JP2004284024A

JP2004284024A - Phase transition optical recording medium

Info

Publication number: JP2004284024A
Application number: JP2003075317A
Authority: JP
Inventors: Mikiko Abe; 美樹子安部; Hajime Yuzurihara; 肇譲原; Koji Deguchi; 浩司出口; Eiko Suzuki; 栄子鈴木; Yuji Miura; 裕司三浦
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2003-03-19
Filing date: 2003-03-19
Publication date: 2004-10-14

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase transition optical recording medium showing successful recording reproduction properties not depending on the frequency of overwrite. <P>SOLUTION: This phase transition optical recording medium has a first protecting layer 2, a phase transition recording layer 3 which enables the reversible phase transition of an amorphous phase and a crystalline phase to occur, a second protecting layer 4 and a reflective layer 6, laminated on the upper surface of a transparent substrate 1 with a laser beam track (a guide groove). In addition, in this medium which records and/or reproduces information by illuminating the laser beam, a spacing in the crystalline phase after initialization of the phase transition recording layer 3, is 2.9 to 3.3Å, and the crystal face which is perpendicular with the upper surface of the substrate 1 is orientated at an angle of 30±15° with the tangential direction of the track. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、レーザ光の案内溝が設けられた透明な基板の上面に、第一保護層、非晶質相と結晶相の可逆的相変化をする相変化記録層、第二保護層、反射層を備え、前記レーザ光を照射して情報の記録及び／または再生を行う相変化光記録媒体に関する。
【０００２】
【従来の技術】
近年、情報量の増大に伴い高密度でかつ高速に大量データの記録・再生ができる記録媒体が求められている。光ビームを照射し、情報の記録・再生を行う相変化光記録媒体、特に相変化光ディスクは、信号品質に優れているため高密度化が可能で、１ビームオーバーライトが容易なことから高速アクセス性に優れた記録媒体である。
相変化光ディスクは、レーザ光の案内溝が設けられた透明な基板の上面に、第一保護層、非晶質相と結晶相の可逆的相変化をする相変化記録層、第二保護層、金属からなる反射層をこの順に備え、さらに反射層の上に樹脂保護層を備えてなる。また、貼り合わせ型光ディスクの場合には、上述した構成を片方の面に用いるか、または、接着層を介して両面に反射層どうしを向かい合わせて貼り合わせる構成となる。
