In-plane field type liquid crystal display device comprising liquid crystal molecules with more than two kinds of reorientation directions Number:7,046,324 from the United States Patent and Trademark Office (PTO) owispatent

Title: In-plane field type liquid crystal display device comprising liquid crystal molecules with more than two kinds of reorientation directions

Abstract: An active matrix liquid crystal display device having a pair of substrates, a liquid crystal layer, scanning lines and video signal lines provided in a matrix manner, at least one pixel electrode and at least one common electrode. The at least one pixel electrode is bent so as to be inclined in first and second directions which are symmetrical relative to the alignment direction of the liquid crystal. The first direction of the pixel electrode is at a plus predetermined angle relative to the alignment direction, while the second direction of the pixel electrode is at a minus predetermined angle relative to the alignment direction.

Patent Number: 7,046,324 Issued on 05/16/2006 to Ohta,   et al.

---

Inventors:	Ohta; Masuyuki (Mobara, JP); Yanagawa; Kazuhiko (Mobara, JP); Ogawa; Kazuhiro (Mobara, JP); Ashizawa; Keiichiro (Mobara, JP); Yanai; Masahiro (Mobara, JP); Konishi; Nobutake (Mobara, JP); Kondo; Katsumi (Hitachinaka, JP); Ohe; Masahito (Mobara, JP); Aratani; Sukekazu (Hitachi, JP); Klausmann; Hagen (Hitachi, JP)
Assignee:	Hitachi, Ltd. (Tokyo, JP)
Appl. No.:	237756
Filed:	September 10, 2002

---

Related U.S. Patent Documents

---

	Application Number	Filing Date	Patent Number	Issue Date
	09841100	Apr., 2001	6545658
	08722849	Sep., 1996	6266116

---

Foreign Application Priority Data

---

Oct 04, 1995 [JP]			7-257366
Oct 09, 1995 [JP]			7-261235
Mar 27, 1996 [JP]			8-071787

Current U.S. Class:	349/141 ; 349/139
Current International Class:	G02F 1/1343 (20060101)
Field of Search:	349/141,143,139

---

References Cited [Referenced By]

---

U.S. Patent Documents

	5434690		July 1995		Hisatake et al.
	5504604		April 1996		Takatori et al.
	5598285		January 1997		Kondo et al.
	5600464		February 1997		Ohe et al.
	5745207		April 1998		Asada et al.
	5754266		May 1998		Ohta et al.
	5793459		August 1998		Toko
	5864376		January 1999		Takatori
	5914761		June 1999		Ohe et al.
	5977562		November 1999		Hirakata et al.
	6266116		July 2001		Ohta et al.
	6288763		September 2001		Hirota

Foreign Patent Documents

	63-187218		Aug., 1988		JP
	1-277215		Nov., 1989		JP
	6-082617		Mar., 1994		JP
	7-134301		May., 1995		JP
	7-191336		Jul., 1995		JP

Other References

Ohta et al, Development of Super TFT LCDs with In-Plane Switching Display Mode, Asia Display '95, pp 707-710. cited by other.

Primary Examiner: Nguyen; Dung T.
Attorney, Agent or Firm: Antonelli, Terry, Stout and Kraus, LLP.

---

Parent Case Text

---

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/841,100, filed Apr. 25, 2001, now U.S. Pat. No. 6,545,658 which is a continuation U.S. application Ser. No. 08/722,849, filed Sep. 26, 1996, now U.S. Pat. No. 6,266,116, the subject matter of which is incorporated by reference herein.

---

Claims

---

The invention claimed is:

1. An active matrix liquid crystal display device, comprising: a pair of substrates, at least one of which is transparent; a liquid crystal composite layer provided between said substrates; a plurality of scanning lines and video signal lines provided in a matrix manner on a surface of one of said substrates facing the other substrate; at least one pixel electrode, and at least one common electrode; an active element connected to said pixel electrode, said scanning line and said video signal line, respectively; wherein said pixel electrode is bent so as to be inclined in first and second directions which are symmetrical relative to the alignment direction of the liquid crystal, where the first direction of said pixel electrode is at a plus predetermined angle relative to the alignment direction of the liquid crystal, while the second direction of the pixel electrode is at a minus predetermined angle relative to the alignment direction with substantially the same absolute angle with that of the first direction, thereby making the first and second directions symmetrical relative to the alignment direction; wherein the pixel electrode has an elongated portion which extends in parallel to the scanning lines, and the elongated portion overlaps with a portion where a counter voltage is supplied.

2. An active matrix liquid crystal display device as defined in claim 1, wherein the liquid crystal composite layer has a positive dielectric constant.

3. An active matrix liquid crystal display device as defined in claim 2, wherein said pixel electrode which is bent so as to be inclined in the first and second directions forms a zigzag shape which is symmetrical relative to the alignment direction.

4. An active matrix liquid crystal display device as defined in claim 2, wherein said pixel electrode has a comb-like shape and is interdigitally aligned with said common electrode.

5. An active matrix liquid crystal display device as defined in claim 4, wherein said common electrode has a comb-like shape and is interdigitally aligned with said pixel electrode.

6. An active matrix liquid crystal display device as defined in claim 2, wherein the plus predetermined angle and the minus predetermined angle is within an angle ranging greater than 0 degrees and smaller than 90 degrees.

7. An active matrix liquid crystal display device as defined in claim 6, wherein the plus predetermined angle and the minus predetermined angle is within a range of 1 30 degrees relative to the alignment direction.

8. An active matrix liquid crystal display device as defined in claim 7, wherein the plus predetermined angle and the minus predetermined angle is within a range of 10 20 degrees relative to the alignment direction.

9. A liquid crystal display device as defined in claim 2, further comprising a color filter and a black mask which extend in parallel and along the video signal lines.

---

Description

---

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a liquid crystal display device and its manufacturing method, particularly to an art to be effectively applied to an in-plane field type active-matrix liquid crystal display device.

