JP3818886B2 - Micro corner cube array, manufacturing method thereof, and display device using the same - Google Patents

Description

【０１４８】
以上の結果により、偏光板１３や位相差板１４を用いる代わりにマイクロコーナーキューブアレイを用いた本実施形態の液晶表示装置は、明るく、コントラストも比較的高く、視認性の良い表示が可能となることがわかった。
【０１４９】
（実施形態６）
以下、自発光型表示装置である有機ＥＬ（エレクトロルミネッセンス）表示装置において実施形態１または２で説明したマイクロコーナーキューブアレイを用いる例を説明する。
【０１５０】
図１５は、本実施形態の有機ＥＬ表示装置の構成を示す。有機ＥＬ表示装置２００は、ガラスや高分子フィルムなどの透明材料から形成される上側基板３０と、これに対向するように設けられた下側基板３４と、これらの基板間に位置する有機ＥＬ層４２とを備える。有機ＥＬ層４２は、正孔注入層、正孔輸送層、発光層、電子輸送層または電子注入層などの複数の薄膜により形成されている。また、有機ＥＬ層４２と上側基板３０との間には、ＩＴＯ（インジウム錫酸化物）などの透明導電性材料から形成された陰極（透明電極）３２が設けられている。また、有機ＥＬ層４２と下側基板３４との間には陽極４０が設けられている。陽極４０は、例えば３０ｎｍの厚さを有するアルミニウム膜から形成されており、このように薄い膜を用いていることで光を透過させることができる。
【０１５１】
下側基板３２の有機ＥＬ層４２側表面には、実施形態１または２で説明した方法によって作製されたマイクロコーナーキューブアレイ３６が設けられている。このマイクロコーナーキューブアレイ３６の表面には、例えばアルミニウムから形成される反射膜（不図示）が形成されており、マイクロコーナーキューブアレイ３６に入射した光は再帰反射される。このような反射膜が設けられたマイクロコーナーキューブアレイ３６の表面の凹凸は、透明平坦化部材３８によって埋められている。陽極４０は、このようにして平坦化された表面上において設けられている。
【０１５２】
有機ＥＬ表示装置２００では、陰極３２と陽極４０との間に所定の電圧を印加することによって、陰極３２からの電子と陽極４０からの正孔とを有機ＥＬ層４２において再結合させ、これによって有機ＥＬ層４２を発光させることで所定の表示を行なうことができる。なお、このような有機ＥＬ層４２は、種々の公知の材料を用いて種々の公知の方法によって作製され得る。
【０１５３】
このような有機ＥＬ表示装置２００では、有機ＥＬ層４２が非発光のとき（黒表示時）に、観察者の周囲に位置する電灯や太陽などの光源からの外部光は、マイクロコーナーキューブアレイ３６によって入射方向へと再帰反射され、観察者の目に届かない。従って、外部光の映り込みが防止され、良好な黒表示を実現することができる。
【０１５４】
また、有機ＥＬ層４２が発光しているとき（白表示時）は、有機ＥＬ層４２から観察者方向に進む光だけでなく、有機ＥＬ層４２から下側基板３４の方向に進む光もマイクロコーナーキューブアレイ３６によって再帰反射されて観察者方向に戻る。従って、有機ＥＬ層４２で発生した光をより効率良く利用することができ、明度の高い良好な白表示を実現することができる。また、白表示の際にも観察者の周囲の光源からの外部光の映り込みが防止される。
【０１５５】
この有機ＥＬ表示装置２００においても、実施形態５の液晶表示装置と同様に、マイクロコーナーキューブアレイ３６の単位要素のサイズが、絵素領域のサイズ以下であることが望ましい。有機ＥＬ表示装置２００の有機ＥＬ層４２は、例えば、図１５に示すようにＲ、Ｇ、Ｂの各色を発光する複数の発光領域を含んでおり、この発光領域のそれぞれが絵素領域に対応する。マイクロコーナーキューブアレイ３６の単位要素のサイズが、絵素領域のサイズ以下である場合、所定の色の発光領域で生じた光がマイクロコーナーキューブアレイ３６によって反射されたときに、隣接する他の色の発光領域を通過することがない。従って、混色が生じず、輝度および色度の低下が防止される。
【０１５６】
（実施形態７）
本実施形態では、基材の基準面の法線方向から傾いた光軸を有するマイクロコーナーキューブアレイを作製する方法を説明する。なお、このようなマイクロコーナーキューブアレイを用いた表示装置が、例えばＲａｙｃｈｅｍ ＣｏｒｐｏｒａｔｉｏｎによってＵＳＰ５，１８２，６６３に開示されている。
【０１５７】
まず、その表面が結晶の（１１１）Ｂ面から約５度傾いているガリウム砒素基板を用意する。なお、本実施形態では実施形態１と同様にガリウム砒素基板を用いているが、結晶の｛１１１｝面から所定の角度（０°〜１０°）だけ傾いた表面を有している限り、他の材料からなる立方晶単結晶基板（例えば、実施形態２のゲルマニウム単結晶基板）をも使用し得る。
【０１５８】
次に、用意したガリウム砒素基板に対し、実施形態１と同様に、鏡面加工、レジスト形成、およびウエットエッチングを行なうことによって、結晶の｛１００｝面で構成される凹凸を基板表面上に形成する。このように形成された凹凸は、互いに直交する３つの面（例えば、（１００）面、（０１０）面、および（００１）面）を有し、コーナーキューブアレイを構成する。ただし、実施形態１と異なり、結晶の｛１１１｝Ｂ面から約５度傾いた表面を有するガリウム砒素基板を用いているため、基板の基準面（すなわちエッチングを行なう前の基板表面）に対して、コーナーキューブの各面が為す角度が、実施形態１の場合とは異なる。また、このようにして形成されたコーナーキューブの各面の形状は、長方形であり得る。
【０１５９】
なお、上述のように結晶の｛１１１｝面から傾いた表面を有する単結晶基板を用いる場合、その傾きに応じて、エッチングの際に用いるマスク層におけるマスク部の形状の縦横の長さの比率を変更することが好ましい。これは、形成されるコーナーキューブを上から見たときに、実施形態１の場合（例えば図２（ｄ））のように完全な正六角形にはならず、上記の傾きに応じて、わずかに縦長（または横長）になる場合もあるからである。また、本実施形態のようにしてコーナーキューブを作製する場合、マスク部の重心位置は、上述したハニカム格子点と完全に一致しておらず、わずかにハニカム格子点から外れた、略ハニカム格子点上に位置するものであってよい。
【０１６０】
このようにしてガリウム砒素基板上に形成されたコーナーキューブアレイは、実施形態１または２で説明したように表面に反射膜を形成することで再帰性反射板として用いられ得る。
【０１６１】
ただし、本実施形態では、図１６に示すように、ガリウム砒素基板の表面に形成されたマイクロコーナーキューブアレイを樹脂２０に転写し、樹脂からなるマイクロコーナーキューブアレイを作製する。このために、まず、上記のガリウム砒素基板から電鋳型１８を作製する。この電鋳型１８の作製は、公知の方法によって行なうことができる。次に、この電鋳型１８をロール１９に貼り付け、このローラ１９を用いて型押し樹脂成形を行なうことによって、樹脂２０にマイクロコーナーキューブアレイを転写する。
【０１６２】
図１６には、ローラーの回転方向２１および樹脂移動方向２２が示されている。ここで、図に示す直線Ａ−Ｂは樹脂移動方向２２と平行な直線を表すものとする。なお、ローラ１９の回転および樹脂２０の移動に伴って、樹脂２０に電鋳型１８の表面が押しつけられ、その後、電鋳型１８から樹脂２０が剥離されるが、この剥離方向も直線Ａ−Ｂと平行な方向である。
【０１６３】
図１７（ａ）および（ｂ）は、上述のようにして樹脂２０の表面上に形成（転写）されたマイクロコーナーキューブアレイを示す。これらの図においても、上記図１６で示した直線Ａ−Ｂを示している。マイクロコーナーキューブアレイが転写された樹脂２０は、上述のように直線Ａ−Ｂに沿って剥離される。本実施形態では、樹脂２０の剥離方向と、コーナーキューブを構成する正方形の３面のうちの１面２４に垂直な方向（法線方向）２３とが同一平面内に存在するように剥離が行なわれる。すなわち、図１７（ｂ）からわかるように、法線方向２３の樹脂表面への射影と、樹脂２０の剥離方向とが平行な関係にある。この場合、法線方向２３の樹脂表面への射影に対して平行でない方向に剥離した時よりも樹脂２０の剥離・抜きが容易になる。
【０１６４】
このような樹脂の剥離を行なうためには、図１６に示した樹脂の移動方向２２と、電鋳型１８に設けられたマイクロコーナーキューブを構成する３面のうちの１面に対して垂直な方向とが常に同一平面内（例えば紙面内）に存在するように転写を行なえば良い。このことは、電鋳型１８をローラ１９の表面に貼りつける際に、電鋳型１８の向きを適切に調節することによって容易に実現することができる。
【０１６５】
また、本実施形態のように、表面が（１１１）Ｂ面から５度傾いているガリウム砒素基板から形成された電鋳型を用いた場合、実施形態１のように表面が（１１１）Ｂ面のガリウム砒素基板（実施形態１）から形成された電鋳型を用いた場合よりも、樹脂２０の剥離・抜きを容易にすることができた。
【０１６６】
このようにして形成されたマイクロコーナーキューブアレイの光軸は、基板の基準面に垂直な方向から傾いている。これを用いて形成された再帰性反射板では、その傾いた光軸の方向を中心として、再帰反射が適切に行なわれる入射光領域が規定される。この入射光領域から再帰性反射板に向かう光は適切に再帰反射されるが、入射光領域の外側の領域から再帰性反射板に向かう光は適切に再帰反射されないおそれがある。従って、表示装置のパネル面の法線方向に対して上側に傾いた方向に光軸が位置するように再帰性反射板を設ければ、表示装置の上方に位置している光源からの光を確実に再帰反射し得る。これにより、より良好な黒表示を行ない得る。
【０１６７】
なお、上記には結晶の｛１１１｝面に対して５°傾いた表面を有する基板を用いる形態を説明したが、この角度は、０°より大きく１０°以下であることが望ましい。基板表面と｛１１１｝面とが為す角度は、形成されるマイクロコーナーキューブの光軸（ここでは、コーナーキューブを形成する互いに直交する３面からの距離が等しい直線）と基板表面に対する法線とが為す角度と同等であるが、マイクロコーナーキューブはその光軸の方向における再帰性性能が最も良い。すなわち、光源の方向に光軸を向ければ、その光源から入射した光は適切に再帰反射されるため、良好な黒表示が行なわれる。しかし、基板法線に対して光軸を傾けすぎると、基板表面の法線方向から観察する観察者にとっての再帰性性能は悪化し、黒表示時に、観察者の眼（瞳）の近傍以外の場所からの入射光も観察し得る。これによって、良好な黒表示が行なえなくなるおそれがある。これらのことを踏まえて発明者が検討した結果、コーナーキューブの光軸の傾斜角度の適切な範囲は０°以上１０°以下であることがわかった。従って、このような光軸を有するコーナーキューブを作製するためには、｛１１１｝面に対して０°以上１０°以下の角度だけ傾いた表面を有する基板を用いることが望ましい。
【０１６８】
また、図２０に示すように、結晶の｛１１１｝面に対して角度θだけ傾いた表面Ｓ０を有する単結晶基板を用いる場合、｛１１１｝面と表面Ｓ０との交線Ｌ３の方向が、単結晶結晶基板における所定のヘキ開面（ガリウム砒素基板の場合は（０，１，−１）面）に対して垂直であることが好ましい。言いかえると、｛１１１｝面の法線Ｌ４と基板表面Ｓ０の法泉Ｌ５とを含む面が、基板の所定のヘキ開面と平行であることが好ましい。この場合コーナーキューブを構成する各面の対称性を向上させることができ、例えば図１７（ｂ）に示したように、各コーナーキューブの形状を上下線対称な形状とすることができる。また、このように形成されたコーナーキューブを型として用いる場合には、型抜きが容易になるという効果も得られる。
【０１６９】
【発明の効果】
本発明によれば、立方晶単結晶基板の｛１１１｝面に対して異方性エッチング処理を施し、エッチング速度の遅い面（例えば｛１００｝面）を有する凹凸を形成することによってマイクロコーナーキューブアレイを作製するので、表示装置の絵素領域（例えば数十μｍ）よりも小さい微小単位要素を持ち、且つ、形状精度の高いマイクロコーナーキューブアレイを比較的容易な工程で作製することができる。
【０１７０】
このようなマイクロコーナーキューブアレイを用いた表示装置は、偏光板を使用せずとも黒表示が可能であり、明るく、コントラストが高く、色純度が高く、視認性の良い表示が可能である。
【図面の簡単な説明】
【図１】本発明の実施形態１にかかるマイクロコーナーキューブアレイの作製プロセスを表わす断面図であり、（ａ）〜（ｆ）はそれぞれ別の工程を示す。
【図２】本発明の実施形態１にかかるマイクロコーナーキューブアレイの作製プロセスを表わす図であり、（ａ）は図１（ｄ）に対応する平面図、（ｂ）および（ｃ）は図１（ｅ）に対応する平面図および斜視図、（ｄ）および（ｅ）は図１（ｆ）に対応する平面図および斜視図である。
【図３】本発明の実施形態１にかかるマイクロコーナーキューブアレイ作製方法に用いるフォトマスクを示す平面図である。
【図４】図３に示すフォトマスクとは異なる形態のフォトマスクを示す平面図である。
【図５】本発明の実施形態２にかかるマイクロコーナーキューブアレイの作製プロセスを表わす断面図であり、（ａ）〜（ｉ）はそれぞれ別の工程を示す。
【図６】本発明の実施形態２にかかるマイクロコーナーキューブアレイの作製プロセスを表わす図であり、（ａ）および（ｂ）は図５（ｃ）または（ｄ）に対応する平面図および斜視図、（ｃ）および（ｄ）は図５（ｅ）または（ｆ）に対応する平面図および斜視図である。
【図７】本発明の実施形態２にかかるマイクロコーナーキューブアレイの作製プロセスを表わす図であり、（ａ）および（ｂ）は図５（ｇ）または（ｈ）に対応する平面図および斜視図、（ｃ）および（ｄ）は図５（ｉ）に対応する平面図および斜視図である。
【図８】本発明の実施形態２にかかるマイクロコーナーキューブアレイ作製方法に用いるフォトマスクを示す平面図である。
【図９】本発明の実施形態５にかかる反射型液晶表示装置の構造を示す断面図である。
【図１０】本発明の実施形態５にかかる反射型液晶表示装置において、マイクロコーナーキューブアレイの単位要素のピッチに応じて混色が発生し得ることを説明するための図であり、（ａ）はマイクロコーナーキューブアレイの単位要素のピッチが絵素領域のサイズより大きい場合を示し、（ｂ）はマイクロコーナーキューブアレイの単位要素のピッチが絵素領域のサイズより小さい場合を示す。
【図１１】単位要素が直角二等辺三角形３面からなるコーナーキューブを示し、（ａ）はコーナーキューブの単位要素を示す斜視図であり、（ｂ）はコーナーキューブのアレイを示す斜視図であり、（ｃ）はこれらの平面図である。
【図１２】単位要素が正方形３面からなるコーナーキューブを示し、（ａ）はコーナーキューブの単位要素を示す斜視図であり、（ｂ）はコーナーキューブのアレイを示す斜視図であり、（ｃ）はこれらの平面図である。
【図１３】比較例の反射型液晶表示装置の構造を示す断面図である。
【図１４】反射型液晶表示装置の反射率測定器の構成図である。
【図１５】本発明の実施形態６にかかる有機ＥＬ型表示装置の構成を示す断面図である。
【図１６】本発明の実施形態７における、型から樹脂に転写してマイクロコーナーキューブアレイを作製するプロセスを表わす概略図である。
【図１７】本発明の実施形態７における、樹脂に転写されたマイクロコーナーキューブアレイを示し、（ａ）は斜視図、（ｂ）は平面図である。
【図１８】従来のマイクロコーナーキューブアレイを用いた反射型液晶表示装置の構造を示す断面図である。
【図１９】ガリウム砒素結晶の｛１１１｝Ｂ面を示す平面図である。
【図２０】｛１１１｝面から傾いた表面を有する基板を示す斜視図である。
【図２１】本発明の実施形態３において、エッチング速度比の関係について説明するための図であり、（ａ）は異なるエッチング液を用いた場合に形成される凹部の断面形状を示し、（ｂ）はエッチング速度比が異なる場合に形成される凹部の断面形状を示している。
【図２２】本発明の実施形態３において、エッチング速度比の関係について説明するための図であり、（ａ）はエッチング速度比が十分大きくない場合、（ｂ）はエッチング速度比が十分大きい場合を示す。
【図２３】本発明の実施形態４における３角形のマスク部を有するエッチングマスク層を示す平面図である。
【図２４】本発明の実施形態４における図２３に示したものとは別の３角形のマスク部を有するエッチングマスク層を示す平面図である。
【図２５】本発明の実施形態４における６角形のマスク部を有するエッチングマスク層を示す平面図であり、マスク部の占める面積が大きい場合を示す。
【図２６】本発明の実施形態４における６角形のマスク部を有するエッチングマスク層を示す平面図であり、マスク部の占める面積が図２５に示すものより小さい場合を示す。
【図２７】本発明の実施形態４における６角形のマスク部を有するエッチングマスク層を示す平面図であり、マスク部の占める面積が図２６に示すものよりさらに小さい場合を示す。
【図２８】本発明の実施形態４における、図２５〜図２７に示したものとは別の６角形のマスク部を有するエッチングマスク層を示す平面図である。
