JP3755303B2

JP3755303B2 - Measuring method of liquid crystal layer thickness and twist angle in liquid crystal element

Info

Publication number: JP3755303B2
Application number: JP18134798A
Authority: JP
Inventors: 浩之藤井
Original assignee: Casio Computer Co Ltd
Current assignee: Casio Computer Co Ltd
Priority date: 1998-06-15
Filing date: 1998-06-15
Publication date: 2006-03-15
Anticipated expiration: 2018-06-15
Also published as: JP2000002864A

Description

【０００１】
【発明の属する技術分野】
この発明は、液晶表示素子の液晶層厚とツイスト角度の測定方法に関するものである。
【０００２】
【従来の技術】
従来、対向面に電極がそれぞれ形成された一対の基板の間に液晶分子がツイスト配向した液晶層を設けてなる液晶セルにおいて、その液晶層の層厚の測定は、（１）液晶セルにその一方の面から光を入射させ、一対の基板のそれぞれの内面と液晶層との２つの界面で反射した光の干渉光強度を測定して液晶層厚を算出する方法、或いは、（２）液晶セルを偏光軸が互いに平行に配置された一対の偏光板で挟み、透過光の透過率が極小となる波長を検出し、その波長からGooch and Tarry の理論式により液晶層厚を算出する方法が知られている。
上記（１）の測定方法は、液晶セルの一対の基板のうちの光の入射方向から見て前方の基板と液晶層との界面で反射した光と、背面側の基板の内面と液晶層との界面で反射される光との位相差による光の干渉に基づいて液晶層厚を算出するものである。
【０００３】
この位相差は液晶層の屈折率と光路長に依存するが、基板間に封入された状態で液晶層の屈折率を正確に求めることは困難であり、特にツイスト配向された液晶層を透過した光の偏光状態を求めることは極めて困難である。さらに、実際の液晶セルでは基板内面の配向膜面と液晶層との界面だけでなく、基板面に形成された電極と基板との界面や、前記電極と配向膜との界面などでも光が反射するため、液晶層厚を精度良く測定することが困難である。
【０００４】
また、上記（２）の測定方法は、液晶層のΔndに対する透過光強度の依存性に基づいて、透過光が極小を与える波長を求め、この波長からセルギャップを算出するものである。
【０００５】
この測定方法では、液晶セルの基板間に分散状態で挟持されているギャップ材部分（液晶が存在しない部分）や液晶分子の配向が乱れた部分などのような液晶層の屈折率とは異なる屈折率を示す部分を透過したノイズ光の影響により測定精度が低下する。また、透過率が極小となる波長の検出にも大きな誤差が生じるため、液晶層厚を精度良く測定することが困難である。
【０００６】
一方、液晶セルの液晶層厚及びツイスト角度の両方を測定する方法として、（３）ストークス・パラメータを求め、このストークスパラメータに基づいて、液晶層厚及びツイスト角を求める方法も提案されている。
【０００７】
この測定方法は、Jpn.J.Appl.Phys.Vol.36(1997)pp.2760-2764に記述されているように、偏光子と検光子の間に液晶セルを配置し、ｙ軸と平行な直線偏光を液晶セルに入射させ、透過光のｘ軸成分強度Ix，y軸成分強度Iy，及び４５゜方向の成分強度I45゜を測定し、また１／４波長板を液晶セルと検光子との間に遅相軸をｙ軸と平行に配置した４５゜方向の成分強度Iq,45゜を測定する。
【０００８】
そして、これらのｘ軸成分強度Ix，ｙ軸成分強度Iy，４５゜方向の成分強度I45，及び１／４波長板を用いたときの４５゜方向の成分強度Iq,45゜の測定値により、ストークス・パラメータＳ１，Ｓ２，Ｓ３を算出し、これらのストークス・パラメータＳ１，Ｓ２，Ｓ３から液晶層厚とツイスト角度を算出する方法である。
【０００９】
【発明が解決しようとする課題】
しかし、上記（１）および（２）の液晶層厚測定方法は、いずれも、液晶層厚は測定できるもの、液晶分子がツイスト配向した液晶層のツイスト角度を測定することができず、また、液晶層厚の測定精度が悪いという問題をもっている。
【００１０】
上記（３）の測定方法は、液晶層厚と、ツイスト角度を測定することができるが、この測定方法においても液晶層厚とツイスト角度とを高い精度で測定することがで困難である。
【００１１】
すなわち、上記（３）の方法により、ツイスト角度を８４゜〜９６゜まで２゜間隔に選び、液晶層厚を４．６μｍ〜５．２μｍまで変化せたときのストークス・パラメータＳ１，Ｓ２を求め、図７に示すように各液晶層厚に対応する点をＳ１，Ｓ２座標上にプロットした。
【００１２】
この図７から明らかなように、ツイスト角度が８４°，８６゜の場合は、各液晶層厚に対応する点が曲線ａ，ｂに示すように異なる曲線上に存在するが、ツイスト角度が８８゜〜９６゜の範囲では、各液晶層厚に対応する点が実質的に曲線Ｃ上に分散して存在することとなり、前記ツイスト角度の違いを読み取ることが事実上困難である。
したがって、上記（３）の方法でも、液晶層厚とツイスト角度とを精度良く測定することができなかった。
この発明は、液晶セルの液晶層厚、及びツイスト角度とを高い精度で測定することができる液晶層厚とツイスト角度の測定方法を提供することを目的としたものである。
【００１３】
【課題を解決するための手段】
上記目的を達成するため、この発明にかかる液晶層厚とツイスト角度の測定方法は、ツイスト配向させた液晶層を有する被測定用の液晶セルを挟んで、光学軸が互いに平行な一対の偏光板を配置した光学系において、前記偏光板の光学軸を前記液晶セルの一方の基板近傍の液晶分子の配向方向と所定の角度の第１の方向に向けた第１の偏光板配置で測定した透過光の分光分布に基づいて第１の色度を算出し、色度図上での前記第１の色度により表される第１の色度点と無彩色点を結ぶ直線の第１の傾きを求め、前記偏光板の光学軸を前記第１の方向とは異なる第２の方向に向けた第２の偏光板配置で測定した透過光の分光分布に基づいて第２の色度を算出し、色度図上での前記第２の色度により表される第２の色度点と無彩色点とを結ぶ直線の第２の傾きを求め、前記第１の傾きと前記第２の傾きに基づいて、前記液晶セルの液晶層厚とツイスト角とを求める前記液晶セルの液晶層厚とツイスト角とを求めることを特徴とする。
【００１４】