(2) Description of the Prior Art

An active-matrix liquid crystal display device using an active element such as thin film transistor (TFT) has been widely spread as a display terminal of OA equipment because it is thin and lightweighted and has a high image quality equal to that of a cathode-ray tube.

The display system of the active-matrix liquid crystal display device is roughly divided into the following types.

One of them is a type, in which a liquid crystal layer is enclosed between a pair of substrates with two transparent electrodes formed on the substrates, a driving voltage is applied to the transparent electrodes, thereby driving the liquid crystal layer by an electric field almost perpendicular to the surfaces of the substrates, and the light passing the transparent electrodes and entering the liquid crystal layer is modulated (hereafter referred to as a vertical field type). Every product spread at present uses this type.

However, an active-matrix liquid crystal display device using the vertical field type has the problems on practical use that a contrast of an image extremely varies when changing viewing angles and particularly, a gradation level is inverted depending on a viewing angle when displaying half tone images.

The other of them is a type, in which a liquid crystal layer is enclosed between a pair of substrates, a driving voltage is applied to two stripe-like or line-like electrodes formed on either or both of the substrates, thereby driving a liquid crystal layer by an electric field almost parallel with the surfaces of the liquid crystal layer, and the light entering the liquid crystal layer from the gap between the two electrodes is modulated (hereafter referred to as an in-plane field type).

An active-matrix liquid crystal display device using the in-plane field type can realize wide viewing-angle characteristics. However, any active-matrix liquid crystal display device using the in-plane field type is not practically used yet.

Features of an active-matrix liquid crystal display device using the in-plane field type are shown in the official gazettes of Japanese Patent Application No. 505247/1993, Japanese Patent Publication No. 21907/1988, and Japanese Patent Laid-Open No. 160878/1994.

SUMMARY OF THE INVENTION

A conventional active-matrix liquid crystal display device using the in-plane field type modulates incoming light to a liquid crystal layer by rotating homogeneously initial-orienting liquid crystal molecules with no twisting, where an initial orientation direction is at an inclination to a pixel electrode and a counter electrode arranged in parallel, to create a reorientation state of liquid crystal molecules with twisting, whose major-axes are rotated substantially parallel with the surfaces of the liquid crystal layer, and displays images by a driving voltage enough small for conventional video signal drivers and with a response speed enough high to display animation.

Furthermore, the conventional active-matrix liquid crystal display device using the in-plane field type has extremely wide viewing angle characteristics compared with the active-matrix liquid crystal display device using the vertical field type.

However, the active-matrix liquid crystal display device using the in-plane field type cited above has a problem that viewing angle characteristics equal to those of a self-light-emitting display device such as a cathode ray tube (CRT) cannot be achieved because a homogeneous color tone cannot be realized and the viewing angle range of isochromaticity narrows when tilting a viewing angle to a certain direction.

That is, when liquid crystal molecules are twisted by rotation and viewing angle is tilted to the major-axis direction of the molecules, the birefringence anisotropy of the liquid crystal molecules more easily changes compared with the case of tilting the viewing angle to other directions, so that gradation level is more easily inverted and color tone more easily changes in the major-axis direction than in other directions.

Particularly, when a white image is displayed in the normally black mode, the color tone of white shifts to blue in the major-axis direction of the liquid crystal molecules.

Moreover, though the birefringence anisotropy does little change in the minor-axis direction of the liquid crystal molecules perpendicular to the major-axis direction of them, the color tone of white shifts to yellow in the minor-axis direction because the optical path length increases as the viewing angle tilts to the minor-axis direction.

The present invention has been made to solve the above mentioned problems of the prior art and its object is to provide an art for realizing wide viewing angle characteristics equal to those of a CRT and improving the image quality for an active-matrix liquid crystal display device using the in-plane field type.

The above and other objects and novel features of the present invention will become more apparent by the description of the present specification and the accompanying drawings.

The outline of a typical invention out of the inventions disclosed in this application is briefly described below.

(1) An active-matrix liquid crystal display device comprises a pair of substrates, a liquid crystal layer held between the substrates, a plurality of video signal lines formed on a first substrate of the pair, a plurality of scanning signal lines formed on the first substrate of the pair and intersecting the video signal lines, and a plurality of picture elements formed in a matrix in the intersecting regions between the video signal lines and the scanning signal lines;

wherein each of the picture elements has at least an active element formed on the first substrate, at least a pixel electrode connected to the active element, and at least a counter electrode formed on either of the substrates to generate an electric field almost parallel with the surfaces of the liquid crystal layer between the counter electrode and the pixel electrode;

and wherein liquid crystal molecules of the liquid crystal layer have at least two kinds of driving (reorientation) directions for neighboring picture elements or in one picture element.

(2) For the means in the above Item (1), the liquid crystal molecules of the liquid crystal layer between the counter electrode and the pixel electrode have one initial orientation direction.

(3) For the means in the above Item (2), each of the picture elements has a plurality of pairs of pixel electrodes and counter electrodes; wherein each pair of a pixel electrode and a counter electrode have a pair of facing sides faced almost parallel each other and the plurality of pairs of the facing sides have a tilt angle to the initial orientation direction of the liquid crystal molecules.

(4) For the mean in the above Item (3), wherein the initial orientation direction of the liquid crystal molecules is almost vertical to the scanning signal lines or parallel with the video signal lines, and picture elements with tilt angles .theta. and -.theta. are alternately arranged into a matrix.

(5) For the means in the above Item (4), the angle .theta. is kept in a range of 10.degree..ltoreq..theta..ltoreq.200.

(6) For the means in the above Item (2), each of the picture elements has a plurality of pairs of pixel electrodes and counter electrodes; wherein each pair of a pixel electrode and a counter electrode have a pair of linear facing sides faced each other; and one of the pair of linear facing sides has a tilt angle to the initial orientation direction while the other of the pair is parallel with the initial orientation direction.

