JP4053715B2 - Optical information recording medium - Google Patents
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- JP4053715B2 JP4053715B2 JP2000210235A JP2000210235A JP4053715B2 JP 4053715 B2 JP4053715 B2 JP 4053715B2 JP 2000210235 A JP2000210235 A JP 2000210235A JP 2000210235 A JP2000210235 A JP 2000210235A JP 4053715 B2 JP4053715 B2 JP 4053715B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、書き換え可能な高密度な光学的情報記録用媒体（以下、光記録媒体と称することもある。）に関する。特に、透過率が大きく、複数の光記録媒体が積層された多層化記録媒体への用途が期待される相変化型記録媒体に関する。
【０００２】
【従来の技術】
情報量の増大に伴い高密度でかつ高速に大量のデータの記録・再生ができる記録媒体が求められているが、光記録媒体はまさにこうした用途に応え得る記録媒体の一つとして期待されている。光記録媒体には一度だけ記録が可能な追記型と、記録・消去が何度でも繰り返し可能な書き換え型がある。書き換え型光記録媒体としては、光磁気効果を利用した光磁気記録媒体や、可逆的な結晶−アモルファス状態の変化に伴う反射率変化を利用した相変化型記録媒体があげられる。相変化型記録媒体では通常、誘電体層、記録層、誘電体層及び金属反射層をこの順に設けた層構造を有する。金属反射層は、熱拡散を促進して放熱効果を高め、アモルファスマークをより安定に形成するために用いられ、金属放熱層とも言われる。その為、金属放熱層は、アモルファス形成に必要な十分な放熱効果を得るために重要であり、通常、高反射率・高熱伝導率の金属を主成分とする材料から形成されている。又、記録層と金属放熱層の間に設けられる誘電体層は、記録時に記録層からの熱拡散を促進してアモルファスマーク形成に寄与し、消去時には蓄熱層として作用するので、放熱効果を制御するために重要である。
【０００３】
近年は、より膨大な情報量を高速度で記録・再生するためにさらなる高密度化を目指し記録媒体の多層化が検討されている。すなわち使用光学系の焦点深度より大きな距離を隔てて２以上の光記録媒体を積み重ねて作製することにより記録密度を大きくする試みである。ここで積層される個々の光記録媒体を、以下記録媒体ユニットと称することもある。この場合レーザー光の入射方向から見て最も遠い記録媒体ユニット以外の記録媒体ユニットでは、レーザー光を透過する事が必要になる。レーザー光透過のためには、光透過性が求められる記録媒体ユニットにおいては前記の金属放熱層は基本的には用いないことが好ましく、用いる場合には十分な光透過が得られる程度に薄くすることが必要となる。
【０００４】
しかしながら、金属放熱層がない場合または薄い場合には放熱効果が十分でなくなる。その為、光透過性が求められる記録媒体ユニットが相変化型記録媒体の場合、アモルファスを形成したい部分が溶融後冷却されるとき再結晶化してしまいアモルファスマークの形成が不十分になるという問題がある。記録層の組成等を変化させ結晶化速度を小さくし再結晶化を防ぐと、こんどは消去用レーザー照射部のアモルファスマークの結晶化が不十分になってしまう。すなわち書換可能記録媒体としての使用可能な結晶化速度の範囲が狭くなってしまう。
【０００５】
【発明が解決しようとする課題】
本発明は上記問題点を解決するためになされたもので、その目的は、記録媒体の多層化に用い得る記録媒体ユニットとして必要とされる十分な透過率と記録マーク形成に必要な十分な放熱効果の両立を達成することにある。放熱効果を大きくするには金属放熱層はある程度の膜厚を必要とするが、他方、膜が厚いと透過光量が小さくなるという問題点がある。金属放熱層の膜厚と透過光量の制御について検討した結果、金属放熱層上にさらに誘電体層と半透明反射層を設けることにより改善されることを見出し本発明を完成した。
【０００６】
【課題を解決するための手段】
本発明は、記録媒体の多層化に用い得る光学的情報記録用媒体、特に光透過性が求められる記録媒体ユニットとしての用途が期待される光学的情報記録用媒体を提供するものであり、その要旨は、少なくとも、第１誘電体層、記録層、第２誘電体層、金属を主成分とする半透明放熱層、第３誘電体層、及び半透明反射層をこの順に有し、且つ透過率が２０％以上であることを特徴とする光学的情報記録用媒体に存する。
本発明の他の要旨は、２以上の記録媒体が積層された光学的情報記録用媒体であって、少なくとも１つの記録媒体が、少なくとも、第１誘電体層、記録層、第２誘電体層、金属を主成分とする半透明放熱層、第３誘電体層、及び半透明反射層をこの順に有し、且つ透過率が２０％以上の光記録媒体であり、該光記録媒体に他の光記録媒体が積層されてなることを特徴とする光学的情報記録用媒体に存する。
【０００７】
本発明の好適な態様としては、上記光学的情報記録用媒体において、半透明放熱層が銀を主成分とする材料からなり、又その膜厚が２〜５０ｎｍであること、第２誘電体層の膜厚が３０ｎｍ以下であること、第３誘電体層の膜厚をｄ、屈折率をｎ、使用レーザー波長をλとしたとき［λ／（８ｎ）］＜ｄ＜［λ／（２ｎ）］であり、かつ、半透明反射層が金属を主成分とする材料であること、及び記録層が、相変化型記録層であることを挙げることが出来る。
更に、２以上の記録媒体が積層された光学的情報記録用媒体において、少なくとも、第１誘電体層、記録層、第２誘電体層、金属を主成分とする半透明放熱層、第３誘電体層、及び半透明反射層をこの順に有し、且つ透過率が２０％以上の光記録媒体が、入射光側に近接して設けられること、及び光記録媒体の半透明放熱層及び半透明反射層は、銀を主成分とする金属材料からなり、且つ半透明反射層の膜厚は半透明放熱層の膜厚以下とすることも好適な態様として挙げられる。
【０００８】
【発明の実施の形態】
本発明の光学的情報記録用媒体は、上記の如く、多層化記録媒体を構成する記録媒体ユニットとして用いられ、少なくとも、第１誘電体層、記録層、第２誘電体層、金属を主成分とする半透明放熱層、第３誘電体層、及び半透明反射層をこの順に有し、且つ透過率が２０％以上のものである。
一般的に、誘電体層、記録層、誘電体層及び金属放熱層から構成される相変化型記録媒体の金属放熱層は、高い放熱効果が必要とされているため、その効果を十分発揮するのにある程度の膜厚を有している。しかし、この様な有効な放熱効果を有する膜厚では、レーザー光に対する反射率が高く、記録媒体としての光透過率は小さくなってしまうので、大きな透過率が必要とされる多層化記録媒体における記録媒体ユニットとしては適用できず、記録媒体ユニットの場合には一般的には金属放熱層は設けることができないと考えられていた。
【０００９】
本発明の記録媒体は上記の層構成からなるが、金属放熱層の膜厚を適度に調整すると共に、さらに位相調整用誘電体層と半透明反射層を追加し多重反射させることにより、結果として反射率を小さく透過率を大きくすることができると共に高い放熱性も確保できるとの新規な知見に基づくのである。