この測定方法によれば、一対の偏光板の間に被測定用液晶セルを配置し、前記偏光板の光学軸と液晶セルの液晶分子の配列方向との成す角度を異ならせた少なくとも２つの状態で透過光の分光分布特性を測定し、それらの複数の透過光の色度図上での色度点と無彩色点とを結ぶ直線の傾きを求めるものであるため、被測定用液晶セルのセルギャップのみならず、ツイスト配向セルのツイスト角度をも精度良く測定することができる。
【００１５】
そして、上記透過光の色度図上での色度点と無彩色点とを結ぶ直線の傾きは、液晶層を通過する際に生じるノイズ光の影響を受けないので、より高精度の測定が可能になる。
【００１６】
上記少なくとも２回の透過光の測定は、前記偏光板の透過軸と液晶セルの液晶分子の配列方向との成す角度を４５°ずらせて測定するのが望ましい。すなわち、第１の方向に対して第２の方向は、偏光板の透過軸と液晶セルの液晶分子の配列方向を、前記第１の方向に対してほぼ４５゜の角度で交差する方向に配置して２つの偏光板配置における透過光の分光特性が測定される。
【００１７】
被測定用の液晶セルは、前記液晶セルの液晶層の厚さ方向の中央に位置する液晶分子の配列方向とほぼ４５°で交差する第１の方向に配置して透過光を測定し、この透過光の分光分布から第１の色度点の傾きが求められ、また液晶層のツイスト角度を二等分する第２の方向に配置して透過光を測定し、この透過光の分光分布から第２の色度点の傾きが求められる。
【００１８】
被測定用の液晶セルが、９０°ツイストテットネマチック型の液晶素子であるときは、前記第１の方向を、前記液晶セルの入射側基板近傍の液晶分子の配向方向とほぼ平行な方向に設定し、前記第２の方向は、前記液晶セルの入射側基板近傍の液晶分子の配向方向とほぼ４５゜の角度で交差する方向に設定してそれぞれの透過光が測定され、それぞれの色度点と無彩色点とを結ぶ直線の傾きを求め、この傾きに基づいて液晶素子のツイスト角とセルギャップとを求めることができる。
【００１９】
また、この発明にかかる液晶層厚とツイスト角度の測定方法は、ツイスト配向させた液晶層を有する被測定用の液晶セルを挟んで配置された一対の偏光板の互いに平行な光学軸を、前記液晶セルの一方の基板近傍の液晶分子の配向方向に対して所定の角度の第１の方向に向けた配置で測定した透過光の分光分布を表す第１の分光分布データと、前記偏光板の光学軸を前記第１の方向とは異なる第２の方向に向ける配置で測定した透過光の分光分布を表す第２の分光分布データを測定する分光分布測定ステップと、前記分光分布測定ステップで得られた第１、第２の分光分布データに基づいてそれぞれの透過光の色度を表す第１の色度及び第２の色度を算出し、色度図上での前記第１及び第２の色度によりそれぞれ表される第１の色度点及び第２の無彩色点とを結ぶ直線の第１の傾き及び第２の傾きとを求めるパラメータ算出ステップと、前記パラメータ算出ステップにより算出された第１の傾きと前記第２の傾きに基づいて、前記液晶セルの液晶層厚とツイスト角とを求めるステップとからなることを特徴とする。
【００２０】
この測定方法によれば、一対の偏光板の間に被測定用液晶セルを配置し、前記偏光板と液晶セルの液晶分子の配列方向との成す角度を異ならせた少なくとも２つの状態で透過光の分光分布を求め、それぞれの透過光の色度図上での色度点と無彩色点とを結ぶ２つの直線の傾きをパラメータとして用いているので、被測定用液晶セルのセルギャップと液晶層のツイスト角度を精度良く測定することがでる。
【００２１】
【発明の実施の形態】
以下、この発明の１つの実施の形態にかかる測定方法を説明する。
【００２２】
この発明のセルギャップとツイスト角度の測定方法は、一対の偏光板の間に被測定用の液晶セルを配置した光学系を用い、先ず前記偏光板の光学軸と液晶セルの液晶分子の配列方向とを所定の角度に設定した第１の状態で透過光の分光分布を測定し、その分光分布より色度図上の第１の色度点を算出し、その色度点と無彩色点とを結ぶ直線の第１の傾きを求める。
【００２３】
次に、前記偏光板の光学軸と液晶セルの液晶分子の配列方向との角度を他の異なる角度に設定した第２の状態で透過光の分光分布を測定し、その分光分布より色度図上の第２の色度点を算出し、その色度点と無彩色点とを結ぶ直線の第２の傾きを求める。
【００２４】
そして、これらの第１，第２の傾きをパラメータとして、予め求めておいた前記第１，第２の傾き、セルギャップとツイスト角度との関係に基づいて、液晶素子のセルギャップとツイスト角度を求めるものである。
【００２５】
図１は、この発明の第１の実施の形態にかかる測定方法に用いる光学系の概略を示す概略構成図である。
【００２６】
図１に示すように、この発明にかかる測定方法に用いる光学系は、一対の偏光板からなる偏光子１と検光子２と、この偏光子１と検光子２の間に配置された被測定用のツィストネマチック液晶セル３と、測定光を照射する光源４と、液晶セル３を透過した光の強度を検出する光検出器５とから構成されている。
【００２７】
液晶セル３は、図２に示すように、対向する内面にそれぞれ電極３１，３２と配向膜３３，３４とが形成された下基板（光入射側基板）３５と上基板（光出射側基板）３６とが平行に配置され、前記上下基板３５，３６はシール材３７により接合され、前記上下基板３５，３６間に液晶３８が封入されている。
【００２８】
図２及び図３は、９０°ツイスト型のＴＮ液晶セルの一例を示しており、前記上下基板３５，３６の内面に形成された配向膜３３，３４はそれぞれ配向処理が施されており、この配向膜３３，３４に隣接する液晶分子は、その分子長軸を配向処理方向３３ａ，３４ａに向けて配向している。
【００２９】
前記上下基板３５，３６間に封入されて液晶層を形成する前記液晶３８は、それぞれの配向膜３３，３４に施された配向処理方向３３ａ，３４ａが約９０°ずれているので、液晶層の液晶分子は、下基板３５に形成された配向膜３３の配向処理方向３３ａから上基板３６に形成された配向膜３４の配向処理方向３４ａ向かって図面上で矢印ｔで示すように、右回りにほぼ９０°（φ）ツイスト配向している。
【００３０】
そして、前記液晶３８が形成する液晶層の厚さ方向の中央に位置する液晶分子３８ａは、下基板３５の配向膜３３の配向処理方向３３ａに対して、前記ツイスト角度φのほぼ１／２の角度で交差する方向に配向している。
【００３１】
図１の光学系において、偏光子１と検光子２との間に液晶分子をツイスト配向させた液晶セル３を配置したときの透過光強度は、ジョーンズ行列に基づく解析により下記の式（１）で表される。この解析において、偏光子１と検光子２の透過軸１ａ，２bの方向、液晶セル３の光入射側の基板３５の配向処理方向３３ａ、及び光出射側基板３６の配向処理方向３４ａは、それぞれ図４に示すように定義される。
【００３２】
即ち、偏光子１と検光子２の透過軸１ａ，２ａを互い平行に配置し、前記光入射側の基板の配向処理方向３３ａを基準にして、偏光子１と検光子２の透過軸１ａ，２ａの成す角度をθ、前記光出射側基板の配向処理方向３４ａの成す角をφとし、光は図４の紙面裏側から垂直に入射する。
【００３３】
【数１】

