JPWO2002102598A1 - Optical recording medium - Google Patents

Optical recording medium Download PDF

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JPWO2002102598A1
JPWO2002102598A1 JP2003505163A JP2003505163A JPWO2002102598A1 JP WO2002102598 A1 JPWO2002102598 A1 JP WO2002102598A1 JP 2003505163 A JP2003505163 A JP 2003505163A JP 2003505163 A JP2003505163 A JP 2003505163A JP WO2002102598 A1 JPWO2002102598 A1 JP WO2002102598A1
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recording medium
optical recording
wavelength
recording
layer
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光明 小山田
光明 小山田
貴 岩村
貴 岩村
田村　眞一郎
眞一郎 田村
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Sony Corp
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Sony Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/246—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes
    • G11B7/247—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes methine or polymethine dyes
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/246—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/246—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes
    • G11B7/247—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes methine or polymethine dyes
    • G11B7/2472—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes methine or polymethine dyes cyanine
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/253—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/253—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates
    • G11B7/2533—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates comprising resins
    • G11B7/2534—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates comprising resins polycarbonates [PC]
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/254—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of protective topcoat layers
    • G11B7/2542—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of protective topcoat layers consisting essentially of organic resins
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
    • G11B7/2578—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/258—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers

Abstract

凹部１Ｇを有する基板１上に、成膜層を有し、この成膜層が、少なくとも有機色素を含む記録層２と、誘電体層３と、光透過性の保護膜４が形成され、記録層に含まれる有機色素が、吸収ピークを示す波長λｍａｘと、記録および再生を行う使用レーザー光の波長λとの関係が、λｍａｘ＞λを有する構成として波長が３８０ｎｍ〜４５０ｎｍのレーザー光に対応した記録および再生可能な追記型光記録媒体を構成する。On a substrate 1 having a concave portion 1G, a film formation layer is formed, and the film formation layer is formed by forming a recording layer 2 containing at least an organic dye, a dielectric layer 3, and a light-transmissive protective film 4, The organic dye contained in the layer has a relationship between the wavelength λmax showing the absorption peak and the wavelength λ of the laser light used for recording and reproduction, and the wavelength is 380 nm to 450 nm as a configuration having λmax> λ. A write-once optical recording medium that can be recorded and reproduced is configured.

Description

技術分野
本発明は、レーザー光により、情報の記録および読み出しを行う光記録媒体、特にその記録が一度だけ可能な追記型光記録媒体に関する。
背景技術
レーザー光により情報の記録および読み出しを行うことができる光記録媒体の開発および実用化が進んでいる。特に動画等の膨大なデータを保存でき、安価な媒体として、一度だけ書き込むことが可能な追記型光記録媒体が注目されている。
この追記型光記録媒体としては、ＣＤ−ＲＯＭ（Ｃｏｍｐａｃｔ Ｄｉｓｃ−Ｒｅａｄ Ｏｎｌｙ Ｍｅｍｏｒｙ）と同様のフォーマットで記録再生ができるようになされたいわゆるＣＤ−Ｒが広く使われている。
更に、ＣＤ−ＲＯＭよりも記録容量が大きい光記録媒体として、ＤＶＤ−ＲＯＭ（Ｄｉｇｉｔａｌ Ｖｅｒｓａｔｉｌｅ Ｄｉｓｃ−ＲＯＭ））も開発実用化され、ＤＶＤ−ＲＯＭと同様のフォーマットで記録再生できる追記型のＤＶＤ−Ｒの開発も進んでいる。
追記型媒体のＣＤ−Ｒ、ＤＶＤ−Ｒは、それぞれ波長７８０ｎｍ、６５０ｎｍのレーザー光により記録再生を行っている。
光データの記録密度は、原理的に光波長の２乗に反比例して大きくなる。より高密度に記録を行うためには、使用するレーザー波長が短波長化されることが必要になる。
近年、ＧａＮレーザー、あるいはＳＨＧ（第２高調波発生）素子を用いた光源による波長３８０〜４５０ｎｍのレーザー光源が開発され、より大容量の光記録媒体の開発が盛んに行われている。
現在、対物レンズの開口数Ｎ．Ａ．を０．８５とする光学系すなわち対物レンズを用いて、記録面上に形成された薄膜状の光透過性保護膜側から、波長３８０ｎｍ〜４５０ｎｍの青紫色レーザー光を照射して、記録および再生を行う大容量光記録媒体の規格化の検討がなされている。
この大容量光記録媒体において、１回の記録のみが可能とされた例えばアーカイブ目的の追記型の大容量光記録媒体の必要性が高まっている。
ところで、光記録媒体において、記録による信号変調度を大きくするためには、記録前後での記録膜の光学定数ｎ（屈折率）の変化量Δｎが大きいほどよい。
一方、追記型の大容量光記録媒体においても、その記録膜を、ＣＤ−Ｒにおけるように、有機色素によって構成することが、製造の簡易化、コストの低廉化において望ましいと思われる。
従来のＣＤ−Ｒ、ＤＶＤ−Ｒで使用されてきた有機色素、例えばシアニン系色素の波長に対する光学定数（ｎ：屈折率，ｋ：吸収係数）の波長依存性特性は、図７に示すように、破線曲線で示す吸収係数曲線の吸収ピークＰｋより短波長側で、屈折率ｎが低く、吸収ピークより長波長側の、吸収の立ち下がりの部分でｎの値が高くなる特性を有する。
そして、ＣＤ−Ｒ、ＤＶＤ−Ｒにおいては、使用波長が、その吸収係数曲線のピークＰｋより長波長側であって屈折率ｎが高い領域を利用し、所要パワーの記録レーザー光照射によって、色素分解による光学定数の変化を生じさせ、この記録による屈折率の低下によって大きなΔｎ、したがって、記録変調度を得る。
しかしながら、このような有機色素を、波長が３８０ｎｍ〜４５０ｎｍという短波長レーザー光による上述の大容量光記録媒体の記録膜にそのまた適用し難い。
発明の開示
本発明においては、波長３８０ｎｍ〜４５０ｎｍの短波長のレーザー光において記録再生特性にすぐれた追記型の大容量光記録媒体を提供するものである。
本発明による光記録媒体においては、凹部、例えばトラッキング案内用の連続的グルーブ、あるいは断続的グルーブによる凹部を有する基板上に、成膜層を有し、この成膜層が、少なくとも有機色素を含む記録層と、誘電体層と、光透過性の保護膜が形成され、波長が３８０〜４５０ｎｍのレーザー光による記録および再生が可能な追記型光記録媒体にあって、記録層に含まれる有機色素が、図６Ａおよび図６Ｂに記録前および記録後のそれぞれの光学定数（ｎ，ｋ）のスペクトル図を示すように、その記録前において、吸収ピークを示す波長λｍａｘと、記録および再生を行う使用レーザー光の波長λとの関係が、λｍａｘ＞λを有する構成とする。
また、記録層に含まれる有機色素が、記録後の屈折率より小さい値の１．５以下の有機色素によって構成する。
上述した記録層に含まれる有機色素としては、上述した波長３８０ｎｍ〜４５０ｎｍでの値が１．５より小である下記（化３）および（化４）のシアニン系色素を用いて、光記録媒体の記録層を構成する。
【化３】

Figure 2002102598
（化３）中、Ｒ１およびＲ２は、それぞれ水素原子、アルキル基、置換アルキル基、アリール基、置換アリール基を表し、両者は同一であっても異なっていてもよい。また、Ｘ−は、Ｉ−、ＣｌＯ４ −、ＢＦ４ −、ＰＦ６ −を表す。
【化４】