【図２９】本発明の実施形態４における９角形のマスク部を有するエッチングマスク層を示す平面図である。
【図３０】本発明の実施形態４における１２角形のマスク部を有するエッチングマスク層を示す平面図である。
【図３１】本発明の実施形態４における正方形のマスク部を有するエッチングマスク層を示す平面図である。
【図３２】図２３に示すマスク層を用いた場合に作製されるマイクロコーナーキューブアレイを示す平面図である。
【図３３】図２４に示すマスク層を用いた場合に作製されるマイクロコーナーキューブアレイを示す平面図である。
【図３４】本発明の実施形態４におけるエッチング時間をかえた時の実験結果を説明するための図であり、（ａ）は適切な時間（３分）の場合を示し、（ｂ）はより長い時間の場合を示す。
【図３５】本発明の実施形態４におけるマスク層の形態を説明するための図である。
【符号の説明】
１ ガリウム砒素基板
２ フォトレジスト
３ フォトマスク
４ ゲルマニウム基板
５ ＳｉＯ₂層
６ 液晶層
７ カラーフィルタ層
８ 入射側基板
９ 反射側基板
１０ マイクロコーナーキューブアレイ
１１ 反射電極
１２ 透明電極
１３ 偏光板
１４ 位相差板
１５ 積分球
１６ サンプル
１７ 受光器
１８ 電鋳型
１９ ローラー
２０ 樹脂（被転写材料）
２１ ローラー回転方向
２２ 樹脂移動方向
２３ コーナーキューブを構成する面の法線方向
１０１ ガリウム砒素基板
１０２ エッチングマスク層のマスク部
１０３ （１１１）Ｂ面に対するエッチング（速度）を示す矢印
１０４ （１００）面に対するエッチング（速度）を示す矢印
１０５ エッチングマスク層の開口部
１０６ マスク部のピッチ
１０７ 重なり部
１１０ エッチングマスク層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a micro corner cube array and a display device including the micro corner cube array.
[0002]
[Prior art]
In recent years, development of very small optical elements (micro optical elements) such as microlenses, micromirrors, and microprisms has been promoted, and they are being used in the fields of optical communication and display devices. The realization of such a micro optical element is expected to further develop and enhance the fields of optical technology and display technology.
[0003]
As such an optical element, there is known a reflector (corner cube reflector) formed by regularly arranging corner cubes having shapes corresponding to one corner of a cube and having three surfaces orthogonal to each other. A corner cube reflector is one of retroreflectors that reflect incident light on a plurality of reflecting surfaces to reflect the light in the original direction regardless of the incident direction. Hereinafter, a conventional method for producing a corner cube will be described.
[0004]
(Plate method)
In the plate method, a plurality of flat plates having two planes parallel to each other are overlapped, and V-grooves are cut at equal pitches in a direction perpendicular to the plane at the end surfaces of the stacked flat plates, and the apex angle is about 90 °. A continuous roof-shaped projection group is formed. Next, by arranging each flat plate so that the top of the roof of the roof-type projection group formed on each flat plate coincides with the bottom of the V groove formed on the adjacent flat plate, the gold for the corner cube array is arranged. A mold is produced and a corner cube array is produced using the mold. However, in this method, it is necessary to rearrange and fix the flat plate on which the roof-shaped protrusion is formed so as to have an appropriate positional relationship with respect to the adjacent flat plate, so that the corner having a small size (for example, 100 μm or less) is used. It is difficult to make a cube.
[0005]
(Pin binding method)
In the pin bundling method, a prism having three square surfaces orthogonal to each other is provided at the tip of a metal pin having a hexagonal column shape, and a prism assembly is produced by bundling them. A corner cube is formed by using one surface of each prism provided on each of the three adjacent pins. However, in this method, prisms formed on separate pins are collected to form a corner cube, so that it is actually difficult to manufacture a corner cube having a small size. The limit of the corner cube that can be manufactured using this method is about 1 mm.
[0006]
(Triangular prism method)
In the triangular prism method, a plurality of triangular pyramid-shaped protrusions are formed by cutting V-grooves from three directions on the surface of a flat plate made of metal or the like, and a prism aggregate is formed using these. However, in this method, the form of the prism that can be formed is limited to a triangular pyramid prism.
[0007]
Furthermore, Japanese Patent Application Laid-Open No. 7-205322 describes a method for producing a micro corner cube using a photochemical method. In this method, a mask having a plurality of equilateral triangular transmission regions (or light shielding regions) is used. The transmittance or light shielding rate of each transmissive region (or light shielding region) of the mask gradually decreases from the central portion to the peripheral portion of the transmissive region (or light shielding region). By performing exposure and development using this mask, a plurality of triangular pyramidal photoresists are formed on the substrate. By performing anisotropic etching (dry etching or the like) on the substrate on which such a resist is formed so that protrusions similar to the shape of the resist are formed, isosceles triangles 3 that are orthogonal to each other. A plurality of triangular pyramidal protrusions having a surface are formed on the substrate.
[0008]
Japanese Patent Application Laid-Open No. 9-76245 discloses a method for manufacturing a microlens array, wherein a predetermined region is irradiated with a light beam selectively.
[0009]
A liquid crystal display device using a corner cube reflector as a retroreflector is described in, for example, US Pat. No. 5,182,663. Hereinafter, an example of a liquid crystal display device including such a corner cube reflector will be described with reference to FIG.
[0010]
In the liquid crystal display device 900 shown in FIG. 18, the scattering type liquid crystal layer 6 is sandwiched between the pair of transparent substrates 8 and 9. A corner cube array 90 and a transparent electrode 12 used as a retroreflector are formed on the liquid crystal layer side surface of the substrate 9 on the non-observer side, and on the liquid crystal layer side surface of the substrate 8 on the viewer side, A color filter layer 7 and a transparent electrode 12 are formed. The light transmittance (or scattering state) of the scattering liquid crystal layer 6 is controlled by controlling the voltage applied to the pair of transparent electrodes 12 that sandwich the scattering liquid crystal layer. At the time of white display, the scattering type liquid crystal layer 6 is controlled to be in a scattering state. At this time, light incident on the scattering liquid crystal layer 6 from a light source (for example, the sun) outside the apparatus is scattered by the scattering liquid crystal layer 6. A part of the incident light is reflected by the corner cube array 90 and then scattered by the liquid crystal layer 6. If the incident light is scattered in this way, a bright display state can be obtained. Further, at the time of black display, the scattering type liquid crystal layer 6 is controlled to a light transmission state. At this time, the light transmitted through the scattering liquid crystal layer 6 is reflected by the corner cube array 90 in the same direction as the incident direction. For this reason, only light emitted from the vicinity of the observer reaches the observer's eyes. Therefore, a dark display can be realized. In addition, since regular reflection light of ambient light does not reach the observer's eyes, reflection of the surrounding scenery is prevented.
[0011]
The unit element size L1 of the corner cube array 90 used in the liquid crystal display device 900 is required to be equal to or smaller than the picture element region size L2. When the size L1 of the unit element is larger than the size L2 of the picture element area, the light that has passed through the predetermined picture element area may be reflected by the corner cube and then return through another picture element area. This is because proper display cannot be performed.
