JP2000066624A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the number of the manufacturing processes from being increased even when an illuminance detection sensor to control the brightness of the light from a back light is provided in a liquid crystal display device provided with a thin film transistor as a switching device. SOLUTION: A thin film transistor provided with one gate electrode 91 and a pixel electrode 98 are formed in a thin film transistor forming area of a transparent substrate 3 on the back side out of a pair of transparent substrates of a liquid crystal display panel. An illuminance detection sensor comprising a double gate type photoelectric transfer thin film transistor provided with two gate electrodes 71, 80 is formed in an illuminance detection sensor forming area of the transparent substrate 3. A top gate electrode 80 of the illuminance detection sensor is formed simultaneously with the formation of the pixel electrode 98. As a result, the illuminance detection sensor is simultaneously formed with the formation of the thin film transistor and the pixel electrode 98 to prevent the number of manufacturing processes from being increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a non-light emitting type display panel such as a liquid crystal display panel.

[0002]

2. Description of the Related Art A display device having a non-light-emitting type display panel such as a liquid crystal display panel is roughly classified into a transmission-type display device using transmitted light and a reflection-type display device using reflected light. There is a reflective type for displaying, and a reflective and transmissive type that combines these two types. In the case of a reflective and transmissive display device, although not shown, a transflective semi-reflective plate is generally arranged on the back side of a non-emissive display panel, and a backlight is arranged on the back side. It has a structure. And when used as a transmissive type, the backlight is turned on, the light from the backlight is transmitted through the semi-transmissive semi-reflective plate and the display panel, and emitted to the front side of the display panel,
The display is thereby performed. On the other hand, when used as a reflection type, the backlight is not turned on, and external light incident from the front side of the display panel is transmitted through the display panel and reflected by the transflective plate, and the reflected light is displayed. The light is transmitted through the panel and emitted to the front side of the display panel, thereby performing display.

[0003]

By the way, in such a display device, display can be performed by simultaneously using both light from the backlight and external light. However, in an environment where sufficient screen brightness can be obtained with only external light, if display is performed using both light from the backlight and external light simultaneously, the screen brightness of the liquid crystal display panel becomes too high. There was a problem that it might be difficult.
An object of the present invention is to make it possible to always keep the screen brightness of a display panel suitable even when a display is performed by simultaneously using both light from a backlight and external light.

[0004]

According to the present invention, there is provided a non-light emitting display panel provided with a MIS type thin film transistor as a switching element, and a light source disposed on the back side of the display panel for directing light toward the back side of the display panel. Reflection and light emission means for reflecting external light incident from the front side of the display panel and transmitted through the display panel toward the back surface of the display panel, and An illuminance detection sensor formed of the same MIS type thin film transistor as the thin film transistor formed, and emission light brightness control means for controlling the brightness of light emitted from the reflection and light emission means based on the illuminance detected by the illuminance detection sensor. It was done. According to this invention, for example, the illuminance detection sensor detects the illuminance of both the external light and the backlight, and the luminance of the light emitted from the reflection and light emission means is controlled by the emission light luminance control means based on the detected illuminance. Therefore, even when the display is performed by simultaneously using both the light from the reflection and light emission unit and the external light, the screen brightness of the display panel can always be made suitable. Moreover, in this case, since the illuminance detection sensor is constituted by the MIS thin film transistor formed on the thin film transistor forming surface of the display panel, the illuminance detection sensor can be formed simultaneously with the formation of the MIS thin film transistor as the switching element. The number of manufacturing steps can be prevented from increasing.

[0005]

FIG. 1 shows a main part of a reflection / transmission type liquid crystal display device to which an embodiment of the present invention is applied. This liquid crystal display device includes an active matrix type liquid crystal display panel 1 having a switching element such as a thin film transistor between a data line and each pixel electrode. Although not shown in detail, the liquid crystal display panel 1 has a pair of glass substrates 2 and 3 bonded to each other with a substantially frame-shaped sealing material 4 interposed between the two glass substrates 2 and 3 inside the sealing material 4. Liquid crystal is sealed and each glass substrate 2, 3
Is formed by attaching polarizing plates 5 and 6 to the surface of the substrate.

On the back side of the liquid crystal display panel 1, a backlight (reflection / light emitting means) 11 having a reflection function is arranged. The backlight 11 includes an optical sheet 12 provided on the back surface of the liquid crystal display panel 1 and the optical sheet 12.
A light diffusion layer 13 provided on the back surface of the light diffusion layer 13;
An optical member 14 provided on the back surface of the optical member 14;
And a light source 16 provided on a predetermined one end surface side of the light guide 15.
The light source 16 includes a linear fluorescent tube 17 and a reflector 18 for reflecting light from the fluorescent tube 17 toward one end surface of the light guide 15.