Figure 2002102598
（化４）中、Ｒ３およびＲ４は、それぞれ水素原子、アルキル基、置換アルキル基、アリール基、置換アリール基を表し、両者は同一であっても異なっていてもよい。また、Ｘ−は、Ｉ−、ＣｌＯ４ −、ＢＦ４ −、ＰＦ６ −を表す。
図４は、上記（化３）の構造式を有し、Ｒ１およびＲ２が水素原子を有する有機色素における光学定数のスペクトル図を示すものであり、λｍａｘ＞λを示す。
すなわち、本発明においては、上述したように、波長３８０ｎｍ〜４５０ｎｍのレーザー光を用いる大容量光記録媒体において、λｍａｘ＞λであり、屈折率が記録前の屈折率より大に変化する構成、具体的には、記録前の屈折率が１．５以下である構成の光記録媒体とするとき、記録前後の屈折率差Δｎが大となることを見出したことによるものである。
発明を実施するための最良の形態
本発明をより詳細に説述するために、図面に従って説明する。
図１は、本発明による光記録媒体の構造の一例の概略断面図を示す。すなわちこの例においては、例えばトラッキング用のグルーブ等の連続的、あるいは断続的に形成された凹部１Ｇが一主面に形成された基板１上に、順次有機色素を含む記録層２と、誘電体層３と、光透過性保護膜４が形成されて成る。
基板１は、例えば熱可塑性樹脂、例えばポリカーボネート、ポリメタクリレート、ポリオレフィン等の樹脂より成り、射出成形によってこの基板１の成形と同時に、射出成形金型のキャビティ内に配置されたスタンパによって凹部１Ｇの形成がなされる。
あるいは、２Ｐ法（Ｐｈｏｔｏｐｏｌｙｍｅｒｉｚａｔｉｏｎ法）によって基板１を構成する。この２Ｐ法は、基板上に、例えば紫外線硬化型の樹脂を塗布し、この樹脂層に、スタンパを押圧し、その後樹脂層を紫外線硬化することによって樹脂層に凹部１Ｇを形成することによって凹部１Ｇを有する基板１を構成するものである。
基板１は、光透過性、非光透過性を問わない。
そして、基板１の凹部１Ｇの形成面上に、記録層２を形成する。
記録層２は、有機色素を含む層から成る。
この記録層の形成方法としては、有機色素を溶媒に溶解させ、その溶液をスピンコートで塗布して、乾燥させて形成するスピンコート法や、真空蒸着装置の、真空槽内に基板１と有機色素を配置し、有機色素を加熱することで昇華させ、有機色素を基板１の凹部１Ｇの形成面上に堆積させる真空蒸着法などによることができる。
また、本発明による光記録媒体は、例えば図２にその一例の概略断面図を示すように、基板１上に、例えば金属層による反射膜５を形成することができる。
図２において、図１と対応する部分には同一符号付して重複説明を省略する。
また、本発明による光記録媒体は、例えば図３にその一例の概略断面図を示すように、基板１上に、第１の誘電体層３１を成膜し、この上に記録層２、第２の誘電体層３２、光透過性保護膜４を形成する構成とすることができる。この場合、第１および第２の誘電体層３１および３２の厚さの選定によって、所要の反射と、エンハンス効果を得る。
そして、本発明による光記録媒体に対する記録、再生レーザー光Ｌは、その波長が３８０ｎｍ〜４５０ｎｍの青紫色レーザー、なかんずく４０５±５ｎｍのレーザー光Ｌが用いられ、図示しないが、開口数Ｎ．Ａ．が、例えば０．８±０．０５の対物レンズを介して、記録面に集光されるようになされる。
記録層２は、記録時の変調度が大きいこと、つまり、記録時の記録前と記録後とでの記録層２の光学定数ｎの変化量Δｎが大に選定される。
本発明においては、前述した図４の光学定数ｎおよびｋのスペクトル図を有するように、吸収ピークを示す波長λｍａｘと、記録および再生を行う使用レーザー光の波長λとの関係が、λｍａｘ＞λの特性を有し、記録前の屈折率が１．５より小さい有機色素によって構成する。
この有機色素としては、前述した（化１）（化３）あるいは（化２）（化４）による、シアニン系色素、フタロシアニン系色素等が挙げられる。また、記録層に、耐候性を向上させるため一重項酸素失活剤（クエンチャー）を含むことも可能である。
誘電体層３，３１および３２は、Ｍｇ，Ａｌ，Ｓｉ，Ｔｉ，Ｚｎ，Ｇａ，Ｇｅ，Ｚｒ，Ｉｎ，Ｓｎ，Ｓｂ，Ｂａ，Ｈｆ，Ｔａ，Ｓｃ，Ｙなどの希土類元素の酸化物、窒化物、硫化物、弗化物等の単体およびその混合物から構成される材料、特に窒化珪素、酸化珪素、フッ化マグネシウムなどからなり、反応性スパッタリング法、蒸着法で作製することができる。
また、これら誘電体層３，３１および３２は、複数の材料層の積層構造とすることもできる。
更に、第１および第２の誘電体層３１および３２は、同一構成とすることも、異なる構成とすることもできる。
光透過性保護膜４は、光透過性の熱可塑性樹脂やガラスおよび光透過性の接着層からなり、厚さは１００μｍ程度とする。また光透過性の接着層は、光透過性の両面粘着シートや光硬化剤樹脂によることができる。
反射膜５は、Ａｌ，Ａｕ，Ａｇの単体あるいは合金を、例えばスパッタリング法によって成膜する。
次に、本発明による光記録媒体の実施例を挙げて説明する。
〔実施例１〕
この実施例では、図１の構造とした場合で、凹部１Ｇ、この例ではトラッキング用のグルーブが形成されたポリカーボネート樹脂基板１を用意した。
この基板１の凹部１Ｇの形成面上に、スピンコート法により、下記（化５）の構造式を有する有機色素であるシアニン系色素（波長４０５ｎｍでの屈折率１．３０）の膜厚が５０ｎｍの記録層２を形成した。この有機色素は、λｍａｘ＝５７０ｎｍである。
そして、この記録層２上に誘電体層３として窒化珪素を厚さ５０ｎｍにスパッタリングし、この誘電体層３上に光透過性保護膜４として、基板１と同サイズの、厚さ１００μｍのポリカーボネート樹脂製シートを、同様に光透過性の接着フィルムを介して貼り合わせた。
【化５】
Figure 2002102598
