JPH1138389A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of reducing occurrence of a flicker. SOLUTION: This device is constituted of a first substrate 13, many switching elements 1 consisting of MOS type transistors formed on this first substrate 13 in matrix, a switching element drive circuit 11 arranged on the periphery of many transistors on the matrix for driving these switching elements 1, many pixel electrodes 2 connected to the individual switching elements 1, a second transparent substrate 17 arranged oppositely at a prescribed interval for the first substrate 13, a common electrode 5 formed on this second substrate 17 and a liquid crystal 6 sealed between the first substrate 13 and the second substrate 17 through an oriented film. In such a case, a metallic film electrode 24 is arranged at a position different from the pixel electrode 2 on the first substrate 13, and a DC voltage 25 is applied between this metallic film electrode 24 and the common electrode 5 on the second substrate 17. Thus, concentration of movable ions in the liquid crystal is reduced, and a flicker phenomenon is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type liquid crystal display device in which liquid crystal display elements are arranged in a matrix.

[0002]

2. Description of the Related Art Generally, a molecular arrangement maintains a certain order like a solid, while it has fluidity like a liquid, and easily changes its arrangement in response to an electric field and appears as a change in optical properties. A liquid crystal display device is known as an element using liquid crystal. This liquid crystal display device encloses liquid crystal between a common electrode and a number of individually controllable pixel electrodes disposed opposite to the common electrode, and selectively applies an image data signal to these pixel electrodes. The optical characteristics of the liquid crystal between the corresponding pixel electrodes are changed. In a method of driving the liquid crystal, an AC voltage is generally applied to each pixel electrode with respect to a common electrode. In this type of liquid crystal display device, a reflection type liquid crystal display element has been proposed for the purpose of miniaturization of the device and high definition of a display image.

Here, as an example of a conventional reflection type liquid crystal display device, a reflection type liquid crystal display device using MOS transistors will be described. FIG. 3 is a circuit diagram showing a general reflection type liquid crystal display device. FIG. 4 is a partial cross-sectional view showing a scanning circuit portion provided around a unit pixel and a display portion of a pixel having a matrix structure in the device shown in FIG. 3, and FIG. 5 is a schematic plan view of the entire device. In FIG. 3, the transistor 1, the capacitor 3, and the liquid crystal 6 (expressed in the form of a capacitor) as switching elements arranged in a matrix form one pixel each in combination. Here, the gate of each transistor 1 is connected to the X-direction scanning circuit Xscn, and the source or drain is connected to the Y-direction scanning circuit Yscn. The pixel signal selects a line to be displayed by the X-direction scanning circuit Xscn, and turns on the gate of the corresponding transistor 1 in synchronization with the selection. On the other hand, a corresponding signal is applied to each transistor 1 by the Y-direction scanning circuit Yscn.

[0004] The switching elements 1, which are transistors, are, for example, MOS transistors, and are arranged in a matrix in a matrix on a first substrate 13 made of a glass substrate or a silicon substrate. The source 8 or the drain 7 of the switching element 1 is connected to the pixel electrode 2 and a charge storage capacitor 3 having one terminal common to the pixel electrode 2. The gate electrode 4 of the switching element 1 is connected to a gate line Xi for passing a selection signal, and the source 8 or the drain 7 not connected to the pixel electrode 2 is connected to a signal line Yj for passing a video signal or the like. The gate electrode Xi is driven by an X-direction scanning circuit Xscn, and the signal line Yj is driven by a Y-direction scanning circuit Yscn. In the illustrated example, the case where the pixel electrode 2 is connected to the source 8 is shown.

Each pixel electrode 2 is provided with a transparent common electrode 5 opposed thereto.
The liquid crystal 6 is sealed between the electrodes to form a pixel for each electrode. The operation of this element is as follows. For example, when a selection signal is applied to the gate electrode 4 via the gate line Xi, the switching element 1 composed of a MOS transistor is turned on,
The video signal on the signal line Yj passes through the switching element 1 to charge the capacitor 3 and at the same time is applied to the pixel electrode 2.

