JPH0667166A - Plasma address liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve dependency on visual angle in a plasma address liquid crystal display device. CONSTITUTION:A liquid crystal cell 4 is constituted by superposing an upper substrate 3 on the surface side of an intermediate substrate 1 through a liquid crystal layer 2, and a plasma cell 6 is constituted by superposing a bottom side substrate 5 on the rear surface side of the intermediate substrate 1 through a space filled with a plasma gas. Pixels in a matrix state are formed by intersecting orthogonally and arranging a column drive unit consisting of a signal electrode D with a stripe shape formed in the inner surface of the upper substrate 3 and a row scanning unit consisting of a plasma room 7 with a stripe shape with each other. The thickness 12 of the intermediate substrate 1 is varied from the rear surface side within a width in individual row scanning unit. To put it concretely, the thickness of the intermediate substrate 1 is set relatively small in a width part center 13 in individual row scanning unit, and the thickness is set relatively large in a width part periphery 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma addressed liquid crystal display device having a two-layer structure of a liquid crystal cell and a plasma cell. More specifically, it relates to a structure for removing the viewing angle dependence of a liquid crystal cell.

[0002]

2. Description of the Related Art Conventionally, a switching device such as a thin film transistor is provided for each pixel and is driven line-sequentially as a means for improving the resolution and the contrast of a matrix type display device using a liquid crystal cell. A method of doing so-called so-called active matrix address method is generally known. However, in this case, it is necessary to provide a large number of semiconductor elements such as thin film transistors on the substrate, and there is a disadvantage that the manufacturing yield is deteriorated especially when the area is increased.

Therefore, as a means for solving this disadvantage,
Buzaku et al., In Japanese Patent Laid-Open No. 1-217396, propose a method of using a plasma switch instead of a switching element composed of a thin film transistor or the like. Less than,
The configuration of a plasma addressed display device that drives a liquid crystal cell using a switch based on plasma discharge will be briefly described. As shown in FIG. 4, this device has a laminated flat panel structure including a liquid crystal cell 101, a plasma cell 102, and an intermediate plate 103 interposed therebetween. The plasma cell 102 is formed using a lower glass substrate 104, and a plurality of grooves 105 are provided on the surface thereof.
The grooves 105 extend, for example, in the row direction of the matrix. Each groove 105 is sealed by an intermediate plate 103 and constitutes a plasma chamber 106 which is individually separated. The plasma chamber 106 is filled with an ionizable gas. A partition wall 107 that separates adjacent grooves 105 separates the individual plasma chambers 106 from each other and also serves as a gap spacer. At the bottom of each groove 105, a pair of parallel plasma electrodes 108, 10 are provided.
9 is provided. The pair of electrodes function as an anode and a cathode and ionize the gas in the plasma chamber 106 to generate discharge plasma. The discharge area is a row scanning unit.

On the other hand, the liquid crystal cell 101 is constructed by using an upper glass substrate 110. This glass substrate 110
Are opposed to the intermediate plate 103 with a predetermined gap therebetween, and a liquid crystal layer 111 is filled in the gap. The liquid crystal layer 111 is, for example, twisted nematic (TN) aligned. A signal electrode 112 made of a transparent conductive material is formed on the inner surface of the glass substrate 110. The signal electrode 112 is orthogonal to the plasma chamber 106 and serves as a column drive unit. Matrix-like pixels are defined at the intersections of the column driving units and the row scanning units.

In the display device having such a structure,
Display driving is performed by line-sequentially switching and scanning the plasma chamber 106 in which plasma discharge is performed, and applying an analog drive voltage to the signal electrode 112 on the liquid crystal cell side in synchronization with this scanning. When a plasma discharge is generated in the plasma chamber 106, the inside becomes substantially uniformly at the anode potential, and pixel selection is performed for each row. That is, the plasma chamber 106 functions as a sampling switch. When a driving voltage is applied to each pixel while the plasma sampling switch is in a conducting state, sampling and holding is performed, and lighting or extinction of the pixel can be controlled. Even after the plasma sampling switch is turned off, the analog drive voltage is retained in the pixel as it is.

