JP2004078099A - Method for manufacturing liquid crystal element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing liquid crystal element which enables the improvement of contrast of a liquid crystal element having chiral smectic liquid crystal. <P>SOLUTION: In the process of cooling that is specified in MDL, the formation of batonnet is aligned in one direction by performing the zone cooling and, thereby, the monostable positions are uniformized in the surface. As a result, the black luminance is reduced and the contrast is improved. <P>COPYRIGHT: (C)2004,JPO

Description

【００２９】
Ｒ_１，Ｒ_２：炭素原子数が１〜２０である置換基を有していてもよい直鎖または分岐状のアルキル基
Ｘ_１，Ｘ_２：単結合、Ｏ、ＣＯＯ、ＯＯＣ
Ｙ_１，Ｙ_２，Ｙ_３，Ｙ_４：ＨまたはＦ
ｎ：０または１
（２）
【００３０】
【化２】

【００３１】
Ｒ_１，Ｒ_２：炭素原子数が１〜２０である置換基を有していてもよい直鎖または分岐状のアルキル基
Ｘ_１，Ｘ_２：単結合、Ｏ、ＣＯＯ、ＯＯＣ
Ｙ_１，Ｙ_２，Ｙ_３，Ｙ_４：ＨまたはＦ
（３）
【００３２】
【化３】

【００３３】
Ｒ_１，Ｒ_２：炭素原子数が１〜２０である置換基を有していてもよい直鎖または分岐状のアルキル基
Ｘ_１，Ｘ_２：単結合、Ｏ、ＣＯＯ、ＯＯＣ
Ｙ_１，Ｙ_２，Ｙ_３，Ｙ_４：ＨまたはＦ
（４）
【００３４】
【化４】

【００３５】
Ｒ_１，Ｒ_２：炭素原子数が１〜２０である置換基を有していてもよい直鎖または分岐状のアルキル基
Ｘ_１，Ｘ_２：単結合、Ｏ、ＣＯＯ、ＯＯＣ
Ｙ_１，Ｙ_２，Ｙ_３，Ｙ_４：ＨまたはＦ
ところで、本実施の形態では、カイラルスメクチック液晶２については、その液晶材料の組成を調整し、更に液晶材料の処理や素子構成、例えば配向制御膜５ａ，５ｂの材料、処理条件等を適宜設定することにより、駆動電圧が印加されていない場合には、該液晶の平均分子軸（液晶分子）が単安定化されている配向状態を示し、一の極性の駆動電圧が印加されて駆動される場合には、液晶分子の平均分子軸が駆動電圧の大きさに応じた角度で前記単安定化された位置から一方の側にチルトし、他方の極性（前記一の極性に対する逆極性をいう。以下、同じ）の電圧が印加されている場合には、液晶分子の平均分子軸が駆動電圧の大きさに応じた角度で前記単安定化された位置から他方の側（すなわち、前記一の極性の電圧を印加したときにチルトする側とは反対の側）にチルトする、ような特性を示すようにすると良い。つまり、本実施の形態に用いる液晶２は、カイラルスメクチック液晶本来のメモリ性（双安定性）が消失されたものであって、チルト角の大きさを印加電圧によって連続的に制御することができ、それに伴って液晶素子の光量も連続的に変化させることができ、階調表示を可能とするものである。この場合、前記一の極性の駆動電圧を印加することによって最大チルト状態とした場合におけるチルト角は、前記他の極性の電圧を印加することによって最大チルト状態とした場合におけるチルト角と異ならせると良い。例えば、該他の極性の電圧を印加した場合、該電圧の大きさにかかわらず、液晶の平均分子軸がほとんどチルトしないような特性にしても良い。
【００３６】
（３−２）次に、カイラルスメクチック液晶２以外の各構成部材等について説明する。
【００３７】
上述した基板１ａ，１ｂには、ガラスやプラスチック等の透明性の高い材料を用いれば良い。
【００３８】
また、電極３ａ，３ｂには、Ｉｎ_２Ｏ_３やＩＴＯ（インジウム・ティン・オキサイド）等の材料を用いれば良く、これらの電極３ａ，３ｂはそれぞれの基板１ａ，１ｂに形成すると良い。なお、アクティブ素子４を接続する方の電極３ｂは、ドット状にマトリクス状に配置し、他方の電極３ａは、基板１ａのほぼ全面（或いは特定の領域）に形成すると良い。さらに、アクティブ素子４としては、ＴＦＴやＭＩＭ（Ｍｅｔａｌ−Ｉｎｓｕｌａｔｏｒ−Ｍｅｔａｌ）等を用いれば良い。図１上ではＴＦＴ素子を例として図示する。
【００３９】
また、カイラルスメクチック液晶２に接する位置には、その配向状態を制御するために一軸配向処理を施した配向制御膜５ａ，５ｂを配置すると良い。かかる配向制御膜５ａ，５ｂとしては、
＊ポリイミド、ポリイミドアミド、ポリアミド、ポリビニルアルコール等の有機材料からなる溶液を塗布して膜を形成し、該膜の表面にラビング処理を施したものや、
＊ＳｉＯ等の酸化物や窒化物からなる無機材料を基板１ａ，１ｂに斜め方向から所定の角度で蒸着させて形成した斜方蒸着膜、
＊紫外線照射等によって一軸配向規制力を発生しうる光配向膜を用いたもの、を挙げることができる。なお、この配向制御膜５ａ，５ｂの材質や一軸配向処理の条件等により、液晶分子のプレチルト角（すなわち、配向制御膜５ａ，５ｂの界面近傍において液晶分子が配向制御膜５ａ，５ｂに対してなす角度）が調整される。
【００４０】
このような配向制御膜５ａ，５ｂは、カイラルスメクチック液晶２の両側に配置してそれらの両方に一軸配向処理を施せば良く、その場合における一軸配向処理方向（特にラビング方向）の関係は、用いる液晶材料を考慮して、
＊アンチパラレル（両一軸配向処理方向が平行かつ逆方向）、
＊パラレル（両一軸配向処理方向が平行かつ同方向）、
＊４５°以下の範囲でクロスする関係、
のいずれかになるように設定すれば良い。なお、４５°以下の範囲でクロスする関係とは、２つのベクトル（一軸配向処理方向を示すベクトル）が４５°以下の範囲内でクロスする場合であって、それぞれのベクトル方向が同方向（正確には、４５°以下の角度ズレを有する。）である場合や、それぞれのベクトル方向が逆方向である場合の両方を挙げることができる。そして、互いのベクトルの交差角度（狭い方の交差角度）の値が４５°以下で且つ０°に近いような場合は、それぞれのベクトルの関係が実質的にアンチパラレル乃至パラレルの関係とみなしてもよい。また、上述のアンチパラレル或いはパラレルの関係もそれぞれベクトル同士が必ず平行である以外に、例えば数°程度ずれているような場合でも実質的にアンチパラレル乃至パラレルの関係とみなしてもよい。本明細書において配向制御膜とは、一軸配向処理された膜以外に、液晶に直接接触されることによって液晶の配向に何らかの影響を与える膜のことを言う。なお、両側の配向制御膜に一軸配向処理を施さなくても、片側の配向制御膜のみに一軸配向処理を施しても良い。
【００４１】
さらに、基板１ａ，１ｂの間隙には、シリカビーズ等からなるスペーサー（不図示）を配置して、かかるスペーサーによってその間隙寸法を規定するようにしてもよい。なお、間隙寸法は、液晶材料を考慮して最適範囲になるように調整すれば良いが、均一な一軸配向性を達成させたり、電圧が印加されていない状態での液晶分子の平均分子軸を配向処理軸Ｒの平均方向の軸と実質的に一致させるために、０．３〜１０μｍの範囲に設定することが好ましい。
【００４２】
またさらに、基板１ａ，１ｂの間隙にエポキシ樹脂等からなる接着粒子（不図示）を分散配置して、両基板１ａ，１ｂの接着性や、液晶素子の耐衝撃性を向上させると良い。
【００４３】
さらに、液晶素子は、透過型としても良く、反射型としても良い。なお、透過型の場合には両方の基板１ａ，１ｂを透明にする必要があり、反射型の場合には、基板１ａ，１ｂの一方に光を反射させる機能を付与する必要がある。ここで、光を反射させる機能を付与する方法としては、
＊反射板や反射膜を、基板１ａ又は１ｂとは別体に設ける方法や、
＊基板１ａ又は１ｂ自体を反射部材で形成する方法や、