Here, even if the signal on the gate line Xi becomes "0" and becomes unselected, the potential of the pixel electrode 2 is held by the charge stored in the corresponding capacitor 3. During this time,
A potential difference between the pixel electrode 2 and the common electrode 5 is applied to the liquid crystal 6, and the voltage changes the light transmittance of the liquid crystal. Therefore, by controlling this potential difference, an optical signal whose electric signal is modulated is modulated. Can be converted to By arranging such unit pixels in a matrix and scanning signals in the vertical and horizontal directions, an image can be formed. This scanning method uses, for example, X along the gate line Xi.
The switching elements 1 are turned on all at once in the direction, the video signal is written to the capacitor 3, and the scanning is sequentially performed in the Y direction.

A large number of pixels arranged in a matrix form a display unit 10 as shown in FIG.
0 and an X- and Y-direction scanning circuit Xs for scanning and driving each of the switching elements 1 so as to surround it.
A switching element drive circuit 11 including cn and Yscn is arranged. This arrangement minimizes the propagation loss of the signal to the switching element 1 and also allows the drive circuit 11 to be formed simultaneously with the formation of the switching element 1, which is advantageous in terms of miniaturization and cost reduction. There is.

Next, the structure of the unit pixel portion will be described in detail with reference to FIG. FIG. 4 shows unit pixels at the end of the display unit. The switching element 1 composed of the MOS transistor is composed of a gate electrode 4, a drain 7 and a source 8. The gate electrode 4 is provided via a gate oxide film 9, and a gate in the X direction is formed thereon by, for example, polycrystalline silicon. The line Xi is wired (see FIG. 3). The drain 7 is connected to a signal line Yj extending in the Y direction.
(See FIG. 3).

Next to the source 8, a capacitor 3 for storing electric charge is formed by sandwiching an insulating film 15 of, for example, SiO ₂ between a single crystal silicon substrate 13 as a substrate and a capacitor electrode 14. This capacitor electrode 14 is connected to the source 8. The pixel electrode 2 is provided above the switching element 1 and the capacitor 3, for example, an insulating film 1
3, the pixel electrode 2 and the source 8
Are electrically connected. The pixel electrode 2 is made of a material having a high readout light reflectance such as aluminum. In the switching element drive circuit 11, a drive transistor 20 required for drive scanning is formed on the surface of the substrate 13. In FIG. 4, reference numeral 23 denotes the liquid crystal 6.
Is a spacer for sealing the space between the substrates 13 and 17 to maintain a predetermined distance.

[0010] The second common substrate is formed so as to face the surface of the first substrate 13 formed as described above, and to form a transparent common electrode 5 on the surface (lower surface in the figure) with a slight interval L1 therebetween.
A transparent glass 17 is provided as a substrate, and alignment films 18 and 19 are formed on the surface of the common electrode 5 and the pixel electrode 2, respectively, to seal the liquid crystal 6 between the electrodes 2 and 5. A liquid crystal panel is formed, whereby a reflective liquid crystal display device is obtained. And transparent glass 1
The incident light 21 coming from above the light 7 passes through the liquid crystal 6, is reflected on the surface of the pixel electrode 2, and exits as modulated light 22.

[0011]

By the way, when the above-mentioned liquid crystal display device is actually manufactured, Proc.
IEEE, 59, No. 11, 1566 (1971), a DC component is applied to the liquid crystal in a display portion by a field-through voltage, but flicker occurs due to the applied DC component. Problem has occurred. As a countermeasure, Pr
oc. Eurodisplay '87, p. 63 (19
87), a line inversion operation or a television society technical report ED87-5, p. It has been proposed to make the flicker less noticeable by performing a column inversion operation, a pixel inversion operation, or the like as shown in J. 25 (1987). However, these methods have a disadvantage that the circuit configuration is complicated.

