JP3644653B2

JP3644653B2 - Liquid crystal display

Info

Publication number: JP3644653B2
Application number: JP20865996A
Authority: JP
Inventors: 康裕森井; 文雄松川; 顕津村; 伸田畑; 昌也水沼; 晃玉谷; 雅之藤井
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1996-08-07
Filing date: 1996-08-07
Publication date: 2005-05-11
Anticipated expiration: 2016-08-07
Also published as: JPH1048671A

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device which allows driving with a low voltage and has excellent display characteristics. SOLUTION: Comb-shaped pixel electrodes 11 and common electrodes 12 are arranged on a substrate 13 and a counter substrate 14 in such a manner that the teeth of respective combs are paralleled and alternated with each other. When voltage is impressed on the liquid crystal display device, an electric field in a diagonal direction is generated by the pixel electrodes 11 and the common electrodes 12 and liquid crystal molecules 10b having positive dielectric anisotropy are oriented along the electric field in a diagonal direction. The pixel electrodes 11 and the common electrodes 12 are preferably arranged by parting the spacings therebetween in such a manner that the electric field in a diagonal direction is made more nearly horizontal in order to eliminate the dependence of the liquid crystal molecules 10b on visual field angles. On the other hand, a higher driving voltage is made necessary in order to make the inter-electrode spacing larger. Then, the angle A formed by the electric field direction with the substrate surface with respect to the liquid crystal display device having a cell gap of 4 to 10μm is set larger than 20 deg. and below 45 deg..

Description

【０００１】
【発明の属する技術分野】
この発明は、液晶表示装置、特にその駆動電圧の低下と表示特性の向上に関するものである。
【０００２】
【従来の技術】