等を挙げることができる。ここで、透過型の液晶素子の場合には両方の基板１ａ，１ｂに偏光板を（それらの偏光軸が互いに直交するように）配置すれば良く、反射型の液晶素子の場合には少なくとも一方の基板１ａ又は１ｂに偏光板を設ければ良い。
【００４４】
（３−３）次にＴＦＴ素子をアクティブ素子として用いた場合の詳細な構造について説明する。
【００４５】
図１の基板１ｂの側には、図２に示すように、ゲート線Ｇ_１，Ｇ_２，…が図示横方向に多数配置され、ゲート線Ｇ_１，Ｇ_２，…とは絶縁された状態のソース線Ｓ_１，Ｓ_２，…が図示縦方向に多数配置されている。そして、これらのゲート線Ｇ_１，Ｇ_２，…及びソース線Ｓ_１，Ｓ_２，…の各交点の画素には、アクティブ素子としての薄膜トランジスタ（アモルファスＳｉＴＦＴ）４や、ＩＴＯ膜等の透明導電膜からなる画素電極３ｂ及び保持容量電極６等が配置されている。
【００４６】
このうち、アモルファスＳｉＴＦＴ４は、図１に示すように、ゲート電極４２と、窒化シリコン（ＳｉＮｘ）からなる絶縁膜（ゲート絶緑膜）４３と、半導体層であるａ−Ｓｉ層４４やｎ＋ａ−Ｓｉ層４５，４６と、ソース電極４７と、ドレイン電極４８と、チャネルを保護するチャネル保護膜４９と、によって構成されている。すなわち、ガラス基板１ｂには各画素毎にゲート電極４２が形成され、該ゲート電極４２の表面は絶縁膜４３にて覆われ、絶縁膜４３の表面であってゲート電極４２を形成した位置にはａ−Ｓｉ層４４が形成されている。また、このａ−Ｓｉ層４４の表面には、互いに離間するようにｎ＋ａ−Ｓｉ層４５，４６が形成されており、各ｎ＋ａ−Ｓｉ層４５，４６にはソース電極４７やドレイン電極４８が互いに離間した状態に形成されている。さらに、これらのａ−Ｓｉ層４４や電極４７，４８を覆うようにチャネル保護膜４９が形成されている。
【００４７】
そして、ＴＦＴ４のゲート電極４２は上述したゲート線Ｇ_１，Ｇ_２，…を介して走査信号ドライバ７に接続され、ＴＦＴ４のソース電極４７はソース線Ｓ_１，Ｓ_２，…を介して情報信号ドライバ８に接続され、ＴＦＴ４のドレイン電極４８は画素電極３ｂに接続されている。
【００４８】
ところで、上述した保持容量電極６はガラス基板１ｂの表面に形成されており、上述した絶縁膜４３は、この保持容量電極６及びガラス基板１ｂを覆う位置まで形成され、上述したソース電極４７や画素電極３ｂはこの絶縁膜４３の表面に形成されている。これにより、保持容量電極６と画素電極３ｂとは、絶縁膜４３を挟んだ状態に配置されることとなり、これらによって、液晶２と並列の形で設けられた保持容量Ｃｓが構成されることとなる。なお、この保持容量電極６は、面積を大きくした場合における開口率低下を防止するため、透明なＩＴＯによって形成すると良い。
【００４９】
また、図１に示すように、上述したＴＦＴ４や画素電極３ｂの表面には配向制御膜５ｂが形成されており、その表面には一軸配向処理（ラビング処理）が施されている。
【００５０】
さらに、これらのガラス基板１ａ，１ｂの間隙であって、画素電極３ｂと共通電極３ａとの間には、自発分極を有するカイラルスメクチック液晶２が配置されていて、液晶容量Ｃｌｃが構成されることとなる。
【００５１】
また、このような液晶素子の両側には、互いに偏光軸が直交した関係にある一対の偏光板（不図示）が配置されている。
【００５２】
なお、図１に示す液晶素子ではアモルファスＳｉＴＦＴを用いているが、もちろんこれに限る必要はなく、多結晶Ｓｉ（Ｐ−Ｓｉ）ＴＦＴや単結晶Ｓｉ（Ｃ−Ｓｉ）ＴＦＴを用いても良い。
【００５３】
（３−４）次に、上述した液晶素子Ｐの駆動方法（通常の画像表示を行う場合の駆動方法）の一例について説明する。
【００５４】
上述した液晶素子においては、走査信号ドライバ７から各ゲート線Ｇ_１，Ｇ_２，…にはゲート電圧が線順次に印加され、ＴＦＴ４はゲート電圧が印加されることによってオン状態となる。
【００５５】
一方、ゲート電圧の印加に同期して、情報信号ドライバ８からソース線Ｓ_１，Ｓ_２，…にはソース電圧（各画素に書き込む情報に応じた情報信号電圧）が印加される。したがって、ＴＦＴ４がオン状態にある画素では、ソース電圧がＴＦＴ４及び画素電極３ｂを介して液晶２に印加され、液晶２のスイッチングが画素単位で行われる。
【００５６】
そして、このような駆動を一定期間（フレーム期間）毎に繰り返し、画像の書き換えを行うようになっている。
【００５７】
ところで、コレステリック相からカイラルスメクチックＣ相へと相転移する相転移過程を詳細に偏光顕微鏡観測したとき、スメクチックＡ相と酷似した配向状態が観測される場合がある。しかしながら本発明に使用される素子の本質はスメクチック層の法線方向と一軸配向処理方向とが大きく異なっており電圧無印加時に安定な分子位置がラビング方向に近い位置にあることである。つまり、こうした関係の層形成方向が実現されている場合には上記スメクチックＡ相的な液晶相は配向には寄与しないこととなるため、本願においてはこうした材料についてもスメクチックＡ相を含まない材料と定義する。
【００５８】
（４）次に、本実施の形態の効果について説明する。
【００５９】
本実施の形態によれば、初めに液晶の相転移温度まで冷却された液晶素子の一方の端で発生したバトネが、液晶素子の他方の端に向かって一様に順次成長していく。このため単安定位置むらが生じるということはない。それにより黒状態での光りぬけを抑えることが出来、良好なコントラストを得ることが出来る。
【００６０】
【実施例】
以下、実施例に沿って本発明を更に詳細に説明する。
【００６１】
（１）液晶組成物の調製
まず、下記液晶性化合物を、それぞれの右側に併記した重量比率で混合し液晶組成物ＬＣ−１を調製した。
【００６２】
【化５】

【００６３】
上記液晶組成物ＬＣの物性パラメータを以下に示す。
【００６４】
８６．３　　６１．２　　−７．２
相転移温度（℃）：ＩＳＯ．　→　Ｃｈ　→　ＳｍＣ^＊　→　Ｃｒｙ
自発分極（３０℃）：Ｐｓ＝２．９ｎＣ／ｃｍ^２
ＳｍＣ^＊相でのらせんピッチ（３０℃）：２０μｍ以上
（２）　単画素液晶セルの作製
本実施例では、本発明の効果を確認するための単画素液晶セルを作製した。なお、この単画素液晶セルは、所定間隙を開けた状態に配置された一対のガラス基板を備えたものであって、各ガラス基板の表面には透明電極が形成され、各透明電極を覆うように配向膜が形成され、基板間隙にはカイラルスメクチック液晶が配置されたものであって、透明電極をマトリクス化せずに１つの画素を構成させたものである。
【００６５】
この単画素液晶セルを作製するに当たっては、２枚のガラス基板（厚さ１．１ｍｍ）の表面に７００Å厚のＩＴＯ膜（透明電極）を形成した。そして、各透明電極を覆うように、市販のＴＦＴ用配向膜（日産化学社製のＳＥ７９９２）をスピンコート法により塗布し、その後、８０℃の温度で５分間の前乾燥を行ない、さらに２００℃で１時間加熱焼成を施し膜厚１５０Åのポリイミド被膜（配向膜）を得た。
【００６６】
続いて、それぞれのポリイミド膜に対して一軸配向処理としてナイロン布によるラビング処理を施した。このラビング処理には、外周面にナイロン（ＮＦ−７７／帝人製）を貼り付けた径１０ｃｍのラビングロールを用い、押し込み量を０．７ｍｍとし、送り速度を１０ｃｍ／ｓｅｃとし、回転数を１０００ｒｐｍとし、送り回数を４回とした。
【００６７】
その後、一方の基板上にはスペーサーとしてのシリカビーズ（平均粒径１．５μｍ）を散布し、ラビング処理方向が互いに反平行（アンチパラレル）となるように２枚の基板を貼り合わせた。そして、基板間隙に液晶組成物ＬＣ−１をＣｈ相の温度で注入し、単画素液晶セルを作製した。
【００６８】
このような単画素液晶セルを２個作製した。一方の液晶セルに対して、基板の片側の端部にＩＴＯヒータをとりつけ端部より面内方向に向かって熱が伝わるようにし、コレステリック液晶層を示す温度まで加熱した。このあと、ＩＴＯヒータの温度を下げ、カイラルスメクチック液晶層を示す温度まで冷却した。この際、−２Ｖの直流オフセット電圧を印加した。冷却中の液晶層の様子を偏光光学顕微鏡により目視観察したところ、コレステリック相からカイラルスメクチック相への転移は端部のある一部分より始まり、面内方向に向かって一様に広がっていった。この際、コレステリック相を示す部分とカイラルスメクチック層を示す部分の境界は、０．２５ｘ１０^−３ｍ／ｓの速度で移動するのが観察された。
