JP4488671B2

JP4488671B2 - Display device and driving method thereof

Info

Publication number: JP4488671B2
Application number: JP2002273300A
Authority: JP
Inventors: 康夫都甲; 正志赤羽; 和也小林; 泰樹高橋
Original assignee: Sharp Corp; Stanley Electric Co Ltd
Current assignee: Sharp Corp; Stanley Electric Co Ltd
Priority date: 2002-09-19
Filing date: 2002-09-19
Publication date: 2010-06-23
Anticipated expiration: 2022-09-19
Also published as: JP2004109612A

Description

【０００１】
【発明の属する技術分野】
本発明は媒質として働く液晶などの誘電性流体に光制御媒体として働く微粒子を分散させて電気制御により各種画像を得られるようにした表示装置およびその駆動方法に関する。
【０００２】
【従来の技術】
従来、互いに平行に配設され、互いに対向する内面もしくは同一内面側に少なくとも一対の電極を備えた二枚の基板と、これらの基板の間に封入された液晶性材料層とからなり、前記液晶性材料層には液晶性材料層の厚みよりも小さな外径を有する不溶性の光制御媒体が均一に分散混入されており、上記した電極間に電界を加えることにより、前記光制御媒体が移動して、光制御媒体が密に分散する領域と、疎に分散する領域を形成して透過率差を生じさせて光制御を行うことを特徴とする光学スイッチング装置が知られる（例えば、特許文献１参照。）。
【０００３】
また、流体中の粒子を移動させて光学的表示を行う光学スイッチング装置において、簡易な構成で高い表示コントラストが得られるようにする光学スイッチング装置が知られる（例えば、特許文献２参照。）。
【０００４】
そして、透明な第１の基板と、第１の基板に対して所定のギャップを介して対向配置された第２の基板と、両基板間に狭持された分散媒と、分散媒中に分散する多数の微粒子と、第１の基板の一表面上に形成された複数の電極と、第１の基板と前記第２の基板との対向面のうち少なくともいずれか一方の表面であって、隣接する電極のいずれか一方の電極の近傍の第１の領域または第１の領域とほぼ対向する第２の基板表面の第２の領域のうち少なくともいずれか一方に形成され、微粒子を収容することができる複数の収容部とを含む表示装置とその製造方法が知られる（例えば、特許文献３参照。）。
【０００５】
本出願人は、かねてより液晶などの誘電性流体に微粒子を分散させ、かつ上下基板上に電極を配置したディスプレイであって、微粒子の動きを横方向に制御しその微粒子の位置で表示を切り替える流動性微粒子ディスプレイ（ＭｏｂｉｌｅＦｉｎｅＰａｒｔｉｃｌｅＤｉｓｐｌａｙ、以下、ＭＦＰＤという。）を提案し開発を行ってきた。このＭＦＰＤは、明るく高ＣＲの反射表示をすることができ、表示切り替え後は、電界を切っても、その表示状態を長時間保持するという表示のメモリー性を有しているという特徴を持ち、特に、電子の紙即ち電子ペーパーに適している。
【０００６】
ここに先願の特願２００１−２８９７２４号のＭＦＰＤの断面構造を図９に示す。図面において垂直もしくは水平に配向された液晶１中に微粒子２を分散させておく。この微粒子２は光制御媒体として、また液晶１は媒質として働く。そして、一般には、微粒子２としてはＴｉＯ_２、ＳｉＯ_２、ＺｎＯ等の各種金属酸化物やその中空体、スチレンボール等の有機物及びそれらの着色物等を用いることができる。図５では微粒子２として白色微粒子や着色微粒子を用いた場合であり、下基板３上に光吸収層４を設けている。なお、黒色微粒子や着色微粒子の場合、下基板３上に反射層（図示せず）を設けても良い。したがって、前者の場合、ノーマリーブラック表示、後者はノーマリーホワイト表示になる。なお、上基板５の内側には上電極６が、また光吸収層４の内側には下電極７が設けられている。
【０００７】
微粒子２の光制御媒体を移動させる媒質として例えば液晶性有機材料の液晶１等の絶縁性の流動性材料を用いるが液晶１としては、誘電率異方性が正もしくは負の材料いずれでも良い。液晶１に誘電率異方性により微粒子２の挙動に影響を与え、大まかに言うと誘電率異方性の絶対値が大きい方が微粒子２の移動速度が速い傾向がある。液晶１中に分散させる微粒子２の添加量は１から５０ｗｔ％程度、望ましくは１０から３０ｗｔ％程度が良く、微粒子２の粒径は０．５から１００μｍ程度、望ましくは２から２０μｍ程度がよい。ガラス、プラスチックなどの透明上下基板５，３上に形成する上下電極６，７は、ＩＴＯのような透明電極でもＡｌ、Ｍｏ等の不透明電極でも良い。セル厚Ａは２から３００μｍ程度、望ましくは２０から１００μｍ程度がよいとされている。
【０００８】
つぎに、基本的な電極配置における微粒子２の挙動を図１０に示す。
【０００９】
図１０（ａ）は、上電極６を陽極、下電極７を陰極として用いて電界を形成したときの媒質の液晶１の流動方向および微粒子２の移動方向を概略的に示しており、上電極６と下電極７との間に直流電圧または単極性矩形パルス（数十Ｈｚ〜数十ｋＨｚ）を印加して電界を形成すると、図中に矢印Ａ１〜Ａ４、Ｂ１〜Ｂ２で示す方向に媒質の液晶１が流動し、これらの方向に微粒子２が移動する。
【００１０】
媒質１および微粒子２は、基本的に陽極から電気的引力を受け、陰極から電気的斥力を受けたように振る舞う。
【００１１】
つぎに図１０（ｂ）は、上電極６を陰極、下電極７を陽極として用いて電界を形成したときの媒質の液晶１の流動方向および微粒子２の移動方向を概略的に示しており、同図に示すように、上電極６と下電極７との間に電界を形成すると、図中に矢印Ａ５〜Ａ８、Ｂ５〜Ｂ６で示す方向に媒質の液晶１が流動し、これらの方向に微粒子２が移動する。
