JP3903811B2 - Optical information recording medium and recording erasing method - Google Patents

Description

【００７３】
得られたディスクのうち比較例１、２のディスクは、ディスク作製直後の反射率がそれぞれ１４％、８％で、線速度１．２〜２４ｍ／ｓの範囲でパワー１２ｍＷ以下のいかなるＤＣレ−ザ−光照射によっても反射率は変化しなかった。従って、少なくともこの線速度範囲においては、相変化型光ディスクの初期結晶化ができず、相変化型光ディスクとしての使用はできなかった。これは、準安定結晶相が安定に存在できず、常に安定結晶相となっているためと考えられる。
【００７４】
比較例３、４のディスクは、ディスク作製直後の反射率がそれぞれ４％、４％で、線速度１．２〜２４ｍ／ｓの範囲で１２ｍＷ以下のいかなるＤＣレ−ザ−光照射によっても均一な反射率上昇は見られなかった。従って少なくともこの線速度範囲においては、相変化型光ディスクの初期結晶化が良好に行えず、相変化型光ディスクとしての使用は困難であった。これは、アモルファス相から準安定結晶相への相変化速度が遅いため均一な準安定相が得られず、ＤＣレーザー光照射によっても、記録層がほとんどアモルファス相のまま変化しないためと考えられる。
【００７５】
次に実施例１、２、参考例１のディスクについて、初期結晶化した後、レ−ザ−波長７８０ｎｍ、ＮＡ０．５のピックアップを有するディスク評価装置を用い、以下の手順で案内溝内に記録・消去を行ったのち再生してディスク特性を評価した。
まず、線速度２４ｍ／ｓ、基準クロック周期Ｔ＝１１．６ｎｓ、Ｐｗ＝２１ｍＷ、Ｐｅ＝１０．５ｍＷ、Ｐｂ＝０．８ｍＷで、ＥＦＭランダム信号を図１に示すレーザー波形を用いて記録した。
【００７６】
すなわち、長さｎＴ（Ｔは基準クロック周期で、ｎは３〜１１の自然数）のマーク（アモルファス相）を形成する際には、時間ｎＴの期間を上記数式（３）のように分割し、記録パワーＰｗを持つ記録パルス、バイアスパワーＰｂを持つオフパルスを交互に照射し、一部消去パワーＰｅを照射した。マーク間（準安定結晶相）を形成する期間は消去パワーＰｅを持つ消去光を照射した。
【００７７】
詳しくは、各マーク形成時はＰｗとＰｂのパルス列を次のように照射した（Ｔは基準クロック周期）。
【００７８】
【表２】
３Ｔマーク部：１．５ＴのＰｗ、１．２ＴのＰｂ
４Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
５Ｔマーク部：１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
６Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
７Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
８Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
９Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
１０Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
１１Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
以上のように記録したＥＦＭランダム信号を、線速度２．４ｍ／ｓで再生し、マーク間部とマーク部の反射率を測定した。結果を初期反射率として表−１に示す。なお、マーク間部は未記録部・消去部に対応し、マーク部は記録部に対応する。
【００７９】
その後１０５℃の環境にディスクを３時間保ち（加速試験）、以上のように記録しておいた信号のマーク間部とマーク部の反射率を再度測定した。結果を加速試験後反射率として表−１に示す。
実施例１では、マーク間部の反射率は、初期及び加速試験後においてほとんど同等であり、加速試験によるマーク間部の反射率低下はほとんど見られなかった。実施例２では、加速試験後によるマーク間部の反射率低下は約７％であった。これは、実施例２の記録層組成は、実施例１の記録層組成に比べてＡｕの含有量が少ないため、準安定相の保存安定性が多少低下していることによるものと考えられる。しかし、上記反射率の低下のレベルは、実使用レベルから考えれば問題とはならないものである。参考例１では、加速試験によるマーク間部の反射率低下は約９％であった。これは、実施例１、２の記録層組成と比較して、実施例３の記録層組成においては、Ａｕ含有量が少ないため、準安定相の保存安定性が低下したことによるものと考えられる。したがって、準安定相の保存安定性について、優れているものから順に挙げれば実施例１、実施例２、参考例１となる。
【００８０】
次に、実施例１、２のディスクにおける、記録層の相状態についてより詳細に考察する。
これらのディスクでは、初期の記録消去において、２４ｍ／ｓの線速度で消去パワー１０．５ｍＷの光照射によりマーク部は消去可能である一方、マーク部の形成は少なくとも１７ｍＷ以上の記録パワーが必要であった。つまり、初期のマーク部をＬ相、マーク間部をＭ相とすると、Ｌ相からＭ相への相変化がＭ相からＬ相への相変化よりも低温で起こり得るのでＬ相よりＭ相の方が安定である。
【００８１】
実施例１のディスクにおいては、記録層のマーク部は、初期においては線速度２．４ｍ／ｓ、パワー５ｍＷのＤＣレ−ザ−光照射で消去可能であったのに対し、加速試験後には、上記と同条件でＤＣレーザー光照射を行っても、記録層のマーク部によっては消去されない部分があった。これは、初期のマーク部をＬ相、マーク間部をＭ相とすると、信号記録時に形成されたマークのＬ相の一部が、１０５℃での加速試験後に、Ｌ相と同程度の反射率を持ち、Ｌ相でもＭ相でもないＮ相へ相変化したことを意味する。
【００８２】
実際、線速度２．４ｍ／ｓで、記録層を溶融させる程は大きくないと考えられるパワー５ｍＷのＤＣレ−ザ−光を該ディスクに１０００回照射したのち、このディスクに再生光を照射し、オシロスコ−プで再生信号波形を観察したところ、上記の消去されない部分（Ｎ相）がマーク間部（Ｍ相）にも広がる傾向にあった。これはマーク間部のＭ相が少しずつより安定なＮ相に相変化していることを示している。
【００８３】
Ｎ相は、線速度２．４ｍ／ｓで、記録層を溶融させると考えられるパワー１０ｍＷのＤＣレ−ザ−光照射により未記録状態の反射率に戻った。Ｍ相に相変化したと考えられる。しかし６ｍＷ以下のＤＣレーザー光照射ではＮ相はＭ相に相変化しなかった。
これらのことより、Ｍ相からＮ相への相変化がＮ相からＭ相への相変化よりも低温で起こり得るのでＭ相よりＮ相の方が安定である。
【００８４】
実施例２のディスクでも、線速度２．４ｍ／ｓで５ｍＷのＤＣレーザー光を１０００回照射することによりマーク間部反射率が低下した。これは、Ｍ相がＮ相に相変化したためと考えられる。この部分は記録層が溶融すると思われる１０ｍＷのＤＣレ−ザ−光照射により未記録状態の反射率に戻ったが、６ｍＷ以下のＤＣレーザー光照射では戻らなかった。つまり、実施例２のディスクにおいても、Ｍ相からＮ相への相変化が、Ｎ相からＭ相への相変化よりも低温で起こり得るのでＭ相よりＮ相の方が安定であることがわかる。
【００８５】
以上のことから、実施例１、２において、Ｌ相よりＭ相の方が安定であり、Ｍ相よりもＮ相の方が安定である。従って、Ｌ相はＡ相に該当し、アモルファス相であると、Ｍ相はＢ相に該当し、準安定結晶相であると、Ｎ相はＣ相に該当し、安定結晶相であると考えられる。また、初期の消去記録においては、Ｂ相（Ｍ相、準安定結晶相）を未記録・消去状態とし、Ａ相（Ｌ相、アモルファス相）を記録状態としている。そして、実施例１、２のディスクにおいては、Ａ相とＢ相との間での相変化を利用しているため、２４ｍ／ｓという高線速においても記録消去ができるのである。
【００８６】
なお、実施例１、２のディスクの記録層の相状態の詳細な考察を行うための実験において、線速度をマーク記録時の２４ｍ／ｓから２．４ｍ／ｓに低下させた理由は、レーザー照射時の冷却速度を遅くし温度が上昇している時間を長くすることにより、最も安定なＮ相への相変化を観察しやすくするためである。
【００９０】
つぎにＡｕが含まれないＧｅＳｂ系に関して同様の測定を試みた。結晶化速度の点で上記記録条件に適した組成と思われるＧｅ₁₆Ｓｂ₈₄（比較例５）とＧｅ₁₇Ｓｂ₈₃（比較例６）を試みた。しかしながら、比較例５、６のいずれのディスクも初期結晶化後にオシロスコープで再生波形を観察すると、結晶相（未記録状態）の反射率レベルが一定ではなく幅を持って太い線となっていた。これは、初期結晶化後において記録層が均一に結晶化されていないためと考えられる。また、これらディスクのジッタの値は２５ｎｓ以下にはならず信号振幅も小さく、とても使用可能なディスクとはいえない。
【００９１】
以上より、（Ａｕ_xＳｂ_1-x）_1-yＧｅ_yの組成において、０．２≦ｘ≦０．４、０＜ｙ≦０．３とすることにより、記録信号保存安定性に特に優れる光学的情報記録用媒体を得ることができる。
（実施例５〜９、比較例７、８）
溝幅０．５μｍ、溝深さ４０ｎｍ、溝ピッチ１．６μｍの案内溝を有する直径１２０ｍｍ、１．２ｍｍ厚のディスク状ポリカ−ボネ−ト基板上に、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（１００ｎｍ）、Ａｕ−Ｇｅ−Ｓｂ−Ｔｅ記録層（１８ｎｍ）、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（４０ｎｍ）、Ａｌ_99.5Ｔａ_0.5合金反射層（２００ｎｍ）をスパッタリング法により成膜し、相変化型光ディスクを作製した。
【００９２】
なお、記録層組成は表−２に示す７種類とした。またこれらの組成を（（Ａｕ_xＳｂ_1-x）_1-yＧｅ_y）_1-zＴｅ_zで表記した場合のｘ、ｙ、ｚの値も併せて表−２に記載した。
【００９３】
【表４】

【００９４】
得られたディスクのうち、比較例７のディスクは、ディスク作製直後の反射率は１４％で、線速度１．２〜２４ｍ／ｓの範囲でパワー１２ｍＷ以下のいかなるＤＣレ−ザ−光照射によっても反射率は変化しなかった。従って、少なくともこの線速度範囲においては、相変化型光ディスクの初期結晶化ができず、相変化型光ディスクとしての使用はできなかった。これは、準安定結晶相が安定に存在できず、常に記録層が安定結晶相となっているためと考えられる。
【００９５】
比較例８のディスクは、ディスク作製直後の反射率は４％で、線速度１．２〜２４ｍ／ｓの範囲で１２ｍＷ以下のいかなるＤＣレ−ザ−光照射によっても均一な反射率上昇は見られなかった。従って、少なくともこの線速度範囲においては、相変化型光ディスクの初期結晶化ができず、相変化型光ディスクとしての使用はできなかった。これは、アモルファス相から準安定結晶相への相変化速度が遅いため、均一な準安定相が得られず、記録層がほとんどアモルファス相のままであるためと考えられる。
【００９６】
これに対し、実施例５〜９の各ディスクは、線速度１．２〜２４ｍ／ｓの範囲で１２ｍＷ以下のＤＣレ−ザ−光照射によって均一な反射率上昇が観察された。初期結晶化した実施例５〜９の各ディスクについて、レ−ザ−波長７８０ｎｍ、ＮＡ０．５のピックアップを有するディスク評価装置を用い、以下の手順で案内溝内に記録・消去を行ったのち再生してディスク特性を評価した。
【００９７】
まず、線速度２４ｍ／ｓ、基準クロック周期Ｔ＝１１．６ｎｓ、Ｐｗ＝２１ｍＷ、Ｐｅ＝１０．５ｍＷ、Ｐｂ＝０．８ｍＷで、ＥＦＭランダム信号を図１に示すレーザー波形を用いて記録した。
図１において横軸は時間、縦軸はレーザーパワーであり、記録パワーＰｗ、消去パワーＰｅ、バイアスパワーＰｂの３種類のパワーを使用している。図１（ａ）は長さ３Ｔのマークを記録する場合のレーザー波形を表し、図１（ｂ）、（ｃ）、（ｄ）、（ｅ）、（ｆ）、（ｇ）、（ｈ）、（ｉ）はそれぞれ長さ４Ｔ、５Ｔ、６Ｔ、７Ｔ、８Ｔ、９Ｔ、１０Ｔ、１１Ｔのマークを記録する場合のレーザー波形を表す。
【００９８】
すなわち、長さｎＴ（Ｔは基準クロック周期で、ｎは３〜１１の自然数）のマーク（アモルファス相）を形成する際には、時間ｎＴの期間を上記数式（３）のように分割し、記録パワーＰｗを持つ記録パルス、バイアスパワーＰｂを持つオフパルスを交互に照射し、一部消去パワーＰｅを照射した。マーク間（準安定結晶相）を形成する期間は消去パワーＰｅを持つ消去光を照射した。
【００９９】
詳しくは、各マーク形成時はＰｗとＰｂのパルス列を次のように照射した（Ｔは基準クロック周期）。
【０１００】
【表５】
３Ｔマーク：１．５ＴのＰｗ、１．２ＴのＰｂ
４Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
５Ｔマーク：１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ６Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
７Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
８Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
９Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
１０Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
１１Ｔマーク：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
以上のように記録したＥＦＭランダム信号を、線速度２．４ｍ／ｓで再生し、マーク間部とマーク部の反射率を測定した。結果を初期反射率として表−２に示す。なお、マーク間部は未記録部・消去部に対応し、マーク部は記録部に対応する。
【０１０１】
実施例５〜９の初期状態では、マーク間部（未記録部・消去部）は準安定相であり、マーク部（記録部）はアモルファス相であると推定される。また、一般的にアモルファス相は１種しかなく他は結晶相であることから、準安定相は準安定結晶相であると推定される。
その後１０５℃の環境にディスクを３時間保ち（加速試験）、以上のように記録しておいた信号のマーク間部とマーク部の反射率を再度測定した。結果を加速試験後反射率として表−２に示す。
【０１０２】
実施例５、６のディスクでは、初期と加速試験後でマーク間部の反射率低下はほとんど見られず、相変化型光ディスクとして良好な性能を示していることがわかる。また、実施例７のディスクは、加速試験後におけるマーク間部の反射率の低下率は、約７％であった。これは、実施例５、６のディスクに比べて、実施例７の光ディスクの記録層中に含有されるＡｕ量が少ないため準安定相の保存安定性が多少低下しているためと考えられる。しかし、上記反射率の低下のレベルは、実使用レベルから考えれば問題とはならないものである。
【０１０３】
実施例８、９のディスクでは、マーク間部反射率の低下は見られず良好な保存安定性を示す。一方、マーク部においては、上記加速試験によりその反射率が若干上昇する結果となった。これは、加速試験により、アモルファスマークが未記録状態の準安定相に相変化するためと考えられる。
次に、実施例５〜７での記録層の相状態についてより詳細に考察する。
【０１０４】
これらのディスクでは初期の記録消去において、２４ｍ／ｓの線速度で消去パワー１０．５ｍＷの光照射によりマーク部は消去可能である一方、マーク部の形成は少なくとも１７ｍＷ以上の記録パワーが必要であった。つまり、初期のマーク部をＬ相、マーク間部をＭ相とすると、Ｌ相からＭ相への相変化がＭ相からＬ相への相変化よりも低温で起こり得るのでＬ相よりＭ相の方が安定である。
【０１０５】
実施例５、６では、マーク部は初期には線速度２．４ｍ／ｓ、パワー５ｍＷのＤＣレ−ザ−光照射で消去可能であったのに対し、加速試験後にはマーク部に同条件で消去されない部分が生じていた。つまり、初期のマーク部をＬ相、マーク間部をＭ相とすると、信号記録時に形成されたマークのＬ相の一部が、１０５℃での加速試験後に、Ｌ相と同程度の反射率を持ち、Ｌ相でもＭ相でもないＮ相へ相変化した。
【０１０６】
実際、線速度２．４ｍ／ｓで、照射により記録層が溶融しないと思われるパワー５ｍＷのＤＣレ−ザ−光を該ディスクに１０００回照射した後、ディスクに再生光を照射してオシロスコ−プで再生信号波形を観察したところ、上記の消去されない部分（Ｎ相）がマーク間部（Ｍ相）にも広がる傾向にあった。これはマーク間部のＭ相が少しずつより安定なＮ相に相変化していることを示している。
【０１０７】
Ｎ相となる領域は、実施例５より実施例６のディスクでより多く観察された。また、Ｎ相は、線速度２．４ｍ／ｓで、記録層が溶融すると思われるパワー１０ｍＷのＤＣレ−ザ−光照射により未記録状態の反射率に戻った。Ｎ相がＭ相に相変化したと考えられる。しかし６ｍＷ以下のＤＣレーザー光照射ではＮ相はＭ相に相変化しなかった。
【０１０８】
これらのことより、Ｍ相からＮ相への相変化がＮ相からＭ相への相変化よりも低温で起こり得るのでＭ相よりＮ相の方が安定である。
実施例７のディスクでも、線速度２．４ｍ／ｓで５ｍＷのＤＣレーザー光を１０００回照射することによりマーク間部反射率が低下した。Ｍ相がＮ相に相変化したと考えられる。この部分は、記録層が溶融すると思われる１０ｍＷのＤＣレ−ザ−光照射により未記録状態の反射率に戻ったが、６ｍＷ以下のＤＣレーザー光照射では未記録状態の反射率に戻らなかった。Ｍ相からＮ相への相変化がＮ相からＭ相への相変化よりも低温で起こり得るのでＭ相よりＮ相の方が安定である。
【０１０９】
以上のことから、実施例５〜７の各ディスクにおいて、Ｌ相はアモルファス相、Ｍ相は準安定相（準安定結晶相）、Ｎ相は安定相（安定結晶相）であると考えられる。
なお、実施例５〜７のディスクの記録層の相状態の詳細な考察を行うための実験において、線速度をマーク記録時の２４ｍ／ｓから２．４ｍ／ｓに低下させた理由は、レーザー照射時の冷却速度を遅くし温度が上昇している時間を長くすることにより、最も安定なＮ相への相変化を観察しやすくするためである。
（参考例２、実施例１１〜１３、比較例９〜１１）