【００３４】
ここで、入射側基板３５の配向処理方向３３ａに対して、偏光子１と検光子２の透過軸の方向１ａ，２ａをツイスト角度φの１／２から４５°を差し引いた角度θ（φ／２−π／４）に配置した第１の偏光板配置のとき、即ち、図３（ａ）で示すように、液晶層の層厚方向の中央の液晶分子３８ａの配向方向に対して４５°で交差する方向に偏光子１と検光子２の透過軸の方向１ａ，２ａを設置したときの透過光強度T(NB)は、下記の式（２）で表される。
【００３５】
【数２】

【００３６】
また、入射側基板３５の配向処理方向３３ａに対して、偏光子１と検光子２の透過軸１ａ，２ａの方向をツイスト角度φの１／２の角度θに配置した第２の偏光板配置、即ち図３（ｂ）で示すように、液晶層の層厚方向の中央の液晶分子３８ａの配向方向に偏光子１と検光子２の透過軸１ａ，２ａの方向一致させて設置したときの透過光強度T(DAP)は、下記の式（３）で表される。
【００３７】
【数３】

【００３８】
上記第１，第２の偏光板配置において、透過光の分光分布特性は、上記式（２）及び上記式（３）において、各波長毎の透過光強度T(NB)，T(DAP)を算出することにより得られる。
【００３９】
図１の光学系において、白色光を入射したときの出射光の色度座標Ｐ（ｘ、ｙ）は、前記透過光の分光分布から求めることができる。図５に示すように、色度図上の色度点Ｐと無彩色点Ｃとを結ぶ直線Ｌのｘ軸またはｙ軸に対する傾き角度Ｆは、前記色度座標Ｐ（ｘ、ｙ）と無彩色点Ｃの色度座標とから求めることができる。色度図上の色度点Ｐと無彩色点Ｃとを結ぶ直線Ｌの傾き角度Ｆは、液晶セル３のセルギャップｄまたはツイスト角度φに対応している。
【００４０】
即ち、第１の偏光板配置の透過光の色度座標Ｐ１（ｘ１、ｙ１）を求めて色度図上にプロットした色度点Ｐ１と無彩色点Ｃとを結ぶ直線Ｌ１のｘ軸に対する角度Ｆ１は、液晶層の層厚（セルギャップｄ）に対応する。そして、第２の偏光板配置の透過光の色度座標Ｐ２（ｘ２、ｙ２）を求めて、色度図上にプロットした色度点Ｐ２と無彩色点Ｃとを結ぶ直線Ｌ２のｘ軸に対する角度Ｆ２は、液晶層のツイスト角度φに対応する。
【００４１】
このようにして求めた角度Ｆ２を横軸に，角度Ｆ１を縦軸にとり、ツイスト角度φを８４°から９６°まで２°おきに、セルギャップｄを４．４μｍから５．２μｍまで０．１μｍおきに設定して各ツイスト角度φに対するセルギャップｄの値の関係を図６に示した。
【００４２】
図６において、曲線Iはツイスト角度φを８４°曲線IIはツイスト角度φを８６°、曲線IIIはツイスト角度φを８８°、曲線IVはツイスト角度φを９０°、曲線Vはツイスト角度φを９２°、曲線VIはツイスト角度φを９４°、曲線VIIはツイスト角度φを９６°にそれぞれ設定した液晶セルにおいて、セルギャップｄを４．４μｍから０．１μｍずつ増加させたときの角度Ｆ１とＦ２との関係を示している。
【００４３】
図６から明らかなように、偏光板１，２の透過軸１ａ，２ａの設置角度を異ならせた２つの状態での透過光の分光分布特性から色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）を求め、色度図上での無彩色点Ｃとを結ぶそれぞれの直線Ｌ１，Ｌ２の傾き角度Ｆ１及びＦ２の値に基づいて、液晶セル３のセルギャップ（液晶層厚）ｄと、液晶層のツイスト角度φを求めることができる。
【００４４】
すなわち、図１に示した光学系において、光源４から発生する光を偏光子１，液晶セル３，検光子２に照射し、透過軸１ａ，２ａを互いに平行に配置した偏光子１と検光子２の間に被測定用の液晶セル３を配置する。偏光子１と検光子２の透過軸１ａ，２ａと前記液晶セル３の配向処理方向３３ａ，３４ａを異ならせた２つの配置で透過光を光検出器５により検出して、２つの配置における透過光の分光分布を測定する。
【００４５】
これらの分光分布から色度図上での各色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）を求め、これらの色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）からそれぞれ無彩色点Ｃとを結ぶ２つの直線Ｌ１、Ｌ２のそれぞれの傾き角度Ｆ１，Ｆ２を求め、これらの傾き角度Ｆ１，Ｆ２により、前記図６に示した関係に基づいて、被測定用の液晶セル３のセルギャップ（液晶層厚）ｄと、ツイスト角度φが得られる。
【００４６】
上記分光分布の測定において、液晶セル３を透過しない光、及び液晶セル３内のギャップ材等を透過した光等のノイズ光も検出されるが、そのノイズ光は透過光の色純度を低下させるものであり、ノイズ光強度の変化は色度図上の色度点Ｐ１，Ｐ２が無彩色点Ｃから延びる直線Ｌ１、Ｌ２上での変化に対応する。
【００４７】
よって、測定された分光分布により求めた色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）により求められる色度点Ｐ１，Ｐ２と、無彩色点Ｃとを結ぶ直線Ｌ１、Ｌ２の傾き角度Ｆ１，Ｆ２は、ノイズ光による影響を受けることがないから、高い精度でセルギャップｄとツイスト角度φの測定を行うことができる。
【００４８】
本発明のセルギャップｄとツイスト角度φの測定方法は、液晶分子がほぼ９０°ツイスト配向したＴＮ型の液晶セル、あるいは、液晶分子を１８０°〜２５０°ツイスト配向させたＳＴＮ型の液晶セルの測定に適用することができる。
【００４９】
９０°ツイスト型のＴＮ液晶セルのセルギャップｄとツイスト角度φを測定する場合、偏光子１及び検光子２の透過軸１ａ，２ａと、光入射側基板３５の配向処理方向３３ａとをほぼ一致させたノーマリーブラック型の第１の偏光板配置により透過光の分光分布を測定し、測定した分光分布から色度図上の色度座標Ｐ１（ｘ１、ｙ１）を算出し、この色度座標に基づいて無彩色点Ｃとを結ぶ直線Ｌ１の傾き角度Ｆ１を算出する。
【００５０】
偏光子１及び検光子２の透過軸１ａ，２ａと光入射側基板３５の配向処理の方向３３ａとがほぼ４５°で交差する複屈折効果型の第２の偏光板配置により透過光の分光分布を測定し、測定した分光分布から色度図上の色度座標Ｐ２（ｘ２、ｙ２）を算出し、この色度座標に基づいて無彩色点Ｃとを結ぶ直線Ｌ２の傾き角度Ｆ２を算出する。
【００５１】
ノーマリーブラック型の偏光板配置により得られた傾き角度Ｆ１と、複屈折効果型の偏光板配置により得られた傾き角度Ｆ２とを基に、図６に示す傾き角度Ｆ１，傾き角度Ｆ２，セルギャップｄ，及びツイスト角度φとの関係から、被測定用のＴＮ液晶セル３のセルギャップｄとツイスト角度φを求めることができる。
【００５２】
尚、上述した測定方法では、９０°ツイストのＴＮ型液晶セルのセルギャップとツイスト角度の測定方法について述べたが、本発明の測定方法は、これに限ることなく、１８０°〜２７０°ツイスト配向させたＳＴＮ型の液晶セルについても同様に測定することができる。
【００５３】
この場合、与えられた液晶の屈折率異方性Δnを基に、複数のツイスト角度φ及び複数のセルギャップにそれぞれ対応する分光分布を式（１）〜（３）により算出し、その分光分布から色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）を求め、この色度座標から無彩色点Ｃとを結ぶ直線Ｌ１、Ｌ２の傾き角度Ｆ１，Ｆ２を算出して、傾き角度Ｆ１，傾き角度Ｆ２，セルギャップｄ，及びツイスト角度φとの関係を予め求めておく。以下、ＴＮ型液晶セルと同様にしてＳＴＮ型液晶セルのセルギャップｄ，及びツイスト角度φとを求めることができる。
【００５４】
また、上記測定方法では、液晶セル３の透過光強度の計算を簡略化するために、液晶セル３の分光分布の測定にあたって、偏光子１と検光子２の透過軸１ａ，２ａに対して、液晶セル３の液晶層厚の中央に位置する液晶分子３８ａの配向方向を４５°で交差する方向に配置した第１の偏光板配置と、前記液晶分子３８ａの配向方向を平行または直交する方向に配置した第２の偏光板配置を用いたが、これに限ることなく、偏光子１と検光子２の透過軸１ａ，２ａに対する液晶分子の配向方向は任意に設定しても良く、偏光子１と検光子２の透過軸１ａ，２ａに対する液晶分子の配向方向を少なくとも２つの異なる角度に配置したときの分光分布を測定することにより、液晶セルのセルギャップｄ，及びツイスト角度φとを求めることができる。
【００５５】
以下に、９０°ツイストのＴＮ型液晶セルのセルギャップｄとツイスト角度φを測定する場合について説明する。
【００５６】
先ず、被測定用の液晶セル３に用いられている液晶の屈折率異方性Δnを求め、式（１）〜（３）によりノーマリーブラック型の偏光板配置と複屈折効果型の偏光板配置の分光分布を算出し、それらの分光分布から各配置における色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）を求め、この色度座標から無彩色点Ｃとを結ぶ直線Ｌ１，Ｌ２の傾き角度であるＦ１，Ｆ２を算出して、傾き角度Ｆ１，Ｆ２，セルギャップｄ，及びツイスト角度φとの関係を求める。
【００５７】
次に、被測定用の液晶セル３における液晶層厚の中央に位置する液晶分子３８ａの配列方向を求め、光学軸１ａ，２ａを互いに平行に配置した偏光子１と検光子２との間に被測定用液晶セル３を配置し、前記偏光子１と検光子２の光学軸１ａ，２ａを前記液晶層厚の中央に位置する液晶分子の配列方向と４５°で交差する方向、即ち液晶セル３の光入射側基板３５の配向処理方向３３ａとほぼ平行な方向に配置して分光分布を測定する。
【００５８】
また、前記偏光子１と検光子２の光学軸１ａ，２ａを前記液晶層厚の中央に位置する液晶分子の配列方向と平行な方向、即ち液晶セル３の光入射側基板３６の配向処理方向３４ａとほぼ４５°で交差する方向に配置して分光分布を測定する。
【００５９】
測定したそれぞれの分光分布から色度図上の各色度点の色度座標Ｐ１（ｘ１、ｙ１），Ｐ２（ｘ２、ｙ２）を算出し、各色度点Ｐ１，Ｐ２と無彩色点Ｃとを結ぶ直線Ｌ１、Ｌ２のｘ軸に対する傾き角度Ｆ１，Ｆ２を算出する。
【００６０】
上記計算により求めた傾き角度であるＦ１，Ｆ２に、測定により求められた傾き角度Ｆ１，傾き角度Ｆ２を対応させることにより，被測定用の液晶セル３のギャップｄとツイスト角度φとを求めることがでる。
【００６１】
ツイスト角度を９０°、セルギャップを４．８μｍの値に設計された液晶セルを上述した方法によりツイスト角度φとセルギャップｄを測定した。分光分布の光学的測定により得られた各傾き角度Ｆ１，Ｆ２は、それぞれ約−４３°，−１０°であり、図６に示した各傾き角度Ｆ１，Ｆ２とツイスト角度φとセルギャップｄとの関係から、前記液晶セルのツイスト角度φは９０．２°、セルギャップｄは４．７５μｍという測定結果が得られた。
【００６２】
上記測定方法によれば、液晶セルのツイスト角度φを１／１０度、セルギャップｄを１／１００μｍの精度で正確に測定することができる。
【００６３】
【発明の効果】
以上説明したように、この発明によれば、一対の偏光板１，２の間に被測定用の液晶セル３を配置し、前記偏光板１，２の光学軸１ａ，２ａと液晶セル３の液晶分子の配列方向との成す角度θを異ならせた少なくとも２つの状態で透過光の分光分布特性を測定し、それらの複数の透過光の色度図上での色度点Ｐ１，Ｐ２と無彩色点Ｃとを結ぶ直線の傾きＦ１，Ｆ２を求めるものであるため、被測定用液晶セル３のセルギャップｄのみならず、液晶層のツイスト角度φも精度良く測定することがでる。
【００６４】
そして、上記透過光の色度図上での色度点Ｐ１，Ｐ２と無彩色点Ｃとを結ぶ直線の傾きＦ１，Ｆ２は、液晶層を通過する際に生じるノイズ光の影響を受けないので、より高精度の測定ができる。
【図面の簡単な説明】
【図１】この発明の第１の実施の形態にかかる測定方法に用いる光学系の構成を示す概略構成図である。
【図２】この発明の第１の実施の形態にかかる測定方法を適用してセルギャップｄとツイスト角度φが測定される液晶セル３の構造を示す断面図である。
【図３】この測定方法に用いる液晶セル３の配向処理方向３３ａ，３４ａと、偏光子１と検光子２の透過軸１ａ，２ａとの関係を示し、（ａ）は配向処理方向３３ａに対して、偏光子１と検光子２の透過軸の方向１ａ，２ａをツイスト角度φの１／２から４５°を差し引いた角度θに配置した第１の偏光板配置を示す平面図である。（ｂ）は、配向処理方向３３ａに対して、偏光子１と検光子２の透過軸１ａ，２ａの方向をツイスト角度φの１／２の角度θに配置した第２の偏光板配置を示す平面図である。
【図４】図１に示した光学系において、入射側基板と出射側基板の配向処理方向３３ａ，３４ａと、偏光子１及び検光子２の光学軸１ａ，２ａと、相互の角度の定義を示する図である。
【図５】本発明の測定方法で用いられる透過光の色度点Ｐと、この色度点Ｐと無彩色点Ｃとを結ぶ直線Ｌの角度Ｆを表す色度図である。
【図６】本発明の測定方法により求められた傾き角度Ｆ１，Ｆ２と、液晶セル３のセルギャップｄと、ツイスト角度φとの関係を表すグラフである。
【図７】ストークスパラメータ法によるストークスパラメータＳ１，Ｓ２と、セルギャップｄとツイスト角度φとの関係を表すグラフである。
【符号の説明】
１・・・偏光子、１ａ・・・透過軸、２・・・検光子、２ａ・・・透過軸、３・・液晶セル、３３，３４・・・配向膜、３３ａ，３４ａ・・・配向処理方向、３５・・・光入射側基板、３６・・・光出射側基板、３７・・・シール材、３８・・・液晶、３８ａ・・・液晶層中央の液晶分子、４・・・光源、５・・・光検出器、 θ・・・偏光板の設置角度、φ・・・ツイスト角度、ｄ・・・セルギャップ、Ｐ・・・色度点、Ｃ・・・無彩色点、Ｆ１，Ｆ２・・・傾き角度[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring a liquid crystal layer thickness and a twist angle of a liquid crystal display element.
[0002]
[Prior art]
Conventionally, in a liquid crystal cell in which a liquid crystal layer in which liquid crystal molecules are twist-aligned is provided between a pair of substrates each having electrodes formed on opposite surfaces, the thickness of the liquid crystal layer can be measured by: (1) A method of calculating the thickness of the liquid crystal layer by measuring the interference light intensity of light reflected from two interfaces between the inner surface of each of the pair of substrates and the liquid crystal layer, or (2) liquid crystal The cell is sandwiched between a pair of polarizing plates whose polarization axes are arranged parallel to each other, the wavelength at which the transmittance of transmitted light is minimized is detected, and the liquid crystal layer thickness is calculated from the wavelength using the theoretical equation of Gooch and Tarry. Are known.
In the measurement method of (1), the light reflected by the interface between the front substrate and the liquid crystal layer as viewed from the light incident direction of the pair of substrates of the liquid crystal cell, the inner surface of the back substrate, the liquid crystal layer, The liquid crystal layer thickness is calculated based on the interference of light due to the phase difference with the light reflected at the interface.
[0003]
This phase difference depends on the refractive index of the liquid crystal layer and the optical path length, but it is difficult to accurately determine the refractive index of the liquid crystal layer in a state where it is sealed between the substrates, and in particular, it has passed through the twist-aligned liquid crystal layer. It is extremely difficult to determine the polarization state of light. Furthermore, in an actual liquid crystal cell, light is reflected not only at the interface between the alignment film surface on the substrate inner surface and the liquid crystal layer, but also at the interface between the electrode formed on the substrate surface and the substrate, or the interface between the electrode and the alignment film. Therefore, it is difficult to accurately measure the liquid crystal layer thickness.