[0012]
In the present specification, the minimum unit for displaying “color” which is a minimum unit for displaying “pixels” and displaying different colors is called “picture element (or dot)”. In a full-color display device, typically, one “pixel” is configured using three “picture elements” of R (red), G (green), and B (blue). In addition, an area corresponding to a portion for displaying one picture element in the display device is referred to as a picture element area.
[0013]
[Problems to be solved by the invention]
Thus, the size of the corner cube used in a liquid crystal display device or the like needs to be very small (for example, 100 μm or less). However, in the method of mechanically producing a corner cube as described above, it is often difficult in the manufacturing process to form such a fine corner cube. In addition, when a corner cube having a fine size is produced by the above-described method, the specularity of each reflecting surface is lowered, and the corner curvature (R) at the intersection of the reflecting surfaces is increased, so that the efficiency of retroreflecting is low. The problem that becomes.
[0014]
In addition, it is difficult to increase the surface accuracy (flatness) of the side surface (reflecting surface) in the micro corner cube manufactured by using a photochemical method as described in JP-A-7-205322. It is. In the above method, the surface accuracy of the side surface of the micro corner cube depends on the surface accuracy of the triangular pyramid-shaped photoresist formed on the substrate. To increase the surface accuracy of this photoresist, the transmittance or shading rate of the mask is required. It is necessary to strictly control the exposure / development process of the photoresist, for example, by making the change rate of the film uniform. However, this is actually difficult. Furthermore, the shape of the corner cube produced by this method is limited to a shape constituted by three surfaces of right-angled isosceles triangles.
[0015]
Further, as a photochemical production method, the method disclosed in the above Japanese Patent Laid-Open No. 9-76245 is a microlens array manufacturing method using a light beam, but even if this is applied to a microcorner cube array, As with the above, it is difficult to obtain sufficient surface accuracy (flatness) of the surfaces constituting the corner cube.
[0016]
The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a method for manufacturing a micro corner cube array that is fine and has high shape accuracy, and a display device using the method.
[0017]
[Means for Solving the Problems]
The method for producing a microcorner cube array of the present invention includes a step of preparing a single crystal substrate made of cubic crystals and having a surface substantially parallel to the {111} plane of the crystal; And performing an anisotropic etching process on the surface of the single crystal substrate, and by the anisotropic etching process, a crystal plane having an etching rate slower than the {111} plane of the crystal is formed. The unevenness to have is formed.
[0018]
In a preferred embodiment, the crystal plane having a low etching rate is the {100} plane of the crystal.
[0019]
In a preferred embodiment, the unevenness has three {100} planes orthogonal to each other.
[0020]
In a preferred embodiment, the single crystal substrate is formed of a compound semiconductor having a zinc flash structure.
[0021]
In a preferred embodiment, the compound semiconductor is gallium arsenide, and the {111} plane of the crystal is a {111} B plane formed by arsenic.
[0022]
In a preferred embodiment, the single crystal substrate is formed of a material having a diamond structure.
[0023]
In a preferred embodiment, the single crystal substrate is formed of germanium crystals.
[0024]
In a preferred embodiment, a value obtained by dividing the etching rate of the {111} plane by the etching rate of the crystal plane having the slow etching rate is larger than 1.73.
[0025]
In a preferred embodiment, the etching mask having at least one mask portion and at least one opening portion disposed on the surface of the single crystal substrate in a predetermined pattern before the step of performing the anisotropic etching treatment. The method further includes a step of covering with a layer.
[0026]
In a preferred embodiment, the size of the unit element of the micro corner cube array is controlled according to the pattern of the etching mask layer.
[0027]
In a preferred embodiment, the etching mask layer has a plurality of the mask portions each having a center of gravity located substantially on a honeycomb lattice point.
[0028]
In a preferred embodiment, the plurality of mask portions are separated from each other.
[0029]
In a preferred embodiment, the mask portion has a planar shape including at least three sides parallel to each of the (100) plane, the (010) plane, and the (001) plane of the crystal.
[0030]
In a preferred embodiment, the mask portion has a triangular planar shape formed from the three parallel sides.
[0031]
In a preferred embodiment, the mask portion has a planar shape including at least three sides parallel to the (11-1) plane, (1-11) plane, and (-111) plane of the crystal.
[0032]
In a preferred embodiment, the mask portion has a triangular planar shape formed from the three parallel sides.
[0033]
In a preferred embodiment, the mask portion has a three-fold rotationally symmetric planar shape.
[0034]
In a preferred embodiment, the mask portion has a hexagonal shape, a hexagonal shape, or a dodecagonal planar shape.
[0035]
In a preferred embodiment, the etching mask layer has a plurality of openings each having a center of gravity located substantially on a honeycomb lattice point.
[0036]
In a preferred embodiment, the etching mask layer has a total area occupied by the mask portion larger than a total area occupied by the opening at the start of the etching process.
[0037]
In a preferred embodiment, the anisotropic etching treatment step includes a step of stopping etching when a contact area between the surface of the single crystal substrate and the mask portion is substantially minimized.
[0038]
In a preferred embodiment, the method further includes a step of covering a selected region of the surface of the single crystal substrate with a resist layer before the step of performing the anisotropic etching process, and depending on the pattern of the resist layer, The size of the unit element of the formed micro corner cube array is controlled.
[0039]
In a preferred embodiment, the anisotropic etching process includes wet etching.
[0040]
In a preferred embodiment, the anisotropic etching process further includes at least one dry etching.
[0041]
In a preferred embodiment, the method further includes a step of transferring the irregularities formed on the single crystal substrate to a material to be transferred.
[0042]
In a preferred embodiment, the unevenness has three substantially square surfaces that are orthogonal to each other.
[0043]
In a preferred embodiment, an angle formed by the surface of the single crystal substrate and a {111} plane of the crystal is greater than 0 ° and equal to or less than 10 °.
[0044]
In a preferred embodiment, the direction of the line of intersection between the surface of the single crystal substrate and the {111} plane of the crystal is substantially perpendicular to the cleavage plane of the single crystal substrate.
[0045]
The method for producing a micro corner cube array of the present invention is a method for producing an array of micro corner cubes having a predetermined crystal plane in a crystal having a predetermined structure as a surface, and the predetermined crystal plane is automatically applied to the surface. It is formed through an exposure process.
[0046]
In a preferred embodiment, the process of automatically exposing the crystal plane is performed by an anisotropic etching process.
[0047]
The micro corner cube array of the present invention is produced by any one of the production methods described above. Moreover, the mold of the micro corner cube array of the present invention is also produced using any one of the production methods described above.
[0048]
The micro corner cube array of the present invention is a micro corner cube array formed on the surface of a single crystal substrate made of a cubic crystal, and is formed from irregularities having {100} planes of the crystal.
[0049]
The display device of the present invention includes any one of the above-mentioned micro corner cube arrays and a light modulation layer provided on the micro corner cube array.
[0050]
In a preferred embodiment, the micro corner cube array has a plurality of unit elements, and the size of the unit elements is equal to or smaller than the size of the pixel region of the display device.
[0051]
The method for producing a micro corner cube array of the present invention includes a step of transferring the array of micro corner cubes to a transfer material using a substrate on which the array of micro corner cubes is formed as a mold. When the material to be transferred is peeled off, the normal direction of any one of a plurality of faces constituting the micro corner cube and the peeling direction are in the same plane.
[0052]
DETAILED DESCRIPTION OF THE INVENTION
In the method for manufacturing a micro corner cube array according to the present invention, a single crystal substrate (hereinafter referred to as “cubic single crystal”) made of a cubic crystal, such as a compound semiconductor having a zinc flash structure or a substrate formed from a material having a diamond structure. A micro corner cube array is manufactured using a “substrate”. Specifically, a cubic single crystal substrate having a surface arranged substantially parallel to the {111} plane of the crystal is prepared, and an anisotropic etching process is performed on the surface of the substrate to obtain a surface. Processing.
[0053]
In the present specification, the “substrate having a surface substantially parallel to the {111} plane of the crystal” is not only a substrate having a surface parallel to the {111} plane of the crystal, but also 0 ° to 10 °. It shall include a substrate having an inclined surface.
[0054]
The present invention has one of the features in that when processing the substrate surface, anisotropic etching with different etching rates depending on the crystal plane is performed. As a substrate material, for example, in the case of a gallium arsenide crystal having a zinc flash structure (see FIG. 19), the etching rate on the {111} B plane ({111} plane formed by arsenic) of the crystal is high, and the {100} plane ( Etching rates in the (100) plane, (010) plane, (001) plane, etc.) are slow. Therefore, anisotropic etching proceeds so that the {100} plane of the crystal remains, and as a result, irregularities having the {100} plane of the crystal are formed on the substrate surface. The unevenness formed in this way has three surfaces (for example, (100) surface, (010) surface, and (001) surface) orthogonal to each other, and forms a corner cube.
[0055]
The reflection surface of the corner cube array produced by the method as described above has a shape along the crystal plane of the cubic crystal, and its shape accuracy is very high. The planarity of the three surfaces constituting each corner cube is good, and the shape (corner or ridge) where each surface intersects is sharp. Further, the above-mentioned corner cube array can take a three-dimensional shape including a plurality of irregularities regularly arranged, but the height levels of the vertices of the irregularities are uniform, and these are located in substantially the same plane. . Such a corner cube array can be appropriately used as a retroreflector that retroreflects incident light.
[0056]
Further, the size of the unit element (one corner cube) of the corner cube array produced by the present invention can be set to several tens of μm or less by adjusting the pattern of the resist (or mask) used in the etching process. . Accordingly, it is possible to produce a fine corner cube array that is appropriately used as a retroreflector used in a liquid crystal display device or the like.
[0057]
Note that the cubic single crystal substrate used in the present invention includes a substrate having a single crystal layer on a support substrate made of an amorphous or polycrystalline material. Moreover, it may have various three-dimensional shapes as long as it includes a flat surface as well as a flat plate.
[0058]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, the same reference numerals are assigned to similar members.
[0059]
(Embodiment 1)
FIG. 1 shows a manufacturing process of the micro corner cube array of the present embodiment. In this embodiment, a single crystal substrate formed of gallium arsenide which is a compound semiconductor having a zinc flash structure is used as a cubic single crystal substrate, and a micro corner cube array is manufactured on the surface of the substrate.
[0060]
First, a gallium arsenide single crystal substrate 1 having a {111} B surface is prepared, and this surface is finished to a mirror surface (FIG. 1A). The {111} plane formed by gallium is the {111} A plane, and the {111} plane formed by arsenic is the {111} B plane. FIG. 19 shows the {111} B plane of the gallium arsenide single crystal when the substrate 1 is viewed from above. In the figure, the outline of the unit cell of the gallium arsenide crystal is indicated by a one-dot chain line.
[0061]
Next, a positive photoresist layer 2 having a thickness of 1 μm is formed on the substrate surface by spin coating (FIG. 1B). For example, OFPR-800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) can be used as the material of the photoresist layer 2.
[0062]
Next, after pre-baking the photoresist layer 2 at about 100 degrees for 30 minutes, a photomask 3 is disposed on the photoresist layer 2 and exposure is performed (FIG. 1C). As the photomask 3, as shown in FIG. 3, a photomask 3 in which a light shielding area of an equilateral triangle and a transmission area of an inverted equilateral triangle are alternately provided in each side direction of the triangle is used. The photomask 3 is arranged on the substrate so that one side of one of the equilateral triangles that is the pattern of the mask 3 is parallel to the <01-1> direction of the gallium arsenide crystal (see FIG. 19). In the present embodiment, the length of one side of the equilateral triangle that is the pattern of the mask 3 is about 10 μm.
[0063]
Next, the photoresist layer 2 is developed (FIG. 1D). For example, NMD-32.38% (manufactured by Tokyo Ohka Kogyo Co., Ltd.) can be used as the developer. As a result, a patterned resist 2 ′ (etching mask portion) is formed as shown in FIG. Note that FIG. 1D corresponds to a cross section taken along line xx of FIG.
[0064]
In the present embodiment, the size of the corner cube to be formed is controlled according to the pattern of the resist 2 ′ (or the pattern of the mask 3). More specifically, the size of the corner cube to be formed is the same size as the pitch Pr (about 10 μm in the present embodiment) of the openings R0 where the resist 2 ′ is not provided. In the present specification, the resist 2 ′ may be referred to as a mask portion, and the portion including the mask portion and the opening R0 may be referred to as an etching mask layer. That is, the etching mask layer is a patterned photoresist layer 2.
