JP2005258463A - Liquid crystal electrooptical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent display characteristics, by improving the nonuniformity of electric lines of force along the thickness of a liquid crystal cell in an electrooptical device which drives a liquid crystal material by applying an electric field in parallel with a substrate. <P>SOLUTION: The liquid crystal electrooptical device having a liquid crystal material sandwiched in between a couple of light-transmissive substrates 101 and 102 has, on one substrate 101, a switching element 111, a drain electrode 115 for driving the liquid crystal material, a common electrode 107, and a gate electrode 105, and applies an electric field parallel to the substrate between the drain electrode and the common electrode. On the other substrate 102, elements and respective electrodes, such as a drain electrode 116 and a common electrode 108, are formed and an electric field parallel to the substrate is applied by the electrodes on the couple of substrates to drive the liquid crystal material. Further, the electric field between the drain electrode 115 and common electrode 107 is smoothed with the electric field produced between the drain electrode 116 and common electrode 108. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal electro-optical device having good electrical characteristics and viewing angle characteristics and capable of obtaining uniform display on the entire screen.

  As a method for widening the viewing angle of the liquid crystal electro-optical device, a method in which the direction of the electric field applied to the liquid crystal is substantially parallel to the substrate surface (hereinafter referred to as a super TFT method) is disclosed, for example, in JP-A-6-160878. ing. In this case, an electric field is induced between the source electrode and the common electrode formed on one substrate, and liquid crystal molecules are aligned in the direction of the electric field. In Japanese Patent Laid-Open No. 6-214244, the electric field applied to the liquid crystal is made uniform by setting the electrode to the height of the cell thickness.

  In such an electro-optical device, since the liquid crystal molecule major axis is switched while maintaining a state parallel to the substrate, the change in the optical characteristics of the liquid crystal due to the viewing angle is small. For this reason, the light leakage due to the viewing angle, the decrease in contrast, and the like are small compared to the conventional TN and STN systems.

  However, the conventional super TFT electrode arrangement is formed only on one of a pair of substrates, and an electric field is easily applied to a region close to the electrode, but in a region directly above the electrode, There is a problem that the electric field strength is lowered, and thus the switching of the liquid crystal material varies in the cell.

  This is a defect that appears particularly conspicuously in the super TFT method in which liquid crystal driving is performed using a lateral electric field.

  The variation of the electric field will be described with reference to FIG. Here, for the sake of simplicity, a pair of insulating substrates (301) and (303) are arranged so as to overlap each other with a certain interval, and are formed on one substrate (301) with a trapezoidal cross section and an electrode interval. Are applied to a plurality of parallel electrodes (302), (305) each having a constant polarity, and electric lines of force (304) around the electrodes when voltages having different polarities are applied alternately to positive, negative, positive, negative,. ) Will be described. (For details on the electric field lines formed by electric charges, see Electromagnetics books such as Kazuyoshi Nagata's "Electromagnetism", Asakura Shoten, and Goto and Yamazaki's "Detailed Electromagnetics Exercise", Kyoritsu Publishing, etc.)

  The electric lines of force (304) emitted from one electrode (302) on the substrate (301) change direction when approaching the substrate (303) and head toward the other electrode (305). As can be seen, the electric flux density (proportional to the number of electric field lines per unit area) differs between the vicinity of the substrate surface on which the electrode is formed and the vicinity of the other substrate surface.

  Here, as an example, an electric field between electrodes having a trapezoidal cross section is shown, but the same applies to electrodes having other shapes such as a rectangular cross section. This is because the electric field is formed perpendicular to the electrode surface, and the distribution of the lines of electric force is nonuniform in the vicinity of the electrode and the other portions.

  The electric lines of force represent the direction of the electric field at each location. The liquid crystal material changes its orientation by interaction with the electric field. When the dielectric anisotropy of the liquid crystal material is positive, the liquid crystal molecular long axis is parallel to the electric field, and when negative, it is perpendicular to the electric field. Will be oriented.

  Taking the case of FIG. 3 as an example, there is a curved region between the pair of substrates so that the lines of electric force are convex upward, which means that the electric field is not a component parallel to the substrate. It also shows that it also has. Therefore, when an electric field is applied with the electrode arrangement as described above, according to the above matters, the liquid crystal molecules can be aligned in a direction other than parallel to the substrate in the substrate. In such a case, alignment failure of the liquid crystal material occurs.

  Such variations in the lines of electric force are disadvantages that cannot be ignored when the pixels are miniaturized. This is because the number of electrodes increases due to miniaturization, and a discontinuous electric field is distributed at a high density when the distance between the electrodes decreases.

  As another solution to the above problem, Japanese Patent Laid-Open No. 6-214244 proposes an invention in which the electrode is made to have a cell thickness height in order to apply an electric field uniformly to the liquid crystal in the cell thickness direction. However, the following technical difficulties arise in producing an extremely high electrode.

  First, if the height of the electrode is about the cell thickness, the difference in the electrode thickness in the lateral direction tends to be large between the top and bottom of the electrode. In the super TFT method in which the liquid crystal is driven by a horizontal electric field, the difference in electrode thickness is a difference in distance between electrodes. Therefore, since the electric field strength in the cell thickness direction is different within the same pixel, it becomes difficult to drive the liquid crystal.

  Second, if the electrode height is extremely high, the coverage of the layer formed thereon is poor, and disconnection is likely to occur when the layer formed thereon is an electrode.

  Third, it is technically difficult to obtain a large taper angle by thinning the film thickness in the lateral direction with an extremely high electrode even when the pixel is miniaturized.

