JP3042079B2 - Image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type image display device having a laminated structure in which an electro-optical cell such as a liquid crystal cell and a plasma cell are stacked. Plasma cells are used for addressing liquid crystal cells. More specifically, the present invention relates to a material configuration of a partition wall interposed between a liquid crystal cell and a plasma cell.

[0002]

2. Description of the Related Art For example, as means for achieving high resolution and high contrast of a matrix liquid crystal display device, a switching element such as a thin film transistor is provided for each display pixel, and this is driven in a line-sequential manner (so-called active type). (Matrix address method) is generally adopted. However, in this method, it is necessary to form a large number of semiconductor elements such as thin film transistors on a substrate, and there is a disadvantage that the yield is deteriorated particularly when the area is increased.

In order to solve this drawback, Buzak et al. In Japanese Patent Application Laid-Open No. 1-217396 propose a system using a plasma switch instead of a switching element such as a thin film transistor. Hereinafter, the configuration of an image display device that drives an electro-optical cell such as a liquid crystal cell using a discharge plasma switch will be briefly described. This image display device has a liquid crystal cell 101 and a plasma cell 102 as shown in FIG.
Have a structure in which they are stacked with a common partition wall 103 interposed therebetween. The plasma cell 102 includes a plurality of grooves 10 parallel to each other.
5 is formed of an insulating substrate 104 on which is formed. Each groove 1
05 is completely sealed by a partition 103. A gas that can be ionized by discharge is sealed in the sealed groove 105 to form a discharge region. Also, each groove 105
Are provided with a pair of plasma electrodes 106 and 107 at the bottom. A voltage is applied to the sealed gas using one of the pair of electrodes 106 and 107 as an anode and the other as a cathode to ionize and generate discharge plasma. On the other hand, the liquid crystal cell 101 includes a liquid crystal layer 109 sandwiched between an upper substrate 108 and a partition 103. Substrate 10
A plurality of transparent electrodes 110 that are parallel to each other are formed on the inner surface of 8. This transparent electrode 110 is connected to the lower substrate 10.
4 are arranged so as to intersect with the grooves 105 formed. Individual pixels are defined at the intersections in a matrix.

In the above-described image display device, each groove 1
The discharge area formed at 05 is a row scanning unit, and the transparent electrode 110 is a column driving unit. Each discharge region is sequentially activated by selective plasma discharge, and line-sequential scanning is performed for each row. In synchronization with this, a drive signal is applied to each of the transparent electrodes 110 constituting the column drive unit to drive the pixels. When activated, the entire discharge region becomes substantially at the anode potential, and one end of each pixel is connected to the anode potential via the partition 103.
Therefore, the discharge region forms a so-called plasma switch.
A drive signal is applied to the other end of each pixel in synchronization with the time when the switch is turned on. The drive signals applied to both sides of each pixel are held as they are after the plasma switch is turned off, and a so-called sample hold is performed.

[0005]

By the way, the above-mentioned partition wall 103 functions not only to seal the liquid crystal layer 109 but also to function as an insulation barrier between the liquid crystal layer 109 and the discharge region. The partition 103 has conventionally been formed of a dielectric made of a thin glass material. Since it is a dielectric, it acts as a capacitor interposed between the pixel and the plasma switch. Therefore, it is preferable that the thickness be as small as possible in order to sufficiently secure the electrical connection between the liquid crystal layer constituting the sampling capacitor and the plasma switch. However, when the glass plate is made extremely thin, there is a problem that handling becomes extremely difficult, especially when the size of the image display device is increased. Not only is it difficult to process the glass plate to a uniform thickness over the entire display screen, but also the breakage and cracks occur very easily due to careless handling and the like. Therefore, in practice, the limit of the thickness of the glass plate is about 50 μm. On the other hand, the thickness of the liquid crystal layer is considerably smaller than this, for example, about 5 μm. Therefore, the effective component of the drive voltage applied to the pixel directly applied to the liquid crystal layer is, for example, about one tenth of the drive voltage, depending on the dielectric constant of the material. In other words, there is a problem that the drive voltage needs to be about 10 times the effective component and the load on the drive circuit is extremely large. Further, when the driving voltage is large, there is a problem that a lateral leakage of an electric field occurs between adjacent transparent electrodes, and so-called crosstalk occurs. The image quality is significantly impaired by this crosstalk.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, an object of the present invention is to provide a partition wall material structure which is excellent in workability and workability and can be made thin. As means for achieving this object, a polyimide film is employed. This polyimide film is a sheet material mainly composed of a polyimide resin, and its thickness can be reduced to, for example, about 13 μm. Alternatively, a polysulfone film may be employed as a partition between the liquid crystal cell and the plasma cell.