【０００３】
上述の相変化光ディスクは一般に、スパッタリング法、真空蒸着法などによる真空プロセスで成膜して製造されるが、これらの方法で成膜される相変化記録層は、成膜直後の状態、即ち、ａｓ−ｄｅｐｏ（アズ・デポ）状態では、非晶質である場合が多い。オーバーライト時にも、非晶質（マーク）が形成されるが、ａｓ−ｄｅｐｏ状態において、相変化記録層には結晶核が殆どないことから、ａｓ−ｄｅｐｏ状態の非晶質は、オーバーライト時に形成される非晶質とは異なり、結晶化に要する時間が非常に長い。そのため、相変化光ディスクを製造後、出荷前に相変化記録層を結晶化するための初期化工程を設けている。
【０００４】
次に、相変化光ディスクに１ビームオーバーライト方式で情報を記録する手順について説明する。
相変化記録層の非晶質相と結晶相の可逆的相変化は、パルス化された３つの出力レベルの集束レーザビームによって行う。なお、最も高い出力レベルのレーザビームは、相変化記録層の溶融に用い、中間の出力レベルのレーザビームは、融点直下、結晶化温度よりも高い温度まで相変化記録層を加熱するのに用い、最も低いレベルのレーザビームは、相変化記録層の加熱または冷却の制御に用いる。
【０００５】
相変化光ディスクに情報を記録するには、最も高い出力レベルのレーザビームを所望の箇所に照射して、相変化記録層を急激に熱して溶融し、それに続けて急冷する。すると、相変化記録層の原子配列が乱れたまま固定化して非晶質または微結晶となり、反射率が低下して記録マークとなる。一方、所望の箇所以外には、中間の出力レベルのレーザビームを照射して、徐熱徐冷して相変化記録層の原子配列を元に戻すことにより結晶質にする。これにより、相変化記録層に結晶領域と非晶質領域が作成され、情報が記録される。
また、情報の記録された相変化光ディスクの情報を新たな情報に書き換える場合も、上述の記録の方法と同様である。
【０００６】
このようにして情報が記録または書き換えられた相変化光ディスクを再生するには、再生用のレーザビームを照射して、通常、相変化記録層の非晶質−結晶間の可逆的相変化現象に伴う反射率差又は反射光位相差を利用して再生する。
【０００７】
相変化光記録媒体は、今後、高密度画像記録への用途拡大が予想され、そのため記録媒体の容量・密度の増加が求められるため、高線速記録が必須となる。しかしながら、上述のような１ビームオーバーライト方式で高線速記録を行う場合、繰り返し記録初期（オーバーライト回数が１回から１０回程度まで）の消去率が低く、初期化後に情報の書換えを何回か繰り返さなければ安定した消去率を得ることができないという問題があり、それを解決すべく技術が開示されてきた（例えば、特許文献１など）。
【０００８】
【特許文献１】
特許第２８３０３３６号公報
【０００９】
【発明が解決しようとする課題】
このような繰り返し記録初期に起こる消去率の低下の原因の一つとして、初期化後の相変化記録層の結晶状態と、非晶質マークをオーバーライト消去して再形成した結晶状態とが異なるために反射率の不均一が生じ、その結果、ジッターが増大することが考えられる。一方、オーバーライト回数が１０回程度以降で消去率が安定する理由は、オーバーライト回数１０回までに初期化後の結晶状態が全て非晶質マークをオーバーライト消去した後の結晶状態へ移り、反射率が均一になるためと考えられる。
【００１０】
そこで、この発明の目的は、オーバーライト回数に依らない良好な記録再生特性を有する相変化光記録媒体を提供することにある。
【００１１】
【課題を解決するための手段】
このため、請求項１に記載の発明は、レーザ光の案内溝が設けられた透明な基板の上面に、第一保護層、非晶質相と結晶相の可逆的相変化をする相変化記録層、第二保護層、反射層を備え、前記レーザ光を照射して情報の記録及び／または再生を行う相変化光記録媒体において、
前記相変化記録層の初期化後の結晶相にあって、面間隔が２．９〜３．３Å、かつ前記基板の上面に垂直である結晶面が、前記案内溝の接線方向と３０±１５°をなす角で配向することを特徴とする。
【００１２】