【００６９】
もう一方の液晶セルに対しては、メトラートレド社製ホットステージを用いて面内に一様な温度勾配を設けずにコレステリック液晶層を示す温度まで加熱した。その後、ホットステージの温度を下げカイラルスメクチック液晶層を示す温度まで冷却した。この際、−２Ｖの直流オフセット電圧を印加した。この様子を偏光光学顕微鏡により観察したところ、セル内の複数の点を起点として相転移が生じるのを確認した。
【００７０】
このようにして作成した２個の単画素液晶セルの配向をニコン社製偏光光学顕微鏡ＢＸ５０を用いて観察したところ、温度勾配を維持したまま冷却したセル中の平均分子位置はセル全面で均一であったが、温度勾配を設けずに冷却したセル中の平均分子位置は不ぞろいであった。
【００７１】
また、浜松フォトニクス社製フォトマルシステムを前述光学顕微鏡に接続し、コントラストを測定したところ、温度勾配を維持したまま冷却したセルのコントラストは２００であったが、温度勾配を設けずに冷却したセルのコントラストは１３０程度であり、冷却時の面内の温度勾配によってコントラストが上昇していることが確認できた。
【００７２】
（３）アクティブマトリクス型液晶パネルの作製
次に、図１及び図２に示すアクティブマトリクス型液晶パネル（液晶素子）を作成した。
【００７３】
なお、基板１ａ，１ｂには厚さ１．１ｍｍのガラス基板を用い、それらには透明電極３ａ，３ｂを形成した。また、一方のガラス基板１ａにはＲＧＢのカラーフィルター（不図示）を形成した。そして、画面サイズは１０．４インチとし、画素数は８００×６００とした。
【００７４】
さらに、アクティブ素子４にはａ−ＳｉＴＦＴを用い、該ＴＦＴ４のゲート絶縁膜４３には窒化シリコン膜を用いた。
【００７５】
また、配向制御膜５ａ，５ｂは、ポリイミド膜にて形成した。具体的には、市販のＴＦＴ用配向膜（日産化学社製のＳＥ７９９２）をスピンコート法により電極３ａ，３ｂを覆うように塗布し、その後、８０℃の温度で５分間の前乾燥を行ない、さらに２００℃の温度で１時間の加熱焼成を施すことによって形成し、その膜厚を１５０Åとした。なお、これらの配向制御膜５ａ，５ｂには、ナイロン布によるラビング処理（一軸配向処理）を施した。このラビング処理には、外周面にコットン布を貼り合わせた径１０ｃｍのラビングロールを用い、押し込み量を０．７ｍｍ、送り速度を１０ｃｍ／ｓｅｃとし、回転数を１０００ｒｐｍ、送り回数を４回とした。
【００７６】
続いて、一方の基板上には、平均粒径１．５μｍのシリカビーズ（スペーサー）を散布し、各基板１ａ，１ｂのラビング処理方向が互いにアンチパラレルとなるように貼り合わせ、均一な基板間隙のセルを得た。
【００７７】
このようなプロセスで作製したセルに液晶組成物ＬＣ−１をＣｈ相の温度で注入し液晶パネルを作製した。
【００７８】
次に、２台並べたホットプレートの上に厚さ５ｍｍのガラス板をのせ、その上に作成した液晶パネルＰをのせた。ホットプレートの温度はそれぞれ７０℃から６５℃の温度勾配がパネル面内に生じるように設定された。
【００７９】
その後、液晶がカイラルスメクチック液晶相を示す温度まで温度勾配を保ちつつ、液晶がＣｈ相からＳｍＣ^＊相に相転移する際に−２Ｖのオフセット電圧（直流電圧）を印加した。
【００８０】
以上の方法により温度勾配を保ちつつ冷却を施した液晶セルＰに特定の画像（白黒市松模様等）を４時間程度表示した。その後、全画面黒画像、全画面中間調画像、全画面白画像を表示したが、先の特定の画像に対応する焼き付きパターンは確認されなかった。これは前述の単画素液晶セルにおいて確認された平均分子軸位置の均一化によるものと思われる。
【００８１】
【発明の効果】
以上説明したように、本発明によると、温度勾配を保ちつつ冷却を施したことにより、コレステリック−カイラルスメクチック転移後の平均分子軸位置を均一にすることが出来る。したがって、黒表示状態での偏光子の光軸と分子軸位置を面内のあらゆる点で一致させることが出来、コントラストの向上が実現できる。
【図面の簡単な説明】
【図１】本発明によって作製される液晶パネルの構造を示す断面図。
【図２】電極の形状等を示す平面図。
【図３】強誘電性液晶を用いた液晶素子の駆動原理等を説明するための分解斜視図。
【符号の説明】
１ａ，１ｂ　基板
２　カイラルスメクチック液晶
３ａ　共通電極
３ｂ　画素電極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a liquid crystal device having a chiral smectic liquid crystal.
[0002]
[Prior art]
(1) Conventionally, a nematic liquid crystal has been used for a liquid crystal element, but in the case of this nematic liquid crystal, there is a problem that a response speed is slow. Hereinafter, this point will be described in detail.
[0003]
Conventionally, as a liquid crystal element using a nematic liquid crystal, an active matrix type liquid crystal element (that is, a liquid crystal element in which an active element such as a transistor is arranged in each pixel) has been developed.
[0004]
As a mode of a nematic liquid crystal used in the active matrix type liquid crystal element, a twisted nematic (Twisted Nematic) mode is widely known. The details of the mode are described in "Applied Physics Letters," Vol. 128 ".
[0005]
However, in such a twisted nematic mode, the [TN mode] has a problem that the response speed of the liquid crystal is as slow as several tens of ms, so that it cannot cope with the video rate and is not suitable for displaying a moving image.
[0006]
(2) Unlike such a nematic liquid crystal, a smectic liquid crystal such as a ferroelectric liquid crystal or an antiferroelectric liquid crystal can perform a reversal switching by spontaneous polarization, thereby increasing a response speed. Application is expected. Hereinafter, the liquid crystal will be described.
[0007]