[0007]

The polyimide resin is an aromatic polyimide produced by a reaction between pyromellitic anhydride and an aromatic diamine, and is particularly excellent in heat stress resistance. It can withstand a high temperature of 400 ° C. or more, and there is no problem even when a high-temperature sealing treatment of a plasma cell is performed. In addition, it has excellent toughness and flexibility, and can be made considerably thinner than a glass plate. For example, even if the thickness is reduced to about 13 μm, there is no fear that the glass is broken or cracked like a glass plate, and it is easy to handle. The drive voltage can be reduced as much as the partition walls are made thinner than in the past, and the load on the drive circuit can be greatly reduced. at the same time,
By lowering the driving voltage, crosstalk, which has conventionally been a problem, is reduced, and the display quality is improved.

However, the polyimide film is generally colored yellow and has birefringence depending on the stretching direction, which may adversely affect the electro-optical effect of the liquid crystal layer. Therefore, when high heat resistance is not required, a polysulfone film can be used instead of the polyimide film. Although this polysulfone film has a heat resistance temperature of about 175 ° C., it is excellent in toughness and transparency, and can almost completely eliminate the optical influence.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing one embodiment of the image display device according to the present invention. As shown, the image display device includes a liquid crystal cell 1 and a plasma cell 2.
And a common partition 3 interposed therebetween. The liquid crystal cell 1 is configured using a first substrate 4. A plurality of first electrodes or signal electrodes 5 formed in parallel with each other along the inner main surface of the substrate 4 are formed. The signal electrodes 5 are obtained by etching a transparent conductive material such as ITO and are arranged in rows. The signal electrodes 5 constitute a column drive unit. The substrate 4 is opposed to the partition 3 with a predetermined gap via a spacer.
A liquid crystal layer 6 is sealed in this gap as an electro-optical material layer. The liquid crystal layer 6 is oriented according to various electro-optical operating modes. The thickness of the liquid crystal layer 6 is set to, for example, 5 μm. In this example, a fluid liquid crystal material is used as the electro-optic layer, but the invention is not limited to this. For example, a solid material such as PLZT can be used.

[0010] The plasma cell 2 is configured using a second substrate 7. A plurality of grooves 8 aligned in the row direction are formed on the inner surface of the second substrate 7. A pair of anode electrodes A and cathode electrodes K are formed at the bottom of each groove 8 so as to be separated from each other. The pair of electrodes A and K constitute the second electrode or the plasma electrode 9. The plasma electrode 9 is disposed so as to cross the signal electrode 5. Each groove 8 is hermetically sealed by the partition wall 3 and an ionizable gas 10 is sealed therein. This gas comprises, for example, helium, neon, argon, or a mixture thereof. A discharge region 11 is formed by the plasma electrode 9 formed at the bottom of each groove 8 and the enclosed ionizable gas 10. The discharge region 11 serves as a row scanning unit and defines an individual pixel 12 between itself and the signal electrode 5 which is a column driving unit. Since this embodiment is a transmission type image display device, both the second substrate 7 and the first substrate 4 are made of a transparent material. However, when a reflective image display device is manufactured, at least one substrate may be made transparent.

The partition 3 is made of a polyimide film. The film thickness is set to, for example, 13 μm. Polyimide film is 400
It has a heat resistance of not less than ° C. and can sufficiently withstand the processing temperature when the groove 8 is hermetically sealed. Also, unlike thin glass, it is flexible and does not break or crack during handling. Further, it has a function of performing desired alignment control on the liquid crystal layer 6 by rubbing the surface of the polyimide film. In this embodiment, the discharge regions 11 are individually separated. However, it is not always necessary to separate them, and a side wall between the grooves 8 may be removed to form a so-called open cell structure. In this case, since the discharge region is a continuous space over the entire screen, the resolution may be degraded due to the diffusion of ions generated by the plasma discharge. However, there is a suitable solution for this. That is, as is well known, the higher the pressure of the gas sealed in the discharge region, the smaller the mean free path of ions and the more localized the plasma. Therefore, it is possible to substantially localize the discharge plasma to the discharge region 11 by setting the sealing gas pressure to a certain high level.

In another embodiment of the present invention, a polysulfone film can be used as the material of the partition walls 3 instead of the polyimide film. Since the polysulfone film is colorless and transparent unlike the polyimide film, no coloring occurs on the display image surface. Further, since it has no birefringence, the electro-optical effect of the liquid crystal layer 6 is not adversely affected. However, since the heat resistance temperature is about 175 ° C. as compared with the polyimide film, it is not suitable for high temperature treatment.