なお、本明細書中において、膜が「半透明」であるとは、通常、光の透過率が３％以上である状態を示す。本発明の「半透明放熱層」及び「半透明反射層」での光透過率は、３％以上が好ましく、特に好ましくは５％以上、さらに好ましくは１０％以上、最も好ましくは１５％以上である。透過率は、使用する波長の光に対する複素屈折率と膜厚から計算することができる。本発明の「記録媒体」としての光透過率は、通常２０％以上、好ましくは３０％以上である。
【００１０】
本発明は上記の如く、多重反射を利用して反射光量を小さく透過光量を大きくするものであるが、このような場合、半透明放熱層や半透明反射層は光を吸収しやすくなる傾向にある。したがって半透明放熱層や半透明反射層を構成する材料としてはできるだけ光吸収の小さい材料を選ぶことが好ましい。
半透明放熱層は上記のようにある程度の透過光を有するが、記録媒体全体としての透過率を大きくするためには、比較的薄い膜厚で用いられる。
比較的薄い膜厚で有効な放熱効果を得るには、半透明放熱層として用いる材料は熱伝導度が十分に大きいものである必要がある。熱伝導度が大きい材料としてはＡｇ、Ａｕ、Ａｌ、Ｃｕ等を主成分とする金属が挙げられる。この中で熱伝導度が最も大きいものはＡｇであるため、熱伝導度の点ではＡｇが最も好ましい。
【００１１】
一方、光吸収を考慮すると上記の金属の中ではＡｇが最も好ましい。特に短波長ではＡｕ、Ｃｕ、ＡｌはＡｇと比較して光を吸収しやすくなるため、６５０ｎｍ以下の短波長レーザーを使用する場合にはＡｇを用いることが特に好ましい。さらにＡｇはスパッタリングターゲットとしての値段が比較的安く、放電が安定で成膜速度が速く、空気中で安定であるため生産性、経済性の点で好ましい。したがって総合的に見て半透明放熱層としてはＡｇが最も好ましい材料である。
更に、半透明放熱層を形成し得る材料主成分としての金属Ａｇ、Ａｌ、Ａｕ、Ｃｕは、不純物が混ざると熱伝導度が低下し光の吸収が大きくなる欠点を有してはいるが、安定性や膜表面平坦性が改善されることもあり、５ａｔ．％以下程度の不純物元素を含んでいてもよい。不純物元素としては、Ｃｒ、Ｍｏ、Ｍｇ、Ｚｒ、Ｖ、Ａｇ、Ｉｎ、Ｇａ、Ｚｎ、Ｓｎ、Ｓｉ、Ｃｕ、Ａｕ、Ａｌ、Ｐｄ、Ｐｔ、Ｐｂ、Ｃｒ、Ｃｏ、Ｏ、Ｓｅ、Ｖ、Ｎｂ、Ｔｉ、Ｏ、Ｎ等が挙げられる。
【００１２】
半透明放熱層の膜厚については、用いる材料や使用するレーザー波長により最適膜厚は変化するが、材料がＡｇでレーザー波長が４００〜６５０ｎｍ付近の場合は、膜厚は２〜５０ｎｍ程度が良く、より好ましくは５〜３０ｎｍである。２ｎｍより薄いと放熱効果が小さくなり、他方５０ｎｍより厚いと透過光量が小さくなるので好ましくない。Ａｇは短波長で複素屈折率の虚数部分の絶対値が小さくなるため同じ膜厚であっても短波長の方が透過率が大きくなる傾向にある。したがって十分な放熱効果と十分な透過率の両立は短波長の方が達成しやすい傾向にあり、本発明の効果は短波長でより有利になる。ただし相変化型光ディスクの記録層の信号強度は短波長で小さくなる傾向にある。
【００１３】
半透明放熱層と、第２または第３誘電体層との間でこれらの層を形成する材料により元素拡散等の相互作用が生ずる場合には、放熱層と誘電体層間の界面に拡散防止層等をさらに設けることが好ましい。拡散防止層材料としては、酸化ケイ素、窒化ケイ素、炭化ケイ素、酸化タンタル、酸化セリウム、酸化ランタン、酸化イットリウム、酸化アルミニウム、酸化銀等が好ましい材料として挙げられる。なお、ダイヤモンドは熱伝導度がさらに大きく透明になり得るため放熱層として好ましい材料であるが、製膜上に難点がある。
【００１４】
半透明反射層は、半透明放熱層に第３誘電体層を介して設けられており、記録層から距離がやや離れているため大きな放熱効果は期待できない。半透明反射層は光学的にはある程度の反射率が得られ光吸収の小さいものであることが重要である。半透明反射層が金属を主成分とする材料から形成される場合、この条件は上記半透明放熱層としての必要条件でもあるので、半透明放熱層として使用される好ましい材料を金属半透明反射層として使用可能である。前記のＡｇ、Ａｕ、Ａｌ、Ｃｕ等を主成分とする金属材料の中ではやはりＡｇが最も好ましい。
【００１５】
半透明反射層の膜厚については、用いる材料や使用するレーザー波長により最適膜厚は変化するが、材料がＡｇでレーザー波長が４００〜６５０ｎｍの場合は膜厚は５０ｎｍ程度以下が良い。５０ｎｍより厚いと透過光量が小さくなり、記録媒体全体としての透過率が低下し、特に多層記録媒体における記録媒体ユニットとしての使用に適しない場合がある。半透明反射層の最適膜厚は半透明放熱層膜厚等と関係しており、相互の材料や使用レーザーの波長によっても異なるが、半透明放熱層以下の膜厚、特に同等或いは多少薄い膜厚とした場合の多くが良好である。ただし、あまりに薄いのも記録媒体の特性や製造上の困難が伴うので、通常１ｎｍ以上である。
半透明反射層と第３誘電体層との間または半透明反射層とその上に必要に応じ設けられる紫外線硬化樹脂層もしくは接着剤層等との間に元素拡散等の相互作用が生ずる場合には、それぞれの層間の界面に拡散防止層等をさらに設けることが好ましい。拡散防止層の材料としては、上記半透明放熱層と誘電体層間に設けられる拡散防止層に使用される材料が使用できる。
【００１６】
半透明反射層としては、屈折率の異なる２種類以上の透明誘電体層を積層して作製する誘電体ミラーも使用可能である。誘電体ミラーは、半透明反射層が必要とするある程度の反射率が得られ吸収の小さいものという条件を満たす最も好ましい材料であろう。誘電体ミラーの例としてはＺｎＳ-ＳｉＯ2とＳｉＯ2の積層膜等が挙げられる。誘電体ミラーは、使用するレーザー波長をλ、誘電体屈折率をｎとし、各積層誘電体膜の膜厚をλ／（４ｎ）として積層することが好ましい。しかし、誘電体ミラーは金属半透明反射層と比較して、作製のための時間や作製装置の複雑さの点で不利であり、又保存安定性についても問題になる場合がある。
【００１７】
半透明放熱層と半透明反射層の間に設けられる誘電体層（第３誘電体層）は多重反射時の位相を調整する役割がある。誘電体層の材料は、屈折率、熱伝導率、化学的安定性、機械的強度、密着性、膜形成速度等に留意して決定される。一般的には透明性が高く高融点である金属や半導体の酸化物、硫化物、窒化物やＣａ、Ｍｇ、Ｌｉ等のフッ化物を用いることができる。これらの酸化物、硫化物、窒化物、フッ化物は必ずしも化学量論的組成をとる必要はなく、屈折率等の制御のために組成を制御したり、混合して用いることも有効である。より具体的にはＺｎＳや希土類硫化物と酸化物、窒化物、炭化物等の耐熱化合物の混合物が挙げられ、繰り返し記録特性を考慮すると誘電体混合物がよい。
【００１８】
具体的には、硫化亜鉛、硫化タンタル、希土類（Ｙ、Ｌａ、Ｃｅ、Ｎｄ等）硫化物のような硫化物を単独或いは混合物として２０ｍｏｌ％以上９０ｍｏｌ％以下含むものが好ましい。混合物の残部は、融点又は分解温度が１０００℃以上の耐熱性化合物であることが好ましい。融点又は分解温度が１０００℃以上の耐熱性化合物としては、Mg,Ca,Sr,Y,La,Ce,Ho,Er,Yb,Ti,Zr,Hf,V,Nb,Ta,Zn,Al,Si,Ge,Pb等の酸化物、窒化物、炭化物やＣａ、Ｍｇ、Ｌｉ等のフッ化物が挙げられる。これらの中、ＺｎＳとＳｉＯ2とからなる混合物が相変化型光記録媒体の誘電体層に用いられる場合が多い。又、誘電体層の膜密度はバルク状態の８０％以上であることが機械的強度の面から望ましい（Thin Solid Films、第２７８巻（１９９６年）、７４〜８１ページ）。
【００１９】