As shown in FIG. 2, the light guide 15 is made of an acrylic resin or the like, and has a flat back surface and a predetermined one end surface perpendicular to the back surface.
The surface has a step-like structure that gradually becomes thinner from the light incident surface 21 side to the other end surface side. In this case, the step-like surface includes a plurality of step surfaces 22 parallel to the back surface and a step surface (light emitting surface) 23 perpendicular to these step surfaces 22. On each of the step surfaces 22, a reflection film 24 made of a deposited film of aluminum or the like is provided via a base film (not shown) made of silicon oxide. A reflection plate 25 is provided on the back surface of the light guide 15. The light guide 15 is disposed on the back surface side of the liquid crystal display panel 1 with its back surface appropriately inclined with respect to the liquid crystal display panel 1.

As shown in FIG. 2, the optical member 14 is made of an acrylic resin or the like, has a flat surface, and has a plurality of triangular projections 31 on the rear surface.
Are formed at a constant pitch. In this case, the interface between one side surface of the protrusion 31 and the air is a first optical interface 32, and the interface between the other side surface of the protrusion 31 and the air is a second optical interface 33. The interface between the back surface of the optical member 14 and the air between the projections 31 is a third optical interface 34. And the optical member 1
Numeral 4 is arranged on the light guide 15 with the apex of the protruding portion 31 approaching or in contact with the reflection film 24. In this state, the angle of the first optical interface 32 with respect to the step surface 22 of the light guide 15 (the angle of the first optical interface 32 on the side facing the step surface 23) is 90 ° or less, and the step surface 23
The surface is substantially parallel to or an inclined surface close thereto. The second optical interface 33 is an inclined surface whose angle with respect to a perpendicular to the surface of the optical member 14 is larger than the angle between the perpendicular and the first optical interface 32. The third optical interface 34 is a surface substantially parallel to the step surface 22 of the light guide 15 or an inclined surface close thereto. Note that the pitch of the projecting portions 31 of the optical member 14 is substantially the same as the pixel pitch of the liquid crystal display panel 1 or is a fraction of the pixel pitch. Further, the pitch of the step surface 22 of the light guide 15 is slightly larger than the pitch of the protruding portions 31 of the optical member 14.

The light diffusion layer 13 is formed by applying a transparent adhesive in which light scattering fine particles are dispersed on the surface of the optical member 14, for example. And the optical sheet 12
It is attached to the surface of the optical member 14 via the light diffusion layer 13. The liquid crystal display panel 1 is attached to the surface of the optical sheet 12 via a transparent adhesive or a double-sided adhesive sheet 35. As shown in FIG. 3, the optical sheet 12 has a transmission axis P and a reflection axis S that are substantially orthogonal to each other.
And transmits light of a polarization component (P polarization component) along the transmission axis P, and a polarization component (S polarization component) along the reflection axis S.
Light is reflected. That is, when light including both the P-polarized light component along the transmission axis P and the S-polarized light component along the reflection axis S is incident from the back surface side of the optical sheet 12, the incident light The light of the P polarization component along the transmission axis P is transmitted through the optical sheet 12, and the light of the S polarization component along the reflection axis S is reflected by the optical sheet 12.
Such a semi-transmissive and semi-reflective characteristic is the same for incident light from the surface side of the optical sheet 12.

When the liquid crystal display device is used as a transmission type, the fluorescent tube 17 is turned on. Then, the light from the fluorescent tube 17 and the reflected light reflected by the reflector 18 are incident on the light incident surface 21 of the light guide 15. The incident light is reflected by the reflection film 24 and the reflection plate 25 while being reflected by the light guide 1 as shown by a solid arrow in FIG. 2, for example.
5 travels in the horizontal direction, and is emitted from each step surface (light emitting surface) 23. The outgoing light is also applied to the first optical interface 32 of the optical member 14 as shown by the solid arrow in FIG.
And is totally reflected by the second optical interface 33, exits from the surface of the optical member 14, enters the light scattering layer 13 and is scattered. Of the scattered light, the light of the P-polarized component passes through the optical sheet 12 and is incident on the back surface of the liquid crystal display panel 1, and the light of the S-polarized component is reflected by the optical sheet 12. However, the light reflected by the optical sheet 12 is reflected by the reflection film 24 and is scattered again by the light scattering layer 13. Of the scattered light, the light of the P-polarized component passes through the optical sheet 12 and is incident on the back surface of the liquid crystal display panel 1, and the light of the S-polarized component is reflected by the optical sheet 12. By repeating such a process, most of the light emitted from each step surface 23 is incident on the back surface of the liquid crystal display panel 1. Note that the transmission axis of the optical sheet 12 and the transmission axis of the polarizing plate 6 on the back side of the liquid crystal display panel 1 are substantially parallel to each other. Then, the light incident on the back surface of the liquid crystal display panel 1 passes through the liquid crystal display panel 1 and is emitted to the front surface side of the liquid crystal display panel 1, whereby display is performed.

On the other hand, when the liquid crystal display device is used as a reflection type, external light is used without turning on the fluorescent tube 17. That is, external light (linearly polarized light) incident from the surface side of the liquid crystal display panel 1 is
Through. The transmitted light is transmitted through the optical sheet 12, the light diffusion layer 13 and the optical member 14 in order, as shown by a dotted arrow in FIG.
This reflected light passes through the optical member 14 and is diffused by the light diffusion layer 13. Most of the diffused light passes through the optical sheet 12 and is transmitted through the liquid crystal display panel 1 in the same manner as described above.
Is incident on the back surface of. This incident light is transmitted to the liquid crystal display panel 1
And is emitted to the front side of the liquid crystal display panel 1 to perform display.