[0065]
Further, as shown in FIG. 4A, the pattern of the resist 2 ′ is a pattern in which the openings R0 of the equilateral triangles are arranged apart from each other at the vertices of the virtual equilateral triangle T, or FIG. As shown in FIG. 4, a pattern in which a plurality of rectangular openings R0 are provided at the vertices of a virtual equilateral triangle T may be used. Even when these resist patterns are used, the size of the corner cube to be formed is controlled to the same size as the pitch Pr of the openings R0. In any of these patterns, it is desirable that one side of the virtual triangle T shown in the figure is positioned in parallel to the <0, 1, -1> direction of the gallium arsenide crystal.
[0066]
Next, a wet etching process is performed while stirring the etching solution with a magnet stirrer (FIGS. 1E and 1F). Etching solution is NH _Four OH: H ₂ O ₂ : H ₂ A mixed solution of O = 4: 1: 20 was used, the etching temperature was 0 degree, and the etching time was 30 minutes.
[0067]
In the middle stage of the etching shown in FIG. 1E (for example, after 15 minutes), the substrate 1 is large in the region R1 where the resist 2 ′ is not provided, as shown in FIGS. 2B and 2C. Etched. Further, since the wet etching is performed as described above, the substrate 1 is also etched from the side surface direction in the region R2 where the resist 2 'is provided. At this time, the {100} plane ((100) plane, (010) plane, and (001) plane) of the gallium arsenide single crystal is less likely to be etched than the other planes, and this {100} plane is formed. Anisotropic etching proceeds.
[0068]
Thereafter, when the etching proceeds as shown in FIG. 1 (f), asperities having {100} plane S of the gallium arsenide single crystal are formed as shown in FIGS. 2 (d) and 2 (e). Thereby, a micro corner cube array is obtained. Note that, at the stage where the etching has progressed, the resist 2 'is also peeled off.
[0069]
The micro corner cube array produced in this way has a three-dimensional shape in which convex portions and concave portions are combined, as can be seen from FIG. Further, the unit element (one corner cube) is constituted by three substantially square surfaces orthogonal to each other, and shows a substantially hexagonal shape when viewed from the upper surface as can be seen from FIG. As described above, the corner cube formed in the present embodiment has a more complicated shape than the conventional corner cube composed of three faces of a right-angled isosceles triangle, but its size is about a dozen μm or so. Very small. Further, the shape accuracy (the flatness of each of the three substantially square surfaces) is also high.
[0070]
When the microcorner cube array formed in this way is used as a retroreflector, a substantially uniform thickness is formed on the gallium arsenide substrate on which the above irregularities are formed, for example, along the surface shape of the irregularities by vapor deposition or the like. A thin film of a reflective material such as aluminum or silver is formed at a thickness (for example, 200 nm). Thereby, a retroreflection board provided with three substantially square reflective surfaces which intersect perpendicularly can be produced.
[0071]
Furthermore, a micro corner cube array may be used in which an electroforming mold is taken from the substrate on which the concavo-convex is formed and the concavo-convex is transferred to a resin material using the electroforming mold.
[0072]
Although an example using a gallium arsenide single crystal substrate has been described above, a single crystal substrate formed from another compound having a zinc flash structure such as InP, InAs, ZnS, or GaP may be used.
[0073]
(Embodiment 2)
FIG. 5 shows a manufacturing process of the micro corner cube array of this embodiment. In this embodiment, a single crystal substrate made of a germanium crystal having a diamond structure is used as a cubic single crystal substrate, and a micro corner cube array is manufactured on the surface of the substrate.
[0074]
First, a germanium single crystal substrate 4 whose surface is parallel to the (111) plane of the germanium crystal is prepared, and this surface is finished to a mirror surface. On top of that, a 200 nm thick SiO2 film is formed by CVD. ₂ A layer 5 is formed, and a positive photoresist layer 2 having a thickness of 1 μm is further formed thereon by spin coating (FIG. 5A). For example, OFPR-800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) can be used as the resist material.
[0075]
Next, after pre-baking the photoresist layer 2 at about 100 degrees for 30 minutes, the photoresist layer is used by using a mask 3a provided with a plurality of relatively small equilateral triangular transmission regions as shown in FIG. 2 exposure and development are performed.
[0076]
Next, using the resist formed as described above, SiO ₂ Etching treatment of the layer 5 is performed, and thereby SiO 2 having an opening having the same shape as the mask 3a shown in FIG. ₂ A layer is formed (FIG. 5B). Furthermore, this SiO ₂ A dry etching process is performed on the germanium single crystal substrate 4 using the layer as a mask (FIG. 5C). Thereby, as shown in FIGS. 6A and 6B, a recess C1 is formed in a predetermined region on the substrate surface.
[0077]
Next, as shown in FIG. 8B, the photoresist layer 2 was again exposed and developed using a mask 3b in which the area of the transmissive region was enlarged compared to the mask 3a, and further developed. SiO with photoresist as mask ₂ By performing the etching treatment of the layer 5, SiO having an opening having the same shape as the mask 3b is obtained. ₂ A layer is formed (FIG. 5D). Next, this SiO ₂ A dry etching process is performed on the germanium single crystal substrate 4 using the film as a mask (FIG. 5E). As a result, as shown in FIGS. 6C and 6D, a recess C2 having a two-stage depth whose center is deeper than the periphery is formed in a predetermined region of the substrate.
[0078]
Next, exposure and development of the photoresist are performed using a mask 3c in which the area of the transmission region is further expanded as compared with the mask 3b as shown in FIG. ₂ By etching the layer, SiO having an opening having the same shape as the mask 3c is obtained. ₂ A mask is formed (FIG. 5F), and dry etching is performed on the substrate 4 using the mask (FIG. 5G). As a result, stepped irregularities C3 as shown in FIGS. 7A and 7B are formed on the substrate surface.
[0079]
In each of the above exposure steps, the masks 3a, 3b and 3c are arranged on the substrate so that one side of the equilateral triangle which is the mask pattern is parallel to the <01-1> direction of the germanium crystal. is doing. Also in this embodiment, the pattern pitch Pr of the masks 3a, 3b, and 3c is set to about 10 μm as in the first embodiment. In each of the above dry etching steps, the etching gas is CF. _Four / O ₂ Gas is used.
[0080]
Finally, resist and SiO ₂ After peeling off the film (FIG. 5 (h)), wet etching is performed while manually shaking the substrate. HF: H as etchant ₂ O ₂ : H ₂ A mixed solution of O = 1: 1: 4 was used, the etching temperature was 0 degree, and the etching time was 5 minutes (FIG. 5 (i)). At this time, the {100} plane ((100) plane, (010) plane, and (001) plane) of the germanium crystal has a slower etching rate than the other planes, so that this {100} plane remains. Anisotropic etching proceeds. Thereby, the unevenness | corrugation which has {100} surface of a germanium crystal as shown in FIG.7 (c) and (d) is formed on the substrate surface.
[0081]
As described above, in this embodiment, stepped irregularities that approximate a corner cube are formed on the substrate in advance by a dry etching process using a plurality of masks having different opening sizes, and then germanium is formed by a wet etching process. Irregularities having a {100} plane of the crystal are formed.
[0082]
When the microcorner cube array formed in this way is used as a retroreflector, a substantially uniform thickness is formed on the gallium arsenide substrate on which the above irregularities are formed, for example, along the surface shape of the irregularities by vapor deposition or the like. A thin film of a reflective material such as aluminum or silver may be formed with a thickness (for example, 200 nm). Thereby, a retroreflection board provided with three substantially square reflective surfaces which intersect perpendicularly can be produced.
[0083]
Furthermore, a micro corner cube array may be used in which an electroforming mold is taken from the substrate on which the concavo-convex is formed and the concavo-convex is transferred to a resin material using the electroforming mold.
[0084]
(Embodiment 3)
Also in this embodiment, a micro corner cube array is produced on a single crystal substrate by anisotropic etching as in the above embodiment, but a case where a different kind of solution is used as an etching solution for anisotropic etching. explain.
[0085]
As shown in FIG. 21A, a gallium arsenide substrate 101 is used as a single crystal substrate, an etching mask (mask portion of an etching mask layer) 102 is provided thereon, and then the substrate 101 is subjected to anisotropic etching. Thus, a micro corner cube array is produced.
[0086]
In this embodiment, ammonia water, hydrogen peroxide water, and water (NH _Four OH: H ₂ O ₂ : H ₂ O = 15: 15: 70) mixed solution (etching solution A), concentrated sulfuric acid, hydrogen peroxide solution and water (H ₂ SO _Four : H ₂ O ₂ : H ₂ Two types of etching solutions were used together with a mixed solution (etching solution B) of O = 80: 5: 15). Using these etchants, anisotropic etching was performed at an etching temperature of 20 ° C. and an etching time of 3 minutes, respectively. A micro corner cube array was manufactured by the same process as the process in Embodiment 1 except for the above etching conditions.
[0087]
FIG. 21A shows the results when the etching solution A is used and when the etching solution B is used. [A1] shows the result when the etching solution A (mixed solution of ammonia water, hydrogen peroxide solution and water) is used, and [a2] shows the etching solution B (mixed solution of concentrated sulfuric acid, hydrogen peroxide solution and water). ) Shows the results when used. In the figure, both results are shown on the same substrate for easy understanding, but they are actually formed on different substrates.
[0088]
As can be seen from the figure, when the etching solution A is used [a1], the bottom of the micro corner cube shape is the apex (that is, a sharp corner is formed at the bottom), whereas the etching solution B is used. In the case [a2], the bottom was a surface.
[0089]
From this result, it can be seen that it is preferable to use the etching solution A rather than the etching solution B in manufacturing the micro corner cube array. Hereinafter, the influence of the etching solution used on the shape of the produced micro corner cube will be described with reference to FIG.
[0090]
[B1], [b2], and [b3] in FIG. 21B are the ratios of the etching rate of the (111) B surface and the etching rate of the (100) surface of the gallium arsenide single crystal substrate ((111) B The value obtained by dividing the surface etching rate by the (100) surface etching rate) is larger than 1.73, equal to 1.73, and smaller than 1.73. In FIG. 21B, the etching rate of the (111) B surface is represented by the length of the arrow 103, and the etching rate of the (100) surface is represented by the length of the arrow 104 (however, in the following description, the speed 103, the speed). The arrow may be indicated as a velocity (vector) indicating the direction and speed of etching, such as 104. The etching rate for each crystal plane means the etching amount (etching depth) per hour in the direction perpendicular to the crystal plane.
[0091]
In [b1], the rate 103 at which the (111) B surface is etched is sufficiently faster than the rate 104 at which the (100) surface is etched, so that the bottom 101b of the formed recess 101a has a vertex. ing. Further, in [b3], the rate 103 at which the (111) B plane is etched is not sufficiently faster than the rate 104 at which the (100) plane is etched, so the bottom 101b forms a plane. In [b2], a planar bottom 101b having the same shape as the opening 105 is formed.
[0092]
Next, the ratio between the speed 103 and the speed 104 will be considered quantitatively. The normal vector of the (111) B plane and the normal vector of the (100) plane form an angle of about 54.7 degrees. At this time, as shown in FIG. 22A, when the ratio of the etching rate 103 on the (111) B surface and the etching rate 104 on the (100) surface is equal to about 1.73, Etching proceeds while the size of the opening 105 of the etching mask layer is maintained. That is, the etching proceeds with the bottom 101b and the opening 105 having the same size.
[0093]
On the other hand, as shown in FIG. 22B, when the ratio of the etching rate 103 on the (111) B surface and the etching rate 104 on the (100) surface is larger than about 1.73, The planar bottom portion 101b is gradually narrowed as the etching progresses. As a result, a micro corner cube having a bottom at the top can be produced. Such a retroreflector manufactured using a micro-corner cube having a square bottom can more reliably reflect incident light retroreflectingly.
[0094]
As described above, when a micro corner cube having a bottom at the top is manufactured, the ratio between the etching rate of the (111) B surface and the etching rate of the (100) surface needs to be larger than 1.73. I understand that. The ratio of the (111) B surface etching rate 103 to the (100) surface etching rate 104 is preferably 1.8 or more, and more preferably 3 or more.
[0095]
Therefore, in order to manufacture a micro corner cube array with high shape accuracy, it is desirable to use an etching solution having an etching selectivity ratio between the (111) B surface and the (100) surface of at least 1.73. As such an etchant, in addition to the above-described etchant A, for example, sodium hydroxide, hydrogen peroxide solution, and water (mixing ratio NaOH: H ₂ O ₂ : H ₂ O = 5 g: 5 g: 90 g) or the like can be used.