A device in which the liquid crystal exhibits bistability (SSFLC / Surface Stabilized FLC) has been proposed by Clark and Lagerwall (JP-A-56-107216, US Pat. No. 4,368,924). As the liquid crystal exhibiting the bistability, a ferroelectric liquid crystal exhibiting a chiral smectic C phase is generally used. In this ferroelectric liquid crystal, when a voltage is applied, a voltage acts on the spontaneous polarization of liquid crystal molecules, and the molecules undergo inversion switching, so that a very fast response speed is obtained and a bistable state with memory properties is developed. Can be done. Furthermore, since the viewing angle characteristics are also excellent, it is considered that they are suitable for high-speed, high-definition, large-area display elements or light valves.
[0008]
Here, a liquid crystal element (SSFLC) using a bistable ferroelectric liquid crystal will be briefly described with reference to FIG. In the drawing, reference numerals 124 and 125 indicate polarizers, and reference numerals 124a and 125a indicate the directions of the respective polarization axes. Reference numeral 122 denotes a liquid crystal element, and the liquid crystal average molecular axis selectively takes a position indicated by 122a or 122b according to the polarity of the applied voltage. Here, strictly speaking, the liquid crystal average molecular axis indicates one of a high refractive index axis and a low refractive index axis in a liquid crystal layer plane of a refractive index ellipsoid formed by the liquid crystal layer.
[0009]
Now, when the liquid crystal average molecular axis is at 122a, the light beam passing through the polarizer 124 passes through the liquid crystal element 122 and reaches the polarizer 125 while maintaining the polarization state. Is orthogonal to the polarization direction 122a of the light beam, the light beam cannot pass through the polarizer 125 and assumes a black state. On the other hand, when the liquid crystal average molecular axis is at 122b, the light beam passing through the polarizer 124 is rotated by the birefringence characteristic of the liquid crystal panel 122 to take the direction indicated by the reference numeral 125a. The white light is transmitted through the light emitting element 125. The transmittance at this time is
sin ² (2θ) · sin ² (π · Δnd / λ)
(See “Liquid Crystal Device Handbook (edited by the 142nd Committee of the Japan Society for the Promotion of Science)”). Here, θ is the cone angle of the chiral smectic liquid crystal, Δn is the birefringence of the liquid crystal, d is the distance between the substrates, and the input is the wavelength of the light. In the design of a display element, a wavelength near 550 nm, which is the peak wavelength of a human relative luminous efficiency curve, is often used. This is because this wavelength range most affects the light intensity and contrast felt by humans. At this time, the retardation amount Δn · d of the liquid crystal panel is preferably set to a half of 550 nm from the condition of the maximum transmittance.
[0010]
In addition, recently, in addition to the ferroelectric liquid crystal exhibiting bistability as described above, an antiferroelectric liquid crystal exhibiting a three-stable state has attracted attention. This antiferroelectric liquid crystal, like the ferroelectric liquid crystal, performs reversal switching of molecules by the action on the spontaneous polarization of liquid crystal molecules, so that a very fast response speed is obtained. This liquid crystal material is characterized in that there is no spontaneous polarization when no voltage is applied because the liquid crystal molecules have a molecular arrangement structure in which the spontaneous polarization cancels each other when no voltage is applied.