液晶表示装置は、薄型、軽量、低消費電力等の特長を有するため、腕時計、電卓等の表示装置として広く用いられている。特に、薄膜トランジスタ（ＴＦＴ）等によりアクティブ駆動を行うツイストネマティック（ＴＮ）型液晶表示装置は、ワードプロセッサー、パーソナルコンピュータ等の表示装置やテレビ等において、従来の最も一般的な表示装置であるＣＲＴに置き換わりつつある。しかしこのＴＮ型液晶表示装置は、一般的に視野角が狭く、斜め方向から眺めた時に、コントラスト低下、階調反転として観察されるという問題を持っている。特に近年液晶表示装置の大型化が進み、同一の観察点から表示面の上下左右端を眺めた場合にでさえ表示に差が見られるため、視野角の拡大が求められている。
【０００３】
この斜め方向から観察したときの表示品位低下の原因としては、ＴＮ型液晶表示装置では液晶分子の電界による立ち上がりを利用して表示を行っており、その立ち上がり方向に異方性があるために生じると考えられている。つまり、一方向から立ち上がる液晶分子を種々の方向から眺めると、その光学的寄与が変化するため視野角に対する表示変化が生じると考えられ、ＴＮ型液晶表示装置の本質的問題であると言える。このような問題を解決するために、最近、面内応答型液晶表示装置が提案されている。
【０００４】
図３は、従来の面内応答型液晶表示装置を示す構造図である。図３−ａは、従来より用いられている櫛型の面内応答型液晶表示装置の１画素の上面図を示す。図において、１はソース線、２はゲート線、３は画素部、４および５は櫛型の電極、６はスイッチング素子である薄膜トランジスタ（ＴＦＴ）部、７はコモン線をそれぞれ示す。一般的な画素構成は、従来よりＴＮ液晶を用いたアクティブマトリクス型ＴＦＴ素子と同様に、映像信号を伝えるデータ用信号線いわゆるソース線１と画素部３に信号を入力するための走査用信号線いわゆるゲート線２および画素部３に映像信号を書き込むＴＦＴ６を有する。面内応答型液晶表示装置の特徴は画素部３にあり、画素部３は、映像信号が書き込まれる櫛型の電極４とこれに面内方向で対応する櫛型の電極５を有し、かつ電極５はコモン線７と接続されている。図３−ｂは、画素部３の拡大図を示す。ＴＦＴ６から書き込まれた映像信号は、電極４に一定の電位を発生する。電極５は、コモン線７と接続されているため、コモン線７の電位を調節することにより、ある電位を電極４、５間に与えることができる。
【０００５】
図４−ａは、上記従来の面内応答型液晶表示装置の電極４、５から発生する電界を示す断面図である。図において、８は櫛形の電極４、５が形成された画素電極基板、９は対向基板である。対向基板９は、従来のＴＮ型液晶用ＴＦＴパネルとは異なり、電極を有する必要はなく、画素電極基板８との一定のパネル間隙内に液晶を封入するためのものである。電極４、５間に発生した電界は、図に示すように対向基板９側に近づくにつれ若干山型になる。図４−ｂは、負の誘電異方性を有する液晶材料を用いた時の図４−ａに示す電界に対する液晶の配向状態を示す断面図である。図において１０ａは負の誘電異方性を有する液晶を示す。負の液晶材料１０ａは、分子の短軸方向に誘電異方性を有するため、電界方向に対し短軸が沿う。対向基板９方向から見た視野角はＴＮ型液晶用ＴＦＴパネルに比べて広くなり、且つ電極４、５間全域にわたりディスクリネーションを発生することがない。
【０００６】
【発明が解決しようとする課題】
以上のように、従来の面内応答型液晶表示装置では、表示特性が良好であることから一般的に負の誘電異方性を有する液晶１０ａが用いられていた。しかし、現在発見されている負の誘電異方性をもつ液晶材料は数が少なく、ディスプレイ用液晶として使用できる特性を持つものは誘電異方性の絶対値が小さく、液晶を駆動するために高い電圧が必要になるという問題があった。このため、現在のＴＮ液晶に代表される正の誘電異方性を有する液晶材料の適用が望まれている。図４−ｃは、従来の面内応答型液晶表示装置に正の誘電異方性を有する液晶を用いた時の、電界に対する液晶の配向状態を示す断面図である。図において１０ｂは正の誘電異方性を有する液晶を示す。正の誘電異方性を有する液晶材料１０ｂは、駆動電圧、応答速度、電圧保持率等の諸特性は安定しているが、従来の面内応答型液晶表示装置に用いた場合、山型になった電界方向に液晶分子長軸が沿って配向するため、その頂点部分に異なる配向状態の液晶のぶつかりであるディスクリネーションラインが発生する。このディスクリネーションラインの発生／消失はヒステリシスを描くため残像が発生し、表示品位が低下するという問題があった。
