JP2004354407A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a liquid crystal display device in which a moving picture blurring is suppressed and which can deal with moving pictures in high quality by heightening the response speed and in particular, shortening the response time of falling. <P>SOLUTION: A third electrode, different from a first electrode (a pixel electrode) and a second electrode (a common electrode) formed on one substrate, is formed on the other substrate side. The electric potential of the third electrode 5 is varied within a frame period. Liquid crystal molecules are driven by utilizing a lateral electric field produced between the first and second electrodes 3, 4 during a picture display time period and with a vertical electric field produced between the first and second electrodes 3, 4 and the third electrode 5 in the initial stage of a picture non-display time period. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【数２】

ここで、γ_１ は液晶の粘度、Δεは誘電率異方性、Ｋ_２ は弾性定数、ｄは液晶層の厚み（ギャップ）、Ｅは液晶に印加される電界強度である。
【００１３】
（式１）から分かるように、液晶の立上り応答時間は、液晶の粘度や弾性定数、誘電率などの材料物性に加え、液晶に印加される電界強度に大きく影響される。従って、立上り応答時間を短縮するために、以下２つのアプローチがある。
【００１４】
▲１▼ 液晶材料開発によるアプローチ
▲２▼ 電界強度の高効率化によるアプローチ
▲１▼については、液晶の低粘度化や、高Δε化などが提案されている。また、▲２▼については、一時的に必要以上の電圧を印加し、実効的な電界強度を大きくするオーバードライブ駆動や、「特許文献３」に示されているように、対向基板側に新規に共通電極を配置し、液晶に印加される電界の効率を向上させる手段が提案されている。このように２つのアプローチ（材料開発と駆動の改善）により十分に立上り応答時間を改善することは可能である。
【００１５】
一方、立下り応答時間は（式２）から分かるように、材料物性だけで決まり、電界強度に影響されないため、上記のオーバードライブ駆動や、「特許文献３」に示された電極構造によって改善することは困難である。現状では、主に液晶材料の低粘度化によってのみ立下り時間を改善しているに過ぎない。しかし、今後の動画対応の液晶表示装置の画質向上を考えれば、特に立下り応答時間のさらなる短縮化は必須であり、液晶材料物性の改良だけでは困難な状況である。
【００１６】
また、特に動画対応の液晶表示装置では、上記「動画ぼやけ」の原因（２）を改善し、インパルス型表示を実現するために、例えば１フレーム内で映像信号を書き込んだ後に黒レベルに相当する信号を書き込み、液晶の透過率を間欠にする黒書き込み駆動が「特許文献２」などに提案されている。これらの提案された技術においても、立下り応答時間は大きく影響する。
【００１７】
図３１はＩＰＳ方式の液晶表示装置における黒書き込み駆動する場合の信号波形例の説明図である。図３１では、１フレーム（１ｆｒａｍｅ）内で黒レベルに相当する信号を書き込む２倍速駆動の例である。波形（ａ）のＶ_Ｇ は走査配線に供給される信号波形（Ｖ_ＧＨはハイレベル、Ｖ_ＧＬはローレベル）、波形（ｂ）のＶ_Ｄ は信号配線に供給される信号波形（Ｖ_ＤＨはハイレベル、Ｖ_ＤＬはローレベル）、波形（ｃ）のＶ_Ｓ は画素電極に印加される信号波形である。なお、波形（ｄ）のＶ_Ｃ は共通電極に印加される信号波形、ＧＮＤはグランドレベルを示す。
【００１８】
このとき、図３１（ｅ）に示すように、立下り応答が遅い場合には輝度立下り時において十分な黒レベルまで低下しないために理想的な間欠表示とはならない。従って、現行のように液晶の応答速度が遅い場合には、黒書き込み駆動により、「動画ぼやけ」をある程度改善すること可能であるが、十分に改善することはできない。
【００１９】
さらに、インパルス型表示を実現するための別の手段として、光源を１フレーム内で点灯状態と消灯状態を有するブリンクバックライト方式が提案されている。図３２はブリンクバックライト方式における液晶透過率変化を説明する波形図である。図３２における（ａ）は液晶パネル（図では単にパネルと表記）の上段における液晶透過率、（ｂ）はパネル中段における液晶透過率、（ｃ）はパネル下段における透過率、（ｄ）はバックライト（ＢＬ）の点灯（ｏｎ）・消灯（ｏｆｆ）のタイミングを示す。液晶表示装置では一般に線順次駆動がなされ、液晶パネルの上段（走査開始側）から下段に向かって、１フレーム内で信号の書き込みが行われ、その信号に応じて液晶の透過率が変化する。そして、バックライトはパネル中央部の液晶透過率が所定の透過率に達した時点で点灯される。このとき、信号書き込みのタイミングによりパネル上段では液晶透過率は立下り始めており、パネル下段では立ち上がる途中である。このような場合、本来の画像のデータ（映像信号）とは無関係な輝度（斜線部分）が人間の視覚で積算されることになり、ゴーストと呼ばれる二重像を生じる。このゴーストは、液晶表示装置において動画質の大きな劣化を招いており、この現象を抑制するためにも液晶の応答速度向上技術は必須である。
【００２０】
以上からわかるように、液晶応答速度の向上（特に立下り応答時間の短縮）は、動画対応液晶表示装置において必須の課題である。先に述べたように、液晶の立上り応答時間については、液晶材料物性の改良に加え、駆動や電極構造の工夫により向上することが提案されているが、立下り応答時間については、今のところ材料物性の改良でしか向上できない。しかし、今後の開発にはさらなる立下り応答時間の短縮は必須であり、それを可能とする液晶材料開発以外での新規な技術が必要である。
【００２１】
従って、本発明の目的は、液晶表示装置の輝度応答時間のうち、特に立下り応答時間を短縮することにより、動画質を大きく左右する「動画ぼやけ」を抑制し、高速応答を実現した高品質な動画対応液晶表示装置を提供することにある。
【００２２】
【課題を解決するための手段】
上記目的を達成するために、本発明は、少なくとも一方が透明な一対の基板と、前記一対の基板間に挟持された液晶の層と、前記一対の基板の一方にマトリクス状に配列された複数の画素の各画素毎にそれぞれ形成された電極群を有し、前記電極群の間に電圧を印加して前記液晶の配向方向を制御し、前記一対の基板の外側に設置した光源から入射する光の光量を調整することにより画像表示を行う液晶表示装置において、
画像表示期間では、前記一対の基板面にほぼ平行な電界により液晶を駆動し、画像非表示期間の初期段階では、前記一対の基板面にほぼ垂直な電界により前記液晶の配向方向を制御する液晶駆動手段を設けた。
【００２３】
上記液晶駆動手段を実現する一つの構成例として、前記一対の基板の前記第１の電極と第２の電極を形成した前記一方の基板に対向する他方の基板上に第３の電極を設け、
画像表示期間では、前記第１の電極と前記第２の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ平行な電界により液晶の配向方向を制御し、
画像非表示期間の初期段階では、前記第１の電極と前記第３の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ垂直な電界と、前記第２の電極と前記第３の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ垂直な電界により液晶の配向方向を制御する液晶駆動手段を設けた。
【００２４】
このとき、第１の電極と第２の電極は、櫛歯形状であることが望ましい。あるいは、第１の電極と第２の電極のうち、一方の電極は櫛歯形状であり、もう一方の電極は、画素のほぼ全面を覆うベタ状電極であり、櫛歯形状電極が絶縁膜を介してベタ状電極と重畳している構造でもよい。
【００２５】
さらに、第３の電極は、画素のほぼ全面を覆うベタ状電極であることが望ましい。また、このベタ状電極は、各画素で個別に駆動できることが望ましく、さらには全画素で一括駆動できることが望ましい。
【００２６】
また、上記手段を実現する他の構成例として、前記一対の基板の前記第１の電極と第２の電極を形成した前記一方の基板に対向する他方の基板上に第３の電極が形成され、
前記第１の電極及前記第２の電極と前記一方の基板との間に絶縁膜を介して形成された第４の電極を有し、
画像表示期間では、前記第１の電極と前記第２の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ平行な電界により液晶を駆動し、画像非表示期間の初期段階では、前記第３の電極と前記第４の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ垂直な電界により液晶の配向方向を制御する液晶駆動手段を設けた。
【００２７】
このとき、第１の電極と第２の電極は、櫛歯形状であることが望ましい。あるいは、第３の電極と第４の電極のうち少なくとも一方の電極は、画素のほぼ全面を覆うベタ状電極であってもよい。
【００２８】
さらに、ベタ状電極のうち、少なくとも一方のベタ状電極は、各画素で個別に駆動できることことが望ましく、さらには全画素で一括駆動できることが望ましい。
【００２９】
上記手段を実現するさらに他の構成例として、前記第１の電極と前記第２の電極が形成した前記一方の基板に対向する他方の基板上に第３の電極及び第４の電極が形成され、
画像表示期間は、前記第１の電極と前記第２の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ平行な電界と、前記第３の電極と前記第４の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ平行な電界により液晶の配向方向を制御し、画像非表示期間の初期段階では前記第１の電極と前記第３の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ垂直な電界と、前記第２の電極と前記第４の電極には異なる電位が与えられ該電極間に生じる基板面にほぼ垂直な電界により前記液晶の配向方向を制御する液晶駆動手段を設けた。
【００３０】
このとき、第１から第４の電極は、櫛歯形状であることが望ましい。あるいは、第１の電極と第３の電極は櫛歯形状であり、第２の電極と第４の電極は画素のほぼ全面を覆うベタ状電極であり、第１の電極は第２の電極上に絶縁膜を介して重畳し、さらに第３の電極は第４の電極上に絶縁膜を介して重畳していてもよい。
【００３１】
さらに、ベタ状電極は、各画素で個別に駆動できることが望ましく、さらには、全画素で一括駆動できることが望ましい。
【００３２】
また、上記電極構造において、効率よく本発明の効果を得るためには、以下の構成を用いることが望ましい。すなわち、３つの異なる電極を有する場合には、画像非表示期間の初期段階で第１の電極と第２の電極の電位をほぼ等しく、第３の電極の電位のみを異なる電位とする。
【００３３】
また、４つの異なる電極を有する場合には、画像非表示期間の初期段階で、第１の電極と第２の電極と第４の電極の電位をほぼ等しく、第３の電極の電位のみを異なる電位とする。さらには、画像非表示期間の初期段階で、第１の電極と第２の電極の電位をほぼ等しく、第３の電極と第４の電極との電位をほぼ等しく、そして、第１の電極と第３の電極を異なる電位とする。
【００３４】
上記手段を用いることにより、液晶表示装置の輝度応答時間のうち特に立下り応答時間を短縮し、これにより、動画質を大きく左右する「動画ぼやけ」を抑制した高品質な動画対応液晶表示装置を提供することができる。
【００３５】
なお、前記液晶層の液晶分子はホモジニアス配向であり、その誘電率異方性は正であることが望ましい。また、前記電極のうち少なくとも一つは透明導電膜で形成し、前記櫛歯電極は、くの字型に形成することが望ましい。また、前記対向基板に前記第３の電極のみが形成される構成においては、前記第３の電極と前記液晶の層との間に、配向膜を除く少なくとも１層以上の誘電体層を形成することが望ましい。
【００３６】
さらに、１フレーム内に画像表示期間と画像非表示期間を有し、１フレーム内で間欠表示駆動を有する構成とする。
【００３７】
そして、前記光源は、１フレーム内で点灯状態と消灯状態を有する構成とすることができる。
【００３８】
なお、本発明は、上記の構成および後述する実施の形態で説明する構成に限定されるものではなく、本発明の技術思想を逸脱することなく、種々の変更が可能であることは言うまでもない。
【００３９】
【発明の実施の形態】
以下、本発明の実施の形態につき、添付の図面を参照して詳細に説明する。具体的な実施の形態に先立ち、本発明による液晶表示装置の基本構成を説明する。図１と図２は本発明の基本概念の説明図であり、図１は液晶駆動の各状態において画素内で発生する電界の方向と液晶分子の動きの説明図である。図１左列の図は各状態における液晶パネルの断面から見た液晶分子の動きを示し、右列の図は平面図を示している。また、図２は液晶駆動の各状態に対応する液晶透過率（液晶パネル輝度）の時間変化の説明図である。
【００４０】
なお、図１での（ａ）状態Ｉ、（ｂ）状態ＩＩ及び（ｃ）状態ＩＩＩ と図２での状態Ｉ、状態ＩＩ及び状態ＩＩＩ はそれぞれ対応しており、状態Ｉから状態ＩＩへの変化を過程Ｉ、状態ＩＩから状態ＩＩＩ への変化を過程ＩＩ、さらに状態ＩＩＩ から状態Ｉへの変化を過程ＩＩＩ と定義する。またここで、画像表示期間とは、過程Ｉにおける光を透過する期間であり、画像非表示期間とは、黒レベルの信号を書き込まれる過程ＩＩ及び過程ＩＩＩの期間と定義している。
【００４１】
本発明の基本構成では、少なくとも一方が透明な一対の基板１Ａ，１Ｂと、これら一対の基板間に挟持された液晶の層２（液晶分子で表記）と、基板１Ａ上に画素毎に形成された電極、すなわち第１の電極３及び第２の電極４と、基板１Ｂ上に形成された第３の電極５からなる。そして、第１の電極３及び第２の電極４の間に電圧を印加することにより、液晶（液晶分子）２の配向方向を制御し、一対の基板１Ａ，１Ｂの外側に配置された光源（図示せず）からの光量を調整して画像表示を行う。すなわち、画像表示期間（過程Ｉ）では、第１の電極３と第２の電極４の間に電圧が印加され、一対の基板１Ａ，１Ｂの基板面にほぼ平行な電界１８により液晶分子を駆動し、画像非表示期間の初期段階（過程ＩＩ）では、第１の電極３と第２の電極４の間に電圧を印加せず第１の電極３及び第２の電極４と第３の電極５の間に電圧を印加する。そして、一対の基板面にほぼ垂直な電界１９により液晶分子を駆動する。
【００４２】
このような液晶分子の駆動では、従来のＩＰＳ方式の液晶表示装置に比べ、特に立下り応答時間を短縮することが可能となる。これについて以下に詳細に説明する。
【００４３】
図１の状態Ｉでは、各電極に電圧を印加せず、電界は発生していない。従って、液晶分子２は初期配向方向２０（ラビング方向）に一様に配向している。このとき、一対の基板のそれぞれの外面に積層して配置された偏光板１７Ａ、１７Ｂはクロスニコル配置とし、一方の偏光板の透過軸は液晶の初期配向方向に一致している。従って、状態Ｉにおいては図２に示すように液晶透過率（輝度）はほぼゼロであり黒色表示となる。
【００４４】
次に、第１の電極３（例えば、画素電極とする）と第２の電極４（例えば、共通電極とする）の間に電圧を印加すると、これらの電極間に生じる基板面にほぼ平行な電界１８（横電界）により、液晶分子２の配向方向は基板面にほぼ平行な面内で回転し、光を透過する（過程Ｉ）。この過程Ｉは従来のＩＰＳ方式液晶表示装置における液晶分子の駆動と同じである。そして、立上り応答時間は従来のＩＰＳ方式液晶表示装置と同等である。
【００４５】
表示をオフ（画像非表示）する場合には、まず基板１Ｂ（以下、対向基板とも称する）上に形成された第３の電極５に電圧を印加する。これにより、第３の電極５と第１の電極３の間、または第３の電極５と第２の電極４の間で基板面にほぼ垂直な電界１９（縦電界）が発生する。この電界１９を利用して液晶分子を基板面に対して立ち上がるように駆動する。なお、図１のように縦電界により液晶分子を立ち上がらせるためには液晶はポジ型（誘電率異方性が正）である必要がある。このとき、上記したように、偏光板１７Ａ、１７Ｂはクロスニコル配置であるために、液晶分子２を基板面にほぼ垂直に立てることにより黒色表示とすることができる。図２に示すように状態ＩＩＩ では黒色表示となる。
【００４６】
液晶分子２を基板面にほぼ垂直な電界により起き上がらせることによって、黒を表示した後、各電極（画素電極である第１の電極３、共通電極である第２の電極４、第３の電極５）の電位を同電位に設定すると、画素内では無電界状態となる。これにより、立ちあがっていた液晶分子は、初期配向方向に向かって倒れていく。この液晶分子が倒れていく過程（過程ＩＩＩ ）では、偏光板１７Ａ、１７Ｂがクロスニコル配置のため黒色表示のままである。
【００４７】
ここで、重要な点は、時間的に横電界と縦電界を使い分け、特に立下り応答については縦電界により液晶を駆動し黒を表示することである。従来の表示モードでは、黒表示すなわち立下り応答時間は粘度や弾性定数など液晶材料の材料物性で決まっていたが、本発明では、材料物性以外に縦電界１９を利用して立下り応答時間を制御できるため応答時間を短縮することが可能である。
【００４８】
またこのとき、縦電界を有効に作用させるためには、第３の電極に電圧を印加するときに第１の電極３と第２の電極４の電位がほぼ等しいことが望ましい。すなわち、これら第１の電極３と第２の電極４の間には電界が生じないことが望ましい。同一基板上に形成された電極間での電位差により生じる電界を小さくすることで、対向電極である第３電極との間に生じる縦電界強度を有効に利用することができる。
【００４９】
このような液晶分子の駆動により、従来のＩＰＳ方式液晶表示装置に比較して、立下り応答時間を短縮することが可能である。そして、この液晶分子の駆動を実現できる電極構造としては、図３に示すように大別して５つの電極構造が考えられる。
【００５０】
図３は本発明の液晶表示装置における液晶分子駆動のための代表的な電極構造と電界形成の説明図である。なお、図３中の図１と同一参照符号は同一機能部分に対応し、参照符号６は第４の電極である。代表的な電極構造の一つは、図３（ａ）に示すように、一方の基板１Ａ側に異なる２種類の櫛歯電極（第１の電極３と第２の電極４）を形成し、もう一方の基板１Ｂ上には画素のほぼ全面を覆う第３の電極５としてベタ状電極を形成する構造である。画像表示期間では、一方の基板１Ａ上に形成された第１の電極３と第２の電極４に異なる電位を与えて基板面にほぼ平行な電界１８により液晶を駆動し、画像非表示期間の初期段階では、第１の電極３と第２の電極４を、例えばゼロ電位と同電位に設定し、同時に第３の電極５に所定の電位を与えることにより第１の電極３及び第２の電極４との間に縦電界１９を発生させる。この縦電界１９により液晶分子を立ち上げて黒を表示する。その後、全電極を例えばゼロ電位に設定し、液晶に電界が印加されない状態とすることで、液晶分子は初期の配向状態の戻る。この過程では、黒色表示のままである。