[0096]
Thus, a micro corner cube array with improved shape accuracy can be produced by appropriately selecting the ratio of the etching rates on the respective crystal planes. In this embodiment, an array of micro corner cubes having {100} planes in a cubic single crystal as a surface is produced. By performing an appropriate anisotropic etching process as described above, {100} planes are obtained. The micro corner cube array is formed through a process in which the exposure is automatically performed. The micro corner cube formed by such a process has high surface accuracy (planarity) of the surface ({100} surface of a cubic single crystal) constituting the micro corner cube.
[0097]
In addition, although the form which produces a micro corner cube array by the anisotropic etching process was demonstrated above, it replaces with an anisotropic etching process and produces a micro corner cube array using the selective growth process of a crystal. Is also possible. Also in this case, a micro corner cube array with high shape accuracy can be produced by growing the crystal so that a predetermined crystal plane is automatically exposed.
[0098]
(Embodiment 4)
As a fourth embodiment of the present invention, for example, as shown in FIG. 23, after an etching mask layer 110 constituted by a mask portion 102 and an opening portion 105 is disposed on a gallium arsenide substrate 101, the substrate 101 is formed. A case where a micro corner cube array is manufactured by performing anisotropic etching processing will be described. In this embodiment, in order to examine the influence of the pattern of the etching mask layer 110 (the mask portion 102 and the opening portion 105) on the shape of the formed micro corner cube array, various patterns as shown in FIGS. Etching was performed using the mask layer 110.
[0099]
Note that each etching mask layer 110 described below can be formed by patterning a photoresist film provided over the substrate 101 using a photomask, as described in Embodiment 1. In this case, the portion where the resist remains after patterning (that is, the resist 2 ′) becomes the mask portion 102 of the etching mask layer 110, and the portion where the resist is removed becomes the opening portion 105 of the etching mask layer 110.
[0100]
In this embodiment, the unit structure of the mask portion 102 in the etching mask layer 110 is periodically located in a predetermined direction. More specifically, the unit structure of the mask portion 102 is periodically arranged in each of the three directions 106A, 106B, and 106C (see FIG. 23) that intersect at an angle of 60 ° within the substrate surface. Here, in the three directions 106A, 106B, and 106C, the center-of-gravity position or the center position pitch 106 of the unit structure of the mask portion 102 is set to 13 μm.
[0101]
Note that the unit structure of the mask portion 102 typically means each of the plurality of mask portions 102 having the same planar shape and spaced apart from each other. However, the unit structure of the mask part 102 does not necessarily need to be composed of one mask part 102. In the case of a plurality of mask portions, these mask portions are not necessarily separated from each other, and adjacent mask portions may be slightly connected to each other.
[0102]
In addition, an anisotropic etching process is performed after the etching mask layer 110 having various patterns is provided on the single crystal substrate 101. As an etchant, ammonia water, hydrogen peroxide water, and water (NH _Four OH: H ₂ O ₂ : H ₂ A mixed solution of O = 15: 15: 70) is used. The etching temperature is 20 degrees, and the etching time is set to 3 minutes and 5 minutes.
[0103]
Hereinafter, each pattern of the etching mask layer 110 will be described with reference to FIGS. 23 to 31.
[0104]
A mask layer 110 shown in FIG. 23 is a mask layer having a pattern similar to that used in the first embodiment. Each planar shape of the mask portion 102 of the mask layer 110 is an equilateral triangle having three sides parallel to the (100) plane, the (010) plane, and the (001) plane of the single crystal substrate 101. That is, the edge sides of each mask portion 102 are parallel to the (100) plane, the (010) plane, and the (001) plane.
[0105]
In the following, as shown in FIG. 35, the abc axis of the crystal is defined so that the [111] direction of the crystal and the normal direction of the substrate surface to be etched are the same, that is, different from usual. The shape of the mask portion 102 will be described in detail with the {111} B plane being defined as the [111] direction. In the crystal structure shown in FIG. 35, the {111} B plane of the crystal is a plane corresponding to the substrate surface, and the mask portion is formed on the {111} B plane. In this specification, when the edge of the mask portion 102 is referred to as “a side parallel to the (100) plane”, it means a side as indicated by a line segment a1 in FIG. That is, the direction of the vector A1 (also shown in FIG. 23) in the mask plane orthogonal to the side (line segment a1) and from the inside to the outside of the mask portion is substantially the same as the [−211] direction of the crystal. In this case, the side is referred to as “a side parallel to the (100) plane”. In addition, the phrase “side parallel to the (010) plane” refers to a side as indicated by a line segment a2 in FIG. That is, the orientation of the vector A2 (also shown in FIG. 23) in the mask plane orthogonal to the side (line segment a2) and from the inside to the outside of the mask portion is substantially the [1-21] direction of the crystal. If they are the same, the side is referred to as a “side parallel to the (010) plane”. In addition, the phrase “side parallel to the (001) plane” refers to a side as indicated by a line segment a3 in FIG. That is, the direction of the vector A3 (also shown in FIG. 23) in the mask plane orthogonal to the side (line segment a3) and from the inside to the outside of the mask portion is substantially the [11-2] direction of the crystal. If they are the same, the side is called a side parallel to the (001) plane.
[0106]
Reference is again made to FIG. The mask portions 102 slightly overlap each other at the overlapping portion 107. That is, the area ratio of the mask portion 102 to the etching mask layer 110 is 50% or more. In other words, the total area of the mask part 102 is larger than the total area of the opening part 105.
[0107]
The position of the center of gravity (or center position) of each mask portion 102 is disposed substantially on the honeycomb lattice point. In this specification, the honeycomb lattice point refers to a point corresponding to the vertex of each regular hexagon and the center of gravity of each regular hexagon when a predetermined plane is laid with a plurality of congruent regular hexagons without gaps. ing. Alternatively, each of the honeycomb lattice points extends along the first direction in a predetermined plane, and each of the first plurality of parallel lines is arranged at the same interval (predetermined interval). It is also a point that extends along a direction different from the direction of 60 °, and all correspond to intersections of the first plurality of parallel lines and the second plurality of parallel lines arranged at the same predetermined interval.
[0108]
The mask layer 110 shown in FIG. 24 has the same pattern as that of the first embodiment or FIG. 23, but the orientation of the mask portion 102 with respect to a predetermined crystal plane of the single crystal substrate 101 is different. For this reason, the mask layer 110 shown in FIG. 24 has a pattern in which the mask portion 102 and the opening portion 105 are inverted as compared with the mask layer 110 shown in FIG.
[0109]
Each planar shape of the mask portion 102 of the mask layer 110 is an equilateral triangle having three sides parallel to the (11-1) plane, the (1-11) plane, and the (−111) plane of the single crystal substrate 101. ing. That is, the edge sides of each mask portion 102 are parallel to the (11-1) plane, the (1-11) plane, and the (−111) plane.
[0110]
Note that in this specification, when the edge of the mask portion 102 is referred to as “a side parallel to the (11-1) plane”, it means a side as indicated by a line segment b1 in FIG. That is, the direction of the vector B1 (also shown in FIG. 24) in the mask plane orthogonal to the side (line segment b1) and from the inside to the outside of the mask portion is the [-1-12] direction of the crystal. When they are substantially the same, the side is called a side parallel to the (11-1) plane. In addition, the phrase “side parallel to the (1-11) plane” refers to a side as indicated by a line segment b2 in FIG. That is, the direction of the vector B2 (also shown in FIG. 24) in the mask plane orthogonal to the side (line segment b2) and from the inside to the outside of the mask portion is the [−12-1] direction of the crystal. When they are substantially the same, the side is called a side parallel to the (1-11) plane. In addition, the phrase “side parallel to the (−111) plane” refers to a side as indicated by a line segment b3 in FIG. That is, the direction of the vector B3 (also shown in FIG. 23) in the mask plane orthogonal to the side b3 and directed from the inside to the outside of the mask portion is substantially the same as the [2-1-1] direction of the crystal. In this case, the side is called a side parallel to the (−111) plane.
[0111]
FIG. 24 will be referred to again. The mask portions 102 slightly overlap each other at the overlapping portion 107. That is, the area ratio of the mask portion 102 to the etching mask layer 110 is 50% or more. In other words, the total area of the mask part 102 is larger than the total area of the opening part 105. In addition, the center of gravity (or center position) of each mask portion 102 is disposed substantially on the honeycomb lattice point.
[0112]
The mask portion 102 of the etching mask layer 110 shown in FIGS. 25 to 27 has a regular hexagonal planar shape, and the mask portions 102 are separated from each other. 25, 26, and 27, the ratio of the area occupied by the mask portion 102 in the mask layer 110 is about 75%, about 60%, and about 50%, respectively. The etching mask layer 110 shown in FIGS. 25 to 27 also has a pattern in which the center of gravity (or center position) of each mask portion 102 is arranged on a substantially honeycomb lattice point.
[0113]
Note that the area of the mask layer 102 is the sum of the area of the mask portion 102 and the area of the opening 105, but in the region where the mask portion 102 and the opening 105 are provided in a uniform pattern. This means the total area of the mask portion 102 and the opening 105. Further, the ratio of the area of the mask portion 102 to the area of the mask layer 102 is a quadrangular region formed by connecting the center points of the four adjacent mask portions 102 (for example, surrounded by a broken line 106D in FIG. 25). It can also be expressed as the ratio of the area occupied by the mask portion 102 in the region.
[0114]
In the mask layer 110 shown in FIG. 28, the edges of the mask portion 102 are (100) plane, (010) plane, (001) plane, (11-1) plane, (1-11) plane, (− 111), each of the mask portions 102 is spaced apart from each other. Further, the center position of the mask portion 102 is arranged substantially on the honeycomb lattice point. The regular hexagonal mask portion 102 shown in FIG. 28 is similar to the regular hexagonal mask portion 102 shown in FIGS. 25 to 27 rotated 90 degrees in the substrate plane. The area ratio occupied by the mask portion 102 in the mask layer 110 shown in FIG. 28 is about 60%.
[0115]
The mask portion 102 of the mask layer 110 shown in FIG. 29 has a nine-sided planar shape whose edges are parallel to the (100) plane, the (010) plane, and the (001) plane. . The mask portions 102 are separated from each other. Further, the center position of each mask portion 102 is located substantially on the honeycomb lattice point.
[0116]
The mask portion 102 of the mask layer 110 shown in FIG. 30 has (100) plane, (010) plane, (001) plane, (11-1) plane, (1-11) plane, -111) A dodecagonal planar shape having a side parallel to the plane. The mask portions 102 are separated from each other. Further, the center position of each mask portion 102 is located substantially on the honeycomb lattice point.
[0117]
Each of the mask portions 102 of the etching mask layer 110 shown in FIG. 31 has a square planar shape, and the center position of this mask portion 102 is also located substantially on the honeycomb lattice point.
[0118]
When anisotropic etching was performed on the substrate 101 using the mask layer 110 having the patterns shown in FIGS. 23 to 31, the following results were obtained.
[0119]
When any one of the mask layers 110 shown in FIGS. 23 to 31 is used, the apex (top) of the convex portion of the micro corner cube is formed at the center position of the mask portion 102. That is, as described above, the center position of the mask portion 102 of the mask layer 110 is positioned substantially on the honeycomb lattice point, but the micro corner cube is formed so as to have the topmost portion corresponding to the honeycomb lattice point. From this, it can be seen that the center position of the mask portion 102 of the mask layer 110 preferably corresponds to the position where the apex of the micro corner cube array is formed (that is, the position on the honeycomb lattice point). In addition, since the size of the micro corner cube is controlled in accordance with the pitch 106 at the center position of the mask portion 102, it can be seen that a micro corner cube having a desired size can be manufactured by appropriately selecting the mask layer pattern.
[0120]
FIGS. 32 and 33 show, as examples, micro corner cube arrays formed when the etching mask layer 110 shown in FIGS. 23 and 24 is used. In these drawings, ◯ indicates the topmost part (vertex of the convex part) of the micro corner cube, and ● indicates the bottommost part (vertex of the concave part) of the micro corner cube. Further, Δ indicates an intermediate portion thereof. As can be seen from the figure, the topmost portion ◯ of the micro corner cube is provided at the center of gravity of the mask portion 102 when any of the etching mask layers 110 shown in FIGS. 23 and 24 is used. However, the micro corner cube has a (100) plane, a (010) plane, and a (001) plane. When the mask layer 110 shown in FIG. In contrast to the bottom portion ●, when the mask layer 110 shown in FIG. 24 is used, the intermediate portion Δ of the corner cube corresponds to the center position of the opening 105.