【０００７】
この発明は、上記のような問題点を解消するためになされたもので、低電圧駆動が可能で、残像が無く、表示特性に優れた液晶表示装置を得ることを目的とする。
【０００８】
【課題を解決するための手段】
この発明に係わる液晶表示装置は、基板上に配置された複数本の走査用信号線とデータ用信号線の各交点に設けられた薄膜トランジスタに接続され、互いに平行に配置された遮光性を有する導電体からなる複数の画素電極、基板と対をなす対向基板上に、画素電極の中間位置に対向して互いに平行に配置された遮光性を有する導電体からなる複数のコモン電極、一対の基板間に配向膜を介して挟持された正の誘電異方性を有する液晶を備え、画素電極およびコモン電極間に電圧を印加し、基板面に斜め方向に電界を発生させ液晶を面内応答させることにより光学特性を制御する液晶表示装置であって、一対の基板の間隔を約４〜１０μｍとすると共に、斜め方向の電界の角度すなわち画素電極およびコモン電極間の最短距離を結ぶ線と基板とのなす角度が２０度より大きく４５度以下であるものである。
また、画素電極およびコモン電極は、櫛型電極としたものである。
【０００９】
【発明の実施の形態】
実施の形態１．
以下に、本発明の実施の形態１である液晶表示装置を図について説明する。図１−ａは、本発明の実施の形態１である液晶表示装置の１画素に対する上下電極パターンを示す斜視図、図１−ｂは、１画素に対する電極の上面図、図２は電界に対する液晶分子の配向状態を示す断面図である。図において、１１は櫛型の画素電極、１２は同じく櫛型のコモン電極、１３は画素電極１１が形成された基板、１４はコモン電極１２が形成された基板、１５は配向膜をそれぞれ示す。なお、図中、同一、相当部分には同一符号を付し、説明を省略する。また、図１に示す電極構成は、１画素を示しているが、同構造は１画素に限定されるものでなく、基板全面が１画素構造をとる場合もある。本実施の形態では、全画素にわたり同様の画素構造をとるものである。
【００１０】
本実施の形態による液晶表示装置の作成方法について説明する。例えばガラスよりなる基板１３上に、櫛型の画素電極１１を形成する。画素電極１１は、薄膜トランジスタ（ＴＦＴ）部６を有し、ゲート線２とソース線１に接続されている。次に対向基板であるガラス基板１４上に、櫛型のコモン電極１２を形成する。コモン電極１２は一定信号が基板面全域の電極に伝わる構造であればどのような構造でもよい。画素電極１１およびコモン電極１２は、一画素ピッチ毎に櫛型をしており、櫛の歯の部分に当たる電極に対して、櫛の歯の隙間に当たる部分は非導電部であり、光が透過するように透明に近い絶縁体、例えばＳｉＮ、ＳｉＯ2 等が形成されているか、またはガラス基板１４が見える構造になっている。また、電極部は、遮光性を有する導電体、例えばＣｒ、ＡｌまたはＭｏ等であることが望ましい。なお、画素電極１１およびコモン電極１２の電極幅は５〜５０μｍ程度であり、間隔は２〜５０μｍ程度である。ただし、電極幅および電極間隔は、上記の数値に限定するものではなく、電極幅は細いほど、電極間隔は広いほど、開口率が向上するため望ましい。これらの２つの櫛型の電極は、互いにそれぞれの櫛の歯が平行且つ交互に等間隔で配置されている。すなわち、コモン電極１２の櫛の歯の隙間に相当する非導電部の中央部に、画素電極１１の櫛の歯に相当する電極が配置され、同様に、画素電極１１の櫛の歯の隙間に相当する非導電部の中央部に、コモン電極１３の櫛の歯に相当する電極が配置されている。このように配置することで、各電極間で発生する電界の強さが等しくなる。
【００１１】
画素電極１１およびコモン電極１２の形成後、それぞれの基板１３、１４表面にポリイミド配向膜１５、例えば日本合成ゴム製Ａｌ−１０４４を形成する。次に、基板１３、１４を図１−ａ中に示すＲ、Ｆの方向にそれぞれラビングする。ラビング方向は、基本的には画素電極１１およびコモン電極１２に対し水平方向に行うが、電界が加わった時の液晶分子の回転方向を規制するために、電極に対し０度以上４５度以下の角度を有してラビングする場合が多い。
上記のように形成された２枚の基板１３、１４をそれぞれのラビング方向Ｆ、Ｒが反平行または平行に重ねあわせ、上下基板の間隔を４〜１０μｍとしてセルを作成する。この基板間に正の誘電異方性を有するネマティック液晶、例えばチッソ製ＭＳ５０１７を注入し、所望の液晶セルが得られる。