【００１２】
媒質１および微粒子２は、基本的に、陽極から電気的斥力を受け、陰極から電気的引力を受けたように振る舞う。
【００１３】
図１０（ａ）および（ｂ）のいずれの場合でも、媒質１を電界に従って流動させると、微粒子２の多くは、平面視上、面内方向に移動する。微粒子２を容器の厚さ方向に電気泳動させる場合に比べ、低い電圧で微粒子２をより高速に移動させることが可能である。
【００１４】
つぎに、上述の微粒子２の挙動に基づいて、表示原理を図１１に示す。ノーマリーホワイトの場合は、微粒子（白）２が集まった所では微粒子２の散乱反射により白表示が得られ（図１１（ａ）参照）、微粒子２が移動して無くなったところでは、液晶１が透明なので下基板３上の光吸収層４により外光が吸収され、黒く見える（図１１（ｂ）参照）。
【００１５】
さらに、表示特性を図１２に示す。視角によらず明るい白表示と暗い黒表示が得られている事がわかる。
【００１６】
図１３（ａ）に、白表示の際の表示装置の様子を拡大して示し、図１３（ｂ）に、黒表示の際の表示装置の様子を拡大して示す。これらの図に示した表示装置は、上電極６のパターンおよび下電極７のパターンそれぞれでの電極ピッチを３００μｍ、上下電極６，７の線幅を１５０μｍとし、各電極６，７をモリブデンで形成したときのものである。
【００１７】
【特許文献１】
特開２００１−３１８６２９号公報
【特許文献２】
特開２００２−２４４１６４号公報
【特許文献３】
特開２００２−１６２６４９号公報
【００１８】
【発明が解決しようとする課題】
しかし乍ら、このようなＭＦＰＤにあっては、白表示特性を得るためにディスプレイのセル厚を厚くすると上下電極間の横電界を用いている本ディスプレイでは電極中央付近の微粒子を十分に制御できず表示の切り替えを所望通りに行えないという問題があった。
【００１９】
本発明は叙上の点に着目して成されたものでこのようなＭＦＰＤのディスプレイを始め、各種の表示手段の厚いセル厚であっても高速に制度よく、微粒子位置を制御可能にできるようにした表示装置およびその駆動方法を提供することを目的とする。
【００２０】
【課題を解決するための手段】
本発明は下記の構成により上記課題を解決するものである。
【００２１】
（１）透明な上基板と下基板の間に液晶性を有する有機材料からなる誘電性の流体（分散媒）とその流体に分散された白色もしくは着色された微粒子とをはさみ、前記上基板上には上電極、前記下基板上には下電極が横電界を生ずるようそれぞれ配置され、さらに前記上電極と前記下電極はそれぞれ格子状とされ、一方の格子状電極に対して他方の格子状電極が幅広く形成され、前記一方の格子状電極における電極交差部と前記他方の格子状電極における電極開口部が対向配置するよう構成され、さらに前記一方の格子状電極が形成された基板上に、該一方の格子状電極とは電気的に絶縁された形で前記他方の格子状電極と対向するように補助電極が形成されることを特徴とする表示装置。
【００２２】
（２）前記微粒子は、前記各電極に印加する電圧によりその位置が制御され、その位置により表示を切り替えることを特徴とする前記（１）記載の表示装置。
【００２３】
（３）前記補助電極は、前記一方の格子状電極における電極開口部である画素に相当する表示部分の中央付近に形成されることを特徴とする前記（１）記載の表示装置。
【００２５】
（４）前記上基板と前記下基板の間の距離に相当するセル厚が１００ミクロン以上であることを特徴とする前記（１）記載の表示装置。
【００２６】
（５）前記（１）の表示装置を備えると共に、前記他方の格子状電極と前記一方の格子状電極間に直流もしくは直流成分を含んだ単極性交流電圧を印加するタイミングと同期させたタイミングで前記直流とは逆極性の直流もしくは前記直流成分とは逆極性の直流成分を含んだ単極性交流電圧を前記他方の格子状電極と前記補助電極間に印加することを特徴とする表示装置の駆動方法。
【００２７】
（６）前記微粒子は、前記一方の格子状電極、前記他方の格子状電極及び前記補助電極に印加される電圧により横方向に移動することを特徴とする前記（５）記載の表示装置の駆動方法。
【００２８】
【発明の実施の形態】
以下に本発明の一実施の形態について図面と共に説明する。
【００２９】
図１は、本発明の一実施の形態を示す表示装置の上下電極および補助電極のパターン構成を平面から見た拡大構造図、図２は、図１のII−II線を断面で見た表示装置の拡大模式図である。
【００３０】
そして、この表示装置は図９に示す従来例と同様に垂直もしくは水平に配向された液晶１中に微粒子２を分散させて置き、微粒子２は光制御媒体として、また液晶１は媒質として働く。
【００３１】
さらに図面では、格子状の上電極６と板状の下電極７を上下基板５，３上に直接または光吸収層４を介して配設してあるが、この実施の形態では上基板５側に補助電極８を絶縁膜９を介して形成している。この補助電極８は下基板３側に形成してもよいが、その場合、上下電極６，７の位置も逆になり上電極６が微粒子２を隠す不透明電極にならないため別途微粒子２を隠すためのパターンを上基板５上に形成する必要があるため製造面からは上基板５側が望ましい。
【００３２】
前記絶縁膜９としてアクリル系絶縁性有機膜を用いたが、その他の有機絶縁膜やＳｉＯ_２、ＳｉＮｘ等の無機絶縁膜及びそれらの組み合わせでもよい。
【００３３】
微粒子２としてはＴｉＯ_２と有機物の混合系を用いた。図示では微粒子２として白色微粒子や着色微粒子を用いた場合であり、下基板３上に光吸収層４を設けている。黒色微粒子や着色微粒子の場合、下基板３上に反射層を設けても良い。前者の場合ノーマリーブラック表示、後者はノーマリーホワイト表示になる。
【００３４】