溝幅０．５μｍ、溝深さ４０ｎｍ、溝ピッチ１．６μｍの案内溝を有する直径１２０ｍｍ、１．２ｍｍ厚のディスク状ポリカ−ボネ−ト基板上に、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（８０ｎｍ）、Ａｕ−Ｇｅ−Ｓｂ−Ｓｎ記録層（１５ｎｍ）、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（３０ｎｍ）、Ａｌ_99.5Ｔａ_0.5合金反射層（２００ｎｍ）をスパッタリング法により成膜し、相変化型光ディスクを作製した。
【０１１０】
なお、記録層組成は表−３に示した。またこれらの組成を（（Ａｕ_xＳｂ_1-x）_1-yＧｅ_y）_1-zＳｎ_zで表記した場合のｘ、ｙ、ｚの値も併せて表−３に記載した。
これらのディスクは、レ−ザ−波長７８０ｎｍ、ＮＡ０．５のピックアップを有するディスク評価装置を用い、２．４ｍ／ｓ、１０ｍＷのＤＣレーザー光を照射することにより初期結晶化を試みた。
【０１１１】
【表６】

【０１１２】
得られたディスクのうち比較例１１のディスクは、前記の初期化操作による均一な反射率上昇は見られなかった。また初期化操作後のディスクの反射率は７％と低かった。つまり、記録層の初期結晶化をすることができなかった。従って相変化型光ディスクとしての使用は困難である。これは、アモルファス相から準安定結晶相への相変化速度が遅いため均一な準安定相が得られないため、またはＡｕ−Ｓｂ系準安定相のような構造が安定に存在し得なくなったためと考えられる。
【０１１３】
比較例１０のディスクは、ディスク作製直後の反射率は１０％で、前記の初期化操作による反射率変化はみられなかった。つまり、記録層を初期結晶化をすることができなかった。従ってこの組成では相変化型光ディスクとしての使用はできない。これは、準安定結晶相が安定に存在できず、記録層が常に安定結晶相となっているためと考えられる。
【０１１４】
比較例９のディスクは、前記の初期化操作による均一な反射率上昇は見られなかった。従って、この組成では相変化型光ディスクの初期結晶化が良好に行えず、相変化型光ディスクとしての使用は困難であった。このディスクの記録層は、初期化操作によって結晶化はするものの、このディスクの再生波形をオシロスコープで観察すると、結晶相の反射率レベルが一定ではなく幅を持って太い線となっていた。これは、均一な結晶化ができていないためである。このように均一な結晶化ができない理由は、Ａｕ−Ｓｂ系準安定相が形成されないためと思われる。
【０１１５】
実施例１１〜１３のディスクは、初期化操作により、記録層が均一に初期結晶化した。つまり、上記比較例９〜１１の各ディスクと比較して、良好な相変化型光ディスクを得ることができた。さらに、実施例１１〜１３の各ディスクではＡｓ−ｄｅｐｏアモルファス状態の反射率は６％以下であり、結晶状態の反射率との差は良好であった。
【０１１６】
実施例１１〜１３の各ディスクは、上記測定の後、１０５℃の環境に保持された後（加速試験）、初期結晶化部とＡｓ−ｄｅｐｏ部反射率を再度測定した。結果を表−３に示す。また、（（初期結晶部反射率）−（加速試験後結晶部反射率））／（初期結晶部反射率）で定義した反射率低下率も記載した。Ｓｎの含有量の増加と共に反射率低下率が小さくなっていくことがわかる。
（実施例１４〜１８、比較例１２〜１６）
溝幅０．５μｍ、溝深さ４０ｎｍ、溝ピッチ１．６μｍの案内溝を有する直径１２０ｍｍ、１．２ｍｍ厚のディスク状ポリカ−ボネ−ト基板上に、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（１００ｎｍ）、Ａｕ−Ｓｂ−Ｇｅ−Ｉｎ記録層（１８ｎｍ）、（ＺｎＳ）₈₀（ＳｉＯ₂）₂₀層（４０ｎｍ）、Ａｌ_99.5Ｔａ_0.5合金反射層（２００ｎｍ）をスパッタリング法により成膜し、さらにその上に紫外線硬化樹脂層を設けた相変化型光ディスクを作製した。
【０１１７】
なお、記録層組成は表−４に示す１０種類とした。またこれらの組成を（（Ａｕ_xＳｂ_1-x）_1-yＧｅ_y）_1-zＩｎ_zで標記した場合のｘ、ｙ、ｚの値も併せて表―４に示した。
【０１１８】
【表７】

【０１１９】
各ディスクの初期結晶化は良好に行うことができた。初期結晶化した後、レ−ザ−波長７８０ｎｍ、ＮＡ０．５のピックアップを有する光ディスク評価装置を用いて、以下の手順で基板を通して案内溝内にＤＣレーザー光を照射するレーザー照射試験を行った。
レーザー照射試験とは、線速度を２．４ｍ／ｓとし、１０ｍＷのＤＣ光を１００回、９ｍＷのＤＣ光を１００回、８ｍＷのＤＣ光を１００回、７ｍＷのＤＣ光を１００回、６ｍＷのＤＣ光を１００回、５ｍＷのＤＣ光を１００回、４ｍＷのＤＣ光を１００回、３ｍＷのＤＣ光を１００回この順に照射する試験である。そして、レーザー照射試験前後の反射率を測定し、反射率低下を測定した。結果を表−４に示す。尚、反射率低下率は、（（初期反射率）−（レーザー照射試験後反射率））／（初期反射率）として定義した。
【０１２０】
レーザー照射試験は、初期結晶状態よりも安定な相が存在する場合にこの安定相への相変化が起こりやすい状況を作っている。理由は以下の通りである。つまり、常温で複数の相が存在する場合、すべての相は最も安定な相に相変化する傾向にあるが、温度を適度に上昇させることによりこの相変化速度は速くなる。１０ｍＷのＤＣ光を照射するとトラック中心部は溶融するが、ビーム中心から離れるにつれレーザー光の強度は小さくなるため、トラック中心からある程度離れた位置では安定相への相変化速度が相対的に速くなるような温度範囲になる。１００回のＤＣ光照射をおこなうのはこの温度に保たれる累積時間を長くするためである。次にレーザーパワーを９ｍＷにすると、安定相への相変化速度が相対的に速くなるような温度範囲になる位置は１０ｍＷのときより多少トラック中心に近くなる。このとき、１０ｍＷのＤＣ光照射により安定相に変化した部分はそのまま安定相として留まる。このように次第にＤＣ光のパワーを小さくしていくことにより安定相となる領域が広くなっていくと考えられる。
【０１２１】
表−４に見られるように、実施例１４〜１８の各ディスクのレーザー照射試験での反射率の低下率は、比較例１２〜１６の各ディスクのそれよりも小さかった。比較例のすべてのディスクで、レーザー照射試験による反射率の低下率は５５％を越える大きなものであった。これは、比較例１２〜１６の各ディスクの記録層は、実施例１４〜１８の各ディスクの記録層と比較して、記録消去には使用しない初期結晶相より安定な結晶相により相変化しやすいことを意味している。尚、表−４においては、比較例１６のディスクの「レーザー照射試験後反射率」、「反射率低下率」の欄には反射率のデータが記載されていない。これは、比較例１６のディスクにおいては、レーザー照射試験後は反射率が低くなりすぎて再生が不可能となったためである。
【０１２２】
実施例１４〜１８のディスクでは、反射率の低下が明らかに抑えられており、安定結晶相への相変化が起こりにくくなっていることがわかる。特に、実施例１８のディスクの結果と実施例１４〜１７のディスクの結果とを比較してわかるように、記録層組成を、Ａｕ−Ｓｂ系合金にＧｅ、さらにはＩｎを含有させる組成とすることにより、安定結晶相への相変化がさらに起こりにくくなる。
【０１２３】
比較例１２〜１６の各ディスクと比較例５、６及び９の各ディスクとは、記録層にＡｕを含有しない点で共通するが、比較例１２〜１６の各ディスクは、比較例５、６及び９の各ディスクよりも、ディスクの初期結晶化を良好に行うことができる点で優れている。これは、Ａｕを含まない記録層組成においてもＳｂ、Ｇｅ、及びＩｎの含有量を制御することにより、初期結晶化が可能となるようなディスクを得ることができることを意味する。しかしながら、初期結晶化が良好に行えるような比較例１２〜１６の各ディスクにおいても、これらディスクは記録層にＡｕを含有していないため、レーザー照射試験により安定結晶相への相変化が起こりやすくなり、結果として記録層の反射率の低下が大きくなる。
【０１２４】
一方、本発明の光学的情報記録用媒体の記録層は、Ａｕを所定量含有することを必須とする。これは、前にも説明した通り、Ａｕを所定量含有するからこそ準安定結晶が安定に存在し、安定結晶相への相変化が抑制されるからである。そしてこのことは、上記実施例１４〜１８の各ディスクのレーザー照射試験の結果からも明らかである。
【０１２５】
また、実施例１４〜１８及び比較例１２〜１６のいずれのディスクにおいても、レーザー照射試験後に５ｍＷ以下のレーザーを照射しても反射率に変化はなかったが、１０ｍＷのＤＣ光を１回照射するとほぼ初期の反射率に戻った。これは、５ｍＷ以下のレーザーでは記録層は溶融しないが、１０ｍＷのＤＣ光照射で記録層が溶融し、準安定相に相当する結晶相に相変化するためと考えられる。尚、表―４に示す比較例１２〜１６の結果より、Ｉｎ−Ｓｂ−Ｇｅ系合金を記録層に用いた場合とＩｎ−Ｓｂ系合金を記録層に用いた場合とでは、ＩｎとＳｂの含有量比においてＩｎが多くなると反射率の低下が大きく安定結晶相に相変化しやすい傾向があることがわかる。
【０１２６】
次に、実施例１５のディスクの初期結晶化部に記録線速度２４ｍ／ｓでＥＦＭランダム信号を１０回オーバーライト記録した後、線速度を２．４ｍ／ｓとして３Ｔマークジッタを測定した。記録時は、基準クロック周期Ｔ＝１１．６ｎｓ、Ｐｗ＝２２ｍＷ、Ｐｅ＝７ｍＷ、Ｐｂ＝０．８ｍＷで、ＥＦＭランダム信号を図１に示すレーザー波形とした。
【０１２７】
すなわち、長さｎＴ（Ｔは基準クロック周期で、ｎは３〜１１の自然数）のマーク（アモルファス相）を形成する際には、時間ｎＴの期間を上記数式（３）のように分割し、記録パワーＰｗを持つ記録パルス、バイアスパワーＰｂを持つオフパルスを交互に照射し、一部消去パワーＰｅを照射した。マーク間（結晶相）を形成する期間は消去パワーＰｅを持つ消去光を照射した。
【０１２８】
詳しくは、各マーク形成時はＰｗとＰｂのパルス列を次のように照射した（Ｔは基準クロック周期）。
【０１２９】
【表８】
３Ｔマーク部：１．５ＴのＰｗ、１．２ＴのＰｂ
４Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
５Ｔマーク部：１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
６Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
７Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
８Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
９Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
１０Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、０．６ＴのＰｂ
１１Ｔマーク部：１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１ＴのＰｂ、１ＴのＰｗ、１．３５ＴのＰｂ、１．５ＴのＰｗ、０．６ＴのＰｂ
以上のように１０回オーバーライト記録したＥＦＭランダム信号を、線速度２．４ｍ／ｓで再生し、３Ｔマークジッタを測定したところ１７．４ｎｓであった。すなわち、１７．５ｎｓ以下というＣＤ−ＲＷ規格（オレンジブックパート３）を満たした。実施例１５のディスクは、記録層組成を多少変化させて結晶化速度を変えることや、記録時のパルスストラテジの改善等によりさらなる記録特性の改善が期待できる。ここで、実施例１５のディスクについてのみ記録特性を評価した理由は、実施例１５のディスクが上記記録条件に比較的適した結晶化速度を示したからである。尚、他の実施例のディスクは異なった記録条件に適した組成になっているものと思われる。
【０１３０】
ここで、Ｇｅ、Ｉｎ、Ａｕの含有量を多くすることにより結晶化速度が遅くなった。従って、例えばＩｎ含有量を少なくしＧｅ含有量を多くすることにより、同程度の結晶化速度を有し異なった組成の記録層を得ることも可能である。
ディスクの未記録状態において、再生光を照射し、オシロスコープで再生波形を観察したところ、従来から知られている記録層組成であるＧｅ₅Ｓｂ₇₉Ｔｅ₁₆等で見られるような、結晶相（未記録状態）の反射率レベルが一定ではなく幅を持って太い線となって見える現象は、実施例１５のディスクでは見られず、ノイズが小さい良好なディスクが得られていることがわかった。
【０１３１】
【発明の効果】
本発明によれば、相変化速度が速く、高速記録消去が可能で保存安定性の高い光学的情報記録用媒体を得ることができる。特に、記録部（マーク部）および未記録・消去部（マーク間部）の保存安定性、高転送レートオーバーライト記録時ジッタ特性に優れる光学的情報記録用媒体を得ることができる。
【図面の簡単な説明】
【図１】 本発明の実施例におけるパルス分割方法の概略図 [0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording medium having, for example, a rewritable phase change recording layer, and in particular, for optical information recording having a phase change recording layer having excellent storage stability in an unrecorded state and a recorded state. The present invention relates to a medium, an optical information recording medium having excellent jitter characteristics in recording at a high transfer rate, and a recording / erasing method thereof.
[0002]
[Prior art]
An optical information recording medium having a phase change recording layer is recorded / reproduced / erased by utilizing a change in reflectance accompanying a reversible change in the crystalline state. Such an optical information recording medium, in particular, a phase change type optical disc (in this specification, a phase change type optical disc may be simply referred to as a disc) has excellent portability, weather resistance, impact resistance, and the like. Development and practical use are progressing as an inexpensive large-capacity recording medium. For example, rewritable CDs such as CD-RW are already in widespread use, and rewritable DVDs such as DVD-RW, DVD + RW, and DVD-RAM are being sold.
[0003]
What is currently in practical use as a recording method for rewritable phase-change recording materials is to use a reversible change between the crystalline phase and the amorphous phase to change the crystalline state to an unrecorded / erased state, An amorphous mark is formed during recording. Usually, the recording layer is heated to a temperature higher than the melting point and rapidly cooled to form an amorphous mark. On the other hand, the recording layer is heated and kept near the crystallization temperature for a certain time to obtain a crystalline state. That is, in general, a reversible change between a stable crystalline phase and an amorphous phase is utilized. As a material for such a phase change recording layer, a chalcogen alloy thin film is often used. For example, GeSbTe-based, InSbTe-based, GeSnTe-based, and AgInSbTe-based alloys can be used.
[0004]
[Problems to be solved by the invention]