[0004]
In the measurement method (2), the wavelength at which transmitted light gives a minimum is obtained based on the dependence of transmitted light intensity on Δnd of the liquid crystal layer, and the cell gap is calculated from this wavelength.
[0005]
In this measurement method, the refractive index is different from the refractive index of the liquid crystal layer, such as a gap material portion (a portion where no liquid crystal exists) sandwiched between the substrates of the liquid crystal cell or a portion where the alignment of liquid crystal molecules is disturbed. The measurement accuracy decreases due to the influence of noise light that has passed through the portion indicating the rate. In addition, since a large error occurs in the detection of the wavelength at which the transmittance is minimized, it is difficult to accurately measure the liquid crystal layer thickness.
[0006]
On the other hand, as a method for measuring both the liquid crystal layer thickness and the twist angle of the liquid crystal cell, (3) a method for obtaining the Stokes parameter and obtaining the liquid crystal layer thickness and the twist angle based on the Stokes parameter has been proposed.
[0007]
In this measurement method, as described in Jpn.J.Appl.Phys.Vol.36 (1997) pp.2760-2764, a liquid crystal cell is arranged between the polarizer and the analyzer, and parallel to the y-axis. Linearly polarized light is incident on the liquid crystal cell, the x-axis component intensity Ix, the y-axis component intensity Iy, and the component intensity I45 ° in the 45 ° direction of the transmitted light are measured, and the quarter-wave plate is connected to the liquid crystal cell and analyzer. Measure the component intensity Iq, 45 ° in the 45 ° direction with the slow axis in parallel with the y-axis.
[0008]
The measured values of the x-axis component intensity Ix, the y-axis component intensity Iy, the component intensity I45 in the 45 ° direction, and the component intensity Iq in the 45 ° direction when using a quarter-wave plate, 45 °, In this method, Stokes parameters S1, S2, and S3 are calculated, and a liquid crystal layer thickness and a twist angle are calculated from the Stokes parameters S1, S2, and S3.
[0009]
[Problems to be solved by the invention]
However, the liquid crystal layer thickness measuring methods of (1) and (2) above can measure the liquid crystal layer thickness, but cannot measure the twist angle of the liquid crystal layer in which the liquid crystal molecules are twist-aligned, There is a problem that the measurement accuracy of the liquid crystal layer thickness is poor.
[0010]
Although the measurement method (3) can measure the liquid crystal layer thickness and the twist angle, it is difficult to measure the liquid crystal layer thickness and the twist angle with high accuracy even in this measurement method.
[0011]
That is, the Stokes parameters S1 and S2 when the twist angle is selected at intervals of 2 ° from 84 ° to 96 ° and the thickness of the liquid crystal layer is changed from 4.6 μm to 5.2 μm are obtained by the method (3). As shown in FIG. 7, points corresponding to the thicknesses of the liquid crystal layers were plotted on the S1 and S2 coordinates.
[0012]
As is apparent from FIG. 7, when the twist angles are 84 ° and 86 °, points corresponding to the thicknesses of the liquid crystal layers exist on different curves as shown by curves a and b, but the twist angle is 88. In the range of 0 ° to 96 °, points corresponding to the thicknesses of the respective liquid crystal layers are substantially dispersed on the curve C, and it is practically difficult to read the difference in twist angle.
Therefore, the method (3) also cannot accurately measure the liquid crystal layer thickness and the twist angle.
An object of the present invention is to provide a method for measuring a liquid crystal layer thickness and a twist angle, which can measure a liquid crystal layer thickness and a twist angle of a liquid crystal cell with high accuracy.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a method for measuring the thickness and twist angle of a liquid crystal layer according to the present invention includes a pair of polarizing plates having optical axes parallel to each other with a liquid crystal cell to be measured having a liquid crystal layer having twist alignment. Is measured in a first polarizing plate arrangement in which the optical axis of the polarizing plate is oriented in a first direction at a predetermined angle with the alignment direction of liquid crystal molecules in the vicinity of one substrate of the liquid crystal cell. A first slope of a straight line connecting the first chromaticity point and the achromatic color point represented by the first chromaticity on the chromaticity diagram is calculated based on the spectral distribution of light. And calculating the second chromaticity based on the spectral distribution of the transmitted light measured with the second polarizing plate arrangement in which the optical axis of the polarizing plate is oriented in a second direction different from the first direction. A straight line connecting the second chromaticity point represented by the second chromaticity and the achromatic color point on the chromaticity diagram Obtaining a second inclination, and obtaining a liquid crystal layer thickness and a twist angle of the liquid crystal cell to obtain a liquid crystal layer thickness and a twist angle of the liquid crystal cell based on the first inclination and the second inclination. Features.
[0014]
According to this measuring method, a liquid crystal cell to be measured is arranged between a pair of polarizing plates, and transmission is performed in at least two states in which the angle formed by the optical axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell is different. Since the spectral distribution characteristics of light are measured and the slope of the straight line connecting the chromaticity point and the achromatic color point on the chromaticity diagram of these transmitted lights is obtained, the cell gap of the liquid crystal cell to be measured In addition, the twist angle of the twist alignment cell can be measured with high accuracy.
[0015]
Since the slope of the straight line connecting the chromaticity point and the achromatic color point on the chromaticity diagram of the transmitted light is not affected by noise light generated when passing through the liquid crystal layer, more accurate measurement can be performed. It becomes possible.
[0016]
The transmitted light is preferably measured at least twice by shifting the angle formed between the transmission axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell by 45 °. That is, the second direction with respect to the first direction is arranged in a direction that intersects the transmission axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell at an angle of approximately 45 ° with respect to the first direction. Then, the spectral characteristics of the transmitted light in the two polarizing plate arrangements are measured.
[0017]
The liquid crystal cell to be measured is arranged in a first direction intersecting with the alignment direction of the liquid crystal molecules located at the center in the thickness direction of the liquid crystal layer of the liquid crystal cell at approximately 45 °, and the transmitted light is measured. The inclination of the first chromaticity point is obtained from the spectral distribution of the transmitted light, and the transmitted light is measured in the second direction that bisects the twist angle of the liquid crystal layer. From the spectral distribution of the transmitted light, The slope of the second chromaticity point is determined.
[0018]