FIG. 2 is a cross-sectional view showing the same embodiment. In contrast to the cross-sectional view of FIG. 1 cut along a column direction parallel to the signal electrode 5, the cross-sectional view of FIG. The figure is cut along a row direction parallel to the plasma electrode 9.
As described above, the pixel 12 is defined at the intersection of the signal electrode 5 as a column drive unit and the discharge region 11 as a row scan unit. When a predetermined discharge voltage is applied between a pair of anode electrode and cathode electrode constituting the plasma electrode 9, the gas 10
Are ionized to generate plasma discharge, and the discharge region 11 is activated. As a result, the discharge region 11 is maintained at the anode potential over substantially the entirety. In the figure, four pixels 12 are shown along the activated discharge region 11. When a predetermined analog drive voltage is applied to the signal electrode 5, an electric field is generated toward the activated discharge region 11 as shown by an arrow, and the liquid crystal layer 6 is driven locally.

Next, the operation of the image display device will be described. FIG. 3 is a schematic block diagram showing a driving circuit of the image display device shown in FIGS. The drive circuit is a signal circuit 21
, A scanning circuit 22, and a control circuit 23. The signal circuit 21 has a plurality of signal electrodes D1 via buffers.
To Dm are connected. This signal electrode is shown in FIG.
And is the same as that shown with reference numeral 5 in FIG. The scanning circuit 22 has a plurality of cathode electrodes K
1 to Kn are respectively connected via buffers.
On the other hand, the plurality of anode electrodes A1 to An are commonly grounded. The control circuit 23 controls the signal circuit 21 and the scanning circuit 22 synchronously. The cathode electrode connected to the scanning circuit 22 is scanned line-sequentially and a discharge voltage is applied between the cathode electrode and the corresponding anode electrode to generate a plasma discharge. On the other hand, an analog drive voltage is applied to the signal electrodes connected to the signal circuit 21 in synchronization with the line sequential scanning. Each pixel 12 is defined at the intersection of a signal electrode serving as a column drive unit and a pair of anode electrode and cathode electrode serving as a row scan unit.

FIG. 4 schematically shows only the four pixels 12 shown in FIG. Therefore, in FIG. 4, only two signal electrodes D1 and D2 and two sets of anode electrodes and cathode electrodes A1, K1 and A2, K2 are shown. The pixel 12 has a stacked structure, and is stacked from the top like a signal electrode (D1, D2), a liquid crystal layer 6, a partition wall 3 made of a polyimide film, and a plasma switch (S1, S2). The plasma switches S1 and S2 functionally represent the discharge region 11 shown in FIGS.
That is, for example, when a scan signal is applied to the second cathode electrode K2, the corresponding discharge region is activated and the anode electrode A
2 ground potential. This action means that the plasma switch S2 has become conductive. On the other hand, the adjacent plasma switch S1 is in a non-conductive state because the discharge region is not activated. When a predetermined analog drive voltage is applied to the signal electrodes D1 and D2 when the plasma switch S2 is turned on, the analog drive voltage is written to the pixel 12. That is, the liquid crystal layer 6 of each pixel 12 constitutes a sampling capacitor, and the corresponding plasma switch becomes a sampling switch. The partition 3 made of a polyimide film becomes a part of the sampling capacitor. The charge accumulated in the sampling capacitor is retained even after the sampling switch is turned off, so that a so-called sampling hold is performed.

FIG. 5 is a schematic equivalent circuit diagram corresponding to one pixel 12 shown in FIG. As described above, the pixel includes a liquid crystal capacitor component _CLC , a partition capacitor component _CS, and a plasma switch S connected in series. The thickness d _{LC of the} liquid crystal layer is set to, for example, 5 μm, and the thickness of the polyimide film can be reduced to, for example, 13 μm. The pixels are supplied with an AC drive voltage. It represents the absolute value V _S. When the plasma switch S is turned on, the drive voltage V _S is divided and applied to the capacitor components C _LC and C _S. At this time, the effective driving voltage V _LC applied to C _LC contributes to the driving of the pixel.
It is. V _LC is represented by V _S × C _S / (C _LC + C _S ). Now, assuming that the dielectric constants of the liquid crystal layer and the polyimide film are substantially equal, V _LC is given by V _S × d _LC / (d _LC + d _S ). At this time, if the value of the drive voltage V _S is 10 V, for example, d _LC = 5 μm and d _S = 13 μm, so that the effective drive voltage V _LC is about 2.8 V. In this way, the liquid crystal cell can be sufficiently driven even with a relatively low drive voltage V _S.

On the other hand, if thin glass is used as a partition as in the prior art, its thickness is limited to d _S = 50 μm. In this case, even if the driving voltage V _S is set to 10 V, the effective driving voltage V _LC depends on the dielectric constant, but is only 0.1 V at most, for example. Therefore, in the prior art, a driving voltage of several tens of volts was required to obtain a predetermined display contrast. For this reason, the load on the drive circuit is increased, causing an increase in cost.