【００５１】
図３（ｂ）では、基板１Ａにベタ電極とした第２の電極４を形成し、その上に絶縁膜１０を介して櫛歯電極状の第１の電極３を重畳させた構造である。本構造では、画像表示期間で重畳している櫛歯電極状の第１の電極３の端部で発生する電界を主に利用して液晶分子を駆動し、白表示を行う。画像非表示期間の初期段階では、これら電極を同電位（例えばゼロ電位）とし、対向基板である基板１Ｂに配置したベタ状電極である第３の電極５に電位を与え、その間に生じる縦電界１９により液晶分子を立ち上がらせて黒表示を行う。その後、先と同様に全電極を例えばゼロ電位とすることで液晶分子は初期の配向状態に戻る。この過程では黒色表示のままである。この構造では、各基板１Ａ、１Ｂ上に形成されたベタ電極（第２の電極４、第３の電極５）により縦電界を発生させるため（ａ）に示した構造に比べ効率よく縦電界を発生し、利用することができる。
【００５２】
図３（ｃ）では、基板１Ａ上に形成された２つの異なる櫛歯状電極（第１の電極３と第２の電極４）間に生じる電界１８により液晶分子を駆動し、白表示を行う。そして、基板１Ａ側の上記第１の電極３と第２の電極４の下層に絶縁膜１０を介して形成したベタ電極状の第１電極６を設け、第１の電極３と第２の電極４および第４電極の電極群と対向する基板１Ｂに配置されたベタ状電極である第３電極５との間に生じる縦電界１９を利用して液晶分子を立ち上がらせて黒表示を行う。
【００５３】
図３（ｄ）では、基板１Ａに設けた櫛歯状の第１の電極３と第２の電極４および基板１Ｂに設けた櫛歯状の第３の電極５と第４の電極６でそれぞれの１Ａ、１Ｂ上で各基板面に平行な横電界１８を形成して白表示を行う。黒表示を行うときには、基板１Ａ上に形成された第１の電極３と第２の電極４、および基板１Ｂ上に形成された第３の電極５と第４の電極６の間に縦電界１９を形成する。
【００５４】
図３（ｅ）では、基板１Ａ上に形成したべた電極状の第２の電極４と、第２の電極４上に絶縁膜１０を介して櫛歯状に形成した第１の電極３を有し、基板１Ｂ上に形成したべた電極状の第５の電極６と、第５の電極６上に絶縁膜１０を介して櫛歯状に形成した第３の電極５を有している。白表示を行う場合は各基板に有する第１の電極３と第２の電極４の間、および第３の電極５と第４の電極６の間に横電界１８を形成し、黒表示を行う場合は基板１Ａの電極群と基板１Ｂの電極群の間に生じる縦電界１９を利用する。
【００５５】
また、図３（ａ）、図３（ｂ）、図３（ｃ）に示されたベタ状の第３の電極５は、画素ごとに薄膜トランジスタ（ＴＦＴ）などのアクティブ素子で個別に駆動してもよいし、基板全面に一括で形成し直接駆動回路に接続して一括駆動するようにしてもよい。個別に駆動する場合には、各画素を独立したタイミングで黒表示を書き込める。一方、全面一括形成の場合には、全面同一タイミングで黒表示を書き込むことが可能である。
【００５６】
さらに、これらベタ状電極は、液晶パネルの透過率を考えて、酸化インジウムスズ（ＩＴＯ）や酸化インジウム亜鉛（ＩＺＯ）、酸化インジウムゲルマニウム（ＩＧＯ）、さらにはこれらの混合物などの透明導電膜が望ましい。櫛歯電極の場合には、透過率を考えれば、透明導電膜を利用することが望ましいが、これに限ることなく光を透過しないクロムやアルミ、銅などの金属材料を用いてもよい。
【００５７】
上記した各構造において、縦電界１９を効率よく生じさせ、立下り応答時間を短縮するためには、画像非表示期間の初期段階において、第１の電極３と第２の電極４の電位をほぼ等しくし、第３の電極５のみの電位を異なるように設定することが望ましい。これは、第１の電極３と第２の電極４の電位が異なる場合には、縦電界と同時に、画像表示期間と同様の横電界を生じ、液晶分子は初期配向方向と異なる方位で立ち上がるために、完全な黒表示をすることが困難になるからである。これはコントラスト低下など画質の劣化を引き起こす。
【００５８】
また同様に、４つの異なる電極を有し、そのうち３つの電極（第１の電極３、第２の電極４、第４の電極６）が同一の基板上に形成されている構造（図３（ｃ））においては、画像非表示期間の初期段階において、第１の電極３と第２の電極４と第４の電極６の電位がほぼ等しく、第３の電極のみが異なることが望ましい。これは上記と同様、画像非表示期間において、同一の基板１Ａ上に形成された３つの電極間で不要な横電界を発生させないためである。
【００５９】
さらに、４つの異なる電極を有し、各基板上に２つずつの電極が形成されている構造（図３（ｄ）、（ｅ））では、画像表示期間において、液晶層の上下でそれぞれ横電界を発生するので、従来の横電界方式液晶表示装置に比較して横電界密度が大きくなるため、有効に液晶分子が駆動され、立上り応答時間の短時間化が期待できる。また、画像非表示期間の初期段階において、第１の電極３と第２の電極４の電位をほぼ等しく、第３の電極５と第４の電極６の電位をほぼ等しくすることにより、上基板に形成された電極群と下基板に形成された電極群の間で効率よく縦電界を発生することが可能となり、立下り応答時間の短縮化を図ることができる。
【００６０】
また、近年、液晶表示装置における動画表示の劣化は、１フレーム内で輝度を保持するホールド型に表示に起因することが指摘されている。動画対応液晶表示装置では、インパルス型表示が必要とされている。これを実現する手段として、先に述べた黒書き込み駆動やブリンクバックライト方式が提案されている。これらの技術により高品質な動画像を表示するためには、前記したように特に立下り応答時間の短縮化は必須である。
【００６１】
黒書き込み駆動では、従来は液晶の立下り応答が遅いために十分な黒レベルまで輝度が低下しないために、１フレーム内で理想的な間欠表示とならず、「動画ぼやけ」をある程度改善することが可能であるが、十分に改善することができない。黒書き込み駆動による間欠表示では、画像表示期間の輝度と画像非表示期間の輝度のコントラスト比が高くなければならない。これはすなわち、立下り応答を速くする必要があるということである。従って、黒書き込み駆動において、上記電極構造及び液晶駆動を利用することにより、立下り応答の速い黒書き込み駆動（理想的な間欠表示）が可能となり、「動画ぼやけ」を十分に改善することができる。
【００６２】
また、ブリンクバックライト方式では、先に述べたように、液晶の立上がり及び立下り応答時間とバックライトの点灯タイミング差によりゴースト現象を生じる。この現象は、前記図３２に斜線部で示した部分の輝度差を人間の目が認知するために生じる現象であり、立上がり及び立下り応答時間を短縮することにより抑制が可能である。従って、ブリンクバックライト方式において、上記電極構造及び液晶駆動を利用することにより、ゴースト現象を抑制することができる。
【００６３】
本発明では、液晶の応答速度、特に立下り応答時間を短縮できるだけでなく、それにより、黒書き込み駆動やブリンクバックライト方式など動画対応技術を適応した場合に新規に生じる課題も解決することが可能であり、従来に比べ高品質な動画対応液晶表示装置を提供することができる。以下、具体的な実施例を示すが、本発明は以下の実施例に限られるものではないことは前記したとおりである。
【００６４】
先ず、本発明の第１実施例と第２実施例を図４乃至図７を参照して説明する。図４は本発明の第１実施例および第２実施例の画素部の電極構のを説明図である。図４（ａ）の上側の図は一方の基板（薄膜トランジスタを形成した基板、以下ＴＦＴ基板１Ａ）の平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図４（ｂ）の上側の図は他方の基板（カラーフィルタを形成した基板、以下ＣＦ基板１Ｂ）の平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図４における前記図１、図３と同一参照符号は同一機能部分に対応し、参照符号８Ａ，８Ｂは信号配線、９ＡはＴＦＴ基板１Ａに有する画素電極駆動用の薄膜トランジスタ、９ＢはＣＦ基板１Ｂに設けた第３の電極５の駆動用の薄膜トランジスタ、１１は薄膜トランジスタ９Ｂの出力電極（ソース電極）と第３の電極５を接続するスルーホール、１３はオーバーコート膜、１４はカラーフィルタ、１５はブラックマトリクスを示す。
【００６５】
また、図５は本発明の第１実施例と第２実施例における画素部の断面図であり、図５（ａ）は第１実施例の画素部を、図５（ｂ）は第２実施例の画素部を示す。図６は本発明の第１実施例と第２実施例における液晶表示装置の駆動システムを説明する等価回路図である。図６における図３０と同一の参照符号は同一機能部分に対応し、参照符号２３Ａ，２３Ｂは信号電極駆動回路、参照符号２７は表示画素部を示す。また、図７は各電極及び配線に供給される信号波形の前記図３１と同様の説明図で、（ａ）のＶ_Ｇ は走査配線に供給される信号波形（Ｖ_ＧＨはハイレベル、Ｖ_ＧＬはローレベル）、波形（ｂ）（ｅ）のＶ_Ｄ１， Ｖ_Ｄ２は第１の信号配線に供給される信号波形、第２の信号配線に供給される信号波形をそれぞれ示し、Ｖ_ＤＨはハイレベル、Ｖ_ＤＬはローレベルである。波形（ｃ）のＶ_Ｓ は画素電極に印加される信号波形、波形（ｄ）のＶ_Ｃ は共通電極に印加される信号波形、またＧＮＤはグランドレベルを示す。波形（ｆ）のＶ_Ｎ は第３の電極５に印加される信号波形、波形（ｇ）は本実施例の駆動における液晶透過率の時間変化を示す。
【００６６】
［第１実施例］
本実施例での構造は前記図３（ａ）に対応する構造である。本発明の第１実施例における液晶表示装置は、表示部の対角サイズが公称１５インチであり、一対の基板は共に透明なガラス基板で、その厚みは０． ７ｍｍである。まず、図４（ａ）に示すように、基板１Ａ上に第１の走査配線７Ａ及び櫛歯状の共通電極４を形成する。次に、絶縁膜１０を窒化シリコンＳｉＮｘを用いて形成し、その上に第１の信号配線８Ａ、第１の電極３としての画素電極を櫛歯状に形成する。なお、マトリクス状に形成された走査配線７Ａと信号配線８Ａの交点付近にアモルファスシリコンを用いて作製される第１の薄膜トランジスタ９Ａが配置され、画素電極である第１の電極３と第１の信号配線８Ａは、この薄膜トランジスタ９Ａを介して電気的に接続している。そして、これらマトリクス状に形成される各配線に囲まれた領域に対応して画素が形成されている。
【００６７】
電極材料としてはクロムモリブデンＣｒＭｏを用いている。信号配線や走査配線の材料には電気抵抗の低いものであれば特に問題はなく、アルミニウムや銅などでもよい。
【００６８】
一方、基板１Ａに対向する基板１Ｂにはストライプ状の３色（赤、緑、青：Ｒ，Ｇ，Ｂ）のカラーフィルタ１４とブラックマトリクス１５を備えている。カラーフィルタ１４とブラックマトリクス１５上には表面を平坦化するためのオーバーコート膜１３を形成する。なお、オーバーコート膜１３としてはエポキシ樹脂などを用いる。
【００６９】
このようなカラーフィルタ基板上に第２の走査配線７Ｂ、絶縁膜１０、第２の信号配線８Ｂを設け、その最上層には画素のほぼ全面を覆うベタ状の第３の電極５が形成されている。ベタ状の第３電極５はＩＴＯで形成され、スルーホール１１及び第２の薄膜トランジスタ９Ｂを介して第２の信号配線８Ｂに電気的に接続している。また、基板１Ａ上に形成する第１の走査配線７Ａと基板１Ｂ上に形成する第２の走査配線７Ｂを基板外部で接続し、これらを一つの走査電極駆動回路（走査ドライバ）２２で駆動する。
【００７０】
なお、前記したように、第１の薄膜トランジスタ９Ａが形成される基板をＴＦＴ基板、カラーフィルタが形成される基板をカラーフィルタ基板（ＣＦ基板）と呼ぶことにする。このようにして作製されるＴＦＴ基板及びＣＦ基板表面に、液晶分子を配向させるためのポリイミドの配向膜１２を、膜厚１００ｎｍで形成する。一般に、ポリイミド膜は、その前駆体であるポリアミック酸を基板表面に印刷機などで塗布し、これらを高温で焼成することにより形成する。ここで形成されたポリイミのド配向膜１２の表面をラビング処理することにより配向処理を施す。ラビング方向は第１の電極（画素電極）３の長手方向から１５°傾いた方向とする。
【００７１】
本実施例においては、画素内に配置された第１の電極と第２の電極（画素電極と共通電極）は図３４の（ａ）に示したように櫛歯状に形成されているが、図３４の（ｂ）に示したように電極延長方向に対して角度θを有するくの字型に形成されていてもよい。第１の電極３と第２の電極４をくの字型に形成することにより、電圧が印加された場合に液晶分子の回転方向が異なる領域を生じる。これにより視角による色付きを抑制することができる。ただし、くの字型電極の場合には液晶分子の初期配向方向として、例えばポジ型液晶（誘電率異方性が正）の場合には液晶分子の長軸が画素の長手方向と一致するように配向処理する必要がある。
【００７２】
次に、これら一対の基板のうち、一方の基板の表示領域周縁部に熱硬化型のシール材を塗布し、対向するもう一方の基板を重ね合わせる。シール材は、後に液晶素子内に液晶を注入するための封入口が形成されるように塗布される。これらの基板を加熱しながら加圧し、両基板を接着固定する。なお、基板間は４マイクロメートルの間隔を保持できるようになっている。その後、封入口から真空封入法により液晶表示素子内に液晶を注入し、その後、封入口を紫外線硬化樹脂などで封止する。なお、ここでは液晶材料として誘電率異方性が正の材料を使用する。組合せた基板の両面に偏光板１７をノーマリークローズ特性（低電圧時に黒表示、高電圧時に白表示）となるようにクロスニコル配置で貼りつける。
【００７３】
図６に示すように、各配線は基板の端部まで延在配置され、第１の信号配線８Ａ、第２の信号配線８Ｂ、走査配線７（第１の走査配線７Ａ、第２の走査配線７Ｂ）、共通電極４は、それぞれに対応して第１の信号ドライバ２３Ａ、第２の信号ドライバ（信号電極駆動回路）２３Ｂ、走査ドライバ２２、共通電極ドライバ（共通電極駆動回路）２４に接続される。また、各ドライバは表示制御装置２１により制御されている。なお、破線で囲まれた領域（表示画素部）２７には一画素に対応する本実施例の電極構造に相当する等価回路を示している。
【００７４】
その後、図３３で示したように、シールドケース３２、拡散板３３、導光板３４、反射板３５、バックライト３６、下側ケース３７、インバータ回路３８を組合せることにより液晶表示装置３９を組み立てる。このようにして得られる液晶表示装置において、図７（ａ）から（ｅ）に示した信号波形を各配線及び電極に印加することによって、本発明の効果を得ることができる。以下、各電極及び配線へ印加する信号波形について説明する。
【００７５】
本実施例では１フレーム内で黒レベルに相当する信号を挿入する２倍速黒書き込み駆動である。図７において、（ａ）走査配線に供給される信号波形Ｖ_Ｇ 、（ｂ）第１の信号配線に供給される信号波形Ｖ_Ｄ１、（ｃ）画素電極に印加される信号波形Ｖ_Ｓ 、（ｄ）共通電極に印加される信号波形Ｖ_Ｃ 、（ｅ）第２の信号配線に供給される信号波形Ｖ_Ｄ２、（ｆ）第３の電極に印加される信号波形Ｖ_Ｎ が対応する信号配線あるいは電極に供給される。なお、図７（ｇ）に本駆動における液晶透過率の時間変化を示す。
【００７６】
図７において、まず、走査配線からの走査信号により時間ｔ＝ｔ_０ において第１及び第２の薄膜トランジスタがオン状態となり、画素電極（第１の電極）３には第１の信号配線からの電圧が印加され、第３の電極５には第２の信号配線からの電圧が印加される。次に、ｔ＝ｔ_１ において再度走査信号が書き込まれ、画素電極３には第１の信号配線からの電圧が印加され、第３の電極５には第２の信号配線からの電圧が印加される。
【００７７】
画像表示期間（ｔ_０ ＜ｔ＜ｔ_１ ）では、第１の電極（画素電極）３と第２の電極（共通電極）４との電位差（Ｖ_ＳＨ−Ｖ_Ｃ ）により生じる横電界を利用して液晶を駆動し画像を表示する。ｔ＝ｔ_１ において、第１の電極（画素電極）３と第２の電極（共通電極）４の電位をほぼ同一に設定し、第３の電極５に電圧Ｖ_ＮＨを印加する。このとき、横方向の電界はほぼゼロとなり、第２の電極（共通電極）４、第１の電極（画素電極）３と第３の電極５との間に生じる縦電界により液晶分子を基板面にほぼ垂直に立ち上げることによって黒色を表示する。
【００７８】
次に、ｔ＝ｔ_２ において、第１の電極（画素電極）３、第２の電極（共通電極）４、第３の電極５を同電位に設定することにより、基板面に対してほぼ垂直に立ちあがっていた液晶分子は初期配向状態に向かって基板面にほぼ平行な面に倒れる。この過程では、液晶分子の長軸方向の基板面への投射軸が一方の偏光板の透過軸と平行であり、もう一方の偏光板の透過軸と垂直であるために表示は黒色のままである。そして、ｔ＝ｔ_３ においては、初期配向の状態に戻っており、ｔ＝ｔ_３ のタイミングで次のフレームが開始される。
【００７９】
ここで、上記の構成とした液晶表示装置を用いて、応答速度に関して評価した。応答速度は、ホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上に全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【００８０】
〔第２実施例〕
本発明の第２実施例の液晶表示装置の断面図を図５（ｂ）に示す。本実施例と図５（ａ）で説明した第１の実施例とは、ＣＦ基板１Ｂ側に形成されたベタ状電極である第３の電極５と配向膜１２の間に誘電率層１６を配置する点で異なる。第１の実施例のように、第３の電極５が直接液晶層に接している場合には、第３の電極５の電位が通常の駆動電圧に大きく影響し、駆動電圧の上昇が懸念される。そこで、本実施例では、誘電体層１６を配置することにより、第３の電極５の電位が直接的に液晶層に影響することを防ぐことができ、駆動電圧の上昇が緩和される。また、同時に第１実施例と同様に、立ち下がり応答時間を短縮でき、動画表示性能の向上を図ることが可能である。
【００８１】
〔第３実施例〕
本発明の第３実施例の構成を図８、図９、図１０、図１１を用いて説明する。図８は本発明の第３実施例の構成を説明する図４と同様の画素部の電極構造を説明する図である。図８（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図８（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図９は本発明の第３実施例に係る液晶表示装置の画素部の断面図であり、図１０は液晶表示装置の駆動システムを説明するための図である。また図１１は各電極及び配線に供給される信号波形の説明図である。なお、本実施例での構造は図３（ａ）に対応する構造である。
【００８２】
本実施例は、第１実施例に比較して、ＣＦ基板１Ｂ側の電極構造が異なる。第１実施例ではＣＦ基板１Ｂ上に形成された第３の電極５が画素ごとに形成され、この第３の電極５をそれぞれの画素に形成された薄膜トランジスタ９Ｂにより個別に駆動している。これに対して、本実施例では、第３の電極５は全画素に共通に形成されている。この第３の電極５は画素部の領域の外に配置された第３電極駆動回路に直接接続され制御される。この構造では、第１実施例のように第３電極５を薄膜トランジスタで駆動するものとは異なり、全画素に対して同時に黒表示を書き込むことが可能である。
【００８３】
本発明の第３実施例の液晶表示装置を用いて、応答速度に関して評価した。応答速度はホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上には全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【００８４】
〔第４実施例〕