However, with the recent increase in the amount of information, there is a demand for obtaining an optical information recording medium capable of recording and reproducing at higher speed. Also, the important performance required for the optical information recording medium is that the recorded information is excellent in storage stability, that is, the information recorded on the optical information recording medium is stable without deterioration even after long-term storage. one of. The present invention has been made to meet such a demand, and an object of the present invention is to provide an optical information recording medium capable of erasing at a higher speed and having high recording signal storage stability. .
[0005]
[Means for Solving the Problems]
That is, the gist of the present invention is an optical information recording medium in which a phase change recording layer capable of taking at least two different phases is provided on a substrate, and the phase change recording layer is represented by the following general formula (1). In the optical information recording medium, the main component is a composition represented by:
[0006]
(Au_xSb_1-x)_1-yGe_y       (1)
Where x and y are0.20≦ x ≦ 0.4 and 0 <y ≦ 0.3.
[0007]
By using a recording layer whose main component is a composition in which a small amount of Ge is added to the Sb-rich Au—Sb alloy, the phase change rate is faster than that of a conventional optical information recording medium. As a result, a medium can be obtained, so that higher-speed recording / erasing can be performed. The reason is considered as follows. That is, it is presumed that the Au—Sb-based alloy has a metastable crystal phase in addition to an amorphous phase and a stable crystal phase. However, in a conventional phase change recording medium, a stable crystal phase and an amorphous phase having a large activation energy. Because the phase change between and was mainly used, the phase change speed was insufficient and recording / erasing at high speed could not be performed. On the other hand, in the present invention, the metastable crystal phase of Au—Sb alloy is effectively used to make the metastable crystal phase having an activation energy smaller than the activation energy between the stable crystal phase and the amorphous phase. The phase change between the amorphous phase and the amorphous phase can be used for recording and erasing, so that a higher phase change speed can be achieved.
[0008]
Another aspect of the present invention is to record two different phases of the phase change recording layer on the optical information recording medium having a recording layer mainly composed of a predetermined Au—Sb alloy composition. And a recording / erasing method in which the phase change type recording layer can take at least three phases of A phase, B phase, and C phase, and the B phase is more stable than the A phase. When the phase C is more stable than the phase, the recording / erasing method is characterized in that the phase B is set in a recording state or an unrecorded / erased state. In the present invention, when the phase change from the A phase to the B phase can occur at a lower temperature than the phase change from the B phase to the A phase, it is defined that the B phase is more stable than the A phase.
[0009]
Still another subject matter of the present invention is that an information signal is recorded only when a reference clock period T is 15 nsec or less with respect to the optical information recording medium having a recording layer whose main component is a predetermined Au—Sb alloy composition. A recording / erasing method for performing erasing, in which recording is performed by alternately irradiating a high-power laser pulse and a low-power laser pulse, and the low-power laser pulse includes a pulse having a pulse width of 0.9 T or more. Lies in the way.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
(A) Optical information recording medium
(A-1) Composition of recording layer
The optical information recording medium of the present invention is an optical information recording medium in which a phase change recording layer capable of taking at least two different phases is provided on a substrate. The main component is a composition represented by the formula (1).
[0011]
(Au_xSb_1-x)_1-yGe_y       (1)
Where x and y are0.20≦ x ≦ 0.4 and 0 <y ≦ 0.3. In the present invention, when “the recording layer is mainly composed of the predetermined composition i”, it means that the predetermined composition i is contained by 50 atomic% or more of the entire recording layer.
[0012]
  In the present invention, an optical information recording medium having a high phase change rate and excellent storage stability is obtained by using a composition containing the above-mentioned predetermined composition as a main component as a recording layer of the optical information recording medium. Can do.
  In the present invention, since the metastable crystal phase of the Au—Sb alloy is used when performing recording / erasing on the optical information recording medium, this metastable crystal phase needs to be formed stably. In order to form a metastable crystal phase stably, in the general formula (1), x is0.20AboveThe ThisAu content likeIf there are manyThus, it is possible to obtain an optical information recording medium in which the reflectance of the metastable crystal phase hardly changes even after a long time. On the other hand, from the viewpoint of the storage stability of the metastable crystalline phase, it is better that the content of Au is large, but the higher the Au content, the slower the phase change rate from the amorphous phase to the metastable crystalline phase. . Further, when the Au content is too large, an Au—Sb-based stable crystal phase is always formed, and there is a tendency that an amorphous phase or a metastable crystal phase does not exist stably. Therefore, in the present invention, the upper limit of x is set to 0.4. Preferably, x is 0.35 or less. More preferably, it is 0.30 or less. Within this range, the balance between the storage stability of the metastable crystal phase and the phase change rate becomes better.
[0013]
That is, by setting the Au—Sb ratio in the above range, a metastable crystal state having excellent storage stability can be obtained. In this range, since the phase change rate from the amorphous phase and the metastable crystal phase to the stable crystal phase is slow, phase change recording between the metastable crystal phase and the amorphous phase becomes possible.
In the present invention, the inclusion of Ge in the Au—Sb-based alloy facilitates the formation of an amorphous phase, and enables a stable phase change between the metastable crystal phase and the amorphous phase. Therefore, the Au—Sb alloy used in the present invention needs to contain more than 0 Ge. Further, if the Ge content is increased, the amorphous phase is more stably present. Therefore, in the composition of the general formula (1), y is preferably 0.01 or more, and 0.03 or more. More preferably. On the other hand, if the Ge content is too high, the phase change rate from the amorphous phase to the metastable crystal phase tends to be slow, so y is set to 0.3 or less, but a faster crystallization rate (from the amorphous phase to the quasi-stable crystal phase). In order to achieve the (phase change rate to stable crystal phase), y is preferably 0.28 or less, and more preferably y is 0.15 or less.
[0014]
Incidentally, in general, a recording layer is irradiated with a light beam (laser) spot emitted from a light irradiation unit while rotating the medium at a high speed, and recording and erasure are performed while relatively moving the light irradiation unit and the medium at a high speed. When the relative movement speed is high, the recording linear velocity is referred to as high, and when the relative movement speed is low, the recording linear velocity is referred to as low.
In a state where the recording linear velocity is high, the recording layer is once heated by the light beam spot and then rapidly cooled. That is, the temperature history of the recording layer is rapidly cooled, and in a recording layer having the same composition, the higher the recording linear velocity, the easier it is to form an amorphous phase and the harder it is to form a crystalline phase.
