JP2004109612A

JP2004109612A - Display device and method for driving the same

Info

Publication number: JP2004109612A
Application number: JP2002273300A
Authority: JP
Inventors: Yasuo Toko; 都甲　康夫; Masashi Akaha; 赤羽　正志; Kazuya Kobayashi; 小林　和也; Yasuki Takahashi; 高橋　泰樹
Original assignee: Stanley Electric Co Ltd
Current assignee: Stanley Electric Co Ltd
Priority date: 2002-09-19
Filing date: 2002-09-19
Publication date: 2004-04-08
Anticipated expiration: 2022-09-19
Also published as: JP4488671B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device in which positions of fine particles are controlled at high speed and with high accuracy even when cell thickness of various display means such as an MFPD display is thick and a method for driving the same. <P>SOLUTION: The display device which is characterized by sandwiching a dielectric fluid (a dispersion medium) and white or colored fine particles dispersed in the fluid between transparent upper and lower substrates 5, 3 wherein an upper electrode 6 is disposed on the upper substrate 5 and a lower electrode 7 and an absorption layer or a transmission layer are respectively disposed on the lower substrate 3 and further an auxiliary electrode 8 is formed on at least one substrate out of the two substrates, which is electrically insulated from the upper electrode 6 or from the lower electrode 7 and a method for driving the display device are provided. <P>COPYRIGHT: (C)2004,JPO