本発明の第４実施例の構成を図１２、図１３、図１４、図１５を用いて説明する。図１２は本発明の第４実施例の液晶表示装置に係る図８と同様の画素部の電極構造を説明する図である。図１２（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図１２（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図１３は本発明の第４実施例に係る液晶表示装置の画素部の断面図であり、図１４は液晶表示装置の駆動システムを説明するための図である。また図１５は各電極及び配線に供給される信号波形の説明図である。なお、本実施例での構造は図３（ａ）に対応する構造である。
【００８５】
本実施例は、第３実施例に比較してＴＦＴ基板側に形成する第２の電極（共通電極）４を画素ごとに形成される薄膜トランジスタ９Ｂで個別に駆動するように構成したものである。このとき、図１５（ｃ）、（ｄ）に示すように黒レベルを書き込む期間の初期（ｔ_１ ＜ｔ＜ｔ_２ ）において、第１の電極（画素電極）３と第２の電極（共通電極）４の電位差をほぼゼロにするために、Ｖ_ＳＨとＶ_ＣＨをほぼ同等の電位とすることが必要である。
【００８６】
このように第２の電極（共通電極）４を画素ごとに駆動することにより、ＣＦ基板１Ｂ側に形成する第３電極５を複雑に駆動制御する必要がなく、液晶表示装置の構造を簡略化できる。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【００８７】
〔第５実施例〕
本実施例の構成を図１６、図１７を用いて説明する。図１６は本発明の第５実施例に係る図１２と同様の画素部の電極構造を説明する図である。図１６（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図１６（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図１７は本発明の第５実施例に係る液晶表示装置の画素部の断面図である。また、本実施例における液晶表示装置の駆動システム及び各配線、電極へ供給される信号波形の概略は第３実施例と同様であるので、信号波形は図１０及び図１１を用いて説明する。なお、本実施例での構造は図３（ｂ）に対応する構造である。
【００８８】
本実施例における液晶表示装置は、表示部の対角サイズが公称１５インチであり、一対の基板は共に透明なガラス基板で、その厚みは０． ７ｍｍである。まず、図１６（ａ）に示すように、基板１Ａ上に第１の走査配線７及び画素のほぼ全面を覆うようにベタ状の第２の電極（共通電極）４を形成する。次いで、絶縁膜１０が窒化シリコンＳｉＮｘを用いて形成され、その上に信号配線８Ａ、櫛歯状の第１の電極（画素電極）３を形成する。なお、マトリクス状に形成された走査配線７と信号配線８Ａの交点付近にアモルファスシリコン等を用いて作製される薄膜トランジスタ９が配置される。第１の電極（画素電極）３と信号配線８Ａは、この薄膜トランジスタ９を介して電気的に接続している。そして、これらマトリクス状に形成される各配線に囲まれた領域に対応して画素が形成されている。
【００８９】
電極材料としては、走査配線や信号配線などの配線にはクロムモリブデンＣｒＭｏを用い、第１の電極（画素電極）や第２の電極（共通電極）には開口率を確保するためにＩＴＯ透明電極を用いている。
【００９０】
一方、基板１Ａに対向する基板１Ｂにはストライプ状の３色（Ｒ，Ｇ，Ｂ）のカラーフィルタ１４とブラックマトリクス１５を備えている。カラーフィルタ１４とブラックマトリクス１５上には、表面を平坦化するためのオーバーコート樹膜１３を形成する。なお、オーバーコート膜としてはエポキシ樹脂などを用いる。
【００９１】
このようなＣＦ基板１Ｂ上にベタ状の第３の電極５を形成する。第３の電極５はＩＴＯで形成する。このようにして作製されるＴＦＴ基板（基板１Ａ）及びＣＦ基板（基板１Ｂ）の内面に、液晶分子を配向させるためのポリイミドの配向膜１２を膜厚１００ｎｍで形成する。一般にポリイミド膜は、その前駆体であるポリアミック酸を基板表面に印刷機などで塗布し、これらを高温で焼成することにより形成する。ここで形成されたポリイミド配向膜１２の表面をラビング処理することにより配向処理を施す。ラビング方向は第１の電極３である画素電極の長手方向から１５°傾いた方向とする。
【００９２】
本実施例においては、第１の電極である画素電極３は図３３（ａ）のように櫛歯状に形成されているが、図３３（ｂ）に示すように電極延長方向に対して角度θを有するくの字型に形成されていてもよい。くの字型に形成されることにより、電圧が印加された場合に液晶分子の回転方向が異なる領域を生じ、これにより前記した色付きを抑制することができる。ただし、くの字型電極の場合には液晶分子の初期配向方向として、例えばポジ型液晶の場合には液晶分子の長軸が画素の長手方向と一致するように配向処理する必要がある。
【００９３】
次に、これら一対の基板１Ａ，１Ｂのうち、一方の基板の表示領域周縁部に熱硬化型のシール材を塗布し、もう一方の対向基板を重ね合わせる。シール材は、後に液晶素子内に液晶を注入するための封入口が形成されるように塗布される。これら基板を加熱しながら加圧し、両基板を接着固定する。なお、基板間は４マイクロメートルの間隔を保持できるようになっている。その後、封入口から真空封入法により液晶を液晶表示素子内に注入し、その後、封入口を紫外線硬化樹脂などで封止する。なお、ここでは液晶材料として誘電率異方性が正の材料を使用する。
【００９４】
組合せた基板の両面に偏光板１７（１７Ａ、１７Ｂ）をノーマリークローズ特性（低電圧で黒表示、高電圧で白表示）となるようにクロスニコル配置で貼りつける。その後、図３３に示したシールドケース３２、拡散板３３、導光板３４、反射板３５、バックライト３６、下側ケース３７、インバータ回路３８を組合せることにより液晶表示装置３９を組み立てる。このようにして得られる液晶表示装置において、各配線及び電極に印加する信号は図１１に示すとおりであり、第３実施例とほぼ同じである。
【００９５】
すなわち、画像表示期間（ｔ_０ ＜ｔ＜ｔ_１ ）では、第１の電極（画素電極）と第２の電極（共通電極）との電位差により生じる電界を利用して液晶を駆動し画像を表示する。櫛歯状の画素電極の端部では特に大きな電界を発生し、従来のＩＰＳに比べ立上り応答速度が速いのが特徴である。具体的には、ｔ＝ｔ_１ において、画素電極と共通電極電位をほぼ同一に設定し、第３の電極５に電圧を印加する。このとき、横方向の電界はほぼゼロとなり、第２の電極（共通電極）、第１の電極（画素電極）と第３の電極との間に生じる縦電界により液晶分子を基板面にほぼ垂直に立ち上げることによって黒色を表示する。
【００９６】
本実施例では、第３実施例に比較して共通電極を画素のほぼ全面を覆うように形成しているために、画像非表示期間の初期段階で発生する縦電界を画素全域でほぼ均一に発生させることができる。このために第３実施例に比較してさらに立下り時間を短縮できる。
【００９７】
次に、ｔ＝ｔ_２ において、第１の電極（画素電極）、第２の電極（共通電極）、第３の電極を同電位に設定することにより、基板面に対してほぼ垂直に立ちあがっていた液晶分子は初期配向状態に向かって基板面にほぼ平行な面に倒れる。この過程では、液晶分子の長軸方向の基板面への投射軸が一方の偏光板の透過軸と平行であり、もう一方の偏光板の透過軸と垂直であるために表示は黒色のままである。そして、ｔ＝ｔ_３ においては、初期配向の状態に戻っており、ｔ＝ｔ_３ のタイミングで次のフレームが開始される。
【００９８】
こうして得られた液晶表示装置を用いて、応答速度に関して評価した。応答速度は、ホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上には全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【００９９】
〔第６実施例〕
本発明の第６実施例の構成を図１８、図１９、図２０を用いて説明する。図１８は本発明の第６実施例に係る液晶表示装置の図１２と同様の画素部の電極構のを説明図である。図１８（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図１８（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図１９は本発明の第６実施例に係る液晶表示装置の画素部の断面図、図２０は各電極及び配線に供給される信号波形の説明図である。なお、本実施例での構造は図３（ｃ）に対応する構造である。
本実施例では、図１８から分かるように、４つの異なる電極を利用する。ただし、後述するように駆動によっては第２の電極である共通電極の下層に重畳して配置する第４の電極６は、共通電極４とすべての時間において同電位とすることができる。この場合は異なる３つの電極を設けたものとなる。
【０１００】
本実施例における液晶表示装置は、表示部の対角サイズが公称１５インチであり、一対の基板は共に透明なガラス基板で、その厚みは０． ７ｍｍである。まず、図１８に示すように、ＴＦＴ基板１Ａ上に第４の電極６、第２の電極（共通電極）４、信号配線８Ａ、第１の電極（画素電極）３を形成する。各電極間は絶縁膜１０により絶縁性を保持している。電極材料は、電気抵抗の低いものであれば特に問題はないが、第４の電極６は画素領域をほぼ全面覆うように形成されているために、透過型液晶表示装置の場合には開口率を確保するためにＩＴＯなどの透明導電膜が望ましい。
【０１０１】
一方、ＣＦ基板には画素領域の全面を覆うように透明導電膜を形成する。そして、これら両基板に第１の実施例に示す所定の処理をした後、張り合わせて液晶表示装置を組み立てる。このようにして得られた液晶表示装置において、各配線及び電極には図２０に示す信号波形を供給する。図２０において、画像表示期間（ｔ_０ ＜ｔ＜ｔ_１ ）では、第２の電極（共通電極）と第１の電極（画素電極）間との電位差により液晶分子を駆動する。そして、画像非表示期間の初期段階（ｔ_１ ＜ｔ＜ｔ_２ ）では、第１の電極（画素電極）と第２の電極（共通電極）の電位をほぼ同じに設定し、両基板に形成されたベタ電極（第３の電極５と第４の電極６）間に生じる縦電界により液晶を基板面にほぼ垂直な方向に立ち上げることにより黒を表示する。本実施例の構造では、画素領域をほぼ全面に覆う電極により縦電界を生じさせているために、第１の実施例に比較して、縦電界の発生効率がよく、立下り時間のさらなる短縮化が可能となる。
【０１０２】
こうして得られた液晶表示装置を用いて、応答速度に関して評価した。応答速度は、ホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上には全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【０１０３】
〔第７実施例〕
本発明の第７実施例の構成を図２１、図２２、図２３、図２４を用いて説明する。図２１は本発明の第７実施例に係る液晶表示装置の画素部の電極構造の説明図であり、図２１（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図２１（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図２２は本発明の第７実施例に係る液晶表示装置の画素部の断面図、図２３は液晶表示装置の駆動システムを説明するための図である。また図２４は各電極及び配線に供給される信号波形の説明図である。なお、本実施例での構造は図３（ｄ）に対応する構造である。各電極及び配線に供給される信号波形の説明図である。
【０１０４】
図２１及び図２２から分かるように、ＴＦＴ基板１Ａ側は従来のＩＰＳ方式液晶表示装置と同じ構造である。一方、ＣＦ基板１Ｂ側も、オーバーコート膜１３を形成した後に、ＴＦＴ基板１Ａ側と同様の電極構造とする。画像表示期間では図２４に示すように第１の電極３である画素電極と第２の電極４である共通電極間に生じる横電界により液晶を駆動する。同時に、第３の電極５と第４の電極間６に生じる横電界によっても液晶を駆動でき、従来のＩＰＳに比べて横電界発生の効率が高いために低電圧で立上り応答速度を向上することが可能である。
【０１０５】
一方、画像非表示期間の初期段階では、第２の電極（共通電極）と第１の電極（画素電極）の電位をほぼ同電位となるように設定し、同時に、第３の電極と第４の電極の電位がほぼ同じになるように設定する。さらに、これらＴＦＴ基板１Ａ側に形成された電極（画素電極及び共通電極）の電位をＣＦ基板１Ｂ側に形成された電極（第３の電極及び第４の電極）の電位より高く設定する。これにより縦電界を生じることができる。
【０１０６】
こうして得られた液晶表示装置を用いて、応答速度に関して評価した。応答速度は、ホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上には全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【０１０７】
〔第８実施例〕
本発明の第８実施例の構成を図２５、図２６を用いて説明する。図２５は画素部の電極構造を説明するための図であり、図２５（ａ）の上側の図はＴＦＴ基板１Ａの平面図、下側の図は上側の図のＡ−Ａ’線に沿った断面図であり、図２５（ｂ）の上側の図はＣＦ基板１Ｂの平面図、下側の図は上側の図のＢ−Ｂ’線に沿った断面図である。図２６は本発明の第８実施例に係る液晶表示装置の画素部の断面図である。なお、本実施例での構造は図３（ｅ）に対応する構造である。
【０１０８】
図２５及び図２６から分かるように、ＴＦＴ基板１Ａ側の電極構造は第５実施例と同様であり、この構造をＣＦ基板１Ｂ側にも形成する。このような電極構造において、図２４に示す信号波形を供給すると、画像表示期間では第１の電極（画素電極）３と第２の電極（共通電極）４間に生じる電界及び第３の電極５と第４の電極６間に生じる電界により液晶を駆動して画像を表示する。一方、画像非表示期間の初期段階では同一基板に形成された電極間の電位を同電位に設定し、ＴＦＴ基板１Ａ上の電極とＣＦ基板１Ｂ上の電極との電位差により縦電界を生じさせる。
【０１０９】
こうして得られた液晶表示装置を用いて、応答速度に関して評価した。応答速度は、ホトダイオードを組み合わせたオシロスコープを用いて評価した。まず、画面上には全面黒色パターンを表示し、その後、最大輝度に相当する白色パターンを表示する。このときの輝度変化をオシロスコープにて読み取り、変化前の輝度Ｂ_０ から変化後の輝度Ｂ_ｆｉｎ への変化量を１００％とし、そのうちの９０％の変化が終了した時点をもって応答時間とする。本実施例の液晶表示装置において、同一の液晶材料を用いた場合に従来のＩＰＳ方式液晶表示装置に比べ応答時間（立下り応答時間）が短縮されたことを確認した。
【０１１０】
〔第９実施例〕
本発明の第９実施例では、第５実施例と同様に、図１６及び図１７に示す電極構造を有する液晶表示装置を利用する。また第５実施例では１フレーム内で２回の書き込みを行う２倍速駆動であるが、図２７は第９実施例における液晶パネルの透過率とバックライトの点灯タイミングの説明図である。本実施例では、１フレーム内に１回の書き込みしか行わない駆動とする。ただし、図２７に示すように液晶表示装置の光源であるバックライトを１フレーム内で点灯状態と消灯状態を有する駆動とする。
【０１１１】
液晶パネルは通常線順次駆動であり、上段から下段に向かってデータを書き込んで行く。その過程で透過率変化を各段において示したのが図２７（ａ）から（ｃ）である。また、図２７（ｄ）にはバックライトの点灯タイミングを示す。このようなブリンクバックライト方式では、パネル中央部での輝度を保つために、パネル中段の液晶が十分に応答した時点でバックライトを点灯する。
【０１１２】
本実施例で得られる液晶表示装置を用いて、先述したゴーストについて評価をしたところ、従来のＩＰＳ液晶表示装置に比較して、ゴースト現象を抑制することができた。これは、図３２に示すように従来のＩＰＳ液晶表示装置では立下り応答時間が長いために、斜線領域の輝度差を積分して感知するためにゴーストと呼ばれる画像輪郭部で２重像として捕らえられる。しかし本実施例のように立下り応答時間を短縮化することにより、斜線部分の面積を低減することができ、結果として、ゴースト現象を低減することが可能である。
【０１１３】
【発明の効果】
以上説明したように、本発明によれば、横電界方式の液晶表示装置において、一方の基板に形成した共通電極及び画素電極とは異なる新規な第３の電極、あるいは第３の電極に加えて第４の電極を一方の基板または他方の基板もしくは一方の基板と他方の基板の何れかに形成し、この第３の電極、あるいは第３の電極と第４の電極の電位を１フレーム周期内で変化させ、画像表示期間では共通電極と画素電極間で生じる横電界を利用し、画像非表示期間の初期段階では共通電極、画素電極と、第３の電極間、あるいは第３の電極と第４の電極間で生じる縦電界を利用することにより、特に立下り応答時間が改善され、動画表示を可能とした高速応答化と「動画ぼやけ」を抑制した高品質な動画対応液晶表示装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の基本概念を説明するための液晶駆動の各状態において画素内で発生する電界の方向と液晶分子の動きの説明図である。
【図２】本発明の基本概念を説明するための液晶駆動の各状態に対応する液晶透過率（液晶パネル輝度）の時間変化の説明図である。
【図３】本発明の液晶表示装置における液晶分子駆動のための代表的な電極構造と電界形成の説明図である。
【図４】本発明の第１実施例および第２実施例の画素部の電極構造の説明図である。
【図５】本発明の第１実施例と第２実施例における画素部の断面図である。
【図６】本発明の第１実施例と第２実施例における液晶表示装置の駆動システムを説明する等価回路図である。
【図７】本発明の第１実施例と第２実施例における各電極及び配線に供給される信号波形の前記図３１と同様の説明図である。
【図８】本発明の第３実施例の構成を説明する図４と同様の画素部の電極構造の説明図である。
【図９】本発明の第３実施例に係る液晶表示装置の画素部の断面図である。
【図１０】本発明の第３実施例に係る液晶表示装置の駆動システムの説明図である。
【図１１】本発明の第３実施例に係る液晶表示装置の各電極及び配線に供給される信号波形の説明図である。
【図１２】本発明の第４実施例の液晶表示装置に係る図８と同様の画素部の電極構造の説明図である。
【図１３】本発明の第４実施例に係る液晶表示装置の画素部の断面図である。
【図１４】本発明の第４実施例に係る液晶表示装置の駆動システムの説明図である。
【図１５】本発明の第４実施例に係る液晶表示装置の各電極及び配線に供給される信号波形の説明図である。
【図１６】本発明の第５実施例に係る図１２と同様の画素部の電極構造の説明図である。
【図１７】本発明の第５実施例に係る液晶表示装置の画素部の断面図である。
【図１８】本発明の第６実施例に係る液晶表示装置の図１２と同様の画素部の電極構造の説明図である。
【図１９】本発明の第６実施例に係る液晶表示装置の画素部の断面図である。
【図２０】本発明の第６実施例に係る液晶表示装置の各電極及び配線に供給される信号波形の説明図である。
【図２１】本発明の第７実施例に係る液晶表示装置の画素部の電極構造の説明図である。
【図２２】本発明の第７実施例に係る液晶表示装置の画素部の断面図である。
【図２３】本発明の第７実施例に係る液晶表示装置の駆動システムの説明図である。
【図２４】本発明の第７実施例に係る液晶表示装置の各電極及び配線に供給される信号波形の説明図である。
【図２５】本発明の第８実施例に係る液晶表示装置の画素部の電極構造を説明するための図である。
【図２６】本発明の第８実施例に係る液晶表示装置の画素部の断面図である。
【図２７】本発明の第９実施例に係る液晶表示装置における液晶パネルの透過率とバックライトの点灯タイミングの説明図である。