第３誘電体層の好ましい膜厚は、誘電体、半透明放熱層、半透明反射層等の材料や膜厚、使用レーザー波長等によって変化する。本発明記録媒体の層構成では半透明放熱層と半透明反射層の透過率と反射率の両方がある程度大きい場合の多重反射となるため現象は複雑ではあるが、半透明放熱層と半透明反射層が金属を主成分とする材料からなる場合は、第３誘電体層の膜厚については以下のように現象を簡略化して考えるとわかりやすい。即ち、半透明放熱層、第３誘電体層、半透明反射層の３層構成の透過率を大きくするには、この部分の反射率を小さくすることが有効と思われる。そのためには半透明放熱層で反射した光の位相と、半透明放熱層を透過して半透明反射層で反射され再度半透明放熱層を透過し戻ってきた光の位相を半波長分ずらして打ち消し合うようにすれば良いと思われる。つまり、第３誘電体層の膜厚をｄ、屈折率をｎ、使用レーザー波長をλとしたとき、ｄ＝λ／（４ｎ）付近に好適な範囲があると思われる。実際には多重反射の効果や半透明放熱層と半透明反射層の膜厚の効果等でこの値から多少ずれることがあるとしても、第３誘電体層の膜厚（ｄ）としては、［λ／(８ｎ)］＜ｄ＜［λ／(２ｎ)］が好ましい。
【００２０】
第２誘電体層は、記録層と半透明放熱層との間に設けられ、この誘電体層は記録層から半透明放熱層へ流れる熱を制御する役割を有する。第２誘電体層の膜厚は２〜３０ｎｍ程度が好ましく、より好ましくは５〜２０ｎｍである。３０ｎｍを超えて厚すぎると放熱効果が不十分になり、他方２ｎｍより薄すぎると記録感度が悪化したり、更には記録層や半透明放熱層との間で元素拡散等が起こってしまい好ましくない。第２誘電体層の材料としては半透明放熱層と半透明反射層の間に設けられる上記第３誘電体層に使用される材料と同様のものが使用可能である。
【００２１】
第１誘電体層は、第２誘電体層と共に記録層の上下を被覆するように設けられ、また、一般的には、第１誘電体層は記録層と基板の間に介在する。
第１誘電体層は熱による基板変形を抑制することが必要であり、その膜厚は３０ｎｍ以上が好ましい。３０ｎｍ未満では、繰り返しオーバーライト中に微視的な基板変形が蓄積され、再生光が散乱されてノイズ上昇が著しくなる。一方、誘電体層の厚みが５００ｎｍを超えると誘電体自体の内部応力や基板との弾性特性の差が顕著になって、クラックが発生しやすくなる。成膜時間の関係から２００ｎｍ程度が実質的に上限となるが、２００ｎｍより厚いと記録層面で見た溝形状が変わってしまう点でも好ましくない。より好ましくは１５０ｎｍ以下である。第１誘電体層の材料としては、半透明放熱層と半透明反射層の間に設けられる上記第３誘電体層に使用される材料と同様のものが使用可能である。
【００２２】
本発明の光記録媒体における記録層としては公知の相変化型光記録層が使用でき、例えばＧｅＳｂＴｅやＩｎＳｂＴｅ、ＡｇＳｂＴｅ、ＡｇＩｎＳｂＴｅといった系列化合物がオーバーライト可能な材料として選ばれる。これらの中、｛（Ｓｂ2Ｔｅ3）1-x（ＧｅＴｅ）x｝1-yＳｂy合金（ただし、０．２＜ｘ＜０．９、０≦ｙ＜０．１）、または（ＳｂxＴｅ1-x）yＭ1-y合金（ただし、０．６＜ｘ＜０．９、０．７＜ｙ＜１、ＭはＧｅ、Ａｇ、Ｉｎ、Ｇａ、Ｚｎ、Ｓｎ、Ｓｉ、Ｃｕ、Ａｕ、Ｐｄ、Ｐｔ、Ｐｂ、Ｃｒ、Ｃｏ、Ｏ、Ｓ、Ｓｅ、Ｖ、Ｎｂ、Ｔａより選ばれる少なくとも１種）を主成分とする薄膜は、結晶・非晶質いずれの状態も安定で、かつ、両状態間の高速の相転移が可能である。さらに、繰り返しオーバーライトを行った時に偏析が生じにくいといった利点があり、最も実用的な材料である。
記録層が（ＳｂxＴｅ1-x）yＭ1-y合金（ただし、０．６＜ｘ＜０．９、０．７＜ｙ＜１、ＭはＧｅ、Ａｇ、Ｉｎ、Ｇａ、Ｚｎ、Ｓｎ、Ｓｉ、Ｃｕ、Ａｕ、Ｐｄ、Ｐｔ、Ｐｂ、Ｃｒ、Ｃｏ、Ｏ、Ｓ、Ｓｅ、Ｖ、Ｎｂ、Ｔａより選ばれる少なくとも１種）を主成分とする相変化型媒体である場合、熱分布の違いがマーク形状に反映されやすいので、本発明では特に重要となる。
【００２３】
記録層が相変化型光記録層の場合、その厚みは３ｎｍから１５ｎｍの範囲が好ましい。記録層の厚みが３ｎｍより薄いと十分なコントラストが得られ難く、また初期結晶化が困難となりやすい。一方１５ｎｍを越すと十分な透過率が得にくくなるので好ましくない。より好ましくは５〜１０ｎｍである。
【００２４】
上記記録層は合金ターゲットを不活性ガス、特にＡｒガス中でスパッタして得られることが多い。なお、記録層および誘電体層の厚みは、上記機械的強度、信頼性の面からの制限の他に、多層構成に伴う干渉効果も考慮して、レーザー光の吸収効率が良く、記録信号の振幅すなわち記録状態と未記録状態のコントラストが大きくなるように選ばれる。
【００２５】
本発明の光記録媒体において、基板としては、ポリカーボネート、アクリル、ポリオレフィンなどの透明樹脂、あるいはガラスを用いることができる。これらの中、ポリカーボネートは実績もあり安価で経済性にも優れているので好ましい。基板の厚さは、通常０．０５〜５ｍｍ、好ましくは０．１〜２ｍｍである。
【００２６】
前述の記録層、第１〜３誘電体層、半透明放熱層、半透明反射層、拡散防止層等はスパッタリング法などによって形成される。これらの層は各層のスパッタリングターゲット、即ち記録膜用ターゲット、誘電体膜用ターゲット、必要な場合には反射層材料用ターゲット等を同一真空チャンバー内に設置したインライン装置で膜形成を行うことが各層間の酸化や汚染を防ぐ点で望ましい。また、生産性の面からも優れている。
【００２７】
本発明の光記録媒体の層構成は、例えば、基板側から記録・再生用レーザー光を入射して使用する場合は、基本的には基板上に第１誘電体層、記録層、第２誘電体層、半透明放熱層、第３誘電体層、半透明反射層をこの順に設け、必要に応じ保護コート層がその上に設けられる。一方、より高密度媒体を得るため対物レンズＮＡをより大きくした光学系に対しては膜面側からの入射が好ましくなることもあり、記録・再生用レーザー光が膜面から入射される場合は、上記構造とは逆の層構成となる。また、場合により基板の両側にこれら各層を構成しても、膜面(保護コート層）を内側にして両側に各層を有する光記録媒体とすることもできる。
更に、本発明の光記録媒体を、２以上の記録媒体が積層された多層化光記録媒体の記録媒体ユニットとして使用する場合には、例えば、入射光が基板側から行われる場合、上記の如き基板、第１誘電体層、記録層、第２誘電体層、半透明放熱層、第３誘電体層、半透明反射層をこの順に積層し、その上に接着層を介して他の光記録媒体ユニットが積層された構造を採ることが出来る。他の光記録媒体ユニットとしては、公知の層構成、例えば誘電体層、記録層、誘電体層及び金属反射層をこの順に設けた層構造を有する相変化型光記録媒体を用いることができる。但し、これらに限定されるものではなく、再生専用型、ライトワンス型、光磁気型等各種のものが使用できる。なお、上記接着層には、十分な光透過性と十分な厚さ（通常１０μｍ以上）が求められる。
【００２８】
【実施例】
以下、本発明を実施例により更に詳細に説明するが、本発明はその要旨を超えない限り、これらの実施例により制限されるものではない。
なお、実施例（光記録媒体の作製）を行うに先立ち、最終目的とする信号強度が大きく、且つ透過率が大きい記録媒体の取得のために、以下のシミュレーションを行った。
【００２９】
最適膜厚の算出
後述の条件１〜５に示す５種類の膜構成について光学計算をおこなった。
計算では、結晶反射率、非晶質反射率、結晶透過率、非晶質透過率を各層膜厚を変化させて計算し、(結晶反射率)−(非晶質反射率)＞０．１を満たし、且つ結晶透過率が最大になるような膜厚を求めた（ここで“結晶反射率”とは相変化記録層が結晶状態であるときの媒体の反射率という意味である。）。
【００３０】
条件１〜５は以下のとおりである。
条件１：