微粒子２の光制御媒体を移動させる媒質として例えば液晶１等の絶縁性の流動性材料を用いる。液晶１としては誘電率異方性が正もしくは負の材料いずれでも良い。液晶１に誘電率異方性により微粒子２の挙動に影響を与え、大まかに言うと誘電率異方性の絶対値が大きい方が微粒子２の移動速度が速い傾向がある。ここでは液晶１としてＲＤＰ−００３３３（大日本インキ製）を用いた。液晶１中に分散させる微粒子２の添加量は１から５０ｗｔ％程度、望ましくは１０から３０ｗｔ％程度が良い。ここでは微粒子２を２０ｗｔ％添加した。微粒子２の粒径は０．５から１００μｍ程度、望ましくは２から２０μｍ程度がよい。ここでは６μｍ粒子を用いた。ガラス、プラスチックなどの透明上下基板５，３上に形成する電極はＩＴＯのような透明電極でもＡｌ、Ｍｏ等の不透明電極でも良い。ここでは上電極６としてＭｏ、下電極７と補助電極８としてＩＴＯを用いた。
【００３５】
ここでＭＦＰＤのセル厚Ａに対する白表示の明るさの変化を図３に示す（微粒子添加量２０ｗｔ％）。図３より新聞紙の明るさ（反射率：約４０％）以上となるのは、セル厚Ａが１００μｍ以上の場合であり、明るさの面から望ましくは１００μｍ以上がよいことがわかる。
【００３６】
ところが従来のＭＦＰＤでは上下電極間の横電界を用いて微粒子２を制御しており、図５におけるＡ（セル厚）／Ｂ（画素サイズの１／２）比が１以下になると、すなわち画素サイズ２００μｍのセルでセル厚Ａが１００μｍ以上になると、画素中央部の微粒子２は全く動かなくなる。その様子を図７の写真（セル厚２００μｍのセル写真）に示す。ここでは透過で写真撮影しているため微粒子２がある部分が黒く、微粒子２のない部分が白く見える（白黒反転）。
【００３７】
このようにセル厚Ａを厚くしてもＡ／Ｂ比が１以上になるため画素サイズを大きくする必要があるが、画素サイズを大きくすれば、当然のこととして解像度が低くなり、また駆動電圧を高くしなければならないという問題があった。また反射率を犠牲にしてセル厚Ａを薄くした場合において画素中央部の微粒子２を制御できるものの中央部から画素周辺部に微粒子が移動するのに要する時間がかかるため、切り替えに数秒以上も時間がかかるという問題があった。
【００３８】
これに対し、本発明に係る補助電極を備えたＭＦＰＤの電圧印加に対する微粒子２の挙動を図８の写真（セル厚２００μｍのセル写真）に示す。ここでも透過で写真撮影しているため微粒子２がある部分が黒く、微粒子２のない部分が白く見える。電圧は上電極６に＋７０Ｖもしくは−７０Ｖ、下電極７に０Ｖ、補助電極８に上電極６と極性逆の電圧を印加した。この写真からわかるように微粒子２は完全に制御されており、画素中央部などの微粒子２が動かなくなるといった現象は見られず、逆に、さらに非常に高速に微粒子２が移動することが確認できた。
【００３９】
本発明に係るＭＦＰＤのレスポンス特性を図４に示す。この図から分るように、非常に高速にスイッチングしており応答時間は２００ｍｓｅｃ（０．２ｓｅｃ）以下であることがわかる。
【００４０】
また、図６に示す写真から分るように、表示切替操作が立ち上がりから２００ｍｓｅｃ以内にセル厚Ａが１５０μｍ、１９０μｍ、２５０μｍと変化させても微粒子２の制御は可能であり、最大４５０μｍまで確認できた。
【００４１】
本発明のＭＦＰＤにおける微粒子２の位置は下電極７を接地した状態で上電極６に印加する電圧の極性を変えることにより制御できるが、その点は従来のＭＦＰＤも同様である。本発明では上電極６に印加する電圧に対し同期させるかもしくはわずかにずらせた状態で同期させる形で補助電極８に電圧を印加する。その動作原理ははっきりしていないが、以下のように考えられる。たとえば白表示即ち画素上に微粒子が分散している状態から黒表示即ち画素外（上電極６の下）に微粒子２が集められている状態に表示を変える場合、補助電極８と下電極７間の電圧差により微粒子２は下電極７側に集められる（縦方向の移動）。次に、下電極７と上電極６の電圧差により微粒子２は上電極６側に集められる（横方向の移動）。上記現象が同時進行して画素上に分散していた微粒子２は画素外（上電極６の下）に微粒子２が集められる。これが本発明における微粒子２の動作原理と仮定できる。
【００４２】
この考えを検証するため、まず補助電極８と下電極７間に所定の電圧を印加し、その後、下電極７と上電極６間に所定の電圧を印加したところ三電極に所定の電圧を同時に印加した時と同様に微粒子２を制御できることを確認した。一方まず上電極６と下電極７間に所定の電圧を印加し、その後、下電極７と補助電極８間に所定の電圧を印加したところ従来のＭＦＰＤと同様に中央部の微粒子２が動かなかったことも上記仮定を裏付けしている。上記仮定によれば検証実験のように補助電極８−下電極７間に印加する電圧と下電極７−上電極６間に印加する電圧を少しずらした方が効率よく微粒子２を移動できるはずであり、好ましいといえる。但し、駆動上同期させた方が製造容易であり、かつ同期させた駆動条件でも図４のように従来のＭＦＰＤに比べ表示性能、応答性能とも著しく改善できていることを確認しており、タイミングをずらす駆動方法は必須ではない。
【００４３】
この実施の形態では補助電極８として下電極７と同じパターン・大きさ（画素電極と同じ大きさ）のものを用いたが異なるパターン・大きさ、例えば画素中央部のみの小さなパターン等でもよい。補助電極８は透明なＩＴＯ電極であるが、ＩＴＯとガラスとの屈折率差により外部光が反射されるため補助電極８は小さいことが望ましい。その場合、特に黒レベルが改善され図４のコントラスト（１２程度）はさらに向上できる。
【００４４】
この実施の形態における構造により、４５０ミクロンのＭＦＰＤにおいても微粒子２を所望の状態に制御できることを確認している。このときの白表示の反射率は６０％以上でありコピー紙（反射率７０％程度）に近い明るい表示と高コントラストを実現できる。
【００４５】
電極パターンは格子状の上電極６とべタに近い幅広い格子状の下電極７及び補助電極８の場合について示したがそれに限らない。例えば上電極６は円周状、蜂の巣状、ストライプ状等でもよく、下電極７や補助電極８はベタ状、円状、多角形、ストライプ状等でもよい。
【００４６】