【図２８】ＩＰＳ方式の液晶表示装置の画素部を構成する電極構成例の説明図である。
【図２９】図２８に示した一方の基板を対向する他方の基板と共に示す断面図である。
【図３０】ＩＰＳ方式の液晶表示装置の駆動システムを説明する等価回路図である。
【図３１】ＩＰＳ方式の液晶表示装置における黒書き込み駆動する場合の信号波形例の説明図である。
【図３２】ブリンクバックライト方式における液晶透過率変化を説明する波形図である。
【図３３】液晶表示装置の分解斜視図である。
【図３４】櫛歯状電極の形状例の説明図である。
【符号の説明】
１（１Ａ、１Ｂ）…基板、２…液晶分子又は液晶の層、３…第１の電極（画素電極）、４…第２の電極（共通電極）、５…第３の電極、６…第４の電極、７（７Ａ、７Ｂ）…走査配線、８（８Ａ、８Ｂ）…信号配線、９（９Ａ、９Ｂ）…薄膜トランジスタ、１０…絶縁膜、１１…スルーホール、１２…配向膜、１３…オーバーコート膜、１４…カラーフィルタ、１５…ブラックマトリクス、１６…高誘電体層、１７（１７Ａ、１７Ｂ）…偏光板、１８…横電界、１９…縦電界、２０…液晶初期配向方向（ラビング方向）、２１…表示制御装置、２２…走査電極駆動回路、２３（２３Ａ、２３Ｂ）…信号電極駆動回路、２４…共通電極駆動回路、２５…第３電極駆動回路、２６…第４電極駆動回路、２７…表示画素部、３１…液晶表示素子（液晶表示パネル）、３２…シールドケース、３３…拡散板、３４…導光板、３５…反射板、３６…バックライト、３７…下側ケース、３８…インバータ回路基板、３９…液晶表示装置。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device suitable for displaying moving images.
[0002]
[Prior art]
The liquid crystal display device includes a liquid crystal panel and a light source, and performs image display by adjusting the amount of light from the light source using the liquid crystal panel. The liquid crystal panel is configured by arranging a pair of substrates, at least one of which is transparent, at a predetermined interval, and injecting liquid crystal into this interval. A polymer thin film called an alignment film is disposed between each of the pair of substrates and the liquid crystal layer, and is subjected to an alignment process for aligning liquid crystal molecules in a predetermined direction (alignment direction). In addition, electrodes such as a pixel electrode and a common electrode are formed on the substrate for each pixel, and by applying a voltage between these electrodes, the orientation direction of the liquid crystal molecules is changed, and the optical characteristics of the liquid crystal layer generated thereby are changed. The light transmittance of the liquid crystal panel is adjusted by the change.
[0003]
In an active matrix type liquid crystal display device, a plurality of pixels are arranged in a matrix on a substrate, and a switching element such as a thin film transistor is arranged for each pixel. It is configured to apply a voltage for display.
[0004]
Conventional active matrix type liquid crystal display devices mainly use TN ( T wished N The liquid crystal display device of the TN mode has a feature that the viewing angle is narrow due to its display principle. As one of means for improving this, IPS (Patent Document 1) and IPS (Patent Document 2) I n- P lane S 2. Description of the Related Art A liquid crystal display device of a switching type is known.
[0005]
28A and 28B are explanatory diagrams of an example of an electrode configuration that forms a pixel portion of an IPS liquid crystal display device. FIG. 28A is a plan view of one pixel, and FIG. 28B is an AA ′ of FIG. FIG. 3C is a cross-sectional view taken along a line BB ′ in FIG. FIG. 29 is a cross-sectional view showing one substrate shown in FIG. 28 together with the other substrate facing the substrate. FIG. 30 is an equivalent circuit diagram for explaining a driving system of the IPS mode liquid crystal display device. The substrate illustrated in FIG. 28 is one substrate (referred to as a TFT substrate because a switching element is usually provided with a thin film transistor). 28, 29, and 30, reference numeral 1 denotes a pair of substrates, 1A denotes one of the substrates constituting the pair of substrates, 1B denotes the other substrate, and the first substrate 1A has a first substrate on the inner surface thereof. , A common electrode 4 as a second electrode, a scanning wiring 7, and a signal wiring 8 are arranged via an insulating film 10. The alignment film 12 is formed on the outermost surface of the inner surface.
[0006]
On the inner surface of the other substrate 1B, a color filter 14, a black matrix 15 for partitioning the color filters are provided, and an alignment film 12 is formed via an overcoat film 13. Polarizing plates 17A and 17B are laminated on the outer surfaces of the substrates 1A and 1B, respectively. In FIG. 30, reference numeral 9 denotes a thin film transistor, 21 denotes a display control device, 22 denotes a scan electrode drive circuit, 23 denotes a signal electrode drive circuit, and 24 denotes a common electrode drive circuit.
[0007]
As shown in FIG. 28, FIG. 29 and FIG. 30, in the IPS mode liquid crystal display device, a pair of substrates 1A and 1B sandwiching a liquid crystal layer (shown as a liquid crystal layer in FIG. 29) is provided. An electrode group (a first electrode which is an electrode pair: a pixel electrode 3 and a second electrode: a common electrode 4) is formed only on one substrate 1A. The pixel electrode 3 and the common electrode 4 are arranged in each pixel region surrounded by the scanning lines 7 and the signal lines 8 formed in a matrix.
[0008]
The pixel electrode 3 is a thin film transistor TFT ( T hin F ilm T The signal line 8 is electrically connected to the signal line 8 via a transcriptor 9. Driving of the liquid crystal is performed by a lateral electric field 18 generated between the pixel electrode 3 and the common electrode 4 and substantially parallel to the substrate surface, and the orientation direction (orientation axis) of the molecules constituting the liquid crystal layer is substantially parallel to the substrate surface. To control the light transmittance from a light source (not shown) disposed outside. Therefore, there is no inversion of gradation or color tone depending on the viewing angle of the screen, and the viewing angle is wider than that of the conventional TN method. Further, the IPS type liquid crystal display device has excellent display performance such as color reproducibility, and is an important technology for a large-screen liquid crystal monitor and a liquid crystal television in the future.
[0009]
[Patent Document 1]
JP-B-63-21907
[Patent Document 2]
U.S. Pat. No. 4,345,249
[Patent Document 3]
JP-A-11-231344
[Non-patent document 1]
"Image quality of moving image display on hold-type display" (IEICE technical report EID99-10 p55)
[Non-patent document 2]
"A Novel Wide-Viewing-Angle Motion-Picture LCD (H. Nakamura, et. Al: SID98 Digest, pp. 143-146 (1998))"
[0010]
[Problems to be solved by the invention]
However, in a conventional liquid crystal display device including the IPS system, when a moving image is displayed, a “moving image blur” phenomenon occurs in which the outline of the moving image becomes unclear. This moving image blur is a major problem that causes deterioration of image quality, and it is necessary to improve this in a moving image compatible liquid crystal display device such as a liquid crystal TV in the future.
[0011]
The details of the “moving image blur” are described in, for example, “Non-patent Document 1”. (1) The response speed of liquid crystal molecules is slow, and (2) the liquid crystal display device is a hold type that holds luminance within one frame. Display. In particular, the problem (1) is a fundamental problem of the liquid crystal display device, and it is difficult to obtain a high quality moving image compatible liquid crystal display device without solving the problem.
[0012]
For example, the rise response time τ of the liquid crystal in the IPS mode liquid crystal display device _on And fall response time τ _off Is generally known to be expressed by the following (Equation 1) and (Equation 2).
(Equation 1)

(Equation 2)

Where γ ₁ Is the viscosity of the liquid crystal, Δε is the dielectric anisotropy, K ₂ Is the elastic constant, d is the thickness (gap) of the liquid crystal layer, and E is the electric field intensity applied to the liquid crystal.
[0013]
As can be seen from (Equation 1), the rise response time of the liquid crystal is greatly affected by the electric field strength applied to the liquid crystal in addition to the material properties such as the viscosity, elastic constant, and dielectric constant of the liquid crystal. Therefore, there are the following two approaches to shorten the rise response time.
[0014]
(1) Approach by liquid crystal material development
(2) Approach by increasing electric field strength
Regarding (1), it has been proposed to lower the viscosity of the liquid crystal and increase the ΔΔ. Regarding (2), an overdrive drive for temporarily increasing the effective electric field strength by applying a voltage more than necessary, or a new substrate is provided on the counter substrate side as described in Patent Document 3. In order to improve the efficiency of an electric field applied to the liquid crystal, a common electrode has been proposed. Thus, it is possible to sufficiently improve the rise response time by the two approaches (material development and drive improvement).
