transistor 16 of the color liquid crystal display element 38 is
The temperature sensor 45 and the illuminance sensor 5 are provided on the surface of the substrate 11 on which the
4. Further, the color sensor 73 is formed. Temperature sensor 45,
As the illuminance sensor 54, the same one as shown in FIG. 9 can be used. As the color sensor 73, for example, the 12th
The one shown is used. That is, the amorphous silicon photosensors 75R, 75G, and 75B are formed in the substrate 11. The photosensors 75R, 75G, and 75B have the same structure, and when the Hpin photodiode is used, the transparent electrode 76 is commonly formed. The electrode 76 can be formed simultaneously with the pixel electrode 15. A p-type layer 77 of amorphous silicon is formed on the electrode 76,
An i-type layer 78 of amorphous silicon is formed on 77
An amorphous silicon n-type layer 79 is formed on the i-type layer 78, and an electrode 81 is formed on the n-type layer 79. Each of these layers of amorphous silicon can be formed by controlling impurities when the semiconductor layer 21 is formed. Each of these optical sensors 75R, 75
A red filter 82R, a green filter 82G, and a blue filter 82B are respectively formed on the inner surface of the substrate 12 so as to face the G and 75B, so that the color sensor 73 is obtained. Outputs corresponding to the respective illuminances of the red component, green component, and blue component of the external light 53 are obtained from the electrodes 81 of the optical sensors 75R, 75G, and 75B, that is, the spectral characteristics of the external light 53 are obtained.

In the example shown in FIG. 11, the output of the temperature sensor 45 controls each gain of the variable gain amplification circuits 66R, 66G, 66B to control the amplitude of the source drive signal supplied to the source drive circuit 41, and the temperature sensor The output of 45 is supplied to the pedestal level compensating circuit 83, the reference voltage supplied to the pedestal level adjusting circuit 67 is controlled, the OFF level fluctuation of the liquid crystal is compensated due to the temperature fluctuation, and the OFF level is kept constant. Get good contrast.

The control of the backlight light source by the output of the illuminance sensor 54 is the same as the case described with reference to FIG.

When the color sensor 73 detects a state where the spectral characteristics of the ambient light, that is, the external light 53 is not balanced, the spectral characteristics of the backlight light are controlled and compensated accordingly. Therefore, a red light source 43R, a green light source 43G, a blue light source 43B are provided as the backlight light source 43, the output of the dimmer 44 is supplied to the dimmers 84R, 84G, 84B, respectively, dimmers 84R, 84G,
Red light source 43R, green light source 43G, blue light source 43B with each output of 84B
Are lit respectively. The dimmers 84R, 84G, 84B are respectively controlled by the outputs of the photosensors 75R, 75G, 75B of the color sensor 73, and the display coloring of the color liquid crystal display element 38 is compensated according to the imbalance of the color components of the external light 53. To be done.

[Advantages of the Invention] As described above, according to the present invention, a temperature sensor and an illuminance sensor are provided on the surface of a substrate of an active liquid crystal display element on which a thin film transistor is formed, and a change in contrast due to a change in ambient temperature and an illuminance of external light It is possible to compensate for the change in contrast due to fluctuations and always obtain good contrast, and these sensors can be manufactured in the same step as the formation of the thin film transistor.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of a liquid crystal display element, FIG. 2 is an electric circuit diagram of the liquid crystal display element, FIG. 3 is a sectional view showing a configuration example of a thin film transistor, and FIG. 4 is a contrast of the liquid crystal display element. -Ambient temperature characteristic diagram, Fig. 5 is a contrast-ambient illuminance characteristic diagram, Fig. 6 is a chromaticity change characteristic diagram according to ambient light illuminance, and Fig. 7 is a block diagram showing an example in which the present invention is applied to a monochrome liquid crystal display device, FIG. 8 is a sectional view thereof, FIG. 9 is a sectional view of the temperature sensor 45 and the illuminance sensor 54, FIG. 10 is a plan view of the temperature sensor, and FIG. 11 shows an example in which the present invention is applied to a color liquid crystal display device. A block diagram and FIG. 12 are sectional views showing a color sensor.

Claims (1)

[Claims] 1. A pixel electrode and a source electrode are formed on a transparent substrate, an amorphous silicon semiconductor layer is formed on the transparent substrate between the pixel electrode and the source electrode, and a gate insulating film is formed on the semiconductor layer. In the active liquid crystal display device in which a thin film transistor formed by forming a gate electrode on the gate insulating film is used as a switching element, a pair of electrodes made of the same material as the pixel electrode and simultaneously formed on the transparent substrate An amorphous silicon layer formed of the same material as the semiconductor layer at the same time as covering the electrodes, and an insulating film formed of the same material as the gate insulating film at the same time as covering the amorphous silicon layer, A temperature sensor that covers the insulating film and comprises a light-shielding layer formed of the same material as the gate electrode at the same time; A pair of electrodes made of the same material as the pixel electrodes and formed on the transparent substrate at the same time, an amorphous silicon layer formed of the same material as the semiconductor layer at the same time and covering the electrodes, and the amorphous silicon layer. And an illuminance sensor formed of an insulating film formed of the same material as the gate insulating film at the same time as the gate insulating film, and formed on the surface of the transparent substrate opposite to the temperature sensor and the illuminance sensor. A liquid crystal display device, comprising: a light-shielding layer that shields each of the illuminance sensors.