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（ＭｏｂｉｌｅＦｉｎｅ　Ｐａｒｔｉｃｌｅ　Ｄｉｓｐｌａｙ、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、上基板上には上電極、下基板上には下電極と吸収層または反射層もしくは透過層がそれぞれ配置され、さらに少なくとも片側の基板上に前記上電極もしくは下電極とは電気的に絶縁された形で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。
【００２４】
（４）前記分散媒は液晶性を有する有機材料であることを特徴とする前記（１）記載の表示装置。
【００２５】
（５）上基板と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】
（６）前記（１）の表示装置を備えると共に、前記上電極、下電極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もしくはわずかにずらしたタイミングで前記直流とは逆極性の直流もしくは直流成分を含んだ単極性交流電圧を補助電極に印加することを特徴とする表示装置の駆動方法。
【００２７】
（７）微粒子は上電極、下電極及び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（６）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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a display device in which fine particles serving as a light control medium are dispersed in a dielectric fluid such as a liquid crystal serving as a medium so that various images can be obtained by electric control, and a driving method thereof.
[0002]
[Prior art]
Conventionally, the liquid crystal includes two substrates provided in parallel with each other and having at least a pair of electrodes on inner surfaces facing each other or on the same inner surface side, and a liquid crystal 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 above-described electrodes. There is known an optical switching device in which a region in which a light control medium is densely dispersed and a region in which a light control medium is sparsely dispersed are formed to perform light control by causing a difference in transmittance (for example, Patent Document 1). reference.).
[0003]
Further, among optical switching devices that perform optical display by moving particles in a fluid, there is known an optical switching device that can obtain high display contrast with a simple configuration (for example, see Patent Document 2).
[0004]
Then, the first transparent substrate, the second substrate opposed to the first substrate with a predetermined gap therebetween, the dispersion medium sandwiched between the two substrates, and the dispersion medium dispersed in the dispersion medium. A plurality of fine particles, a plurality of electrodes formed on one surface of a first substrate, and at least one surface of opposing surfaces of the first substrate and the second substrate. Formed in at least one of the first region in the vicinity of one of the electrodes and the second region on the surface of the second substrate substantially opposed to the first region. A display device including a plurality of accommodating portions and a method for manufacturing the same are known (for example, see Patent Document 3).
[0005]
The present applicant has long been dispersing fine particles in a dielectric fluid such as liquid crystal and a display in which electrodes are arranged on upper and lower substrates, and controls the movement of the fine particles in the horizontal direction and switches the display at the position of the fine particles. A mobile fine particle display (hereinafter, referred to as MFPD) has been proposed and developed. This MFPD has a feature that it has a display memory property that can perform a bright and high CR reflective display, and after display switching, retains its display state for a long time even when the electric field is cut off. In particular, it is suitable for electronic paper, that is, electronic paper.
[0006]
FIG. 9 shows a cross-sectional structure of the MFPD disclosed in Japanese Patent Application No. 2001-289724. In the drawing, fine particles 2 are dispersed in a liquid crystal 1 oriented vertically or horizontally. The fine particles 2 function as a light control medium, and the liquid crystal 1 functions as a medium. In general, as the fine particles 2, various metal oxides such as TiO ₂ , SiO ₂ , ZnO and the like, hollow bodies thereof, organic substances such as styrene balls, and coloring matters thereof can be used. FIG. 5 shows a case where white fine particles or colored fine particles are used as the fine particles 2, and the light absorbing 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, in the former case, normally black display is performed, and in the latter case, normally white display is performed. Note that an upper electrode 6 is provided inside the upper substrate 5, and a lower electrode 7 is provided inside the light absorbing 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 crystalline organic material is used. As the liquid crystal 1, any material having a positive or negative dielectric anisotropy may be used. The behavior of the fine particles 2 is affected by the dielectric anisotropy of the liquid crystal 1. Generally speaking, the larger the absolute value of the dielectric anisotropy, the higher the moving speed of the fine particles 2. The addition amount of the fine particles 2 dispersed in the liquid crystal 1 is preferably about 1 to 50 wt%, preferably about 10 to 30 wt%, and the particle diameter 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 made of glass or 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 the basic electrode arrangement is shown in FIG.
[0009]
FIG. 10A schematically shows the flow direction of the liquid crystal 1 and the moving direction of the fine particles 2 in the medium when an electric field is formed using the upper electrode 6 as an anode and the lower electrode 7 as a cathode. When a DC voltage or a unipolar rectangular pulse (several tens of Hz to several tens of kHz) is applied between the lower electrode 6 and the lower electrode 7 to form an electric field, the medium is moved in the directions indicated by arrows A1 to A4 and B1 to B2 in the drawing. Of the liquid crystal 1 flows, and the fine particles 2 move in these directions.
[0010]