[0015]
On the other hand, as can be seen from (Equation 2), the fall response time is determined only by the physical properties of the material and is not affected by the electric field intensity. Therefore, the fall response time is improved by the overdrive drive described above or the electrode structure disclosed in Patent Document 3. It is difficult. At present, the fall time is only improved mainly by lowering the viscosity of the liquid crystal material. However, considering the improvement of the image quality of a liquid crystal display device that supports moving images in the future, it is particularly necessary to further shorten the fall response time, and it is difficult to improve the physical properties of the liquid crystal material alone.
[0016]
In particular, in a liquid crystal display device that supports moving images, in order to improve the cause (2) of the “moving image blur” and realize an impulse-type display, for example, a video signal is written in one frame and then corresponds to a black level. A black writing drive for writing a signal and intermittently changing the transmittance of a liquid crystal has been proposed in, for example, Japanese Patent Application Laid-Open Publication No. H11-163873. Even in these proposed techniques, the fall response time has a significant effect.
[0017]
FIG. 31 is an explanatory diagram of an example of a signal waveform in the case where black writing driving is performed in the IPS mode liquid crystal display device. FIG. 31 shows an example of double speed drive for writing a signal corresponding to a black level in one frame (1 frame). V of waveform (a) _G Is the signal waveform (V _GH Is high level, V _GL Is low level), V in waveform (b) _D Is the signal waveform (V _DH Is high level, V _DL Is low level), V of waveform (c) _S Is a signal waveform applied to the pixel electrode. Note that V in waveform (d) _C Represents a signal waveform applied to the common electrode, and GND represents a ground level.
[0018]
At this time, as shown in FIG. 31 (e), if the fall response is slow, an ideal intermittent display is not obtained because the black level does not drop to a sufficient level when the luminance falls. Therefore, when the response speed of the liquid crystal is low as in the present case, "moving image blur" can be improved to some extent by the black writing drive, but it cannot be sufficiently improved.
[0019]
Further, as another means for realizing the impulse type display, a blink backlight system in which a light source has a light-on state and a light-off state in one frame has been proposed. FIG. 32 is a waveform diagram illustrating a change in liquid crystal transmittance in the blink backlight method. In FIG. 32, (a) is the liquid crystal transmittance in the upper part of the liquid crystal panel (in the figure, simply referred to as panel), (b) is the liquid crystal transmittance in the middle part of the panel, (c) is the transmittance in the lower part of the panel, and (d) is the back. The timing of turning on (on) and turning off (off) the light (BL) is shown. In a liquid crystal display device, generally, line-sequential driving is performed, a signal is written in one frame from an upper stage (scanning start side) to a lower stage of the liquid crystal panel, and the transmittance of the liquid crystal changes according to the signal. The backlight is turned on when the liquid crystal transmittance at the center of the panel reaches a predetermined transmittance. At this time, the liquid crystal transmittance starts to fall in the upper part of the panel due to the timing of signal writing, and is in the middle of rising in the lower part of the panel. In such a case, luminance (hatched portion) irrelevant to the original image data (video signal) is integrated by human vision, and a double image called a ghost is generated. The ghost causes a large deterioration of the moving image quality in the liquid crystal display device, and a technique for improving the response speed of the liquid crystal is indispensable to suppress this phenomenon.
[0020]
As can be seen from the above, improvement of the liquid crystal response speed (especially, reduction of the fall response time) is an indispensable subject in a moving image compatible liquid crystal display device. As mentioned earlier, it has been proposed that the rise response time of the liquid crystal be improved by improving the physical properties of the liquid crystal material as well as by devising the drive and electrode structure. It can only be improved by improving the material properties. However, further reduction of the fall response time is indispensable for future development, and a new technology other than the liquid crystal material development that makes it possible is required.
[0021]
Accordingly, an object of the present invention is to provide a high quality liquid crystal display device which realizes high-speed response by suppressing "moving image blur" which largely affects the moving image quality by shortening the falling response time among the luminance response times. It is an object of the present invention to provide a moving image compatible liquid crystal display device.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a liquid crystal display device comprising a pair of substrates, at least one of which is transparent, a liquid crystal layer sandwiched between the pair of substrates, and a plurality of substrates arranged in a matrix on one of the pair of substrates. Pixel group, each of which has an electrode group formed for each pixel, controls the alignment direction of the liquid crystal by applying a voltage between the electrode groups, and enters from a light source installed outside the pair of substrates. In a liquid crystal display device that performs image display by adjusting the amount of light,
In the image display period, the liquid crystal is driven by an electric field substantially parallel to the pair of substrate surfaces, and in the initial stage of the image non-display period, the liquid crystal controls the alignment direction of the liquid crystal by the electric field substantially perpendicular to the pair of substrate surfaces. Driving means was provided.
[0023]
As one configuration example for realizing the liquid crystal driving means, a third electrode is provided on the other substrate facing the one substrate on which the first electrode and the second electrode of the pair of substrates are formed,
In the image display period, different potentials are applied to the first electrode and the second electrode, and the orientation direction of the liquid crystal is controlled by an electric field substantially parallel to a substrate surface generated between the electrodes,
In an initial stage of an image non-display period, different electric potentials are applied to the first electrode and the third electrode, and an electric field generated between the electrodes and substantially perpendicular to a substrate surface, and an electric field generated between the second electrode and the third electrode. Liquid crystal driving means for controlling the alignment direction of the liquid crystal by an electric field which is applied with different potentials to the electrodes and is substantially perpendicular to the substrate surface generated between the electrodes was provided.
[0024]
At this time, it is desirable that the first electrode and the second electrode have a comb shape. Alternatively, one of the first electrode and the second electrode is a comb-shaped electrode, the other electrode is a solid electrode covering substantially the entire surface of the pixel, and the comb-shaped electrode forms an insulating film. A structure in which the electrode overlaps with the solid electrode may be used.
[0025]
Further, it is desirable that the third electrode is a solid electrode that covers substantially the entire surface of the pixel. Further, it is desirable that this solid electrode can be individually driven by each pixel, and it is further desirable that it can be driven collectively by all pixels.
[0026]
Further, as another configuration example for realizing the above means, a third electrode is formed on the other substrate facing the one substrate on which the first electrode and the second electrode of the pair of substrates are formed. ,
A fourth electrode formed via an insulating film between the first electrode and the second electrode and the one substrate;
In the image display period, different potentials are applied to the first electrode and the second electrode, and the liquid crystal is driven by an electric field substantially parallel to the substrate surface generated between the electrodes. In an initial stage of the image non-display period, Liquid crystal driving means for controlling the alignment direction of liquid crystal by an electric field which is applied with different potentials to the third electrode and the fourth electrode and is substantially perpendicular to the substrate surface generated between the electrodes is provided.
[0027]
At this time, it is desirable that the first electrode and the second electrode have a comb shape. Alternatively, at least one of the third electrode and the fourth electrode may be a solid electrode that covers substantially the entire surface of the pixel.
[0028]
Further, it is desirable that at least one of the solid electrodes can be individually driven in each pixel, and further desirably that it can be collectively driven in all pixels.
[0029]
As still another configuration example for realizing the above means, a third electrode and a fourth electrode are formed on the other substrate opposite to the one substrate formed by the first electrode and the second electrode. ,
In the image display period, different electric potentials are applied to the first electrode and the second electrode, and an electric field generated between the electrodes and substantially parallel to the substrate surface, and an electric field generated between the third electrode and the fourth electrode. Different potentials are applied, and the orientation direction of the liquid crystal is controlled by an electric field substantially parallel to the substrate surface generated between the electrodes. In the initial stage of the image non-display period, different potentials are applied to the first electrode and the third electrode. An electric field substantially perpendicular to the substrate surface generated between the electrodes and a different electric potential is applied to the second electrode and the fourth electrode between the electrodes to generate an electric field substantially perpendicular to the substrate surface. Liquid crystal driving means for controlling the alignment direction was provided.
[0030]
At this time, it is desirable that the first to fourth electrodes have a comb shape. Alternatively, the first electrode and the third electrode are comb-shaped, the second electrode and the fourth electrode are solid electrodes that cover substantially the entire surface of the pixel, and the first electrode is on the second electrode. And the third electrode may overlap with the fourth electrode via the insulating film.
[0031]
Further, it is desirable that the solid electrode can be individually driven by each pixel, and furthermore, it is desirable that all the pixels can be driven collectively.
[0032]
In the above-mentioned electrode structure, in order to obtain the effect of the present invention efficiently, it is desirable to use the following configuration. That is, when three different electrodes are provided, the potentials of the first electrode and the second electrode are substantially equal at the initial stage of the image non-display period, and only the potential of the third electrode is set to a different potential.
[0033]
When four different electrodes are provided, the potentials of the first electrode, the second electrode, and the fourth electrode are substantially equal and only the potential of the third electrode is different in the initial stage of the image non-display period. Potential. Further, at the initial stage of the image non-display period, the potentials of the first electrode and the second electrode are substantially equal, the potentials of the third electrode and the fourth electrode are substantially equal, and The third electrode is at a different potential.
[0034]
By using the above means, particularly the fall response time of the luminance response time of the liquid crystal display device is shortened, and thereby, a high quality moving image compatible liquid crystal display device which suppresses "moving image blur" which largely affects the moving image quality is provided. Can be provided.
[0035]
The liquid crystal molecules of the liquid crystal layer are preferably homogeneously aligned, and have a positive dielectric anisotropy. Preferably, at least one of the electrodes is formed of a transparent conductive film, and the comb electrode is formed in a V shape. In a configuration in which only the third electrode is formed on the counter substrate, at least one or more dielectric layers excluding an alignment film are formed between the third electrode and the liquid crystal layer. It is desirable.
[0036]
Further, an image display period and an image non-display period are provided in one frame, and intermittent display driving is provided in one frame.
[0037]
The light source may be configured to have a lighting state and a light-off state within one frame.
[0038]
It should be noted that the present invention is not limited to the above configuration and the configuration described in the embodiment described later, and it goes without saying that various modifications can be made without departing from the technical idea of the present invention.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to specific embodiments, a basic configuration of a liquid crystal display device according to the present invention will be described. 1 and 2 are explanatory views of the basic concept of the present invention, and FIG. 1 is an explanatory view of the direction of an electric field generated in a pixel and the movement of liquid crystal molecules in each state of driving the liquid crystal. The diagram in the left column of FIG. 1 shows the movement of liquid crystal molecules as viewed from the cross section of the liquid crystal panel in each state, and the diagram in the right column shows a plan view. FIG. 2 is an explanatory diagram of a temporal change in liquid crystal transmittance (liquid crystal panel luminance) corresponding to each state of liquid crystal driving.
[0040]
Note that (a) state I, (b) state II, and (c) state III in FIG. 1 correspond to state I, state II, and state III in FIG. 2, respectively. The change is defined as process I, the change from state II to state III is defined as process II, and the change from state III to state I is defined as process III. Here, the image display period is a period during which light in step I is transmitted, and the image non-display period is defined as periods II and III in which a black level signal is written.
[0041]
In the basic configuration of the present invention, a pair of substrates 1A and 1B, at least one of which is transparent, a liquid crystal layer 2 (represented by liquid crystal molecules) sandwiched between the pair of substrates, and a pixel formed on the substrate 1A for each pixel. Electrodes, that is, a first electrode 3 and a second electrode 4, and a third electrode 5 formed on the substrate 1B. Then, by applying a voltage between the first electrode 3 and the second electrode 4, the alignment direction of the liquid crystal (liquid crystal molecules) 2 is controlled, and a light source ( (Not shown) to display an image. That is, in the image display period (process I), a voltage is applied between the first electrode 3 and the second electrode 4, and the liquid crystal molecules are driven by the electric field 18 substantially parallel to the substrate surfaces of the pair of substrates 1A and 1B. In the initial stage of the image non-display period (process II), no voltage is applied between the first electrode 3 and the second electrode 4 and the first electrode 3, the second electrode 4, and the third electrode A voltage is applied during 5. Then, the liquid crystal molecules are driven by an electric field 19 substantially perpendicular to the pair of substrate surfaces.
[0042]
In driving such liquid crystal molecules, it is possible to particularly reduce the fall response time as compared with the conventional IPS type liquid crystal display device. This will be described in detail below.
[0043]
In state I of FIG. 1, no voltage is applied to each electrode, and no electric field is generated. Therefore, the liquid crystal molecules 2 are uniformly aligned in the initial alignment direction 20 (rubbing direction). At this time, the polarizing plates 17A and 17B laminated on the outer surfaces of the pair of substrates are arranged in a crossed Nicols arrangement, and the transmission axis of one of the polarizing plates coincides with the initial alignment direction of the liquid crystal. Therefore, in the state I, as shown in FIG. 2, the liquid crystal transmittance (luminance) is almost zero, and a black display is obtained.
[0044]
Next, when a voltage is applied between the first electrode 3 (for example, a pixel electrode) and the second electrode 4 (for example, a common electrode), the voltage is substantially parallel to the substrate surface generated between these electrodes. Due to the electric field 18 (lateral electric field), the alignment direction of the liquid crystal molecules 2 rotates in a plane substantially parallel to the substrate surface, and transmits light (process I). This process I is the same as the driving of liquid crystal molecules in the conventional IPS mode liquid crystal display device. The rise response time is equivalent to that of the conventional IPS mode liquid crystal display device.
[0045]
When the display is turned off (image is not displayed), first, a voltage is applied to the third electrode 5 formed on the substrate 1B (hereinafter, also referred to as a counter substrate). Thereby, an electric field 19 (vertical electric field) substantially perpendicular to the substrate surface is generated between the third electrode 5 and the first electrode 3 or between the third electrode 5 and the second electrode 4. The electric field 19 is used to drive the liquid crystal molecules so as to rise with respect to the substrate surface. Note that the liquid crystal needs to be of a positive type (having a positive dielectric anisotropy) in order for the liquid crystal molecules to rise by a vertical electric field as shown in FIG. At this time, as described above, since the polarizing plates 17A and 17B are in a crossed Nicols arrangement, black display can be achieved by setting the liquid crystal molecules 2 substantially perpendicular to the substrate surface. As shown in FIG. 2, in the state III, black display is performed.
[0046]
After the liquid crystal molecules 2 are raised by an electric field substantially perpendicular to the substrate surface, black is displayed, and then each electrode (the first electrode 3 which is a pixel electrode, the second electrode 4 which is a common electrode, and the third electrode) When the potential of 5) is set to the same potential, no electric field occurs in the pixel. As a result, the rising liquid crystal molecules fall toward the initial alignment direction. In the process in which the liquid crystal molecules fall (process III), the polarizers 17A and 17B maintain a black display due to the crossed Nicols arrangement.
[0047]
Here, the important point is that the horizontal electric field and the vertical electric field are selectively used in terms of time, and particularly for the fall response, the liquid crystal is driven by the vertical electric field to display black. In the conventional display mode, the black display, that is, the fall response time is determined by the material properties of the liquid crystal material such as the viscosity and the elastic constant. However, in the present invention, the fall response time is determined by using the vertical electric field 19 in addition to the material properties. Since control is possible, the response time can be reduced.
[0048]
At this time, in order to effectively apply the vertical electric field, it is desirable that the potentials of the first electrode 3 and the second electrode 4 be substantially equal when a voltage is applied to the third electrode. That is, it is desirable that no electric field is generated between the first electrode 3 and the second electrode 4. By reducing the electric field generated by the potential difference between the electrodes formed on the same substrate, the vertical electric field strength generated between the electrode and the third electrode, which is the counter electrode, can be effectively used.
[0049]
By driving such liquid crystal molecules, it is possible to shorten the fall response time as compared with a conventional IPS mode liquid crystal display device. As electrode structures capable of realizing the driving of the liquid crystal molecules, there are roughly five electrode structures as shown in FIG.
[0050]
FIG. 3 is an explanatory view of a typical electrode structure for driving liquid crystal molecules and the formation of an electric field in the liquid crystal display device of the present invention. Note that the same reference numerals in FIG. 3 as those in FIG. 1 correspond to the same functional portions, and reference numeral 6 is a fourth electrode. One typical electrode structure is to form two different types of comb-shaped electrodes (first electrode 3 and second electrode 4) on one substrate 1A side, as shown in FIG. On the other substrate 1B, a solid electrode is formed as a third electrode 5 covering almost the entire surface of the pixel. In the image display period, the liquid crystal is driven by an electric field 18 substantially parallel to the substrate surface by applying different potentials to the first electrode 3 and the second electrode 4 formed on one of the substrates 1A, and during the image non-display period. In the initial stage, the first electrode 3 and the second electrode 4 are set to the same potential as, for example, zero potential, and at the same time, a predetermined potential is applied to the third electrode 5 so that the first electrode 3 and the second A vertical electric field 19 is generated between the electrodes 4. The liquid crystal molecules are activated by the vertical electric field 19 to display black. Thereafter, all the electrodes are set to, for example, zero potential so that no electric field is applied to the liquid crystal, whereby the liquid crystal molecules return to the initial alignment state. In this process, the display remains black.