[0121]
In addition, when the mask layer 110 having any pattern was used, the shape of the top of the produced micro corner cube array was sharp when the etching time was 3 minutes (see FIG. 34A). When the etching time was 5 minutes, the shape of the top was rounded (see FIG. 34B). This is because the area of the contact portion between the {111} B surface (substrate surface) of the gallium arsenide single crystal substrate 101 and the mask portion 102 becomes smaller as the etching process proceeds, but this contact portion disappears. After that, the etching of the {111} B surface starts from the apex, and as a result, the shape of the apex of the corner cube is considered to be rounded.
[0122]
Therefore, it is desirable to stop the etching process at the same time that the contact portion between the {111} B surface of the gallium arsenide single crystal substrate 101 and the mask portion 102 is eliminated (or the contact area thereof is minimized). all right. Thus, in order to stop the etching when the contact area between the {111} B surface and the mask portion is minimized, the optimum value of the etching time for the above state is tested in advance. You can ask for it. If the etching time is appropriately set in this way, a micro corner cube array having a desired shape with a sharp top can be produced.
[0123]
Further, it was found that the area of the opening 105 in the etching mask layer 110 is preferably small depending on the etching solution used. This is because the ratio of the etching rate of the {111} B surface and the etching rate of the {100} surface (the value obtained by dividing the etching rate of the {111} B surface by the etching rate of the {100} surface) is not sufficiently large. This is because the etching may proceed with the area corresponding to the opening 105 leaving a planar bottom. That is, in order to produce a microcorner cube array structure having an appropriate shape, the etching rate ratio must be relatively large as the area of the opening 105 of the etching mask layer 110 is large. The smaller the area of the portion 105, the smaller the etching rate ratio is. Therefore, the burden on the etching conditions can be reduced by reducing the area of the opening 105 of the etching mask layer 110.
[0124]
For example, when the mask layers shown in FIGS. 25, 26, and 27 are used, the former two (in the case of FIGS. 25 and 26) in which the area ratio of the mask portion 102 is larger than 50% of the whole are appropriate. A micro corner cube array shape was produced, but in the latter case (when FIG. 27 was used) with an area ratio of 50%, an appropriate micro corner cube array shape was not produced, and a flat surface remained at the bottom. Accordingly, the area ratio of the mask portion 102 of the etching mask layer 110 is preferably larger than 50% of the entire mask layer, that is, the area of the mask portion 102 is desirably at least larger than the area of the opening 105. I understood.
[0125]
Next, a comparison result when the etching mask layer 110 of FIGS. 23 and 31 is used will be described. It has been found that a micro corner cube array can be produced using either mask layer 110. However, when the surface accuracy (flatness) of the surfaces constituting the corner cube was evaluated by electron microscope observation, it was found that the surface accuracy was higher when the mask layer 110 of FIG. 23 was used. As a result, the microcorner cube array to be produced has a three-fold rotationally symmetric shape, so that the planar shape of the mask portion 102 (or opening 105) of the mask layer 110 to be used is also three-fold rotationally symmetric. It has been found that it is preferable to have
[0126]
Next, a comparison result when the mask layer 110 of FIGS. 23 and 24 is used will be described. As shown in FIGS. 32 and 33, it was found that the micro corner cube array can be produced by using either mask layer. However, when the surface accuracy (flatness) of the surfaces constituting the corner cube was evaluated by electron microscope observation, the result of using the mask layer 110 in FIG. It was found that there was a portion where an unnecessary vertex (convex portion) was formed on the substrate surface in the portion 107. Therefore, in order to form a corner cube shape uniformly over a large area, the mask layer 110 having the pattern shown in FIG. 23 is used more than the mask layer 110 having the pattern shown in FIG. It is desirable to increase the shape accuracy of the layer 110.
[0127]
In addition, when the mask layer of FIGS. 25 to 31 in which the overlapping portion 107 of the mask portion 102 does not exist, unnecessary protrusions are not formed on the surface of the substrate. Therefore, the unnecessary protrusions are masked. It was found that this was caused by the overlapping portion 107 of the portion 102. Accordingly, it was found that the mask portions 102 of the etching mask layer 110 are preferably separated from each other.
[0128]
Thus, by appropriately selecting the pattern of the etching mask layer used for the etching treatment, a micro corner cube array with improved shape accuracy can be produced. Further, by defining the position of the center of gravity of the mask portion in the etching mask layer, the apex position of the micro corner cube to be formed and the size of the micro corner cube can be determined.
[0129]
(Embodiment 5)
Hereinafter, a reflective liquid crystal display device using a micro corner cube array manufactured by the method described in the above embodiment as a retroreflector will be described.
[0130]
FIG. 9 shows a configuration of the reflective liquid crystal display device 100 of the present embodiment. The liquid crystal display device 100 includes an incident side substrate 8 positioned on the viewer side, a reflection side substrate 9 provided so as to face the substrate 8, and a light modulation layer sandwiched between the pair of substrates. The scattering type liquid crystal layer 6 is provided. The incident side substrate 8 and the reflection side substrate 9 are made of a transparent material such as a glass plate or a polymer film.
[0131]
On the liquid crystal layer 6 side surface of the incident side substrate 8, a color filter layer 7 including three color filters of R, G, and B and a transparent electrode 12 are provided. On the other hand, a micro corner cube array 10 is provided on the liquid crystal layer 6 side of the reflective substrate 9. On the micro corner cube array 10, a reflective electrode 11 formed of a material having a high surface reflectance such as silver or aluminum has a substantially uniform thickness so as to follow the surface shape (unevenness) of the micro corner cube array 10. It is provided. The reflective electrode 11 can be formed by evaporating silver with a thickness of 200 nm, for example, and forms a reflective surface that reflects incident light and is used as an electrode for applying a voltage to the liquid crystal layer 6.
[0132]
In the liquid crystal display device 100 configured as described above, a voltage is applied to the liquid crystal layer 6 using the transparent electrode 12 and the reflective electrode 11, and the light modulation state of the liquid crystal layer 6 is controlled for each pixel to display an image. Is done. As the driving means for the electrodes 11 and 12, for example, a known active element such as a thin film transistor can be used, but other driving means may be used.
[0133]
In the above description, the micro corner cube array 10 is provided on the reflection side substrate 9. However, the micro corner cube array 10 itself may be used as the reflection side substrate without providing the reflection side substrate 9. As described in the first embodiment, the micro corner cube array 10 can be formed from a gallium arsenide substrate. When such a gallium arsenide substrate is used, a circuit for driving the active element or the like can be integrally formed on the substrate in the periphery of the display region. If the driver circuit can be formed on the substrate in this way, the size of the display device can be reduced, which is particularly effective when used as a display for a mobile phone or the like.
[0134]
In the present embodiment, polymer dispersed liquid crystal is used as the material of the light scattering liquid crystal layer 6. However, the material of the liquid crystal layer 6 is not limited to this, and a light scattering liquid crystal such as a nematic-cholesteric phase transition liquid crystal or a liquid crystal gel may be used. Furthermore, various other materials can be used for the liquid crystal layer as long as it has a mode modulated between a transmission state and a state including at least a scattering action. Specifically, it has a cholesteric liquid crystal that switches in a transmissive-reflective state with diffusivity by controlling the domain size of liquid crystal molecules, and a holographic function that switches in a transmissive-reflective state with diffusivity provided by exposure to diffused light. It is possible to use a polymer dispersed liquid crystal or the like.
[0135]
The polymer-dispersed liquid crystal used in the present embodiment is obtained by compatibilizing a mixture of a low-molecular liquid crystal composition and an unpolymerized prepolymer and placing it between substrates, and polymerizing the prepolymer. The kind is not particularly limited as long as it is obtained by polymerizing a prepolymer. Here, a cured product (ultraviolet curable liquid crystal) obtained by photocuring a mixture of an ultraviolet curable prepolymer exhibiting liquid crystallinity and a liquid crystal composition by irradiation with actinic rays such as ultraviolet rays is used. By using an ultraviolet curable liquid crystal as the polymer dispersed liquid crystal, it is not necessary to perform heating when the polymerizable liquid crystal is polymerized, so that adverse effects due to heat on other members are prevented.
[0136]
The above prepolymer liquid crystal mixture can be obtained, for example, by adding a small amount of a polymerization initiator (manufactured by Ciba-Geigy) to a mixture in which an ultraviolet curable material and liquid crystal are mixed at a weight ratio of 20:80. A prepolymer liquid crystal mixture that exhibits a nematic liquid crystal phase at room temperature can be used. The light incident on the liquid crystal layer manufactured as described above is modulated according to the scattering / transmission state of the liquid crystal layer that changes in accordance with the applied voltage. In the present embodiment, the liquid crystal layer is set in a scattering state when no voltage is applied, and is set so that the liquid crystal layer is in a transmissive state when a voltage is applied.
[0137]
Hereinafter, the operation of the reflective liquid crystal display device 100 will be described. First, the operation of white display will be described. In white display, the liquid crystal layer 6 is controlled to be in a scattering state, and light from the outside transmitted through the incident side substrate 8 and the color filter 7 is scattered in the liquid crystal layer 6. At this time, the light backscattered in the liquid crystal layer 6 returns to the viewer side. Further, in the display device of the present embodiment, the straight light and forward scattered light transmitted through the liquid crystal layer 6 are reflected by the reflective electrode 11 provided in the micro corner cube array 10 and pass through the scattered liquid crystal layer 6 again. Sometimes it is scattered and part of it returns to the viewer. As described above, in the white display, not only the back-scattered light but also a part of the forward-scattered light returns to the observer side, so that a display with high brightness can be realized.
[0138]
Next, the black display operation will be described. In black display, the liquid crystal layer 6 is controlled to be in a transmissive state by applying a voltage, and light is transmitted from the outside of the apparatus through the incident side substrate 8, the color filter 7 and the liquid crystal layer 6. The light transmitted through the liquid crystal layer 6 is retroreflected by the reflective electrode 11 on the micro corner cube 10. When the source of light incident on the eyes of the observer observing the display is traced, it is refracted by the substrate 8, the liquid crystal layer 6, etc., and recursed by the micro corner cube array 10, and similarly the substrate. 8 and the liquid crystal layer 6 are refracted and finally reach the vicinity of the observer's eyes. In other words, only incident light from the vicinity of the observer's eyes is emitted light that is observed by the observer. Here, if the vicinity of the observer's eyes is an area that is sufficiently narrow (eg, an area narrower than the pupil of the eye) that there is no light source, good black display is realized.
[0139]
As described above, the light incident on the micro corner cube array 10 is retroreflected so as to be directed in the direction opposite to the incident direction. However, the position of the reflected light beam translates with respect to the position of the incident light in the same degree as the size (or pitch) of the unit element of the corner cube array 10. Therefore, as shown in FIG. 10A, when the size L1 of the unit element of the micro corner cube array 10 is larger than the size L2 of the pixel region, the color of the color filter that passes at the time of incidence (G in the figure) and Unlike the color (B in the figure) of the color filter that passes during emission, color mixing occurs.
[0140]
On the other hand, as shown in FIG. 10B, when the size of the unit element L1 of the micro corner cube array 10 is smaller than the size L2 of the picture element region, the color of the color filter that passes at the time of incidence (in the figure, G) and the color of the color filter that passes at the time of emission are the same, and no color mixing occurs. Therefore, in order to perform a desired display, the size L1 of the unit element of the micro corner cube array 10 needs to be smaller than the size L2 of the picture element region. As described in the first or second embodiment, the size of the unit element of the micro corner cube array 10 used in the present embodiment is sufficiently smaller (for example, about 10 μm) than the normal pixel region size (for example, several tens of μm). 10 μm). Therefore, a desired appropriate display can be performed.
[0141]
Further, the retroreflectance of light incident from the front is compared between the case where the unit element of the corner cube is composed of three planes of right-angled isosceles triangles and the case of three planes of squares. Note that the light incident on the corner cube has a characteristic of exiting from the symmetry point with respect to the center point of the corner cube in the direction opposite to the incident direction, and this characteristic is a necessary and sufficient condition.
[0142]
FIGS. 11A to 11C show a case where the unit element of the corner cube is composed of three surfaces of right-angled isosceles triangles. FIG. 11 (a) shows corner cube unit elements, and FIGS. 11 (b) and 11 (c) show an array of corner cubes. When the unit element of the corner cube is composed of three surfaces of right-angled isosceles triangles, as shown in FIG. 11C, when the surface constituting the unit element is projected onto the reference plane, the shape becomes an equilateral triangle. In this case, the light incident on the portion close to the apex of the regular triangle is not retroreflected because there is no symmetry point with respect to the center point of the corner cube. For this reason, the retroreflectance is 66% at the maximum.