[0006]

Generally, a TN mode liquid crystal display device has a viewing angle dependency, and the transmittance changes depending on the angle at which the screen is observed. When halftone is displayed,
When observed from an oblique direction, the white part and the black part may be reversed. In the case of color display, the color tone may change. Also in the plasma addressed liquid crystal display device described above, for example, a TN mode liquid crystal cell is used to optically control the turning on and off of the pixel, and the viewing angle dependency is a problem to be solved. To facilitate understanding of the present invention, the viewing angle dependence of the liquid crystal cell will be briefly described with reference to FIG. This graph shows the relationship between the viewing angle θ and the transmittance T. The change in transmittance is shown with the effective voltage applied to the liquid crystal cell as a parameter. The curve of is when the effective voltage is 0V. Below, the curve of is set to 2V, the curve of is 2.5V, and the curve of is 3.0V.
The curve of V is set to 3.5V, and the curve of V is set to 4.0V. The liquid crystal cell used in this measurement is in a normally white mode, and the transmittance T is represented by 100% when no voltage is applied at normal incidence (θ = 0). As is clear from this graph, in the viewing angle range larger than θ = 30 °, the transmittance at the halftone display level exceeds the transmittance when no voltage is applied, and the display is inverted.

Next, the cause of the above-mentioned display inversion will be described with reference to FIG. Figure 6 shows T in normally white
6 is a graph showing a relationship between an applied voltage V and a transmittance T for an N-mode liquid crystal cell. The horizontal axis represents the effective voltage applied to the liquid crystal cell, and the vertical axis represents the relative transmittance when the transmittance when vertically applied light is not applied is 100%. In this graph, the viewing angle θ is used as a parameter,
The curve of represents the change in transmittance when θ = 0, the curve of represents the case of θ = + 30 °, and the curve of represents θ =
This is the case of -30 °. In this graph, the viewing angle θ
Is tilted along the y-axis. The definition of the y-axis is shown below the graph. That is, the upper substrate rubbing direction and the lower substrate rubbing direction of the liquid crystal cell are orthogonal to each other, and the axis of symmetry is given as the y-axis. Θ = + when tilted 30 ° in the positive direction of the y-axis with respect to the substrate normal
It is represented by 30 °, and θ = −3 when tilted 30 ° in the negative direction.
It is represented by 0 °.

Here, for example, when an effective voltage of 2 V is applied to the liquid crystal cell, the relative transmittance T becomes 50% at normal incidence. At this time, when observed from a visual angle of θ = + 30 °, the transmittance is almost the same level as the transmittance T when no voltage is applied, and desired modulation cannot be performed. On the other hand, when observed from a viewing angle of θ = −30 °, the transmittance T becomes the minimum level, resulting in overmodulation.

[0009]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, it is an object of the present invention to eliminate or reduce the viewing angle dependence of a plasma addressed liquid crystal display device. The following measures have been taken in order to achieve this object. That is, in the plasma addressed liquid crystal display device according to the present invention, a liquid crystal cell is basically constructed by stacking an upper substrate on the front surface side of the intermediate substrate with a liquid crystal layer interposed therebetween, and plasma gas is sealed on the rear surface side of the intermediate substrate. The lower substrate is superposed through a space to form a plasma cell. A column driving unit formed of a stripe-shaped signal electrode formed on the inner surface of the upper substrate and a row scanning unit formed of a stripe-shaped plasma chamber formed in the plasma cell are orthogonally arranged to form a matrix-shaped pixel. . A feature of the present invention is that the thickness of the intermediate substrate varies from the back surface side within the width of each row scanning unit. Specifically, the thickness of the intermediate substrate is set relatively small at the center of the width portion of each row scanning unit, and the thickness is set relatively large around the width portion. At this time, the thickness of the intermediate substrate is changed stepwise. More specifically, a stripe-shaped irregular cross-section groove is formed along the row scanning unit on the back surface side of the intermediate substrate to change the wall thickness, and a stripe-shaped plasma chamber is also formed. .

[0010]

In the plasma addressed liquid crystal display device, a voltage is applied to the liquid crystal layer through the thickness of the intermediate substrate. Therefore, the effective voltage increases as the wall thickness decreases, and conversely decreases as the wall thickness increases. In the present invention, the thickness of the intermediate substrate is changed from the back surface side within the width of each row scanning unit, and the effective voltage applied to the liquid crystal layer is optimized. In particular,
The voltage-transmittance characteristic of the liquid crystal layer is adjusted to be gentle. Therefore, the viewing angle dependency of the transmittance is suppressed as compared with the related art, and it is possible to effectively suppress a defect such as inversion of black and white display.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial sectional view showing an embodiment of a plasma addressed liquid crystal display device according to the present invention. In the present device, a liquid crystal cell 4 is formed by stacking an upper substrate 3 on the surface side of an intermediate substrate 1 with a liquid crystal layer 2 interposed therebetween.
The lower substrate 5 is superposed on the back surface side of the intermediate substrate 1 via a space filled with plasma gas to form a plasma cell 6. Further, a column driving unit formed of a stripe-shaped signal electrode D formed on the inner surface of the upper substrate 3 and a row scanning unit formed of a stripe-shaped plasma chamber 7 formed in the plasma cell are arranged orthogonally to each other in a matrix. The pixel of the shape. As a feature of the present invention, the thickness of the intermediate substrate 1 is changed from the back surface side within the width of each row scanning unit.

