JP2005309432A - Liquid crystal optoelectronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix type liquid crystal optoelectronic device of what is called a lateral electric field drive system which drives a liquid crystal material with a lateral electric field parallel to a substrate, the optoelectronic device being constituted to have excellent display characteristics by reducing alignment defects of the liquid crystal material and variance of operations. <P>SOLUTION: The active matrix type liquid crystal optoelectronic device has an inverse stagger type thin film transistor, a 2nd substrate opposed to the top of a 1st substrate, and a liquid crystal layer 413 which is sandwiched between the 1st substrate and 2nd substrate and driven with an electric field between a drain electrode 408 and a common electrode 404, the active matrix type liquid crystal optoelectronic device being characterized in that the 2nd substrate is provided with a light-transmissive electrode material. <P>COPYRIGHT: (C)2006,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 conventionally used Super TFT type electrode has a trapezoidal or rectangular structure, and the electric field generated from this electrode is not continuous with the trapezoidal or rectangular apex as a boundary. Thereby, the electric field applied to the liquid crystal changes at a certain point. That is, the electric field (electric flux density) changes rapidly above and below the top of the trapezoid or rectangle. For this reason, the liquid crystal switching by the electric field is not uniformly performed in the cell, and the time from the electric field OFF → ON state or the ON → OFF state (referred to as rise time and fall time, respectively) varies in the cell. It was observed.

  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 discontinuity of the electric field will be described with reference to FIG. Here, for simplicity, a voltage is applied between a pair of parallel electrodes (101, 102) formed on an insulating substrate (103) having a rectangular cross section of height a and width c and an electrode interval of 2b. In this case, the manner of lines of electric force around the electrodes will be described. (Refer to the books of electromagnetism, such as Kazuyoshi Nagata, "Electromagnetism", Asakura Shoten, Goto-Yamazaki, "Detailed Electromagnetism Exercise", Kyoritsu Publishing, etc.) Here, the direction parallel to the substrate and perpendicular to the electrodes is taken as the x-axis, and the direction perpendicular to the substrate surface is taken as the y-axis. Further, the origin is defined so that the electrode plane parallel to the substrate becomes y = 0.
(1) y <0 (−b ≦ x ≦ b), that is, a region sandwiched between electrodes.
Since electric charges can be considered to be uniformly distributed on the electrode surfaces (104, 105), the electric lines of force (106) are perpendicular to the electrodes (parallel to the substrate).
(2) y> 0, that is, the region above the electrode.
Here, for the sake of simplicity, the state of the electric lines of force on the xy plane is examined.
It can be considered that the electric charges are uniformly distributed on the electrode surfaces (107, 108).
For any point in the region where y> 0, the distance from the origin is r, and the angle between r and the x axis is θ. In addition, when z is expressed as a point on the complex plane using x, y, r, and θ,

The relationship holds.
Here, in order to facilitate the analysis, the value w is

(A is a proportionality constant). If the real part and the imaginary part of w are u and v, respectively,

And

It becomes. Therefore,

It is expressed.
Therefore, the curve group represented by u = constant on the w plane is a curve group having r = constant on the xy plane, that is, a concentric circle group centered on the origin.
FIG. 1 shows the above result, and it can be seen that the electric field distribution differs between the electrode side surface and the electrode upper surface.

  Here, as an example, an electric field between electrodes having a rectangular cross section is shown, but the same applies to an electrode having a trapezoidal cross section. This is because the electric field is formed perpendicular to the electrode surface, and the electric field in the tapered portion and the electric field in the portion parallel to the substrate are discontinuous at the electrode apex.

  Such discontinuity of the electric field at the electrode apex becomes a disadvantage that cannot be ignored in pixel miniaturization. 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 between the electrode thicknesses in the lateral direction tends to increase between the top and the base 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.

  Third, even in the miniaturization of pixels, it is difficult to obtain a large taper angle by reducing the film thickness in the lateral direction with an extremely high electrode.

  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.