[0143]
On the other hand, FIGS. 12A to 12C show a case where the unit element of the corner cube is composed of three square surfaces, as shown. FIG. 12 (a) shows the corner cube unit elements, and FIGS. 12 (b) and 12 (c) show an array of corner cubes. When the unit element of the corner cube is composed of three square surfaces, as shown in FIG. 12C, when the surface constituting the unit element is projected onto the reference surface, a regular hexagon is formed. In this case, since there is a symmetric point with respect to the center point of the corner cube, all light incident on an arbitrary position of the regular hexagon is retroreflected. Therefore, from the viewpoint of reliably retroreflecting incident light, the surface constituting the unit element of the micro corner cube array is a square, and the shape of the projection of the surface constituting the unit element onto the reference surface is a regular hexagon. It turns out that one is preferable.
[0144]
As described in the first or second embodiment, the unit element of the micro corner cube array used in the present embodiment has three substantially square three faces composed of {100} faces of a cubic single crystal. Yes. For this reason, incident light can be reliably retroreflected. Therefore, at the time of black display, the observer does not observe unfavorable light, and a dark display can be realized. As a result, the contrast ratio is also improved.
[0145]
Here, the reflective liquid crystal display device (example) provided with the micro corner cube array according to the present embodiment and the reflective liquid crystal display device (comparative example) not provided with the micro corner cube array as shown in FIG. 13 are used. Then, each reflectance and contrast ratio were measured. Since the reflective liquid crystal display device of the comparative example uses a scattering reflector instead of the micro corner cube, when the liquid crystal layer 6 is in a transmissive state, light from a light source existing at a position away from the observer is also observed. It can be reflected towards the person. For this reason, the polarizing plate 13 and the phase difference plate 14 are provided on the front surface of the incident side substrate 8, and these are used to absorb the reflected light as described above so as to perform black display. Except for these configurations, other configurations such as the liquid crystal layer 6 and the color filter layer 7 are the same as those of the liquid crystal display device of the embodiment.
[0146]
As shown in FIG. 14, an apparatus for measuring the reflectance and contrast ratio of each display device irradiates diffused light toward a sample (that is, a reflective display device of an example or a comparative example) 16 by an integrating sphere 15. And it is comprised so that it may light-receive with the light receiver 17 installed in the front direction. Table 1 below shows the measurement results.
[0147]
[Table 1]

[0148]
From the above results, the liquid crystal display device of this embodiment using the micro corner cube array instead of using the polarizing plate 13 and the retardation plate 14 is bright, has a relatively high contrast, and can display with good visibility. I understood it.
[0149]
(Embodiment 6)
Hereinafter, an example in which the micro corner cube array described in the first or second embodiment is used in an organic EL (electroluminescence) display device which is a self-luminous display device will be described.
[0150]
FIG. 15 shows the configuration of the organic EL display device of this embodiment. The organic EL display device 200 includes an upper substrate 30 formed of a transparent material such as glass or a polymer film, a lower substrate 34 provided so as to face the upper substrate 30, and an organic EL layer positioned between the substrates. 42. The organic EL layer 42 is formed of a plurality of thin films such as a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, or an electron injection layer. Further, a cathode (transparent electrode) 32 made of a transparent conductive material such as ITO (indium tin oxide) is provided between the organic EL layer 42 and the upper substrate 30. An anode 40 is provided between the organic EL layer 42 and the lower substrate 34. The anode 40 is formed of an aluminum film having a thickness of 30 nm, for example, and light can be transmitted by using such a thin film.
[0151]
A micro corner cube array 36 manufactured by the method described in the first or second embodiment is provided on the surface of the lower substrate 32 on the organic EL layer 42 side. A reflective film (not shown) made of, for example, aluminum is formed on the surface of the micro corner cube array 36, and light incident on the micro corner cube array 36 is retroreflected. Irregularities on the surface of the micro corner cube array 36 provided with such a reflective film are filled with a transparent planarizing member 38. The anode 40 is provided on the surface flattened in this way.
[0152]
In the organic EL display device 200, by applying a predetermined voltage between the cathode 32 and the anode 40, electrons from the cathode 32 and holes from the anode 40 are recombined in the organic EL layer 42, thereby A predetermined display can be performed by causing the organic EL layer 42 to emit light. In addition, such an organic EL layer 42 can be produced by various known methods using various known materials.
[0153]
In such an organic EL display device 200, when the organic EL layer 42 is not emitting light (during black display), external light from a light source such as an electric lamp or the sun located around the observer is micro-corner cube array 36. Is retroreflected in the incident direction and does not reach the observer's eyes. Therefore, the reflection of external light is prevented and a good black display can be realized.
[0154]
Further, when the organic EL layer 42 emits light (in white display), not only light traveling from the organic EL layer 42 toward the observer but also light traveling from the organic EL layer 42 toward the lower substrate 34 is microscopic. It is retroreflected by the corner cube array 36 and returns to the viewer direction. Therefore, the light generated in the organic EL layer 42 can be used more efficiently, and a good white display with high brightness can be realized. In addition, reflection of external light from the light source around the observer is prevented even during white display.
[0155]
In the organic EL display device 200 as well, as in the liquid crystal display device of the fifth embodiment, it is desirable that the size of the unit element of the micro corner cube array 36 is equal to or smaller than the size of the picture element region. For example, as shown in FIG. 15, the organic EL layer 42 of the organic EL display device 200 includes a plurality of light emitting regions that emit light of R, G, and B, and each of the light emitting regions corresponds to a pixel region. To do. When the size of the unit element of the micro corner cube array 36 is equal to or smaller than the size of the picture element region, when the light generated in the light emitting region of a predetermined color is reflected by the micro corner cube array 36, other adjacent colors It does not pass through the light emitting area. Therefore, no color mixing occurs, and a decrease in luminance and chromaticity is prevented.
[0156]
(Embodiment 7)
In the present embodiment, a method for producing a micro corner cube array having an optical axis inclined from the normal direction of the reference surface of the substrate will be described. A display device using such a micro corner cube array is disclosed in USP 5,182,663, for example, by Raychem Corporation.
[0157]
First, a gallium arsenide substrate whose surface is inclined about 5 degrees from the (111) B plane of the crystal is prepared. In this embodiment, a gallium arsenide substrate is used as in the first embodiment. However, as long as it has a surface inclined by a predetermined angle (0 ° to 10 °) from the {111} plane of the crystal, other A cubic single crystal substrate made of the above material (for example, the germanium single crystal substrate of Embodiment 2) can also be used.
[0158]
Next, as in the first embodiment, the prepared gallium arsenide substrate is mirror-finished, resist-formed, and wet-etched to form irregularities constituted by {100} planes of the crystal on the substrate surface. . The unevenness formed in this way has three surfaces (for example, (100) plane, (010) plane, and (001) plane) orthogonal to each other, and constitutes a corner cube array. However, unlike the first embodiment, since a gallium arsenide substrate having a surface inclined about 5 degrees from the {111} B plane of the crystal is used, it is relative to the reference plane of the substrate (ie, the substrate surface before etching). The angle formed by each surface of the corner cube is different from that in the first embodiment. Moreover, the shape of each surface of the corner cube formed in this way may be a rectangle.
[0159]
Note that when a single crystal substrate having a surface inclined from the {111} plane of the crystal is used as described above, the ratio of the length and width of the shape of the mask portion in the mask layer used for etching according to the inclination Is preferably changed. This is because when the formed corner cube is viewed from above, it does not become a perfect regular hexagon as in the case of the first embodiment (for example, FIG. 2 (d)). This is because it may be vertically long (or horizontally long). Further, when the corner cube is manufactured as in the present embodiment, the center of gravity position of the mask portion is not completely coincident with the above-described honeycomb lattice point and is slightly deviated from the honeycomb lattice point. It may be located above.
[0160]
The corner cube array thus formed on the gallium arsenide substrate can be used as a retroreflector by forming a reflective film on the surface as described in the first or second embodiment.
[0161]
However, in this embodiment, as shown in FIG. 16, the micro corner cube array formed on the surface of the gallium arsenide substrate is transferred to the resin 20 to produce a micro corner cube array made of resin. For this purpose, first, the electromold 18 is produced from the gallium arsenide substrate. The electromold 18 can be produced by a known method. Next, the electroforming mold 18 is attached to a roll 19, and the micro corner cube array is transferred to the resin 20 by performing an embossing resin molding using the roller 19.
[0162]
FIG. 16 shows a roller rotation direction 21 and a resin movement direction 22. Here, a straight line AB shown in the figure represents a straight line parallel to the resin movement direction 22. As the roller 19 rotates and the resin 20 moves, the surface of the electroforming mold 18 is pressed against the resin 20, and then the resin 20 is peeled from the electroforming mold 18. This peeling direction is also a straight line AB. Parallel direction.
[0163]
FIGS. 17A and 17B show the micro corner cube array formed (transferred) on the surface of the resin 20 as described above. Also in these drawings, the straight line AB shown in FIG. 16 is shown. The resin 20 to which the micro corner cube array has been transferred is peeled along the line AB as described above. In the present embodiment, the peeling is performed so that the peeling direction of the resin 20 and the direction (normal direction) 23 perpendicular to one surface 24 of the three square surfaces constituting the corner cube exist in the same plane. It is. That is, as can be seen from FIG. 17B, the projection of the normal direction 23 onto the resin surface and the peeling direction of the resin 20 are in a parallel relationship. In this case, the resin 20 can be peeled and removed more easily than when the peeling is performed in a direction not parallel to the projection of the normal direction 23 onto the resin surface.
[0164]
In order to perform such resin peeling, the resin moving direction 22 shown in FIG. 16 and the direction perpendicular to one of the three surfaces constituting the micro corner cube provided in the electroforming mold 18 are used. May be transferred so that they always exist in the same plane (for example, in the paper). This can be easily realized by appropriately adjusting the direction of the electroforming mold 18 when the electroforming mold 18 is attached to the surface of the roller 19.
[0165]
Further, when an electroforming mold formed of a gallium arsenide substrate whose surface is inclined by 5 degrees from the (111) B plane as in the present embodiment, the surface has a (111) B plane as in the first embodiment. The resin 20 can be easily peeled and removed as compared with the case where an electroforming mold formed from a gallium arsenide substrate (Embodiment 1) is used.
[0166]
The optical axis of the micro corner cube array formed in this way is inclined from the direction perpendicular to the reference plane of the substrate. In the retroreflector formed using this, an incident light region where the retroreflection is appropriately performed is defined around the direction of the inclined optical axis. Although the light traveling from the incident light region toward the retroreflecting plate is appropriately retroreflected, the light traveling from the region outside the incident light region toward the retroreflecting plate may not be appropriately retroreflected. Therefore, if a retroreflector is provided so that the optical axis is positioned in a direction inclined upward with respect to the normal direction of the panel surface of the display device, the light from the light source located above the display device can be transmitted. It can certainly be retroreflected. Thereby, better black display can be performed.
[0167]
In addition, although the form using the board | substrate which has a surface inclined 5 degrees with respect to the {111} plane of the crystal | crystallization was demonstrated above, it is desirable that this angle is larger than 0 degree and 10 degrees or less. The angle formed between the substrate surface and the {111} plane is the optical axis of the micro corner cube to be formed (here, straight lines having the same distance from three mutually orthogonal surfaces forming the corner cube) and the normal to the substrate surface. However, the micro corner cube has the best recursive performance in the direction of its optical axis. That is, when the optical axis is directed to the direction of the light source, the light incident from the light source is appropriately retroreflected, so that a good black display is performed. However, if the optical axis is tilted too much with respect to the normal of the substrate, the recursive performance for the observer observing from the normal direction of the substrate surface deteriorates, and when displaying black, other than the vicinity of the eye (pupil) of the observer Incident light from the location can also be observed. As a result, there is a possibility that good black display cannot be performed. As a result of studies by the inventors based on these matters, it was found that an appropriate range of the inclination angle of the optical axis of the corner cube is 0 ° or more and 10 ° or less. Therefore, in order to produce a corner cube having such an optical axis, it is desirable to use a substrate having a surface inclined by an angle of 0 ° or more and 10 ° or less with respect to the {111} plane.