Further, as disclosed in Japanese Patent Publication No. 2-61725, a light-shielding electrode for giving substantially the same potential to liquid crystal other than the display portion, and an electrode facing the light-shielding electrode are provided on the transparent substrate side and the substrate. Attempts have been made to resolve flicker. However, this method applies a DC component to the pixel display portion, and is not effective in reducing flicker. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in order to solve the problems effectively. It is an object of the present invention to provide a reflective liquid crystal display device capable of reducing the occurrence of flicker. It is in.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a first substrate, a large number of switching elements formed in a matrix on the first substrate, and this switching element. A switching element driving circuit arranged around a large number of transistor elements on the matrix for driving, a large number of pixel electrodes connected to the individual switching elements, and a predetermined distance from the first substrate. A transparent second substrate, which is disposed to face and is spaced apart, a common electrode formed on the second substrate, and sealed between the first substrate and the second substrate via an alignment film. A reflective liquid crystal display device comprising
A metal film electrode is arranged on the substrate at a position different from the pixel electrode, and a DC voltage is applied between the metal film electrode and the common electrode of the second substrate.

First, a metal film is formed on the first substrate at a position different from the number of pixel electrodes formed thereon, and a DC voltage is applied between the metal film and the common electrode of the second substrate. Is applied. As a result, mobile ions in the liquid crystal between the common electrode and the metal film electrode are absorbed and reduced by the alignment film, so that mobile ions in the liquid crystal between the common electrode and the pixel electrode are reduced by the metal film electrode. Move into the side liquid crystal. Thereby, the ion concentration in the liquid crystal between the common electrode and the pixel electrode decreases, and as a result, it is possible to suppress the occurrence of flicker.

The metal film electrodes are formed at positions corresponding to, for example, a switching element driving circuit so as to surround a plurality of pixel electrodes arranged in a matrix. According to this, since the metal film electrode surrounds the display portion corresponding to the matrix-shaped pixel electrodes, it is possible to substantially uniformly reduce the mobile ions from the periphery of the liquid crystal of the display portion. In addition, it is desirable that a DC voltage is constantly applied between the metal film electrode and the common electrode during the operation of the apparatus, so that the effect of suppressing the flicker is prevented from lowering.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reflection type liquid crystal display device according to the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a partial cross-sectional view showing a scanning circuit unit (switching element driving circuit) provided around a unit pixel and a display unit of a pixel having a matrix structure in a reflection type liquid crystal display device of the present invention.
FIG. 2 is a schematic plan view showing the device shown in FIG. In the figure,
The same components as those of the conventional device will be described with the same reference numerals. Further, the driving circuit configuration of the entire liquid crystal display device is completely the same as the configuration shown in FIG. 3, and the description thereof is omitted here.

In the figure, reference numeral 13 denotes a first substrate made of, for example, a silicon single crystal plate, and reference numeral 17 denotes a second substrate made of, for example, transparent glass. The switching element 1 composed of a MOS transistor includes a gate electrode 4, a drain 7 and a source 8. The gate electrode 4 is provided via a gate oxide film 9, and a gate line in the X direction is formed thereon by, for example, polycrystalline silicon. Xi is wired (see FIG. 3). The drain 7 is connected to a signal line Yj extending in the Y direction (see FIG. 3).

Adjacent to the source 8, a capacitor 3 for charge storage is formed by sandwiching an insulating film 15 of, for example, SiO ₂ between a single crystal silicon substrate 13 as a substrate and a capacitor electrode 14. This capacitor electrode 14 is connected to the source 8. The pixel electrode 2 is provided above the switching element 1 and the capacitor 3, for example, an insulating film 1
3, the pixel electrode 2 and the source 8
Are electrically connected. The pixel electrode 2 is made of a material having a high readout light reflectance such as aluminum.