基板、誘電体層１、記録層、誘電体層２、紫外線硬化樹脂層を順に設けた場合を想定した。計算した膜厚は、誘電体１は０〜１６０ｎｍで５ｎｍ刻み、記録層は３〜１５ｎｍで２ｎｍ刻み、誘電体２は０〜１６０ｎｍで５ｎｍ刻みとした。誘電体膜厚に関しては、光学的な性質は周期的に変化するが計算条件においてほぼ１周期に相当する膜厚範囲に設定した。記録層の計算膜厚範囲は前述の好ましい膜厚範囲付近とした。
【００３１】
条件２：
基板、誘電体層１、記録層、誘電体層２、半透明放熱層、紫外線硬化樹脂層を順に設けた場合を想定した。計算した膜厚は、誘電体１は０〜１６０ｎｍで５ｎｍ刻み、記録層は３〜１５ｎｍで２ｎｍ刻み、誘電体２は５〜２０ｎｍで５ｎｍ刻み、半透明放熱層は２０ｎｍとした。半透明放熱層についてはＡｇ膜を想定し、放熱効果がある程度得られそうな２０ｎｍに固定し後述の条件４の場合と透過率を比較した。誘電体２は放熱効果が得られるようにある程度薄い膜厚にする必要があるため、計算範囲は５〜３０ｎｍとした。
【００３２】
条件３：
半透明放熱層の膜厚を３０ｎｍとしたこと以外は条件２と同様の計算条件とした。後述の条件５の場合と透過率を比較した。
【００３３】
条件４：
基板、誘電体層１、記録層、誘電体層２、半透明放熱層、誘電体層３、半透明反射層、紫外線硬化樹脂層を順に設けた場合を想定した。計算した膜厚は、誘電体１は０〜１６０ｎｍで５ｎｍ刻み、記録層は３〜１５ｎｍで２ｎｍ刻み、誘電体２は５〜３０ｎｍで５ｎｍ刻み、半透明放熱層は２０ｎｍ、誘電体層３は０〜１６０ｎｍで５ｎｍ刻み、半透明反射層は０〜５０ｎｍで５ｎｍ刻みとした。
【００３４】
条件５：
半透明放熱層の膜厚を３０ｎｍとしたこと以外は条件４と同様の計算条件とした。
なお、計算に用いた各層の複素屈折率はエリプソメータを用い６５０ｎｍの波長で実測した値を用いた。測定には誘電体層として（ＺｎＳ）80（ＳｉＯ2）20、記録層としてＧｅ5Ｓｂ71Ｔｅ24、半透明放熱層と半透明反射層としてＡｇを用いた。結果は誘電体層は２．１−０ｉ、記録層はアモルファス状態で３．８−２．８ｉ、結晶状態で２．６−４．７ｉ、放熱層、反射層は０．１−４．１ｉであった。基板と紫外線硬化樹脂層は１．５−０ｉとした。
【００３５】
計算結果は表１に示すとおり、条件４、５での透過率は放熱層を設けない条件１よりは小さいものの条件２，３での透過率より大きく、本発明の構成が光学的に有効であることがわかる。
【００３６】
【表１】
実施例
実際に光記録媒体（以下、光ディスクと記す）を作製し、半透明放熱層を設けた構成が半透明放熱層を設けない構成より放熱効果に優れていることを以下のようにして示した。
厚さ０．６ｍｍのポリカーボネート基板上にＺｎＳ-ＳｉＯ2第１誘電体層（５５ｎｍ）、Ｇｅ5Ｓｂ71Ｔｅ24記録層（１０ｎｍ）、ＺｎＳ-ＳｉＯ2第２誘電体層（５ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）、Ａｇ半透明放熱層（２０ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）、ＺｎＳ-ＳｉＯ2第３誘電体層（９０ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）、Ａｇ半透明反射層（１５ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）をスパッタリング法により作製し、この上にさらに紫外線硬化樹脂からなる保護コートをおこなった（実施例）。基板溝幅は０．３５ｕｍ、溝深さは３３ｎｍ、溝ピッチ０．７４ｕｍである。なお、記録層膜厚は、実験上、初期結晶化を容易にするために膜厚（１０ｎｍ）とした。
【００３８】
この光ディスクを初期結晶化した後、波長６３５ｎｍ、ＮＡ０．６の光学系を有する光ディスク評価装置を用いて記録特性を測定した。記録条件は、線速度４ｍ／ｓ、消去パワーＰｅと記録パワーＰｗの比Ｐｅ／Ｐｗ＝０．５、クロック周期を３８．２ｎｓとし、８−１６変調ランダム信号をパルストレイン法を用い溝内に記録した。１０回のダイレクトオーバーライト（ＤＯＷ）後のEdge to clockジッタのパワー依存性の測定結果を図１に示す。ジッタ値はクロック周期で規格化した値を用いた。
【００３９】
この光ディスクの透過率は鏡面部で記録層が結晶状態のとき３０％、記録層がアモルファス状態のとき３７％であった。透過率の算出は、１２０ｎｍ厚のＡｇ膜からの反射光量を０．６ｍｍのポリカーボネート基板を通して測定したときの値をＲ１とし、前記光ディスクを通して測定したときの値をＲ２としたとき、透過率＝（Ｒ２／Ｒ１）1/2の式から求めた。この結果は、記録層が計算値（５ｎｍ）より厚いこともあり、光ディスクの透過率は必ずしも十分に大きいとは言えないが、２層化記録媒体の可能性を示すことは明らかである。
【００４０】
比較例１
厚さ０．６ｍｍのポリカーボネート基板上にＺｎＳ-ＳｉＯ2誘電体層（１０５ｎｍ）、Ｇｅ5Ｓｂ71Ｔｅ24記録層（１０ｎｍ）、ＺｎＳ-ＳｉＯ2誘電体層（１１５ｎｍ）をスパッタリング法により作製し、この上にさらに紫外線硬化樹脂からなる保護コートをおこなった（比較例１）。この光ディスクにつき上記と全く同じ記録特性の評価をおこなった。その結果、８〜１４ｍＷの記録パワーではジッタの測定が可能であるような記録マークは形成されなかった。この光ディスクはアモルファスマークが形成された場合は十分な信号強度がでるように設計されたものであり、記録マークができない理由は放熱が不十分であるため、溶融後その部分が再結晶化しているためと思われる。
以上より実施例での放熱効果は比較例１と比較して十分に大きいことがわかる。透過率をさらに大きくするため記録層を薄くした場合には、逃がすべき熱量が小さくなるためさらに効率よい放熱効果が得られると考えられる。
【００４１】
比較例２
厚さ０．６ｍｍのポリカーボネート基板上にＺｎＳ-ＳｉＯ2誘電体層（５５ｎｍ）、Ｇｅ5Ｓｂ71Ｔｅ24記録層（１０ｎｍ）、ＺｎＳ-ＳｉＯ2誘電体層（５ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）、Ａｇ半透明放熱層（２０ｎｍ）、ＳｉＯ2拡散防止層（２ｎｍ）をスパッタリング法により作製し、この上にさらに紫外線硬化樹脂からなる保護コートをおこなった（比較例２）。この光ディスクの透過率は鏡面部で記録層が結晶状態のとき１６％、記録層がアモルファス状態のとき２０％であり、実施例の透過率より小さかった。
【００４２】
【発明の効果】
本発明の層構成からなる光学的情報記録用媒体においては、信号強度、放熱効果、透過率のすべてを十分に大きくすることが可能になり、特により高密度化のための多層化記録媒体への応用が期待される。
【図面の簡単な説明】
【図１】 図１は実施例のEdge to clockジッタのパワー依存性の測定結果を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rewritable high-density optical information recording medium (hereinafter sometimes referred to as an optical recording medium). In particular, the present invention relates to a phase change recording medium that has a high transmittance and is expected to be used for a multilayered recording medium in which a plurality of optical recording media are stacked.