[0015]
The Au—Sb composition used in the present invention is aimed at controlling the stability of the amorphous phase and the phase change rate from the amorphous phase to the metastable crystal phase by adjusting the Ge content. There is an advantage that an optical information recording medium can be designed according to the recording linear velocity. That is, a medium having a high recording linear velocity may contain a small amount of Ge, and a medium having a low recording linear velocity may contain a large amount of Ge.
[0016]
As described above, the Au—Sb composition used in the present invention freely controls the storage stability and the phase change rate from the amorphous phase to the metastable crystal phase by adjusting the Au content and the Ge content. Has the advantage that can be. This is presumably because the recording / erasing mechanism of the optical information recording medium of the present invention using the Au—Sb composition in the recording layer has the following two aspects.
[0017]
First, the first mode is a mode in which a metastable crystal phase is set in an unrecorded / erased state, and an amorphous phase mark is formed during recording. By effectively utilizing this aspect, an optical information recording medium capable of high-speed recording / erasing can be obtained.
On the other hand, the second mode is a mode in which the metastable crystal phase is set in an unrecorded / erased state, an amorphous phase mark is formed during recording, and then the mark transitions to the stable crystal phase. If this aspect is effectively used, an optical information recording medium having particularly excellent storage characteristics can be obtained.
[0018]
Specific examples of the optical information recording medium using the first embodiment and the optical information recording medium using the second embodiment will be described below in (I) and (II), respectively.
(I) Optical information recording medium using the first aspect
First, in the Au—Sb composition used in the present invention, the Ge content contributes to controlling the phase change rate from the amorphous phase to the metastable crystal phase. Therefore, if the Ge content is controlled, It is possible to erase the record using the mode effectively.
[0019]
  In addition, it is possible to perform recording erasure by effectively using the first aspect by controlling the Au content. In this case, the overwrite jitter characteristic is improved especially in high transfer rate recording.The HighIf the overwrite jitter characteristic at the transfer rate is improved, it is possible to obtain an optical information recording medium that can be used even when the information signal is recorded and erased only when the reference clock period T is 15 nsec or less. it can. More specifically, in the case where recording and erasing of an information signal is performed only when the reference clock period T is 15 nsec or less, a high power laser pulse and a low power laser pulse are alternately irradiated for recording. An optical information recording medium that can be used satisfactorily even in a recording and erasing method in which a laser pulse includes a pulse having a pulse width of 0.9 T or more can be obtained.
[0020]
Here, when the mark forming portion is irradiated with a high-power laser pulse and a low-power laser pulse alternately (such a recording method may be referred to as “pulse division recording” in this specification). It is necessary to lengthen the low power laser pulse in order to obtain a sufficient cooling rate. For this reason, it is preferable that low laser pulses include those longer than 0.9T, where T is the reference clock period. The method for recording and erasing the optical information recording medium of the present invention will be described in detail in (B) below.
(II) Optical information recording medium using the second aspect
In the optical information recording medium of the present invention, depending on the composition of the recording layer, for example, when the amount of Au in the recording layer is large, a phenomenon in which the amorphous phase slowly changes to a stable crystalline phase may be observed. is there. The second aspect utilizes the above phenomenon in which the mark changes into a stable crystal phase after forming an amorphous phase mark. In the composition range of the recording layer used in the optical information recording medium of the present invention, the reflectance of the amorphous phase and the reflectance of the stable crystal phase are approximately the same. Therefore, even if the amorphous phase changes to a stable crystalline phase, the signal can be reproduced. Rather, the storage characteristics of the optical information recording medium are greatly improved by the recording mark having a stable crystal phase. Furthermore, even in the recording layer composition in which the Ge content is reduced and the amorphous phase becomes slightly unstable, the recording mark will not disappear if the second aspect is used.
[0021]
  In order to obtain an optical information recording medium using the second aspect, the general formula (1) is used.YThe value of theTo 0. It is preferable to satisfy 01 ≦ y ≦ 0.3.
  Incidentally, the amorphous phase (amorphous mark) is erased (phase change to a metastable crystal phase) by heating the recording layer and keeping it near the crystallization temperature for a certain time. On the other hand, in order to erase the stable crystal phase (stable crystal mark) (phase change to the metastable crystal phase), it is necessary to once melt the recording layer. Therefore, when the stable crystal mark is used for recording, the power (erasing power) of the light beam irradiated for mark erasing may be increased to the extent that the recording layer is melted.
[0022]
  From the above, in the present invention, the phase change recording layer is made of (Au_xSb_1-x)_1-yGe_yage,0.20By satisfying ≦ x ≦ 0.4 and 0 <y ≦ 0.3, it is possible to obtain a medium that is excellent in the balance between recording signal storage stability and high transfer rate overwrite recording jitter characteristics. Moreover, by setting it as the said composition range, the crystallization rate (phase change rate from an amorphous phase to a metastable crystal phase) can be made sufficiently large. Furthermore, by setting the composition range, an optical information recording medium having excellent reproduction signal reflectance uniformity (reflectance uniformity when the reproduction waveform is observed with an oscilloscope) can be obtained.
[0023]
In an optical information recording medium with a non-uniform crystal phase of the recording layer, the reflectance level of the crystal phase (unrecorded state) is not constant. Therefore, the reproduction waveform observed with an oscilloscope in such an optical information recording medium is a thick line having a width. This is presumably because two or more phases having different reflectivities are mixed in a state that is not sufficiently uniform with respect to the irradiation area of the beam. Such a phenomenon becomes conspicuous in high linear velocity recording with a reference clock period of 15 nsec (nanoseconds) or less. However, in the composition range of the recording layer used in the optical information recording medium of the present invention, even when the composition has a high crystallization speed corresponding to high linear velocity recording in which the reflectance level becomes unstable, the oscilloscope The reproduced waveform observed at is a sharp thin line. This is nothing but the fact that in the optical information recording medium of the present invention, the metastable crystal phase does not become non-uniform and the reflectance level is constant.
[0024]
Therefore, according to the present invention, an optical information recording medium suitable for high linear velocity recording can be obtained. In particular, it is possible to obtain an optical information recording medium suitable for high linear velocity recording / erasing in which recording / erasing of a recording signal is performed only when the reference clock period T is 15 nsec or less. Then, actual high linear velocity recording is performed by using recording conditions (light beam (laser) pulse division recording method, pulse strategy) applied to the crystallization speed of the optical information recording medium. .
(A-2) Preferred composition of recording layer
A preferred embodiment of the recording layer of the optical information recording medium is that the phase change recording layer has a composition represented by the following general formula (2) as a main component.
[0025]
((Au_xSb_1-x)_1-yGe_y)_1-zM2_z (2)
Where x,y is each0.01 ≦ x ≦ 0.4, 0 <y ≦ 0.3It is a number that satisfies. M2 is at least one element represented by Te, In, and Sn.Furthermore, z is 0.01 ≦ z ≦ 0.4 when M2 is Te, 0.03 ≦ z ≦ 0.4 when M2 is In, and 0.1 ≦ z ≦ 0 when M2 is Sn. Is a number satisfying .4.
[0026]
In an optical information recording medium using a recording layer composition in which Ge is further added to an Au—Sb alloy, when further improvement in performance is required, the overwrite jitter characteristic and the quasi It may be difficult to achieve both the stability of the stable crystal phase. In such a case, not only the Ge but also the element M2 can be included in the Au—Sb-based alloy, thereby making it possible to achieve both the jitter characteristics and the stability. An optical information recording medium having the following can be obtained. In particular, it is possible to satisfactorily obtain an optical information recording medium capable of recording and erasing a recording signal only when the reference clock period T is 15 nsec or less.
[0027]
  Content of M2 in the general formula (2)The lower limit ofThe upper limit may be 0.4 or less.
  By using the additive element M2, it is possible to more easily achieve both the overwrite jitter characteristic and the stability of the metastable crystal phase in the high transfer rate recording of the optical information recording medium. Depending on the type of additive element used as the above, the above effect can be further enhanced. Specific examples of such additive elements will be described below.
[0028]
When Te is used as the element M2, the transition rate from the amorphous phase and the metastable crystal phase to the stable crystal phase tends to be slow. As a result, the stability of the metastable crystal phase is further increased, and as a result, the storage stability of the recorded signal is further increased.
That is, when the amount of Au is large in the composition range of the present invention, as described in (II) above, depending on the recording layer composition used, a phenomenon in which an amorphous phase and a metastable crystal phase slowly change to a stable crystal phase tends to occur. Tend to be. This phenomenon is preferable from the viewpoint of further improving the stability of the recording mark, as described in (II) above. However, as a result of the improvement of the stability of the recording mark, an erasing beam for erasing the recording mark is obtained. It is necessary to increase the power of. Increasing the erasing power (beam output) itself is not so difficult, but if the increase of the beam output is very large, the life of the erasing beam may be shortened. Therefore, in such a case, it is most preferable to use a recording layer composition in which the stability of the amorphous phase and the metastable crystal phase is sufficiently high and the phase change to the stable crystal phase as described above does not occur. From such a viewpoint, it is a very preferable embodiment that Te is further added to the composition containing Ge in the Au—Sb alloy. Furthermore, by adding Te, the phase change from the amorphous phase or the metastable crystal phase to the stable crystal phase can be suppressed. Therefore, there is an advantage that the Au content can be further increased in the general formula (2). .
[0029]
The effect of suppressing the phase change is significant when 0.01 ≦ z in the general formula (2), and the effect increases as the Te content increases. On the other hand, if the Te content is too large, the amorphous phase may change to a metastable crystalline phase when stored for a long period of time.
That is, if the Te content is low, the amorphous phase tends to change to a stable crystalline phase, but if the Te content is high, the phase change to the stable crystalline phase is less likely to occur. The phase may change to a metastable crystal phase.
[0030]
Therefore, if the Te content is too large, when the unrecorded state is a metastable crystal phase, a phenomenon may occur in which the record mark disappears due to the phase change of the amorphous mark to the metastable crystal phase. . Therefore, when Te is contained from such a viewpoint, z needs to be 0.4 or less, preferably 0.2 or less, and more preferably 0.1 or less.
[0031]
In the above general formula (2), when the Ge amount is increased, the stability of the amorphous mark can be improved, and as described above, the phase change from the amorphous phase to the stable crystal phase can be suppressed. However, when both Te and Ge contents are increased, the phase change rate (crystallization rate) from the amorphous phase to the metastable crystal phase tends to be slow at the time of recording / erasing. Therefore, if both the Te content and the Ge content are increased at the same time, the crystallization speed may become insufficient. Therefore, increasing the Ge content when the Te content is high may cause an appropriate phase change rate. Sufficient consideration is necessary from the viewpoint of maintenance. In order to improve the storage stability of the amorphous mark while considering the balance with the Ge content, the Te content is preferably 0.10 or less, and more preferably 0.08 or less.
[0032]
Further, the use of Te as the element M2 has an effect of improving the signal characteristics of the optical information recording medium used in the present invention. In other words, when the optical information recording medium is stored for a long period of time, the mark that has become a stable crystal phase spreads, that is, the metastable crystal phase around the mark tends to transition to the stable crystal phase, and the signal characteristics deteriorate. There is a case. Since Te slows the transition rate from the amorphous phase and the metastable crystal phase to the stable crystal phase, this tendency can be reduced by adding Te.
[0033]
In the present invention, In may be used as the element M2. When In is used as the element M2, the unrecorded portion of the recording layer is considered to be composed of a mixed phase of an In—Sb-based and Au—Sb-based metastable crystal phase. The total content of Au and In needs to be in an appropriate range. If the total content of Au and In is too small, the formation of this phase becomes insufficient. On the other hand, if the total content of Au and In is too large, In—Sb-based and Au—Sb-based stable crystal phases are always formed, and phases corresponding to amorphous and metastable crystal phases exist stably. The function as a recording medium may not be performed. In addition, since the crystallization speed decreases as the content of In or Au increases, the amorphous mark may not be erased if the total content of Au and In is too large.
[0034]
From the above, when In is used as the element M2, in the recording layer composition in the general formula (2), the total amount of Au and In is preferably 5 to 50 atomic% of the entire composition, and 10 to 45 It is more preferable to set it as atomic%. Specifically, the total content of Au and In may be controlled by adjusting the values of x and z in the general formula (2) so as to achieve the above content.
[0035]
When In is used as the element M2, the transition rate from the amorphous phase and the metastable crystal phase to the stable crystal phase tends to be slow as in the case of using Te. As a result, the metastable crystal phase can be prevented from changing to a stable crystal phase, the stability of the metastable crystal phase is increased, and the storage stability of the recorded signal is further increased.
This is presumably because the recording layer is in a mixed state of In—Sb alloy and Au—Sb alloy as described above by using In. The reason why the amorphous phase and the metastable crystal phase hardly change to the stable crystal phase by mixing the In—Sb alloy and the Au—Sb alloy is not always clear, but the phase change rate becomes slow. Or, it may be because the stable crystal phase is not the most stable phase by adding In. For example, due to the addition of In, the phase corresponding to the metastable crystal phase in the recording layer before the addition may be the most stable phase even near room temperature.