この実施例による光記録媒体に、４０５ｎｍの励起波長を持つレーザー光を、光透過性保護膜４側から照射し、レーザーパワー６ｍＷで記録を行ったところ、記録層３に記録ピットが形成された。この記録ピットの部分の反射率は８．７％、未記録部分の反射率は２３．８％となり、変調度は６３．４％であった。
図５は、この構成における記録層２すなわち有機色素の屈折率ｎ，膜厚ｄの値についての反射率のシミュレーションマッピングである。
〔実施例２〕
この実施例では図２の構造とした場合で、実施例１と同様の凹部１Ｇを有する基板１を用意した。
そして、この実施例においては、この基板１の凹部１Ｇを有する面上に、スパッタリング法により、Ａｇの反射膜５を、厚さ１２ｎｍに形成した。
この反射膜５上にスピンコート法により、下記（化６）の構造式を有する有機色素であるシアニン系色素（波長４０５ｎｍでの屈折率１．０２）の記録層３を膜厚５０ｎｍに成膜した。この有機色素は、λｍａｘ＝５１０ｎｍである。
更に、記録層２上に誘電体層３として窒化珪素を３０ｎｍの厚さにスパッタリング法で形成し、この誘電体層３上に、実施例１と同様の光透過性保護膜４を、同様の手法で貼り合わせた。
【化６】
Figure 2002102598
この実施例２による光記録媒体に、４０５ｎｍの励起波長を持つレーザーを光透過性の保護膜側から照射し、レーザーパワー６ｍＷで記録を行ったところ、記録層２に記録ピットが形成された。
そして、この場合ピットの部分の反射率は１９．９％、未記録部分の反射率は３１．９％で、変調度は３７．６％であった。
〔実施例３〕
この実施例においては、図３で示した構造とした場合で、この場合においても、実施例１と同様の構成による凹部１Ｇを有する基板１が用意した。
そして、この実施例においては、基板１の凹部１Ｇが形成された面上に、先ず第１の誘電体層３１として、窒化珪素を厚さ５０ｎｍにスパッタリングして形成した。
この第１の誘電体層３１上に、スピンコート法により、下記（化７）の構造式を有する有機色素であるシアニン系色素（波長４０５ｎｍでの屈折率１．３４）を膜厚は５０ｎｍに形成した。この有機色素はλｍａｘ＝５８０ｎｍで、であった。
また、この記録層２上に第２の誘電体層３２として、窒化珪素を厚さ２０ｎｍスパッタリング法によって形成し、この第２の誘電体層３２上に実施例１と同様の構成で光透過性保護膜４を形成した。
【化７】
Figure 2002102598
この実施例による光記録媒体に、４０５ｎｍの励起波長を持つレーザーを光透過性保護膜４側から照射し、レーザーパワー６ｍＷで記録を行ったところ、記録膜に記録ピットが形成された。ピットの部分の反射率は１０．８％、未記録部分の反射率は２１．６％で、変調度は５０％であった。
上述した実施例においては、レーザー光の波長４０５ｎｍとした場合であるが、波長３８０ｎｍ〜４５０ｎｍの青紫色レーザーにおいて、ほぼ同様に高い変調度が得られた。
上述した各実施例から明らかなように、本発明による光記録媒体は、高い変調度、したがって、高い再生出力特性を得ることができる。
尚、上述した各例では、記録層２が単層構造とした場合であるが、多層構造とすることもできるし、また、基板１の片面にのみ記録層が形成され片面側からレーザー光の照射によって記録再生を行うようにした場合であるが、基板１の両面もしくは対の基板１貼合わせ等によって両面からレーザー光照射による記録再生を行う光記録媒体構成とすることのできるなど、上述した例に限定されることなく、本発明構成において、種々の変形変更を行うことができる。
上述したように、本発明による光記録媒体は、波長３８０ｎｍ〜４５０ｎｍのレーザー光を用いる大容量光記録媒体において、λｍａｘ＞λであり、屈折率が記録前の屈折率より大に変化する構成、具体的には、記録前の屈折率が１．５以下である構成の光記録媒体とすることにより、記録前後の屈折率差Δｎが大で、変調度の高い、光記録媒体を構成することができたものである。
すなわち、本発明は、従来の記録前後でのｎが大から小に変化する記録方式とは異なり、記録前後でｎが小から大に変化する新規の記録方式を用いた、変調度の大きい追記型記録媒体を得たものである。
そして、その媒体構造は従来に比し、特段の複雑な構成に変更することなく、簡単な構造、したがって、量産性にすぐれた光記録媒体を得ることができるものである。
【図面の簡単な説明】
図１は、本発明による追記型光記録媒体の一例の概略断面図であり、図２は、本発明による追記型の光記録媒体の他の一例の概略断面図であり、図３は、本発明による追記型光記録媒体の更に他の一例の概略断面図であり、図４は、本発明による有機色素の光学定数（ｎ，ｋ）のスペクトル図であり、図５は、有機色素の厚さと屈折率と反射率との関係を示す図であり、図６Ａおよび図６Ｂは、本発明の説明に供する記録前および記録後のそれぞれの有機色素の光学定数（ｎ，ｋ）のスペクトル図であり、図７は、従来の光記録媒体の有機色素の光学定数（ｎ，ｋ）のスペクトル図である。
引用符号の説明
１ ・・・・・・ 基板
１Ｇ ・・・・・・ 凹部
２ ・・・・・・ 記録層
３ ・・・・・・ 誘電体層
４ ・・・・・・ 光透過性保護膜
５ ・・・・・・ 反射層
３１ ・・・・・・ 第１の誘電体層
３２ ・・・・・・ 第２の誘電体層TECHNICAL FIELD The present invention relates to an optical recording medium for recording and reading information with a laser beam, and more particularly to a write-once optical recording medium on which recording can be performed only once.