(7) For the means in the above Item (6), wherein the initial orientation direction of liquid crystal molecules is almost vertical to the scanning signal lines or parallel with the video signal lines, and the tilt angles of the plurality of pairs of facing sides are equal to .theta. and -.theta..

(8) For the means in the above Item (7), the angle .theta. is kept in a range of 10.degree..ltoreq..theta..ltoreq.20.degree., and the numbers of the pairs of facing sides with tilt angles of .theta. and -.theta. in each of the picture elements are the same.

(9) For the means in the above Item (2), each of the picture elements has a plurality of pairs of pixel electrodes and counter electrodes; wherein each pair of a pixel electrode and a counter electrode have a pair of facing sides faced each other, and a first side of the pair is almost parallel with the initial orientation direction while a second side of the pair is formed by two parts, one part being extended almost parallel with the initial orientation direction and the other part being tilted from the initial orientation direction at a tilt angle and intersecting with the first side at near the edge of the first electrode; and wherein the plurality of pairs of facing sides have a plurality of the tilt angles in each picture element.

(10) For the means in the above Item (9), wherein the initial orientation direction of liquid crystal molecules is almost vertical to the scanning signal lines or almost parallel with the video signal lines, and the plurality of the tilt angles are equal to .theta. and -.theta..

(11) For the means in the above Item (10), the angle .theta. is kept in a range of 30.degree..ltoreq..theta..ltoreq.60.degree., and the numbers of the pairs of facing sides with the tilt angles of .theta. and -.theta. in each of the picture elements are the same.

(12) For the means in the above Item (2), each of the picture elements has a plurality of pairs of pixel electrodes and counter electrodes; wherein each pair of a pixel electrode and a counter electrode have a pair of facing sides faced almost parallel each other and are bent inside the image display region of each of the picture elements.

(13) For the means in the above Item (12), wherein the video signal lines or the scanning signal lines are bent to be almost parallel with the pair of facing sides.

(14) For the means in the above Item (12), there are two or more types of gap distances between pairs of pixel electrodes and counter electrodes in each of the picture elements.

(15) For the means in the above Item (1), the liquid crystal molecules of the liquid crystal layer between the counter electrode and the pixel electrode have two initial orientation directions in each of the picture elements.

(16) For the means in the above Item (15), the liquid crystal layer has a positive dielectric anisotropy, initial orientation angles .phi. LC1 and .phi. LC2 are 90.degree.+.alpha. and 90.degree.-.alpha., respectively, and angles .phi. P1 and .phi. P2 between the transmission axes of two polarizing plates and the direction (EDR)of the applied electric field are 90.degree. and 0.degree. respectively.

(17) For the means in the above Item (15), the liquid crystal layer has a negative dielectric anisotropy, initial orientation angles .phi. LC1 and .phi. LC2 are 0.degree.+.alpha. and 180.degree.-.alpha., respectively, and angles .phi. P1 and .phi. P2 between the transmission axes of two polarizing plates and the direction (EDR) of the applied electric field are 90.degree. and 0.degree., respectively.

(18) For the means in the above Item (16) or (17), the absolute value of .alpha. is 2.5.degree. or less.

(19) For the means in the above Item (15), initial orientation angles .phi. LC1 and .phi. LC2 are 45.degree. and 135.degree., respectively, and angles .phi. P1 and .phi. P2 between the transmission axes of two polarizing plates and the direction (EDR)of the applied electric field are 90.degree. and 0.degree. respectively.

(20) For the means in the above Item (15), the boundary between the two initial orientation directions of liquid crystal molecules is arranged over a pixel electrode or a counter electrode in each of the picture elements.

(21) For the means in the above Item (2) or (15), wherein an initial twist angle of the liquid crystal layer is within 5 degrees of 0.degree..

(22) For a manufacturing method of an active-matrix liquid crystal display device comprising a pair of substrates, a liquid crystal layer held between the substrates, a plurality of active elements formed in a matrix on a first substrate of the pair, a plurality of pixel electrodes connected to the active elements respectively, a plurality of counter electrodes formed on either of the substrates to generate an electric field almost parallel with the surfaces of the liquid crystal layer between the pixel electrodes and the counter electrodes, a pair of orientation films formed between the substrates and contacting the liquid crystal layer, and two polarizing plates formed on surfaces opposite to the surfaces of the substrates for holding the liquid crystal layer; two-directional rubbings are applied to the both orientation films in one picture element.

(23) For a manufacturing method of an active-matrix liquid crystal display device comprising at least a pair of substrates, a liquid crystal layer held between the substrates, a plurality of active elements formed in a matrix on a first substrate of the pair, a plurality of pixel electrodes connected to the active elements respectively, a plurality of counter electrodes formed on either of the substrates to generate an electric field almost parallel with the surfaces of the liquid crystal layer between the pixel electrodes and the counter electrodes, a pair of orientation films formed between the substrates and contacting the liquid crystal layer, and two polarizing plates formed on surfaces opposite to the surfaces of the substrates for holding the liquid crystal layer; a chiral agent is mixed in the liquid crystal layer and two-directional rubbings are applied only to either of the orientation films in one picture element.

(24) For a manufacturing method of an active-matrix liquid crystal display device comprising at least a pair of substrates, a liquid crystal layer held between the substrates, a plurality of active elements formed in a matrix on a first substrate of the pair, a plurality of pixel electrodes connected to the active elements respectively, a plurality of counter electrodes formed on either of the substrates to generate an electric field almost parallel with the substrate surfaces to the liquid crystal layer between the pixel electrodes and the counter electrodes, a pair of orientation films formed between the substrates and contacting the liquid crystal layer, and two polarizing plates formed on surfaces opposite to the surfaces of the substrates for holding the liquid crystal layer; two initial orientation directions of liquid crystal molecules are provided in one picture element by applying a laser beam having two predetermined polarized directions to different regions of the orientation films in the picture element.