[0036]
  From the above, when In is used as the element M2, the value of z in the general formula (2) is0.03It is necessary to be above, but preferablyIs 0. 05 or more, on the other hand, 0.4 or less, but preferably 0.35 or less, more preferably 0.3 or less.
  In the case of the In—Sb alloy and the Au—Sb alloy alone, when the In amount and the Au amount respectively increase, a stable crystal phase is always formed, and the metastable crystal phase cannot exist stably. In contrast, in the present invention, In is added to the AuSbGe-based composition, and the phase change from the amorphous phase and the metastable crystal phase to the stable crystal phase is less likely to occur. Therefore, the contents of In and Au are adjusted as appropriate. This also has the effect of widening the range of the Sb content that can be contained in the recording layer.
[0037]
In the present invention, at least part of In may be replaced with Ga. This is because the functions of In and Ga are equivalent in the recording layer composition.
Next, when Sn is selected as the element M2 in the general formula (2), the storage stability of the metastable crystal phase of the Au—Sb alloy becomes particularly high. In other words, the metastable crystal phase of Au—Sb-based materials is not sufficiently stable, and the reflectance of the recording layer may decrease due to long-term storage (the reflectance may increase depending on the layer structure). .) This means that in the phase change recording between the amorphous phase and the metastable crystal phase, the intensity of the recorded signal is reduced by long-term storage. Furthermore, this reduction in the reflectance of the recording layer deteriorates the signal quality by causing a difference between the reflectance of the region where the amorphous phase is crystallized at the time of rewriting and the reflectance of the region that was originally crystalline. It also means. Therefore, if the metastable crystal phase is not sufficiently stable depending on the recording layer composition, Sn may be used as the element M2.
[0038]
That is, in the present invention, by adding Sn to the Au—Sb alloy, it is possible to suppress a change with time in the reflectance of the metastable crystal phase observed in the Au—Sb alloy. The reason why the reflectance of the Au—Sb metastable crystal phase changes with time is not necessarily clear. In the composition range of the present invention, a phase change to a stable crystal phase is more likely to occur with a larger amount of Au. However, considering that a decrease in reflectance tends to be larger with a smaller amount of Au, the decrease in reflectivity is likely to occur. The reason is not because the phase change to the stable crystal phase occurs gradually, but may be, for example, a change in crystal orientation in the metastable crystal. In any case, it seems that it is gradually changing from a state immediately after crystallization to a stable state. Therefore, it is considered that the rate of change is slowed by the addition of Sn, or that the state after aging of the metastable crystal phase of the Au—Sb alloy does not exist stably.
[0039]
  Therefore, if the Sn content is too small, the effect of suppressing the change in reflectance over time is not sufficient, and if it is too large, the difference in reflectance between crystal and amorphous becomes small, and the signal intensity becomes insufficient.
  From the above, in the above general formula (2), the value of z when Sn is used as the element M2 is0.1≤zIs 0. 15 ≦ z is more preferable. On the other hand, although z ≦ 0.4, z ≦ 0.35 is preferable, and z ≦ 0.3 is more preferable.
[0040]
Furthermore, when Sn is added, the crystallization speed from the amorphous phase to the metastable crystal phase increases, and crystallization at a higher linear velocity becomes possible. Further, since the formation of crystal nuclei is facilitated by the addition of Sn, recording can also be performed by irradiating a laser beam to an As-depo amorphous phase formed by sputtering or the like to form a crystal phase mark.
(A-3) Other matters regarding the recording layer
In the present invention, in order to improve various characteristics, the recording layer is made of Al, Ag, Ga, Zn, Si, Cu, Pd, Pt, Pb, Cr, Co, O, N, S, Se, V, Nb. , Ta, etc. may be added as necessary. In order to obtain the effect of improving the characteristics, the amount added is 0.1 at. % (Atomic%) or more is preferable. However, in order to particularly exhibit the preferable characteristics of the composition of the present invention, 10 at. % Or less is preferable.
[0041]
The film thickness of the recording layer is preferably 5 nm or more in order to obtain a sufficient optical contrast, increase the crystallization speed, and achieve recording erasure in a short time. Further, in order to sufficiently increase the reflectance, the thickness is more preferably set to 10 nm or more.
On the other hand, it is preferable that the film thickness of the recording layer is 100 nm or less in order to prevent cracking and to obtain a sufficient optical contrast.
[0042]
More preferably, it is 50 nm or less. This is to reduce the heat capacity and increase the recording sensitivity. Further, it is possible to reduce the volume change due to the phase change, and to reduce the influence of the repeated volume change due to the repeated overwriting on the recording layer itself and the upper and lower protective layers. As a result, accumulation of irreversible microscopic deformation is suppressed, noise is reduced, and repeated overwrite durability is improved.
[0043]
In a high-density recording medium such as a rewritable DVD, since the requirements for noise are more severe, the recording layer thickness is more preferably 30 nm or less.
As for the phase change recording using the metastable crystal phase of the Au—Sb alloy, one using the phase change with the stable crystal phase is known. For example, U.S. Pat. No. 4,860,274 discloses two different types of Au—Sb alloys having a Sb content of 5 to 25% or Au—Sb alloys having a Sb content of 70 to 90 atomic%. It is described that recording is erased between a metastable crystal phase which is a crystal phase and a stable crystal phase. JP-A-63-225933 discloses that Sb and Au are the main components, the atomic ratio of Sb and Au is between 4: 1 and 1: 1, and Se, Bi, As, Te, In an alloy recording layer containing 2 to 50 atomic% of at least one element selected from the group consisting of Zn, a π phase of the metastable crystal phase is obtained by rapid cooling after melting, and a stable crystal phase is obtained by heat annealing the metastable crystal phase. It is described that
[0044]
However, in the Au-Sb alloys described in these documents, the metastable crystal phase exists relatively stably, and the phase change rate between the metastable crystal phase and the stable crystal phase is slow. It is difficult to erase the record. The fact that the Au—Sb alloys of the above-mentioned documents are not suitable for high-speed recording erasure is supported by the fact that only the static recording is performed in any of the documents. Further, these compositions have a problem that the stability of the metastable crystal phase is not so stable as to ensure the stability of the recording signal.
[0045]
On the other hand, the present inventor, even when using an Au—Sb alloy, adds Ge to the Au—Sb alloy so that the phase change rate is high and the stability of the metastable crystal phase is sufficient. It has been found that an information recording medium can be obtained. This is because the addition of Ge facilitates the formation of an amorphous phase and enables a high-speed phase change between the metastable crystal phase and the amorphous phase.
[0046]
JP-A-1-251342 discloses a composition similar to the recording layer composition of the optical information recording medium used in the present invention.
However, in the recording layer composition disclosed in this publication, the Ge content is 5 to 80 at. %, The range of the Ge amount that can be contained in the Au—Sb alloy composition used in the present invention is 30 at. %. In the present invention, the Ge content is 30 at. % Because the Ge content is 30 at. If the amount exceeds 50%, the phase change rate from the amorphous phase to the metastable crystal phase decreases, and it becomes difficult to record at a high linear velocity. The content is 32 at. %, It is supported by the fact that it becomes difficult to use as a phase change optical disk at any linear velocity of 1.2 to 24 m / s. On the other hand, the Ge content in the recording layer composition specifically disclosed in the above publication is 47 at. % ((Ge₅₅Sb₄₅)₈₅Te_TenAu_FiveIn the experimental examples 3 and 4, 35 at. % ((Ge₅₀Sb_{Five 0})₇₀Te₃₀Calculated from the composition of That is, any of these numbers is 30 at. More than%, the recording layer composition described in the above publication is a recording layer composition unsuitable for high-speed recording. On the other hand, the optical information recording medium of the present invention uses a metastable crystal phase in the Au—Sb alloy composition, which is neither described nor suggested in the above publication. Furthermore, the optical information recording medium of the present invention enables high-speed recording as compared with the optical information recording medium described in the above publication by controlling the amount of Ge contained in the recording layer. It has the special effect of becoming.
(A-3) Layers other than the recording layer
Next, other parts in the structure of the phase change optical disk will be described. Phase change optical disks often have a protective layer, a recording layer, a protective layer, and a reflective layer on a substrate in this order or in the reverse order.
[0047]
As the substrate, resins such as polycarbonate, polyacrylate, and polyolefin, or glass can be used. When recording / reproducing light is incident from the substrate side, the substrate needs to be transparent to the recording / reproducing light.
In many cases, the upper and lower sides of the recording layer are covered with protective layers. A dielectric is often used as a material for the protective layer, and the selection of the dielectric is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. As the dielectric, generally, a metal having high transparency and a high melting point, an oxide, sulfide, nitride, or fluoride such as Ca, Mg, Li or the like is used.
[0048]
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 ZnS or a rare earth sulfide and a heat-resistant compound such as an oxide, nitride, or carbide can be used. For example, ZnS and SiO₂This mixture is often used for a protective layer of a phase change optical disc. The film density of these protective layers is desirably 80% or more of the bulk state from the viewpoint of mechanical strength.
[0049]
The thickness of the protective layer is preferably 5 nm or more in order to make the recording layer have a sufficient deformation preventing effect and function as a protective layer. On the other hand, the film thickness of the protective layer is 500 nm or less in order to reduce the internal stress of the dielectric itself constituting the protective layer and the difference in elastic characteristics with the film in contact with it, and to make it difficult for cracks to occur. Is preferable.
In general, since the material forming the protective layer has a low film formation rate, the film formation time of the protective layer becomes long. Therefore, in order to shorten the film formation time, shorten the manufacturing time, and reduce the cost, it is preferable to suppress the thickness of the protective layer to 200 nm or less. More preferably, the thickness of the protective layer is 150 nm or less.
[0050]
The thickness of the protective layer provided between the recording layer and the reflective layer is preferably 5 nm or more in order to prevent deformation of the recording layer. Generally, microscopic plastic deformation is accumulated in the protective layer due to repeated overwriting. This microscopic compositional deformation causes the reproduction light to scatter and increase noise. Therefore, in order to suppress this microscopic plastic deformation, it is preferable that the thickness of the protective layer is 60 nm or less.
[0051]
On the other hand, the thickness of the protective layer provided between the recording layer and the substrate is preferably 20 nm or more in order to protect the substrate.
Note that the thickness of the recording layer and the protective layer is not limited from the mechanical strength and reliability viewpoints, but also takes into account the interference effect associated with the multilayer structure, so that the absorption efficiency of the laser beam is good and the amplitude of the recording signal That is, the selection is made so that the contrast between the recorded state and the unrecorded state is increased.
[0052]
The reflective layer is preferably made of a material having a high reflectance and thermal conductivity. Examples of the reflective layer material having a high reflectance and thermal conductivity include metals containing Ag, Au, Al, Cu and the like as main components. Among them, Ag has the highest reflectance and thermal conductivity compared to Au, Al, Cu and the like.
For light having a short wavelength, light is more easily absorbed when Au, Cu, or Al is used for the reflective layer than Ag. For this reason, when a short wavelength laser of 650 nm or less is used for recording and reproduction, it is particularly preferable to use a metal containing Ag as a main component as the reflective layer. Furthermore, Ag is preferably used as a reflective layer material because it is relatively inexpensive as a sputtering target, has a stable discharge, has a high film formation rate, and is stable in the air.
[0053]
Ag, Al, Au, Cu, etc. may contain other elements. When these metals are mixed with impurities, thermal conductivity and reflectivity are lowered, but stability and film surface flatness are sometimes improved. Therefore, 5 at. % Or less may be contained. Containing elements include Cr, Mo, Mg, Zr, V, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Al, Pd, Pt, Pb, Ta, Ni, Co, O, Se, V One or more elements selected from the group consisting of Nb, Ti, O, and N are preferred.
[0054]
The thickness of the reflective layer is preferably 50 nm or more in order to obtain sufficient reflectance and heat dissipation effect. On the other hand, the thickness of the reflective layer is preferably 200 nm or less in order to reduce the film stress. In order to shorten the film formation time, the manufacturing time, and the cost, the thickness of the reflective layer is preferably 200 nm or less.
The recording layer, the protective layer, the reflective layer, and the like are formed by a sputtering method or the like according to a conventional method using a predetermined proportion of an alloy target. The formation of the recording layer, protective layer, and reflective layer is preferably performed by an in-line apparatus in which each sputtering target is installed in the same vacuum chamber from the viewpoint of preventing oxidation and contamination between the respective layers. It is also excellent in terms of productivity.
[0055]
You may protect by providing the protective coating layer which consists of ultraviolet curable resin etc. on these layers. In order to increase the recording capacity, two or more recording layers may be provided on the substrate, or after forming each of the above layers on the substrate, they may be bonded with an adhesive.
Other layers than those described above may be added as necessary.
(B) Recording and erasing method of optical information recording medium
Next, the recording / erasing method for the optical information recording medium of the present invention will be described.
[0056]
The recording / erasing method is a recording / erasing method in which two different phases of the phase change recording layer are recorded and unrecorded / erased with respect to the optical information recording medium described above. When the changeable recording layer can take at least three phases of A phase, B phase, and C phase, the B phase is more stable than the A phase, and the C phase is more stable than the B phase, the B phase is recorded or unrecorded. Record / erase state.