The medium 1 and the fine particles 2 basically behave as if they received an electric attraction from the anode and received an electric repulsion from the cathode.
[0011]
Next, FIG. 10B schematically shows the flow direction of the liquid crystal 1 of the medium and the moving 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 medium liquid crystal 1 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 repulsion from the anode and an electric attraction from the cathode.
[0013]
In either case of FIGS. 10A and 10B, when the medium 1 is caused to flow according to an electric field, most of the fine particles 2 move in an in-plane direction in plan view. Compared with the case where the fine particles 2 are electrophoresed in the thickness direction of the container, it is possible to move the fine particles 2 at a lower voltage at a higher speed.
[0014]
Next, a 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 at the place where the fine particles (white) 2 are gathered (see FIG. 11A). Is transparent, the external light is absorbed by the light absorbing layer 4 on the lower substrate 3 and looks black (see FIG. 11B).
[0015]
FIG. 12 shows display characteristics. It can be seen that bright white display and dark black display are obtained irrespective of the viewing angle.
[0016]
FIG. 13A shows an enlarged view of the display device for white display, and FIG. 13B shows an enlarged view of the display device for black display. In the display device shown in these figures, the electrode pitch in each of 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, 7 is 150 μm, and each of the electrodes 6, 7 is formed of molybdenum. It is when you do.
[0017]
[Patent Document 1]
JP 2001-318629 A [Patent Document 2]
JP 2002-244164 A [Patent Document 3]
JP-A-2002-162649
[Problems to be solved by the invention]
However, in such an MFPD, when 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 a 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 by paying attention to the points described above, and it is possible to control the position of fine particles quickly and accurately even in the case of a thick cell thickness of various display means such as the display of the MFPD. It is an object of the present invention to provide a display device and a driving method thereof.
[0020]
[Means for Solving the Problems]
The present invention solves the above problems by the following constitutions.
[0021]
(1) A dielectric fluid (dispersion medium) and white or colored fine particles dispersed in the fluid are sandwiched between a transparent upper substrate and a lower substrate, and an upper electrode is placed on the upper substrate and a lower electrode is placed on the lower substrate. Is characterized in that a lower electrode and an absorption layer or a reflection layer or a transmission layer are respectively disposed, and further, an auxiliary electrode is formed on at least one substrate in a form electrically insulated from the upper electrode or the lower electrode. Display device.
[0022]
(2) The display device according to (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.
[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.
[0024]
(4) The display device according to (1), wherein the dispersion medium is an organic material having a liquid crystal property.
[0025]
(5) The display device according to (1), wherein a cell thickness corresponding to a distance between the upper substrate and the lower substrate is 100 microns or more.
[0026]
(6) With the display device of (1), the direct current is synchronized with the timing of applying a unipolar AC voltage containing a direct current or a direct current component to the upper electrode and the lower electrode or at a timing slightly shifted from the direct current. A method for driving a display device, comprising applying a DC having a reverse polarity or a unipolar AC voltage containing a DC component to an auxiliary electrode.
[0027]
(7) The method for driving a display device according to (6), wherein the fine particles are moved in a horizontal direction by a voltage applied to the upper electrode, the lower electrode, and the auxiliary electrode.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
[0029]
FIG. 1 is an enlarged structural view of a pattern configuration of upper and lower electrodes and an auxiliary electrode of a display device according to an embodiment of the present invention as viewed from a plane, and 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 oriented liquid crystal 1 as in the conventional example shown in FIG. 9, and the fine particles 2 function as a light control medium and the liquid crystal 1 functions as a medium.
[0031]
Further, in the drawing, the grid-like upper electrode 6 and the plate-like lower electrode 7 are disposed directly on the upper and lower substrates 5 and 3 or via the light absorbing layer 4, but in this embodiment, the upper substrate 5 side In addition, an auxiliary electrode 8 is formed via 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 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 hidden separately. It is necessary to form the pattern on the upper substrate 5, so that the upper substrate 5 side is desirable from the manufacturing viewpoint.
[0032]
Although an 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 absorbing 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. In the former case, normally black display is performed, and in the latter case, normally white display is performed.
[0034]