According to the above means, shifts of color tones are offset each other and the dependency of color-tone on a viewing angle can greatly be reduced because the initial orientation angle .phi. LC is made different for neighboring picture elements or in one picture element so as to form two or more kinds of reorientation directions.

For example, in an in-plane field type device utilizing the normally black mode, in which a displayed image is dark when no voltage is applied and bright when a voltage is applied, and also utilizing the birefringence first minimum mode, the transmission axes of the two polarizing plates are perpendicularly intersected each other (cross Nicols), and the maximum transmittance, that is, a white image is obtained when the angle formed between each transmission axis and the major axis of liquid crystal molecules twisted by the electric field becomes almost equal to 45.degree..

When changing viewing directions from an upward direction, which is vertical to the substrate surface, to a tilted direction toward the substrate surface in the major-axis direction of liquid crystal molecules in the direction of about 45.degree. away from the transmission axis under the above twisted state, the birefringence anisotropy changes and the color tone of white shifts to blue in the major-axis direction.

In the minor-axis direction of liquid crystal molecules (at a direction of about -45.degree. away from the transmission axis, and perpendicular to the major-axis direction), the birefringence anisotropy does little change by tilting viewing angles from a vertical direction to an in-plane direction.

However, the color tone of white shifts to yellow in the minor-axis direction because the optical path length increases as the viewing angle tilts from a vertical to a in-plane direction in the minor-axis direction.

The important point is that, because blue and yellow colors are complimentary colors in chromaticity coordinates, white color can be created by mixing these two colors.

Therefore, by rotating liquid crystal molecules in two directions for each picture element or in one picture element, and by creating two reorientation states where the major-axis directions of the two states are nearly perpendicular to each other in displaying a white image or a half-tone image, color tones of the two states are offset each other and the viewing angle dependency of color tone change can greatly be reduced.

Moreover, also for gradation inversion, the characteristics of both the minor-axis direction of liquid crystal molecules to be hardly gradation-reversed and the major-axis direction of them to be easily gradation-reversed are averaged and the no-inversion viewing angle range of a gradation level can be expanded.

Thereby, the homogeneity of gradation and that of color tone are averaged or expanded in every direction and wide viewing angle characteristics close to those of a CRT can be realized.

The foregoing and other objects, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an essential portion showing one picture element and its neighborhood of the active-matrix color liquid crystal display device which is embodiment 1 of the present invention;

FIGS. 2A to 2D are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POLL and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device of embodiment 1 of the present invention;

FIG. 3 is an illustration showing an example of arranging the picture element shown in FIG. 1 or a similar picture element into a matrix;

FIG. 4 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device of embodiment 2 of the present invention;

FIGS. 5A and 5B are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POLL and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device which is embodiment 2 of the present invention;

FIG. 6 is an illustration showing an example of arranging the picture element shown in FIG. 4 or a similar picture element into a matrix;

FIG. 7 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device which is embodiment 3 of the present invention;

FIGS. 8A and 8B are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POL1 and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device of embodiment 3 of the present invention;

FIG. 9 is an illustration showing an example of arranging the picture element shown in FIG. 7 and a similar picture element into a matrix;

FIG. 10 is an illustration showing an example of arranging the picture element shown in FIG. 7 and a similar picture element into a matrix;

FIG. 11 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device which is embodiment 4 of the present invention;

FIGS. 12A and 12B are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POLL and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device of embodiment 4 of the present invention;

FIG. 13 is an illustration showing an example of arranging the picture element shown in FIG. 7 or a similar picture element into a matrix;

FIG. 14 is an illustration showing one picture element and its neighborhood of the active-matrix color liquid crystal display device which is embodiment 5 of the present invention;

FIGS. 15A and 15B are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POL1 and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device of embodiment 5 of the present invention;

FIG. 16 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device which is embodiment 6 of the present invention;

FIGS. 17A, 17B, and 17C are illustrations showing the directions (EDR) of applied electric field, the initial orientation direction (RDR), transmission axes directions (OD1 and OD2) of polarizing plates (POL1 and POL2), and driving directions of liquid crystal molecules (LC) of the liquid crystal display device of embodiment 6 of the present invention;

FIG. 18 is a top view of an unit picture element of example 1 in the liquid crystal display device of embodiment 7 of the present invention;

FIG. 19 is a top view of an unit picture element of example 2 in the liquid crystal display device of embodiment 7 of the present invention;

FIG. 20 is a top view of an unit picture element of example 4 in, the liquid crystal display device of embodiment 7 of the present invention;

FIG. 21 is a top view of an unit picture element of example 5 in the liquid crystal display device of embodiment 7 of the present invention;

FIG. 22 is a top view of an unit picture element of example 6 in the liquid crystal display device of embodiment 7 of the present invention;

FIG. 23 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device of embodiment 8 of the present invention;

FIG. 24 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device of embodiment 11 of the present invention;

FIG. 25 is an illustration showing a method for rubbing a bottom orientation film (ORI1) of the active-matrix color liquid crystal display device of embodiment 8 of the present invention;

FIG. 26 is an illustration showing a method for applying a laser beam having two predetermined polarized directions to different regions of a bottom orientation film (ORI1) of the active-matrix color liquid crystal display device of embodiment 13 of the present invention;

FIGS. 27A and 27B are graphs showing the azimuthal angle (.phi.) dependent characteristics of white color tone when driving the liquid crystal display device of-the present invention and the liquid crystal display device of the comparative example, in which FIG. 27A shows the case of the comparative example and FIG. 27B shows the case of the present invention.

FIGS. 28A and 28B show a color tone constant region (an isochromatic region) in the form of semispherical polar-coordinate (.theta., .phi.) graphs, in which FIG. 28A shows the case of the comparative example and FIG. 28B shows the case of the present invention and both of which show distributions of the white color tone.