Next, in this liquid crystal display device, the light source 1
A case in which display is performed by simultaneously using both the light from the light source 6 and the external light will be described. By the way, the suitable screen luminance of the liquid crystal display panel 1 (the luminance at which the display can be observed with sufficient brightness under the use environment) differs depending on the illuminance of the use environment (hereinafter referred to as environment illuminance). ,
Depending on the ambient illumination, the screen may be too dazzling or too dark. For example, under a high illuminance use environment exceeding 100,000 lux, such as under direct sunlight in summer, it will be too dazzling.

Therefore, in this liquid crystal display device, in order to obtain a suitable screen luminance that is not excessively dazzling even in a use environment of high illuminance exceeding 100,000 lux, such as in direct sunlight in summer, the liquid crystal display device is mainly provided with a reflective surface. The reflectance of the entire device determined by the reflectance of external light by the film 24 and the transmittance of light of the liquid crystal display panel 1 (the intensity of external light incident from the surface side of the liquid crystal display panel 1 and the reflection by the reflective film 24 (Ratio with the intensity of external light emitted to the front side of the liquid crystal display panel 1)
Is set lower than that of a normal reflective liquid crystal display device using only external light.

Further, by controlling the brightness of the light from the light source 16 in accordance with the ambient illuminance, etc., the screen brightness of the liquid crystal display panel 1 due to both the light from the light source 16 and the external light can be adjusted in accordance with the environmental illuminance. Screen brightness. That is, this liquid crystal display device is provided with a light source luminance control means for controlling the luminance of the light from the light source 16 according to the environmental illuminance and the like. Next, the light source luminance control means will be described.

FIG. 4 shows a schematic configuration of a part of the liquid crystal display device. A predetermined side of the rear glass substrate 3 of the pair of glass substrates 2 and 3 of the liquid crystal display panel 1 projects from the front glass substrate 2. An external light illuminance detection sensor 41 is provided on the upper surface of the protruding portion of the glass substrate 3 on the back side. In addition, a backlight illuminance detection sensor 42 is provided at a predetermined position on the upper surface of the glass substrate 3 on the back surface outside the sealing material 4 shown in FIG. In this case, a black mask 43 made of a metal such as chrome is provided on the lower surface of the glass substrate 2 on the front side,
The black mask 43 prevents external light from being incident on the backlight illuminance detection sensor 42. Then, the light from the backlight 11 is transmitted to the black mask 43.
And is incident on the backlight illuminance detection sensor 42. Backlight illuminance detection sensor 4
Reference numeral 2 is for detecting the illuminance of the fluorescent tube 17 which gradually decreases with the passage of time.

Next, FIG. 5 shows a main part of a circuit of the liquid crystal display device. An external light illuminance detection unit 51 is provided at a predetermined location on the upper surface of the glass substrate 3 on the back side of the liquid crystal display panel 1.
Are integrally formed, and a backlight illuminance detection unit 52 is integrally formed at another predetermined position. The two illuminance detectors 51 and 52 have the same structure. That is, the illuminance detection units 51 and 52 are illuminance detection sensors 41 and 42 formed of a double-gate type photoelectric conversion thin film transistor described later.
A first switching element 53, 54 composed of a thin film transistor; a resistor 55 provided between the illuminance detection sensors 41, 42 and the first switching element 53, 54;
56, capacitors 57 and 58, and illuminance detection sensor 4
And second switching elements 59 and 60 made of thin film transistors connected between the first and second resistors 42 and the resistors 55 and 56.

While the signals output from the frequency dividers 61 and 62 for a preset time are input to the second switching elements 59 and 60, the illuminance detection sensor 4
The current corresponding to the detected illuminance is output from the capacitors 57 and
58, and charges are stored in the capacitors 57 and 58. Then, when the first switching elements 53 and 54 are turned on at a predetermined timing, light detection signals corresponding to the electric charges accumulated in the capacitors 57 and 58 are input to the level shift adjusters 63 and 64. Level shift adjusters 63, 6
Reference numeral 4 denotes, for example, an A / D converter, which converts an input photodetection signal into a parallel signal, and outputs the parallel signal to the parallel-serial converters 65 and 66. The parallel-serial converters 65 and 66 convert the input parallel signal into a serial signal, and output the serial signal to the adder 67. The adder 67 adds the two input serial signals and outputs the added signal to the dimming control signal generator 68. The dimming control signal generator 68 outputs a dimming control signal corresponding to the input addition signal to the inverter 69 having a dimming function. The inverter 69 with the dimming function is connected to the light source 16.
The light source 16 (see FIG. 1) emits light having a luminance corresponding to the dimming control signal from the dimming control signal generator 68.
(Fluorescent tube 17) is driven.