BACKGROUND ART Optical recording media capable of recording and reading information with laser light have been developed and put into practical use. In particular, a write-once optical recording medium that can store a huge amount of data such as a moving image and can be written only once has been attracting attention as an inexpensive medium.
As this write-once optical recording medium, a so-called CD-R, which is capable of recording and reproducing in the same format as a CD-ROM (Compact Disc-Read Only Memory), is widely used.
Further, as an optical recording medium having a larger recording capacity than a CD-ROM, a DVD-ROM (Digital Versatile Disc-ROM) has also been developed and put into practical use, and a write-once DVD-R capable of recording and reproducing in the same format as a DVD-ROM. Is also under development.
CD-R and DVD-R as write-once media are recorded and reproduced by laser beams having wavelengths of 780 nm and 650 nm, respectively.
In principle, the recording density of optical data increases in inverse proportion to the square of the optical wavelength. In order to perform recording at higher density, it is necessary to use a shorter laser wavelength.
In recent years, a laser light source having a wavelength of 380 to 450 nm using a GaN laser or a light source using an SHG (second harmonic generation) element has been developed, and an optical recording medium having a larger capacity has been actively developed.
At present, the numerical aperture of the objective lens is N.D. A. The recording and reproduction is performed by irradiating a blue-violet laser beam having a wavelength of 380 nm to 450 nm from the side of the thin light-transmitting protective film formed on the recording surface using an optical system having a value of 0.85, that is, an objective lens. The standardization of a large-capacity optical recording medium for performing the above has been studied.
In this large-capacity optical recording medium, there is an increasing need for a write-once, large-capacity optical recording medium that can be recorded only once, for example, for archival purposes.
By the way, in the optical recording medium, in order to increase the degree of signal modulation by recording, it is better that the variation Δn of the optical constant n (refractive index) of the recording film before and after recording is larger.
On the other hand, even in a write-once, large-capacity optical recording medium, it is considered desirable that the recording film is made of an organic dye, as in the case of CD-R, in order to simplify the production and reduce the cost.
As shown in FIG. 7, the wavelength dependence of the optical constants (n: refractive index, k: absorption coefficient) with respect to the wavelength of organic dyes used in conventional CD-R and DVD-R, for example, cyanine dyes, is shown in FIG. The refractive index n is lower on the shorter wavelength side than the absorption peak Pk of the absorption coefficient curve shown by the broken line curve, and the value of n becomes higher at the fall of the absorption on the longer wavelength side than the absorption peak.
In the case of CD-R and DVD-R, the wavelength used is longer than the peak Pk of the absorption coefficient curve and a region having a high refractive index n is used. The optical constant changes due to decomposition, and a large Δn, and therefore a recording modulation degree, is obtained by the decrease in the refractive index due to this recording.
However, it is difficult to apply such an organic dye to a recording film of the above-mentioned large-capacity optical recording medium using a laser beam having a short wavelength of 380 nm to 450 nm.
DISCLOSURE OF THE INVENTION The present invention provides a write-once, large-capacity optical recording medium having excellent recording / reproducing characteristics with laser light having a short wavelength of 380 nm to 450 nm.
In the optical recording medium according to the present invention, a film layer is formed on a substrate having a concave portion, for example, a continuous groove for tracking guide, or a concave portion formed by an intermittent groove, and the film layer contains at least an organic dye. A write-once optical recording medium on which a recording layer, a dielectric layer, and a light-transmitting protective film are formed and which can be recorded and reproduced by a laser beam having a wavelength of 380 to 450 nm, wherein an organic dye contained in the recording layer However, as shown in FIGS. 6A and 6B, the spectrum diagrams of the respective optical constants (n, k) before and after recording, before recording, the wavelength λ max showing the absorption peak, and recording and reproduction are performed. The relationship with the wavelength λ of the used laser light is such that λ max > λ.
Further, the organic dye contained in the recording layer is constituted by an organic dye having a value smaller than the refractive index after recording of 1.5 or less.
As the organic dye contained in the above-mentioned recording layer, the above-mentioned cyanine dye having the following values of less than 1.5 at a wavelength of 380 nm to 450 nm is used. Of the recording layer.