  In order to solve the above-described problems in pixel miniaturization, an electrode structure that can be produced by a simple method and that does not generate a discontinuous electric field is required.

  As another problem, since the liquid crystal driving electrode and the common electrode are made of metal electrodes made of Al or the like, there is a problem that the aperture ratio is lowered.

  In a conventional liquid crystal electro-optical device, a common electrode is formed on a counter substrate, and the common electrode generally uses a light-transmitting material such as ITO. However, the lateral electric field drive type liquid crystal electro-optical device is effective in that a liquid crystal drive electrode and a common electrode are formed on one of the substrates, and each electrode uses a light-shielding electrode made of Al or the like. There is a drawback that the display area is reduced as compared with the conventional liquid crystal electro-optical device, that is, the aperture ratio is lowered.

  The liquid crystal electro-optical device of the present invention is of a type in which a liquid crystal material is operated by controlling an electric field (lateral electric field) intensity in a direction parallel to the substrate by a plurality of electrodes formed on a pair of substrates. However, the liquid crystal driving and common electrodes are not formed only on one of the substrates as in the conventional lateral electric field driving method, but the electrodes are also formed on the other substrate. Also, an electric field is applied to solve the problems such as non-uniformity of electric field strength, which have been a problem until now.

  Furthermore, it is intended to provide a liquid crystal electro-optical device with good visual characteristics by improving the reduction in aperture ratio due to the use of a light-shielding electrode.

In order to solve the above problems, the present invention provides:
A pair of substrates at least one of which is transparent;
Electrodes formed on both of the substrates;
A liquid crystal layer sandwiched between the substrates,
The electrodes include a pair of electrodes for driving a liquid crystal capable of forming an electric field including a direction parallel to the substrate surface,
The pair of electrodes have portions arranged substantially parallel to each other,
A liquid crystal electro-optical device provided with an electric field applying means for applying an electric field to the liquid crystal layer through the electrode,
The electric field distribution formed between a pair of electrodes on one of the substrates is controlled by the electric field strength formed between the pair of electrodes on the other substrate. It is.

Other configurations of the present invention include:
A pair of substrates at least one of which is transparent;
Electrodes formed on both of the substrates;
A liquid crystal layer sandwiched between the substrates,
The electrodes include a pair of electrodes for driving a liquid crystal capable of forming an electric field including a direction parallel to the substrate surface,
The pair of electrodes have portions arranged substantially parallel to each other,
A liquid crystal electro-optical device provided with an electric field applying means for applying an electric field to the liquid crystal layer through the electrode,
The electric field formed between the pair of electrodes on one of the substrates is made uniform in the cell thickness direction by the interaction with the electric field formed between the pair of electrodes on the other substrate. A liquid crystal electro-optical device.

Other configurations of the present invention include:
A pair of substrates at least one of which is transparent;
Electrodes formed on both of the substrates;
A liquid crystal layer sandwiched between the substrates,
The electrodes include a pair of electrodes for driving a liquid crystal capable of forming an electric field including a direction parallel to the substrate surface,
The pair of electrodes have portions arranged substantially parallel to each other,
A liquid crystal electro-optical device provided with an electric field applying means for applying an electric field to the liquid crystal layer through the electrode,
An electric field distribution between a pair of substrates is controlled by simultaneously applying an electric field in the same direction to the liquid crystal layer by an electrode between the pair of substrates.

Other configurations of the present invention include:
A pair of substrates at least one of which is transparent;
Electrodes formed on both of the substrates;
A liquid crystal layer sandwiched between the substrates,
The electrodes include a pair of electrodes for driving a liquid crystal capable of forming an electric field including a direction parallel to the substrate surface,
The pair of electrodes have portions arranged substantially parallel to each other,
Electric field applying means for applying an electric field to the liquid crystal layer through the electrode;
In the liquid crystal electro-optical device, the pair of electrodes are disposed at positions facing each other on both substrates.

  An example of a configuration using the invention disclosed in this specification is shown in FIGS. FIG. 1 shows an outline of a pixel portion of an active matrix type liquid crystal electro-optical device using nematic liquid crystal, driving the liquid crystal material with a lateral electric field, and using poly-Si TFT as the drive element, This is the case when the device is viewed from above (from a direction perpendicular to the substrate surface). Since some of the wirings are arranged in an overlapping manner, only the wiring on the upper substrate is visible. FIG. 2 shows a cross section in the AA 'direction in FIG.

In the configuration shown in FIGS. 1 and 2, on the first substrate (101), a base SiO ₂ film (103), a gate electrode (105), a common electrode (107), and a layer extending from the gate insulating film ( 109), a switching element (111), a source electrode (113), a liquid crystal driving electrode (115), a protective film (117), and an alignment film (119) are formed.

On the other hand, on the second substrate (102), the underlying SiO ₂ film (104), the gate electrode (106), the common electrode (108), the layer (110) extended from the gate insulating film, the switching element (112), the source An electrode (114), a liquid crystal driving electrode (116), a protective film (118), and an alignment film (120) are formed. Reference numeral (121) denotes a liquid crystal layer.

  The liquid crystal driving electrode (115) and the common electrode (107), or the liquid crystal driving electrode (116) and the common electrode (108) are arranged substantially parallel to each other.

  Here, the gate electrodes (105) and (106) function as gate wirings (scanning lines), and the source electrodes (113) and (114) function as source wirings (signal lines). The common electrodes (107) and (108) correspond to the common electrode. Further, when the alignment state of the liquid crystal layer (121) is described, liquid crystal molecules are also shown.