Next, control of the brightness of the light from the light source 16 by the light source brightness control means according to the ambient illuminance and the like will be described with specific numerical values. First, FIG. 6 shows the relationship between the screen luminance of the liquid crystal display panel 1 and the environmental illuminance in this case. As a prerequisite, a suitable screen luminance of the liquid crystal display panel 1 according to the environmental illuminance is 20 to 200 nits at an ambient illuminance of 50 lux such as under a street lamp at night, such as in a room when indoor lighting is turned on. 1000
Lux ambient illuminance is 30-300 nits, and 30000 lux ambient illuminance such as shade of trees in fine weather is 400-4
000 nits, more preferably 20 to 60 nits at 50 lux environmental illuminance, 60 to 200 nits at 1000 lux environmental illuminance, and 1000 to 3000 nits at 30,000 lux environmental illuminance.

The screen luminance L (nit) of the liquid crystal display panel 1 is represented by I (lux) for the environmental illuminance, B (nit) for the luminance of light from the light source 16, and T (light transmission) for the liquid crystal display panel 1. (%), The reflectance of the above-described device as a whole is R (%)
Is obtained from the following equation (1). L = I × R / 400 + B × T / 100 (1)

Therefore, first, the screen luminance L of the liquid crystal display panel 1 is 20 to 200 nits at an environmental illuminance of 50 lux, and 30 to 300 nits at an environmental illuminance of 1000 lux.
The luminance of the light from the light source 16 is controlled by the light source luminance control means according to the environmental illuminance and the like so that the luminance represented by a quadratic function satisfying the range of 400 to 4000 nits at the environmental illuminance of 30,000 lux, respectively. That is, the control condition of the luminance of the light from the light source 16 in this case is obtained from the above equation (1), and is as shown in the following equation (2). −2 × 10 ⁻⁸ × I ² + 0.015 × I + 20 ≦ L ≦ −3 × 10 ⁻⁷ × I ² + 0.0113 × I + 150 ... (2)

In FIG. 6, curves M ₁ and M ₂ indicate the maximum value and the minimum value of the screen luminance L obtained from the above equation (2). That is, the curves M ₁ and M ₂ are given by the following equation (4):
It is a curve respectively represented by (5). L (M ₁ ) = − 3 × 10 ⁻⁷ × I ² + 0.0113 × I + 150 (4) L (M ₂ ) = − 9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 (5) The range M between the two curves M ₁ and M ₂ is a range of a suitable screen luminance of the liquid crystal display panel 1 according to the environmental illuminance and the like.

Second, the screen luminance L of the liquid crystal display panel 1 is 20 to 60 nits at an ambient illuminance of 50 lux.
60-200 nits at 300 lux lux, 300
The luminance of the light from the light source 16 is controlled by the light source luminance control means according to the environmental illuminance and the like so that the luminance represented by a quadratic function that satisfies the range of 1000 to 3000 nits at the environmental illuminance of 00 lux. That is, the control condition of the luminance of the light from the light source 16 in this case is represented by the above equation (1).
Is obtained from the following equation (3). −9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 ≦ L ≦ −2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 ... (3)

In FIG. 6, curves N ₁ and N ₂ show the maximum value and the minimum value of the screen luminance L obtained from the above equation (3). That is, the curves N ₁ and N ₂ are given by the following equation (6):
It is a curve respectively represented by (7). L (N ₁ ) = − 2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 (6) L (N ₂ ) = − 9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 (7) The range N between the two curves N ₁ and N ₂ is a more preferable range of the screen luminance of the liquid crystal display panel 1 according to the environmental illuminance and the like.

As described above, in this liquid crystal display device, the luminance of the light from the light source 16 is controlled by the light source luminance control means in accordance with the ambient illuminance and the like, so that the screen luminance of the liquid crystal display panel 1 is represented by the curve M ₁ , range M between M _2, more preferably in the range N between curve N _1, N _2. Thereby, the screen luminance of the liquid crystal display panel 1 can be made suitable or more preferable in a wide range of environmental illuminance from low illuminance to high illuminance.

The two-dot chain line in FIG. 6 represents the screen brightness of a normal reflection type liquid crystal display device using only external light for comparison. The screen luminance indicated by the two-dot chain line changes linearly with the change in environmental illuminance. Then, in this conventional reflection type liquid crystal display device, ambient illuminance corresponding to the range M between curves M _1, M ₂ ranges from about 300 to about 5000 lux, the range between the curve N _1, N ₂ N
Is in the range of about 500 to about 2000 lux. Therefore, at a higher ambient illuminance, the screen of the liquid crystal display panel becomes too bright, and for example, under a high illuminance of more than 100,000 lux such as under direct sunlight in summer, the screen of the liquid crystal display panel becomes too dazzling. The display becomes difficult to see. On the other hand, if the ambient illumination is lower than that,
The screen of the liquid crystal display panel becomes too dark, and, for example, in a dark use environment such as outdoors at night, it is not possible to obtain a screen luminance enough to make the display visible.