【００１２】
図２は、本実施の形態による液晶表示装置に電圧を印加した場合の液晶分子の配向状態を示す断面図である。図においてＬは画素電極１１とコモン電極１２との最短距離、Ａは上記Ｌと基板１３面とのなす角度であり、電界方向のなす角を示す。電圧を印加すると、画素電極１１とコモン電極１２により斜め方向の電界が発生し、正の誘電異方性を有する液晶分子１０ｂは、この斜め方向の電界に沿って配向する。本実施の形態による液晶表示装置では、基板１３、１４間に斜め方向の電界を発生させるため、例えば基板１４側から画像を見た場合、液晶分子１０ｂを斜め方向から見ることになる。液晶分子１０ｂは、長軸方向と短軸方向に屈折率の異方性を有するため、視野角の依存性が発生してしまう。これを解消するためには斜め方向の電界がより水平に近くなるように画素電極１１およびコモン電極１２を配置し、液晶１０ｂの長軸方向が、基板に対しほぼ水平に配向することが望ましい。一方、斜め方向の電界をより水平にするためには、画素電極１１およびコモン電極１２それぞれの櫛の歯に相当する電極間隔を大きくとらなければならないため、必要な電圧を液晶分子１０ｂに加えるためにより高い駆動電圧が必要となる。
【００１３】
以上のことから、セルギャップ４〜１０μｍの液晶表示装置に対し、基板表面に対する電界方向のなす角度Ａを２０度より大きく、４５度以下にする必要がある。角度Ａが４５度以上であった場合、ディスクリネーションが大きく発生し、さらに、液晶１０ｂの屈折率異方性が視野角依存性を生じるため、４５度以下にする必要がある。また、２０度以下であった場合、セルギャップ４μｍにおいて画素電極１１と対向するコモン電極１２の距離Ｌに対しＬｃｏｓＡが約１１μｍ以上となり、現在の液晶の駆動電圧と、アクティブマトリクス素子を用いた時に液晶部に加えることができる電圧を考慮すると、１１μｍ以上の間隔にすることは難しい。セルギャップが４μｍ以上の時は、櫛の歯の間隔をさらに大きくする必要があるため、より困難である。なお、セルギャップは薄すぎると駆動電圧が高くなり、厚すぎると応答速度が遅くなるため、本実施の形態における液晶モードには、４〜１０μｍ程度が選択されている。
【００１４】
本実施の形態による液晶表示装置の動画特性を計測した結果、ディスクリネーションラインは発生せず、また、視野角依存性も顕著に現われず、残像のない良好な表示特性が得られた。
【００１５】
【発明の効果】
以上のように、この発明によれば、対向する基板上に形成された遮光性を有する導電体からなる画素電極およびコモン電極間に電圧を印加し、基板面に斜め方向に電界を発生させ液晶を応答させる液晶表示装置において、一対の基板の間隔を約４〜１０μｍとすると共に、斜め方向の電界の角度すなわち画素電極およびコモン電極間の最短距離を結ぶ線と基板とのなす角度を２０度より大きく４５度以下としたので、ディスクリネーションの発生がなく、さらに視野角依存性のない良好な表示特性を有する液晶表示装置を得ることが可能である。
【００１６】
さらに、正の誘電異方性を有する液晶を用いることができるので、低電圧駆動が可能で保持率が高く、信頼性の高い液晶表示装置が得られる効果がある。
【図面の簡単な説明】
【図１】この発明の実施の形態１である液晶表示装置の一画素電極を示す斜視図および上面図である。
【図２】この発明の実施の形態１である液晶表示装置における電圧印加時の液晶の配向状態を示す断面図である。
【図３】従来の面内応答型液晶表示装置を示す上面図および拡大図である。
【図４】従来の面内応答型液晶表示装置における電圧印加時に発生する電界と液晶の配向状態を示す断面図である。
【符号の説明】
１ソース線、２ゲート線、３画素部、４、５電極、
６薄膜トランジスタ（ＴＦＴ）部、７コモン線、８画素電極基板、
９対向基板、１０ａ負の誘電異方性を有する液晶、
１０ｂ正の誘電異方性を有する液晶、１１画素電極、１２コモン電極、
１３、１４基板、１５配向膜。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a reduction in driving voltage and an improvement in display characteristics.