In order to solve the above problems, the present invention provides:
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
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,
In the liquid crystal electro-optical device, at least one of the electrodes has a curved cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
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,
In the liquid crystal electro-optical device, at least one of the electrodes has a semicircular or semi-elliptical cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
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,
In the liquid crystal electro-optical device, at least one of the electrodes has a curved cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
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,
In the liquid crystal electro-optical device, at least one of the electrodes has a semicircular or semi-elliptical cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
Electric field applying means for applying an electric field to the liquid crystal layer through the electrode;
A liquid crystal electro-optical device having a non-linear element connected to the electrode,
In the liquid crystal electro-optical device, at least one of the electrodes has a curved cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
Electric field applying means for applying an electric field to the liquid crystal layer through the electrode;
A non-linear element is connected to the electrode,
A liquid crystal electro-optical device in which a peripheral driving circuit for driving a liquid crystal material is formed on the substrate,
In the liquid crystal electro-optical device, at least one of the electrodes has a curved cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
Electric field applying means for applying an electric field to the liquid crystal layer through the electrode;
A liquid crystal electro-optical device having a non-linear element connected to the electrode,
In the liquid crystal electro-optical device, at least one of the electrodes has a semicircular or semi-elliptical cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
Of the electrodes, the liquid crystal driving electrode and the common electrode have at least one portion formed in parallel on the same substrate,
Electric field applying means for applying an electric field to the liquid crystal layer through the electrode;
A non-linear element is connected to the electrode,
A liquid crystal electro-optical device in which a peripheral driving circuit for driving a liquid crystal material is formed on the substrate,
In the liquid crystal electro-optical device, at least one of the electrodes has a semicircular or semi-elliptical cross section.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
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,
At least one of the electrodes has a curved cross section,
In the liquid crystal electro-optical device, the tangential direction of the electric lines of force around the electrode surface continuously changes over the entire surface of the electrode.

The present invention also provides
A pair of substrates at least one of which is transparent;
An electrode formed on at least one or both of the substrates;
A liquid crystal layer sandwiched between the substrates,
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,
At least one of the electrodes has a semicircular or semi-elliptical cross section,
In the liquid crystal electro-optical device, the tangential direction of the electric lines of force around the electrode surface continuously changes over the entire surface of the electrode.

  An example of a configuration using the invention disclosed in this specification is shown in FIGS. FIG. 4 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 by a lateral electric field, and using a-Si TFT as the drive element. 5 shows a cross section in the AA 'direction in FIG.

4 and 5, 401 is a substrate, 402 is a base SiO ₂ film, 403 is a gate electrode, 404 is a common electrode (common electrode), 405 is a gate insulating film, 406 is a-Si, and 407 is a source. 409 is a drain electrode, 409 is a protective film, 411 is an alignment film, 412 is a polarizing plate, and 413 is a liquid crystal layer.

  The liquid crystal electro-optical device of the present invention controls the electric field (lateral electric field) strength between the drain electrode and the common electrode formed on the TFT substrate to operate the liquid crystal material.

  For the first and second substrates, 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 may be driven by a multiplex method or an active matrix method.

  In the multiplex method, only two types of display electrodes and reference electrodes need be formed on the first substrate. However, in the case of the active matrix method, other non-linear elements such as thin film transistors (TFTs) and diodes are also used as switching elements. Is formed for each pixel.

  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.

Cr, Al, ITO, Ta can be used as the element electrode. The electrode cross section is made to have a gentle cross section or a curved cross section by the following method. 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. Of these, the dry process
(A) A method of combining anisotropic plasma etching and isotropic plasma etching (b) A method of performing plasma isotropic etching using a mask.

  As the method (a), a mask is patterned on the electrode, and anisotropic plasma etching is performed. Next, a mask is removed, and a resist is applied to a portion where isotropic plasma etching is not performed. Thereafter, isotropic plasma etching is performed in a state without a mask on a portion where a curved cross section is desired. Thereby, the convex part is shaved and an electrode having a gentle curved cross section can be produced. Thereafter, the resist is peeled off. Further, as the method (b), it is possible to obtain a clean arc cross section by appropriately determining the discharge gas voltage.