[0011]
On the other hand, there is a chiral smectic liquid crystal which does not show a plurality of stable states as described above but shows only one stable state (Japanese Patent Application No. 10-117145). This liquid crystal is
-When no voltage is applied, the average molecular axis of the liquid crystal assumes a monostable state,
When a voltage of one polarity is applied, the average molecular axis is tilted to one side from a monostable position at an angle corresponding to the magnitude of the applied voltage,
When the voltage of the other polarity is applied, the average molecular axis tilts to the opposite side,
It has become. The liquid crystal is used for gradation display by using a characteristic that a tilt angle (an angle at which an average molecular axis tilts) changes according to an applied voltage.
[0012]
[Problems to be solved by the invention]
However, in the above-mentioned chiral smectic liquid crystal (Japanese Patent Application No. 10-117145), there was a problem that in-plane unevenness was present in the direction of the monostable state. For this reason, when the direction of the polarizer is adjusted to the direction of the average monostable state, there is a problem that the light is lost in each minute region and the contrast is reduced.
[0013]
The inventor manufactured a single-pixel liquid crystal panel having no active element in order to confirm the cause of the above-mentioned phenomenon (a phenomenon in which local unevenness in the direction of a monostable state occurs locally). In order to align the position of the monostable state of the liquid crystal when no voltage is applied, a DC voltage is applied in the process of cooling the liquid crystal panel from the temperature at which it takes a cholesteric phase to the temperature at which it takes a chiral smectic phase, and the state near the phase transition As a result, it was observed that a plurality of chiral smectic portions (battone) were formed near the phase transition temperature, and the growth gradually occurred in the rubbing direction. Further, when the liquid crystal panel was cooled, it was confirmed that the regions formed by growing different bones were regions having slight differences in the monostable positions.
[0014]
Therefore, an object of the present invention is to provide a method for manufacturing a liquid crystal element that prevents in-plane unevenness in the direction of a monostable position.
[0015]
[Means for Solving the Problems]
The present invention provides a step of arranging a pair of substrates with a predetermined gap therebetween, a step of performing a uniaxial alignment process on at least one of the pair of substrates, and arranging a chiral smectic liquid crystal in a gap between the pair of substrates. A step of arranging a pair of electrodes so as to sandwich the chiral smectic liquid crystal and form a plurality of pixels, and a step of arranging the active element in a state of being connected to one electrode for each pixel. In the method of manufacturing a device, the chiral smectic liquid crystal may have an isotropic liquid phase (ISO) -cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or an isotropic liquid phase (ISO .)-Chiral smectic C phase (SmC ^* ), comprising a cholesteric phase (Ch) -chiral smectic. A step of lowering the temperature from a temperature higher than the phase transition temperature of the chic smectic C phase (SmC ^* ) to a temperature lower than the phase transition temperature of the chiral smectic C phase (SmC ^* ) or isotropic liquid phase (ISO.). In the temperature decreasing step, a temperature gradient exists from one end to the other end within the substrate surface.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0017]
(1) First, an overall configuration of a liquid crystal element manufactured and driven in the present embodiment will be described with reference to FIG.
[0018]
As shown in FIG. 1, a liquid crystal element according to the present embodiment has a pair of substrates 1a and 1b arranged with a predetermined gap therebetween, and a chiral smectic arranged in a gap between the pair of substrates 1a and 1b. The liquid crystal 2, a pair of electrodes 3 a and 3 b, which constitute a plurality of pixels and are arranged to sandwich the chiral smectic liquid crystal 2, are connected to one of the pair of electrodes (the electrode 3 b in FIG. 1). And a plurality of active elements 4 arranged for each pixel in a state where the chiral smectic liquid crystal 2 is driven by applying a voltage to the chiral smectic liquid crystal 2 via the pair of electrodes 3a and 3b. Have been.
[0019]
As the chiral smectic liquid crystal 2, the isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or isotropic liquid phase (ISO.)- A material showing a phase transition series of a chiral smectic C phase (SmC ^* ) is used. The liquid crystal 2 may be used in a state where the liquid crystal molecules are stabilized at the edge of the virtual cone or at a position inside the virtual cone without applying a voltage.
[0020]
(2) Next, a method for manufacturing the liquid crystal element according to the present embodiment will be described.
[0021]
When manufacturing the above-described liquid crystal element,
A step of arranging the pair of substrates 1a and 1b with a predetermined gap;
A step of disposing a chiral smectic liquid crystal 2 in a gap between the pair of substrates 1a and 1b;
A step of sandwiching the chiral smectic liquid crystal 2 and arranging a pair of electrodes 3a and 3b so as to constitute a plurality of pixels;
A step of arranging the active element 4 in a state of being connected to one electrode 3b for each pixel;
In the appropriate order.
[0022]
Thereafter, from a temperature higher than the phase transition temperature of the cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or the isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ), the temperature is higher than the phase transition temperature. A step of cooling to a low temperature is performed. At this time, the operation is performed in such a manner that a temperature gradient exists from one end of the liquid crystal element to the other end.
[0023]
As for the method of implementation, the liquid crystal element placed on the heat source may be gradually pushed out from the heat source and gradually cooled from the end. Alternatively, one end and the other end of the liquid crystal element may be placed on different heat sources, respectively, and the temperature of each heat source may be controlled so as to lower the temperature, thereby cooling while maintaining the temperature gradient.
[0024]
The combination of the amount of the temperature gradient and the cooling rate may be such that the place having the phase transition temperature in the liquid crystal element surface moves at a speed of 5.0 × 10 ⁻³ m / s or less during the cooling process. More preferably, it is a combination that moves at a speed of 0.25 × 10 ⁻³ m / s or less.
[0025]
(3) Next, a detailed structure of the liquid crystal element will be described.
[0026]
(3-1) The chiral smectic liquid crystal 2 will be described.
[0027]
The chiral smectic liquid crystal 2 used in the present embodiment has a phase transition series as described above, that is, an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase from a high temperature side. (SmC ^* ) or an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ) phase transition series may be used. The compound shown in (4) can be mentioned.