なお、微粒子２、媒質（液晶１）、電極等その他の構成材料は上記実施の形態に限らず、例えば媒質は、液晶性を有さない液体でも良い。
【００４７】
補助電極８は上基板５上に形成する場合について述べたが、下基板３上もしくは両基板５，３上に形成してもよい。また補助電極８を形成する位置は絶縁膜９を介して上電極６もしくは下電極７の上でも下でもかまわない。
【００４８】
【発明の効果】
以上述べたように本発明によりセル厚、画素サイズ（Ａ／Ｂ比）によらず、しかも微粒子の位置を所望の位置に制御できるためディスプレイのセル条件によらず高いコントラストを得ることができ、図４からも現状でコントラスト１２を確認しており特に、セル厚を厚くするとディスプレイの反射率も現状で反射率６０％を確認しており著しく向上できると共に殊に単位面積あたりの白微粒子の密度を高くできるため新聞紙（新聞紙の反射率４０％程度）より明るく、コピー紙（コピー紙の反射率７０％程度）に近い明るさと、新聞紙（新聞紙のコントラストは５程度）及びコピー紙（コピー紙のコントラストは７から８程度）以上の高コントラストの反射型ディスプレイを実現できる。
【００４９】
また本発明により微粒子の位置を効率よく移動でき、そのためレスポンスが改善され従来数秒かかっていた表示切り替えが２００ｍｓｅｃ以下で行え高速応答を実現できるものであって２００ｍｓｅｃはＳＴＮ−ＬＣＤと同等であり、アニメなどの動画表示も可能になる。
【００５０】
しかも本発明はディスプレイ全般、児童用玩具等、紙・印刷物（雑誌、新聞、ポスターなど）の代替品全般（電子の紙）、カメラの絞り、ストロボの光量調整、印画紙用書き込み光源等の光学部品全般などその応用技術ないし産業分野は、きわめて広範である。
【図面の簡単な説明】
【図１】本発明に係る一実施の形態を示す表示装置であって上下基板、液晶および微粒子を取除いて上下電極および補助電極のパターン構造を示す平面から見た拡大構造図
【図２】図１のII−II線を断面で見た拡大模式図
【図３】セル厚と反射率との関係を示すグラフ
【図４】本発明のレスポンス特性を示すもので電圧の印加時間とコントラスト比および反射率（％）との関係を示すグラフ
【図５】セル厚ＡとＢ（画面サイズの１／２）との相対関係を示す縦断説明図
【図６】本発明に係る表示切替の状態を写真で示すものでセル厚と色調との関係を示す一連の写真
【図７】拡大写真
【図８】拡大写真
【図９】従来例の拡大断面模式図
【図１０】（ａ）は、図９に示した表示装置に所定の電圧を印加したときにおける微粒子分散層中の媒質および微粒子の流動方向ないし移動方向を説明するための模式図であり、（ｂ）は、同装置に他の電圧を形成したときにおける微粒子分散層中の媒質および微粒子の流動方向ないし移動方向を説明するための模式図
【図１１】（ａ），（ｂ）微粒子の表示原理を示す拡大断面模式図
【図１２】白表示と黒表示とを行ったときの反射率と視角との関係を示すグラフ
【図１３】（ａ）は、図９に示した表示装置によって白表示を行った際の顕微鏡写真の写しであり、（ｂ）は、同装置によって黒表示を行った際の顕微鏡写真の写し
【符号の説明】
１液晶（媒質）
２微粒子（光制御媒体）
３下基板
４光吸収層
５上基板
６上電極
７下電極
８補助電極
９絶縁膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device in which fine particles acting as a light control medium are dispersed in a dielectric fluid such as liquid crystal that acts as a medium so that various images can be obtained by electrical control, and a driving method thereof.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, the liquid crystal includes two substrates that are arranged in parallel to each other and that have at least a pair of electrodes on inner surfaces facing each other or on the same inner surface side, and a liquid crystalline material layer sealed between these substrates. An insoluble light control medium having an outer diameter smaller than the thickness of the liquid crystal material layer is uniformly dispersed and mixed in the conductive material layer, and the light control medium moves by applying an electric field between the electrodes. Thus, there is known an optical switching device characterized in that light control is performed by forming a region in which the light control medium is densely dispersed and a region in which the light control medium is sparsely dispersed to generate a transmittance difference (for example, Patent Document 1). reference.).