[0057]
That is, conventionally, recording and erasing was performed by a phase change between the most stable C phase and the most unstable A phase. However, in the present invention, a metastable B phase is recorded on a medium having a recording layer having the above composition. Since it can be used for erasing, recording can be erased at high speed. The B phase may be in an unrecorded / erased state or a recorded state.
In general, when the stability of the A phase, B phase, and C phase that can be taken by the composition of the recording layer is more stable in the order of A phase <B phase <C phase, that is, A phase, B phase, and C phase, The most unstable A phase is an amorphous phase (amorphous phase), and the other B and C phases are crystal phases. For this reason, it is common to consider the A phase as an amorphous phase, the B phase as a metastable crystal phase, and the C phase as a stable crystal phase.
[0058]
Note that whether each phase is amorphous or crystalline, or what kind of crystal it is, can be confirmed by observing the diffraction pattern of the recording layer using an X-ray diffraction method or an electron beam diffraction method.
Preferably, at least the A phase is in a recording state and the B phase is in an unrecorded / erased state, or the A phase is in an unrecorded / erased state and the B phase is in a recorded state. That is, recording / erasing is performed by a phase change between the A phase (amorphous phase) and the B phase (metastable crystal phase). As a result, as described above, a phase change rate faster than that in the conventional method in which recording and erasing is performed by a phase change between the amorphous phase and the stable crystal phase is obtained, and recording and erasing can be performed at a higher speed.
[0059]
The metastable crystal phase may be in an unrecorded / erased state and an amorphous phase mark may be formed during recording, or the amorphous phase may be in an unrecorded / erased state and a metastable crystal phase mark may be formed during recording . Furthermore, the metastable crystal phase may be in an unrecorded / erased state, an amorphous phase mark may be formed during recording, and the phase may further transition to a stable crystal phase.
[0060]
Hereinafter, the case where the metastable crystal phase is in an unrecorded / erased state and an amorphous phase mark is formed during recording will be described as an example.
Usually, a recording track is formed on a disk-shaped medium in a spiral shape or a concentric shape, and information is recorded along the recording track. The recording layer is irradiated with a light beam (laser) spot emitted from the light irradiation unit while rotating the medium at a high speed, and recording / reproducing / erasing is performed while relatively moving the light irradiation unit and the medium at a high speed.
[0061]
The light emitted from the light source is usually irradiated to the medium through the objective lens through various optical systems. The relative movement of the light irradiation unit with respect to the medium means, for example, that the recording track of the medium is irradiated with light from the lens while rotating the disk-shaped medium with the objective lens substantially fixed. When the recording track is spirally formed on the medium, the objective lens is gradually changed in the disk radial direction while rotating the medium.
[0062]
First, when forming an amorphous phase, it is preferable to irradiate a high power laser pulse and a low power laser pulse alternately. Hereinafter, a high-power laser pulse is referred to as a recording pulse, and the power applied at this time is referred to as a recording power Pw. A low-power laser pulse is referred to as an off-pulse, and the power applied at this time is referred to as bias power Pb.
[0063]
By alternately irradiating the high-power laser pulse and the low-power laser pulse, the region heated by the recording pulse can be relatively rapidly cooled during the off-pulse, and an amorphous phase is easily formed. . In order to speed up the rise / fall of the pulse and to make the laser light source used for recording inexpensive, it is preferable that recording can be performed with a small recording power Pw. This leads to easy deterioration. For this reason, the medium is preferably designed so that the recording power Pw is 8 to 25 mW. More preferably, it is 8-20mW.
[0064]
The bias power Pb is preferably 0.5 times or less (Pb / Pw ≦ 0.5) of the recording power Pw, more preferably 0.3 times or less (Pb / Pw ≦ 0.3). Here, considering tracking performance and the like, the bias power Pb is preferably a value close to the value of the power Pr of the reproduction light irradiated during reproduction. The reproduction power Pr is usually 0.5 to 1.0 mW.
[0065]
When it is desired to increase the cooling rate, the bias power Pb is preferably reduced and may be zero. That is, it is not necessary to irradiate light.
When forming the metastable crystal phase, it is preferable to continuously irradiate the recording layer with a laser beam having an erasing power Pe. The erasing power Pe is not particularly limited as long as the recording layer can be heated so that the metastable crystal phase can be erased during overwriting, but is usually larger than the bias power Pb and smaller than the recording power Pw. For example, 0.2 ≦ Pe / Pw <1.0. When the erasing power Pe is continuously irradiated, the recording layer is heated to the vicinity of the crystallization temperature, and the heated region can be gradually cooled to form a metastable crystal phase.
[0066]
However, when the second embodiment as described in (A), (A-1), and (II) is used, that is, an optical information recording medium in which a recording mark changes from an amorphous phase to a stable crystalline phase during storage. When is used, it is preferable to increase the erasing power Pe. Since the stable crystal mark is not erased (phase change to a metastable crystal phase) unless the recording layer is once melted, the erasing power Pe is preferably increased to such an extent that the recording layer is melted. In this case, for example, 0.5 ≦ Pe / Pw ≦ 1.0.
[0067]
By combining the above, an amorphous phase and a metastable crystal phase can be formed and separated, and overwrite recording can be performed.
A specific example of alternately irradiating a recording pulse and an off pulse when forming an amorphous phase is shown below. When forming a mark (amorphous phase) having a length nT (T is a reference clock period and n is a natural number), the time nT is divided as shown in the following formula (3).
[0068]
[Expression 1]
α₁T, β₁T, α₂T, β₂T, ..., α_m-1T, β_m-1T, α_mT, β_mT (3)
(However, α₁+ Β₁+ Α₂+ Β₂+ ... α_m-1+ Β_m-1+ Α_m+ Β_m= N-j, j is a real number greater than or equal to 0, m is an integer greater than or equal to 1, and j and m are values determined by the combination of the medium and the recording conditions. )
In the above equation, recording is performed by irradiating a recording pulse at a time of αiT (1 ≦ i ≦ m) and irradiating an off-pulse at a time of βiT (1 ≦ i ≦ m). In a region between the marks (metastable crystal phase), light having an erasing power Pe is irradiated. As a result, overwrite recording can be performed.
[0069]
The recording / erasing method for the optical information recording medium of the present invention is preferably a recording / erasing of the information signal only with respect to the optical information recording medium described in (A) above at a reference clock period T of 15 nsec or less. In the recording / erasing method, a high power laser pulse and a low power laser pulse are alternately irradiated during recording, and the low power laser pulse includes a pulse having a pulse width of 0.9 T or more. The pulse width of the low-power laser pulse is set to 0.9 T or more when the pulse division recording is used in high-speed recording with a short reference clock period of 15 nsec or less in order to obtain a sufficient cooling rate. This is because it is necessary to lengthen the pulse.
[0070]
【Example】
  The present invention will be described below with reference to examples, but the present invention is not limited to the examples as long as the gist of the present invention is not exceeded.
(Examples 1 and 2 and Reference Example 1Comparative Examples 1-6)
  On a disc-shaped polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm having a guide groove having a groove width of 0.5 μm, a groove depth of 40 nm, and a groove pitch of 1.6 μm, (ZnS)₈₀(SiO₂)₂₀Layer, Au-Ge-Sb recording layer, (ZnS)₈₀(SiO₂)₂₀Layer, Al_99.5Ta_0.5An alloy reflective layer was formed by sputtering to produce a phase change optical disk.
[0071]
  In addition,Examples 1 and 2 and Reference Example 1Table 1 shows the film thickness configurations and the recording layer compositions of Comparative Examples 1 to 6. In addition, these compositions (Au_xSb_1-x)_1-yGe_yTable 1 also shows the values of x and y. In Table 1, the film thickness configuration of Example 1 is described as “Sub./100/18/40/200”. This indicates that the protective layer on the substrate (Sub.) (ZnS )₈₀(SiO₂)₂₀The film thickness of the layer is 100 nm, the film thickness of the Au—Ge—Sb recording layer on the protective layer is 18 nm, and the protective layer (ZnS) on the recording layer.₈₀(SiO₂)₂₀Layer thickness is 40 nm, Al on the protective layer_99.5Ta_0.5This means that the film thickness of the alloy reflective layer is 200 nm ".Example 2, Reference Example 1The same applies to the film thickness configurations of Comparative Examples 1 to 6.
[0072]
[Table 1]

[0073]
Of the obtained discs, the discs of Comparative Examples 1 and 2 have a DC reflectivity of 14% and 8%, respectively, immediately after the production of the disc, and any DC rate with a power of 12 mW or less within a linear velocity range of 1.2 to 24 m / s. The reflectance was not changed by the irradiation with the light. Therefore, at least in this linear velocity range, the initial crystallization of the phase change type optical disk could not be performed, and it could not be used as a phase change type optical disk. This is probably because the metastable crystal phase cannot exist stably and is always a stable crystal phase.
[0074]
The discs of Comparative Examples 3 and 4 have a reflectivity of 4% and 4%, respectively, immediately after the disc production, and are uniform by any DC laser light irradiation of 12 mW or less within a linear velocity range of 1.2 to 24 m / s. No significant increase in reflectivity was observed. Therefore, at least in this linear velocity range, the initial crystallization of the phase change type optical disk cannot be performed well, making it difficult to use it as a phase change type optical disk. This is presumably because a uniform metastable phase cannot be obtained because the phase change rate from the amorphous phase to the metastable crystal phase is slow, and the recording layer remains almost in an amorphous phase even when irradiated with DC laser light.
[0075]
  nextExamples 1 and 2 and Reference Example 1After initial crystallization, a disk evaluation apparatus having a laser wavelength of 780 nm and a pickup with NA of 0.5 was used to record / erase in the guide groove and reproduce the disk characteristics as follows. Evaluated.
  First, an EFM random signal was recorded using the laser waveform shown in FIG. 1 at a linear velocity of 24 m / s, a reference clock period T = 11.6 ns, Pw = 21 mW, Pe = 10.5 mW, and Pb = 0.8 mW.
[0076]
That is, when forming a mark (amorphous phase) having a length nT (T is a reference clock period and n is a natural number of 3 to 11), the period of time nT is divided as in the above equation (3), A recording pulse having a recording power Pw and an off pulse having a bias power Pb were alternately irradiated, and a partial erasing power Pe was irradiated. Erasing light having an erasing power Pe was irradiated during the period between the marks (metastable crystal phase).
[0077]
Specifically, when forming each mark, a pulse train of Pw and Pb was irradiated as follows (T is a reference clock period).
[0078]
[Table 2]
3T mark: 1.5T Pw, 1.2T Pb
4T mark part: 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
5T mark part: 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
6T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
7T mark part: 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
8T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
9T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
10T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
11T mark portion: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
The EFM random signal recorded as described above was reproduced at a linear velocity of 2.4 m / s, and the reflectance between the mark portion and the mark portion was measured. The results are shown in Table 1 as initial reflectivity. It should be noted that the portion between marks corresponds to an unrecorded portion / erased portion, and the mark portion corresponds to a recorded portion.
[0079]
  Thereafter, the disk was kept in an environment of 105 ° C. for 3 hours (acceleration test), and the reflectance between the mark portion and the mark portion of the signal recorded as described above was measured again. The results are shown in Table 1 as reflectivity after the acceleration test.
  In Example 1, the reflectance between the marks was almost the same between the initial stage and after the acceleration test, and almost no decrease in the reflectance between the marks due to the acceleration test was observed. In Example 2, the reflectivity reduction at the mark-to-mark part after the acceleration test was about 7%. This is considered to be because the storage stability of the metastable phase is somewhat lowered because the recording layer composition of Example 2 has a smaller Au content than the recording layer composition of Example 1. However, the level of decrease in reflectance is not a problem when considered from the actual use level.Reference example 1In the acceleration test, the reflectivity reduction between the marks was about 9%. This is considered to be due to a decrease in the storage stability of the metastable phase due to the small Au content in the recording layer composition of Example 3 compared to the recording layer compositions of Examples 1 and 2.The ShiTherefore, if the storage stability of the metastable phase is listed in order from the excellent one, Example 1, Example 2,Reference example 1It becomes.
[0080]
  next,Examples 1 and 2The phase state of the recording layer in this disc will be considered in detail.
  In these discs, in the initial recording and erasing, the mark portion can be erased by irradiation with light having an erasing power of 10.5 mW at a linear velocity of 24 m / s, while the formation of the mark portion requires a recording power of at least 17 mW or more. there were. In other words, if the initial mark portion is the L phase and the inter-mark portion is the M phase, the phase change from the L phase to the M phase can occur at a lower temperature than the phase change from the M phase to the L phase. Is more stable.
[0081]
In the disk of Example 1, the mark portion of the recording layer was erasable by DC laser light irradiation at a linear velocity of 2.4 m / s and power of 5 mW in the initial stage, but after the acceleration test. Even when the DC laser beam was irradiated under the same conditions as described above, there was a portion that was not erased depending on the mark portion of the recording layer. This is because, if the initial mark portion is the L phase and the inter-mark portion is the M phase, a part of the L phase of the mark formed during signal recording is reflected to the same degree as the L phase after the acceleration test at 105 ° C. This means that the phase has changed to the N phase that is neither the L phase nor the M phase.