[0168]
As shown in FIG. 20, when a single crystal substrate having a surface S0 inclined by an angle θ with respect to the {111} plane of the crystal is used, the direction of the intersection line L3 between the {111} plane and the surface S0 is It is preferably perpendicular to a predetermined cleavage plane in the single crystal crystal substrate (in the case of a gallium arsenide substrate, the (0, 1, -1) plane). In other words, the plane including the normal line L4 of the {111} plane and the normal spring L5 of the substrate surface S0 is preferably parallel to a predetermined cleaved surface of the substrate. In this case, the symmetry of each surface constituting the corner cube can be improved. For example, as shown in FIG. 17B, the shape of each corner cube can be made symmetrical with respect to the vertical line. In addition, when the corner cube formed in this way is used as a mold, an effect of facilitating die cutting can be obtained.
[0169]
【The invention's effect】
According to the present invention, the micro corner cube is formed by subjecting the {111} plane of the cubic single crystal substrate to an anisotropic etching process to form irregularities having a plane with a low etching rate (eg, {100} plane). Since the array is manufactured, a micro corner cube array having a small unit element smaller than a picture element region (for example, several tens of μm) of the display device and having high shape accuracy can be manufactured by a relatively easy process.
[0170]
A display device using such a micro corner cube array can perform black display without using a polarizing plate, and can display bright, high contrast, high color purity, and high visibility.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views illustrating a manufacturing process of a micro corner cube array according to a first embodiment of the present invention, wherein FIGS.
2A and 2B are diagrams illustrating a manufacturing process of a micro corner cube array according to a first embodiment of the present invention, in which FIG. 2A is a plan view corresponding to FIG. 1D, and FIG. 2B and FIG. (E) is a plan view and a perspective view, and (d) and (e) are a plan view and a perspective view corresponding to FIG. 1 (f).
FIG. 3 is a plan view showing a photomask used in the micro corner cube array manufacturing method according to the first embodiment of the present invention.
4 is a plan view showing a photomask having a different form from the photomask shown in FIG. 3;
FIGS. 5A and 5B are cross-sectional views showing a manufacturing process of the micro corner cube array according to the second embodiment of the present invention, and FIGS. 5A to 5I show different processes. FIGS.
6A and 6B are diagrams showing a manufacturing process of a micro corner cube array according to a second embodiment of the present invention, and FIGS. 6A and 6B are a plan view and a perspective view corresponding to FIG. 5C or FIG. , (C) and (d) are a plan view and a perspective view corresponding to FIG. 5 (e) or (f).
FIGS. 7A and 7B are diagrams illustrating a manufacturing process of the micro corner cube array according to the second embodiment of the present invention, and FIGS. 7A and 7B are a plan view and a perspective view corresponding to FIG. 5G or FIG. , (C) and (d) are a plan view and a perspective view corresponding to FIG.
FIG. 8 is a plan view showing a photomask used in the micro corner cube array manufacturing method according to the second embodiment of the present invention.
FIG. 9 is a cross-sectional view showing the structure of a reflective liquid crystal display device according to Embodiment 5 of the present invention;
FIG. 10 is a diagram for explaining that color mixture can occur according to the pitch of unit elements of a micro corner cube array in a reflective liquid crystal display device according to Embodiment 5 of the present invention; The case where the pitch of the unit element of the micro corner cube array is larger than the size of the picture element region is shown, and (b) shows the case where the pitch of the unit element of the micro corner cube array is smaller than the size of the picture element region.
11A and 11B show a corner cube having unit elements each having three faces of a right-angled isosceles triangle, FIG. 11A is a perspective view showing unit elements of the corner cube, and FIG. 11B is a perspective view showing an array of corner cubes. (C) is a plan view of these.
FIGS. 12A and 12B show a corner cube having three square units, FIG. 12A is a perspective view showing unit elements of the corner cube, and FIG. 12B is a perspective view showing an array of corner cubes; ) Is a plan view of these.
FIG. 13 is a cross-sectional view showing a structure of a reflective liquid crystal display device of a comparative example.
FIG. 14 is a configuration diagram of a reflectance measuring device of a reflective liquid crystal display device.
FIG. 15 is a cross-sectional view showing a configuration of an organic EL display device according to a sixth embodiment of the present invention.
FIG. 16 is a schematic view showing a process for producing a micro corner cube array by transferring from a mold to a resin in Embodiment 7 of the present invention.
FIGS. 17A and 17B show a micro corner cube array transferred to a resin according to a seventh embodiment of the present invention, where FIG. 17A is a perspective view and FIG. 17B is a plan view.
FIG. 18 is a cross-sectional view showing a structure of a reflective liquid crystal display device using a conventional micro corner cube array.
FIG. 19 is a plan view showing a {111} B plane of a gallium arsenide crystal.
FIG. 20 is a perspective view showing a substrate having a surface inclined from a {111} plane.
FIG. 21 is a diagram for explaining the relationship between etching rate ratios in Embodiment 3 of the present invention, where (a) shows the cross-sectional shape of a recess formed when different etching solutions are used; ) Shows the cross-sectional shape of the recess formed when the etching rate ratio is different.
FIGS. 22A and 22B are diagrams for explaining the relationship between etching rate ratios in Embodiment 3 of the present invention, where FIG. 22A shows a case where the etching rate ratio is not sufficiently high, and FIG. 22B shows a case where the etching rate ratio is sufficiently high. Indicates.
FIG. 23 is a plan view showing an etching mask layer having a triangular mask portion according to Embodiment 4 of the present invention.
24 is a plan view showing an etching mask layer having a triangular mask portion different from that shown in FIG. 23 in Embodiment 4 of the present invention. FIG.
FIG. 25 is a plan view showing an etching mask layer having a hexagonal mask portion according to Embodiment 4 of the present invention, showing a case where the area occupied by the mask portion is large.
FIG. 26 is a plan view showing an etching mask layer having a hexagonal mask portion according to Embodiment 4 of the present invention, showing a case where the area occupied by the mask portion is smaller than that shown in FIG.
27 is a plan view showing an etching mask layer having a hexagonal mask portion according to Embodiment 4 of the present invention, and shows a case where the area occupied by the mask portion is smaller than that shown in FIG.
FIG. 28 is a plan view showing an etching mask layer having a hexagonal mask portion different from that shown in FIGS. 25 to 27 in the fourth embodiment of the present invention.
FIG. 29 is a plan view showing an etching mask layer having a nine-sided mask portion in Embodiment 4 of the present invention.
FIG. 30 is a plan view showing an etching mask layer having a dodecagonal mask portion according to Embodiment 4 of the present invention.
FIG. 31 is a plan view showing an etching mask layer having a square mask portion according to Embodiment 4 of the present invention.
32 is a plan view showing a micro corner cube array manufactured when the mask layer shown in FIG. 23 is used. FIG.
33 is a plan view showing a micro corner cube array produced when the mask layer shown in FIG. 24 is used. FIG.
FIGS. 34A and 34B are diagrams for explaining experimental results when the etching time is changed in Embodiment 4 of the present invention, in which FIG. 34A shows the case of an appropriate time (3 minutes), and FIG. The case of long time is shown.
FIG. 35 is a view for explaining a form of a mask layer in Embodiment 4 of the present invention.
[Explanation of symbols]
1 Gallium arsenide substrate
2 photoresist
3 Photomask
4 Germanium substrate
5 SiO ₂ layer
6 Liquid crystal layer
7 Color filter layer
8 Incident side substrate
9 Reflection side substrate
10 Micro corner cube array
11 Reflective electrode
12 Transparent electrode
13 Polarizing plate
14 Phase plate
15 integrating sphere
16 samples
17 Receiver
18 Electric mold
19 Roller
20 Resin (Transfer material)
21 Roller rotation direction
22 Resin movement direction
23 Normal direction of the faces that make up the corner cube
101 Gallium arsenide substrate
102 Mask part of etching mask layer
103 Arrow indicating etching (velocity) on (111) B surface
104 Arrow indicating etching (rate) to (100) plane
105 Opening of etching mask layer
106 Pitch of mask part
107 Overlap
110 Etching mask layer

Claims (30)

A step of preparing a single crystal substrate made of a cubic crystal and having a surface substantially parallel to the {111} plane of the crystal;
And performing an anisotropic etching process on the surface of the single crystal substrate,
By the anisotropic etching treatment, forming an unevenness having a crystal plane whose etching rate is slower than the {111} plane of the crystal ,
A method of manufacturing a micro corner cube array in which a value obtained by dividing the etching rate of the {111} plane by the etching rate of a crystal plane having a low etching rate is larger than 1.73 .   The method for producing a micro corner cube array according to claim 1, wherein the crystal plane having a low etching rate is a {100} plane of the crystal.   The method for producing a micro corner cube array according to claim 2, wherein the unevenness has three {100} planes orthogonal to each other.   4. The method for manufacturing a micro corner cube array according to claim 2, wherein the single crystal substrate is formed of a compound semiconductor having a zinc flash structure.   5. The method of manufacturing a micro corner cube array according to claim 4, wherein the compound semiconductor is gallium arsenide, and a {111} plane of the crystal is a {111} B plane formed by arsenic.   4. The method for producing a micro corner cube array according to claim 2, wherein the single crystal substrate is formed from a material having a diamond structure.   The method for producing a micro corner cube array according to claim 6, wherein the single crystal substrate is formed of a germanium crystal. Before the step of performing the anisotropic etching process, a step of covering the surface of the single crystal substrate with an etching mask layer having at least one mask portion and at least one opening portion arranged in a predetermined pattern Furthermore, the manufacturing method of the micro corner cube array in any one of Claim 1 to 7 included . The method for producing a micro corner cube array according to claim 8 , wherein the size of the unit element of the micro corner cube array is controlled according to the pattern of the etching mask layer. The etching mask layer, a method for manufacturing a micro-corner cube array according to claim 8 or 9 each gravity center position has a plurality of said mask portion located substantially on a honeycomb lattice points. The method of manufacturing a micro corner cube array according to claim 10 , wherein the plurality of mask portions are separated from each other. The mask portion (100) plane of the crystal, (010) plane, according to any of claims 8 to 11 having a planar shape including at least three parallel sides each of (001) plane Manufacturing method of micro corner cube array. The method of manufacturing a micro corner cube array according to claim 12 , wherein the mask portion has a triangular planar shape formed from the three parallel sides. The mask portion (11-1) plane of the crystal, (1-11) plane, (- 111) plane of the claims 8 to 11 having a planar shape including at least three parallel sides each The manufacturing method of the micro corner cube array in any one. The method of manufacturing a micro corner cube array according to claim 14 , wherein the mask portion has a triangular planar shape formed from the three parallel sides. The mask portion is, a method for manufacturing a micro-corner cube array according to claim 8 which has a 3-fold symmetry planar shape 15. The method for producing a micro corner cube array according to claim 16 , wherein the mask portion has a hexagonal shape, a nine-sided shape, or a dodecagonal planar shape. The etching mask layer, a method for manufacturing a micro-corner cube array according to claim 8 or 9 each gravity center position has a plurality of said openings located on a substantially honeycomb lattice points. The method for producing a micro corner cube array according to any one of claims 8 to 18 , wherein the etching mask layer has a total area occupied by the mask portion larger than a total area occupied by the opening at the start of the etching process. . The anisotropic etching step, any of claims 8 to 19 comprising the step of stopping the etching when the contact area between the surface and the mask portion of the single crystal substrate becomes substantially minimum A method for producing a micro corner cube array described in 1. The method for producing a micro corner cube array according to any one of claims 1 to 20 , wherein the anisotropic etching treatment includes wet etching. The method for producing a micro corner cube array according to claim 21 , wherein the anisotropic etching process further includes at least one dry etching. The method for producing a micro corner cube according to any one of claims 1 to 22 , further comprising a step of transferring the irregularities formed on the single crystal substrate to a resin material. The method for producing a micro corner cube array according to any one of claims 1 to 23 , wherein the irregularities have three substantially square three surfaces orthogonal to each other. The micro corner cube according to any one of claims 1 to 24 , wherein an angle formed between the surface of the single crystal substrate and a {111} plane of the crystal is greater than 0 ° and equal to or less than 10 °. Array fabrication method. The production of the micro corner cube array according to claim 25 , wherein the direction of the line of intersection between the surface of the single crystal substrate and the {111} plane of the crystal is substantially perpendicular to the cleavage plane of the single crystal substrate. Method. Micro corner cube array produced by the method of preparation according to any of claims 1 26. Mold micro corner cube array manufactured using the manufacturing method according to any one of claims 1 26. A micro corner cube array according to claim 27 ;
And a light modulation layer provided on the micro corner cube array. 30. The display device according to claim 29 , wherein the micro corner cube array has a plurality of unit elements, and a size of the unit elements is equal to or smaller than a size of a pixel region of the display device.

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