  On the other hand, in the wet process, first, a resist whose difference in etching selectivity with the electrode to be etched is not changed so much is used. A resist having a smaller taper angle is used. Then, the mask and the electrode to be etched are etched at a similar rate by wet isotropic etching. This makes it possible to produce an electrode with a rounded electrode vertex and a gently curved cross section.

  The above method is an example of a method for manufacturing an electrode having a gentle curved section, and a method for manufacturing an electrode having a gentle curved section is not limited to these methods.

  If the above electrode material is used, after forming a curved section by the above method, an oxide film of metal constituting the electrode material is formed on the electrode surface by a technique such as anodic oxidation, so that this can be used as an interlayer insulating film. Is possible. This makes it possible to improve the insulation between the electrodes even when adjacent electrodes and electrode patterns overlap each other.

Further, silicon oxide (SiO ₂ ) or silicon nitride (SiN) can be used for each interlayer insulating film and TFT protective film.

  Next, for the counter substrate, the same type of material as that of the substrate on which the TFT is formed can be used. In addition, although it is not necessary to form an electrode on the counter substrate, the electrode may be formed on a part or the entire surface of the substrate depending on circumstances. As an electrode material at this time, in addition to the above metal, a light-transmitting material such as ITO can be used.

  In addition, a black matrix is formed by using a resin material in which a metal such as Cr or a black pigment is dispersed in order to shield a portion not related to display on the counter substrate or the TFT substrate or both substrates in order to improve contrast. (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 substrate on which the driving element was formed and the counter substrate. 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 is effective in which the substrate surface is rubbed in one direction directly after coating a film (alignment film) (411) made of an organic resin such as nylon or polyimide.

  The rubbing direction differs depending on the liquid crystal material (413) to be used, and the TFT substrate side is non-parallel to the electric field, preferably 45 ° to the electric field when the dielectric anisotropy is positive. 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 counter substrate side is performed in parallel or antiparallel to the rubbing direction of the TFT substrate.

  The pair of substrates thus manufactured are overlapped at a constant interval to form a liquid crystal cell. A sealing agent (not shown) is formed in a desired pattern as an adhesive on one of the pair of substrates. 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 is injected into the liquid crystal cell by a vacuum injection method or the like.

  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, in order to reduce the influence of birefringence, it is desirable that the refractive index anisotropy is small.

  In addition, since the liquid crystal electro-optical device of the present invention performs display using the birefringence of the liquid crystal material, a pair of polarizing plates (412) are arranged so that their optical axes are orthogonal to each other, and the pair of polarizing plates is interposed between the pair of polarizing plates. The liquid crystal cell is sandwiched. At this time, the orientation direction of the liquid crystal material 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 liquid crystal material is aligned uniaxially with the major axis parallel to the substrate and parallel to the rubbing direction when there is no electric field. Next, when an electric field is applied, the liquid crystal molecules in the vicinity of the alignment film interface having a strong alignment regulating force maintain the orientation parallel to the rubbing direction, and the liquid crystal molecules in the vicinity of the center of the liquid crystal layer having a weak alignment regulating force are aligned with the optical axis by the electric field. Change. When a liquid crystal material having a positive dielectric anisotropy is used, the major axis of the liquid crystal molecule is oriented in parallel to the electric field direction. When the dielectric anisotropy is negative, the major axis of the liquid crystal molecule is The orientation is perpendicular to the electric field direction.

  For this reason, with respect to the light transmitted through the liquid crystal electro-optical device, since the orientation of the liquid crystal material is parallel to the optical axis of the analyzer in the cell when there is no electric field, the incident light cannot pass through the polarizer. Becomes zero. On the other hand, when the electric field is applied, the direction of the optical axis of the liquid crystal material changes, so that incident light becomes elliptically polarized light and passes through the polarizer.