Embedded image
Figure 2002102598
In Chemical Formula 3, R 1 and R 2 each represent a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group, and they may be the same or different. Further, X - is, I -, ClO 4 -, BF 4 -, PF 6 - represents a.
Embedded image
Figure 2002102598
In Chemical Formula 4, R 3 and R 4 each represent a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group, and they may be the same or different. Further, X - is, I -, ClO 4 -, BF 4 -, PF 6 - represents a.
FIG. 4 shows a spectrum diagram of the optical constants of the organic dye having the structural formula (Chem. 3) above and in which R 1 and R 2 each have a hydrogen atom, and shows λ max > λ.
That is, in the present invention, as described above, in a large-capacity optical recording medium using a laser beam having a wavelength of 380 nm to 450 nm, λ max > λ, and the refractive index is significantly changed from the refractive index before recording. Specifically, it has been found that when an optical recording medium having a configuration in which the refractive index before recording is 1.5 or less is used, the refractive index difference Δn before and after recording becomes large.
BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the drawings.
FIG. 1 is a schematic sectional view showing an example of the structure of an optical recording medium according to the present invention. That is, in this example, for example, a recording layer 2 containing an organic dye and a dielectric layer are sequentially formed on a substrate 1 on which a continuous or intermittently formed concave portion 1G such as a tracking groove is formed on one main surface. A layer 3 and a light-transmitting protective film 4 are formed.
The substrate 1 is made of, for example, a thermoplastic resin, for example, a resin such as polycarbonate, polymethacrylate, or polyolefin. Is made.
Alternatively, the substrate 1 is formed by a 2P method (Photopolymerization method). In the 2P method, for example, an ultraviolet curable resin is applied on a substrate, a stamper is pressed on the resin layer, and then the resin layer is cured by ultraviolet light to form a concave portion 1G in the resin layer. This constitutes a substrate 1 having
The substrate 1 may be light-transmissive or non-light-transmissive.
Then, the recording layer 2 is formed on the surface of the substrate 1 on which the concave portion 1G is formed.
The recording layer 2 is composed of a layer containing an organic dye.
The recording layer may be formed by dissolving an organic dye in a solvent, applying the solution by spin coating, and drying the solution, or by spin coating the substrate 1 in a vacuum chamber of a vacuum deposition apparatus. A dye may be disposed, the organic dye may be sublimated by heating, and the organic dye may be deposited on the surface of the substrate 1 on which the concave portion 1G is formed, for example, by a vacuum deposition method.
Further, in the optical recording medium according to the present invention, for example, as shown in a schematic cross-sectional view of one example in FIG. 2, a reflective film 5 made of, for example, a metal layer can be formed on the substrate 1.
2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.
Further, in the optical recording medium according to the present invention, a first dielectric layer 31 is formed on a substrate 1 as shown in a schematic sectional view of one example in FIG. The second dielectric layer 32 and the light-transmitting protective film 4 may be formed. In this case, by selecting the thicknesses of the first and second dielectric layers 31 and 32, required reflection and enhancement effects can be obtained.
As the recording / reproducing laser light L for the optical recording medium according to the present invention, a blue-violet laser having a wavelength of 380 nm to 450 nm, in particular, a laser light L having a wavelength of 405 ± 5 nm is used. A. Is focused on the recording surface via, for example, a 0.8 ± 0.05 objective lens.
The recording layer 2 has a large degree of modulation at the time of recording, that is, a large change Δn of the optical constant n of the recording layer 2 before and after recording during recording.
In the present invention, to have a spectrum of the optical constants n and k of Figure 4 described above, the wavelength lambda max indicating the absorption peak, the relationship between the wavelength lambda of the used laser beam for recording and reproduction, lambda max > Λ, and is composed of an organic dye having a refractive index of less than 1.5 before recording.
Examples of the organic dye include cyanine-based dyes and phthalocyanine-based dyes according to the above-mentioned (Chemical Formula 1) (Chemical Formula 3) or (Chemical Formula 2) (Chemical Formula 4). In addition, the recording layer may contain a singlet oxygen inactivator (quencher) for improving weather resistance.
The dielectric layers 3, 31, and 32 are made of an oxide of a rare earth element such as Mg, Al, Si, Ti, Zn, Ga, Ge, Zr, In, Sn, Sb, Ba, Hf, Ta, Sc, or Y, or nitrided. , Sulfides, fluorides and other simple substances and mixtures thereof, in particular, silicon nitride, silicon oxide, magnesium fluoride, etc., and can be produced by reactive sputtering or vapor deposition.
Further, these dielectric layers 3, 31 and 32 may have a laminated structure of a plurality of material layers.
Further, the first and second dielectric layers 31 and 32 can have the same configuration or different configurations.
The light-transmitting protective film 4 is made of a light-transmitting thermoplastic resin or glass and a light-transmitting adhesive layer, and has a thickness of about 100 μm. The light-transmitting adhesive layer can be made of a light-transmitting double-sided pressure-sensitive adhesive sheet or a light-curing agent resin.