[0082]
Actually, the disk was irradiated with DC laser light with a power of 5 mW at a linear velocity of 2.4 m / s, which is considered not large enough to melt the recording layer, and then this disk was irradiated with reproduction light. When the reproduction signal waveform was observed with an oscilloscope, the above-mentioned non-erased portion (N phase) tended to spread to the mark-to-mark portion (M phase). This indicates that the M phase between the marks gradually changes to a more stable N phase.
[0083]
The N phase returned to the unrecorded reflectivity when irradiated with DC laser light with a power of 10 mW, which is considered to melt the recording layer, at a linear velocity of 2.4 m / s. It is thought that the phase changed to M phase. However, the N phase did not change to the M phase when irradiated with DC laser light of 6 mW or less.
From these things, since the phase change from the M phase to the N phase can occur at a lower temperature than the phase change from the N phase to the M phase, the N phase is more stable than the M phase.
[0084]
  Example2Even in the case of the disk, the mark-to-mark part reflectance was reduced by irradiating a DC laser beam of 5 mW 1000 times at a linear velocity of 2.4 m / s. This is presumably because the M phase changed to the N phase. This portion returned to the unrecorded reflectivity by irradiation with a 10 mW DC laser beam, which was thought to melt the recording layer, but did not return when irradiated with a DC laser beam of 6 mW or less. That is, the example2Also in the disk, the phase change from the M phase to the N phase can occur at a lower temperature than the phase change from the N phase to the M phase, so that the N phase is more stable than the M phase.
[0085]
  From the above, Example 1,2The M phase is more stable than the L phase, and the N phase is more stable than the M phase. Therefore, the L phase corresponds to the A phase, the amorphous phase, the M phase corresponds to the B phase, the metastable crystalline phase, the N phase corresponds to the C phase, and is considered to be a stable crystalline phase. It is done. In the initial erasure recording, the B phase (M phase, metastable crystal phase) is in an unrecorded / erased state, and the A phase (L phase, amorphous phase) is in a recorded state. And Example 1,2Since the disk uses the phase change between the A phase and the B phase, recording and erasing can be performed even at a high linear velocity of 24 m / s.
[0086]
  In addition,Examples 1 and 2The reason why the linear velocity was reduced from 24 m / s at the time of mark recording to 2.4 m / s in the experiment for conducting a detailed study of the phase state of the recording layer of the disc was that the cooling rate at the time of laser irradiation was slow. This is to make it easier to observe the phase change to the most stable N phase by lengthening the time during which the temperature is rising.The
[0090]
Next, the same measurement was attempted for the GeSb system containing no Au. Ge which seems to be a composition suitable for the above recording conditions in terms of crystallization speed₁₆Sb₈₄(Comparative Example 5) and Ge₁₇Sb₈₃(Comparative Example 6) was tried. However, when the reproduced waveform was observed with an oscilloscope after the initial crystallization in each of the disks of Comparative Examples 5 and 6, the reflectance level of the crystal phase (unrecorded state) was not constant but became a thick line with a width. This is presumably because the recording layer is not uniformly crystallized after the initial crystallization. Further, the jitter value of these disks is not less than 25 ns and the signal amplitude is small, so it cannot be said that the disk is very usable.
[0091]
  From the above, (Au_xSb_1-x)_1-yGe_yIn the composition of0.2≦ x ≦ 0.4, 0 <y ≦ 0.3RiAn optical information recording medium having particularly excellent recording signal storage stability can be obtained.
(Examples 5 to 9, Comparative Examples 7 and 8)
  On a disc-shaped polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm having a guide groove having a groove width of 0.5 μm, a groove depth of 40 nm, and a groove pitch of 1.6 μm, (ZnS)₈₀(SiO₂)₂₀Layer (100 nm), Au—Ge—Sb—Te recording layer (18 nm), (ZnS)₈₀(SiO₂)₂₀Layer (40 nm), Al_99.5Ta_0.5An alloy reflective layer (200 nm) was formed by sputtering to produce a phase change optical disk.
[0092]
The recording layer composition was seven types shown in Table-2. The composition of these ((Au_xSb_1-x)_1-yGe_y)_1-zTe_zTable 2 also shows the values of x, y, and z.
[0093]
[Table 4]

[0094]
Of the obtained disks, the disk of Comparative Example 7 had a reflectivity of 14% immediately after the disk was manufactured, and was irradiated with any DC laser light with a power of 12 mW or less within a linear velocity range of 1.2 to 24 m / s. Even the reflectivity did not change. Therefore, at least in this linear velocity range, the initial crystallization of the phase change type optical disk could not be performed, and it could not be used as a phase change type optical disk. This is presumably because the metastable crystal phase cannot exist stably and the recording layer is always a stable crystal phase.
[0095]
The disc of Comparative Example 8 had a reflectivity of 4% immediately after the disc was manufactured, and even with any DC laser light irradiation of 12 mW or less in a linear velocity range of 1.2 to 24 m / s, a uniform increase in reflectivity was observed. I couldn't. Therefore, at least in this linear velocity range, the initial crystallization of the phase change type optical disk could not be performed, and it could not be used as a phase change type optical disk. This is presumably because a uniform metastable phase cannot be obtained because the phase change rate from the amorphous phase to the metastable crystal phase is slow, and the recording layer remains almost amorphous.
[0096]
On the other hand, in each of the disks of Examples 5 to 9, a uniform increase in reflectance was observed by irradiation with DC laser light of 12 mW or less at a linear velocity of 1.2 to 24 m / s. Each disk of Examples 5 to 9 which was initially crystallized was recorded and erased in the guide groove by the following procedure using a disk evaluation apparatus having a laser wavelength of 780 nm and a pickup of NA 0.5, and then reproduced. Then, the disk characteristics were evaluated.
[0097]
First, an EFM random signal was recorded using the laser waveform shown in FIG. 1 at a linear velocity of 24 m / s, a reference clock period T = 11.6 ns, Pw = 21 mW, Pe = 10.5 mW, and Pb = 0.8 mW.
In FIG. 1, the horizontal axis represents time, and the vertical axis represents laser power, and three types of power are used: recording power Pw, erasing power Pe, and bias power Pb. FIG. 1 (a) shows a laser waveform when a mark having a length of 3T is recorded. FIGS. 1 (b), (c), (d), (e), (f), (g), (h) , (I) represent laser waveforms when recording marks of length 4T, 5T, 6T, 7T, 8T, 9T, 10T, and 11T, respectively.
[0098]
That is, when forming a mark (amorphous phase) having a length nT (T is a reference clock period and n is a natural number of 3 to 11), the period of time nT is divided as in the above equation (3), A recording pulse having a recording power Pw and an off pulse having a bias power Pb were alternately irradiated, and a partial erasing power Pe was irradiated. Erasing light having an erasing power Pe was irradiated during the period between the marks (metastable crystal phase).
[0099]
Specifically, when forming each mark, a pulse train of Pw and Pb was irradiated as follows (T is a reference clock period).
[0100]
[Table 5]
3T mark: 1.5T Pw, 1.2T Pb
4T mark: 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
5T mark: 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb6T mark: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
7T mark: 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
8T mark: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
9T mark: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
10T mark: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
11T mark: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pb, 1T Pb, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
The EFM random signal recorded as described above was reproduced at a linear velocity of 2.4 m / s, and the reflectance between the mark portion and the mark portion was measured. The results are shown in Table 2 as initial reflectance. It should be noted that the portion between marks corresponds to an unrecorded portion / erased portion, and the mark portion corresponds to a recorded portion.
[0101]
In the initial states of Examples 5 to 9, it is presumed that the portion between marks (unrecorded portion / erased portion) is a metastable phase, and the mark portion (recorded portion) is an amorphous phase. In general, since there is only one type of amorphous phase and the other is a crystalline phase, the metastable phase is presumed to be a metastable crystalline phase.
Thereafter, the disk was kept in an environment of 105 ° C. for 3 hours (acceleration test), and the reflectance between the mark portion and the mark portion of the signal recorded as described above was measured again. The results are shown in Table 2 as reflectivity after the accelerated test.
[0102]
In the disks of Examples 5 and 6, almost no decrease in reflectivity between the marks was observed after the initial test and after the acceleration test, indicating that the phase change optical disk showed good performance. Further, in the disk of Example 7, the reduction rate of the reflectance between mark portions after the acceleration test was about 7%. This is presumably because the storage stability of the metastable phase is somewhat lowered because the amount of Au contained in the recording layer of the optical disk of Example 7 is smaller than that of the disks of Examples 5 and 6. However, the level of decrease in reflectance is not a problem when considered from the actual use level.
[0103]
In the disks of Examples 8 and 9, there is no decrease in the reflectivity between the marks, and good storage stability is exhibited. On the other hand, in the mark portion, the reflectance was slightly increased by the acceleration test. This is presumably because the amorphous mark changes into an unrecorded metastable phase by the accelerated test.
Next, the phase state of the recording layer in Examples 5 to 7 will be considered in more detail.
[0104]
In these discs, in the initial recording and erasing, the mark portion can be erased by irradiation with light having an erasing power of 10.5 mW at a linear velocity of 24 m / s, while the formation of the mark portion requires a recording power of at least 17 mW. It was. In other words, if the initial mark portion is the L phase and the inter-mark portion is the M phase, the phase change from the L phase to the M phase can occur at a lower temperature than the phase change from the M phase to the L phase. Is more stable.
[0105]
In Examples 5 and 6, the mark portion was initially erasable by DC laser light irradiation with a linear velocity of 2.4 m / s and a power of 5 mW, while the same condition was applied to the mark portion after the acceleration test. There was a part that was not erased. That is, assuming that the initial mark portion is the L phase and the inter-mark portion is the M phase, a part of the L phase of the mark formed at the time of signal recording has the same reflectance as the L phase after the acceleration test at 105 ° C. The phase changed to N phase which is neither L phase nor M phase.
[0106]
Actually, the disk was irradiated 1000 times with a DC laser beam with a power of 5 mW at a linear velocity of 2.4 m / s and the recording layer would not be melted by irradiation, and then the disk was irradiated with reproducing light to oscilloscope. When the reproduced signal waveform was observed, the above non-erased portion (N phase) tended to spread to the mark-to-mark portion (M phase). This indicates that the M phase between the marks gradually changes to a more stable N phase.
[0107]
More regions in the N phase were observed in the disk of Example 6 than in Example 5. The N phase returned to the unrecorded reflectivity when irradiated with DC laser light having a linear velocity of 2.4 m / s and a power of 10 mW, which seems to melt the recording layer. It is considered that the N phase has changed to the M phase. However, the N phase did not change to the M phase when irradiated with DC laser light of 6 mW or less.
[0108]
From these things, since the phase change from the M phase to the N phase can occur at a lower temperature than the phase change from the N phase to the M phase, the N phase is more stable than the M phase.
Even in the disk of Example 7, the mark-to-mark part reflectance was reduced by irradiating 1000 m of 5 mW DC laser light at a linear velocity of 2.4 m / s. It is considered that the M phase has changed to the N phase. This portion returned to an unrecorded reflectivity by irradiation with a 10 mW DC laser beam, which was thought to melt the recording layer, but did not return to an unrecorded reflectivity when irradiated with a DC laser beam of 6 mW or less. . Since the phase change from the M phase to the N phase can occur at a lower temperature than the phase change from the N phase to the M phase, the N phase is more stable than the M phase.
[0109]
  From the above, in each disk of Examples 5 to 7, it is considered that the L phase is an amorphous phase, the M phase is a metastable phase (metastable crystal phase), and the N phase is a stable phase (stable crystal phase).
  The reason why the linear velocity was lowered from 24 m / s at the time of mark recording to 2.4 m / s in the experiments for detailed consideration of the phase states of the recording layers of the disks of Examples 5 to 7 is that laser This is to make it easier to observe the most stable phase change to the N phase by slowing the cooling rate during irradiation and lengthening the time during which the temperature rises.
(Reference Example 2, Example 11To 13, Comparative Examples 9 to 11)
  On a disc-shaped polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm having a guide groove having a groove width of 0.5 μm, a groove depth of 40 nm, and a groove pitch of 1.6 μm, (ZnS)₈₀(SiO₂)₂₀Layer (80 nm), Au—Ge—Sb—Sn recording layer (15 nm), (ZnS)₈₀(SiO₂)₂₀Layer (30 nm), Al_99.5Ta_0.5An alloy reflective layer (200 nm) was formed by sputtering to produce a phase change optical disk.
[0110]
The recording layer composition is shown in Table-3. The composition of these ((Au_xSb_1-x)_1-yGe_y)_1-zSn_zTable 3 also shows the values of x, y, and z.
These disks were subjected to initial crystallization by irradiating 2.4 m / s, 10 mW DC laser light using a disk evaluation apparatus having a laser wavelength of 780 nm and a pickup of NA 0.5.
[0111]
[Table 6]

[0112]
Among the obtained disks, the disk of Comparative Example 11 did not show a uniform increase in reflectance due to the initialization operation. The reflectivity of the disc after the initialization operation was as low as 7%. That is, the initial crystallization of the recording layer could not be performed. Therefore, it is difficult to use as a phase change optical disk. This is because a uniform metastable phase cannot be obtained because the phase change rate from the amorphous phase to the metastable crystal phase is slow, or a structure such as an Au—Sb metastable phase cannot exist stably. Conceivable.