  In the case of the liquid crystal electro-optical device, first, an electric field is applied between the liquid crystal driving electrode (115) for driving the liquid crystal material and the common electrode (107) formed on the first substrate (101). The liquid crystal molecules in the layer (121) are switched in a plane parallel to the substrate (the alignment state changes).

  However, when an electric field is applied only between the electrodes on the first substrate (101), the electric field strength becomes smaller as it is closer to the second substrate (102), so that the alignment direction of the liquid crystal material (121) can be controlled. It becomes insufficient.

  Therefore, the liquid crystal driving electrode (116) and the common electrode (107) are also provided on the second substrate (102). At that time, the electrodes are disposed at positions where the electrodes face each other on the first substrate and the second substrate.

  That is, the liquid crystal driving electrode (116) of the second substrate (102) is placed on the liquid crystal driving electrode (115) on the first substrate (101), and the common electrode ( 107), the common electrode (108) of the second substrate (102) is disposed on the liquid crystal driving electrode (116) -common electrode (108) of the second substrate (102). An electric field is also applied.

  Then, the electric field distribution between the electrodes (115) and (107) on the first substrate (101) is such that the electric lines of force are generated by the electric field between the electrodes (116) and (108) on the second substrate (102). It is deformed and can be controlled to show various states. In particular, the electric field strength between the two electrodes (115), (107) on the first substrate (101) and the two electrodes (116), (108) on the second substrate (102). If the electric field strength is the same, the electric field strength distribution is constant at any location between the upper and lower substrates (101) and (102).

  For the first and second substrates (101) and (102), a material having translucency and a certain degree of strength against external force, for example, an inorganic material such as glass or quartz is used. . Non-alkali glass or quartz glass is used for a substrate on which a TFT or the like is formed (hereinafter referred to as a TFT substrate). For the purpose of reducing the weight of the liquid crystal electro-optical device, a film having low birefringence, such as PES (polyethylene sulfate), can also be used.

  The liquid crystal material (121) may be driven by a multiplex system or an active matrix system.

  In the multiplex system, only two types of liquid crystal driving electrode (115) and common electrode (107) are formed on the first substrate (101). In the active matrix system, however, switching elements ( 111) and (112), nonlinear elements such as thin film transistors (TFTs) and diodes are formed for each pixel. In the case of the thin film transistor, the drain electrode is connected to the liquid crystal driving electrodes (115) and (116), and the common electrode is separately provided as the common electrodes (107) and (108).

  As the TFT, a transistor using amorphous silicon or poly (polycrystalline) silicon as an active layer can be used. In the case of the active matrix system, a known configuration such as a stagger type or an inverted stagger type can be used as the configuration of the driving element. In addition, when a transistor using polysilicon is used, a peripheral driver circuit for driving a liquid crystal material can be formed on a substrate on which a TFT is manufactured. The peripheral driver circuit can be manufactured by the same process as that for manufacturing the TFT. This peripheral drive circuit is formed of complementary elements combining n-ch and p-ch transistors.

  The switching elements (111) and (112) are preferably poly-Si TFTs. In particular, when poly-Si is used for the TFT active layer, the mobility of the active layer is larger than when a-Si is used for the TFT active layer, and characteristics equivalent to a-Si can be obtained in a smaller element region. Therefore, it is possible to miniaturize each element, and thus to increase the aperture ratio. In addition, when applying a lateral electric field, a high-speed response can be realized when poly-Si having a high carrier mobility is used for the TFT active layer. Further, when poly-Si is used, a peripheral driver circuit for driving a liquid crystal material can be formed on the substrate, which contributes to a reduction in device manufacturing process, an improvement in yield, and a reduction in device price.

  As the element electrode, the gate electrode (105) and the source electrode (113) contain a metal made of Al, Ti, Ta or the like, a metal-containing material, a metal oxide, or Si, Si containing phosphorus, boron, or the like. Materials, carbon, carbon-containing materials, and the like can be used. When increasing the pixel density, signal delays at the gate and source electrodes (105) and (113) cannot be ignored. Therefore, it is desirable to use a material having a low volume resistivity. In addition, the liquid crystal driving electrode (115) and the common electrode (107) can be made of ITO or the like in addition to the various materials. In particular, when a light-transmitting material such as ITO is used, the pixel aperture ratio can be improved.

  The electrode cross-sectional shape is rectangular, trapezoidal, or curved. For rectangular and trapezoidal cross sections, a known patterning / etching method may be used, and as a method of forming a curved cross section, anisotropic plasma etching, isotropic plasma etching, etc. may be combined to form a gentle cross section or curved cross section. You may make it have. As a method for manufacturing a cross section having a smooth surface or a curved surface shown in this specification, any of a dry process and a wet process can be used. Note that the above method is an example of a method for manufacturing an electrode having a gentle curved section, and the method for manufacturing an electrode having a gentle curved section is not limited to these methods.

Further, silicon oxide (SiO ₂ ) or silicon nitride (SiN) can be used for each interlayer insulating film (109) and TFT protective film (117). Furthermore, it is also possible to use an organic resin made of acrylic resin or polyimide.

  FIG. 8 is a schematic cross-sectional view of a liquid crystal electro-optical device in which an organic resin is used as a TFT protective film and the other configurations are the same as those described above. In particular, when an organic resin is used as the TFT protective film, a planarizing film (801) for smoothing the substrate surface can be obtained. Since the liquid crystal electro-optical device of the present invention utilizes the birefringence of the liquid crystal material, color unevenness occurs when the distance between the pair of substrates varies. Therefore, it is important that the substrate interval is constant throughout the apparatus, and the planarization process is an important process for improving the yield of manufacturing the apparatus.