[0002]
[Prior art]
As the amount of information increases, a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed is required. However, an optical recording medium is expected as one of recording media that can respond to such applications. . There are two types of optical recording media: a write-once type that can be recorded only once, and a rewritable type that can be repeatedly recorded and erased. Examples of the rewritable optical recording medium include a magneto-optical recording medium using a magneto-optical effect and a phase change recording medium using a change in reflectivity accompanying a reversible change in crystal-amorphous state. A phase change recording medium usually has a layer structure in which a dielectric layer, a recording layer, a dielectric layer, and a metal reflective layer are provided in this order. The metal reflection layer is used to promote thermal diffusion to enhance the heat dissipation effect and form the amorphous mark more stably, and is also referred to as a metal heat dissipation layer. For this reason, the metal heat dissipation layer is important for obtaining a sufficient heat dissipation effect necessary for forming an amorphous layer, and is usually formed of a material mainly composed of a metal having high reflectivity and high thermal conductivity. In addition, the dielectric layer provided between the recording layer and the metal heat dissipation layer promotes thermal diffusion from the recording layer during recording, contributes to the formation of amorphous marks, and acts as a heat storage layer during erasure, thus controlling the heat dissipation effect. Is important to do.
[0003]
In recent years, in order to record / reproduce a huge amount of information at a high speed, a multilayer recording medium has been studied with the aim of further increasing the density. That is, it is an attempt to increase the recording density by stacking two or more optical recording media at a distance larger than the focal depth of the optical system used. The individual optical recording media stacked here may be hereinafter referred to as a recording medium unit. In this case, the recording medium unit other than the recording medium unit farthest from the incident direction of the laser light needs to transmit the laser light. In order to transmit laser light, it is preferable not to use the metal heat-dissipating layer basically in a recording medium unit that requires light transmission, and if used, it should be thin enough to obtain sufficient light transmission. It will be necessary.
[0004]
However, when there is no metal heat dissipation layer or when it is thin, the heat dissipation effect is not sufficient. Therefore, when the recording medium unit that requires light transmission is a phase change type recording medium, there is a problem that the amorphous mark is not sufficiently formed because the portion where the amorphous is to be formed is recrystallized when cooled after being melted. is there. If the composition or the like of the recording layer is changed to reduce the crystallization rate and prevent recrystallization, the amorphous mark in the erasing laser irradiation portion will be insufficiently crystallized. That is, the range of crystallization speeds usable as a rewritable recording medium is narrowed.
[0005]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and its object is to provide sufficient transmittance required as a recording medium unit that can be used for multilayer recording media and sufficient heat dissipation necessary for forming recording marks. The goal is to achieve both effects. In order to increase the heat dissipation effect, the metal heat dissipation layer needs to have a certain thickness. On the other hand, if the film is thick, there is a problem that the amount of transmitted light decreases. As a result of investigating the control of the film thickness of the metal heat dissipation layer and the amount of transmitted light, the present invention has been found out that it can be improved by further providing a dielectric layer and a translucent reflective layer on the metal heat dissipation layer.
[0006]
[Means for Solving the Problems]
The present invention provides an optical information recording medium that can be used for multilayer recording media, and in particular, an optical information recording medium that is expected to be used as a recording medium unit that requires light transmission. The gist is that at least a first dielectric layer, a recording layer, a second dielectric layer, a semi-transparent heat dissipation layer containing metal as a main component, a third dielectric layer, and a semi-transparent reflective layer in this order.And the transmittance is 20% or more.The present invention resides in an optical information recording medium.
Another gist of the present invention is an optical information recording medium in which two or more recording media are laminated, wherein at least one recording medium includes at least a first dielectric layer, a recording layer, and a second dielectric layer. An optical recording medium having a translucent heat dissipation layer mainly composed of metal, a third dielectric layer, and a translucent reflective layer in this order and having a transmittance of 20% or more. An optical information recording medium is characterized in that optical recording media are laminated.
[0007]
As a preferred aspect of the present invention, in the optical information recording medium, the translucent heat dissipation layer is made of a material mainly composed of silver, and the thickness thereof is 2 to 50 nm. The second dielectric layer [Λ / (8n)] <d <[λ / (2n) where d is the thickness of the third dielectric layer, n is the refractive index, and λ is the laser wavelength used. And the semi-transparent reflective layer is a metal-based material, and the recording layer is a phase change recording layer.
Furthermore, in an optical information recording medium in which two or more recording media are laminated,It has at least a first dielectric layer, a recording layer, a second dielectric layer, a translucent heat dissipation layer mainly composed of metal, a third dielectric layer, and a translucent reflective layer in this order, and a transmittance of 20 % Of optical recording mediaProvided close to the incident light side; andOptical recording mediaThe semi-transparent heat radiation layer and the semi-transparent reflection layer are made of a metal material containing silver as a main component, and the thickness of the semi-transparent reflection layer may be less than the film thickness of the semi-transparent heat radiation layer.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The optical information recording medium of the present invention is as described above.Used as a recording medium unit constituting a multilayer recording medium,At least a first dielectric layer, a recording layer, a second dielectric layer, a translucent heat dissipation layer mainly composed of metal, a third dielectric layer, and a translucent reflective layer are provided in this order.And a transmittance of 20% or moreIt is.
Generally, a metal heat dissipation layer of a phase change recording medium composed of a dielectric layer, a recording layer, a dielectric layer, and a metal heat dissipation layer is required to have a high heat dissipation effect, so that the effect is sufficiently exhibited. However, it has a certain film thickness. However, in such a film thickness having an effective heat dissipation effect, the reflectivity with respect to the laser beam is high, and the light transmittance as a recording medium becomes small. Therefore, in a multilayered recording medium that requires a large transmittance. It was not applicable as a recording medium unit, and in the case of a recording medium unit, it was generally considered that a metal heat dissipation layer could not be provided.
[0009]
The recording medium of the present invention has the above-described layer structure, and as a result, the thickness of the metal heat dissipation layer is appropriately adjusted, and a phase adjusting dielectric layer and a semitransparent reflective layer are further added to cause multiple reflection. This is based on a novel finding that the reflectance can be reduced and the transmittance can be increased and high heat dissipation can be secured.
In the present specification, the phrase “semi-transparent” means that the light transmittance is usually 3% or more. The light transmittance in the “semi-transparent heat radiation layer” and “semi-transparent reflective layer” of the present invention is preferably 3% or more, particularly preferably 5% or more, more preferably 10% or more, and most preferably 15% or more. is there. The transmittance can be calculated from the complex refractive index and the film thickness for the light of the wavelength used. The light transmittance of the “recording medium” of the present invention is usually 20% or more, preferably 30% or more.