FIG. 29 is an illustration showing the relation between the directions (EDR) of the applied electric field, initial orientation directions (RDR1 and RDR2), and polarized-light transmission axes (OD1 and OD2).

FIG. 30 is an illustration showing the definition of the viewing angle (.theta., .phi.) of each embodiment of the present invention;

FIG. 31 is a sectional view of the picture element in FIG. 1, taken along the line a--a in FIG. 1;

FIG. 32 is a sectional view of the thin film transistor (TFT) in FIG. 1, taken along the line 4--4 in FIG. 1;

FIG. 33 is a sectional view of the storage capacitance (Cstg) in FIG. 1, taken along the line 5--5 in FIG. 1;

FIG. 34 is a top view for explaining the structure of portions around the matrix of the display panel (PNL) of the liquid crystal display device of each embodiment of the present invention;

FIG. 35 is a sectional view showing the margin of a panel having scanning signal terminals at its left side and having no-external connection terminals at its right side in the liquid crystal display device of each embodiment of the present invention;

FIG. 36 is a flow chart of sectional views of a thin film transistor element portion and a gate terminal portion showing the manufacturing process of steps A to C at the transparent substrate (SUB1) of the liquid crystal display device of each embodiment of the present invention;

FIG. 37 is a flow chart of sectional views of a thin film transistor element portion and a gate terminal portion showing the manufacturing process of steps D to F at the transparent substrate (SUB1) of the liquid crystal display device of each embodiment of the present invention;

FIG. 38 is a flow chart of sectional views of a thin film transistor element portion and a gate terminal portion showing the manufacturing process of steps G to H at the transparent substrate (SUB1) of the liquid crystal display device of each embodiment of the present invention;

FIG. 39 is an illustration showing the equivalent circuit and its peripheral circuits of the display matrix portion (AR) of the liquid crystal display device of each embodiment of the present invention;

FIG. 40 is an illustration showing driving waveforms of the liquid crystal display device of each embodiment of the present invention at driving;

FIG. 41 is a top view showing the state in which peripheral driving circuits are mounted on the liquid crystal panel of each embodiment of the present invention; and

FIG. 42 is an exploded perspective view of a liquid crystal module of the liquid crystal display device of each embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below in detail by referring to the accompanying drawings.

In all drawings for explaining embodiments of the invention, components having the same function are provided with the same symbol and repetitive description of them is omitted.

[Embodiment 1]

First, the in-plane field type active-matrix color liquid crystal display device constituted in accordance with embodiment 1 of the present invention is outlined below.

<<Planar Structure of Matrix Portion (Picture Element Portion)>>

FIG. 1 is a top view showing one picture element and its neighborhood of the active-matrix color liquid crystal display device of embodiment 1 of an invention of the present invention.

Each picture element is arranged in a region (a region enclosed by four signal lines) where two adjacent scanning signal lines (gate signal lines or horizontal signal lines) (GL) and two adjacent video signal lines (drain signal lines or vertical signal lines) (DL) intersect.

Each picture element includes thin film transistor (TFT), storage capacitance (Cstg), a pixel electrode (PX), two counter electrodes (CT), and a counter voltage signal line (a common signal line) (CL).

In FIG. 1, a plurality of scanning signal lines (GL) and a plurality of counter voltage signal lines (CL) are arranged in the vertical direction while extending in the horizontal direction.

Moreover, a plurality of video signal lines (DL) are arranged in the horizontal direction while extending in the vertical direction.

Furthermore, a pixel electrode (PX) is connected to a source electrode (SD1) of a thin film transistor (TFT) and two counter electrodes (CT) are integrated with a counter voltage signal line (CL).

A pixel electrode (PX) and each of two counter electrodes (CT) are faced each other, controlling optical states of liquid crystal layer (LCD) by an electric field between the pixel electrode (PX) and the counter electrode (CT).

The pixel electrode (PX) and the two counter electrodes (CT) are formed like comb teeth. As shown in FIG. 1, the pixel electrode (PX) extends straight diagonally downward, and the two counter electrodes (CT) are formed in a comb tooth shape which protrude upward from a counter voltage signal line (CL) and whose facing sides faced with the pixel electrode (PX) also extend diagonally upward. The region between the pixel electrode (PX) and the two counter electrodes (CT) is divided into two parts in one picture element.

<<Sectional Structure of Display Matrix Portion (Picture Element Portion)>>

FIG. 31 is a sectional view showing the essential portion in FIG. 1, taken along the line 31a--31a in FIG. 1. FIG. 32 is a sectional view showing thin film transistor (TFT) in FIG. 1, taken along the line 4--4 in FIG. 1. FIG. 33 is a sectional view showing a storage capacitance (Cstg) in FIG. 1, taken along the line 5--5 in FIG. 1.

As shown in FIGS. 31 to 35, thin film transistors (TFT), storage capacitances (Cstg), and electrodes group are formed at the bottom transparent glass substrate (SUB1) side, and color filter (FIL) and light shielding black matrix (BM) are formed at the top transparent glass substrate (SUB2) side.

Moreover, orientation films (OR1 and ORI2) for controlling initial orientation directions of liquid crystal molecules (LC) at the surfaces of the liquid crystal layer are provided between transparent glass substrates (SUB1 and SUB2), and polarizing plates (POL1 and POL2) are provided on the outside surfaces of each of transparent glass substrates (SUB1 and SUB2).

More minute structures are described below.

<<TFT Substrate>>

First, the structure of the bottom transparent glass substrate (SUB1) (TFT substrate) is described below in detail.

<<Thin Film Transistor (TFT)>>

Thin film transistor (TFT) operates so that the channel resistance between the source and drain decreases by applying a positive bias to the gate electrode and increases by decreasing the bias to zero.

As shown in FIG. 32, thin film transistor (TFT) comprises gate electrode (GT), gate insulating film (GI), i-type semiconductor layer (AS) made of i-type (intrinsic, or undoped) amorphous silicon (Si), and a pair of a source electrode (SD1), and a drain electrode (SD2).