Further, there is a problem that a crosstalk occurs when the driving voltage is high as in the prior art. This crosstalk will be briefly described with reference to FIG. It is assumed that 40 V is applied as a pixel lighting voltage to a certain signal electrode 5 and 0 V is applied as a pixel extinguishing voltage to an adjacent signal electrode 5. Since a large potential difference occurs between adjacent signal electrodes, a horizontal electric field is generated as shown by a dotted arrow. The liquid crystal between adjacent pixels also operates due to this electric field, and a so-called display blur occurs at an end of the pixel.

To make matters worse, as shown in FIG. 6, this causes vertical stripes which significantly deteriorate image quality. The vertical stripes appear not in the row direction but in the column direction. In particular, if the display density is different between adjacent columns, extremely remarkable vertical stripes appear. As a countermeasure, it is also conceivable to previously form a black stripe between the signal electrodes in a row to mask the vertical stripes. However, when a black stripe is applied to the image surface, there is a problem that the brightness of the entire image is reduced. In contrast, according to the present invention,
Since the driving voltage applied to the signal electrodes can be made smaller than that of the related art, crosstalk generated between adjacent signal electrodes can be suppressed accordingly. Substantially, the black stripe can be removed.

In the above-described embodiment, a polyimide film or a polysulfone film is used as a material for the partition walls. On the other hand, when a normal plastic sheet is used, not only is there a problem in heat resistance, workability, and mechanical strength, but also an impurity gas (outgas) is generated, which impairs the reliability and life of the plasma cell.

[0021]

As described above, according to the present invention, by using a polyimide film or a polysulfone film as a partition wall material for separating a liquid crystal cell and a plasma cell, the thickness of the partition wall can be reduced as compared with the prior art. Even if it is made thin, since it has flexibility, there is no fear of breakage or cracking as in conventional glass materials. In addition, by reducing the thickness of the partition walls, the driving voltage can be reduced and the load on the driving circuit can be reduced. In addition, it is possible to suppress the crosstalk generated between the signal electrodes, to improve the display image quality, and to eliminate the conventionally required black stripe mask.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image display device according to the present invention.

FIG. 2 is a cross-sectional view of the same embodiment, but with a cutting direction of FIG.
And orthogonal.

FIG. 3 is a schematic block diagram illustrating an example of a drive circuit used in the image display device according to the present invention.

FIG. 4 is a schematic diagram showing pixels cut out from the image display device according to the present invention.

FIG. 5 is an equivalent circuit diagram of each pixel.

FIG. 6 is a schematic plan view showing an image plane of a conventional image display device.

FIG. 7 is a partially cutaway perspective view showing the structure of a conventional image display device.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal cell 2 plasma cell 3 partition 4 first substrate 5 signal electrode 6 liquid crystal layer 7 second substrate 8 groove 9 plasma electrode 10 gas 11 discharge region A anode electrode K cathode electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1333 G02F 1/133 505 H01J 11/00 H01J 17/00

Claims (2)

(57) [Claims] A first substrate having a plurality of first electrodes formed parallel to each other along a predetermined main surface; and a first substrate intersecting with the first electrodes along the predetermined main surface and formed parallel to each other. A second substrate having a plurality of second electrodes formed thereon and disposed so that the second electrodes face the first electrodes, and an electro-optical material provided in contact with the plurality of first electrodes. A layer, a polyimide film disposed so as to be in contact with the electro-optical material layer on the side opposite to the plurality of first electrodes, and for filling an ionizable gas between the polyimide film and the second substrate. , The gas is selectively ionized by a discharge between adjacent second electrodes, and the first electrode and the second electrode are used as a scanning unit in a discharge region where the ionized gas is localized. The electro-optic material layer existing at the intersection of An image display device configured to be driven. 2. A first substrate having a plurality of first electrodes formed parallel to each other along a predetermined main surface, and a first substrate intersecting with the first electrodes along the predetermined main surface and formed parallel to each other. A second substrate having a plurality of second electrodes formed thereon and disposed so that the second electrodes face the first electrodes, and an electro-optical material provided in contact with the plurality of first electrodes. A polysulfone film disposed so as to be in contact with the electro-optic material layer on a side opposite to the plurality of first electrodes;
A plasma chamber provided between the polysulfone film and the second substrate for sealing a gas capable of being ionized, wherein the gas is selectively ionized by discharge between adjacent second electrodes; An image display device configured to drive an electro-optic material layer existing at an intersection of the first electrode and the second electrode by using a discharge region in which is localized as a scanning unit.