[0010]
As described above, the present invention uses multiple reflections to reduce the amount of reflected light and increase the amount of transmitted light. In such a case, the translucent heat radiation layer and the translucent reflective layer tend to absorb light easily. is there. Therefore, it is preferable to select a material having as little light absorption as possible as the material constituting the translucent heat radiation layer and the translucent reflection layer.
The translucent heat dissipation layer has a certain amount of transmitted light as described above, but is used with a relatively thin film thickness in order to increase the transmittance of the entire recording medium.
In order to obtain an effective heat dissipation effect with a relatively thin film thickness, the material used as the translucent heat dissipation layer needs to have a sufficiently high thermal conductivity. Examples of the material having high thermal conductivity include metals having Ag, Au, Al, Cu, or the like as a main component. Among these, Ag has the highest thermal conductivity, and therefore Ag is most preferable in terms of thermal conductivity.
[0011]
On the other hand, considering light absorption, Ag is most preferable among the above metals. In particular, Au, Cu, and Al are more likely to absorb light than Ag at short wavelengths, and therefore Ag is particularly preferable when a short wavelength laser of 650 nm or less is used. Further, Ag is preferable in terms of productivity and economy because it is relatively inexpensive as a sputtering target, has a stable discharge, has a high deposition rate, and is stable in the air. Therefore, Ag is the most preferable material for the semitransparent heat dissipation layer from a comprehensive viewpoint.
Furthermore, the metals Ag, Al, Au, Cu as the main component of the material that can form the translucent heat dissipation layer have the disadvantage that the thermal conductivity decreases and the light absorption increases when impurities are mixed. Stability and film surface flatness may be improved. % Of impurity elements may be included. As impurity elements, Cr, Mo, Mg, Zr, V, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Al, Pd, Pt, Pb, Cr, Co, O, Se, V, Nb , Ti, O, N and the like.
[0012]
As for the film thickness of the translucent heat dissipation layer, the optimum film thickness varies depending on the material used and the laser wavelength used. However, when the material is Ag and the laser wavelength is around 400 to 650 nm, the film thickness should be about 2 to 50 nm. More preferably, it is 5-30 nm. If it is thinner than 2 nm, the heat dissipation effect is reduced, and if it is thicker than 50 nm, the amount of transmitted light is reduced. Since the absolute value of the imaginary part of the complex refractive index is small at a short wavelength, Ag tends to have a larger transmittance at the short wavelength even when the film thickness is the same. Therefore, the compatibility between the sufficient heat radiation effect and the sufficient transmittance tends to be achieved at the short wavelength, and the effect of the present invention becomes more advantageous at the short wavelength. However, the signal intensity of the recording layer of the phase change optical disc tends to decrease at a short wavelength.
[0013]
When an interaction such as element diffusion occurs between the translucent heat dissipation layer and the second or third dielectric layer, the diffusion preventing layer is formed at the interface between the heat dissipation layer and the dielectric layer. Etc. are preferably further provided. Examples of the diffusion preventing layer material include silicon oxide, silicon nitride, silicon carbide, tantalum oxide, cerium oxide, lanthanum oxide, yttrium oxide, aluminum oxide, silver oxide, and the like. Diamond is a preferable material for the heat-dissipating layer because of its higher thermal conductivity and can be transparent, but there are difficulties in film formation.
[0014]
The translucent reflective layer is provided on the translucent heat dissipation layer via the third dielectric layer, and since the distance is slightly away from the recording layer, a large heat dissipation effect cannot be expected. It is important that the translucent reflective layer has a certain optical reflectivity and a small light absorption. When the translucent reflective layer is formed from a material containing a metal as a main component, this condition is also a necessary condition for the translucent heat radiating layer. Can be used as Of the above-mentioned metal materials mainly composed of Ag, Au, Al, Cu, etc., Ag is the most preferable.
[0015]
Regarding the film thickness of the translucent reflective layer, the optimum film thickness varies depending on the material used and the laser wavelength used. However, when the material is Ag and the laser wavelength is 400 to 650 nm, the film thickness is preferably about 50 nm or less. If it is thicker than 50 nm, the amount of transmitted light is reduced, the transmittance of the entire recording medium is lowered, and it may not be suitable for use as a recording medium unit particularly in a multilayer recording medium. The optimum film thickness of the semi-transparent reflective layer is related to the film thickness of the semi-transparent heat radiation layer, etc., and varies depending on the material and the wavelength of the laser used. Most of the thicknesses are good. However, it is usually 1 nm or more because it is too thin due to the characteristics of the recording medium and manufacturing difficulties.
When interaction such as element diffusion occurs between the translucent reflective layer and the third dielectric layer or between the translucent reflective layer and the UV curable resin layer or adhesive layer provided on the translucent reflective layer as necessary. It is preferable to further provide a diffusion preventing layer or the like at the interface between the respective layers. As a material of the diffusion preventing layer, a material used for the diffusion preventing layer provided between the translucent heat radiation layer and the dielectric layer can be used.
[0016]
As the translucent reflective layer, a dielectric mirror produced by laminating two or more types of transparent dielectric layers having different refractive indexes can also be used. The dielectric mirror may be the most preferable material that satisfies the condition that a certain degree of reflectance required by the translucent reflective layer is obtained and the absorption is small. Examples of dielectric mirrors are ZnS-SiO2And SiO2And the like. The dielectric mirror is preferably laminated so that the laser wavelength used is λ, the dielectric refractive index is n, and the thickness of each laminated dielectric film is λ / (4n). However, the dielectric mirror is disadvantageous in terms of time for production and complexity of the production apparatus as compared with the metal translucent reflective layer, and may cause a problem in storage stability.
[0017]
A dielectric layer (third dielectric layer) provided between the translucent heat radiation layer and the translucent reflective layer has a role of adjusting the phase during multiple reflection. The material of the dielectric layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, film formation speed, and the like. In general, oxides, sulfides, nitrides, and fluorides such as Ca, Mg, and Li, which are highly transparent and have a high melting point, can be used. These oxides, sulfides, nitrides, and fluorides do not necessarily have a stoichiometric composition, and it is also effective to use a composition or a mixture for controlling the refractive index and the like. More specifically, a mixture of heat-resistant compounds such as ZnS and rare earth sulfides and oxides, nitrides, and carbides can be mentioned. A dielectric mixture is preferable in consideration of repeated recording characteristics.
[0018]
Specifically, those containing 20 mol% or more and 90 mol% or less of sulfides such as zinc sulfide, tantalum sulfide, rare earth (Y, La, Ce, Nd, etc.) sulfides alone or as a mixture are preferable. The balance of the mixture is preferably a heat-resistant compound having a melting point or decomposition temperature of 1000 ° C. or higher. The heat-resistant compound having a melting point or decomposition temperature of 1000 ° C. or more includes Mg, Ca, Sr, Y, La, Ce, Ho, Er, Yb, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Si. , Oxides such as Ge and Pb, nitrides, carbides, and fluorides such as Ca, Mg, and Li. Among these, ZnS and SiO2In many cases, a mixture consisting of is used as a dielectric layer of a phase change optical recording medium. The film density of the dielectric layer is preferably 80% or more of the bulk state from the viewpoint of mechanical strength (Thin Solid Films, Vol. 278 (1996), pages 74 to 81).