(1)
[0028]
Embedded image

[0029]
R ₁ , R ₂ : linear or branched alkyl group X ₁ , X ₂ which may have a substituent having 1 to 20 carbon atoms: single bond, O, COO, OOC
Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F
n: 0 or 1
(2)
[0030]
Embedded image

[0031]
R ₁ , R ₂ : linear or branched alkyl group X ₁ , X ₂ which may have a substituent having 1 to 20 carbon atoms: single bond, O, COO, OOC
Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F
(3)
[0032]
Embedded image

[0033]
R ₁ , R ₂ : linear or branched alkyl group X ₁ , X ₂ which may have a substituent having 1 to 20 carbon atoms: single bond, O, COO, OOC
Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F
(4)
[0034]
Embedded image

[0035]
R ₁ , R ₂ : linear or branched alkyl group X ₁ , X ₂ which may have a substituent having 1 to 20 carbon atoms: single bond, O, COO, OOC
Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F
In the present embodiment, for the chiral smectic liquid crystal 2, the composition of the liquid crystal material is adjusted, and furthermore, the processing of the liquid crystal material and the element configuration, for example, the materials and processing conditions of the alignment control films 5a and 5b are appropriately set. Accordingly, when the driving voltage is not applied, the liquid crystal shows an alignment state in which the average molecular axis (liquid crystal molecules) is monostable, and the liquid crystal is driven by applying a driving voltage of one polarity. In the meantime, the average molecular axis of the liquid crystal molecules is tilted to one side from the mono-stabilized position at an angle corresponding to the magnitude of the driving voltage, and the other polarity (refers to a polarity opposite to the one polarity. , The same) is applied, the average molecular axis of the liquid crystal molecules is shifted from the mono-stabilized position to the other side (that is, the one polarity) at an angle corresponding to the magnitude of the driving voltage. When voltage is applied Tilt the opposite side) to the side of belt, it may be to indicate like properties. In other words, the liquid crystal 2 used in the present embodiment has lost the inherent memory property (bistability) of the chiral smectic liquid crystal, and the magnitude of the tilt angle can be continuously controlled by the applied voltage. Accordingly, the light amount of the liquid crystal element can be continuously changed, thereby enabling gradation display. In this case, the tilt angle in the case of the maximum tilt state by applying the drive voltage of one polarity is different from the tilt angle in the case of the maximum tilt state by applying the voltage of the other polarity. good. For example, when a voltage of the other polarity is applied, the characteristic may be such that the average molecular axis of the liquid crystal hardly tilts regardless of the magnitude of the voltage.
[0036]
(3-2) Next, each constituent member other than the chiral smectic liquid crystal 2 will be described.
[0037]
The substrates 1a and 1b may be made of a highly transparent material such as glass or plastic.
[0038]
The electrodes 3a and 3b may be made of a material such as In ₂ O ₃ or ITO (indium tin oxide), and these electrodes 3a and 3b may be formed on the respective substrates 1a and 1b. The electrodes 3b to which the active elements 4 are connected are preferably arranged in a matrix in the form of dots, and the other electrode 3a is preferably formed on substantially the entire surface (or a specific area) of the substrate 1a. Further, as the active element 4, a TFT, a metal-insulator-metal (MIM), or the like may be used. FIG. 1 illustrates a TFT element as an example.
[0039]
Further, it is preferable to arrange alignment control films 5a and 5b which have been subjected to a uniaxial alignment treatment in order to control the alignment state at positions in contact with the chiral smectic liquid crystal 2. As such alignment control films 5a and 5b,
* A film formed by applying a solution composed of an organic material such as polyimide, polyimide amide, polyamide, or polyvinyl alcohol, and rubbing the surface of the film;
* An oblique deposition film formed by depositing an inorganic material made of an oxide or nitride such as SiO on the substrates 1a and 1b at a predetermined angle from an oblique direction.
* An example using a photo-alignment film capable of generating a uniaxial alignment control force by ultraviolet irradiation or the like can be given. Depending on the material of the alignment control films 5a and 5b and the conditions of the uniaxial alignment treatment, etc., the pretilt angle of the liquid crystal molecules (that is, the liquid crystal molecules are close to the alignment control films 5a and 5b near the interface between the alignment control films 5a and 5b). Angle) is adjusted.
[0040]
Such alignment control films 5a and 5b may be arranged on both sides of the chiral smectic liquid crystal 2 and both of them may be subjected to uniaxial alignment treatment. In that case, the relationship of the uniaxial alignment treatment direction (particularly the rubbing direction) is used. Considering the liquid crystal material,
* Anti-parallel (both uniaxial orientation processing directions are parallel and opposite directions),
* Parallel (both uniaxial orientation processing directions are parallel and the same direction),
* Relationship that crosses within 45 ° or less,
It may be set so as to be one of the following. Note that the relation of crossing in a range of 45 ° or less is a case where two vectors (vectors indicating the uniaxial orientation processing direction) cross in a range of 45 ° or less, and the respective vector directions are in the same direction (accurate). Has an angle deviation of 45 ° or less.) And a case where the respective vector directions are opposite directions. When the value of the intersection angle (the narrower intersection angle) of the vectors is 45 ° or less and close to 0 °, the relationship between the vectors is regarded as substantially an antiparallel or parallel relationship. Is also good. In addition, the anti-parallel or parallel relationship described above may be regarded as substantially an anti-parallel or parallel relationship even when the vectors are displaced by several degrees, for example, in addition to the fact that the vectors are always parallel. In this specification, an orientation control film refers to a film that has some influence on the orientation of liquid crystal by being directly in contact with the liquid crystal, in addition to the film subjected to the uniaxial orientation treatment. Note that the uniaxial alignment treatment may not be performed on the alignment control films on both sides, but may be performed on only one alignment control film.
[0041]
Further, a spacer (not shown) made of silica beads or the like may be disposed in the gap between the substrates 1a and 1b, and the dimension of the gap may be defined by the spacer. The gap size may be adjusted to an optimum range in consideration of the liquid crystal material.However, it is possible to achieve uniform uniaxial orientation or to adjust the average molecular axis of liquid crystal molecules in a state where no voltage is applied. In order to substantially match the axis of the alignment processing axis R in the average direction, it is preferable to set the range of 0.3 to 10 μm.
[0042]
Further, it is preferable to disperse and arrange adhesive particles (not shown) made of epoxy resin or the like in the gap between the substrates 1a and 1b to improve the adhesion between the substrates 1a and 1b and the shock resistance of the liquid crystal element.
[0043]
Further, the liquid crystal element may be of a transmission type or a reflection type. In the case of the transmission type, both substrates 1a and 1b need to be transparent, and in the case of the reflection type, one of the substrates 1a and 1b needs to have a function of reflecting light. Here, as a method of giving the function of reflecting light,
* A method of providing a reflection plate or a reflection film separately from the substrate 1a or 1b,
* A method of forming the substrate 1a or 1b itself with a reflection member,
And the like. Here, in the case of a transmissive liquid crystal element, a polarizing plate may be disposed on both substrates 1a and 1b (so that their polarization axes are orthogonal to each other), and in the case of a reflective liquid crystal element, at least one of them is provided. A polarizing plate may be provided on the substrate 1a or 1b.
[0044]
(3-3) Next, a detailed structure when a TFT element is used as an active element will be described.
[0045]
On the side of the substrate 1b of FIG. 1, as shown in FIG. 2, the gate lines G _1, G 2, _... are arranged in large numbers in the illustrated transverse direction, state the gate lines G _1, G 2, _{which ...} The insulated source lines S _1, S 2, and _... are arranged in large numbers in the illustrated vertical direction. A pixel at each intersection of the gate lines G ₁ , G ₂ ,... And the source lines S ₁ , S ₂ ,... Is provided with a thin film transistor (amorphous SiTFT) 4 as an active element and a transparent conductive film such as an ITO film. And a storage capacitor electrode 6 and the like.