An insulating fluid material such as a liquid crystal 1 is used as a medium for moving the light control medium of the fine particles 2. 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. Generally speaking, the larger the absolute value of the dielectric anisotropy, the higher the moving speed of the fine particles 2. Here, RDP-00333 (manufactured by Dainippon Ink) was used as the liquid crystal 1. The amount of the fine particles 2 to be dispersed in the liquid crystal 1 is about 1 to 50 wt%, preferably about 10 to 30 wt%. Here, 20 wt% of the fine particles 2 were added. The particle size 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 made of glass or plastic may be transparent electrodes such as ITO or opaque electrodes such as Al or Mo. Here, Mo was used as the upper electrode 6, and ITO was used as the lower electrode 7 and the auxiliary electrode 8.
[0035]
FIG. 3 shows a change in brightness of white display with respect to the cell thickness A of the MFPD (the amount of added fine particles is 20 wt%). From FIG. 3, it can be seen that the brightness (reflectance: about 40%) or more of the newspaper is obtained when the cell thickness A is 100 μm or more, and preferably 100 μm or more in terms of brightness.
[0036]
However, in the conventional MFPD, the fine particles 2 are controlled using the horizontal electric field between the upper and lower electrodes. When the ratio of A (cell thickness) / B (1/2 of the pixel size) in FIG. When the cell thickness A is 100 μm or more in a 200 μm cell, the fine particles 2 at the center of the pixel do not move at all. This is shown in the photograph of FIG. 7 (cell photograph having a cell thickness of 200 μm). Here, since the photograph is taken by transmission, the part with the fine particles 2 looks black and the part without the fine particles 2 looks white (black and white reversal).
[0037]
As described above, even if the cell thickness A is increased, the A / B ratio becomes 1 or more, so that it is necessary to increase the pixel size. However, if the pixel size is increased, the resolution naturally decreases, and the driving voltage increases. Had to be raised. When the cell thickness A is reduced at the expense of reflectance, the fine particles 2 at the pixel central portion 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 application of voltage to the MFPD provided with the auxiliary electrode according to the present invention is shown in the photograph of FIG. 8 (cell photograph having a cell thickness of 200 μm). Also in this case, since the photograph is taken by transmission, the part with the fine particles 2 looks black and the part without the fine particles 2 looks white. The voltage was +70 V or −70 V to the upper electrode 6, 0 V 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 the phenomenon that the fine particles 2 do not move at the center of the pixel or the like is not observed. On the contrary, it can be confirmed that the fine particles 2 move at a much higher speed. 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 performed at a very high speed, and the response time is 200 msec (0.2 sec) or less.
[0040]
Also, as can be seen from the photograph shown in FIG. 6, even if 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, control of the fine particles 2 is possible, and it is possible to confirm up to 450 μm. 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, and the same applies to the conventional MFPD. In the present invention, the voltage is applied to the auxiliary electrode 8 in a form synchronized with the voltage applied to the upper electrode 6 or synchronized with the voltage slightly shifted. Although the operating principle is not clear, it is considered as follows. For example, when the display is changed from a white display, that is, a state in which the fine particles are dispersed on the pixel, to a black display, that is, a state in which the fine particles 2 are collected outside the pixel (below the upper electrode 6), the distance between the auxiliary electrode 8 and the lower electrode 7 is changed. Due to this voltage difference, the fine particles 2 are collected on the lower electrode 7 side (movement in the vertical direction). Next, due to the voltage difference between the lower electrode 7 and the upper electrode 6, the fine particles 2 are collected on the upper electrode 6 side (transverse movement). The above-mentioned phenomenon progresses simultaneously, and the fine particles 2 dispersed on the pixel are collected outside the pixel (below the upper electrode 6). This can be assumed as the operation principle of the fine particles 2 in the present invention.
[0042]
In order to verify this idea, a predetermined voltage was first applied between the auxiliary electrode 8 and the lower electrode 7, and then a predetermined voltage was 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 the voltage was applied. On the other hand, when a predetermined voltage is 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 center do not move as in the conventional MFPD. This also supports the above assumption. According to the above assumption, the particles 2 can be moved 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 the manufacturing is easier when the driving is synchronized, and that the display performance and the response performance are remarkably improved as compared with the conventional MFPD as shown in FIG. 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). However, the auxiliary electrode 8 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, the auxiliary electrode 8 is desirably small because external light is reflected by a difference in refractive index between ITO and glass. In this case, the black level is particularly improved, and the contrast (about 12) in FIG. 4 can be further improved.
[0044]
It has been confirmed that the structure in this embodiment can control the fine particles 2 to a desired state even in the MFPD of 450 microns. At this time, the reflectance of white display is 60% or more, and a bright display close to copy paper (about 70% reflectance) and high contrast can be realized.