[0051]
FIG. 3B shows a structure in which the second electrode 4 as a solid electrode is formed on the substrate 1A, and the first electrode 3 in the form of a comb electrode is superposed on the second electrode 4 via the insulating film 10. In this structure, the liquid crystal molecules are driven mainly by using the electric field generated at the end of the comb-shaped electrode-shaped first electrode 3 which is superimposed during the image display period, and white display is performed. In the initial stage of the image non-display period, these electrodes are set to the same potential (for example, zero potential), a potential is applied to the third electrode 5 which is a solid electrode disposed on the substrate 1B which is the opposite substrate, and a vertical electric field generated therebetween. 19 causes the liquid crystal molecules to rise to perform black display. Thereafter, the liquid crystal molecules are returned to the initial alignment state by setting all the electrodes to, for example, zero potential as described above. In this process, the display remains black. In this structure, since a vertical electric field is generated by the solid electrodes (the second electrode 4 and the third electrode 5) formed on each of the substrates 1A and 1B, the vertical electric field is generated more efficiently than the structure shown in FIG. Generated and can be used.
[0052]
In FIG. 3C, liquid crystal molecules are driven by an electric field 18 generated between two different comb-like electrodes (first electrode 3 and second electrode 4) formed on the substrate 1A, and white display is performed. . Then, a first electrode 6 in the form of a solid electrode formed via an insulating film 10 is provided below the first electrode 3 and the second electrode 4 on the substrate 1A side, and the first electrode 3 and the second electrode The liquid crystal molecules rise using the vertical electric field 19 generated between the electrode group of the fourth and fourth electrodes and the third electrode 5 which is a solid electrode disposed on the opposite substrate 1B, and black display is performed.
[0053]
In FIG. 3D, the first and second comb-shaped electrodes 3 and 4 provided on the substrate 1A and the third and fifth comb-shaped electrodes 5 and 6 provided on the substrate 1B respectively. 1A and 1B, a horizontal electric field 18 parallel to each substrate surface is formed to perform white display. When performing black display, a vertical electric field 19 is applied between the first electrode 3 and the second electrode 4 formed on the substrate 1A and between the third electrode 5 and the fourth electrode 6 formed on the substrate 1B. To form
[0054]
In FIG. 3E, a solid electrode-shaped second electrode 4 formed on the substrate 1A and a comb-shaped first electrode 3 formed on the second electrode 4 with an insulating film 10 interposed therebetween are provided. The fifth electrode 6 has a solid electrode-shaped fifth electrode 6 formed on the substrate 1B and a comb-shaped third electrode 5 formed on the fifth electrode 6 with an insulating film 10 interposed therebetween. When white display is performed, a horizontal electric field 18 is formed between the first electrode 3 and the second electrode 4 and between the third electrode 5 and the fourth electrode 6 of each substrate, and black display is performed. In this case, a vertical electric field 19 generated between the electrode group of the substrate 1A and the electrode group of the substrate 1B is used.
[0055]
The solid third electrodes 5 shown in FIGS. 3A, 3B, and 3C are individually driven by an active element such as a thin film transistor (TFT) for each pixel. Alternatively, they may be collectively formed on the entire surface of the substrate and connected directly to a drive circuit to drive them collectively. In the case of driving individually, black display can be written in each pixel at an independent timing. On the other hand, in the case of batch formation on the entire surface, black display can be written at the same timing on the entire surface.
[0056]
Further, these solid electrodes are preferably made of a transparent conductive film such as indium tin oxide (ITO), indium zinc oxide (IZO), indium germanium oxide (IGO), or a mixture thereof in consideration of the transmittance of the liquid crystal panel. . In the case of a comb-shaped electrode, it is preferable to use a transparent conductive film in consideration of transmittance. However, the present invention is not limited to this, and a metal material that does not transmit light, such as chromium, aluminum, or copper, may be used.
[0057]
In each of the above-described structures, in order to efficiently generate the vertical electric field 19 and shorten the fall response time, the potential of the first electrode 3 and the second electrode 4 is substantially reduced in the initial stage of the image non-display period. It is desirable to make them equal and set the potential of only the third electrode 5 to be different. This is because when the potentials of the first electrode 3 and the second electrode 4 are different, a horizontal electric field similar to that during the image display period is generated simultaneously with the vertical electric field, and the liquid crystal molecules rise in an orientation different from the initial orientation direction. This is because it is difficult to perform a complete black display. This causes a deterioration in image quality such as a decrease in contrast.
[0058]
Similarly, a structure having four different electrodes, of which three electrodes (first electrode 3, second electrode 4, and fourth electrode 6) are formed on the same substrate (FIG. In c)), in the initial stage of the image non-display period, it is desirable that the potentials of the first electrode 3, the second electrode 4, and the fourth electrode 6 are substantially equal, and only the third electrode is different. This is because an unnecessary horizontal electric field is not generated between the three electrodes formed on the same substrate 1A during the image non-display period, as in the above case.
[0059]
Further, in a structure having four different electrodes and two electrodes formed on each substrate (FIGS. 3 (d) and 3 (e)), in an image display period, horizontal and vertical lines are formed above and below the liquid crystal layer, respectively. Since an electric field is generated, the horizontal electric field density is increased as compared with the conventional in-plane switching mode liquid crystal display device, so that the liquid crystal molecules are effectively driven, and a short response time can be expected. In the initial stage of the image non-display period, the potential of the first electrode 3 and the potential of the second electrode 4 are substantially equal, and the potential of the third electrode 5 and the potential of the fourth electrode 6 are substantially equal. A vertical electric field can be efficiently generated between the electrode group formed on the lower substrate and the electrode group formed on the lower substrate, and the fall response time can be shortened.
[0060]
Further, in recent years, it has been pointed out that the deterioration of the moving image display in the liquid crystal display device is caused by a hold-type display that maintains the luminance within one frame. In a moving image compatible liquid crystal display device, an impulse type display is required. As means for achieving this, the above-described black writing drive and blink backlight method have been proposed. In order to display a high-quality moving image by using these techniques, it is essential to reduce the fall response time, as described above.
[0061]
In the conventional black writing drive, since the luminance does not decrease to a sufficient black level because the falling response of the liquid crystal is slow, the ideal intermittent display within one frame is not achieved, and "moving image blur" is improved to some extent. Is possible, but cannot be improved sufficiently. In the intermittent display by the black writing drive, the contrast ratio between the luminance in the image display period and the luminance in the image non-display period must be high. This means that the fall response needs to be fast. Therefore, in the black writing drive, by using the above-described electrode structure and liquid crystal driving, a black writing drive (ideal intermittent display) with a fast falling response becomes possible, and “moving image blur” can be sufficiently improved. .
[0062]
Also, in the blink backlight method, as described above, a ghost phenomenon occurs due to a difference between the response time of the rise and fall of the liquid crystal and the lighting timing of the backlight. This phenomenon is caused by human eyes perceiving the luminance difference in the shaded area in FIG. 32, and can be suppressed by shortening the rise and fall response time. Therefore, in the blink backlight system, the ghost phenomenon can be suppressed by utilizing the above-described electrode structure and liquid crystal driving.
[0063]
The present invention not only shortens the response speed of the liquid crystal, particularly the fall response time, but also solves a new problem that arises when a moving image compatible technology such as a black writing drive or a blink backlight method is applied. Thus, it is possible to provide a moving image-compatible liquid crystal display device with higher quality than before. Hereinafter, specific examples will be described, but as described above, the present invention is not limited to the following examples.
[0064]
First, a first embodiment and a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is an explanatory view of the electrode structure of the pixel section according to the first embodiment and the second embodiment of the present invention. 4A is a plan view of one substrate (a substrate on which a thin film transistor is formed, hereinafter referred to as a TFT substrate 1A), and the lower diagram is a cross-sectional view taken along line AA ′ of the upper diagram. 4B is a plan view of the other substrate (a substrate on which a color filter is formed, hereinafter referred to as a CF substrate 1B), and the lower diagram is a cross-sectional view taken along line BB ′ of the upper diagram. It is. 4, the same reference numerals as those in FIGS. 1 and 3 correspond to the same functional portions. Reference numerals 8A and 8B are signal wirings, 9A is a thin film transistor for driving a pixel electrode included in the TFT substrate 1A, and 9B is a CF substrate 1B. The thin film transistor for driving the third electrode 5 provided, 11 is a through hole connecting the output electrode (source electrode) of the thin film transistor 9B and the third electrode 5, 13 is an overcoat film, 14 is a color filter, and 15 is black. 2 shows a matrix.
[0065]
FIGS. 5A and 5B are cross-sectional views of a pixel portion according to the first and second embodiments of the present invention. FIG. 5A shows the pixel portion of the first embodiment, and FIG. 2 illustrates an example pixel portion. FIG. 6 is an equivalent circuit diagram illustrating a driving system of a liquid crystal display device according to the first embodiment and the second embodiment of the present invention. The same reference numerals in FIG. 6 as those in FIG. 30 correspond to the same functional portions, reference numerals 23A and 23B indicate signal electrode driving circuits, and reference numeral 27 indicates a display pixel portion. FIG. 7 is an explanatory diagram similar to FIG. 31 of the signal waveform supplied to each electrode and wiring, and FIG. _G Is the signal waveform (V _GH Is high level, V _GL Is low level), V of waveforms (b) and (e) _D1, V _D2 V represents a signal waveform supplied to the first signal wiring and a signal waveform supplied to the second signal wiring, respectively. _DH Is high level, V _DL Is low level. V of waveform (c) _S Is the signal waveform applied to the pixel electrode, V in waveform (d) _C Represents a signal waveform applied to the common electrode, and GND represents a ground level. V of waveform (f) _N Represents the signal waveform applied to the third electrode 5, and the waveform (g) represents the time change of the liquid crystal transmittance in the driving of the present embodiment.
[0066]
[First embodiment]
The structure of the present embodiment is a structure corresponding to FIG. In the liquid crystal display device according to the first embodiment of the present invention, the diagonal size of the display unit is nominally 15 inches, the pair of substrates are both transparent glass substrates, and the thickness is 0.1 mm. 7 mm. First, as shown in FIG. 4A, a first scanning wiring 7A and a comb-shaped common electrode 4 are formed on a substrate 1A. Next, the insulating film 10 is formed using silicon nitride SiNx, and the first signal wiring 8A and the pixel electrode as the first electrode 3 are formed thereon in a comb-like shape. Note that a first thin film transistor 9A made of amorphous silicon is arranged near an intersection of the scanning wiring 7A and the signal wiring 8A formed in a matrix, and the first electrode 3 serving as a pixel electrode is connected to the first signal 3A. The wiring 8A is electrically connected through the thin film transistor 9A. Pixels are formed corresponding to regions surrounded by the respective wirings formed in a matrix.
[0067]
Chromium molybdenum CrMo is used as an electrode material. There is no particular problem in the material of the signal wiring and the scanning wiring as long as the material has low electric resistance, and aluminum or copper may be used.
[0068]
On the other hand, the substrate 1B opposed to the substrate 1A is provided with color filters 14 of three colors (red, green, and blue: R, G, and B) in a stripe shape and a black matrix 15. An overcoat film 13 for planarizing the surface is formed on the color filter 14 and the black matrix 15. Note that an epoxy resin or the like is used as the overcoat film 13.
[0069]
A second scanning wiring 7B, an insulating film 10, and a second signal wiring 8B are provided on such a color filter substrate, and a solid third electrode 5 covering almost the entire surface of the pixel is formed on the uppermost layer. ing. The solid third electrode 5 is formed of ITO, and is electrically connected to the second signal wiring 8B via the through hole 11 and the second thin film transistor 9B. Further, the first scanning wiring 7A formed on the substrate 1A and the second scanning wiring 7B formed on the substrate 1B are connected outside the substrate, and these are driven by one scanning electrode driving circuit (scan driver) 22. .
[0070]
As described above, the substrate on which the first thin film transistor 9A is formed is called a TFT substrate, and the substrate on which a color filter is formed is called a color filter substrate (CF substrate). A 100-nm-thick polyimide alignment film 12 for aligning liquid crystal molecules is formed on the surface of the TFT substrate and the CF substrate manufactured as described above. In general, a polyimide film is formed by applying a polyamic acid, which is a precursor of the polyimide film, to the surface of a substrate using a printing machine or the like, and firing these at high temperature. The alignment process is performed by rubbing the surface of the polyimide alignment film 12 formed here. The rubbing direction is a direction inclined by 15 ° from the longitudinal direction of the first electrode (pixel electrode) 3.
[0071]
In this embodiment, the first electrode and the second electrode (pixel electrode and common electrode) arranged in the pixel are formed in a comb shape as shown in FIG. As shown in FIG. 34B, it may be formed in a V shape having an angle θ with respect to the electrode extension direction. By forming the first electrode 3 and the second electrode 4 in a dogleg shape, regions where the rotation directions of the liquid crystal molecules are different when a voltage is applied are generated. Thereby, coloring due to the viewing angle can be suppressed. However, in the case of a square-shaped electrode, the initial alignment direction of the liquid crystal molecules is set so that, for example, in the case of a positive type liquid crystal (dielectric anisotropy is positive), the major axis of the liquid crystal molecules coincides with the longitudinal direction of the pixel. It is necessary to perform orientation treatment.
[0072]
Next, a thermosetting sealing material is applied to the periphery of the display area of one of the pair of substrates, and the other opposing substrate is overlaid. The sealing material is applied so as to form a sealing port for injecting liquid crystal into the liquid crystal element later. These substrates are pressurized while being heated, and both substrates are bonded and fixed. In addition, a space of 4 micrometers can be maintained between the substrates. Thereafter, liquid crystal is injected into the liquid crystal display element from the sealing port by a vacuum sealing method, and then the sealing port is sealed with an ultraviolet curable resin or the like. Here, a material having a positive dielectric anisotropy is used as the liquid crystal material. Polarizing plates 17 are attached to both surfaces of the combined substrate in a crossed Nicols arrangement so as to have normally-closed characteristics (black display at low voltage, white display at high voltage).
[0073]
As shown in FIG. 6, each wiring is arranged to extend to the edge of the substrate, and the first signal wiring 8A, the second signal wiring 8B, the scanning wiring 7 (the first scanning wiring 7A, the second scanning wiring 7B), the common electrode 4 is connected to a first signal driver 23A, a second signal driver (signal electrode driving circuit) 23B, a scanning driver 22, and a common electrode driver (common electrode driving circuit) 24, respectively. You. Each driver is controlled by the display control device 21. Note that an equivalent circuit corresponding to the electrode structure of this embodiment corresponding to one pixel is shown in a region (display pixel portion) 27 surrounded by a broken line.
[0074]
Thereafter, as shown in FIG. 33, a liquid crystal display device 39 is assembled by combining the shield case 32, the diffusion plate 33, the light guide plate 34, the reflection plate 35, the backlight 36, the lower case 37, and the inverter circuit 38. In the liquid crystal display device thus obtained, the effects of the present invention can be obtained by applying the signal waveforms shown in FIGS. 7A to 7E to each wiring and electrode. Hereinafter, signal waveforms applied to each electrode and wiring will be described.
[0075]
In the present embodiment, double speed black writing driving is performed in which a signal corresponding to a black level is inserted in one frame. In FIG. 7, (a) the signal waveform V supplied to the scanning wiring _G , (B) the signal waveform V supplied to the first signal wiring _D1 , (C) the signal waveform V applied to the pixel electrode _S , (D) signal waveform V applied to the common electrode _C , (E) the signal waveform V supplied to the second signal wiring _D2 , (F) the signal waveform V applied to the third electrode _N Is supplied to the corresponding signal wiring or electrode. FIG. 7 (g) shows a time change of the liquid crystal transmittance in the main driving.
[0076]
In FIG. 7, first, a time t = t based on a scanning signal ₀ , The first and second thin film transistors are turned on, a voltage from the first signal line is applied to the pixel electrode (first electrode) 3, and a voltage from the second signal line is applied to the third electrode 5. A voltage is applied. Next, t = t ₁ , A scanning signal is written again, a voltage from the first signal line is applied to the pixel electrode 3, and a voltage from the second signal line is applied to the third electrode 5.