[0003]
In addition, an optical switching device that performs high-speed display contrast with a simple configuration in an optical switching device that performs optical display by moving particles in a fluid is known (see, for example, Patent Document 2).
[0004]
Then, the transparent first substrate, the second substrate opposed to the first substrate through a predetermined gap, a dispersion medium sandwiched between the two substrates, and the dispersion in the dispersion medium A plurality of fine particles, a plurality of electrodes formed on one surface of the first substrate, and at least one of the opposing surfaces of the first substrate and the second substrate, and adjacent to each other Formed in at least one of the first region in the vicinity of one of the electrodes or the second region on the surface of the second substrate substantially opposite to the first region, and contains fine particles A display device including a plurality of storage units that can be manufactured and a manufacturing method thereof are known (for example, see Patent Document 3).
[0005]
The present applicant has long been a display in which fine particles are dispersed in a dielectric fluid such as liquid crystal and electrodes are arranged on upper and lower substrates, and the movement of the fine particles is controlled in the lateral direction to switch the display at the position of the fine particles. We have proposed and developed a fluid fine particle display (hereinafter referred to as MFPD). This MFPD is capable of bright and high-CR reflective display, and has a display memory property that maintains its display state for a long time even when the electric field is turned off after switching the display. In particular, it is suitable for electronic paper, that is, electronic paper.
[0006]
FIG. 9 shows a cross-sectional structure of MFPD of Japanese Patent Application No. 2001-289724 of the prior application. In the drawing, fine particles 2 are dispersed in a liquid crystal 1 that is aligned vertically or horizontally. The fine particles 2 function as a light control medium, and the liquid crystal 1 functions as a medium. In general, the fine particles 2 can be various metal oxides such as TiO ₂ , SiO ₂ , ZnO, hollow bodies thereof, organic substances such as styrene balls, and colored substances thereof. In FIG. 5, white fine particles or colored fine particles are used as the fine particles 2, and the light absorption layer 4 is provided on the lower substrate 3. In the case of black fine particles or colored fine particles, a reflective layer (not shown) may be provided on the lower substrate 3. Therefore, the former is normally black display, and the latter is normally white display. An upper electrode 6 is provided inside the upper substrate 5, and a lower electrode 7 is provided inside the light absorption layer 4.
[0007]
As a medium for moving the light control medium of the fine particles 2, for example, an insulating fluid material such as a liquid crystal 1 of a liquid crystal organic material is used. The liquid crystal 1 may be a material having a positive or negative dielectric anisotropy. The behavior of the fine particles 2 is affected by the dielectric anisotropy of the liquid crystal 1, and roughly speaking, the moving speed of the fine particles 2 tends to be higher when the absolute value of the dielectric anisotropy is larger. The addition amount of the fine particles 2 dispersed in the liquid crystal 1 is about 1 to 50 wt%, preferably about 10 to 30 wt%, and the particle size of the fine particles 2 is about 0.5 to 100 μm, preferably about 2 to 20 μm. The upper and lower electrodes 6 and 7 formed on the transparent upper and lower substrates 5 and 3 such as glass and plastic may be transparent electrodes such as ITO or opaque electrodes such as Al and Mo. The cell thickness A is about 2 to 300 μm, preferably about 20 to 100 μm.
[0008]
Next, the behavior of the fine particles 2 in a basic electrode arrangement is shown in FIG.
[0009]
FIG. 10A schematically shows the flow direction of the liquid crystal 1 and the movement direction of the fine particles 2 when an electric field is formed using the upper electrode 6 as an anode and the lower electrode 7 as a cathode. When an electric field is formed by applying a DC voltage or a unipolar rectangular pulse (several tens of Hz to several tens of kHz) between 6 and the lower electrode 7, the medium in the direction indicated by arrows A1 to A4 and B1 to B2 in the figure Liquid crystal 1 flows, and fine particles 2 move in these directions.
[0010]
The medium 1 and the fine particles 2 basically behave as if they received an electrical attraction from the anode and an electrical repulsion from the cathode.
[0011]
Next, FIG. 10B schematically shows the flow direction of the liquid crystal 1 and the movement direction of the fine particles 2 when an electric field is formed using the upper electrode 6 as a cathode and the lower electrode 7 as an anode. As shown in the figure, when an electric field is formed between the upper electrode 6 and the lower electrode 7, the liquid crystal 1 of the medium flows in the directions indicated by arrows A5 to A8 and B5 to B6 in the figure, and in these directions The fine particles 2 move.
[0012]
The medium 1 and the fine particles 2 basically behave as if they received an electric repulsive force from the anode and an electric attractive force from the cathode.
[0013]
10A and 10B, when the medium 1 is caused to flow according to an electric field, most of the fine particles 2 move in the in-plane direction in plan view. Compared to the case where the microparticles 2 are electrophoresed in the thickness direction of the container, the microparticles 2 can be moved at a higher speed with a lower voltage.
[0014]
Next, the display principle is shown in FIG. 11 based on the behavior of the fine particles 2 described above. In the case of normally white, white display is obtained by scattering reflection of the fine particles 2 (see FIG. 11A) when the fine particles (white) 2 gather, and the liquid crystal 1 is removed when the fine particles 2 move and disappear. Is transparent, external light is absorbed by the light absorption layer 4 on the lower substrate 3 and appears black (see FIG. 11B).
[0015]
Further, the display characteristics are shown in FIG. It can be seen that bright white display and dark black display are obtained regardless of the viewing angle.