  Next, the same material as that of the first substrate (101) can be used for the second substrate (102). An electrode for driving the liquid crystal material (121) is also formed on the second substrate (102). As the electrode material at this time, the material used to form the element (111) on the first substrate (101) and the electrodes (105), (107), (113), (115) should be used. I can do it.

  The electrode arrangement pattern is such that the drive electrodes (115) and the common electrodes (107) of the first substrate (101) are alternately arranged at equal intervals.

  Further, the elements (111), (112) and the electrodes (105), (106), (107), (108), (113), (114), In order to form the effective display region, that is, the aperture ratio as much as possible in order to form (115) and (116), the gates (105) and (105) on the pair of substrates (101) and (102) as shown in FIG. 106), the source (113), (114), the liquid crystal driving electrodes (115), (116), and the common electrodes (107), (108) are arranged so as to overlap each other. Good. By doing so, it is possible to obtain the same aperture ratio as when the gate and source wirings are formed on one of the substrates as in the conventional liquid crystal electro-optical device.

  In addition, a metal such as Cr or a black pigment is dispersed on the first substrate (101), the second substrate (102), or both of the substrates in order to shield the portions not related to display in order to improve contrast. A black matrix is formed from the resin material or the like (not shown). Further, in the case of color display, color filters of R (red), G (green), B (blue) or C (cyan), M (magenta), and Y (yellow) are formed at positions corresponding to each pixel. . The arrangement of each color of the color filter can be a stripe arrangement or a delta arrangement.

  Thereafter, alignment treatment was performed on the first substrate (101) and the second substrate (102). The alignment treatment is performed so that the liquid crystal molecules are aligned parallel to the substrate and uniaxially. As the alignment treatment, a rubbing treatment in which the substrate surface is directly rubbed in one direction on the resin surface after applying films (alignment films) (119) and (120) made of an organic resin such as nylon or polyimide is effective. is there. It is possible to eliminate the process of forming the alignment film by subjecting the surface of the TFT protective film (planarization film (801)) made of the organic resin to an alignment process such as a rubbing process as it is.

  5 and 6 show the rubbing directions (502) and (503). The rubbing direction differs depending on the liquid crystal material (121) used, and the first substrate (101) side is non-parallel to the electric field, preferably 45 ° to the electric field, when the dielectric anisotropy is positive. And Furthermore, in the case of a material having a negative dielectric anisotropy, the direction is not perpendicular to the electric field, preferably 45 ° with the electric field. The rubbing process on the second substrate (102) side is performed in parallel or antiparallel to the rubbing direction of the first substrate (101).

  The pair of substrates (101) and (102) manufactured in this way are overlapped at a constant interval to form a liquid crystal cell. A sealant (not shown) is formed in a desired pattern as an adhesive on one of the pair of substrates (101) and (102). As the sealant, a resin material such as a thermosetting type or an ultraviolet curable type is used. As the resin material, it is possible to use an epoxy-based material, a urethane acrylate-based material, or the like. Further, a spacer (not shown) is sprayed on the other substrate in order to keep the distance between the pair of substrates constant throughout the cell.

  After the sealant is cured, the liquid crystal material (121) is injected into the liquid crystal cell by a vacuum injection method or the like. Note that the liquid crystal layer (121) may be formed on one substrate in advance before forming the sealing agent, and then the other substrate may be overlaid by forming the sealing agent.

  Examples of the liquid crystal material that can be used in the present invention include materials exhibiting nematic, cholesteric, and smectic properties, and it is particularly desirable to use a nematic material. Furthermore, among the nematic liquid crystals, those having a dielectric anisotropy that is positive or negative depending on the driving method are appropriately selected and used. Furthermore, if a material having a small refractive index anisotropy is used, a wider viewing angle can be obtained.

  The alignment state of the liquid crystal material of the liquid crystal electro-optical device of the present invention is schematically shown in FIGS. Here, as an example, a case where a material having negative dielectric anisotropy is used is shown. FIG. 5 shows an alignment state when no electric field is applied, and FIG. 6 shows an alignment state when an electric field is applied. In this figure, only the electrodes (107), (115), (108), (116), and the alignment films (119), (120) are shown as the components on the pair of substrates as a schematic diagram. Elements, wiring, etc. are omitted.

  Since the liquid crystal electro-optical device performs display using the birefringence of the liquid crystal material, a pair of polarizing plates (501) and (502) are arranged so that their optical axes (505) and (506) are orthogonal to each other. A liquid crystal cell is sandwiched between the pair of polarizing plates. At this time, the orientation direction of the liquid crystal material (121) is parallel to the optical axis of the polarizing plate closer to the analyzer, that is, the light source.

  In the liquid crystal electro-optical device manufactured in this way, the alignment of the liquid crystal material (121) is such that, when no electric field is applied, the liquid crystal molecules (121) are parallel to the substrate and the rubbing direction (503) as shown in FIG. , (504) is uniaxially oriented in parallel.

  Next, when an electric field is applied to the electrodes (107), (115), (108), and (116), as shown in FIG. 6, the liquid crystal molecules (122) in the vicinity of the alignment film interface having a strong alignment regulating force are rubbed. The liquid crystal molecules (123) in the vicinity of the center of the liquid crystal layer, which maintains a direction parallel to the directions (503) and (504) and has a weak alignment regulating force, change its optical axis by an electric field. When a liquid crystal material having positive dielectric anisotropy is used, the major axis of the liquid crystal molecules (123) is oriented in parallel with the electric field direction. Thus, the orientation is such that the major axis (123) of the liquid crystal molecules is perpendicular to the electric field direction.