[0077]
Image display period (t ₀ <T <t ₁ ), The potential difference (V) between the first electrode (pixel electrode) 3 and the second electrode (common electrode) 4 _SH -V _C The liquid crystal is driven by using the horizontal electric field generated by the method (1) to display an image. t = t ₁ , The potentials of the first electrode (pixel electrode) 3 and the second electrode (common electrode) 4 are set to be substantially the same, and the voltage V _NH Is applied. At this time, the horizontal electric field becomes almost zero, and the vertical electric field generated between the second electrode (common electrode) 4, the first electrode (pixel electrode) 3 and the third electrode 5 causes the liquid crystal molecules to move on the substrate surface. A black color is displayed by standing up almost perpendicularly.
[0078]
Next, t = t ₂ By setting the first electrode (pixel electrode) 3, the second electrode (common electrode) 4, and the third electrode 5 to the same potential, the liquid crystal molecules that have risen almost perpendicularly to the substrate surface It falls on a plane substantially parallel to the substrate surface toward the initial alignment state. In this process, the display axis remains black because the projection axis of the liquid crystal molecules on the substrate surface in the major axis direction is parallel to the transmission axis of one polarizer and perpendicular to the transmission axis of the other polarizer. is there. And t = t ₃ In, the state has returned to the initial orientation, and t = t ₃ The next frame is started at the timing of.
[0079]
Here, the response speed was evaluated using the liquid crystal display device having the above configuration. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0080]
[Second embodiment]
FIG. 5B is a sectional view of a liquid crystal display device according to a second embodiment of the present invention. This embodiment and the first embodiment described with reference to FIG. 5A are different from the first embodiment in that a dielectric layer 16 is provided between the third electrode 5 which is a solid electrode formed on the CF substrate 1B side and the alignment film 12. They differ in the arrangement. When the third electrode 5 is in direct contact with the liquid crystal layer as in the first embodiment, the potential of the third electrode 5 greatly affects the normal driving voltage, and there is a concern that the driving voltage may increase. You. Therefore, in the present embodiment, by arranging the dielectric layer 16, it is possible to prevent the potential of the third electrode 5 from directly affecting the liquid crystal layer, and the rise of the driving voltage is reduced. At the same time, as in the first embodiment, the fall response time can be shortened, and the moving image display performance can be improved.
[0081]
[Third embodiment]
The configuration of the third embodiment of the present invention will be described with reference to FIGS. 8, 9, 10, and 11. FIG. FIG. 8 is a view for explaining an electrode structure of a pixel portion similar to FIG. 4 for explaining the structure of the third embodiment of the present invention. 8A is a plan view of the TFT substrate 1A, the lower view is a cross-sectional view taken along line AA ′ of the upper view, and the upper view of FIG. The plan view of the substrate 1B and the lower view are cross-sectional views along the line BB 'of the upper view. FIG. 9 is a sectional view of a pixel portion of a liquid crystal display according to a third embodiment of the present invention, and FIG. 10 is a diagram for explaining a driving system of the liquid crystal display. FIG. 11 is an explanatory diagram of signal waveforms supplied to each electrode and wiring. Note that the structure in this embodiment is a structure corresponding to FIG.
[0082]
This embodiment is different from the first embodiment in the electrode structure on the CF substrate 1B side. In the first embodiment, a third electrode 5 formed on the CF substrate 1B is formed for each pixel, and the third electrode 5 is individually driven by a thin film transistor 9B formed for each pixel. On the other hand, in the present embodiment, the third electrode 5 is commonly formed for all pixels. The third electrode 5 is directly connected to and controlled by a third electrode drive circuit disposed outside the pixel area. In this structure, unlike the first embodiment in which the third electrode 5 is driven by a thin film transistor, black display can be simultaneously written to all pixels.
[0083]
Using the liquid crystal display device according to the third embodiment of the present invention, the response speed was evaluated. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0084]
[Fourth embodiment]
The configuration of the fourth embodiment of the present invention will be described with reference to FIGS. 12, 13, 14, and 15. FIG. FIG. 12 is a view for explaining an electrode structure of a pixel portion similar to FIG. 8 according to the liquid crystal display device of the fourth embodiment of the present invention. The upper part of FIG. 12A is a plan view of the TFT substrate 1A, the lower part is a cross-sectional view along the line AA ′ of the upper part, and the upper part of FIG. The plan view of the substrate 1B and the lower view are cross-sectional views along the line BB 'of the upper view. FIG. 13 is a sectional view of a pixel portion of a liquid crystal display according to a fourth embodiment of the present invention, and FIG. 14 is a diagram illustrating a driving system of the liquid crystal display. FIG. 15 is an explanatory diagram of signal waveforms supplied to each electrode and wiring. Note that the structure in this embodiment is a structure corresponding to FIG.
[0085]
This embodiment is different from the third embodiment in that a second electrode (common electrode) 4 formed on the TFT substrate side is individually driven by a thin film transistor 9B formed for each pixel. At this time, as shown in FIG. 15C and FIG. ₁ <T <t ₂ ), To make the potential difference between the first electrode (pixel electrode) 3 and the second electrode (common electrode) 4 substantially zero, _SH And V _CH Need to be set to substantially the same potential.
[0086]
By driving the second electrode (common electrode) 4 for each pixel in this way, it is not necessary to drive and control the third electrode 5 formed on the CF substrate 1B side, and the structure of the liquid crystal display device is simplified. it can. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0087]
[Fifth embodiment]
The configuration of the present embodiment will be described with reference to FIGS. FIG. 16 is a view for explaining an electrode structure of a pixel portion similar to FIG. 12 according to the fifth embodiment of the present invention. The upper part of FIG. 16A is a plan view of the TFT substrate 1A, the lower part is a sectional view taken along line AA ′ of the upper part, and the upper part of FIG. The plan view of the substrate 1B and the lower view are cross-sectional views along the line BB 'of the upper view. FIG. 17 is a sectional view of a pixel portion of a liquid crystal display according to a fifth embodiment of the present invention. In addition, since the driving system of the liquid crystal display device and the waveforms of the signals supplied to the wirings and the electrodes in this embodiment are substantially the same as those in the third embodiment, the signal waveforms will be described with reference to FIGS. Note that the structure in this embodiment is a structure corresponding to FIG.
[0088]
In the liquid crystal display device according to the present embodiment, the diagonal size of the display unit is nominally 15 inches, the pair of substrates are both transparent glass substrates, and the thickness is 0.1 mm. 7 mm. First, as shown in FIG. 16A, a solid second electrode (common electrode) 4 is formed on the substrate 1A so as to cover almost the entire surface of the first scanning wiring 7 and the pixel. Next, the insulating film 10 is formed using silicon nitride SiNx, and the signal wiring 8A and the comb-shaped first electrode (pixel electrode) 3 are formed thereon. A thin film transistor 9 made of amorphous silicon or the like is arranged near the intersection of the scanning wiring 7 and the signal wiring 8A formed in a matrix. The first electrode (pixel electrode) 3 and the signal wiring 8A are electrically connected through the thin film transistor 9. Pixels are formed corresponding to regions surrounded by the respective wirings formed in a matrix.
[0089]
As the electrode material, chromium molybdenum (CrMo) is used for wiring such as scanning wiring and signal wiring, and an ITO transparent electrode is used for the first electrode (pixel electrode) and the second electrode (common electrode) in order to secure an aperture ratio. Is used.
[0090]
On the other hand, a substrate 1B opposed to the substrate 1A is provided with a color filter 14 of three colors (R, G, B) in a stripe shape and a black matrix 15. On the color filter 14 and the black matrix 15, an overcoat resin film 13 for flattening the surface is formed. Note that an epoxy resin or the like is used as the overcoat film.
[0091]
The solid third electrode 5 is formed on such a CF substrate 1B. The third electrode 5 is formed of ITO. On the inner surfaces of the TFT substrate (substrate 1A) and CF substrate (substrate 1B) thus manufactured, a polyimide alignment film 12 for aligning liquid crystal molecules is formed with a thickness of 100 nm. In general, a polyimide film is formed by applying a polyamic acid, which is a precursor thereof, to the surface of a substrate using a printing machine or the like, and baking these at a high temperature. The alignment process is performed by rubbing the surface of the polyimide alignment film 12 formed here. The rubbing direction is a direction inclined by 15 ° from the longitudinal direction of the pixel electrode serving as the first electrode 3.
[0092]
In the present embodiment, the pixel electrode 3 as the first electrode is formed in a comb-teeth shape as shown in FIG. 33 (a), but as shown in FIG. It may be formed in a V shape having θ. By forming it in a V shape, regions where the rotation directions of the liquid crystal molecules are different when a voltage is applied are generated, whereby the coloring can be suppressed. However, it is necessary to perform the alignment treatment so that the long axis of the liquid crystal molecules coincides with the longitudinal direction of the pixel as the initial alignment direction of the liquid crystal molecules in the case of the V-shaped electrode, for example, in the case of the positive type liquid crystal.
[0093]
Next, a thermosetting sealing material is applied to the periphery of the display area of one of the pair of substrates 1A and 1B, and the other counter substrate is overlaid. The sealing material is applied so as to form a sealing port for injecting liquid crystal into the liquid crystal element later. These substrates are pressed while being heated, and both substrates are bonded and fixed. In addition, a space of 4 micrometers can be maintained between the substrates. Thereafter, liquid crystal is injected into the liquid crystal display element from the sealing port by a vacuum sealing method, and then the sealing port is sealed with an ultraviolet curing resin or the like. Here, a material having a positive dielectric anisotropy is used as the liquid crystal material.
[0094]
Polarizing plates 17 (17A, 17B) are attached to both surfaces of the combined substrate in a crossed Nicols arrangement so as to have normally-closed characteristics (black display at low voltage, white display at high voltage). Thereafter, a liquid crystal display device 39 is assembled by combining the shield case 32, the diffusion plate 33, the light guide plate 34, the reflection plate 35, the backlight 36, the lower case 37, and the inverter circuit 38 shown in FIG. In the liquid crystal display device thus obtained, signals applied to each wiring and electrode are as shown in FIG. 11, which is almost the same as in the third embodiment.
[0095]
That is, the image display period (t ₀ <T <t ₁ In), the liquid crystal is driven using an electric field generated by a potential difference between the first electrode (pixel electrode) and the second electrode (common electrode) to display an image. A particularly large electric field is generated at the end of the comb-shaped pixel electrode, and is characterized in that the rising response speed is faster than that of the conventional IPS. Specifically, t = t ₁ , The pixel electrode and the common electrode are set to have substantially the same potential, and a voltage is applied to the third electrode 5. At this time, the horizontal electric field becomes almost zero, and the vertical electric field generated between the second electrode (common electrode), the first electrode (pixel electrode) and the third electrode causes the liquid crystal molecules to be almost perpendicular to the substrate surface. To display black.
[0096]
In the present embodiment, since the common electrode is formed so as to cover almost the entire surface of the pixel as compared with the third embodiment, the vertical electric field generated in the initial stage of the image non-display period is substantially uniform throughout the pixel. Can be generated. Therefore, the fall time can be further reduced as compared with the third embodiment.
[0097]
Next, t = t ₂ By setting the first electrode (pixel electrode), the second electrode (common electrode), and the third electrode at the same potential, the liquid crystal molecules that have risen almost perpendicularly to the substrate surface are in the initial alignment state. Toward a surface substantially parallel to the substrate surface. In this process, the display axis remains black because the projection axis of the liquid crystal molecules on the substrate surface in the major axis direction is parallel to the transmission axis of one polarizer and perpendicular to the transmission axis of the other polarizer. is there. And t = t ₃ In, the state has returned to the initial orientation, and t = t ₃ The next frame is started at the timing of.
[0098]
Using the liquid crystal display device thus obtained, the response speed was evaluated. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0099]
[Sixth embodiment]
The configuration of the sixth embodiment of the present invention will be described with reference to FIGS. 18, 19 and 20. FIG. 18 is an explanatory view of an electrode structure of a pixel portion similar to that of FIG. 12 of the liquid crystal display device according to the sixth embodiment of the present invention. The upper part of FIG. 18A is a plan view of the TFT substrate 1A, the lower part is a cross-sectional view taken along line AA ′ of the upper part, and the upper part of FIG. The plan view of the substrate 1B and the lower view are cross-sectional views along the line BB 'of the upper view. FIG. 19 is a sectional view of a pixel portion of a liquid crystal display device according to a sixth embodiment of the present invention, and FIG. 20 is an explanatory diagram of signal waveforms supplied to each electrode and wiring. Note that the structure in this embodiment is a structure corresponding to FIG.
In this embodiment, four different electrodes are used, as can be seen from FIG. However, as will be described later, depending on driving, the fourth electrode 6 which is arranged to overlap the lower layer of the common electrode as the second electrode can have the same potential as the common electrode 4 at all times. In this case, three different electrodes are provided.
[0100]
In the liquid crystal display device according to the present embodiment, the diagonal size of the display unit is nominally 15 inches, the pair of substrates are both transparent glass substrates, and the thickness is 0.1 mm. 7 mm. First, as shown in FIG. 18, a fourth electrode 6, a second electrode (common electrode) 4, a signal wiring 8A, and a first electrode (pixel electrode) 3 are formed on a TFT substrate 1A. The insulation between the electrodes is maintained by the insulating film 10. There is no particular problem as long as the electrode material has a low electric resistance. However, since the fourth electrode 6 is formed so as to cover almost the entire pixel region, the aperture ratio is low in the case of a transmission type liquid crystal display device. It is desirable to use a transparent conductive film such as ITO in order to secure the thickness.
[0101]
On the other hand, a transparent conductive film is formed on the CF substrate so as to cover the entire surface of the pixel region. Then, after performing the predetermined processing shown in the first embodiment on both of these substrates, they are attached to each other to assemble a liquid crystal display device. In the liquid crystal display device thus obtained, a signal waveform shown in FIG. 20 is supplied to each wiring and electrode. In FIG. 20, the image display period (t ₀ <T <t ₁ In), liquid crystal molecules are driven by a potential difference between the second electrode (common electrode) and the first electrode (pixel electrode). Then, the initial stage of the image non-display period (t ₁ <T <t ₂ In), the potentials of the first electrode (pixel electrode) and the second electrode (common electrode) are set to be substantially the same, and the solid electrodes (third electrode 5 and fourth electrode 6) formed on both substrates are formed. Black is displayed by raising the liquid crystal in a direction substantially perpendicular to the substrate surface by a vertical electric field generated therebetween. In the structure of the present embodiment, the vertical electric field is generated by the electrode covering almost the entire pixel region, so that the generation efficiency of the vertical electric field is higher and the fall time is further reduced as compared with the first embodiment. Is possible.
[0102]
Using the liquid crystal display device thus obtained, the response speed was evaluated. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0103]
[Seventh embodiment]
The configuration of the seventh embodiment of the present invention will be described with reference to FIGS. 21, 22, 23, and 24. FIG. 21 is an explanatory view of the electrode structure of the pixel portion of the liquid crystal display device according to the seventh embodiment of the present invention. The upper part of FIG. 21 (a) is a plan view of the TFT substrate 1A, and the lower part is the upper part. 21B is a cross-sectional view taken along line AA ′ of FIG. 21B. The upper part of FIG. 21B is a plan view of the CF substrate 1B, and the lower part of FIG. 21B is along the line BB ′ of the upper part. It is sectional drawing. FIG. 22 is a sectional view of a pixel portion of a liquid crystal display device according to a seventh embodiment of the present invention, and FIG. 23 is a diagram for explaining a drive system of the liquid crystal display device. FIG. 24 is an explanatory diagram of signal waveforms supplied to each electrode and wiring. The structure according to the present embodiment is a structure corresponding to FIG. FIG. 3 is an explanatory diagram of signal waveforms supplied to each electrode and wiring.
[0104]
As can be seen from FIGS. 21 and 22, the TFT substrate 1A has the same structure as the conventional IPS mode liquid crystal display device. On the other hand, the CF substrate 1B also has the same electrode structure as the TFT substrate 1A after the overcoat film 13 is formed. In the image display period, the liquid crystal is driven by a horizontal electric field generated between the pixel electrode as the first electrode 3 and the common electrode as the second electrode 4 as shown in FIG. At the same time, the liquid crystal can be driven by a lateral electric field generated between the third electrode 5 and the fourth electrode 6, and the rising response speed is improved at a low voltage because the efficiency of generating the lateral electric field is higher than that of the conventional IPS. Is possible.