[0016]
FIG. 13A shows an enlarged view of the display device during white display, and FIG. 13B shows an enlarged view of the display device during black display. In the display device shown in these drawings, the electrode pitch in the pattern of the upper electrode 6 and the pattern of the lower electrode 7 is 300 μm, the line width of the upper and lower electrodes 6 and 7 is 150 μm, and the electrodes 6 and 7 are formed of molybdenum. It is a thing when I did it.
[0017]
[Patent Document 1]
JP 2001-318629 A [Patent Document 2]
JP 2002-244164 A [Patent Document 3]
JP 2002-162649 A
[Problems to be solved by the invention]
However, in such an MFPD, if the cell thickness of the display is increased in order to obtain white display characteristics, fine particles near the center of the electrode can be sufficiently controlled in this display using the horizontal electric field between the upper and lower electrodes. There is a problem that the display cannot be switched as desired.
[0019]
The present invention has been made paying attention to the above points, and it is possible to control the position of fine particles at high speed and in a high-speed system even with a thick cell thickness of various display means such as the display of MFPD. An object of the present invention is to provide a display device and a driving method thereof.
[0020]
[Means for Solving the Problems]
This invention solves the said subject with the following structure.
[0021]
(1) Between a transparent upper substrate and a lower substrate, a dielectric fluid (dispersion medium) made of an organic material having liquid crystallinity and white or colored fine particles dispersed in the fluid are sandwiched between the upper substrate and the upper substrate. The upper electrode and the lower electrode are arranged on the lower substrate so as to generate a lateral electric field, respectively, and the upper electrode and the lower electrode are each in a lattice shape, with respect to one lattice electrode. electrode is widely formed, the electrode openings in the lattice-shaped electrodes of the the electrode crossing portion in the one of the grid-shaped electrode and the other is configured to opposed, on a further substrate on which the the one of the grid-shaped electrode is formed, display device, characterized in that the auxiliary electrode so as to face the other of the lattice-shaped electrode in an electrically insulated form is formed with one of the grid-shaped electrode the.
[0022]
(2) The display device according to (1), wherein the position of the fine particles is controlled by a voltage applied to each electrode, and the display is switched according to the position.
[0023]
(3) The display device according to (1) , wherein the auxiliary electrode is formed near a center of a display portion corresponding to a pixel which is an electrode opening in the one grid electrode .
[0025]
(4) The electrolyte cell thickness corresponding to the distance between the substrate the lower substrate is characterized in that 100 microns or more (1) The display device according.
[0026]
(5) the provided with a display device (1), is synchronized with the timing of applying a pre-Symbol unipolar alternating voltage including a direct current or a direct current component between the other of the grid-shaped electrode and the one of the grid-shaped electrode Timing And a unipolar AC voltage including a DC component having a polarity opposite to the DC component or a DC component having a polarity opposite to the DC component is applied between the other grid electrode and the auxiliary electrode. Driving method.
[0027]
(6) The driving of the display device according to (5) , wherein the fine particles move in a lateral direction by a voltage applied to the one grid electrode, the other grid electrode, and the auxiliary electrode. Method.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0029]
FIG. 1 is an enlarged structural view in which a pattern configuration of upper and lower electrodes and auxiliary electrodes of a display device according to an embodiment of the present invention is viewed from above, and FIG. 2 is a display in which a II-II line in FIG. It is an expansion schematic diagram of an apparatus.
[0030]
In this display device, fine particles 2 are dispersed and placed in vertically or horizontally aligned liquid crystal 1 as in the conventional example shown in FIG. 9, and fine particles 2 serve as a light control medium and liquid crystal 1 serves as a medium.
[0031]
Further, in the drawing, the grid-like upper electrode 6 and the plate-like lower electrode 7 are arranged on the upper and lower substrates 5 and 3 directly or via the light absorption layer 4, but in this embodiment, the upper substrate 5 side is arranged. In addition, an auxiliary electrode 8 is formed through an insulating film 9. The auxiliary electrode 8 may be formed on the lower substrate 3 side, but in this case, the positions of the upper and lower electrodes 6 and 7 are also reversed, and the upper electrode 6 does not become an opaque electrode that hides the fine particles 2, so that the fine particles 2 are separately hidden. Since it is necessary to form the above pattern on the upper substrate 5, the upper substrate 5 side is desirable from the manufacturing surface.
[0032]
Although the acrylic insulating organic film is used as the insulating film 9, other organic insulating films, inorganic insulating films such as SiO ₂ and SiNx, and combinations thereof may be used.
[0033]
As the fine particles 2, a mixed system of TiO ₂ and an organic substance was used. In the drawing, white fine particles or colored fine particles are used as the fine particles 2, and the light absorption layer 4 is provided on the lower substrate 3. In the case of black fine particles or colored fine particles, a reflective layer may be provided on the lower substrate 3. The former is normally black, and the latter is normally white.
[0034]
As a medium for moving the light control medium of the fine particles 2, for example, an insulating fluid material such as the liquid crystal 1 is used. The liquid crystal 1 may be a material having a positive or negative dielectric anisotropy. The behavior of the fine particles 2 is affected by the dielectric anisotropy of the liquid crystal 1, and roughly speaking, the moving speed of the fine particles 2 tends to be higher when the absolute value of the dielectric anisotropy is larger. Here, RDP-00333 (Dainippon Ink) was used as the liquid crystal 1. The addition amount of the fine particles 2 dispersed in the liquid crystal 1 is about 1 to 50 wt%, preferably about 10 to 30 wt%. Here, 20 wt% of fine particles 2 was added. The particle diameter of the fine particles 2 is about 0.5 to 100 μm, preferably about 2 to 20 μm. Here, 6 μm particles were used. The electrodes formed on the transparent upper and lower substrates 5 and 3 such as glass and plastic may be transparent electrodes such as ITO or opaque electrodes such as Al and Mo. Here, Mo is used as the upper electrode 6, and ITO is used as the lower electrode 7 and the auxiliary electrode 8.