  For this reason, with respect to the light transmitted through the liquid crystal electro-optical device, the orientation of the liquid crystal material (121) is parallel to the optical axis (505) of the analyzer (501) in the cell when no electric field is applied. 502) cannot be transmitted, and the amount of transmitted light at this time is zero. On the other hand, when the electric field is applied, the direction of the optical axis of the liquid crystal material (121) changes, so that the incident light becomes elliptically polarized light and passes through the polarizer (502).

  When performing display, first, a selection signal (scanning signal) is applied to the gate electrode (105) of the first substrate in an arbitrary period, and the video data applied to the source electrode (113) is a switching element during the selection period. Since (111) becomes conductive, it is applied to the liquid crystal driving electrode (115). On the other hand, the common electrode (107) is grounded or an arbitrary waveform is applied.

  Then, an electric field having a component parallel to the substrate and perpendicular to the longitudinal direction of the liquid crystal driving electrode (115) and the common electrode (107) is formed between the liquid crystal driving electrode (115) and the common electrode (107). By this electric field, the liquid crystal molecules (121) are switched in a plane parallel to the substrates (101) and (102) (the orientation state is changed), and the video data is written in the pixels.

  After the selection period ends, the switching element (111) is turned off. The previously applied electric field is held between the liquid crystal driving electrode (115) and the common electrode (107), and the written video data is stored.

  Thereafter, scanning signals are sequentially applied to the gate electrodes (105) on the first substrate (101), and video data is written on the entire substrate (101).

  However, when an electric field is applied only to the first substrate (101), the electric field strength increases in the vicinity of the electrode of the first substrate (101), but the electric field strength decreases as the second substrate (102) is approached. . In addition, there are many electric fields of components other than those parallel to the substrate. Therefore, with respect to the liquid crystal driving electrode (116) and the common electrode (108) provided on the second substrate (102), the liquid crystal driving electrode (115) -common electrode (107) of the first substrate (101). ) An electric field is applied to control the distribution state of the electric field formed therebetween.

  As for the method of applying an electric field, an electric field is applied simultaneously to the first substrate (101) and the second substrate (102). Furthermore, the direction of the electric field is set to be the same in the upper and lower substrates (101) and (102).

  Accordingly, the same video data is written between the electrodes on the second substrate (102) at the same timing as the video data writing between the electrodes on the first substrate (101). Thus, an electric field having a component parallel to the substrate is formed in each part between the pair of substrates (101) and (102), and the lines of electric force are parallel in the pixel.

  In the above description, two polarizing plates (501) are used. However, if a reflecting plate made of metal or the like is formed on one of the pair of substrates (101) and (102), the polarizing plate is used. A liquid crystal electro-optical device can be manufactured using only one sheet, and a bright display can be realized. The metallic reflector can also serve as an electrode for a pixel or the like.

  With the configuration of the liquid crystal electro-optical device shown in the present specification, the electric flux density in the cell thickness direction in the cell becomes uniform as compared with the conventional liquid crystal electro-optical device of the lateral electric field drive system. As a result, most liquid crystal molecules in the cell thickness direction change the orientation vector in the same manner when an electric field is applied. As a result, the rise of display and response characteristics are improved.

  This continuity of the electric field is apparent from the appearance of lines of electric force around the electrode when a voltage is applied to the electrode. Hereinafter, the mode of electric lines of force around the electrodes will be described with reference to FIG.

  When an electric field is applied to the inside of the cell by the above driving method, as shown in FIG. 4, the electricity formed when an electric field is applied only between the electrodes (107) and (115) on one substrate (101). The force line (304) (curved line in FIG. 4) is deformed in the direction of the arrow (307) in the figure by the electric field formed between the electrodes (116) and (108) on the other substrate, Effectively, the electric force line (306) as represented by the solid line in the figure is obtained. Therefore, the distribution of the electric lines of force of the liquid crystal electro-optical device of the present invention is more uniform than when the electrodes are formed only on one substrate.

  In the above description, the trapezoidal electrode cross section has been described as an example. However, the present invention is not limited to this, and the same effect can be obtained even when the electrode cross section uses a circular or elliptical curvature. Further, the same effect can be obtained not only when the cross-sectional shape is a regular semicircle but also when it is formed as an arc. Furthermore, the edge cross section of the electrode may have a curved surface such as an arc. Of course, an electrode having a polygonal shape with a gradual boundary change may be used.

  Furthermore, a film formed on a thin film such as an electrode having a gentle curved section has good coverage due to the roundness of the thin film. For this reason, there is an effect of preventing contamination of impurities, disconnection, and the like due to poor coverage.

  In the present invention, a liquid crystal electro-optical device that applies a lateral electric field to a liquid crystal material has been described. However, the present invention is not limited to this, and for example, a conventional liquid crystal electro-optical device that applies a vertical electric field such as a TN method. Also in the case of this, the disturbance of the electric field in the cell can be reduced, and an electro-optical device with good coverage can be manufactured. Embodiments of the present invention will be described below with reference to the drawings.

  As described above, the liquid crystal electro-optical device according to the present invention has a good rise characteristic of liquid crystal and can be obtained by a simple process as compared with the conventional liquid crystal electro-optical device of the lateral electric field drive system. Furthermore, the present invention can cope with the miniaturization of the pixel portion.

  In this embodiment, a monolithic active matrix circuit in which the peripheral drive circuit is also formed on the substrate is used. This production process will be described with reference to FIG. FIG. 7 is a schematic view of the vicinity of the peripheral drive circuit, and the left side shows the TFT fabrication process of the drive circuit and the right side shows the TFT fabrication process of the active matrix circuit. This process is for the low temperature polysilicon process.