請求項２に記載の発明は、請求項１に記載の相変化光記録媒体において、前記相変化記録層がＧｅ_αＳｂ_βＴｅ_{（１−α―β）}からなり、その原子比率が０．０２≦α≦０．０７、０．６５≦β≦０．８０であることを特徴とする。
【００１３】
請求項３に記載の発明は、請求項１または２に記載の相変化光記録媒体において、前記相変化記録層が添加元素を原子比率で０．０１〜０．１０含み、前記添加元素として、Ｇａ、Ｉｎ、Ｔｌ、Ｐｂ，Ｓｎ、Ｂｉ、Ｃｄ，Ｈｇ、Ａｇ、Ｃｕ、Ｍｎ、Ｄｙのうち、少なくとも一種類を用いることを特徴とする。
【００１４】
請求項４に記載の発明は、請求項２または３に記載の相変化光記録媒体において、照射光パワー密度が１０〜３０ｍＷ／μｍ^２であり、かつ照射光ビーム線速度が前記相変化記録層の結晶化限界速度に対し±２ｍ／ｓの範囲で前記初期化が行われることを特徴とする。
【００１５】
請求項５に記載の発明は、請求項１ないし４のいずれかに記載の相変化光記録媒体において、前記相変化記録層と前記第一保護層との間及び／又は前記相変化記録層と前記第二保護層との間に酸化物層を備えることを特徴とする。
【００１６】
請求項６に記載の発明は、請求項５記載の相変化光記録媒体において、前記酸化物層が、ＺｒＯ_２、Ａｌ_２Ｏ_３ＴｉＯ_２、ＳｉＯ_２、ＺｎＯ、Ｉｎ_２Ｏ_３、ＳｎＯ、ＰｂＯのうちの少なくとも一種類からなることを特徴とする。
【００１７】
請求項７に記載の発明は、請求項５または６に記載の相変化光記録媒体において、前記酸化物層の膜厚が、８ｎｍ未満であることを特徴とする。
【００１８】
【発明の実施の形態】
以下、上記発明について具体的に説明する。
この発明の相変化光記録媒体は、例えば、レーザ光の案内溝が設けられた透明な基板の上面に、第一保護層、非晶質相と結晶相の可逆的相変化をする相変化記録層、第二保護層、反射層を備えてなる。
初期化後の相変化記録層の結晶構造は、初期化方法に大きく依存する。そこで本発明者らは、この事実に注目して様々な条件で初期化を行い、相変化記録層の結晶状態と繰り返し記録初期の記録特性（オーバーライト回数が１回から１０回程度までの記録特性、以下「繰り返し記録初期の特性」という。）との関係を調査したところ、基板面に対して垂直な結晶面に対し、ある特定の結晶の結晶面がある特定の方向に強く配向するとき、繰り返し記録初期の特性が改善されることが判った。
ここで「ある特定の結晶」とは、面間隔が２．９〜３．３Åの結晶を意味し、また「ある特定の方向」とは、基板に垂直な結晶面がトラック接線方向に対して３０±１５°の角度をなす方向をいう。
【００１９】
相変化記録層中でこのような条件を満たす結晶が多く存在すると、繰り返し記録初期の特性が改善できる理由としては、次のようなことが考えられる。すなわち、非晶質マークをオーバーライト消去により結晶へと再形成する際に、結晶化の進む方向（レーザ走査方向＝トラック方向）に沿って非晶質マーク周辺にある特定の方向に配向した結晶が多く存在すると、マーク周辺の構造を下地としてエピタキシャル成長が起こりやすくなり、初期化による結晶化後の相変化記録層の結晶組織と非晶質マークをオーバーライト消去により再形成した結晶の結晶組織との間の不均一性が解消されるためであると考えられる。
また、ノイズ発生の原因の一つと考えられている、結晶相に微細な結晶粒界が存在する場合に対しても、このように結晶粒（結晶面）がある一定の方向に揃うことで回避することができる。
【００２０】
本発明の相変化光記録媒体に備える相変化記録層は、後述するように初期化によって結晶化した相変化記録層の面内回折測定の結果において、ある特徴的な強度分布を示すことを特徴としている。
この特徴的な配向の面は、回折角２θ＝２７〜３０度に回折ピークを有する面（面間隔が２．９〜３．３Åの結晶）であり、この面に関して試料を３６０°回転させながら強度変化を測定した際、φ＝４５°、２２５°においてある特定の結晶面の極大値が存在し、この方向以外に他に配向が少ないことを特徴としている。
【００２１】