When the liquid crystal cell to be measured is a 90 ° twisted nematic liquid crystal element, the first direction is set to a direction substantially parallel to the alignment direction of the liquid crystal molecules in the vicinity of the incident side substrate of the liquid crystal cell. The second direction is set to a direction intersecting with the alignment direction of liquid crystal molecules in the vicinity of the incident side substrate of the liquid crystal cell at an angle of about 45 °, and each transmitted light is measured, and each chromaticity point is measured. And the twist angle of the liquid crystal element and the cell gap can be obtained based on the inclination.
[0019]
Also, the method for measuring the thickness and the twist angle of the liquid crystal layer according to the present invention is such that the optical axes parallel to each other of a pair of polarizing plates arranged with a liquid crystal cell to be measured having a twist-aligned liquid crystal layer interposed therebetween, First spectral distribution data representing a spectral distribution of transmitted light measured in an arrangement oriented in a first direction at a predetermined angle with respect to the alignment direction of liquid crystal molecules in the vicinity of one substrate of the liquid crystal cell; Obtained in a spectral distribution measuring step for measuring second spectral distribution data representing a spectral distribution of transmitted light measured in an arrangement in which the optical axis is directed in a second direction different from the first direction, and in the spectral distribution measuring step Based on the obtained first and second spectral distribution data, a first chromaticity and a second chromaticity representing the chromaticity of each transmitted light are calculated, and the first and second chromaticities on the chromaticity diagram are calculated. The first chromaticity point and the first chromaticity point respectively represented by the chromaticity of A parameter calculating step for obtaining a first inclination and a second inclination of a straight line connecting the achromatic point of the liquid crystal, and the liquid crystal based on the first inclination and the second inclination calculated by the parameter calculating step. And a step of obtaining a liquid crystal layer thickness and a twist angle of the cell.
[0020]
According to this measuring method, a liquid crystal cell to be measured is disposed between a pair of polarizing plates, and the transmitted light is split in at least two states in which the angle between the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell is different. Since the distribution is obtained and the slope of two straight lines connecting the chromaticity point and the achromatic color point on the chromaticity diagram of each transmitted light is used as a parameter, the cell gap of the liquid crystal cell to be measured and the liquid crystal layer It is possible to measure the twist angle with high accuracy.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The measurement method according to one embodiment of the present invention will be described below.
[0022]
The cell gap and twist angle measuring method of the present invention uses an optical system in which a liquid crystal cell to be measured is disposed between a pair of polarizing plates. First, the optical axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell are determined. A spectral distribution of transmitted light is measured in a first state set at a predetermined angle, a first chromaticity point on the chromaticity diagram is calculated from the spectral distribution, and the chromaticity point and the achromatic color point are connected. Find the first slope of the straight line.
[0023]
Next, the spectral distribution of the transmitted light is measured in a second state in which the angle between the optical axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell is set to another different angle, and a chromaticity diagram is obtained from the spectral distribution. The upper second chromaticity point is calculated, and the second slope of the straight line connecting the chromaticity point and the achromatic color point is obtained.
[0024]
Then, using the first and second inclinations as parameters, the cell gap and the twist angle of the liquid crystal element are determined based on the relationship between the first and second inclinations, the cell gap and the twist angle, which are obtained in advance. It is what you want.
[0025]
FIG. 1 is a schematic configuration diagram showing an outline of an optical system used in the measurement method according to the first embodiment of the present invention.
[0026]
As shown in FIG. 1, the optical system used in the measurement method according to the present invention includes a polarizer 1 and an analyzer 2 made up of a pair of polarizing plates, and a device to be measured disposed between the polarizer 1 and the analyzer 2. The twisted nematic liquid crystal cell 3, a light source 4 for irradiating measurement light, and a photodetector 5 for detecting the intensity of light transmitted through the liquid crystal cell 3.
[0027]
As shown in FIG. 2, the liquid crystal cell 3 includes a lower substrate (light incident side substrate) 35 and an upper substrate (light emitting side substrate) having electrodes 31, 32 and alignment films 33, 34 formed on the inner surfaces facing each other. 36 is arranged in parallel, and the upper and lower substrates 35 and 36 are joined by a sealing material 37, and a liquid crystal 38 is sealed between the upper and lower substrates 35 and 36.
[0028]
2 and 3 show an example of a 90 ° twist type TN liquid crystal cell, and the alignment films 33 and 34 formed on the inner surfaces of the upper and lower substrates 35 and 36 are respectively subjected to an alignment treatment. The liquid crystal molecules adjacent to the alignment films 33 and 34 are aligned with their molecular long axes in the alignment processing directions 33a and 34a.
[0029]
In the liquid crystal 38 encapsulated between the upper and lower substrates 35 and 36 to form a liquid crystal layer, the alignment processing directions 33a and 34a applied to the alignment films 33 and 34 are shifted by about 90 °. The liquid crystal molecules are rotated clockwise as indicated by an arrow t in the drawing from the alignment treatment direction 33a of the alignment film 33 formed on the lower substrate 35 to the alignment treatment direction 34a of the alignment film 34 formed on the upper substrate 36. The orientation is almost 90 ° (φ).
[0030]
The liquid crystal molecules 38a located at the center in the thickness direction of the liquid crystal layer formed by the liquid crystal 38 are approximately ½ of the twist angle φ with respect to the alignment treatment direction 33a of the alignment film 33 of the lower substrate 35. Oriented in a direction that intersects at an angle.
[0031]
In the optical system of FIG. 1, the transmitted light intensity when the liquid crystal cell 3 in which liquid crystal molecules are twist-aligned is disposed between the polarizer 1 and the analyzer 2 is expressed by the following equation (1) by analysis based on the Jones matrix. It is represented by In this analysis, the directions of the transmission axes 1a and 2b of the polarizer 1 and the analyzer 2, the alignment processing direction 33a of the substrate 35 on the light incident side of the liquid crystal cell 3, and the alignment processing direction 34a of the light emission side substrate 36 are respectively It is defined as shown in FIG.
[0032]
That is, the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are arranged in parallel to each other, and the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are set with reference to the alignment processing direction 33a of the substrate on the light incident side. The angle formed by 2a is θ, the angle formed by the alignment direction 34a of the light emission side substrate is φ, and the light enters perpendicularly from the back side of the sheet of FIG.
[0033]
[Expression 1]