A large number of the unit pixels thus formed are arranged in a matrix as described above, and form a display section 10 for displaying an image as a whole. Note that the unit pixel in FIG. 1 indicates a unit pixel at an end of the display unit 10, and a switching element driving circuit 11 is provided next to the unit pixel. The switching element driving circuit 11 is located in the periphery of the display unit 10 so as not to block the reflected light from the display unit 10 as shown in FIGS. Direction scanning circuit Xsc
n, Yscn, and the like.

In the switching element drive circuit 11, a drive transistor 20 and the like necessary for drive scanning of each switching element 1 are formed on a first substrate 13. The drive transistor 20 is formed of, for example, a MOSFET, and is formed simultaneously with the formation of the switching element 1 and the like. Then, a metal film electrode 24 which is a feature of the present invention is provided above the drive transistor 20, that is, above the switching element drive circuit 11 via the insulating film 16. The metal film electrode 24 is connected to the drive circuit 1
1, as shown in FIG.
Is provided entirely on the outer periphery of the.

The metal film electrode 24 is made of, for example, an aluminum film, and is of course electrically isolated from the pixel electrode 2 at the end of the display section 10. The entire area of the metal film electrode 24 is desirably, for example, about 10% of the area of the display unit 10 in order to exhibit the necessary effect of suppressing the flicker phenomenon, but is naturally limited to this value. Not something. An alignment film 19 extending from the display unit 10 is provided on the upper surface of the metal film electrode 24. In addition, the common electrode 5 of the display unit 10 and the alignment film 18 are provided on the second substrate 17 in a portion facing the metal film electrode 24 so as to extend. Further, the liquid crystal is sandwiched between the common electrode 5 and the metal film electrode 24 in the switching element circuit 11 so as to communicate with the liquid crystal 6 in the display unit 10, thereby forming a reflective liquid crystal display device. ing. In the drawing, reference numeral 23 denotes a spacer for holding the liquid crystal 6 and maintaining a predetermined distance between the substrates 13 and 17.

Next, the operation of the apparatus configured as described above will be described. Assuming that light for projection, for example, polarized incident light 21 passes through the first substrate 17 made of transparent glass and the common electrode 5 and enters the direction of the pixel electrode 2, the incident light 21 After passing through the liquid crystal 6, the light is reflected at the pixel electrode 2 and passes through the liquid crystal 6 and the common electrode 5 again. At this time, light modulated by the incident light 21 passing through the liquid crystal 6 is output as modulated light 22. During this operation, a predetermined DC voltage 25 is constantly applied between the common electrode 5 and the metal film electrode 24 formed in the switching element drive circuit 11. In actual operation, the applied DC voltage causes mobile ion components existing in the liquid crystal 6 and the alignment films 18 and 19 to be adsorbed and fixed on the alignment films 18 and 19. The effect extends not only to the liquid crystal 6 between the common electrode 5 and the metal film electrode 24 on the switching element drive circuit 11 side but also to the liquid crystal portion between the common electrode 5 and the pixel electrode 2 on the display unit 10 side.

That is, mobile ions contained in the liquid crystal 6 between the common electrode 5 and the pixel electrode 2 are affected by the ion concentration of the liquid crystal 6 between the common electrode 5 and the metal film electrode 24, The liquid crystal moves between the portion of the liquid crystal and the portion of the metal film electrode 24. When a DC voltage 25 is applied between the common electrode 5 and the metal film electrode 24, the alignment films 18 and 19 in this portion are applied.
Mobile ions are adsorbed on the upper portion, and the ion component concentration in the liquid crystal between the common electrode 5 and the metal film electrode 24 decreases. Therefore,
Mobile ions in the liquid crystal between the common electrode 5 and the pixel electrode 2 move into the liquid crystal between the common electrode 5 and the metal film electrode 24, and the ion concentration in the liquid crystal between the common electrode 5 and the pixel electrode 2 is increased. Decrease. As a result, the occurrence of flicker is reduced.