具体的には図１及び図２に示すように、試料の回転角（φ）を、Ｘ線の入射方向と基板上のトラック接線方向とが互いに平行である場合を便宜上φ＝０°と定め、検出器をθ＝２７〜３０°付近で固定したまま試料を回転させ、出射してくるＸ線回折強度を測定したとき、φ＝４５°および２２５°においてＸ線回折強度のピークが認められることを意味している。このことは、Ｘ線の回折原理より、結晶の結晶面がトラック接線方向と３０°前後（本発明においては、３０±１５°とする。）をなす角で配向している状態であることを意味している。
【００２２】
上記の結晶状態を実現することが可能な相変化記録材料としては、不均一核形成により結晶化が進行するＳｂ０．７Ｔｅ０．３近傍組成のＳｂ−Ｔｅ２元系合金を母相に、これに必須元素としてＧｅが含まれ、更にＧａ、Ｉｎ、Ｔｌ、Ｐｂ，Ｓｎ、Ｂｉ、Ｃｄ，Ｈｇ、Ａｇ、Ｃｕ、Ｍｎ、Ｄｙから選ばれた少なくとも一種の元素が原子比率で０．０１〜０．１０添加された相変化記録材料であることが好ましい。
【００２３】
ここで均一核形成による結晶化とは、比較的低温でまず結晶の核形成が均一に起こり、その後形成された核を中心に比較的高温で結晶成長することによって進行する結晶化のことである。不均一核形成による結晶化とは、核形成はほとんど起こらず、既に存在する結晶領域と非晶質（マーク）領域の界面からの結晶成長により結晶化が進行することを指す。本発明においては、不均一核形成により結晶化が進行することで、この発明が効果を奏する。
【００２４】
以下に、本発明の相変化記録層を構成する各元素の最適組成範囲について述べる。ＳｂとＴｅのモル比が７：３であるＳｂ７０Ｔｅ３０近傍組成のＳｂ−Ｔｅ二元系合金は、オーバーライトによる組成偏析が起こり難く、繰り返し記録特性に優れた相変化記録材料である。ＳｂとＴｅの配合比を変えることで後述する「結晶化限界速度」を調整することが可能であり、Ｓｂ比率を高くすると結晶化限界速度が速くなり転送速度を高速にすることができる。本発明の対象となる相変化光記録媒体においては、Ｓｂの最適組成範囲は、Ｓｂの原子比率が０．６５以上、０．８０以下である。これは、Ｓｂの原子比率が０．６５より少ないとオーバーライトによるジッター増加が大きくなり、記録特性を改善することが困難となってしまうからであり、また逆にＳｂが過剰な場合は、結晶化速度の上昇が急激となりマーク形成が困難となるほか、保存信頼性が劣化してしまうからである。
【００２５】
一方Ｇｅは、Ｇａほど結晶化温度を上昇させることなく、少量の添加で相変化光記録媒体の保存信頼性を飛躍的に向上させることができるため、必須の添加元素である。このとき添加するＧｅの原子比率は、０．０２以上で結晶化速度の速い記録層のアモルファス安定性を向上させる効果が現れ、添加量が増えるに従いその効果は高くなるが、過剰の添加は、オーバーライトによるジッタ−上昇などの弊害を招くことから上限は原子比率で０．０７とする必要がある。
【００２６】
またＧａは、少ない添加量で結晶化限界速度、記録層材料の結晶化温度を高める効果を持つことから、非晶質マークの安定性に優れた相変化光記録媒体を提供することが可能である。しかし、Ｇａの添加量が多すぎると結晶化温度が高くなり過ぎ、初期化時に均一な結晶相を得ることが難しくなるためＧａの組成範囲は、原子比率で０．１０以下とすることが好ましい。
【００２７】
ＩｎもＧａと同様の効果を持つが、Ｇａほど結晶化温度を上昇させないので、初期化の問題を考慮した場合、Ｇａを補う元素として用いると有効である。更にＧａ、Ｉｎ以外に、Ｔｌ、Ｐｂ、Ｓｎ、Ｂｉ、Ｃｄ、Ｈｇにも結晶化限界速度を速くする効果がある。これらの元素を添加することにより、結晶化限界速度が速くなる理由は不明であるが、仮にＳｂ−Ｔｅ合金の結晶化が促進されることに依るならば、これらの元素の中でもＳｂと同じ価数を取り易いＧａ、Ｉｎ、Ｂｉはより好ましく、また、Ｓｂに最も原子番号が近くＳｂとの親和性が高いと思われるＳｎも好ましい。しかし、添加量が多すぎると再生光劣化や繰り返し記録初期の特性劣化を引き起すことが予想されるため、組成範囲は何れも１０ａｔ％以下とする必要がある。また、本発明者らの調査により、添加元素として、ＭｎやＤｙについてもＩｎと同様の効果を奏することが分っており、特にＭｎは、結晶化速度を速め、かつ、Ｇｅ添加量をそれほど増やす必要のない保存信頼性にも優れた添加元素であることも分っている。