[0034]
Here, with respect to the alignment processing direction 33a of the incident-side substrate 35, the transmission axis directions 1a and 2a of the polarizer 1 and the analyzer 2 are obtained by subtracting 45 ° from 1/2 of the twist angle φ (φ / φ / When the first polarizing plate is disposed at 2-π / 4), that is, as shown in FIG. 3A, 45 ° with respect to the alignment direction of the central liquid crystal molecule 38a in the layer thickness direction of the liquid crystal layer. The transmitted light intensity T (NB) when the transmission axis directions 1a and 2a of the polarizer 1 and the analyzer 2 are installed in the direction intersecting with (1) is expressed by the following equation (2).
[0035]
[Expression 2]

[0036]
Further, a second polarizing plate arrangement in which the directions of the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are arranged at an angle θ that is ½ of the twist angle φ with respect to the alignment processing direction 33a of the incident side substrate 35. That is, as shown in FIG. 3B, when the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are aligned with the alignment direction of the central liquid crystal molecule 38a in the thickness direction of the liquid crystal layer. The transmitted light intensity T (DAP) is expressed by the following formula (3).
[0037]
[Equation 3]

[0038]
In the first and second polarizing plate arrangements, the spectral distribution characteristics of the transmitted light are the transmitted light intensity T (NB) and T (DAP) for each wavelength in the above formula (2) and the above formula (3). It is obtained by calculating.
[0039]
In the optical system of FIG. 1, the chromaticity coordinates P (x, y) of the outgoing light when white light is incident can be obtained from the spectral distribution of the transmitted light. As shown in FIG. 5, the inclination angle F with respect to the x-axis or y-axis of the straight line L connecting the chromaticity point P and the achromatic color point C on the chromaticity diagram is the same as the chromaticity coordinate P (x, y). It can be obtained from the chromaticity coordinates of the chromatic point C. The inclination angle F of the straight line L connecting the chromaticity point P and the achromatic color point C on the chromaticity diagram corresponds to the cell gap d or the twist angle φ of the liquid crystal cell 3.
[0040]
That is, the angle with respect to the x axis of the straight line L1 connecting the chromaticity point P1 and the achromatic color point C plotted on the chromaticity diagram by obtaining the chromaticity coordinates P1 (x1, y1) of the transmitted light of the first polarizing plate arrangement. F1 corresponds to the layer thickness (cell gap d) of the liquid crystal layer. Then, the chromaticity coordinates P2 (x2, y2) of the transmitted light of the second polarizing plate arrangement are obtained, and the x-axis of the straight line L2 connecting the chromaticity point P2 and the achromatic color point C plotted on the chromaticity diagram. The angle F2 corresponds to the twist angle φ of the liquid crystal layer.
[0041]
The angle F2 thus determined is taken on the horizontal axis, the angle F1 is taken on the vertical axis, the twist angle φ is changed every 2 ° from 84 ° to 96 °, and the cell gap d is set to 0.1 μm from 4.4 μm to 5.2 μm. FIG. 6 shows the relationship between the value of the cell gap d with respect to each twist angle φ set every other time.
[0042]
In FIG. 6, curve I is twist angle φ 84 ° curve II is twist angle φ 86 °, curve III is twist angle φ 88 °, curve IV is twist angle φ 90 °, and curve V is twist angle φ. In a liquid crystal cell in which the twist angle φ is set to 94 ° and the twist angle φ is set to 96 °, the curve VI is an angle F1 when the cell gap d is increased from 4.4 μm by 0.1 μm. The relationship with F2 is shown.
[0043]
As apparent from FIG. 6, chromaticity coordinates P1 (x1, y1), P2 (from the spectral distribution characteristics of transmitted light in two states where the installation angles of the transmission axes 1a, 2a of the