By the way, as is apparent from FIG. 6, as an example, when the ambient illuminance is 1000 lux or less, if the screen brightness of the liquid crystal display panel 1 is at least 40 nits, a suitable screen brightness can be obtained. . Therefore, in this case, even if the brightness of the light source 16 is fixed at a certain value at which the screen brightness of the liquid crystal display panel 1 is at least 40 nits, the illuminance of external light increases and the amount of light reflected by the reflective film 24 shown in FIG. Only increases, so that a suitable screen luminance can be obtained.

When the ambient illuminance is 1000 to 10000 lux, the screen brightness of the liquid crystal display panel 1 is at least 2
If there are 00 nits, a suitable screen luminance can be obtained. Therefore, in this case, even if the luminance of the light source 16 is fixed at a certain value at which the screen luminance of the liquid crystal display panel 1 is at least 200 nits, the illuminance of the external light increases and FIG.
Since only the amount of light reflected by the reflective film 24 shown in FIG.

Further, when the ambient illuminance is 10000 lux or more, even if the fluorescent tube 17 is turned off, the screen brightness of the liquid crystal display panel 1 can be set to a suitable screen brightness of about 300 nits or more. That is, in this case, the fluorescent tube 1
It is under the use environment of high illuminance that does not need to light 7;
Display is performed using only external light. However, also in this case, the illuminance of the external light increases and the amount of light reflected by the reflective film 24 shown in FIG. 1 increases.
Since the reflectivity of the entire device is set lower than that of a normal reflective liquid crystal display device using only external light, a suitable screen luminance can be obtained.

As described above, first, the brightness of the light source 16 is fixed at a certain value such that the screen brightness of the liquid crystal display panel 1 is at least 40 nits. Third, the liquid crystal display panel 1 can be controlled in a wide range of illuminance from low illuminance to high illuminance by three types of control (adjustment) of setting the brightness to a certain value of at least 200 nits and turning off the fluorescent tube 17. Screen brightness can be made preferable.

Since the light source 16 is controlled in three types in this case, three external light illuminance detection sensors 41 may be provided. That is, for example, three types of capacitors having different times for outputting signals from the frequency dividers 61 and 62 and the capacitances of the capacitors 57 and 58 shown in FIG. 16 may be controlled in three types. In this case, these three types of control may be performed manually. Note that four or more external light illuminance detection sensors 41 may be provided, and the control of the light source 16 may be four or more. Further, a plurality of backlight illuminance detection sensors 42 may be provided.

Next, the specific structure of the illuminance detection sensors 41 and 42 will be described with reference to FIG. A bottom gate electrode 71 made of a light-shielding electrode made of aluminum or the like is provided on the upper surface of the glass substrate 3 on the back side, and a bottom gate insulating film 72 made of silicon nitride is provided on the entire upper surface. A semiconductor layer 73 made of amorphous silicon or polysilicon is provided in a portion corresponding to the bottom gate electrode 71 on the upper surface of the bottom gate insulating film 72. At the center of the upper surface of the semiconductor layer 73, a blocking layer 74 made of silicon nitride is provided. Semiconductor layers 7 on both sides of the upper surface of blocking layer 74 and on both sides thereof
On the upper surface of 3, n ⁺ silicon layers 75 and 76 are provided. A source electrode 77 and a drain electrode 78 made of a light-shielding electrode made of aluminum or the like are provided on the upper surfaces of the n ⁺ silicon layers 75 and 76, and a top gate insulating film 79 made of silicon nitride is provided on the entire upper surface. A top gate electrode 80 made of a transparent electrode such as ITO is provided on a portion corresponding to the semiconductor layer 73 on the upper surface of the top gate insulating film 79, and an overcoat film 81 made of silicon nitride is provided on the entire upper surface. . And
In the illuminance detection sensors 41 and 42, the light incident from the lower surface side is shielded by the bottom gate electrode 71 so that the light does not directly enter the semiconductor layer 73.

In the illuminance detection sensors 41 and 42, a bottom gate type transistor is constituted by the bottom gate electrode (BG) 71, the semiconductor layer 73, the source electrode (S) 77, the drain electrode (D) 78, etc. The (TG) 79, the semiconductor layer 73, the source electrode (S) 77, the drain electrode (D) 78, and the like constitute a top-gate transistor. That is, the illuminance detection sensors 41 and 42 are constituted by double-gate photoelectric conversion thin film transistors in which a bottom gate electrode (BG) 71 and a top gate electrode (TG) 79 are arranged below and above the semiconductor layer 73, respectively. The equivalent circuit can be shown as in FIG.