[0019]
The preferred film thickness of the third dielectric layer varies depending on the material, film thickness, laser wavelength used, etc., such as the dielectric, translucent heat radiation layer, and translucent reflective layer. In the layer structure of the recording medium of the present invention, the phenomenon is complicated because multiple reflection occurs when both the transmissivity and reflectivity of the translucent heat dissipation layer and the translucent reflection layer are large to some extent, but the phenomenon is complicated, but the translucent heat dissipation layer and the translucent reflection When the layer is made of a material whose main component is a metal, the film thickness of the third dielectric layer can be easily understood by simplifying the phenomenon as follows. That is, in order to increase the transmittance of the three-layer structure of the semitransparent heat dissipation layer, the third dielectric layer, and the semitransparent reflection layer, it is considered effective to decrease the reflectance of this portion. For that purpose, the phase of the light reflected by the translucent heat dissipation layer and the light transmitted through the translucent heat dissipation layer, reflected by the translucent reflection layer, and transmitted again through the translucent heat dissipation layer.LightIt is considered that the phase of each other should be offset by half a wavelength so as to cancel each other. That is, when the film thickness of the third dielectric layer is d, the refractive index is n, and the laser wavelength used is λ, there seems to be a suitable range near d = λ / (4n). Actually, even if there is a slight deviation from this value due to the effects of multiple reflections or the film thickness of the semi-transparent heat radiation layer and the semi-transparent reflection layer, the film thickness (d) of the third dielectric layer is [ λ / (8n)] <d <[λ / (2n)] is preferable.
[0020]
The second dielectric layer is provided between the recording layer and the translucent heat dissipation layer, and this dielectric layer has a role of controlling heat flowing from the recording layer to the translucent heat dissipation layer. The film thickness of the second dielectric layer is preferably about 2 to 30 nm, more preferably 5 to 20 nm. If the thickness exceeds 30 nm, the heat dissipation effect becomes insufficient. On the other hand, if the thickness is less than 2 nm, the recording sensitivity deteriorates, and further element diffusion occurs between the recording layer and the translucent heat dissipation layer. . As the material for the second dielectric layer, the same materials as those used for the third dielectric layer provided between the translucent heat dissipation layer and the translucent reflective layer can be used.
[0021]
The first dielectric layer is provided so as to cover the upper and lower sides of the recording layer together with the second dielectric layer. In general, the first dielectric layer is interposed between the recording layer and the substrate.
The first dielectric layer needs to suppress substrate deformation due to heat, and the film thickness is preferably 30 nm or more. If it is less than 30 nm, microscopic substrate deformation is accumulated during repeated overwriting, and reproduction light is scattered, resulting in a significant increase in noise. On the other hand, if the thickness of the dielectric layer exceeds 500 nm, the internal stress of the dielectric itself and the difference in elastic properties with the substrate become significant, and cracks are likely to occur. Although the upper limit is substantially about 200 nm from the relationship with the film formation time, if it is thicker than 200 nm, the groove shape seen on the recording layer surface is not preferable. More preferably, it is 150 nm or less. As the material for the first dielectric layer, the same materials as those used for the third dielectric layer provided between the translucent heat radiation layer and the translucent reflective layer can be used.
[0022]
As the recording layer in the optical recording medium of the present invention, a known phase change type optical recording layer can be used. For example, a series compound such as GeSbTe, InSbTe, AgSbTe, or AgInSbTe is selected as a material that can be overwritten. Among these, {(Sb2TeThree)1-x(GeTe)x}1-ySbyAlloy (where 0.2 <x <0.9, 0 ≦ y <0.1), or (SbxTe1-x)yM1-yAlloy (however, 0.6 <x <0.9, 0.7 <y <1, M is Ge, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Pd, Pt, Pb, Cr, A thin film composed mainly of at least one selected from Co, O, S, Se, V, Nb, and Ta) is stable in both crystalline and amorphous states, and has a high-speed phase transition between the two states. Is possible. Furthermore, there is an advantage that segregation hardly occurs when repeated overwriting, and it is the most practical material.
The recording layer is (SbxTe1-x)yM1-yAlloy (however, 0.6 <x <0.9, 0.7 <y <1, M is Ge, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Pd, Pt, Pb, Cr, In the case of a phase change medium mainly composed of at least one selected from Co, O, S, Se, V, Nb, and Ta), the difference in heat distribution is easily reflected in the mark shape. It becomes important.
[0023]
When the recording layer is a phase change optical recording layer, the thickness is preferably in the range of 3 nm to 15 nm. When the thickness of the recording layer is less than 3 nm, it is difficult to obtain sufficient contrast, and initial crystallization tends to be difficult. On the other hand, if it exceeds 15 nm, it is difficult to obtain a sufficient transmittance. More preferably, it is 5-10 nm.
[0024]
The recording layer is often obtained by sputtering an alloy target in an inert gas, particularly Ar gas. Note that the thickness of the recording layer and the dielectric layer has good laser light absorption efficiency in consideration of the interference effect associated with the multilayer structure in addition to the limitations on the mechanical strength and reliability, and the recording signal The amplitude, that is, the contrast between the recorded state and the unrecorded state is selected to be large.
[0025]
In the optical recording medium of the present invention, as the substrate, a transparent resin such as polycarbonate, acrylic or polyolefin, or glass can be used. Among these, polycarbonate is preferable because it has a track record and is inexpensive and excellent in economic efficiency. The thickness of the substrate is usually 0.05 to 5 mm, preferably 0.1 to 2 mm.
[0026]
The recording layer, the first to third dielectric layers, the translucent heat dissipation layer, the translucent reflection layer, the diffusion prevention layer, and the like are formed by a sputtering method or the like. Each of these layers can be formed by an in-line apparatus in which a sputtering target of each layer, that is, a recording film target, a dielectric film target, and, if necessary, a reflective layer material target is installed in the same vacuum chamber. This is desirable in terms of preventing interlayer oxidation and contamination. It is also excellent in terms of productivity.
[0027]
The layer structure of the optical recording medium of the present invention is basically such that when a recording / reproducing laser beam is incident from the substrate side, the first dielectric layer, the recording layer, the second dielectric layer are basically formed on the substrate. A body layer, a translucent heat dissipation layer, a third dielectric layer, and a translucent reflective layer are provided in this order, and a protective coating layer is provided thereon as necessary. On the other hand, for an optical system having a larger objective lens NA in order to obtain a higher density medium, incidence from the film surface side may be preferable. When recording / reproducing laser light is incident from the film surface, The layer structure is the reverse of the above structure. Moreover, even if each of these layers is formed on both sides of the substrate, an optical recording medium having each layer on both sides with the film surface (protective coat layer) inside can be obtained.
Further, when the optical recording medium of the present invention is used as a recording medium unit of a multilayer optical recording medium in which two or more recording media are laminated, for example, when incident light is performed from the substrate side, A substrate, a first dielectric layer, a recording layer, a second dielectric layer, a translucent heat dissipation layer, a third dielectric layer, and a translucent reflective layer are laminated in this order, and another optical recording is performed thereon via an adhesive layer. A structure in which medium units are stacked can be adopted. As another optical recording medium unit, a known layer configuration, for example, a phase change optical recording medium having a layer structure in which a dielectric layer, a recording layer, a dielectric layer, and a metal reflection layer are provided in this order can be used. However, the present invention is not limited to these, and various types such as a reproduction-only type, a write-once type, and a magneto-optical type can be used. In addition, sufficient adhesiveness and sufficient thickness (usually 10 μm or more) are required for the adhesive layer.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not restrict | limited by these Examples, unless the summary is exceeded.
Prior to performing the example (production of an optical recording medium), the following simulation was performed in order to obtain a recording medium having a large final signal strength and high transmittance.
[0029]
Calculation of optimum film thickness
Optical calculation was performed for five types of film configurations shown in Conditions 1 to 5 described later.
In the calculation, the crystal reflectance, the amorphous reflectance, the crystal transmittance, and the amorphous transmittance are calculated by changing the film thickness of each layer, and (crystal reflectance) − (amorphous reflectance)> 0.1 And a film thickness that maximizes the crystal transmittance (herein, “crystal reflectivity” means the reflectivity of the medium when the phase change recording layer is in the crystalline state).
[0030]
Conditions 1 to 5 are as follows.