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

(Function)
With the configuration of the liquid crystal electro-optical device shown in this specification, the electric field around the electrode is continuous as compared with the electrode having a rectangular or trapezoidal cross section used in the conventional liquid crystal electro-optical device. 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 aspect of electric lines of force around the electrodes will be described in detail with reference to FIG.

First, for the sake of simplicity, consider the case where point charges q ₁ and q ₂ are present in O ₁ and O ₂ .
Here, the straight line connecting O ₁ and O ₂ is the x axis, and the direction perpendicular to the x axis is the y axis. The midpoint of O ₁ and O ₂ is defined as the origin.
Consider electric lines of force that pass through an arbitrary point P as shown in FIG. This is on the plane formed by the P, O ₁ and O ₂ axes.
When this electric field line is rotated once around the O ₁ and O ₂ axes, one rotationally symmetric surface is obtained, but the electric flux passing through an arbitrary cross section of this rotating surface should be constant.
Therefore, the electric flux passing through the vertical cross section S passing through P is obtained.
O ₁ P and O ₂ P is O ₁ O ₂ axis and angle, respectively theta _1, When theta _2, the electric flux [psi ₁ through S by q ₁ is

The electric flux ψ ₂ passing through S due to q ₂ is

  Therefore, the total electric flux ψ passing through S is

It is expressed. Therefore, on one electric field line,

It becomes.

Then, the electric field lines are

Have a relationship. FIG. 3 shows the lines of electric force (110) formed by the pair of point charges and the equipotential surface (111).

  The distribution of the lines of electric force does not change even if charges having the same charge amount as the point charges are distributed on the surface of the conductor having the radius a. Furthermore, the region of y ≧ 0 can be approximated as an electric field generated by two semicircular electrodes. Therefore, if the electrode cross section is semicircular, the distribution of the electric lines of force is continuous in the cell thickness direction.

  In the above description, the entire electrode cross section has a shape using the curvature of a circle as an example. However, the present invention is not limited to this, and the same effect can be obtained by using an ellipse 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.

  Needless to say, the technique of the present invention in which the electrode cross section is a curved surface or a gentle cross section can be used not only for the a-Si type TFT described above but also for a poly-Si type TFT.

  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 are obtained in a smaller element region. Therefore, each element can be miniaturized and, consequently, the aperture ratio can be increased. 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.

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 by using, it is possible to reduce the disturbance of the electric field at the end and to manufacture an electro-optical device with good coverage.
Examples of the present invention will be given below.

  As described above, the liquid crystal electro-optical device according to the present invention has better liquid crystal start-up characteristics than a conventional lateral electric field drive type liquid crystal electro-optical device, and can be obtained in a simple process. Furthermore, the present invention can cope with the miniaturization of the pixel portion.

  A silicon oxide film having a thickness of 1000 to 3000 mm was formed as a base oxide film (402) on Corning # 7059 (401) as an insulating substrate. As a method for forming this silicon oxide film, a sputtering method or a plasma CVD method in an oxygen atmosphere may be used. On top of that, 1000 to 5000 liters of Cr was formed and patterned. Thereafter, isotropic plasma etching was performed using the resist as a mask. At this time, the discharge gas voltage was set appropriately, and the electrode was curved. Thus, a gate electrode (403) and a common electrode (common electrode) (404) were formed.

Next, a gate insulating film (405) made of silicon oxide (SiO ₂ ) was produced so as to cover these electrodes. This may be silicon nitride (SiN). An amorphous silicon film (406) was formed on the gate electrode through a gate insulating film. A source electrode (407) and a drain electrode (408) made of Al were formed so as to overlap a part of the pattern of the amorphous silicon film. At this time, isotropic plasma etching was performed using the resist as a mask, the discharge gas voltage was set appropriately, and the electrode was curved. Next, a silicon oxide insulating film (409) was formed as a TFT protective film. This insulating film may be a SiN film.

  In addition, on the counter substrate or the TFT substrate or both substrates, a black matrix is formed with a resin material in which a metal such as Cr or a black pigment is dispersed in order to shield a portion not related to display in order to improve contrast. Formed.