[0002]
[Prior art]
Liquid crystal display devices are widely used as display devices for wristwatches, calculators, and the like because they have features such as thinness, light weight, and low power consumption. In particular, twisted nematic (TN) type liquid crystal display devices that are actively driven by thin film transistors (TFTs) and the like are replacing CRTs, which are the most common conventional display devices, in display devices such as word processors and personal computers, and televisions. is there. However, this TN type liquid crystal display device has a problem that the viewing angle is generally narrow, and when viewed from an oblique direction, it is observed as a decrease in contrast and gradation inversion. Particularly, in recent years, liquid crystal display devices have been increased in size, and even when the top, bottom, left, and right edges of the display surface are viewed from the same observation point, a difference in display can be seen.
[0003]
The cause of the deterioration in display quality when observed from the oblique direction is that the TN type liquid crystal display device performs display using the rising of the liquid crystal molecules due to the electric field, and the rising direction has anisotropy. It is believed that. That is, when the liquid crystal molecules rising from one direction are viewed from various directions, the optical contribution is changed, so that it is considered that the display changes with respect to the viewing angle, which is an essential problem of the TN liquid crystal display device. In order to solve such a problem, an in-plane response type liquid crystal display device has been recently proposed.
[0004]
FIG. 3 is a structural view showing a conventional in-plane response type liquid crystal display device. FIG. 3A is a top view of one pixel of a conventional comb-type in-plane response liquid crystal display device. In the figure, 1 is a source line, 2 is a gate line, 3 is a pixel portion, 4 and 5 are comb-shaped electrodes, 6 is a thin film transistor (TFT) portion which is a switching element, and 7 is a common line. A general pixel configuration is a data signal line for transmitting a video signal, a so-called source line 1 and a scanning signal line for inputting a signal to the pixel unit 3 in the same manner as an active matrix TFT element using a TN liquid crystal. A so-called gate line 2 and a TFT 6 for writing a video signal to the pixel portion 3 are provided. The in-plane response type liquid crystal display device is characterized in the pixel unit 3, which has a comb-shaped electrode 4 to which a video signal is written and a comb-shaped electrode 5 corresponding to this in the in-plane direction, and The electrode 5 is connected to the common line 7. FIG. 3B shows an enlarged view of the pixel unit 3. The video signal written from the TFT 6 generates a constant potential at the electrode 4. Since the electrode 5 is connected to the common line 7, a certain potential can be applied between the electrodes 4 and 5 by adjusting the potential of the common line 7.
[0005]
FIG. 4A is a cross-sectional view showing an electric field generated from the electrodes 4 and 5 of the conventional in-plane response type liquid crystal display device. In the figure, 8 is a pixel electrode substrate on which comb-shaped electrodes 4 and 5 are formed, and 9 is a counter substrate. Unlike the conventional TN type liquid crystal TFT panel, the counter substrate 9 does not need to have electrodes, and is for sealing liquid crystal in a certain panel gap with the pixel electrode substrate 8. As shown in the figure, the electric field generated between the electrodes 4 and 5 becomes slightly mountain-shaped as it approaches the counter substrate 9 side. FIG. 4-b is a cross-sectional view showing the alignment state of the liquid crystal with respect to the electric field shown in FIG. 4-a when a liquid crystal material having negative dielectric anisotropy is used. In the figure, reference numeral 10a denotes a liquid crystal having negative dielectric anisotropy. Since the negative liquid crystal material 10a has dielectric anisotropy in the minor axis direction of the molecule, the minor axis is aligned with the electric field direction. The viewing angle viewed from the direction of the counter substrate 9 is wider than that of the TN liquid crystal TFT panel, and disclination does not occur across the entire area between the electrodes 4 and 5.