A source electrode (SD1) and a drain electrode (SD2) are originally determined by the bias polarity between them. Because the polarity of the circuit of the present liquid crystal display device is inverted during operation, a source electrode (SD1) and a drain electrode (SD2) are replaced each other during operation.

In the following description, however, one is fixed to source electrode (SD1) and the other is fixed to drain electrode (SD2) for convenience sake.

The embodiment of the present invention uses an amorphous-silicon thin film transistor as thin film transistor (TFT). However, it is also possible to use a two-terminal device such as a polysilicon thin film transistor, MOS transistor on a silicon wafer, organic TFT, or MIM (Metal-Insulator-Metal) diode (though each of them is not strictly an active element, it is assumed as an active element in the case of the present invention).

<<Counter Electrode (CT)>>

Counter electrode (CT) is made of conductive film (g1) on the same layer as gate electrode (GT) and scanning signal line (GL).

Moreover, anodic oxide film (AOF) made of aluminum oxide is formed on counter electrode (CT).

Counter electrode (CT) is constituted so that counter voltage (Vcon)) is applied to counter electrode (CT).

<<Counter Voltage Signal Line (CL>>

Counter voltage signal line (CL) is made of conductive film (g1).

Counter voltage signal line (CL) is formed in the same manufacturing process as that of conductive films (g1) of gate electrode (GT), scanning signal line (GL), and counter electrode (CT).

Counter voltage (Vcom) is supplied to counter electrode (CT) from an external circuit through counter voltage signal, line (CL).

Moreover, anodic oxide film (AOF) made of aluminum oxide is formed on counter voltage signal line (CL).

Furthermore, it is possible to form counter electrode (CT) and counter voltage signal line (CL) at the top transparent-glass substrate (SUB2)(color filter substrate) side.

<<Insulating Film (GI)>>

Insulating film (GI) is used as a gate insulating film for providing an electric field for semiconductor layer (AS) together with gate electrode (GT) in thin film transistor (TFT).

Insulating film (GI) is formed over gate electrode (GT) and scanning signal line (GL). Insulating film (GI) uses, for example, a silicon nitride film formed by plasma CVD and is formed at a thickness of 1,200 to 2,700A (approx. 2,400A for the embodiment of the present invention).

Gate insulating film (GI) is formed so as to entirely enclose display Matrix portion (AR) and its margin is removed so that external terminals (DTM and GTM) are exposed.

Insulating film (GI) also contributes to electrical insulation between counter voltage signal line (CL) and video signal line (DL).

<<Pixel Electrode (PX)>>

Pixel electrode (PX) comprises conductive film (d1), and conductive film (d2) formed on conductive film (d1).

Moreover, pixel electrode (PX) is formed on the same layer as source electrode (SD1) and drain electrode (SD2). Furthermore, pixel electrode (PX) is integrated with source electrode (SD1).

<<Storage Capacitance (Cstg)>>

Pixel electrode (PX) is constituted so as to overlap with counter voltage signal line (CL) at the end opposite to the end connected with thin film transistor (TFT).

As shown in FIG. 33, this overlap constitutes storage capacitance (Cstg) using pixel electrode (PX) as one electrode (PL2) and counter voltage signal (CL) as other electrode (PL1).

The dielectric film of storage capacitance (Cstg) comprises insulating film (GT) used as a gate insulating film of thin film transistor (TFT) and anodic oxide film (AOF).

As shown in FIG. 1, planar storage capacitance (Cstg) is arranged on a part of conductive film (g1) of a counter voltage signal line (CL).

<<Color Filter Substrate>>

Then, the structure of the top transparent-glass substrate (SUB2) (color filter substrate) is described in detail below by referring to FIGS. 1 and 31.

<<Light Shielding Film (BM)>>

Light shielding film (BM) (so-called black matrix) is formed at the top transparent glass substrate (SUB2) side so that contrast of a displayed image is not deteriorated due to the light transmitted through an unnecessary gap other than the gap between a pixel electrode (PX) and a counter electrode (CT) and emitted to the display surface side.

Light shielding film (BM) also has a function for preventing external light or backlight from entering semiconductor layer (AS).

That is, i-type semiconductor layer (AS) of thin film transistor (TFT) is sandwiched between light shielding film (BM) and slightly-large gate electrode (GT) from the top and bottom and thereby protected from external natural light or backlight.

The inside of the closed polygonal contour of light shielding film (BM) shown in FIG. 1 shows an opening where light shielding film (BM) is not formed.

Light shielding film (BM) has a shielding characteristic to light and is made of a film with a high insulating property not so as to influence the electric field between a pixel electrode (PX) and a counter electrode (CT). For the embodiment of the present invention, light shielding film (BM) uses a mixture obtained by mixing black pigment with resist and formed at a thickness of approx. 1.2 .mu.m.

Light shielding film (BM) is formed like a lattice around each picture element and the lattice partitions the effective display region of one picture element.

Therefore, the contour of each picture element is made clear by light shielding film (BM).

That is, light shielding film (BM) has a function for serving as a black matrix and a function for shielding light to i-type semiconductor layer (AS).

Light shielding film (B) is also formed on the margin like a frame and its pattern is formed continuously with the pattern of the matrix portion provided with a plurality of dot-like openings shown in FIG. 1.

Light shielding film (BM) at the margin is extended to the outside of sealing portion (SL) to prevent leak light such as reflected light due to a real machine such as a personal computer from entering the display matrix portion.

Moreover, light shielding film (BM) is kept in a range approx. 0.3 to 1.0 mm inside from the peripheral edge of top transparent-glass substrate (SUB2) and formed so as to avoid the cutting region of top transparent-glass substrate (SUB2).

<<Color Filter (FIL)>>

Color filter (FIL) is formed like a stripe in repetition of red, green, and blue and moreover, it is formed so as to overlap with the edge of light shielding film (BM).