さらに、上述の添加元素と共に、Ｃｕ及び／又はＡｕを含有させることが望ましい。Ｃｕ，Ａｕは、保存信頼性に効果のある添加元素であることから、上述の添加元素と共に適当に組み合わせることによって、所望の高線速度光記録媒体を実現し、かつ初期化後反射率とオーバーライト反射率の不均一性を解消し易い記録材料を設計することができる。
【００２８】
相変化記録層の膜厚については、８〜２０ｎｍの範囲が望ましい。８ｎｍより薄いと繰り返し記録特性の劣化が著しくなる。２０ｎｍより厚いと、相変化記録層の均一な初期化が行い辛くなり、また光透過率が不十分となるため高反射率が得られず変調度も低下してしまう。
【００２９】
また、成膜条件によっても相変化記録層の初期化直後の非晶質状態（ａｓ−ｄｅｐｏ状態）は変化する。ａｓ−ｄｅｐｏ状態では、基板上で原子が乱雑に配列しており、その乱雑さが大きいほど初期化に長く時間を要し、所望の結晶状態を得ることが困難となる。しかし、低ガス圧、かつ高電圧でのスパッタリング法による成膜において基板上に飛来するスパッタ粒子は、通常のスパッタリングにおけるスパッタ粒子に比べて大きな運動エネルギーを持っていると考えられており、ある程度の秩序性を持った配向膜が形成されやすく、初期化後に所望の結晶状態を得やすい。従って、相変化記録層の成膜に際し、低ガス圧、かつ高電圧でのスパッタリング法を採用することが好ましい。
【００３０】
なお、本発明者らは、相変化記録層と第一保護層との間及び／又は相変化記録層と第二保護層との間に酸化物層を設けると、所望の結晶状態を得やすいことも判った。これは、従来、保護層として用いられているＺｎＳ−ＳｉＯ_２に比べ、一般に酸化物層の熱伝導率が低いために、初期化のエネルギーを効率よく相変化記録層に吸収させることによると考えられる。このような効果は、酸化物層を例えば１ｎｍ程度設けた場合でも期待できるが、膜厚が厚くなると記録媒体の保存信頼性が劣化する不具合が生じてしまうため、酸化物層の膜厚は８ｎｍ未満、好ましくは２〜４ｎｍ程度に薄くして保存信頼性の劣化を防止する必要がある。
【００３１】
また、酸化物層は、ＺｒＯ_２、Ａｌ_２Ｏ_３、ＴｉＯ_２、ＳｉＯ_２、ＺｎＯ、Ｉｎ_２Ｏ_３、ＳｎＯ、ＰｂＯから選ばれた少なくとも一種の酸化物からなることが望ましい。このうち、特にＺｒＯ_２は、機械的強度に極めて優れるため、繰り返し記録初期の特性を改善するばかりでなく、オーバーライト１０００回以上の多数回の書換えに対しても記録特性を劣化させることがない。加えて、熱伝導率が極めて低いので、低い記録パワーでも記録時の記録層到達温度がＺｎＳ−ＳｉＯ_２保護層のみを設けただけの従来の記録媒体に比べて高くなり、マーク形成に必要な急冷構造が実現されるため感度の向上も図ることが可能である。
【００３２】
さらに、ＺｒＯ_２を主成分とする酸化物層には、ＺｒＯ_２以外に酸化チタンを含むことが望ましく、更には希土類酸化物又はベリリウムを除くＩＩａ族の酸化物を含むことが望ましい。これは、酸化チタンを添加することで酸化物層の熱伝導率を更に低下させることが可能であり、また、光学特性の調整や信頼性劣化の低減にも効果的であること、一方、希土類酸化物又はベリリウムを除くＩＩａ族の酸化物に関してはＺｒＯ_２の温度に対する体積変化を小さくする効果があり、初期化や記録時の温度変化に対する安定性を向上させることなどがその理由である。
【００３３】
このような効果を得る為には、酸化チタンの含有量を、酸化物層材料全体の６０モル％以下とすること、希土類酸化物又はベリリウムを除くＩＩａ族の酸化物の含有量はＺｒＯ_２に対して１〜１０モル％とすることが望ましい。酸化チタンの含有量は、必ずしもこの範囲に限定はされないが、６０モル％を超えるとＺｒＯ_２を含む酸化物層の効果が不明瞭となることから上記範囲が適している。また、好ましい希土類酸化物又はベリリウムを除くＩＩａ族の酸化物としては、Ｙ、Ｍｇ、Ｃａなどの酸化物が挙げられる。ＺｒＯ_２にＹ、Ｍｇ、Ｃａ等の酸化物を固溶させただけの酸化物層の場合は、記録媒体の保存信頼性劣化が顕著となるため、ＴｉＯ_２などの酸化物と併用して添加することが望ましい。
【００３４】
その他の酸化物材料Ａｌ_２Ｏ_３、ＴｉＯ_２、ＳｉＯ_２、ＺｎＯ、Ｉｎ_２Ｏ_３、ＳｎＯ、ＰｂＯについても、ＺｒＯ_２とほぼ同等の効果を有すことがわかっている。