[0006]
[Problems to be solved by the invention]
As described above, in the conventional in-plane response type liquid crystal display device, the liquid crystal 10a having negative dielectric anisotropy is generally used because of its good display characteristics. However, there are few liquid crystal materials with negative dielectric anisotropy that have been discovered at present, and those with characteristics that can be used as display liquid crystals have a small absolute value of dielectric anisotropy and are high for driving liquid crystals. There was a problem that voltage was required. For this reason, application of a liquid crystal material having positive dielectric anisotropy represented by the current TN liquid crystal is desired. FIG. 4C is a cross-sectional view showing the alignment state of the liquid crystal with respect to the electric field when a liquid crystal having positive dielectric anisotropy is used in the conventional in-plane response type liquid crystal display device. In the figure, reference numeral 10b denotes a liquid crystal having positive dielectric anisotropy. The liquid crystal material 10b having positive dielectric anisotropy has stable characteristics such as drive voltage, response speed, voltage holding ratio, etc., but when used in a conventional in-plane response type liquid crystal display device, it has a mountain shape. Since the major axis of the liquid crystal molecules is aligned along the direction of the electric field, a disclination line, which is a collision of liquid crystals with different alignment states, is generated at the apex portion. The occurrence / disappearance of this disclination line has a problem that a residual image is generated due to a hysteresis and the display quality is deteriorated.
[0007]
The present invention has been made to solve the above problems, and an object of the present invention is to obtain a liquid crystal display device that can be driven at a low voltage, has no afterimage, and has excellent display characteristics.
[0008]
[Means for Solving the Problems]
The liquid crystal display device according to the invention is connected to a thin film transistor provided at each intersection of the plurality of scanning signal lines and data signal lines disposed on the substrate, having a light-shielding property which are arranged parallel to each other A plurality of pixel electrodes made of a conductor, a plurality of common electrodes made of a light-shielding conductor disposed in parallel with each other on a counter substrate that is paired with the substrate, facing a middle position of the pixel electrode, and a pair of substrates A liquid crystal having a positive dielectric anisotropy sandwiched between alignment films is applied. A voltage is applied between the pixel electrode and the common electrode to generate an electric field in an oblique direction on the substrate surface, thereby causing the liquid crystal to respond in-plane. a liquid crystal display device which controls the optical properties by, while about 4~10μm the gap between the pair of substrates, the lines and the substrate connecting the shortest distance between the oblique direction of the electric field of the angles, or the pixel electrode and the common electrode Nasu angle is not more than 45 degrees greater than 20 degrees.
Further, the pixel electrode and the common electrode are comb electrodes.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
The liquid crystal display device according to the first embodiment of the present invention will be described below with reference to the drawings. 1A is a perspective view showing an upper and lower electrode pattern for one pixel of the liquid crystal display device according to Embodiment 1 of the present invention, FIG. 1B is a top view of an electrode for one pixel, and FIG. 2 is a liquid crystal against an electric field. It is sectional drawing which shows the orientation state of a molecule | numerator. In the figure, 11 is a comb-shaped pixel electrode, 12 is a comb-shaped common electrode, 13 is a substrate on which the pixel electrode 11 is formed, 14 is a substrate on which the common electrode 12 is formed, and 15 is an alignment film. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof is omitted. Further, although the electrode configuration shown in FIG. 1 shows one pixel, the structure is not limited to one pixel, and the entire substrate surface may have a one-pixel structure. In the present embodiment, the same pixel structure is adopted over all pixels.