Condition 1:
It was assumed that the substrate, the dielectric layer 1, the recording layer, the dielectric layer 2, and the ultraviolet curable resin layer were provided in this order. The calculated thicknesses of the dielectric 1 were 0 to 160 nm in increments of 5 nm, the recording layer was 3 to 15 nm in increments of 2 nm, and the dielectric 2 was 0 to 160 nm in increments of 5 nm. Regarding the dielectric film thickness, the optical properties change periodically, but the film thickness range corresponding to approximately one period is set in the calculation conditions. The calculated film thickness range of the recording layer was set in the vicinity of the aforementioned preferable film thickness range.
[0031]
Condition 2:
The case where the board | substrate, the dielectric material layer 1, the recording layer, the dielectric material layer 2, the translucent heat dissipation layer, and the ultraviolet curable resin layer was provided in order was assumed. The calculated thicknesses of dielectric 1 were 0 to 160 nm in increments of 5 nm, the recording layer was 3 to 15 nm in increments of 2 nm, dielectric 2 was 5 to 20 nm in increments of 5 nm, and the translucent heat dissipation layer was 20 nm. The translucent heat radiation layer was assumed to be an Ag film, fixed to 20 nm where a heat radiation effect could be obtained to some extent, and the transmittance was compared with the case of Condition 4 described later. Since the dielectric 2 needs to be thin to some extent so as to obtain a heat dissipation effect, the calculation range is set to 5 to 30 nm.
[0032]
Condition 3:
The calculation conditions were the same as those in Condition 2 except that the thickness of the semitransparent heat radiation layer was 30 nm. The transmittance was compared with the
[0033]
Condition 4:
A case was assumed in which a substrate, a dielectric layer 1, a recording layer, a dielectric layer 2, a translucent heat dissipation layer, a dielectric layer 3, a translucent reflective layer, and an ultraviolet curable resin layer were provided in this order. The calculated thicknesses of the dielectric 1 are 0 to 160 nm in increments of 5 nm, the recording layer is 3 to 15 nm in increments of 2 nm, the dielectric 2 is in increments of 5 to 30 nm and 5 nm, the translucent heat dissipation layer is 20 nm, and the dielectric layer 3 is The semi-transparent reflective layer was set at 0 to 50 nm in increments of 5 nm at 0 to 160 nm.
[0034]
Condition 5:
The calculation conditions were the same as those in Condition 4 except that the thickness of the translucent heat radiation layer was 30 nm.
The complex refractive index of each layer used for the calculation was a value measured at a wavelength of 650 nm using an ellipsometer. (ZnS) as dielectric layer for measurement80(SiO2)20, Ge as the recording layerFiveSb71Tetwenty fourAg was used as the semitransparent heat dissipation layer and the semitransparent reflective layer. As a result, the dielectric layer was 2.1-0i, the recording layer was 3.8-2.8i in the amorphous state, 2.6-4.7i in the crystalline state, and the heat dissipation layer and the reflective layer were 0.1-4.1i. Met. The substrate and the ultraviolet curable resin layer were 1.5-0i.
[0035]
As shown in Table 1, the transmittance under
[0036]
[Table 1]
Example
It was shown as follows that an optical recording medium (hereinafter referred to as an optical disk) was actually produced, and the configuration provided with the semitransparent heat dissipation layer was superior in heat dissipation effect to the configuration provided with no translucent heat dissipation layer.
ZnS-SiO on a polycarbonate substrate with a thickness of 0.6 mm2First dielectric layer (55 nm), GeFiveSb71Tetwenty fourRecording layer (10 nm), ZnS-SiO2Second dielectric layer (5 nm), SiO2Diffusion prevention layer (2 nm), Ag translucent heat dissipation layer (20 nm), SiO2Diffusion prevention layer (2nm), ZnS-SiO2Third dielectric layer (90 nm), SiO2Diffusion prevention layer (2 nm), Ag translucent reflection layer (15 nm), SiO2An anti-diffusion layer (2 nm) was produced by a sputtering method, and a protective coat made of an ultraviolet curable resin was further formed thereon (Example). The substrate groove width is 0.35 μm, the groove depth is 33 nm, and the groove pitch is 0.74 μm. The film thickness of the recording layer was experimentally set to a film thickness (10 nm) to facilitate initial crystallization.
[0038]
After the initial crystallization of this optical disk, the recording characteristics were measured using an optical disk evaluation apparatus having an optical system with a wavelength of 635 nm and NA of 0.6. The recording conditions were a linear velocity of 4 m / s, a ratio Pe / Pw = 0.5 of erase power Pe and recording power Pw, a clock period of 38.2 ns, and an 8-16 modulated random signal in the groove using the pulse train method. Recorded. FIG. 1 shows the measurement result of the power dependency of edge to clock jitter after 10 direct overwrites (DOW). As the jitter value, a value normalized by the clock cycle was used.
[0039]
The transmittance of this optical disk was 30% when the recording layer was in the mirror state and the recording layer was 37% when the recording layer was in the amorphous state. The transmittance is calculated when R1 is a value when the amount of reflected light from a 120 nm thick Ag film is measured through a 0.6 mm polycarbonate substrate, and R2 is a value when measured through the optical disk. R2 / R1)1/2It was obtained from the formula of This result shows that the recording layer may be thicker than the calculated value (5 nm), and the transmittance of the optical disc is not necessarily sufficiently high, but it clearly shows the possibility of a two-layer recording medium.
[0040]
Comparative Example 1
ZnS-SiO on a polycarbonate substrate with a thickness of 0.6 mm2Dielectric layer (105 nm), GeFiveSb71Tetwenty fourRecording layer (10 nm), ZnS-SiO2A dielectric layer (115 nm) was produced by a sputtering method, and a protective coat made of an ultraviolet curable resin was further formed thereon (Comparative Example 1). This optical disk was evaluated for the same recording characteristics as described above. As a result, a recording mark capable of measuring jitter was not formed with a recording power of 8 to 14 mW. This optical disk is designed so that sufficient signal strength is obtained when an amorphous mark is formed. The reason why a recording mark cannot be made is that heat radiation is insufficient, and that part is recrystallized after melting. It seems to be because.
From the above, it can be seen that the heat dissipation effect in the example is sufficiently larger than that in Comparative Example 1. If the recording layer is made thinner in order to further increase the transmittance, it is considered that a more efficient heat dissipation effect can be obtained because the amount of heat to be released becomes smaller.
[0041]
Comparative Example 2
ZnS-SiO on a polycarbonate substrate with a thickness of 0.6 mm2Dielectric layer (55 nm), GeFiveSb71Tetwenty fourRecording layer (10 nm), ZnS-SiO2Dielectric layer (5 nm), SiO2Diffusion prevention layer (2 nm), Ag translucent heat dissipation layer (20 nm), SiO2A diffusion prevention layer (2 nm) was produced by a sputtering method, and a protective coating made of an ultraviolet curable resin was further formed thereon (Comparative Example 2). The transmittance of this optical disk was 16% when the recording layer was in the mirror state and the recording layer was 20% when the recording layer was in an amorphous state.
[0042]
【The invention's effect】
In the optical information recording medium having the layer structure of the present invention, it is possible to sufficiently increase all of the signal intensity, the heat dissipation effect, and the transmittance, and in particular, to a multilayered recording medium for higher density. Is expected to be applied.
[Brief description of the drawings]
FIG. 1 shows a measurement result of power dependency of edge to clock jitter in an embodiment.
Claims (9)
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| JP2000210235A JP4053715B2 (en) | 2000-07-11 | 2000-07-11 | Optical information recording medium |
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| JP2000210235A JP4053715B2 (en) | 2000-07-11 | 2000-07-11 | Optical information recording medium |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| TW200306559A (en) * | 2002-04-22 | 2003-11-16 | Tdk Corp | Optical recording medium |
| WO2006098503A1 (en) | 2005-03-17 | 2006-09-21 | Ricoh Company, Ltd. | Two-layered optical recording medium |
| JP4415271B2 (en) | 2005-08-30 | 2010-02-17 | 日本電気株式会社 | Optical recording medium |
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