The liquid crystal cell 4 and the plasma cell 6 will be described in detail below. The intermediate substrate 1 is made of a dielectric material such as a glass plate, and its surface has a highly accurate flatness. The upper substrate 3 is also made of a glass plate or the like, and a predetermined gap (for example, 5 μm) is formed by the sealing material 8.
It is adhered to the surface of the intermediate substrate 1 via. The liquid crystal layer 2 filled and sealed in the gap between the two substrates is, for example, twisted nematic, and the transmittance thereof has a viewing angle dependency. Or instead of TN mode, STN mode or EC
It is also possible to adopt the B mode. It has a predetermined viewing angle dependence in any mode. A polarizing plate 9 is attached to the outer surface of the upper substrate 3. Similarly, the polarizing plate 10 is attached to the outer surface of the lower substrate 5. In this embodiment, the pair of polarizing plates 9 and 10 are set in a crossed Nicol relationship, and display in a so-called normally white mode is performed. However, the present invention is not limited to this display mode and may be a normally black mode.

A stripe-shaped groove 11 is formed along the row scanning unit on the back surface side of the intermediate substrate 1 to form a plasma chamber 7. Each groove 11 has an irregular cross section, and the thickness 12 of the intermediate substrate 1 is changed from the back surface side within the width of the row scanning unit. That is, the thickness is set to be relatively small in the central portion 13 in the width direction of each row scanning unit, and the peripheral portion 14
It is set relatively large in. In this embodiment, the wall thickness is 1
The number 2 changes stepwise, but the number is not limited to this, and may be changed continuously. A plasma electrode is provided along the bottom surface of the partition wall 15 that separates the adjacent grooves 11 from each other. This plasma electrode alternately functions as the anode A and the cathode K. In each groove 11, the end faces of the pair of anodes A and cathodes K are exposed and face each other, and a plasma discharge is generated by applying a voltage between them. In this embodiment, the stripe-shaped groove 11 and the plasma electrode are integrally formed on the intermediate substrate 1 side, and can be obtained by, for example, sandblasting or powder beam processing via a stripe pattern mask. According to this structure, the thick portion 12 and the partition wall portion 15 of the intermediate substrate 1 are integrally connected to each other, and the mechanical strength is excellent. Therefore, even if a large pressure is applied from the surface side of the intermediate substrate 1 due to the negative pressure in the plasma chamber 7 or the like, there is no fear of deformation. Therefore, the intermediate substrate 1
It is possible to maintain the flatness of the surface constant. Finally, the lower substrate 5 is also made of a glass plate or the like, and is adhesively sealed to the back surface side of the intermediate substrate 1 via a frit seal 16.

FIG. 2 shows an equivalent circuit of the plasma addressed liquid crystal display device shown in FIG. In this equivalent circuit, a dielectric layer composed of a ceiling portion of a groove 11 formed in the intermediate substrate 1 has a relatively thin central portion 13 and a relatively thick peripheral portion 14.
Are shown separately for convenience of explanation. The capacitance CL1 of the liquid crystal layer and the capacitance CE1 of the thick dielectric layer are connected in series between the power source V0 and the plasma switch S. Similarly, the capacitance CL2 of the liquid crystal layer and the capacitance CE2 of the thin dielectric layer are connected in series between the power source V0 and the plasma switch S. The plasma switch S is equivalent to the function of the plasma chamber 7 shown in FIG. The magnitude of the effective voltage applied to the liquid crystal layer is determined according to the capacitance division ratio between the capacitance CL of the liquid crystal layer itself and the capacitance CE of the dielectric layer. The larger the capacitance of the dielectric layer,
That is, the thinner the dielectric layer thickness, the larger the effective voltage applied to the liquid crystal layer. By appropriately changing the thickness of the dielectric layer, the viewing angle dependence of the liquid crystal cell can be effectively reduced.

Finally, an example of setting the thickness of the dielectric layer will be described with reference to FIG. In this graph, the thickness of the dielectric layer is set so that the voltage-transmittance characteristic of the liquid crystal layer region corresponding to the thin center portion has a thin curve A. On the other hand, the thickness of the dielectric layer is set so that the transmittance-voltage characteristic of the liquid crystal layer region corresponding to the thick peripheral portion has a thin curve B. For example, when the transmittance T of the thick central portion is 10%,
The thickness of the dielectric layer is controlled so that the transmittance T of the thin peripheral portion is 90%. In this case, the average transmittance-voltage characteristic per pixel is represented by the bold curve. Note that this curve shows the data at the viewing angle θ = 0.
The steepness of the transmittance-voltage characteristics decreases as the thickness of the dielectric layer increases because of the dielectric anisotropy of liquid crystal molecules.
However, since this difference is practically negligible, both curves A and B are drawn with the same steepness in the graph of FIG. 3, and only the threshold value is shifted.