The reflection film 5 is formed of a simple substance or an alloy of Al, Au, and Ag by, for example, a sputtering method.
Next, embodiments of the optical recording medium according to the present invention will be described.
[Example 1]
In this example, a polycarbonate resin substrate 1 having a concave portion 1G, in this example, a tracking groove was prepared in the case of the structure shown in FIG.
The thickness of a cyanine-based dye (refractive index: 1.30 at a wavelength of 405 nm), which is an organic dye having the following structural formula, is 50 nm on the surface of the substrate 1 on which the concave portion 1G is formed by spin coating. Was formed. This organic dye has λ max = 570 nm.
Then, silicon nitride is sputtered to a thickness of 50 nm as a dielectric layer 3 on the recording layer 2, and a 100 μm thick polycarbonate of the same size as the substrate 1 is formed on the dielectric layer 3 as a light-transmitting protective film 4. The resin sheet was similarly bonded via a light-transmitting adhesive film.
Embedded image
Figure 2002102598
Laser light having an excitation wavelength of 405 nm was applied to the optical recording medium according to this example from the light-transmitting protective film 4 side, and recording was performed with a laser power of 6 mW. As a result, recording pits were formed in the recording layer 3. . The reflectance of the recorded pit portion was 8.7%, the reflectance of the unrecorded portion was 23.8%, and the degree of modulation was 63.4%.
FIG. 5 is a simulation mapping of the reflectance with respect to the refractive index n and the film thickness d of the recording layer 2, that is, the organic dye in this configuration.
[Example 2]
In this example, a substrate 1 having the concave portion 1G similar to that of Example 1 was prepared in the case of the structure shown in FIG.
In this example, a reflective film 5 of Ag was formed to a thickness of 12 nm on the surface of the substrate 1 having the concave portion 1G by a sputtering method.
A recording layer 3 of a cyanine dye (refractive index: 1.02 at a wavelength of 405 nm), which is an organic dye having the following structural formula, is formed to a thickness of 50 nm on the reflective film 5 by spin coating. did. This organic dye has λ max = 510 nm.
Further, silicon nitride is formed as a dielectric layer 3 to a thickness of 30 nm on the recording layer 2 by a sputtering method, and a light-transmitting protective film 4 similar to that of the first embodiment is formed on the dielectric layer 3 by a sputtering method. Pasted by technique.
Embedded image
Figure 2002102598
The optical recording medium according to Example 2 was irradiated with a laser having an excitation wavelength of 405 nm from the light-transmitting protective film side, and recording was performed with a laser power of 6 mW. As a result, recording pits were formed on the recording layer 2.
In this case, the reflectance of the pit portion was 19.9%, the reflectance of the unrecorded portion was 31.9%, and the degree of modulation was 37.6%.
[Example 3]
In this embodiment, the structure shown in FIG. 3 was adopted. In this case, the substrate 1 having the concave portion 1G having the same configuration as that of the first embodiment was prepared.
In this embodiment, first, silicon nitride was sputtered to a thickness of 50 nm as the first dielectric layer 31 on the surface of the substrate 1 on which the concave portion 1G was formed.
On this first dielectric layer 31, a cyanine dye (refractive index 1.34 at a wavelength of 405 nm) which is an organic dye having the following structural formula (Formula 7) is formed to a thickness of 50 nm by spin coating. Formed. The organic dye had a λ max = 580 nm.
Further, as the second dielectric layer 32, silicon nitride is formed to a thickness of 20 nm on the recording layer 2 by a sputtering method, and a light-transmitting layer having the same configuration as that of the first embodiment is formed on the second dielectric layer 32. The protective film 4 was formed.
Embedded image
Figure 2002102598
The optical recording medium according to this example was irradiated with a laser having an excitation wavelength of 405 nm from the light transmitting protective film 4 side, and recording was performed with a laser power of 6 mW. As a result, recording pits were formed in the recording film. The reflectance of the pit portion was 10.8%, the reflectance of the unrecorded portion was 21.6%, and the degree of modulation was 50%.
In the above-described embodiment, the case where the wavelength of the laser beam is 405 nm is used. In the case of the blue-violet laser having a wavelength of 380 nm to 450 nm, a high degree of modulation was obtained in almost the same manner.
As is clear from the above-described embodiments, the optical recording medium according to the present invention can obtain a high degree of modulation and thus a high reproduction output characteristic.
In each of the above-described examples, the recording layer 2 has a single-layer structure. However, the recording layer 2 may have a multi-layer structure. Alternatively, the recording layer may be formed only on one side of the substrate 1 and the laser beam may be applied from one side. This is the case where recording / reproduction is performed by irradiation. However, it is possible to adopt an optical recording medium configuration in which recording / reproduction is performed by laser light irradiation from both surfaces of the substrate 1 or by bonding both substrates 1 to each other. Without being limited to the examples, various modifications and changes can be made in the configuration of the present invention.