  First, a base oxide film (103) was formed on Corning # 1737 as a first insulating substrate (101). As a method for forming this silicon oxide film, a sputtering method or a plasma CVD method in an oxygen atmosphere may be used.

  Thereafter, an amorphous silicon film was formed to 300 to 1500 mm, preferably 500 to 1000 mm, by plasma CVD or LPCVD. Then, thermal annealing was performed at a temperature of 500 ° C. or higher, preferably 500 to 600 ° C., to crystallize the silicon film or improve the crystallinity. After crystallization by thermal annealing, light (laser or the like) annealing may be performed to further increase crystallization. Further, at the time of crystallization by thermal annealing, as described in JP-A-6-244103 and 6-244104, an element (catalytic element) that promotes crystallization of silicon such as nickel may be added.

Next, the silicon film is etched to form islands, and TFT active layers (701) (for P-channel TFTs) and (702) (for N-channel TFTs) in the drive circuit and TFTs (pixel TFTs) in the matrix circuit ) Active layer (703) was formed. Further, a silicon oxide gate insulating film (704) having a thickness of 500 to 2000 mm was formed by sputtering in an oxygen atmosphere. As a method for forming the gate insulating film, a plasma CVD method may be used. When forming a silicon oxide film by plasma CVD, it was preferable to use dinitrogen monoxide (N ₂ O) or oxygen (O ₂ ) and monosilane (SiH ₄ ) as a source gas.

Thereafter, aluminum having a thickness of 2000 to 6000 mm was formed on the entire surface of the substrate by sputtering. Here, aluminum may contain silicon, scandium, palladium, or the like in order to prevent hillocks from being generated by a subsequent thermal process. Then, isotropic plasma etching was performed to form gate electrodes (705), (706), and (707), and a common electrode (708) (common electrode) (FIG. 7A). At this time, the discharge gas voltage was set appropriately, and the electrode was curved. Thereafter, phosphorus is implanted into all island-like active layers by ion doping in a self-aligning manner using the gate electrode as a mask and phosphine (PH ₃ ) as a doping gas. The dose is 1 × 10 ^{12 to} 5 × 10 ¹³ atoms / cm ² . As a result, weak N-type regions (709), (710), and (711) were formed. (Fig. 7 (B))

Next, of the photoresist mask (712) covering the P channel type active layer and the active layer (713) of the pixel TFT, the photoresist covering a portion 3 μm away from the end of the gate electrode (708) parallel to the gate electrode. The mask (713) is formed. Then, phosphorus is implanted again using phosphine as a doping gas by ion doping. The dose is 1 × 10 ^{14 to} 5 × 10 ¹⁵ atoms / cm ² . As a result, strong N-type regions (source and drain) (714) and (715) are formed. The region (716) covered with the photoresist (713) on the pixel TFT remains weak N-type because phosphorus is not implanted in this doping. (Fig. 7 (C))

Next, the active layers (702) and (703) of the N-channel TFT are covered with a photoresist mask (717), and island regions (701) are formed by ion doping using diborane (B ₂ H ₆ ) as a doping gas. ) Is injected with boron. The dose is 5 × 10 ¹⁴ to 8 × 10 ¹⁵ atoms / cm ² . In this doping, since the dose amount of boron exceeds the dose amount of phosphorus in FIG. 7C, the weak N-type region (708) formed previously is inverted into a strong P-type region (718). By the above doping, strong N-type regions (source / drain) (714) and (715), strong P-type regions (source / drain) (718), and weak N-type regions (low-concentration impurity regions) (716) are formed. Is done. (Fig. 7 (D))

  Thereafter, thermal annealing was performed at 450 to 850 ° C. for 0.5 to 3 hours to recover the damage caused by doping, to activate the doping impurities, and to recover the crystallinity of silicon. Thereafter, a silicon oxide film having a thickness of 3000 to 6000 mm was formed as an interlayer insulator (719) on the entire surface by plasma CVD. This may be a silicon nitride film or a multilayer film of a silicon oxide film and a silicon nitride film. Then, the interlayer insulating film (719) was etched by wet etching or dry etching to form contact holes in the source / drain.

  Then, an aluminum film having a thickness of 2000 to 6000 mm or a multilayer film of titanium and aluminum is formed by sputtering. This was subjected to isotropic plasma etching using a resist as a mask. At this time, the discharge gas voltage is set appropriately, the electrode is curved, and the electrodes / wirings (720), (721), (722) of the peripheral circuit and the electrodes / wirings (723), (724) of the pixel TFT. Formed. The electrode (724) has a wiring pattern that also serves as the liquid crystal driving electrode (115). Further, a silicon nitride film (725) having a thickness of 1000 to 3000 mm was formed as an interlayer film by plasma CVD. (Fig. 7 (E))

  In addition, a TFT and a common electrode were formed on the second substrate (102) similarly to the first substrate (101). As shown in FIG. 2, the patterns of the elements and the wiring electrodes on the first substrate (101) and the second substrate (102) are as follows. First, the liquid crystal driving electrodes (115) and (116) and the common electrode (107). , (108), and the gate electrodes (105), (106), the source electrodes (113), (114) and the TFTs (111), (112) are basically the same. It arrange | positioned in the appropriate position so that an aperture ratio may become the largest. In addition, the wiring patterns of the first substrate (101) and the second substrate (102) have a relationship that the left and right are reversed.

  In addition, a metal such as Cr or a black pigment is dispersed on the first substrate (101), the second substrate (102), or both of the substrates in order to shield the portion not related to display in order to improve contrast. A black matrix was formed from the resin material formed.