As is apparent from a comparison of the graph of FIG. 3 and the graph of FIG. 6, according to the present invention, the fall of the curve is gentle. The thick curve in the graph of Figure 3 is θ
Shows the transmittance-voltage characteristics when set to = + 30 °,
The other thick line curves represent the characteristic curves when θ = −30 ° is set. As is clear from comparison with the graph of FIG. 6, these characteristic curves also become smooth in the same manner. Examining the viewing angle dependence when an effective voltage is applied so that the relative transmittance becomes 50% at normal incidence, θ =
When + 30 °, the transmittance is 78%, and when θ = −30 °, the transmittance is 20%. As is apparent from comparison with the graph of FIG. 6, the viewing angle dependency is reduced. This reduction effect becomes remarkable because the effective voltage applied to the liquid crystal layer in the pixel varies as the variation in the thickness of the dielectric layer increases. On the other hand, the driving voltage must be increased as the thickness of the dielectric layer is increased. Finally, estimating the optimum thickness of the dielectric layer, assuming that the dielectric constant of the intermediate substrate and the dielectric constant of the liquid crystal layer are the same, assuming that the thickness of the liquid crystal layer is 5 μm and the thickness of the thick dielectric layer is 50 μm. The thickness of the thin dielectric layer may be about 30 μm.

[0017]

As described above, according to the present invention, the viewing angle dependence of the liquid crystal cell is significantly increased by changing the thickness of the intermediate substrate from the back surface side within the width of each row scanning unit. The effect is that it can be improved. In addition, the stripe-shaped irregular cross-section groove is formed along the row scanning unit on the back surface side of the intermediate substrate to change the wall thickness, and the stripe-shaped plasma chamber is also configured to provide excellent mechanical strength. There is an effect that a plasma cell can be constructed.
Therefore, even if a large external pressure is applied to the intermediate substrate due to the negative pressure, the intermediate substrate is not deformed and the flatness can be kept constant, so that the operation characteristics on the liquid crystal cell side are stabilized.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view showing the basic configuration of a plasma addressed liquid crystal display device according to the present invention.

FIG. 2 is an equivalent circuit diagram of the plasma addressed liquid crystal display device shown in FIG.

3 is a graph showing transmittance-voltage characteristics of the plasma addressed liquid crystal display device shown in FIG.

FIG. 4 is a schematic perspective view showing an example of a conventional plasma addressed liquid crystal display device.

FIG. 5 is a graph showing general viewing angle dependence of a liquid crystal cell.

FIG. 6 is a graph showing a transmittance-voltage characteristic of a conventional plasma addressed liquid crystal display device.

[Explanation of symbols]

 1 Intermediate Substrate 2 Liquid Crystal Layer 3 Upper Substrate 4 Liquid Crystal Cell 5 Lower Substrate 6 Plasma Cell 7 Plasma Chamber 11 Groove 12 Wall Thickness 13 Central Part 14 Peripheral Part 15 Partition A Anode K Cathode D Signal Electrode

Claims (5)

[Claims] 1. A liquid crystal cell is constructed by stacking an upper substrate on a front surface side of an intermediate substrate via a liquid crystal layer, and a lower substrate is stacked on a rear surface side of the intermediate substrate via a space filled with plasma gas to form a plasma. A cell is formed, and a column driving unit formed of a stripe-shaped signal electrode formed on the inner surface of the upper substrate and a row scanning unit formed of a stripe-shaped plasma chamber formed in the plasma cell are arranged orthogonally to each other to form a pixel. A plasma addressed liquid crystal display device characterized in that the thickness of the intermediate substrate is changed from the back surface side within the width of each row scanning unit. 2. The plasma address according to claim 1, wherein the thickness of the intermediate substrate is set relatively small at the center of the width portion of each row scanning unit and the thickness is set relatively large around the width portion. Liquid crystal display device. 3. The plasma addressed liquid crystal display device according to claim 1, wherein the thickness of the intermediate substrate is changed stepwise. 4. A striped plasma chamber is formed along with a row-shaped scanning unit by forming stripe-shaped irregular cross-section grooves on the back surface side of the intermediate substrate to change the wall thickness. The plasma addressed liquid crystal display device according to claim 1. 5. The plasma addressed liquid crystal display device according to claim 4, wherein a plasma electrode is provided along a bottom surface of the partition wall separating adjacent grooves from each other.