[0046]
As shown in FIG. 1, the amorphous Si TFT 4 includes a gate electrode 42, an insulating film (gate insulating film) 43 made of silicon nitride (SiNx), an a-Si layer 44 and n + a-Si It is composed of layers 45 and 46, a source electrode 47, a drain electrode 48, and a channel protection film 49 for protecting a channel. That is, the gate electrode 42 is formed for each pixel on the glass substrate 1b, the surface of the gate electrode 42 is covered with the insulating film 43, and the surface of the insulating film 43 is formed at the position where the gate electrode 42 is formed. An a-Si layer 44 is formed. On the surface of the a-Si layer 44, n + a-Si layers 45 and 46 are formed so as to be separated from each other, and a source electrode 47 and a drain electrode 48 are formed on each of the n + a-Si layers 45 and 46. It is formed in a separated state. Further, a channel protective film 49 is formed so as to cover the a-Si layer 44 and the electrodes 47 and 48.
[0047]
The gate electrode 42 of the TFT 4 is connected to the scanning signal driver 7 via the above-described gate lines G ₁ , G ₂ ,..., And the source electrode 47 of the TFT 4 is connected to the information signal via the source lines S ₁ , S ₂ ,. The drain electrode 48 of the TFT 4 is connected to the pixel electrode 3b.
[0048]
Meanwhile, the above-mentioned storage capacitor electrode 6 is formed on the surface of the glass substrate 1b, and the above-mentioned insulating film 43 is formed to a position covering the storage capacitor electrode 6 and the glass substrate 1b, and the above-described source electrode 47 and pixel The electrode 3b is formed on the surface of the insulating film 43. As a result, the storage capacitor electrode 6 and the pixel electrode 3b are arranged with the insulating film 43 interposed therebetween, thereby forming a storage capacitor Cs provided in parallel with the liquid crystal 2. Become. The storage capacitor electrode 6 is preferably formed of transparent ITO in order to prevent a decrease in aperture ratio when the area is increased.
[0049]
As shown in FIG. 1, an alignment control film 5b is formed on the surface of the above-described TFT 4 and pixel electrode 3b, and a uniaxial alignment process (rubbing process) is performed on the surface.
[0050]
Furthermore, a chiral smectic liquid crystal 2 having spontaneous polarization is disposed in the gap between the glass substrates 1a and 1b and between the pixel electrode 3b and the common electrode 3a, thereby forming a liquid crystal capacitor Clc. It becomes.
[0051]
Further, on both sides of such a liquid crystal element, a pair of polarizing plates (not shown) whose polarization axes are orthogonal to each other are arranged.
[0052]
Although an amorphous Si TFT is used in the liquid crystal element shown in FIG. 1, it is needless to say that the present invention is not limited to this, and a polycrystalline Si (P-Si) TFT or a single crystal Si (C-Si) TFT may be used.
[0053]
(3-4) Next, an example of a driving method of the above-described liquid crystal element P (a driving method for performing a normal image display) will be described.
[0054]
In the above-described liquid crystal element, a gate voltage is applied to each of the gate lines G ₁ , G ₂ ,... In a line-sequential manner from the scanning signal driver 7, and the TFT 4 is turned on by the application of the gate voltage.
[0055]
On the other hand, in synchronization with the application of the gate voltage, a source voltage (an information signal voltage corresponding to information to be written to each pixel) is applied from the information signal driver 8 to the source lines S ₁ , S ₂ ,. Therefore, in a pixel in which the TFT 4 is in the ON state, a source voltage is applied to the liquid crystal 2 via the TFT 4 and the pixel electrode 3b, and the switching of the liquid crystal 2 is performed in pixel units.
[0056]
Such driving is repeated at regular intervals (frame periods) to rewrite an image.
[0057]
By the way, when the phase transition process from the cholesteric phase to the chiral smectic C phase is observed in detail by a polarizing microscope, an orientation state very similar to the smectic A phase may be observed. However, the essence of the device used in the present invention is that the normal direction of the smectic layer is largely different from the uniaxial orientation treatment direction, and the stable molecular position is close to the rubbing direction when no voltage is applied. In other words, when the layer formation direction having such a relationship is realized, the smectic A-phase liquid crystal phase does not contribute to the alignment. Therefore, in the present application, such a material is also referred to as a material not including the smectic A phase. Define.
[0058]
(4) Next, the effect of the present embodiment will be described.
[0059]
According to the present embodiment, the batney generated at one end of the liquid crystal element which is first cooled to the phase transition temperature of the liquid crystal grows uniformly and sequentially toward the other end of the liquid crystal element. For this reason, the monostable position unevenness does not occur. As a result, light leakage in a black state can be suppressed, and good contrast can be obtained.
[0060]
【Example】
Hereinafter, the present invention will be described in more detail by way of examples.
[0061]
(1) Preparation of Liquid Crystal Composition First, the following liquid crystal compounds were mixed at the weight ratios shown on the right side of each, to prepare a liquid crystal composition LC-1.
[0062]
Embedded image

[0063]
The physical property parameters of the liquid crystal composition LC are shown below.
[0064]
86.3 61.2 -7.2
Phase transition temperature (° C.): ISO. → Ch → SmC ^* → Cry
Spontaneous polarization (30 ° C.): Ps = 2.9 nC / cm ²
Spiral pitch in SmC ^* phase (30 ° C.): 20 μm or more (2) Fabrication of Single Pixel Liquid Crystal Cell In this example, a single pixel liquid crystal cell for confirming the effects of the present invention was fabricated. This single-pixel liquid crystal cell includes a pair of glass substrates arranged with a predetermined gap therebetween, and a transparent electrode is formed on the surface of each glass substrate so as to cover each transparent electrode. An alignment film is formed on the substrate, and a chiral smectic liquid crystal is arranged in a gap between the substrates. One pixel is formed without forming a transparent electrode into a matrix.
[0065]
In producing this single pixel liquid crystal cell, an ITO film (transparent electrode) having a thickness of 700 mm was formed on the surface of two glass substrates (thickness: 1.1 mm). Then, a commercially available alignment film for TFT (SE7992 manufactured by Nissan Chemical Industries, Ltd.) is applied by a spin coating method so as to cover each transparent electrode, and thereafter, pre-drying is performed at a temperature of 80 ° C. for 5 minutes, and a further 200 ° C. For 1 hour to obtain a polyimide film (alignment film) having a thickness of 150 °.
[0066]
Subsequently, each polyimide film was subjected to a rubbing treatment with a nylon cloth as a uniaxial orientation treatment. For this rubbing treatment, a 10 cm diameter rubbing roll having nylon (NF-77 / manufactured by Teijin) adhered to the outer peripheral surface was used, the pushing amount was 0.7 mm, the feed speed was 10 cm / sec, and the rotation speed was 1000 rpm. And the number of times of feeding was set to four times.
[0067]
Thereafter, silica beads (average particle size: 1.5 μm) as spacers were sprayed on one of the substrates, and the two substrates were bonded so that the rubbing directions were antiparallel to each other. Then, the liquid crystal composition LC-1 was injected into the gap between the substrates at the temperature of the Ch phase to produce a single pixel liquid crystal cell.