[0035]
Here, the change in brightness of white display with respect to the cell thickness A of MFPD is shown in FIG. 3 (fine particle addition amount 20 wt%). It can be seen from FIG. 3 that the brightness of the newspaper (reflectance: about 40%) or more is when the cell thickness A is 100 μm or more, and is preferably 100 μm or more in terms of brightness.
[0036]
However, in the conventional MFPD, the fine particles 2 are controlled using a lateral electric field between the upper and lower electrodes, and when the A (cell thickness) / B (1/2 pixel size) ratio in FIG. When the cell thickness A is 100 μm or more in a 200 μm cell, the fine particles 2 in the center of the pixel do not move at all. This is shown in the photograph of FIG. 7 (cell photograph of cell thickness 200 μm). Here, since the photograph is taken with transmission, the portion with the fine particles 2 appears black and the portion without the fine particles 2 appears white (black and white reversal).
[0037]
In this way, even if the cell thickness A is increased, the A / B ratio becomes 1 or more, so it is necessary to increase the pixel size. However, if the pixel size is increased, the resolution is naturally lowered and the drive voltage is increased. There was a problem that had to be raised. In addition, when the cell thickness A is reduced at the sacrifice of the reflectance, the fine particles 2 in the central portion of the pixel can be controlled, but it takes time for the fine particles to move from the central portion to the peripheral portion of the pixel. There was a problem that it took.
[0038]
On the other hand, the behavior of the fine particles 2 with respect to the voltage application of the MFPD having the auxiliary electrode according to the present invention is shown in the photograph of FIG. 8 (cell photograph of cell thickness 200 μm). Again, since the photograph was taken through, the portion with the fine particles 2 appears black and the portion without the fine particles 2 appears white. As for the voltage, +70 V or −70 V was applied to the upper electrode 6, 0 V was applied to the lower electrode 7, and a voltage having a polarity opposite to that of the upper electrode 6 was applied to the auxiliary electrode 8. As can be seen from this photograph, the fine particles 2 are completely controlled, and there is no phenomenon that the fine particles 2 at the center of the pixel stop moving. On the contrary, it can be confirmed that the fine particles 2 move at a very high speed. It was.
[0039]
FIG. 4 shows the response characteristics of the MFPD according to the present invention. As can be seen from this figure, switching is very fast and the response time is 200 msec (0.2 sec) or less.
[0040]
In addition, as can be seen from the photograph shown in FIG. 6, the fine particles 2 can be controlled even when the cell thickness A is changed to 150 μm, 190 μm, and 250 μm within 200 msec from the start of the display switching operation, and can be confirmed up to 450 μm. It was.
[0041]
The position of the fine particles 2 in the MFPD of the present invention can be controlled by changing the polarity of the voltage applied to the upper electrode 6 while the lower electrode 7 is grounded. This is also the case with the conventional MFPD. In the present invention, the voltage is applied to the auxiliary electrode 8 in the form of being synchronized with the voltage applied to the upper electrode 6 or being slightly shifted. The operating principle is not clear, but it can be considered as follows. For example, when the display is changed from white display, that is, a state where fine particles are dispersed on the pixel, to black display, that is, the state where the fine particles 2 are collected outside the pixel (under the upper electrode 6), between the auxiliary electrode 8 and the lower electrode 7 Due to the voltage difference, the fine particles 2 are collected on the lower electrode 7 side (vertical movement). Next, the fine particles 2 are collected on the upper electrode 6 side by the voltage difference between the lower electrode 7 and the upper electrode 6 (lateral movement). The fine particles 2 that have been dispersed on the pixel as the above phenomenon progresses simultaneously are collected outside the pixel (under the upper electrode 6). This can be assumed as the operating principle of the fine particles 2 in the present invention.
[0042]
In order to verify this idea, first, a predetermined voltage is applied between the auxiliary electrode 8 and the lower electrode 7, and then a predetermined voltage is applied between the lower electrode 7 and the upper electrode 6. It was confirmed that the fine particles 2 could be controlled in the same manner as when applied. On the other hand, when a predetermined voltage is first applied between the upper electrode 6 and the lower electrode 7, and then a predetermined voltage is applied between the lower electrode 7 and the auxiliary electrode 8, the fine particles 2 in the central portion do not move as in the conventional MFPD. This also supports the above assumption. According to the above assumption, the fine particles 2 should move more efficiently if the voltage applied between the auxiliary electrode 8 and the lower electrode 7 and the voltage applied between the lower electrode 7 and the upper electrode 6 are slightly shifted as in the verification experiment. Yes, it is preferable. However, it has been confirmed that it is easier to manufacture when synchronized in terms of driving, and that display performance and response performance are significantly improved compared to the conventional MFPD as shown in FIG. 4 even under synchronized driving conditions. A driving method for shifting is not essential.
[0043]
In this embodiment, the auxiliary electrode 8 has the same pattern and size as the lower electrode 7 (the same size as the pixel electrode), but may have a different pattern and size, for example, a small pattern only at the center of the pixel. Although the auxiliary electrode 8 is a transparent ITO electrode, it is desirable that the auxiliary electrode 8 is small because external light is reflected by the difference in refractive index between ITO and glass. In that case, the black level is particularly improved, and the contrast (about 12) in FIG. 4 can be further improved.
[0044]
With the structure in this embodiment, it has been confirmed that the fine particles 2 can be controlled to a desired state even in a 450-micron MFPD. At this time, the reflectance of white display is 60% or more, and a bright display close to copy paper (with a reflectance of about 70%) and high contrast can be realized.