Next, the operation of the illuminance detection sensors 41 and 42 will be described. First, as shown in FIG.
When a positive voltage (for example, +10 V) is applied to the bottom gate electrode (BG) in a state where a positive voltage (for example, +5 V) is applied between the source electrode (S) and the drain electrode (D), a channel is formed in the semiconductor layer 73. Is formed, and a drain current flows. In this state, when a negative voltage (for example, −20 V) is applied to the top gate electrode (TG) to eliminate a channel due to the electric field of the bottom gate electrode (BG), the electric field from the top gate electrode (TG) becomes lower. The gate electrode (BG) acts in a direction that hinders channel formation due to the electric field, and the channel is pinched off. At this time, the semiconductor layer 73 is placed from the top gate electrode (TG) side.
Is irradiated with light, electron-hole pairs are induced on the top gate electrode (TG) side of the semiconductor layer 73. The electron-hole pairs are accumulated in the channel region of the semiconductor layer 73 and cancel the electric field of the top gate electrode (TG). Therefore, a channel is formed in the semiconductor layer 73, and a drain current flows. This drain current changes according to the amount of light incident on the semiconductor layer 73. Then, by this drain current, FIG.
Are stored in the capacitors 57 and 58 shown in FIG.

Next, a case where the illuminance detection sensors 41 and 42 are reset will be described with reference to FIG. When a positive voltage (+10 V) is applied to the bottom gate electrode (BG) and the top gate electrode (TG) is set to, for example, 0 V, holes from the trap level between the semiconductor layer 73 and the top gate insulating film 79 are removed. To be refreshed, that is, reset. That is, when used continuously, the trap level between the semiconductor layer 73 and the top gate insulating film 79 is filled with holes generated by light irradiation and holes injected from the drain electrode (D). As a result, the channel resistance in the light non-incident state decreases, and the drain current increases in the light non-incident state.
Therefore, the top gate electrode (TG) is set to 0 V, and the holes are discharged to reset.

Incidentally, the illuminance detection sensors 41, 42
The reaction time required for the drain current to reach 1 μA with respect to the illuminance of external light was examined. As a result, the result shown in FIG. 10 was obtained. As is clear from this figure, the reaction time until the drain current of the illuminance detection sensors 41 and 42 reaches 1 μA becomes shorter as the illuminance of external light increases. As a result, the environmental illuminance and the backlight illuminance can be obtained from the reaction time. Therefore, for example, the timing at which the first switching elements 53 and 54 shown in FIG. 5 are turned on may be the time when a current of 1 μA or more flows from the illuminance detection sensors 41 and 42. When the drain current reaches 0.1 μA, the reaction time becomes about 1/10, and when the drain current reaches 10 μA, the reaction time becomes about 10 times.

Next, an example of a method of forming the illuminance detection sensors 41 and 42, together with a method of forming a MIS thin film transistor as a switching element in an active matrix type liquid crystal display device, will be described with reference to FIG. A gate electrode 91 made of aluminum or the like is formed in a region where a thin film transistor or the like is formed on the upper surface of the glass substrate 3 on the back surface, and a bottom gate electrode 71 made of aluminum or the like is formed in a region where the illuminance detection sensor is formed on the upper surface. Next, a bottom gate insulating film 72 made of silicon nitride is formed on the entire upper surface. Next, a semiconductor layer 92 made of amorphous silicon or polysilicon is formed in a thin film transistor formation region on the upper surface of the bottom gate insulating film 72, and a semiconductor layer 73 made of amorphous silicon or polysilicon is formed in the illuminance detection sensor formation region on the same upper surface.
To form Next, blocking layers 93 and 74 made of silicon nitride are formed at the center of the upper surfaces of the semiconductor layers 92 and 73. Next, n ⁺ silicon layers 94, 95, 75 and 76 are formed on both sides of the upper surfaces of the blocking layers 93 and 74 and on the upper surfaces of the semiconductor layers 92 and 73 on both sides thereof. Then, n ⁺
A source electrode 96, a drain electrode 97, a source electrode 77, and a drain electrode 78 made of aluminum or the like are formed on the upper surfaces of the silicon layers 94, 95, 75, and 76. Next, a top gate insulating film 79 made of silicon nitride is formed on the entire upper surface.
To form Next, a pixel electrode 98 made of a transparent electrode such as ITO is formed in a region where a thin film transistor or the like is formed on the upper surface of the top gate insulating film 79, and a top gate electrode formed of a transparent electrode such as ITO is formed in a region where the illuminance detection sensor is formed on the same upper surface. Form 80. In this case, the pixel electrode 98
It is connected to source electrode 96 via contact hole 99 formed in top gate insulating film 79. Next, an overcoat film 81 made of silicon nitride is formed on the entire upper surface of the pixel electrode 98 except for a predetermined portion. Thus, the MIS thin film transistor and the pixel electrode 98 are formed in the thin film transistor formation region, and the illuminance detection sensor including the MIS thin film transistor is formed in the illuminance detection sensor formation region. As described above, since the illuminance detection sensor can be formed simultaneously with the formation of the MIS thin film transistor as the switching element and the pixel electrode 98, the number of manufacturing steps can be prevented from increasing.