  Thereafter, alignment films (119) and (120) made of polyimide were formed on the first substrate (101) and the second substrate (102). As the alignment film, polyimide was formed by a known spin coating method or DIP method. Next, the alignment film surface was rubbed.

  The rubbing directions (503) and (504) vary depending on the liquid crystal material (121) used, and the direction (503) on the first substrate (101) side is the electric field direction when the dielectric anisotropy is a positive material. The direction is 45 ° to the electric field direction or an angle closer to the electric field direction. Furthermore, in the case of a material having a negative dielectric anisotropy, the direction is non-perpendicular to the electric field and forms an angle of 45 ° in the direction perpendicular to the electric field or closer to the direction perpendicular to the electric field. Further, the rubbing process (504) on the second substrate (102) side is made parallel or antiparallel to the rubbing direction of the first substrate (101).

  The first substrate (101) thus formed and the second substrate (102) were overlapped to form a liquid crystal panel. The pair of substrates (101) and (102) was made to have a uniform substrate interval over the entire panel surface by sandwiching a spherical spacer having a diameter of 3 μm between the substrates. Further, the pair of substrates (101) and (102) was sealed with an epoxy-based adhesive in order to bond and fix them. The seal pattern surrounds the pixel region and the peripheral drive circuit region. Thereafter, the pair of substrates (101) and (102) was cut into a predetermined shape, and a liquid crystal material (121) was injected between the substrates.

  Next, two polarizing plates (501) and (502) were bonded to the outside of the substrate. Regarding the arrangement of the polarizing plates, a pair of polarizing plates are arranged so that their optical axes (505) and (506) are perpendicular to each other, and the optical axis of one of the polarizing plates, for example, the optical axis (505) of the polarizing plate (501). ) In parallel with the rubbing direction (503).

  When the optical characteristics of the liquid crystal electro-optical device were measured, a good display with less variation in the start-up characteristics was obtained than a liquid crystal display having a conventional electrode shape.

  The configuration in this embodiment has an advantage that the manufacturing cost can be reduced because the driving circuit is manufactured on the same substrate as the pixel portion TFT.

  FIG. 8 shows a cross-sectional view of the liquid crystal electro-optical device of the present embodiment. In this example, pixel TFTs and peripheral drive circuits were formed as in the first example as the first substrate (101) and the second substrate (102). However, instead of directly forming the alignment film after forming the TFT protective film, the planarization film (801) was formed, and then the alignment films (119) and (120) were formed.

  The planarizing film (801) was made of a material made of acrylic resin or polyimide resin, here acrylic resin. As the acrylic resin, a two-component thermosetting resin was used. The flattened film was formed by a known spin coating method or the like, and the film thickness was 1 to 2 μm, and here, the maximum was 1.5 μm. As a result, the level difference on the substrate surface caused by forming an element such as a TFT was greatly reduced.

  Thereafter, alignment films (119) and (120) were formed in the same manner as in Example 1, and a rubbing treatment was performed. The rubbing direction was made parallel or antiparallel between the pair of substrates (101) and (102) as in Example 1.

  The first substrate (101) and the second substrate (102) thus fabricated are assembled as a liquid crystal cell in the same manner as in Example 1, and the liquid crystal material (121) is used as the pair of substrates (101). ), (102). Further, the polarizing plate (501) was disposed in the same manner as in Example 1.

  The above-described liquid crystal electro-optical device was able to produce a good device with good yield without causing uneven color due to uneven cell thickness.

  In this embodiment, an example in which the planarizing film (801) is formed after the TFT protective film is formed is shown. However, the planarizing film (801) is used instead of the protective film (725), and the TFT protective film is formed. At the same time, it may have a function of flattening the substrate surface. Further, instead of forming the alignment films (119) and (120) after the planarization film (801) is formed and performing an alignment treatment such as rubbing, the planarization film (801) may be directly rubbed. By doing so, it is not necessary to form the TFT protective film and the alignment films (119) and (120), and the number of manufacturing steps can be greatly reduced.

In this embodiment, as in the first and second embodiments, an active matrix circuit in which a peripheral drive circuit is formed on a substrate is used. FIG. 9 shows a manufacturing process of the active matrix substrate of this embodiment.
In this example, pixel TFTs and peripheral drive circuits were formed as the first substrate (101) and the second substrate (102) basically in the same manner as in Example 1. However, ITO was used for the liquid crystal driving electrode (901) and the common electrode (902) as the pixel electrode.

  The steps for producing each element and each electrode on the substrate are the same as in Example 1 up to the formation of a layer made of aluminum for the gate electrode, and the gate electrode (705) by isotropic plasma etching. , (706) and (707) were formed, and a 1000 to 3000 ITO film was formed by a known method, and a common electrode (902) was formed by isotropic plasma etching (FIG. 9A).

  Thereafter, the same steps as in Example 1 are performed until a layer made of aluminum or the like for wiring of the peripheral driving circuit or the like is formed, and electrodes / wirings (720) and (721) of the peripheral driving circuit are performed by isotropic plasma etching. , (722) and pixel TFT electrodes / wirings (723), (724) are formed, then 1000-3000 mm of ITO is formed by a known method, and the liquid crystal driving electrode (901) is formed by isotropic plasma etching. Formed. This electrode is connected to the drain electrode (724) of the pixel TFT (FIG. 9E).

  Next, the silicon nitride film (722) of Example 1 was formed as a TFT protective film. Thereafter, an organic resin film (801) as in Example 2 may be formed as a planarizing film.

  On the other hand, each element, each electrode, and the like were formed on the second substrate (102) by the same process as described above. The relationship between the wiring patterns of the first substrate (101) and the second substrate (102) is the same as in the first embodiment.