Color filter (FIL) can be formed as shown below.

First, a dyeing base material such as an acrylic resin is formed on the surface of top transparent-glass substrate (SUB2) and then the dyeing base material other than that in a red-filter forming region is removed by photolithography.

Thereafter, the dyeing base material is dyed by a red dye and fixed to form red filter (R).

Then, green filter (G) and blue filter (B) are successively formed by the same process.

<<Overcoat Film (OC)>>

Overcoat film (OC) is used to prevent a dye from leaking from color filter (FIL) to a liquid crystal layer and flatten steps due to color filter (FIL) and light shielding film (BM).

Overcoat film (OC) is made of, for example, a transparent resin such as acrylic resin or epoxy resin.

<<Structure Around Display Matrix Portion (AR)>>

FIG. 34 is an illustration showing a top view of an essential portion around display matrix (AR) portion of display panel (PNL) including top and bottom transparent-glass substrates (SUB1 and SUB2).

FIG. 35 is an illustration showing the cross section of the neighborhood of external connection terminal (GTM) to which a scanning circuit should be connected at the left side and the cross section of the neighborhood of a sealing portion free from external connection terminal at the right side.

Terminal groups (Tg and Td) are named by collecting every several scanning-circuit connection terminals (GTM), video-signal-circuit connection terminals (DTM), and their outgoing wiring portions for connection with tape carrier packages (TCP).

Counter electrode terminal (CTM) is a terminal for supplying counter voltage (Vcom) to counter electrode (CT) from an external circuit.

Counter voltage signal line (CL) of the display matrix portion is extended to the opposite side (right side in drawings) to scanning-circuit terminal (GTM), and counter voltage signal lines (CL) are collected by common bus line (CB)(counter electrode connection signal line) and connected to counter electrode terminal (CTM).

Layers of orientation films (ORI1 and ORI2) are formed inside of sealing pattern (SL) and polarizing plates (POL1 and POL2) are formed on the outside surfaces of bottom transparent glass substrate (SUB1) and top transparent glass substrate (SUB2), respectively.

Liquid crystal layer (LCD) is sealed in a region partitioned by sealing pattern (SL) between bottom orientation film (ORI1) and top orientation film (ORI2) for setting the orientation of liquid crystal molecules.

Bottom orientation film (ORI1) is formed on protective coat (PSV) over the bottom transparent-glass substrate (SUB1).

The liquid crystal display device of each embodiment of the present invention is fabricated by superposing various layers to separately form bottom transparent glass substrate (SUB1) and top transparent glass substrate (SUB2), thereafter forming sealing pattern (SL) on the top transparent glass substrate (SUB2), superposing top transparent glass substrate (SUB2) on bottom transparent glass substrate (SUB1) and, injecting liquid crystal (LCD) through opening portion (INJ) of sealing pattern (SL), sealing injection port (INJ) with epoxy resin or the like, and cutting the top and bottom substrates.

<<Equivalent Circuit of Whole Display Device>>

FIG. 39 is a connection diagram of an equivalent circuit of display matrix portion (AR) and its peripheral circuits.

In FIG. 39, symbol AR denotes a display matrix portion (matrix array) in which a plurality of picture elements are two-dimensionally arranged.

In FIG. 39, symbol PX denotes a pixel electrode, in which additional characters G and B are added correspondingly to green and blue respectively. Symbols y0, y1, . . . , and yend of scanning signal line (GL) denote the sequence of scanning timing.

Scanning signal line (GL) is connected to vertical scanning circuit (V) and video signal line (DL) is connected to video signal driving circuit (H). Circuit (SUP) includes a power supply circuit for obtaining a plurality of stabilized voltage sources of divided voltages obtained from one voltage source and a circuit for converting the information for an CRT (cathode ray tube) sent from a host (host arithmetic processing unit) to the information for a (TFT) liquid crystal display device.

<<Driving Method>>

FIG. 40 is an illustration showing driving waveforms when driving the liquid crystal display device of the embodiment of the present invention. V.sub.G(i-1) and V.sub.G(i) denote the gate voltages (scanning signal voltages) applied to the (i-1)-th and (i)-th scanning signal lines (GL) respectively.

Moreover, V.sub.D(j) denotes a video signal voltage applied to video signal line (DL) and Vc denotes counter voltage (Vcom) applied to counter electrode (CT).

Furthermore, Vs(i,j) denotes a pixel electrode voltage applied to pixel electrode (PX) of the picture element at row (i) and column (j) and V.sub.LC(i,j) denotes a voltage applied to a liquid crystal layer of the picture element at row (i) and column (j).

The method for driving the liquid crystal display device of each embodiment of the present invention converts counter voltage (Vcom) applied to counter electrode (CT) to two AC rectangular waves of VCH and VCL as shown by Vc and changes non-selective voltages of gate voltage (VG) applied to gate electrode (GT) in two values of VGLH and VGLL for each scanning period synchronously with the AC rectangular waves.

In this case, the amplitude of counter voltage (Vcom) is made equal to that of non-selective voltages of gate voltage (VG).

Video signal voltage (VD) applied to video signal line (DL) is equal to voltage (VSIG) obtained by subtracting 1/2 of the amplitude of counter voltage (VC) from a voltage to be applied to a liquid crystal layer.

DC voltage, instead of AC voltage, can be used for counter voltage (Vcom) to be applied to counter electrode (CT). However, by using AC for counter voltage (Vcom), the maximum amplitude of video signal voltage (VD) can be reduced and a circuit with a low withstand voltage can be used for the video signal driving circuit (signal-side driver).

<<Functions of Storage Capacitance (Cstg)>>

Storage capacitance (Cstg) is used to store the video information written in picture elements for a long time after thin film transistor (TFT) is turned off.