[0010]
A method for manufacturing a liquid crystal display device according to this embodiment will be described. For example, a comb-shaped pixel electrode 11 is formed on a substrate 13 made of glass. The pixel electrode 11 has a thin film transistor (TFT) portion 6 and is connected to the gate line 2 and the source line 1. Next, a comb-shaped common electrode 12 is formed on a glass substrate 14 which is a counter substrate. The common electrode 12 may have any structure as long as the constant signal is transmitted to the electrodes on the entire substrate surface. The pixel electrode 11 and the common electrode 12 are comb-shaped for each pixel pitch, and the portion of the comb electrode corresponding to the gap between the comb teeth is a non-conductive portion, and light is transmitted to the electrode corresponding to the portion of the comb teeth. Thus, an insulator that is almost transparent, such as SiN, SiO2, or the like, is formed, or the glass substrate 14 can be seen. The electrode portion is preferably a light-shielding conductor such as Cr, Al, or Mo. The electrode width of the pixel electrode 11 and the common electrode 12 is about 5 to 50 μm, and the interval is about 2 to 50 μm. However, the electrode width and the electrode interval are not limited to the above numerical values, and the thinner the electrode width and the wider the electrode interval, the better the aperture ratio. These two comb-shaped electrodes have their comb teeth arranged in parallel and alternately at equal intervals. That is, an electrode corresponding to the comb teeth of the pixel electrode 11 is arranged in the center of the non-conductive portion corresponding to the gap of the comb teeth of the common electrode 12. An electrode corresponding to a comb tooth of the common electrode 13 is arranged at the center of the corresponding non-conductive portion. By arranging in this way, the strength of the electric field generated between the electrodes becomes equal.
[0011]
After the formation of the pixel electrode 11 and the common electrode 12, a polyimide alignment film 15, for example, Al-1044 made of Japan Synthetic Rubber, is formed on the surfaces of the substrates 13 and 14, respectively. Next, the substrates 13 and 14 are rubbed in the directions of R and F shown in FIG. The rubbing direction is basically performed in a horizontal direction with respect to the pixel electrode 11 and the common electrode 12, but in order to regulate the rotation direction of the liquid crystal molecules when an electric field is applied, the rubbing direction is not less than 0 degree and not more than 45 degrees with respect to the electrode. Rubbing is often performed at an angle.
The two substrates 13 and 14 formed as described above are overlapped so that the rubbing directions F and R are antiparallel or parallel to each other, and a cell is formed with an interval between the upper and lower substrates of 4 to 10 μm. Nematic liquid crystal having positive dielectric anisotropy, for example, MS5017 manufactured by Chisso, is injected between the substrates to obtain a desired liquid crystal cell.
[0012]
FIG. 2 is a cross-sectional view showing the alignment state of liquid crystal molecules when a voltage is applied to the liquid crystal display device according to the present embodiment. In the figure, L is the shortest distance between the pixel electrode 11 and the common electrode 12, and A is an angle formed by L and the surface of the substrate 13, and indicates an angle formed by the electric field direction. When a voltage is applied, an oblique electric field is generated by the pixel electrode 11 and the common electrode 12, and the liquid crystal molecules 10b having positive dielectric anisotropy are aligned along the oblique electric field. In the liquid crystal display device according to the present embodiment, since an electric field in an oblique direction is generated between the substrates 13 and 14, for example, when the image is viewed from the substrate 14 side, the liquid crystal molecules 10b are viewed from the oblique direction. Since the liquid crystal molecules 10b have refractive index anisotropy in the major axis direction and the minor axis direction, dependency on the viewing angle occurs. In order to solve this problem, it is desirable that the pixel electrode 11 and the common electrode 12 are arranged so that the electric field in the oblique direction is closer to the horizontal, and the major axis direction of the liquid crystal 10b is aligned substantially horizontally with respect to the substrate. On the other hand, in order to make the electric field in the oblique direction more horizontal, the electrode interval corresponding to the comb teeth of the pixel electrode 11 and the common electrode 12 must be made large, so that a necessary voltage is applied to the liquid crystal molecules 10b. Therefore, a higher driving voltage is required.