[0105]
On the other hand, in the initial stage of the image non-display period, the potentials of the second electrode (common electrode) and the first electrode (pixel electrode) are set to be substantially the same, and at the same time, the third electrode and the fourth electrode are set to the same potential. Are set so that the potentials of the electrodes are substantially the same. Further, the potentials of the electrodes (pixel electrode and common electrode) formed on the TFT substrate 1A side are set higher than the potentials of the electrodes (third electrode and fourth electrode) formed on the CF substrate 1B side. Thereby, a vertical electric field can be generated.
[0106]
Using the liquid crystal display device thus obtained, the response speed was evaluated. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0107]
[Eighth embodiment]
The configuration of the eighth embodiment of the present invention will be described with reference to FIGS. FIG. 25 is a diagram for explaining the electrode structure of the pixel portion. The upper diagram in FIG. 25A is a plan view of the TFT substrate 1A, and the lower diagram is along the line AA ′ in the upper diagram. 25B is a plan view of the CF substrate 1B, and the lower view is a cross-sectional view taken along line BB ′ of the upper view. FIG. 26 is a sectional view of a pixel portion of a liquid crystal display according to an eighth embodiment of the present invention. Note that the structure in the present embodiment is a structure corresponding to FIG.
[0108]
As can be seen from FIGS. 25 and 26, the electrode structure on the TFT substrate 1A side is the same as that of the fifth embodiment, and this structure is also formed on the CF substrate 1B side. In such an electrode structure, when the signal waveform shown in FIG. 24 is supplied, the electric field generated between the first electrode (pixel electrode) 3 and the second electrode (common electrode) 4 and the third electrode 5 The liquid crystal is driven by an electric field generated between the first and fourth electrodes 6 to display an image. On the other hand, in the initial stage of the image non-display period, the potential between the electrodes formed on the same substrate is set to the same potential, and a vertical electric field is generated by the potential difference between the electrode on the TFT substrate 1A and the electrode on the CF substrate 1B.
[0109]
Using the liquid crystal display device thus obtained, the response speed was evaluated. The response speed was evaluated using an oscilloscope combined with a photodiode. First, a black pattern is displayed on the entire screen, and then a white pattern corresponding to the maximum luminance is displayed. The luminance change at this time is read by an oscilloscope, and the luminance B before the change is read. ₀ Brightness after change from _fin The amount of change to 100% is defined as 100%, and the time at which 90% of the change is completed is defined as the response time. In the liquid crystal display device of this example, it was confirmed that the response time (falling response time) was shorter when the same liquid crystal material was used than in the conventional IPS type liquid crystal display device.
[0110]
[Ninth embodiment]
The ninth embodiment of the present invention uses a liquid crystal display device having the electrode structure shown in FIGS. 16 and 17 as in the fifth embodiment. In the fifth embodiment, double-speed driving is performed in which writing is performed twice in one frame. FIG. 27 is a diagram illustrating the transmittance of the liquid crystal panel and the lighting timing of the backlight in the ninth embodiment. In this embodiment, the driving is performed such that only one writing is performed in one frame. However, as shown in FIG. 27, a backlight which is a light source of the liquid crystal display device is driven to have a lighting state and a light-off state in one frame.
[0111]
The liquid crystal panel is usually driven in a line-sequential manner, and writes data from the upper stage to the lower stage. FIGS. 27 (a) to 27 (c) show transmittance changes in each stage in the process. FIG. 27D shows the lighting timing of the backlight. In such a blink backlight system, the backlight is turned on when the liquid crystal in the middle stage of the panel has sufficiently responded in order to maintain the luminance at the center of the panel.
[0112]
When the above-mentioned ghost was evaluated using the liquid crystal display device obtained in this example, the ghost phenomenon could be suppressed as compared with the conventional IPS liquid crystal display device. This is because, as shown in FIG. 32, in the conventional IPS liquid crystal display device, since the fall response time is long, the luminance difference in the shaded area is integrated and sensed. It is. However, by shortening the fall response time as in the present embodiment, the area of the hatched portion can be reduced, and as a result, the ghost phenomenon can be reduced.
[0113]
【The invention's effect】
As described above, according to the present invention, in a horizontal electric field type liquid crystal display device, in addition to a new third electrode different from the common electrode and the pixel electrode formed on one substrate, The fourth electrode is formed on one of the substrates, the other substrate, or the one and the other substrates, and the potential of the third electrode or the potential of the third and the fourth electrodes is set within one frame period. During the image display period, the horizontal electric field generated between the common electrode and the pixel electrode is used. In the initial stage of the image non-display period, the common electrode, the pixel electrode and the third electrode, or the third electrode and the third electrode are used. By using the vertical electric field generated between the four electrodes, the fall response time is improved, and a high-speed response that enables moving image display and a high-quality moving image-compatible liquid crystal display device that suppresses “moving image blur” are provided. can do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the direction of an electric field generated in a pixel and the movement of a liquid crystal molecule in each state of driving a liquid crystal for explaining a basic concept of the present invention.
FIG. 2 is an explanatory diagram of a time change of a liquid crystal transmittance (liquid crystal panel luminance) corresponding to each state of liquid crystal driving for explaining a basic concept of the present invention.
FIG. 3 is a diagram illustrating a typical electrode structure for driving liquid crystal molecules and the formation of an electric field in the liquid crystal display device of the present invention.
FIG. 4 is an explanatory diagram of an electrode structure of a pixel section according to the first embodiment and the second embodiment of the present invention.
FIG. 5 is a sectional view of a pixel portion according to the first and second embodiments of the present invention.
FIG. 6 is an equivalent circuit diagram illustrating a driving system of the liquid crystal display device according to the first embodiment and the second embodiment of the present invention.
FIG. 7 is an explanatory diagram similar to FIG. 31 of the signal waveform supplied to each electrode and wiring in the first embodiment and the second embodiment of the present invention.
FIG. 8 is an explanatory diagram of an electrode structure of a pixel portion, similar to FIG. 4, for describing the configuration of a third embodiment of the present invention.
FIG. 9 is a sectional view of a pixel portion of a liquid crystal display according to a third embodiment of the present invention.
FIG. 10 is an explanatory diagram of a driving system of a liquid crystal display device according to a third embodiment of the present invention.
FIG. 11 is an explanatory diagram of signal waveforms supplied to each electrode and wiring of a liquid crystal display according to a third embodiment of the present invention.
FIG. 12 is an explanatory diagram of an electrode structure of a pixel portion similar to FIG. 8 according to a liquid crystal display device of a fourth embodiment of the present invention.
FIG. 13 is a sectional view of a pixel portion of a liquid crystal display according to a fourth embodiment of the present invention.
FIG. 14 is an explanatory diagram of a driving system of a liquid crystal display device according to a fourth embodiment of the present invention.
FIG. 15 is an explanatory diagram of signal waveforms supplied to each electrode and wiring of a liquid crystal display according to a fourth embodiment of the present invention.
FIG. 16 is an explanatory view of an electrode structure of a pixel portion similar to FIG. 12 according to a fifth embodiment of the present invention.
FIG. 17 is a sectional view of a pixel portion of a liquid crystal display according to a fifth embodiment of the present invention.
FIG. 18 is an explanatory diagram of an electrode structure of a pixel portion of a liquid crystal display device according to a sixth embodiment of the present invention, similar to FIG.
FIG. 19 is a sectional view of a pixel portion of a liquid crystal display according to a sixth embodiment of the present invention.
FIG. 20 is an explanatory diagram of signal waveforms supplied to each electrode and wiring of a liquid crystal display according to a sixth embodiment of the present invention.
FIG. 21 is an explanatory diagram of an electrode structure of a pixel portion of a liquid crystal display according to a seventh embodiment of the present invention.
FIG. 22 is a sectional view of a pixel portion of a liquid crystal display according to a seventh embodiment of the present invention.
FIG. 23 is an explanatory diagram of a driving system of a liquid crystal display device according to a seventh embodiment of the present invention.
FIG. 24 is an explanatory diagram of signal waveforms supplied to each electrode and wiring of the liquid crystal display device according to the seventh embodiment of the present invention.
FIG. 25 is a view illustrating an electrode structure of a pixel portion of a liquid crystal display according to an eighth embodiment of the present invention.
FIG. 26 is a sectional view of a pixel portion of a liquid crystal display according to an eighth embodiment of the present invention.
FIG. 27 is an explanatory diagram of transmittance of a liquid crystal panel and lighting timing of a backlight in a liquid crystal display device according to a ninth embodiment of the present invention.
FIG. 28 is an explanatory diagram of an example of an electrode configuration forming a pixel portion of an IPS mode liquid crystal display device.
FIG. 29 is a cross-sectional view showing one substrate shown in FIG. 28 together with the other substrate facing it.
FIG. 30 is an equivalent circuit diagram illustrating a driving system of an IPS mode liquid crystal display device.
FIG. 31 is an explanatory diagram of an example of a signal waveform in a case where black writing driving is performed in an IPS liquid crystal display device.
FIG. 32 is a waveform diagram illustrating a change in liquid crystal transmittance in a blink backlight method.
FIG. 33 is an exploded perspective view of the liquid crystal display device.
FIG. 34 is an explanatory diagram of a shape example of a comb-shaped electrode.
[Explanation of symbols]
1 (1A, 1B) ... substrate, 2 ... layer of liquid crystal molecules or liquid crystal, 3 ... first electrode (pixel electrode), 4 ... second electrode (common electrode), 5 ... third electrode, 6 ... 4 electrode, 7 (7A, 7B) ... scanning wiring, 8 (8A, 8B) ... signal wiring, 9 (9A, 9B) ... thin film transistor, 10 ... insulating film, 11 ... through hole, 12 ... alignment film, 13 ... Overcoat film, 14: color filter, 15: black matrix, 16: high dielectric layer, 17 (17A, 17B): polarizing plate, 18: horizontal electric field, 19: vertical electric field, 20: initial alignment direction of liquid crystal (rubbing direction) ), 21: display control device, 22: scan electrode drive circuit, 23 (23A, 23B): signal electrode drive circuit, 24: common electrode drive circuit, 25: third electrode drive circuit, 26: fourth electrode drive circuit, 27: display pixel portion, 31: liquid crystal display element (liquid Display panel), 32 ... shield case, 33 ... diffusing plate, 34 ... light guide plate, 35 ... reflector, 36 ... backlight, 37 ... lower case, 38 ... inverter circuit board, 39 ... liquid crystal display device.

Claims (20)

At least one of a pair of transparent substrates, a liquid crystal layer sandwiched between the pair of substrates, and an electrode formed for each of a plurality of pixels arranged in a matrix on one of the pair of substrates. Have a group,
A liquid crystal display device that performs image display by applying a voltage between the electrode groups to control the orientation direction of the liquid crystal and adjusting the amount of light incident from a light source installed outside the pair of substrates. hand,
In the image display period, the liquid crystal is driven by an electric field substantially parallel to the pair of substrate surfaces, and in the initial stage of the image non-display period, the liquid crystal controls the alignment direction of the liquid crystal by the electric field substantially perpendicular to the pair of substrate surfaces. A liquid crystal display device comprising a driving unit. At least one of a pair of transparent substrates, a layer of liquid crystal sandwiched between the pair of substrates, and a first electrode and a second electrode formed on one of the pair of substrates,
A voltage is applied between the first electrode and the second electrode to control the alignment direction of the liquid crystal, and the amount of light incident from a light source installed outside the pair of substrates is adjusted to adjust the image. A liquid crystal display device for displaying,
A third electrode on the other substrate facing the one substrate on which the first electrode and the second electrode of the pair of substrates are formed;
In the image display period, different potentials are applied to the first electrode and the second electrode, and the orientation direction of the liquid crystal is controlled by an electric field substantially parallel to a substrate surface generated between the electrodes,
In an initial stage of an image non-display period, different electric potentials are applied to the first electrode and the third electrode, and an electric field generated between the electrodes and substantially perpendicular to a substrate surface, and an electric field generated between the second electrode and the third electrode. A liquid crystal display device comprising liquid crystal driving means for controlling the alignment direction of liquid crystal by an electric field substantially perpendicular to a substrate surface generated between the electrodes by applying different potentials to the electrodes. The liquid crystal display device according to claim 2, wherein the first electrode and the second electrode have a comb shape. One of the first electrode and the second electrode is a comb-shaped electrode, the other electrode is a solid electrode covering substantially the entire surface of each pixel, and the comb-shaped electrode is an insulating film. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device overlaps with the solid electrode through a gap. The liquid crystal display device according to claim 2, wherein the third electrode is a solid electrode that covers substantially the entire surface of each of the pixels. The liquid crystal display device according to claim 5, wherein the solid electrode is individually driven by each of the plurality of pixels. The liquid crystal display device according to claim 5, wherein the solid electrode can be driven collectively by all of the plurality of pixels. At least one of the substrates includes a pair of transparent substrates, a liquid crystal layer sandwiched between the pair of substrates, and a first electrode and a second electrode formed on one of the substrates. By applying a voltage between the first electrode and the second electrode, the alignment direction of the liquid crystal is controlled, and the amount of light incident from a light source installed outside the pair of substrates is adjusted to form an image. A liquid crystal display device for displaying,
A third electrode is formed on the other substrate facing the one substrate on which the first electrode and the second electrode of the pair of substrates are formed;
A fourth electrode formed via an insulating film between the first electrode and the second electrode and the one substrate;
In the image display period, different potentials are applied between the first electrode and the second electrode, and the liquid crystal is driven by an electric field substantially parallel to the substrate surface generated between the electrodes. In an initial stage of the image non-display period, And a liquid crystal driving means for controlling the alignment direction of the liquid crystal by an electric field which is applied to the third electrode and the fourth electrode with different electric potentials and is substantially perpendicular to the substrate surface generated between the electrodes. Display device. The liquid crystal display device according to claim 8, wherein the first electrode and the second electrode have a comb shape. 10. The liquid crystal display device according to claim 8, wherein at least one of the third electrode and the fourth electrode is a solid electrode covering substantially the entire surface of each of the pixels. The liquid crystal display device according to claim 10, wherein at least one of the solid electrodes provided on the third electrode and the fourth electrode is individually driven by each of the plurality of pixels. . The liquid crystal display device according to claim 10, wherein at least one of the solid electrodes provided on the third electrode and the fourth electrode is driven collectively by all of the plurality of pixels. . At least one has a pair of transparent substrates, a layer of liquid crystal sandwiched between the pair of substrates, and a first electrode and a second electrode formed on one of the substrates,
A voltage is applied between the first electrode and the second electrode to control the alignment direction of the liquid crystal, and the amount of light incident from a light source installed outside the pair of substrates is adjusted to adjust the image. A liquid crystal display device for displaying,
A third electrode and a fourth electrode are formed on the other substrate facing the one substrate formed by the first electrode and the second electrode;
In the image display period, different electric potentials are applied to the first electrode and the second electrode, and an electric field generated between the electrodes and substantially parallel to the substrate surface is applied to the third electrode and the fourth electrode. Different potentials are applied and the orientation direction of the liquid crystal is controlled by an electric field substantially parallel to the substrate surface generated between the electrodes. In the initial stage of the image non-display period, different potentials are applied to the first electrode and the third electrode. Is applied to the second electrode and the fourth electrode, and a different electric potential is applied to the second electrode and the fourth electrode. A liquid crystal display device comprising a liquid crystal driving means for controlling the alignment direction of the liquid crystal. 14. The liquid crystal display device according to claim 13, wherein the first to fourth electrodes have a comb shape. The first electrode and the third electrode are comb-shaped, the second electrode and the fourth electrode are solid electrodes that cover substantially the entire surface of each pixel, and the first electrode is 14. The liquid crystal according to claim 13, wherein the second electrode overlaps with the insulating film via an insulating film, and the third electrode overlaps with the fourth electrode via an insulating film. Display device. The liquid crystal display device according to claim 15, wherein the solid electrode is individually driven by each of the plurality of pixels. The liquid crystal display device according to claim 15, wherein the solid electrode is driven collectively by all of the plurality of pixels. 8. The method according to claim 2, wherein in an initial stage of the image non-display period, the potentials of the first electrode and the second electrode are substantially equal, and only the potential of the third electrode is different. The liquid crystal display device according to the above. 9. The method according to claim 8, wherein in the initial stage of the image non-display period, the potentials of the first electrode, the second electrode, and the fourth electrode are substantially equal, and only the potential of the third electrode is different. 13. The liquid crystal display device according to any one of items 1 to 12. In the initial stage of the image non-display period, the potentials of the first electrode and the second electrode are substantially equal, the potentials of the third electrode and the fourth electrode are substantially equal, and the first electrode and the fourth electrode are substantially equal. 18. The liquid crystal display device according to claim 13, wherein the potentials of the third electrodes are different.

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