In the case of an in-plane field type device, which is used for each embodiment of the present invention, video information cannot be stored in picture elements unless there is storage capacitance (Cstg) because a liquid crystal capacitance (Cpix) constituted between a pixel electrode (PX) and a counter electrode (CX) is so smaller than a capacitance (Cpix) of a vertical field type device that this capacitance (Cpix) can be hardly worked as a holding capacitance.

Therefore, storage capacitance (Cstg) is an indispensable component for the in-plane field type device.

Moreover, storage capacitance (Cstg) operates so as to decrease influences of gate potential change OVG) on pixel electrode potential (Vs) when thin film transistor (TFT) is switched.

This state is shown by an expression below.

[Mathematical Expression 1] .DELTA.Vs={Cgs/(Cgs+Cstg+Cpix)}.times..DELTA.VG

In the above expression, Cgs denotes a parasitic capacitance formed between gate electrode (GT) and source electrode (SD1) of thin film transistor (TFT), Cpix denotes a capacitance formed between pixel electrode (PX) and counter electrode (CT), and .DELTA.Vs denotes a change of a pixel electrode potential due to .DELTA.VG, that is, a so-called feed-through voltage.

Though the above change (.DELTA.Vs) is a cause of a DC component added to a liquid crystal layer, it can be decreased by increasing holding capacitance (Cstg).

Decrease of the DC component applied to liquid crystal layer (LCD) makes it possible to improve the life time of liquid crystal layer (LCD) and reduce the so-called sticking in which a latent image is left on a liquid crystal display screen.

As described above, because gate electrode (GT) is increased in size so as to cover i-type semiconductor layer (AS), the region overlapped with source electrode (SD1) and drain electrode (SD2) increases by the increased region of electrode (GT) and therefore, the disadvantages occur that parasitic capacitance (Cgs) increases and pixel electrode potential (Vs) is effected by gate voltage (scanning signal voltage)(VG).

However, by using storage capacitance (Cstg), the disadvantages can be settled.

<<Manufacturing Method>>

Then, a method for manufacturing the bottom transparent-glass substrate (SUB1) side of the liquid crystal display device described above is explained below by referring to FIGS. 36 to 38.

In FIGS. 36 to 38, characters at the center show abbreviations of step names, the left side shows the thin film transistor (TFT) portion shown in FIG. 32, and the right side shows the processing flow of sectional shapes nearby a gate terminal.

Steps A to I are classified correspondingly to each photographic processing except steps B and D. Any sectional view of each step shows a stage in which processing after photographic treatment is completed and photoresist is removed.

In the following description, photographic treatment is defined as a series of operations from application of photoresist to selective exposure using a mask and development of it and repetitive description is avoided.

Description is made below in accordance with classified steps.

(Step A, FIG. 36)

Conductive film (g1) with a thickness of 3,000 .ANG. comprising aluminum(Al)-palladium(Pd), aluminum(Al)-silicon(Si), aluminum(Al)-tantalum(Ta), or aluminum(Al)-titanium(Ti)-tantalum(Ta) is formed on bottom transparent-glass substrate (SUB1) by sputtering.

After photographic treatment, conductive film (g1) is selectively etched by a mixed acid solution of phosphoric acid, nitric acid, glacial acetic acid, and water.

Thereby, anodic oxide bus line (SHg) (not illustrated) for connecting gate electrode (GT), scanning signal line (GL), counter electrode (CT), counter voltage signal line (CL), electrode (PL1), first conductive film of common bus line (CB), first conductive film of counter electrode terminal (CTM), and gate terminal (GTM) and anodic oxide pad (not illustrated) connected to anodic oxide bus line (SHg) are formed.

(Step B, FIG. 36)

Anodic oxide mask (AO) is formed by direct drawing and thereafter, bottom transparent-glass substrate (SUB1) is soaked in an anodic oxide solution obtained by diluting a solution which is obtained by preparing 3% tartaric acid with ammonia to PH of 6.25.+-.0.05 with an ethylene glycol solution to 1:9 to make adjustment so that a formation-current density comes to 0.5 mA/cm.sup.2 (constant current formation).

Then, anodizing is performed until a formation voltage of 125 V is reached which is necessary to obtain aluminum oxide film (AOF) with a predetermined thickness.

Thereafter, it is preferable to keep aluminum oxide film (AOF) under the above state for tens of minutes (constant voltage formation).

This is important to obtain homogeneous aluminum oxide film (AOF).

Thereby, conductive film (g1) is anode-oxidized and anodic oxide film (AOF) with a thickness of 1,800A is formed on gate electrode (GT), scanning signal line (GL), counter electrode (CT), counter voltage signal line (CL), and electrode (PL1).

(Step C, FIG. 36)

Transparent conductive film (g2) made of an ITO film with a thickness of 1,400 .ANG. is formed by sputtering.

After photographic treatment, transparent conductive film (g2) is selectively etched by a mixed acid solution of hydrochloric acid and nitric acid as an etching solution to form the highest layer of gate terminal (GTM), drain terminal (DTM), and the second conductive film of counter electrode terminal (CTM).

(Step D, FIG. 37)

Ammonia gas, silane gas, and nitrogen gas are introduced into a plasma CVD system to form a silicon nitride film (SiNx) with a thickness of 2,200 .ANG. and moreover, silane gas and hydrogen gas are introduced into the plasma CVD system to form an i-type amorphous silicon (Si) film with a thickness of 2,000 .ANG.. Thereafter, hydrogen gas and phosphine gas are introduced into the plasma CVD system to form N(+)-type amorphous silicon (Si) film with a thickness of 300 .ANG..

(Step E, FIG. 37)

After photographic treatment, i-type semiconductor pattern (AS) is formed by using carbon tetrachloride (CCl.sub.4) and sulfur hexafluoride (SF.sub.6) as dry etching gases and thereby selectively etching an N(+)-type amorphous silicon (Si) film and i-type amorphous silicon (Si) film.

(Step F, FIG. 37)

After photographic treatment, a silicon nitride film is selectively etched by using sulfur hexa