[0045]
Although the electrode pattern is shown for the case of the upper electrode 6 and the lower electrode 7 and the auxiliary electrode 8 having a wide lattice shape close to a solid shape, the present invention is not limited to this. For example, the upper electrode 6 may have a circumferential shape, a honeycomb shape, a stripe shape, or the like, and the lower electrode 7 or the auxiliary electrode 8 may have a solid shape, a circular shape, a polygonal shape, a stripe shape, or the like.
[0046]
The other constituent materials such as the fine particles 2, the medium (liquid crystal 1), and the electrodes are not limited to the above embodiment, and the medium may be a liquid having no liquid crystallinity, for example.
[0047]
Although the auxiliary electrode 8 is formed on the upper substrate 5, it may be formed on the lower substrate 3 or both the substrates 5 and 3. The position where the auxiliary electrode 8 is formed may be above or below the upper electrode 6 or the lower electrode 7 via the insulating film 9.
[0048]
【The invention's effect】
As described above, according to the present invention, high contrast can be obtained regardless of the cell condition of the display because the position of the fine particles can be controlled to a desired position regardless of the cell thickness and the pixel size (A / B ratio). FIG. 4 shows that the contrast 12 is confirmed at present, and in particular, when the cell thickness is increased, the reflectance of the display is confirmed to be 60% at present, and the density of white fine particles per unit area can be significantly improved. Is brighter than newspaper (about 40% of newspaper reflectivity), close to copy paper (about 70% of copy paper reflectivity), newspaper (contrast of newspaper is about 5) and copy paper (of copy paper) A high-contrast reflective display with a contrast of about 7 to 8) can be realized.
[0049]
In addition, the present invention can efficiently move the position of the fine particles, so that the response is improved and the display switching which has conventionally taken several seconds can be performed at 200 msec or less and a high-speed response can be realized. 200 msec is equivalent to STN-LCD, It is also possible to display videos such as
[0050]
In addition, the present invention is a general display, a toy for children, paper / printed materials (magazines, newspapers, posters, etc.), general replacements (electronic paper), camera aperture, strobe light adjustment, optical writing light for photographic paper, etc. The applied technology and industrial fields such as general parts are very wide.
[Brief description of the drawings]
FIG. 1 is a display device showing an embodiment according to the present invention, and is an enlarged structural view seen from a plane showing a pattern structure of upper and lower electrodes and auxiliary electrodes by removing upper and lower substrates, liquid crystals and fine particles. FIG. 3 is a graph showing the relationship between the cell thickness and the reflectance. FIG. 4 shows the response characteristics of the present invention, and shows the voltage application time and contrast ratio. FIG. 5 is a longitudinal explanatory view showing the relative relationship between the cell thickness A and B (1/2 of the screen size). FIG. 6 is a display switching state according to the present invention. Is a series of photographs showing the relationship between cell thickness and color tone. [Fig. 7] Enlarged photo [Fig. 8] Enlarged photo [Fig. 9] Fig. 10 (a) is an enlarged cross-sectional schematic diagram of a conventional example. In the fine particle dispersed layer when a predetermined voltage is applied to the display device shown in FIG. FIG. 4B is a schematic diagram for explaining the flow direction and movement direction of the particle and the fine particles, and FIG. Schematic diagram for explanation [FIG. 11] (a), (b) Schematic enlarged sectional view showing the display principle of fine particles [FIG. 12] The relationship between reflectance and viewing angle when white display and black display are performed FIG. 13A is a copy of a micrograph when white display is performed by the display device shown in FIG. 9, and FIG. 13B is a micrograph when black display is performed by the device. Copy of [Description of sign]
1 Liquid crystal (medium)
2 Fine particles (light control medium)
3 Lower substrate 4 Light absorption layer 5 Upper substrate 6 Upper electrode 7 Lower electrode 8 Auxiliary electrode 9 Insulating film

Claims

A dielectric fluid (dispersion medium) made of an organic material having liquid crystallinity is sandwiched between a transparent upper substrate and a lower substrate, and white or colored fine particles dispersed in the fluid are sandwiched between the upper substrate and the upper substrate. The lower electrode is disposed on the lower substrate so as to generate a transverse electric field, and the upper electrode and the lower electrode are each in a lattice shape, and the other lattice electrode is wider than the other lattice electrode. is formed, the electrode opening in the other of the grid-shaped electrode and the electrode crossing portion in the one of the grid-shaped electrodes are arranged to face each further wherein one of the grid-shaped electrode is formed on the substrate, one of the display device, characterized in that the auxiliary electrode so as to face the other of the lattice-shaped electrode in an electrically insulated form is formed from a lattice-like electrode.

The display device according to claim 1, wherein the position of the fine particles is controlled by a voltage applied to each of the electrodes, and the display is switched according to the position.

The display device according to claim 1 , wherein the auxiliary electrode is formed near a center of a display portion corresponding to a pixel which is an electrode opening in the one grid-like electrode .

2. The display device according to claim 1, wherein a cell thickness corresponding to a distance between the upper substrate and the lower substrate is 100 microns or more.

Provided with a display device according to claim 1, and the DC at a timing synchronized with the timing of applying a unipolar alternating voltage including a direct-current or direct-current component between before SL other grid-like electrode and the one of the grid-shaped electrode A method for driving a display device, comprising: applying a unipolar AC voltage having a reverse polarity direct current or a direct current component having a reverse polarity to the direct current component between the other grid electrode and the auxiliary electrode.

6. The method of driving a display device according to claim 5 , wherein the fine particles move in the horizontal direction by a voltage applied to the one grid electrode, the other grid electrode, and the auxiliary electrode.