[0013]
From the above, for a liquid crystal display device with a cell gap of 4 to 10 μm, the angle A formed by the electric field direction with respect to the substrate surface needs to be greater than 20 degrees and less than 45 degrees. When the angle A is 45 degrees or more, a large disclination occurs, and furthermore, since the refractive index anisotropy of the liquid crystal 10b has a viewing angle dependency, it is necessary to make it 45 degrees or less. When the angle is 20 degrees or less, LcosA is about 11 μm or more with respect to the distance L of the common electrode 12 facing the pixel electrode 11 in the cell gap of 4 μm, and when the current liquid crystal driving voltage and the active matrix element are used. Considering the voltage that can be applied to the liquid crystal part, it is difficult to set the interval to 11 μm or more. When the cell gap is 4 μm or more, it is more difficult because the interval between the comb teeth needs to be further increased. Note that if the cell gap is too thin, the driving voltage becomes high, and if it is too thick, the response speed becomes slow. Therefore, about 4 to 10 μm is selected as the liquid crystal mode in the present embodiment.
[0014]
As a result of measuring the moving image characteristics of the liquid crystal display device according to the present embodiment, no disclination line was generated, the viewing angle dependency was not remarkably exhibited, and good display characteristics without an afterimage were obtained.
[0015]
【The invention's effect】
As described above, according to the present invention, a voltage is applied between the pixel electrode made of a light-shielding conductor formed on the opposing substrate and the common electrode to generate an electric field in an oblique direction on the surface of the liquid crystal. In the liquid crystal display device that responds to the above, the distance between the pair of substrates is about 4 to 10 μm, and the angle formed between the substrate and the angle of the oblique electric field, that is, the line connecting the shortest distance between the pixel electrode and the common electrode is 20 degrees. Since the angle is larger than 45 degrees, it is possible to obtain a liquid crystal display device having good display characteristics that is free from disclination and has no viewing angle dependency.
[0016]
Further, since a liquid crystal having positive dielectric anisotropy can be used, there is an effect that a liquid crystal display device that can be driven at a low voltage, has a high retention rate, and has high reliability can be obtained.
[Brief description of the drawings]
1 is a perspective view and a top view showing one pixel electrode of a liquid crystal display device according to Embodiment 1 of the present invention;
FIG. 2 is a cross-sectional view showing a liquid crystal alignment state when a voltage is applied in the liquid crystal display device according to the first embodiment of the present invention.
FIG. 3 is a top view and an enlarged view showing a conventional in-plane response type liquid crystal display device.
FIG. 4 is a cross-sectional view showing an electric field generated when a voltage is applied and a liquid crystal alignment state in a conventional in-plane response type liquid crystal display device.
[Explanation of symbols]
1 source line, 2 gate line, 3 pixel part, 4 and 5 electrode,
6 thin film transistor (TFT) section, 7 common line, 8 pixel electrode substrate,
9 counter substrate, 10a liquid crystal having negative dielectric anisotropy,
10b liquid crystal having positive dielectric anisotropy, 11 pixel electrode, 12 common electrode,
13, 14 Substrate, 15 Alignment film.

Claims

Is connected to a thin film transistor provided at each intersection of the plurality of scanning signal lines and data signal lines disposed on the substrate, a plurality of pixel electrodes made of a conductive material having a light shielding property which are arranged parallel to each other,
A plurality of common electrodes made of a light-shielding conductor disposed in parallel with each other on a counter substrate that is paired with the substrate, facing an intermediate position of the pixel electrode;
A liquid crystal having positive dielectric anisotropy sandwiched between the pair of substrates via an alignment film, and applying a voltage between the pixel electrode and the common electrode to generate an electric field in an oblique direction on the substrate surface; A liquid crystal display device that controls optical characteristics by causing liquid crystal to respond,
The distance between the pair of substrates is about 4 to 10 μm, and the angle formed between the line connecting the shortest distance between the pixel electrode and the common electrode and the pixel electrode substrate is greater than 20 degrees and less than 45 degrees. A liquid crystal display device.

The liquid crystal display device according to claim 1, wherein the pixel electrode and the common electrode are comb electrodes.