[0045]
The electrode patterns are shown for the case of the upper electrode 6 in the form of a lattice and the lower electrode 7 and the auxiliary electrode 8 in the form of a lattice that is almost solid but are not limited thereto. For example, the upper electrode 6 may have a circular 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]
Note that the other constituent materials such as the fine particles 2, the medium (the liquid crystal 1), and the electrodes are not limited to those in the above-described embodiment. For example, the medium may be a liquid having no liquid crystal property.
[0047]
Although the case where the auxiliary electrode 8 is formed on the upper substrate 5 has been described, it may be formed on the lower substrate 3 or on both 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, a high contrast can be obtained irrespective of the cell thickness and pixel size (A / B ratio) and the position of the fine particles can be controlled to a desired position regardless of the cell condition of the display. FIG. 4 shows that the contrast 12 has been confirmed at present. In particular, when the cell thickness is increased, the reflectivity of the display is also confirmed to be 60% at present, and the density of white fine particles per unit area can be significantly improved. The brightness can be higher than that of newsprint (newspaper reflectance of about 40%), close to that of copy paper (copies paper reflectance of about 70%), and can be obtained by using newspapers (newspaper contrast of about 5) and copy paper (copy paper of about 5%). A high-contrast reflective display having a contrast of about 7 to 8) or more can be realized.
[0049]
In addition, the present invention can efficiently move the position of the fine particles, thereby improving the response and switching the display, which took several seconds in the past, in less than 200 msec and realizing a high-speed response. 200 msec is equivalent to STN-LCD, It is also possible to display moving images such as.
[0050]
In addition, the present invention is applicable to all kinds of displays, children's toys, etc., alternatives to paper and printed matter (magazines, newspapers, posters, etc.) (electronic paper), camera aperture, strobe light adjustment, optical light sources for photographic paper, etc. The applied technologies and industrial fields such as general parts are extremely wide.
[Brief description of the drawings]
FIG. 1 is an enlarged structural view of a display device according to an embodiment of the present invention, showing a pattern structure of upper and lower electrodes and auxiliary electrodes by removing upper and lower substrates, liquid crystal, and fine particles. FIG. 3 is an enlarged schematic view of a section taken along line II-II of FIG. 1; FIG. 3 is a graph showing a relationship between cell thickness and reflectance; FIG. 4 is a graph showing response characteristics of the present invention; FIG. 5 is a vertical sectional view showing a relative relationship between cell thicknesses 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 in a photograph. FIG. 7 is an enlarged photograph. FIG. 8 is an enlarged photograph. FIG. 9 is an enlarged schematic sectional view of a conventional example. When a predetermined voltage is applied to the display device shown in FIG. FIG. 3B is a schematic diagram for explaining the flow direction or moving direction of the fine particles, and FIG. 4B is a schematic diagram illustrating the flowing direction or moving direction of the medium and the fine particles in the fine particle dispersion layer when another voltage is formed in the apparatus. FIGS. 11A and 11B are enlarged schematic cross-sectional views showing the principle of displaying fine particles. FIG. 12 shows the relationship between the reflectance and the viewing angle when white display and black display are performed. Graph (a) is a copy of a micrograph when white display is performed by the display device shown in FIG. 9, and (b) is a copy of a micrograph when black display is performed by the display device. Copy [explanation of sign]
1 liquid crystal (medium)
2 Fine particles (light control medium)
3 lower substrate 4 light absorbing layer 5 upper substrate 6 upper electrode 7 lower electrode 8 auxiliary electrode 9 insulating film

Claims

A dielectric fluid (dispersion medium) and white or colored fine particles dispersed in the fluid are sandwiched between a transparent upper substrate and a lower substrate, and an upper electrode is placed on the upper substrate and a lower electrode is placed on the lower substrate. And an absorption layer, a reflection layer, or a transmission layer, respectively, and an auxiliary electrode is formed on at least one substrate in a form electrically insulated from the upper electrode or the lower 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.

The display device according to claim 1, wherein the dispersion medium is an organic material having a liquid crystal property.

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.

A DC having a polarity opposite to that of the DC at a timing synchronized with or slightly shifted from the timing of applying a DC or a unipolar AC voltage containing a DC component to the upper electrode and the lower electrode, the display having the display device according to claim 1. Alternatively, a method for driving a display device, wherein a unipolar AC voltage including a DC component is applied to an auxiliary electrode.

7. The method according to claim 6, wherein the fine particles move in a horizontal direction by a voltage applied to the upper electrode, the lower electrode, and the auxiliary electrode.