  The pair of substrates (101) and (102) on which the elements, electrodes, etc. are formed in this way are aligned by the method shown in Example 1, seal printing, substrate superposition / adhesion, liquid crystal injection, and polarizing plate installation. A liquid crystal electro-optical device was manufactured through a series of liquid crystal panel manufacturing processes.

  Since the liquid crystal electro-optical device uses light-transmitting ITO as a pixel electrode, the pixel aperture ratio is high, and a bright display that can effectively use light from a light source is obtained.

  In this example, the liquid crystal electro-optical device manufactured in Example 1, Example 2, and Example 3 is displayed by performing dot-sequential driving and displaying.

  In the case of this embodiment, video signals necessary for forming one screen are simultaneously applied to the pair of substrates. As a result, one frame was formed, and this was repeated thereafter.

  In one section, scanning signals are sequentially applied to the gate lines of one substrate, and video data sampled by the sampling pulse within a period in which one gate line is selected is sequentially held by the source lines, and immediately thereafter. Video data is written to each pixel. The video data written in the pixel is held for one section by the liquid crystal and the capacitive component. During this period, the same image data is applied to the other substrate as the same image as the display image formed on the other substrate is formed.

  In this embodiment, the frame frequency is 60 Hz. Therefore, the frequency of one section is 120 Hz. By doing so, even if the output of video data is switched between the upper and lower substrates as in this embodiment, it cannot be recognized with the naked eye, and it appears as if one screen is formed and displayed. It was.

In this embodiment, dot sequential driving is described as an example, but line sequential driving may be performed.

FIG. 3 is a diagram illustrating an outline of a pixel region of the liquid crystal electro-optical device in Embodiment 1. FIG. 5 is a diagram schematically illustrating a cross section of a liquid crystal electro-optical device according to Example 1. FIG. 6 is a diagram showing lines of electric force when an electric field is applied between electrodes in a conventional liquid crystal electro-optical device. FIG. 3 is a diagram showing electric lines of force when an electric field is applied to an electrode in the liquid crystal electro-optical device in Example 1. FIG. 3 is a diagram illustrating an outline of liquid crystal alignment when no electric field is applied to the liquid crystal electro-optical device according to the first embodiment. FIG. 3 is a diagram illustrating an outline of liquid crystal alignment when an electric field is applied to the liquid crystal electro-optical device according to the first embodiment. FIG. 3 is a diagram schematically illustrating a cross section of the liquid crystal electro-optical device according to the first embodiment. FIG. 6 is a diagram schematically illustrating a cross section of a liquid crystal electro-optical device according to a second embodiment. FIG. 6 is a diagram schematically illustrating a cross section of a liquid crystal electro-optical device according to a third embodiment.

Explanation of symbols

101, 102 Substrate 103, 104 Base film 105, 106 Gate electrode 107, 108 Common electrode 109, 110 Gate insulating film 111, 112 Switching element 113, 114 Source electrode 115, 116 Liquid crystal driving electrode 117, 118 Protective film 119, 120 Alignment film 121 Liquid crystal layer (liquid crystal molecule)
122, 123 Liquid crystal molecules 301, 303 Substrate 302, 305 Electrodes 304, 306 Electric field lines 307 Direction of deformation of electric field lines (arrows)
501 Polarizing plate (analyzer)
502 Polarizing plate
503, 504 Rubbing directions 505, 506 Optical axes 701, 702, 703 of polarizing plate Active layer 704 Gate insulating film (silicon oxide)
705, 706, 707 Gate lines 708, 902 Common (common) electrodes 709, 710, 711 Weak N-type regions 712, 713 Photoresist masks 714, 715 Strong N-type regions (source / drain)
716 Low-concentration impurity region 717 Photoresist mask 718 Strong P-type region (source / drain)
719 Interlayer insulating films 720 to 724, 901 Peripheral driving circuit, pixel TFT electrode / wiring 725 Silicon nitride film 801 Flattening film

Claims (6)

A liquid crystal driving electrode and a common electrode formed on one of the pair of substrates and forming an electric field in the liquid crystal layer;
A thin film transistor connected to the liquid crystal driving electrode;
The liquid crystal electro-optical device, wherein the liquid crystal driving electrode and the common electrode are made of a light-transmitting material. A liquid crystal driving electrode and a common electrode formed on one of a pair of substrates and formed of a light-transmitting material while forming an electric field in the liquid crystal layer;
A thin film transistor connected to the liquid crystal driving electrode;
A reflector made of metal provided on the one of the pair of substrates;
A liquid crystal electro-optical device comprising: a polarizing plate provided on the other of the pair of substrates. A first liquid crystal driving electrode and a first common electrode, which are formed on a first substrate and formed of a light-transmitting material while forming an electric field in a liquid crystal layer;
A second liquid crystal driving electrode and a second common electrode, which are formed on a second substrate and formed of a light-transmitting material while forming an electric field in the liquid crystal layer;
A first thin film transistor connected to the first liquid crystal driving electrode;
A second thin film transistor connected to the second liquid crystal driving electrode;
A reflector made of metal provided on the first substrate;
A liquid crystal electro-optical device comprising: a polarizing plate provided on the second substrate.   3. The liquid crystal electro-optical device according to claim 1, wherein the cross section of the liquid crystal driving electrode and the common electrode uses a curvature of a circle or an ellipse.   4. The cross section of the first liquid crystal driving electrode, the first common electrode, the second liquid crystal driving electrode, and the second common electrode according to claim 3, using a circular or elliptical curvature. A liquid crystal electro-optical device.   6. The liquid crystal electro-optical device according to claim 1, wherein ITO is used as the light-transmitting material.

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