polarizing plates

1, 2 are different. x2, y2) is determined, and the cell gap (liquid crystal layer thickness) d of the liquid crystal cell 3 is determined based on the values of the inclination angles F1 and F2 of the straight lines L1 and L2 connecting the achromatic color point C on the chromaticity diagram. Then, the twist angle φ of the liquid crystal layer can be obtained.
[0044]
That is, in the optical system shown in FIG. 1, the polarizer 1, the liquid crystal cell 3, and the analyzer 2 are irradiated with light generated from the light source 4, and the transmission axes 1a and 2a are arranged in parallel to each other. A liquid crystal cell 3 to be measured is disposed between the two. The transmitted light is detected by the photodetector 5 in two arrangements in which the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are different from the alignment processing directions 33a and 34a of the liquid crystal cell 3, and transmission in the two arrangements is performed. Measure the spectral distribution of light.
[0045]
From these spectral distributions, chromaticity coordinates P1 (x1, y1) and P2 (x2, y2) on the chromaticity diagram are obtained, and from these chromaticity coordinates P1 (x1, y1) and P2 (x2, y2), respectively. The respective inclination angles F1 and F2 of the two straight lines L1 and L2 connecting the achromatic color point C are obtained, and based on the relation shown in FIG. 6 based on the inclination angles F1 and F2, the liquid crystal cell to be measured 3 cell gap (liquid crystal layer thickness) d and a twist angle φ are obtained.
[0046]
In the spectral distribution measurement, noise light such as light that does not pass through the liquid crystal cell 3 and light that passes through the gap material in the liquid crystal cell 3 is also detected, but the noise light reduces the color purity of the transmitted light. Therefore, the change in the noise light intensity corresponds to the change on the straight lines L1 and L2 where the chromaticity points P1 and P2 on the chromaticity diagram extend from the achromatic color point C.
[0047]
Therefore, the slopes of the straight lines L1 and L2 connecting the chromaticity points P1 and P2 obtained from the chromaticity coordinates P1 (x1, y1) and P2 (x2, y2) obtained from the measured spectral distribution and the achromatic color point C. Since the angles F1 and F2 are not affected by noise light, the cell gap d and the twist angle φ can be measured with high accuracy.
[0048]
The method for measuring the cell gap d and the twist angle φ of the present invention is based on a TN type liquid crystal cell in which liquid crystal molecules are twisted by about 90 °, or an STN type liquid crystal cell in which liquid crystal molecules are twisted by 180 ° to 250 °. It can be applied to measurement.
[0049]
When measuring the cell gap d and the twist angle φ of the 90 ° twist type TN liquid crystal cell, the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are substantially coincident with the alignment processing direction 33a of the light incident side substrate 35. The spectral distribution of the transmitted light is measured by the normally black first polarizing plate arrangement, and the chromaticity coordinates P1 (x1, y1) on the chromaticity diagram are calculated from the measured spectral distribution, and the chromaticity coordinates Based on the above, the inclination angle F1 of the straight line L1 connecting the achromatic color point C is calculated.
[0050]
Spectral distribution of transmitted light due to the birefringence effect type second polarizing plate arrangement in which the transmission axes 1a, 2a of the polarizer 1 and the analyzer 2 and the orientation processing direction 33a of the light incident side substrate 35 intersect at about 45 °. Then, chromaticity coordinates P2 (x2, y2) on the chromaticity diagram are calculated from the measured spectral distribution, and an inclination angle F2 of a straight line L2 connecting the achromatic color point C is calculated based on the chromaticity coordinates. .
[0051]
Based on the inclination angle F1 obtained by the arrangement of the normally black type polarizing plates and the inclination angle F2 obtained by the arrangement of the birefringence effect type polarizing plates, the inclination angle F1, the inclination angle F2, and the cell shown in FIG. From the relationship between the gap d and the twist angle φ, the cell gap d and the twist angle φ of the TN liquid crystal cell 3 to be measured can be obtained.
[0052]
In the measurement method described above, the measurement method of the cell gap and the twist angle of the TN type liquid crystal cell of 90 ° twist has been described. However, the measurement method of the present invention is not limited to this, and the 180 ° to 270 ° twist alignment. The same measurement can be performed for the STN liquid crystal cell.
[0053]
In this case, based on the refractive index anisotropy Δn of the given liquid crystal, spectral distributions respectively corresponding to a plurality of twist angles φ and a plurality of cell gaps are calculated by the equations (1) to (3), and the spectral distribution is calculated. Chromaticity coordinates P1 (x1, y1) and P2 (x2, y2) are obtained from the chromaticity coordinates, and inclination angles F1 and F2 of straight lines L1 and L2 connecting the achromatic color point C are calculated from the chromaticity coordinates to obtain the inclination angle F1. , The inclination angle F2, the cell gap d, and the twist angle φ are obtained in advance. Hereinafter, the cell gap d and the twist angle φ of the STN type liquid crystal cell can be obtained in the same manner as the TN type liquid crystal cell.
[0054]
Further, in the above measurement method, in order to simplify the calculation of the transmitted light intensity of the liquid crystal cell 3, when measuring the spectral distribution of the liquid crystal cell 3, the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 are A first polarizing plate arrangement in which the alignment direction of the liquid crystal molecules 38a located at the center of the liquid crystal layer thickness of the liquid crystal cell 3 is crossed at 45 ° and a direction in which the alignment directions of the liquid crystal molecules 38a are parallel or orthogonal to each other. Although the arranged second polarizing plate arrangement is used, the alignment direction of the liquid crystal molecules with respect to the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 may be arbitrarily set. And the cell gap d of the liquid crystal cell and the twist angle φ are determined by measuring the spectral distribution when the alignment directions of the liquid crystal molecules with respect to the transmission axes 1a and 2a of the analyzer 2 are arranged at at least two different angles. Can do.
[0055]
Hereinafter, a case where the cell gap d and the twist angle φ of the 90 ° twist TN liquid crystal cell are measured will be described.
[0056]
First, the refractive index anisotropy Δn of the liquid crystal used in the liquid crystal cell 3 to be measured is obtained, and the normally black type polarizing plate arrangement and the birefringent effect type polarizing plate are obtained by the equations (1) to (3). The spectral distribution of the arrangement is calculated, chromaticity coordinates P1 (x1, y1) and P2 (x2, y2) in each arrangement are obtained from the spectral distribution, and the straight lines L1, L1 connecting the achromatic point C from the chromaticity coordinates are calculated. F1 and F2 which are inclination angles of L2 are calculated, and the relationship between the inclination angles F1 and F2, the cell gap d, and the twist angle φ is obtained.
[0057]
Next, the alignment direction of the liquid crystal molecules 38a located at the center of the liquid crystal layer thickness in the liquid crystal cell 3 to be measured is obtained, and between the polarizer 1 and the analyzer 2 in which the optical axes 1a and 2a are arranged in parallel to each other. A liquid crystal cell 3 to be measured is arranged, and the direction in which the optical axes 1a and 2a of the polarizer 1 and the analyzer 2 intersect at 45 ° with the alignment direction of the liquid crystal molecules located in the center of the liquid crystal layer thickness, that is, the liquid crystal cell 3 is arranged in a direction substantially parallel to the alignment processing direction 33a of the light incident side substrate 35 and the spectral distribution is measured.
[0058]
In addition, the optical axes 1a and 2a of the polarizer 1 and the analyzer 2 are parallel to the alignment direction of the liquid crystal molecules located in the center of the liquid crystal layer thickness, that is, the alignment processing direction of the light incident side substrate 36 of the liquid crystal cell 3. The spectral distribution is measured by arranging in a direction intersecting with 34a at approximately 45 °.
[0059]
Chromaticity coordinates P1 (x1, y1) and P2 (x2, y2) of each chromaticity point on the chromaticity diagram are calculated from each measured spectral distribution, and each chromaticity point P1, P2 and achromatic color point C are connected. The inclination angles F1 and F2 of the straight lines L1 and L2 with respect to the x axis are calculated.
[0060]
The gap d and the twist angle φ of the liquid crystal cell 3 to be measured are obtained by associating the inclination angles F1 and F2 obtained by the measurement with the inclination angles F1 and F2 obtained by the above calculation. I get out.
[0061]
A liquid crystal cell designed to have a twist angle of 90 ° and a cell gap of 4.8 μm was measured for the twist angle φ and the cell gap d by the method described above. The inclination angles F1 and F2 obtained by optical measurement of the spectral distribution are about −43 ° and −10 °, respectively. The inclination angles F1 and F2, the twist angle φ, the cell gap d and the cell gap d shown in FIG. From the relationship, the measurement results were obtained that the twist angle φ of the liquid crystal cell was 90.2 ° and the cell gap d was 4.75 μm.
[0062]
According to the above measuring method, the twist angle φ of the liquid crystal cell can be accurately measured with an accuracy of 1/10 degree and the cell gap d with an accuracy of 1/100 μm.
[0063]
【The invention's effect】
As described above, according to the present invention, the liquid crystal cell 3 to be measured is disposed between the pair of