  Thereafter, an alignment film (411) made of polyimide was formed on the substrate on which the TFT was formed and the counter substrate. 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 direction differs depending on the liquid crystal material used, and the TFT substrate side is not parallel to the electric field, preferably 45 ° to the electric field when the dielectric anisotropy is positive. In the case of a material having a negative dielectric anisotropy, the direction is not perpendicular to the electric field, preferably a direction that forms 45 ° with the electric field. The rubbing process on the counter substrate side is performed in parallel or antiparallel to the rubbing direction of the TFT substrate.

  The TFT substrate thus formed and the counter substrate were overlapped to form a liquid crystal panel. The pair of substrates was made to have a uniform substrate spacing over the entire panel surface by sandwiching a spherical spacer having a diameter of 3 μm between the substrates. Further, in order to bond and fix the substrates to the pair, they were sealed with an epoxy adhesive. The seal pattern surrounds the pixel region and the peripheral drive circuit region. Then, after cutting the pair of substrates into a predetermined shape, a liquid crystal material was injected between the substrates.

  Next, two polarizing plates (412) were bonded to the outside of the substrate. Regarding the arrangement of the polarizing plates, a pair of polarizing plates were arranged so that their optical axes were orthogonal to each other, and the optical axis of one of the polarizing plates was made parallel to the rubbing direction.

  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.

  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 FIGS. FIG. 6 is a schematic view of the periphery of the pixel portion of this embodiment. FIG. 7 is a cross-sectional view taken along the line BB′-B ″ of FIG. 6. The left side shows the TFT manufacturing process of the drive circuit, and the right side shows the TFT manufacturing process of the active matrix circuit. It was. This process is for the low temperature polysilicon process.

  First, a base oxide film (402) was formed on Corning # 1737 as a first insulating substrate (601). The method for forming this silicon oxide film may be the same as the method shown in the first embodiment.

  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, and the active layer (602) (for P-channel TFT) and (603) (for N-channel TFT) of the TFT of the island-shaped drive circuit and the TFT (pixel TFT) of the matrix circuit An active layer (604) was formed. Further, a silicon oxide gate insulating film (605) 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 (606, 607, 608) and a common electrode (609) (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 (610, 611, 612) were formed. (Fig. 7 (B))

Next, of the photoresist mask (613) covering the P-channel type active layer and the active layer (614) of the pixel TFT, the photoresist covering a portion 3 μm away from the end of the gate electrode (608) parallel to the gate electrode. The mask (614) 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, drain) (615, 616) are formed. The region (617) covered with the photoresist (614) on the pixel TFT remains weak N-type because phosphorus is not implanted in this doping. (Fig. 7 (C))

Next, the active layer (603, 604) of the N-channel TFT is covered with a photoresist mask (618), and diborane (B ₂ H ₆ ) is used as a doping gas to form the island region (602) by ion doping. Boron is injected. 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 (610) formed previously is inverted to the strong P-type region (619).
By the above doping, strong N-type regions (source / drain) (615, 616), strong P-type regions (source / drain) (619), and weak N-type regions (low-concentration impurity regions) (617) are formed. . (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 on the entire surface as an interlayer insulator (620) 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 (620) 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 used as a resist mask for isotropic plasma etching. At this time, the discharge gas voltage was set appropriately, the electrodes were curved, and the peripheral circuit electrodes / wirings (621, 622, 623) and the pixel TFT electrodes / wirings (624, 625) were formed.
Further, a silicon nitride film (626) having a thickness of 1000 to 3000 mm was formed as an interlayer film by plasma CVD. (Fig. 7 (E))

  Thereafter, a liquid crystal cell was produced in the same manner as in Example 1. Here, the seal pattern is a pattern surrounding the pixel region and the peripheral drive circuit region. Thereafter, in the same manner as in Example 1, each of the polarizing plates was pasted onto a pair of substrates to obtain a liquid crystal electro-optical device.

  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.