As described above, the optical recording medium according to the present invention has a configuration in which, in a large-capacity optical recording medium using laser light having a wavelength of 380 nm to 450 nm, λ max > λ, and the refractive index changes significantly from the refractive index before recording. Specifically, by using an optical recording medium having a configuration in which the refractive index before recording is 1.5 or less, an optical recording medium having a large refractive index difference Δn before and after recording and a high degree of modulation is formed. It was something that could be done.
That is, unlike the conventional recording method in which n changes from large to small before and after recording, the present invention uses a new recording method in which n changes from small to large before and after recording, and additionally records with a large modulation factor. A type recording medium was obtained.
Then, the optical recording medium can be obtained with a simple structure and, therefore, with excellent mass productivity without changing the medium structure to a particularly complicated structure.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an example of a write-once optical recording medium according to the present invention, FIG. 2 is a schematic sectional view of another example of a write-once optical recording medium according to the present invention, and FIG. FIG. 4 is a schematic cross-sectional view of still another example of the write-once optical recording medium according to the present invention. FIG. 4 is a spectrum diagram of optical constants (n, k) of the organic dye according to the present invention. FIG. 6A and FIG. 6B are spectral diagrams of optical constants (n, k) of organic dyes before and after recording for explanation of the present invention, respectively. FIG. 7 is a spectrum diagram of the optical constants (n, k) of organic dyes in a conventional optical recording medium.
Explanation of reference numerals 1 ... substrate 1G ... recess 2 ... recording layer 3 ... dielectric layer 4 ... light transmission protection Film 5 Reflective layer 31 First dielectric layer 32 Second dielectric layer

Claims (5)

凹部を有する基板上に、成膜層を有し、該成膜層が、少なくとも有機色素を含む記録層と、誘電体層と、光透過性の保護膜が形成され、波長が３８０〜４５０ｎｍのレーザー光により記録および再生可能な追記型光記録媒体にあって、
上記記録層に含まれる有機色素が、吸収ピークを示す波長λｍａｘと、上記記録および再生を行う使用レーザー光の波長λとの関係が、λｍａｘ＞λであることを特徴とする光記録媒体。A film formation layer is provided over a substrate having a concave portion, and the film formation layer is formed with a recording layer containing at least an organic dye, a dielectric layer, and a light-transmitting protective film, and has a wavelength of 380 to 450 nm. In a write-once optical recording medium that can be recorded and reproduced by laser light,
An optical recording medium characterized in that the relationship between the wavelength λ max at which the organic dye contained in the recording layer exhibits an absorption peak and the wavelength λ of the laser beam used for recording and reproduction is λ max > λ. . 上記有機色素が、シアニン系色素であることを特徴とする請求の範囲第１項に記載の光記録媒体。2. The optical recording medium according to claim 1, wherein the organic dye is a cyanine dye. 上記有機色素が、記録前において波長３８０ｎｍ〜４５０ｎｍにおいて、屈折率ｎが１．５より小なる特性を有する有機色素であることを特徴とする請求の範囲第１項に記載の光記録媒体。2. The optical recording medium according to claim 1, wherein the organic dye has a characteristic that the refractive index n is smaller than 1.5 at a wavelength of 380 nm to 450 nm before recording. 上記シアニン系色素が、下記（化１）であることを特徴とする請求の範囲第２項に記載の光記録媒体。
Figure 2002102598
（化１）中、Ｒ１およびＲ２は、それぞれ水素原子、アルキル基、置換アルキル基、アリール基、置換アリール基を表し、両者は同一であっても異なっていてもよい。また、Ｘ−は、Ｉ−、ＣｌＯ４ −、ＢＦ４ −、ＰＦ６ −を表す。3. The optical recording medium according to claim 2, wherein the cyanine dye is represented by the following formula (1).
Figure 2002102598
 In Chemical Formula 1 , R 1 and R 2 each represent a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group, and they may be the same or different. Further, X - is, I -, ClO 4 -, BF 4 -, PF 6 - represents a. 上記シアニン系色素が、下記（化２）であることを特徴とする請求項２に記載の光記録媒体。
Figure 2002102598
（化２）中、Ｒ３およびＲ４は、それぞれ水素原子、アルキル基、置換アルキル基、アリール基、置換アリール基を表し、両者は同一であっても異なっていてもよい。また、Ｘ−は、Ｉ−、ＣｌＯ４ −、ＢＦ４ −、ＰＦ６ −を表す。3. The optical recording medium according to claim 2, wherein the cyanine dye is represented by the following formula (2).
Figure 2002102598
 In Formula 2, R 3 and R 4 each represent a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group, and they may be the same or different. Further, X - is, I -, ClO 4 -, BF 4 -, PF 6 - represents a.
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