polarizing plates

1 and 2, and the optical axes 1 a and 2 a of the

polarizing plates

1 and 2 and the liquid crystal cell 3 The spectral distribution characteristics of the transmitted light are measured in at least two states with different angles θ with respect to the alignment direction of the liquid crystal molecules, and the chromaticity points P1 and P2 on the chromaticity diagram of the plurality of transmitted lights are not present. Since the slopes F1 and F2 of the straight line connecting the chromatic point C are obtained, not only the cell gap d of the liquid crystal cell 3 to be measured but also the twist angle φ of the liquid crystal layer can be measured with high accuracy.
[0064]
The slopes F1 and F2 of the straight line connecting the chromaticity points P1 and P2 and the achromatic color point C on the chromaticity diagram of the transmitted light are not affected by noise light generated when passing through the liquid crystal layer. , More accurate measurement is possible.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of an optical system used in a measurement method according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a structure of a liquid crystal cell 3 in which a cell gap d and a twist angle φ are measured by applying the measurement method according to the first embodiment of the present invention.
FIG. 3 shows the relationship between the alignment treatment directions 33a and 34a of the liquid crystal cell 3 used in this measurement method and the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2. FIG. 3A shows the alignment treatment direction 33a. FIG. 6 is a plan view showing a first polarizing plate arrangement in which the transmission axis directions 1a and 2a of the polarizer 1 and the analyzer 2 are arranged at an angle θ obtained by subtracting 45 ° from ½ of the twist angle φ. (B) shows the 2nd polarizing plate arrangement | positioning which has arrange | positioned the direction of the transmission axes 1a and 2a of the polarizer 1 and the analyzer 2 to angle (theta) of 1/2 of twist angle (phi) with respect to the alignment process direction 33a. It is a top view.
4 is a diagram illustrating the definition of mutual angles between the orientation processing directions 33a and 34a of the incident side substrate and the outgoing side substrate and the optical axes 1a and 2a of the polarizer 1 and the analyzer 2 in the optical system shown in FIG. FIG.
FIG. 5 is a chromaticity diagram showing a chromaticity point P of transmitted light used in the measurement method of the present invention and an angle F of a straight line L connecting the chromaticity point P and the achromatic color point C.
FIG. 6 is a graph showing the relationship between tilt angles F1 and F2 obtained by the measurement method of the present invention, the cell gap d of the liquid crystal cell 3, and the twist angle φ.
FIG. 7 is a graph showing the relationship between Stokes parameters S1, S2 by the Stokes parameter method, the cell gap d, and the twist angle φ.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Polarizer, 1a ... Transmission axis, 2 ... Analyzer, 2a ... Transmission axis, 3 ... Liquid crystal cell, 33, 34 ... Orientation film, 33a, 34a ... Orientation Processing direction, 35... Light incident side substrate, 36... Light emitting side substrate, 37... Sealing material, 38... Liquid crystal, 38 a. 5 ... photodetector, θ ... installation angle of polarizing plate, φ ... twist angle, d ... cell gap, P ... chromaticity point, C ... achromatic point, F1 , F2 ... Tilt angle

Claims

In an optical system in which a pair of polarizing plates whose optical axes are parallel to each other are arranged across a liquid crystal cell to be measured having a liquid crystal layer with twist alignment, the optical axis of the polarizing plate is set near one substrate of the liquid crystal cell. The first chromaticity is calculated on the basis of the spectral distribution of the transmitted light measured by the first polarizing plate arrangement in the first direction at a predetermined angle with the alignment direction of the liquid crystal molecules, and on the chromaticity diagram Determining a first slope of a straight line connecting a first chromaticity point represented by the first chromaticity and an achromatic color point;
A second chromaticity is calculated based on a spectral distribution of transmitted light measured by a second polarizing plate arrangement in which the optical axis of the polarizing plate is directed in a second direction different from the first direction, and the chromaticity is calculated. Determining a second slope of a straight line connecting the second chromaticity point represented by the second chromaticity on the figure and the achromatic color point;
A method for measuring a liquid crystal layer thickness and a twist angle in a liquid crystal element, wherein a liquid crystal layer thickness and a twist angle of the liquid crystal cell are obtained based on the first tilt and the second tilt.

The method for measuring a liquid crystal layer thickness and a twist angle in a liquid crystal element according to claim 1, wherein the second direction intersects the first direction at an angle of approximately 45 °.

3. The first direction according to claim 1, wherein the first direction is a direction that intersects with an alignment direction of liquid crystal molecules located at a center of a thickness direction of the liquid crystal layer of the liquid crystal cell at approximately 45 °. Measuring method of liquid crystal layer thickness and twist angle in liquid crystal element.

4. The method for measuring a liquid crystal layer thickness and a twist angle in a liquid crystal element according to claim 3, wherein the second direction is a direction that bisects the twist angle of the liquid crystal layer.

The liquid crystal cell to be measured is a 90 ° twisted nematic liquid crystal element,
The first direction is a direction substantially parallel to the alignment direction of liquid crystal molecules in the vicinity of the incident side substrate of the liquid crystal cell,
5. The second direction according to claim 1, wherein the second direction is a direction intersecting with an alignment direction of liquid crystal molecules in the vicinity of an incident side substrate of the liquid crystal cell at an angle of approximately 45 °. Measuring method of liquid crystal layer thickness and twist angle in liquid crystal element.

The optical axes parallel to each other of a pair of polarizing plates arranged with a liquid crystal cell to be measured having a twist-aligned liquid crystal layer interposed therebetween are predetermined with respect to the alignment direction of liquid crystal molecules in the vicinity of one substrate of the liquid crystal cell. The first spectral distribution data representing the light distribution of the transmitted light measured in the first direction of the angle and the optical axis of the polarizing plate are directed in a second direction different from the first direction. A spectral distribution measurement step of measuring second spectral distribution data representing the spectral distribution of transmitted light measured in the arrangement;
Based on the first and second spectral distribution data obtained in the spectral distribution measurement step, a first chromaticity and a second chromaticity representing the chromaticity of each transmitted light are calculated, and are displayed on the chromaticity diagram. Parameters for determining the first slope and the second slope of the straight line connecting the first chromaticity point and the second chromaticity point and the achromatic color point respectively represented by the first and second chromaticities A calculation step;
A liquid crystal layer thickness in a liquid crystal element, comprising: obtaining a liquid crystal layer thickness and a twist angle of the liquid crystal cell based on the first inclination and the second inclination calculated in the parameter calculation step; And twist angle measurement method.