The DC voltage 25 applied between the common electrode 5 and the metal film electrode 24 is larger than the DC component equivalently applied to this portion when the common electrode 5 and the pixel electrode 2 are driven by AC. is necessary. However, the effect of adsorbing the applied DC component and the mobile ion component has a non-linear relationship. When the DC voltage 25 exceeds a certain value, the adsorption effect starts to be saturated. If the applied DC voltage 25 is too high, a deterioration phenomenon of the liquid crystal itself occurs. Therefore, a DC voltage that produces these optimal effects is applied. Such a DC voltage 25 is preferably in a range of, for example, about 0.5 volt to 3 volts. This DC voltage 25 must always be applied. The reason is that when this DC voltage is applied in synchronization with, for example, a power supply voltage, the mobile ions are detached from the alignment films 18 and 19 in a state where no DC voltage is applied, and the flicker suppressing effect is reduced. . Therefore, this DC voltage 25 is set in a different system from the other power supply voltages, and the DC voltage 25 is applied between the common electrode 5 and the metal film electrode 24.
Is set to be always applied.

As described above, in the present invention, by applying a DC voltage between the metal film electrode 24 provided on the peripheral side of the display unit and the common electrode 5, the mobile ion concentration in the liquid crystal in the display unit 10 is increased. Can be reduced, so that the occurrence of a flicker phenomenon can also be suppressed. Further, the polarity of the applied DC voltage 25 is
The same effect can be obtained regardless of whether the polarity of the metal film electrode 24 is positive or negative. In the above embodiment, a case where a silicon substrate is used as the first substrate 13 and a MOS transistor is formed as a switching element thereon is described as an example. However, the present invention is not limited to this. The same effect can be obtained even when a glass substrate is used as a substrate and a TFT (thin film transistor) is formed thereon.

[0026]

As described above, according to the reflection type liquid crystal display device of the present invention, the following excellent functions and effects can be exhibited. By applying a DC voltage between the metal film electrode provided on the first substrate side and the common electrode on the second substrate side, the concentration of mobile ions in the liquid crystal in the display portion can be reduced. In addition, generation of flicker can be suppressed.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a scanning circuit section (switching element driving circuit) provided around a unit pixel and a display section of a pixel having a matrix structure in a reflective liquid crystal display device of the present invention.

FIG. 2 is a schematic plan view showing the device shown in FIG.

FIG. 3 is a circuit diagram showing a general reflection type liquid crystal display device.

FIG. 4 is a partial cross-sectional view showing a scanning circuit portion provided around a unit pixel and a display portion of a pixel having a matrix structure in the device shown in FIG. 3;

FIG. 5 is a schematic plan view of the entire apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transistor (switching element), 2 ... Pixel electrode, 3 ... Capacitor, 5 ... Common electrode, 6 ... Liquid crystal, 10 ...
Display unit, 11: switching element drive circuit, 13: silicon substrate (first substrate), 17: glass substrate (second substrate), 18, 19: alignment film, 24: metal film electrode, 25 ...
DC voltage.

Claims (3)

[Claims] 1. A first substrate, a plurality of switching elements formed in a matrix on the first substrate, and a plurality of transistor elements on the matrix arranged to drive the switching elements. A switching element driving circuit, a plurality of pixel electrodes connected to the individual switching elements, a transparent second substrate disposed opposite to the first substrate at a predetermined distance from the first substrate, A reflection type liquid crystal display device comprising: a common electrode formed on two substrates; and a liquid crystal sealed between the first substrate and the second substrate with an alignment film interposed therebetween. A metal film electrode is arranged on the substrate at a position different from the pixel electrode, and a DC voltage is applied between the metal film electrode and the common electrode of the second substrate. Type liquid crystal display apparatus. 2. The reflective liquid crystal display device according to claim 1, wherein the position different from the pixel electrode is a position corresponding to the switching element drive circuit. 3. The reflection-type liquid crystal display device according to claim 1, wherein the DC voltage is constantly applied while the liquid crystal display device is driven.