In the above embodiment, as shown in FIG. 4, the case where the external light illuminance detection sensor 41 is formed on the upper surface of the projecting portion of the glass substrate 3 on the back side has been described. However, the present invention is not limited to this. Absent. For example, as shown in FIG. 11, an external light illuminance detection sensor 41 is formed at a predetermined portion of the upper surface of the glass substrate 3 on the back surface outside the sealing material 4 shown in FIG. You may make it. In this case, external light is emitted from the glass substrate 2 on the front side (when a color filter made of a resin containing pigment is formed on the lower surface of the glass substrate 2, the glass substrate 2 and the color filter) Further, since the light passes through the opening 43a formed in the black mask 43 and enters the external light illuminance detection sensor 41, the light amount of the external light is reduced by about several tens%. Therefore, as compared with the case shown in FIG.
1 can slightly increase the reaction time to external light. Therefore, when two types of external light illuminance detection sensors 41 are installed, the case shown in FIG. 4 and the case shown in FIG. 11, the sensitivity range can be widened.

In the above embodiment, the case where the double-gate type photoelectric conversion thin film transistor is used as the illuminance detection sensors 41 and 42 has been described.
A pn-type photodiode or the like which can be formed simultaneously with the formation of the thin film transistor as a switching element may be used. In the above embodiment, the case where the fluorescent tube 17 is used has been described. However, the present invention is not limited to this, and a linear light emitting diode array or the like may be used. Further, in the above embodiment, the case where the backlight 11 including the light guide 15 having the reflection film 24 on the stepped step surface 22 is used has been described, but the present invention is not limited to this. For example, although not shown, an optical sheet may be arranged on the back side of the liquid crystal display panel, and a backlight made of EL or the like may be arranged on the back side. Furthermore, in the above embodiment, the case where the present invention is applied to a liquid crystal display device has been described. However, the present invention is not limited to this, and can be applied to a display device having another non-light emitting display panel.

[0039]

As described above, according to the present invention, the illuminance detecting sensor detects, for example, the illuminance of both the external light and the backlight, and based on the detected illuminance, the reflected and emitted light is controlled by the emitted light luminance control means. Since the brightness of the light emitted from the means is controlled, the screen brightness of the display panel is always suitable even when the display is performed by simultaneously using both the light from the reflection and light emitting means and the external light. it can. Moreover,
In this case, since the illuminance detection sensor is constituted by the MIS thin film transistor formed on the thin film transistor forming surface of the display panel, the illuminance detection sensor can be formed simultaneously with the formation of the MIS thin film transistor as the switching element. The number can be kept from increasing.

[Brief description of the drawings]

FIG. 1 is a side view of a main part of a liquid crystal display device to which an embodiment of the present invention is applied.

FIG. 2 is a diagram illustrating the progress of light in a part of a liquid crystal display device.

FIG. 3 is a perspective view illustrating an optical sheet.

FIG. 4 is a side view showing a schematic configuration of a part of the liquid crystal display device.

FIG. 5 is a circuit diagram of a main part of the liquid crystal display device.

FIG. 6 is a diagram showing a relationship between screen luminance of a liquid crystal display panel and environmental illuminance.

FIG. 7 is a sectional view showing a specific structure of the illuminance detection sensor.

8 is an equivalent circuit diagram of the illuminance detection sensor shown in FIG.

FIGS. 9A and 9B are diagrams for explaining the operation of the illuminance detection sensor.

FIG. 10 is a diagram showing a reaction time until a drain current of the illuminance detection sensor reaches 1 μA with respect to external light illuminance.

FIG. 11 is a sectional view illustrating an example of a method for forming the illuminance detection sensor.

FIG. 12 is a side view showing another example of installation of the external light illuminance detection sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 2, 3 Glass substrate 11 Backlight 41 External light illuminance detection sensor 42 Backlight illuminance detection sensor

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[Procedure amendment]

[Submission date] October 12, 1998 (1998.10.
12)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

FIG. 1 shows a main part of a reflection / transmission type liquid crystal display device to which an embodiment of the present invention is applied. This liquid crystal display device includes an active matrix type liquid crystal display panel 1 having a switching element such as a thin film transistor between a data line and each pixel electrode. Although not shown in detail, the liquid crystal display panel 1 has a pair of glass substrates 2 and 3 bonded to each other with a substantially frame-shaped sealing material 4 interposed between the two glass substrates 2 and 3 inside the sealing material 4. Liquid crystal is sealed and each glass substrate 2, 3
It is made from what was only with the polarizing plate 5 and 6 are bonded to the surface of.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

Therefore, first, the screen luminance L of the liquid crystal display panel 1 is 20 to 200 nits at an environmental illuminance of 50 lux, and 30 to 300 nits at an environmental illuminance of 1000 lux.
The luminance of the light from the light source 16 is controlled by the light source luminance control means according to the environmental illuminance and the like so that the luminance represented by a quadratic function satisfying the range of 400 to 4000 nits at the environmental illuminance of 30,000 lux, respectively. That is, the control condition of the luminance of the light from the light source 16 in this case is obtained from the above equation (1), and is as shown in the following equation (2). −2 × 10 ⁻⁸ × I ² + 0.015 × I + 20 ≦ L ≦ −3 × 10 ⁻⁷ × I ² + 0.113 × I + 150 (2)