In a conventional liquid crystal electro-optical device, electric lines of force when an electric field is applied between electrodes are shown. A simplified diagram of the electric field lines and equipotential surfaces formed by two point charges is shown. The electric lines of force around a pair of electrodes having a curved cross section are shown. 1 illustrates an outline of a pixel region of a liquid crystal electro-optical device according to Embodiment 1 of the present invention. 1 shows an outline of a cross section of a liquid crystal electro-optical device in Example 1 of the present invention. 6 shows an outline of a pixel region of a liquid crystal electro-optical device in Example 2 of the present invention. FIG. 3 shows a schematic cross section of a liquid crystal electro-optical device according to Example 2 of the present invention. FIG.

Explanation of symbols

101, 102 Electrode 103 Substrate surface 104, 105 Electrode side surface 106, 109, 110 Electric field lines 107, 108 Electrode upper surface 111 Equipotential surface 401, 601 Substrate 402 Base film 403 Gate electrode 404 Common electrode 405 Gate insulating film 406 a-Si Silicon film 407 Source electrode 408 Drain electrode 409 TFT protective film 411 Alignment film 412 Polarizing plate 413 Liquid crystal layer 602, 603, 604 Active layer 605 Gate insulating film (silicon oxide)
606, 607, 608 Gate line 608 Common (common) electrodes 610, 611, 612 Weak N-type regions 613, 614 Photoresist masks 615, 616 Strong N-type regions (source / drain)
617 Low-concentration impurity region 618 Photoresist mask 619 Strong P-type region (source / drain)
620 Interlayer insulating films 621 to 625 Peripheral drive circuit, pixel TFT electrode / wiring 626 Silicon nitride film

Claims (6)

A gate electrode and a common electrode provided on the first substrate;
A gate insulating film provided to cover the gate electrode;
A semiconductor film provided on the gate electrode through the gate insulating film;
An inverted staggered thin film transistor having a source electrode and a drain electrode provided so as to overlap with a part of the semiconductor film;
A second substrate facing the first substrate;
An active matrix liquid crystal electro-optical device having a liquid crystal layer sandwiched between the first substrate and the second substrate and driven by an electric field between the drain electrode and the common electrode,
An active matrix type liquid crystal electro-optical device, wherein the second substrate is provided with a light-transmitting electrode material. A gate electrode and a common electrode provided on the first substrate;
A gate insulating film provided to cover the gate electrode;
A semiconductor film provided on the gate electrode through the gate insulating film;
An inverted staggered thin film transistor having a source electrode and a drain electrode provided so as to overlap with a part of the semiconductor film;
A second substrate facing the first substrate;
An active matrix liquid crystal electro-optical device having a liquid crystal layer sandwiched between the first substrate and the second substrate and driven by an electric field between the drain electrode and the common electrode,
An active matrix liquid crystal electro-optical device, wherein a translucent electrode material is provided on the entire surface of the second substrate. A gate electrode and a common electrode provided on the first substrate;
A gate insulating film provided to cover the gate electrode;
A semiconductor film provided on the gate electrode through the gate insulating film;
An inverted staggered thin film transistor having a source electrode and a drain electrode provided so as to overlap with a part of the semiconductor film;
A second substrate facing the first substrate;
An active matrix liquid crystal electro-optical device having a liquid crystal layer sandwiched between the first substrate and the second substrate and driven by an electric field between the drain electrode and the common electrode,
An active matrix liquid crystal electro-optical device, wherein a part of the second substrate is provided with a light-transmitting electrode material. In any one of Claims 1 thru | or 3,
2. The active matrix liquid crystal electro-optical device according to claim 1, wherein the drain electrode has a round shape at the apex of the electrode cross section, and the electrode cross section has a shape using a curvature of a circle or an ellipse. In any one of Claims 1 thru | or 4,
2. The active matrix liquid crystal electro-optical device according to claim 1, wherein the common electrode has a round shape at the apex of the electrode cross section, and the electrode cross section has a shape using a curvature of a circle or an ellipse. In any one of Claims 1 thru | or 5,
An active matrix type liquid crystal electro-optical device, wherein the translucent electrode material is ITO.

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