[0068]
Two such single pixel liquid crystal cells were produced. One of the liquid crystal cells was provided with an ITO heater at one end of the substrate so that heat was transmitted from the end toward the in-plane direction, and heated to a temperature at which the cholesteric liquid crystal layer was shown. Thereafter, the temperature of the ITO heater was lowered, and the temperature was lowered to a temperature at which the chiral smectic liquid crystal layer was displayed. At this time, a DC offset voltage of -2 V was applied. The state of the liquid crystal layer during cooling was visually observed with a polarizing optical microscope. As a result, the transition from the cholesteric phase to the chiral smectic phase started from a part of the edge, and spread uniformly in the in-plane direction. At this time, it was observed that the boundary between the portion showing the cholesteric phase and the portion showing the chiral smectic layer moved at a speed of 0.25 × 10 ⁻³ m / s.
[0069]
The other liquid crystal cell was heated using a hot stage manufactured by METTLER TOLEDO Co., Ltd. to a temperature at which the cholesteric liquid crystal layer was shown without providing a uniform temperature gradient in the plane. Thereafter, the temperature of the hot stage was lowered and cooled to a temperature at which the chiral smectic liquid crystal layer was displayed. At this time, a DC offset voltage of -2 V was applied. When this state was observed with a polarization optical microscope, it was confirmed that a phase transition occurred starting from a plurality of points in the cell.
[0070]
Observation of the orientation of the two single-pixel liquid crystal cells thus prepared using a polarizing optical microscope BX50 manufactured by Nikon Corporation revealed that the average molecular position in the cell cooled while maintaining the temperature gradient was uniform over the entire surface of the cell. However, the average molecular position in the cell cooled without providing a temperature gradient was irregular.
[0071]
Further, the photomultiplier system manufactured by Hamamatsu Photonics was connected to the optical microscope described above, and the contrast was measured. The contrast of the cell cooled while maintaining the temperature gradient was 200, but the cell cooled without the temperature gradient was provided. Was about 130, and it was confirmed that the contrast was increased due to the in-plane temperature gradient during cooling.
[0072]
(3) Production of Active Matrix Liquid Crystal Panel Next, an active matrix liquid crystal panel (liquid crystal element) shown in FIGS. 1 and 2 was produced.
[0073]
Note that glass substrates having a thickness of 1.1 mm were used as the substrates 1a and 1b, and the transparent electrodes 3a and 3b were formed thereon. An RGB color filter (not shown) was formed on one glass substrate 1a. The screen size was 10.4 inches, and the number of pixels was 800 × 600.
[0074]
Further, an a-Si TFT was used for the active element 4, and a silicon nitride film was used for the gate insulating film 43 of the TFT 4.
[0075]
The orientation control films 5a and 5b were formed of a polyimide film. Specifically, a commercially available alignment film for TFT (SE7992 manufactured by Nissan Chemical Industries, Ltd.) is applied by spin coating so as to cover the electrodes 3a and 3b, and then pre-dried at a temperature of 80 ° C. for 5 minutes. Further, the film was formed by baking for 1 hour at a temperature of 200 ° C., and the film thickness was set to 150 °. Note that these alignment control films 5a and 5b were subjected to a rubbing treatment (uniaxial orientation treatment) using a nylon cloth. For this rubbing treatment, a rubbing roll having a diameter of 10 cm and a cotton cloth bonded to the outer peripheral surface was used. .
[0076]
Subsequently, on one of the substrates, silica beads (spacers) having an average particle size of 1.5 μm are scattered and bonded so that the rubbing directions of the substrates 1a and 1b are anti-parallel to each other. Cell was obtained.
[0077]
The liquid crystal composition LC-1 was injected into the cell manufactured by such a process at the temperature of the Ch phase to manufacture a liquid crystal panel.
[0078]
Next, a glass plate having a thickness of 5 mm was placed on two hot plates arranged side by side, and the liquid crystal panel P created was placed thereon. The temperature of the hot plate was set so that a temperature gradient from 70 ° C. to 65 ° C. was generated in the panel surface.
[0079]
Thereafter, while maintaining the temperature gradient to a temperature at which the liquid crystal exhibits a chiral smectic liquid crystal phase, an offset voltage (DC voltage) of -2 V was applied when the liquid crystal transitioned from the Ch phase to the SmC ^* phase.
[0080]
A specific image (black and white checkered pattern, etc.) was displayed for about 4 hours on the liquid crystal cell P cooled while maintaining the temperature gradient by the above method. Thereafter, a full-screen black image, a full-screen halftone image, and a full-screen white image were displayed, but no burn-in pattern corresponding to the specific image was confirmed. This is thought to be due to the uniformity of the average molecular axis position confirmed in the aforementioned single-pixel liquid crystal cell.
[0081]
【The invention's effect】
As described above, according to the present invention, by performing cooling while maintaining the temperature gradient, the average molecular axis position after the cholesteric-chiral smectic transition can be made uniform. Therefore, the position of the optical axis of the polarizer and the position of the molecular axis in the black display state can be made coincident with each other at any point in the plane, and an improvement in contrast can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of a liquid crystal panel manufactured according to the present invention.
FIG. 2 is a plan view showing the shape and the like of an electrode.
FIG. 3 is an exploded perspective view for explaining a driving principle and the like of a liquid crystal element using a ferroelectric liquid crystal.
[Explanation of symbols]
1a, 1b substrate 2 chiral smectic liquid crystal 3a common electrode 3b pixel electrode

Claims (3)

Arranging a pair of substrates with a predetermined gap therebetween, performing a uniaxial alignment process on at least one of the pair of substrates, arranging a chiral smectic liquid crystal in a gap between the pair of substrates, A method for manufacturing a liquid crystal element, comprising: a step of interposing a chiral smectic liquid crystal and arranging a pair of electrodes so as to constitute a plurality of pixels; and a step of arranging an active element connected to one electrode for each pixel. At
The chiral smectic liquid crystal is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or isotropic liquid phase (ISO.)-Chiral smectic C from the high temperature side. A liquid crystal exhibiting a phase transition series of a phase (SmC ^* ),
A temperature higher than the phase transition temperature of the cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or the isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ), and lower than the phase transition temperature It has a process of cooling down to
The method for manufacturing a liquid crystal device, wherein a temperature gradient exists from one end to the other end in the substrate surface in the temperature lowering step. 2. The method according to claim 1, wherein, in the temperature decreasing step, a moving speed at a point where the temperature in the liquid crystal element surface is the phase transition temperature is 5 × 10 ⁻³ m / s. ³ . 2. The method according to claim 1, wherein, in the temperature decreasing step, a moving speed at a point where the temperature in the liquid crystal element surface is the phase transition temperature is 0.25 × 10 ⁻³ m / s. ^3. .

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