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

In FIG. 6, curves M ₁ and M ₂ show the maximum and minimum values of the screen luminance L obtained from the above equation (2). That is, the curves M ₁ and M ₂ are expressed by the following equation ( 3 ):
It is a curve respectively represented by ( 4 ). L (M ₁ ) = − 3 × 10 ⁻⁷ × I ² + 0.113 × I + 150 ( 3 ) L (M ₂ ) = − 2 × 10 ⁻⁸ × I ² + 0.015 × I + 20 ( 4) Therefore, the range M between the two curves M ₁ and M ₂ is a range of a suitable screen luminance of the liquid crystal display panel 1 according to the environmental illuminance and the like.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

Second, the screen luminance L of the liquid crystal display panel 1 is 20 to 60 nits at an ambient illuminance of 50 lux.
60-200 nits at 300 lux lux, 300
The luminance of the light from the light source 16 is controlled by the light source luminance control means according to the environmental illuminance and the like so that the luminance represented by a quadratic function that satisfies the range of 1000 to 3000 nits at the environmental illuminance of 00 lux. That is, the control condition of the luminance of the light from the light source 16 in this case is represented by the above equation (1).
From the following equation ( 5 ). −9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 ≦ L ≦ −2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 ... ( 5 )

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

In FIG. 6, curves N ₁ and N ₂ show the maximum value and the minimum value of the screen luminance L obtained from the above equation ( 5 ). That is, the curves N ₁ and N ₂ are given by the following equation (6):
It is a curve respectively represented by (7). L (N ₁ ) = − 2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 (6) L (N ₂ ) = − 9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 (7) The range N between the two curves N ₁ and N ₂ is a more preferable range of the screen luminance of the liquid crystal display panel 1 according to the environmental illuminance and the like.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

In the illuminance detection sensors 41 and 42, a bottom gate type transistor is constituted by the bottom gate electrode (BG) 71, the semiconductor layer 73, the source electrode (S) 77, the drain electrode (D) 78, etc. The (TG) 80 , the semiconductor layer 73, the source electrode (S) 77, the drain electrode (D) 78, and the like constitute a top-gate transistor. That is, the illuminance detection sensors 41 and 42 are constituted by double-gate photoelectric conversion thin film transistors in which a bottom gate electrode (BG) 71 and a top gate electrode (TG) 80 are arranged below and above the semiconductor layer 73, respectively. The equivalent circuit can be shown as in FIG.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0037

[Correction method] Change

[Correction contents]

In the above embodiment, as shown in FIG. 4, the case where the external light illuminance detection sensor 41 is formed on the upper surface of the projecting portion of the glass substrate 3 on the back side has been described. However, the present invention is not limited to this. Absent. For example, as shown in FIG. 12 , an external light illuminance detection sensor 41 is formed at a predetermined portion of the upper surface of the glass substrate 3 on the back surface outside the sealing material 4 shown in FIG. You may make it. In this case, external light is emitted from the glass substrate 2 on the front side (when a color filter made of a resin containing pigment is formed on the lower surface of the glass substrate 2, the glass substrate 2 and the color filter) Further, since the light passes through the opening 43a formed in the black mask 43 and enters the external light illuminance detection sensor 41, the light amount of the external light is reduced by about several tens%. Therefore, as compared with the case shown in FIG.
1 can slightly increase the reaction time to external light. Therefore, when two types of external light illuminance detection sensors 41 are installed, the case shown in FIG. 4 and the case shown in FIG. 12 , the sensitivity range can be widened.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C094 AA07 AA15 AA22 AA43 AA51 BA03 BA43 CA19 DA13 DB04 EA04 EA05 ED01 ED11 ED14 FA01 FA02 FB02 GB10 5G435 AA01 AA17 BB12 BB15 BB16 CC09 DD11 EE11 FF27 FF03 GG03 FF02 HH12 HH13 KK05 KK07

Claims (4)

[Claims] 1. A non-luminous display panel provided with a MIS type thin film transistor as a switching element, and disposed on a back side of the display panel to emit light toward the back side of the display panel, Reflection / light emitting means for reflecting external light incident from the front side of the display panel and passing through the display panel toward the back surface of the display panel; and the same as the thin film transistor formed on the surface of the display panel where the thin film transistor is formed. A display device comprising: an illuminance detection sensor composed of an MIS type thin film transistor; and emission light brightness control means for controlling the brightness of light emitted from the reflection and light emission means based on the illuminance detected by the illuminance detection sensor. . 2. The display device according to claim 1, wherein the illuminance detection sensor detects illuminance of external light or illuminance of the backlight. 3. The illuminance detection sensor according to claim 1, wherein the illuminance detection sensor comprises an external light illuminance detection sensor for detecting illuminance of external light and a backlight illuminance detection sensor for detecting illuminance of the backlight. Characteristic display device. 4. The illuminance detection sensor according to claim 1, wherein the illuminance detection sensor has a first gate electrode made of a material having a light-shielding property disposed on a back side, and has a light-transmitting property on a front side. A display device comprising a photoelectric conversion thin film transistor in which a second gate electrode made of a material having the same is arranged.