[0113]
The disc of Comparative Example 10 had a reflectivity of 10% immediately after the disc was produced, and no change in reflectivity due to the initialization operation was observed. That is, the recording layer could not be initially crystallized. Therefore, this composition cannot be used as a phase change optical disk. This is presumably because the metastable crystal phase cannot exist stably and the recording layer is always a stable crystal phase.
[0114]
The disc of Comparative Example 9 did not show a uniform increase in reflectance due to the initialization operation. Therefore, with this composition, the initial crystallization of the phase change optical disk cannot be performed well, and it has been difficult to use it as a phase change optical disk. Although the recording layer of this disk is crystallized by the initialization operation, when the reproduction waveform of this disk is observed with an oscilloscope, the reflectivity level of the crystal phase is not constant but becomes a thick line with a width. This is because uniform crystallization has not been achieved. The reason why uniform crystallization cannot be achieved in this way is thought to be because the Au—Sb metastable phase is not formed.
[0115]
  Example11In the discs Nos. 13 to 13, the recording layer was initially crystallized uniformly by the initialization operation. That is, a favorable phase change type optical disk could be obtained as compared with the disks of Comparative Examples 9-11. Further examples11In each of discs -13, the reflectivity in the As-depo amorphous state was 6% or less, and the difference from the reflectivity in the crystalline state was good.
[0116]
  Example11After the above measurement, each of discs 13 to 13 was held in an environment of 105 ° C. (acceleration test), and then the initial crystallized portion and As-depo portion reflectivity were measured again. The results are shown in Table-3. Further, the reflectance reduction rate defined by ((initial crystal part reflectivity) − (crystal part reflectivity after acceleration test)) / (initial crystal part reflectivity) is also described. It can be seen that the reflectance decrease rate decreases with increasing Sn content.
(Examples 14-18, Comparative Examples 12-16)
  On a disc-shaped polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm having a guide groove having a groove width of 0.5 μm, a groove depth of 40 nm, and a groove pitch of 1.6 μm, (ZnS)₈₀(SiO₂)₂₀Layer (100 nm), Au—Sb—Ge—In recording layer (18 nm), (ZnS)₈₀(SiO₂)₂₀Layer (40 nm), Al_99.5Ta_0.5A phase change type optical disk in which an alloy reflective layer (200 nm) was formed by sputtering and an ultraviolet curable resin layer was further provided thereon was produced.
[0117]
The recording layer composition was 10 types shown in Table-4. The composition of these ((Au_xSb_1-x)_1-yGe_y)_1-zIn_zTable 4 also shows the values of x, y, and z.
[0118]
[Table 7]

[0119]
The initial crystallization of each disk was successfully performed. After the initial crystallization, a laser irradiation test was performed in which a DC laser beam was irradiated into the guide groove through the substrate by the following procedure using an optical disk evaluation apparatus having a laser wavelength of 780 nm and an NA of 0.5.
In the laser irradiation test, the linear velocity is 2.4 m / s, 10 mW DC light 100 times, 9 mW DC light 100 times, 8 mW DC light 100 times, 7 mW DC light 100 times, 6 mW In this test, DC light is irradiated 100 times, 5 mW DC light is 100 times, 4 mW DC light is 100 times, and 3 mW DC light is irradiated 100 times in this order. And the reflectance before and behind a laser irradiation test was measured, and the reflectance fall was measured. The results are shown in Table-4. The reflectance reduction rate was defined as ((initial reflectance) − (reflectance after laser irradiation test)) / (initial reflectance).
[0120]
The laser irradiation test creates a situation in which a phase change to a stable phase is likely to occur when a phase more stable than the initial crystalline state exists. The reason is as follows. That is, when there are a plurality of phases at room temperature, all the phases tend to change to the most stable phase, but this phase change rate is increased by appropriately raising the temperature. The center of the track melts when irradiated with 10 mW DC light, but the intensity of the laser light decreases with increasing distance from the beam center, so the phase change speed to the stable phase is relatively high at a position some distance from the track center. It becomes such a temperature range. The reason why 100 times of DC light irradiation is performed is to lengthen the accumulated time maintained at this temperature. Next, when the laser power is set to 9 mW, the position in the temperature range in which the phase change rate to the stable phase becomes relatively fast becomes slightly closer to the track center than at 10 mW. At this time, the portion that has changed to a stable phase by irradiation with 10 mW of DC light remains as a stable phase. Thus, it is considered that the region that becomes a stable phase becomes wider by gradually reducing the power of the DC light.
[0121]
As can be seen from Table-4, the reduction rate of the reflectivity in each laser irradiation test of each disk of Examples 14 to 18 was smaller than that of each disk of Comparative Examples 12 to 16. In all the disks of the comparative examples, the reduction rate of the reflectance by the laser irradiation test was a large one exceeding 55%. This is because the recording layer of each disk of Comparative Examples 12 to 16 changes in phase with a crystalline phase that is more stable than the initial crystalline phase that is not used for recording erasure, as compared with the recording layer of each disk of Examples 14 to 18. It means easy. In Table 4, reflectance data is not described in the “Reflectance after laser irradiation test” and “Reflectance reduction rate” columns of the disk of Comparative Example 16. This is because the reflectance of the disc of Comparative Example 16 was too low after the laser irradiation test, making it impossible to reproduce.
[0122]
In the disks of Examples 14 to 18, it is apparent that the decrease in reflectance is clearly suppressed, and the phase change to the stable crystal phase is less likely to occur. In particular, as can be seen by comparing the results of the disk of Example 18 and the results of the disks of Examples 14 to 17, the recording layer composition is a composition in which an Au—Sb alloy contains Ge and further In. As a result, the phase change to a stable crystal phase is less likely to occur.
[0123]
The disks of Comparative Examples 12 to 16 and the disks of Comparative Examples 5, 6 and 9 are common in that they do not contain Au in the recording layer, but the disks of Comparative Examples 12 to 16 are Comparative Examples 5 and 6 respectively. And 9 are superior in that the initial crystallization of the disk can be performed satisfactorily. This means that even in a recording layer composition that does not contain Au, by controlling the contents of Sb, Ge, and In, it is possible to obtain a disc that allows initial crystallization. However, even in each of the disks of Comparative Examples 12 to 16 in which the initial crystallization can be performed satisfactorily, these disks do not contain Au in the recording layer, so that a phase change to a stable crystal phase is likely to occur in the laser irradiation test. As a result, the decrease in the reflectance of the recording layer is increased.
[0124]
On the other hand, it is essential that the recording layer of the optical information recording medium of the present invention contains a predetermined amount of Au. This is because the metastable crystal exists stably because a predetermined amount of Au is contained as described above, and the phase change to the stable crystal phase is suppressed. This is also apparent from the results of laser irradiation tests on the disks of Examples 14-18.
[0125]
Also, in any of the disks of Examples 14 to 18 and Comparative Examples 12 to 16, the reflectance did not change even when a laser of 5 mW or less was irradiated after the laser irradiation test, but 10 mW of DC light was irradiated once. Then, it returned to the initial reflectivity. This is presumably because the recording layer does not melt with a laser of 5 mW or less, but the recording layer melts upon irradiation with DC light of 10 mW and changes into a crystalline phase corresponding to a metastable phase. In addition, from the results of Comparative Examples 12 to 16 shown in Table-4, in the case where the In—Sb—Ge based alloy is used for the recording layer and the case where the In—Sb based alloy is used for the recording layer, In and Sb It can be seen that when the amount of In increases in the content ratio, the reflectance is greatly decreased and the phase tends to change to a stable crystalline phase.
[0126]
Next, an EFM random signal was overwritten and recorded 10 times at an initial crystallization portion of the disk of Example 15 at a recording linear velocity of 24 m / s, and 3T mark jitter was measured at a linear velocity of 2.4 m / s. At the time of recording, the reference clock cycle T = 11.6 ns, Pw = 22 mW, Pe = 7 mW, Pb = 0.8 mW, and the EFM random signal has the laser waveform shown in FIG.
[0127]
That is, when forming a mark (amorphous phase) having a length nT (T is a reference clock period and n is a natural number of 3 to 11), the period of time nT is divided as in the above equation (3), A recording pulse having a recording power Pw and an off pulse having a bias power Pb were alternately irradiated, and a partial erasing power Pe was irradiated. Erase light having an erase power Pe was irradiated during the period between the marks (crystal phase).
[0128]
Specifically, when forming each mark, a pulse train of Pw and Pb was irradiated as follows (T is a reference clock period).
[0129]
[Table 8]
3T mark: 1.5T Pw, 1.2T Pb
4T mark part: 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
5T mark part: 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
6T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
7T mark part: 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
8T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
9T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
10T mark part: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 0.6T Pb
11T mark portion: 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pw, 1T Pb, 1T Pb, 1T Pw, 1.35T Pb, 1.5T Pw, 0.6T Pb
The EFM random signal overwritten 10 times as described above was reproduced at a linear velocity of 2.4 m / s, and 3T mark jitter was measured to be 17.4 ns. That is, the CD-RW standard (Orange Book Part 3) of 17.5 ns or less was satisfied. The disk of Example 15 can be expected to further improve the recording characteristics by changing the composition of the recording layer to change the crystallization speed and improving the pulse strategy during recording. Here, the reason why the recording characteristics were evaluated only for the disk of Example 15 is that the disk of Example 15 exhibited a crystallization speed relatively suitable for the above recording conditions. The disks of other examples are considered to have compositions suitable for different recording conditions.
[0130]
Here, the crystallization speed was slowed by increasing the contents of Ge, In, and Au. Accordingly, for example, by reducing the In content and increasing the Ge content, it is possible to obtain recording layers having different crystallization speeds and different compositions.
In the unrecorded state of the disc, the playback light was irradiated and the playback waveform was observed with an oscilloscope._FiveSb₇₉Te₁₆The phenomenon that the reflectance level of the crystal phase (unrecorded state) is not constant but appears as a thick line with a width as seen in the above is not seen in the disk of Example 15, and the noise is good. I found that the disc was obtained.
[0131]
【The invention's effect】
According to the present invention, it is possible to obtain an optical information recording medium having a high phase change rate, high-speed recording / erasing, and high storage stability. In particular, it is possible to obtain an optical information recording medium that is excellent in storage stability of the recording part (mark part) and unrecorded / erased part (inter-mark part) and high transfer rate overwrite recording jitter characteristics.
[Brief description of the drawings]
FIG. 1 shows an outline of a pulse division method in an embodiment of the present invention.Figure

Claims (7)

An optical information recording medium provided with a phase change recording layer capable of taking at least two different phases on a substrate, wherein the phase change recording layer has a composition represented by the following general formula (1). An optical information recording medium characterized by comprising a component.
(Au _x Sb _1-x ) _1-y Ge _y (1)
However, x and y are numbers satisfying 0.20 ≦ x ≦ 0.4 and 0 <y ≦ 0.3, respectively. An optical information recording medium having a phase change recording layer capable of taking at least two different phases on a substrate, wherein the phase change recording layer has a composition represented by the following general formula (2). An optical information recording medium comprising a component.
_{((Au x Sb 1-x} ) 1-y Ge y) 1-z M2 z (2)
However, x and y are 0.01 ≦ x ≦ 0.4 and 0 <y ≦ 0. It is a number satisfying 3 . The element M2 is at least one element represented by Te, In, and Sn. Furthermore, z is 0.01 ≦ z ≦ 0.4 when M2 is Te, 0.03 ≦ z ≦ 0.4 when M2 is In, and 0.1 ≦ z ≦ 0 when M2 is Sn. Is a number satisfying .4.   3. The optical information recording medium according to claim 1, wherein the recording signal is erased only when the reference clock period T is 15 nsec or less. An optical information recording medium in which an information signal is recorded and erased only when a reference clock period T is 15 nsec or less, and at the time of recording, a high power laser pulse and a low power laser pulse are alternately irradiated, and the low power the optical information recording medium according to any one of claims 1 to 2 laser pulses comprises more pulse pulse width 0.9T of.   A recording and erasing method for setting two different phases of the phase change recording layer to a recorded state and an unrecorded / erased state with respect to the optical information recording medium according to any one of claims 1 to 4. When the phase change recording layer can take at least three phases of A phase, B phase and C phase, the B phase is more stable than the A phase, and the C phase is more stable than the B phase, the B phase is recorded. A recording / erasing method, wherein the recording / erasing state is set to a state or unrecorded / erased state.   6. The recording / erasing method according to claim 5, wherein at least the A phase is recorded and the B phase is unrecorded / erased, or the A phase is unrecorded / erased and the B phase is recorded.   5. A recording / erasing method for performing recording / erasing of an information signal only when the reference clock period T is 15 nsec or less with respect to the optical information recording medium according to claim 1, wherein a high power is used for recording. A recording and erasing method in which a laser pulse and a low-power laser pulse are alternately irradiated, and the low-power laser pulse includes a pulse having a pulse width of 0.9 T or more.

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