このうち、Ａｌ_２Ｏ_３はＺｒＯ_２を界面層材料として使用した記録媒体に比べて保存信頼牲をそれ程損なわないため、保存安定性が問題となる記録媒体の場合には最適材料である。
【００３５】
次に、上述の相変化記録層を備える相変化光記録媒体の初期化方法について説明する。
照射光パワー密度を１０〜３０ｍＷ／μｍ^２で、照射光ビーム線速度を相変化記録層の結晶化限界速度に対し±２ｍ／ｓの速度範囲で初期化する。
【００３６】
照射光パワー密度は、高線速記録用に結晶化限界速度の速い記録層材料を用いると、記録層材料の結晶化限界速度が速くなるにつれて初期化がし難くなり、高出力のパワーが必要であったこと、また、高出力の初期化パワーであっても、線速度と送り幅が一定の場合、照射光パワー密度が１０〜３０ｍＷ／μｍ^２であると繰り返し記録初期の特性（特にオーバーライト回数１回目の記録特性、以下「ＤＯＷ１」という。）が一層改善されたことから、照射光パワー密度を１０〜３０ｍＷ／μｍ^２に決定した。
【００３７】
また、照射光ビーム線速度は、本発明者らが照射光パワー密度範囲において高線速記録時の繰り返し記録初期の特性とビーム線速度の関係を調査したところ、相変化記録層の結晶化限界速度に対し±２ｍ／ｓの線速度範囲内で初期化された記録媒体は、繰り返し記録初期の特性が良好であったことから、相変化記録層の結晶化限界速度に対し±２ｍ／ｓに決定した。
【００３８】
なお、「結晶化限界速度」とは、本発明者らが経験に基づき考案して定義した記録層材料の特性を表す物性値であり、回転する光ディスクに一定パワーのＤＣ光を照射し、光ディスク反射率の照射光ビーム線速度（すなわち、光ディスク回転速度）依存性（但し記録／再生系での線速度依存性）を評価したとき、図３に示すような反射率の急激な低下が始まる時の線速度のことを意味する。これは、「一定パワーのＤＣ光」を前述の記録原理における中間出力のレーザパルス（消去パルス）に見立て、記録／再生系の照射光ビーム線速度を上昇させたときにどの線速度まで結晶化（消去）が可能であるかについて着目した評価方法である。
【００３９】
図３を例にとると、記録層材料の結晶化限界速度（図中太線）に対して２ｍ／ｓを超える速い線速度で初期化を行うと満足な結晶化が実現されず、また記録層材料の結晶化限界速度に対して２ｍ／ｓよりも遅い線速度で初期化を行うと、初期化プロセスに時間がかかり実用的でないばかりか、繰り返し記録初期の特性劣化の問題を解消し難くなることが判る。
【００４０】
図４には、ＤＯＷ１ジッターの初期化パワー依存性を示し、また図５では、図４においてＡで示すＤＯＷ１ジッターが高くなる初期化条件（Ｐｉ＝９．３ｍＷ／μｍ^２）と、Ｂで示すＤＯＷ１ジッターが低くなる初期化条件（Ｐｉ＝１２ｍＷ／μｍ^２）でそれぞれ初期化した場合の相変化記録層のＸ線面内回折の測定結果を示した。
【００４１】
図５によると、φ＝４５°および２２５°に観察されるＸ線回折強度のピークは、ＤＯＷ１ジッターが高くなる初期化条件で初期化した場合に比べて、ＤＯＷ１ジッターが低くなる初期化条件で初期化した場合の方が顕著になっていることがわかる。すなわち、ＤＯＷ１ジッターが低くなる初期化条件（Ｐｉ＝１２ｍＷ／μｍ^２）で初期化した相変化記録層は、ＤＯＷ１ジッターが高くなる初期化条件（Ｐｉ＝９．３ｍＷ／μｍ^２）で初期化した相変化記録層に比べて、結晶がトラック接線方向と３０±１５°をなす角でより強く配向し、相変化記録層の記録特性を向上させることができる。
【００４２】
なお、φ＝１３５°または３１５°の角度においてもＸ線回折強度のピークが観察されているが、これは、相変化記録層を構成するＳｂ−Ｔｅ二元系共晶合金が立方晶系である性質上、結晶面がトラック接線方向と３０±１５°をなす角で配向する結晶が増大する（あるいは大きく成長する）につれ、４５°から９０°ずれた１３５°、２２５°から９０°ずれた３１５°においてもＸ線回折強度のピークが同様に観察されるためと思われる。
【００４３】
このように上記範囲において「ある特定の条件を満たす結晶構造」が相変化記録層中で最大に存在するように適切な初期化条件を選択すれば、繰り返し記録初期の特性に優れた光記録媒体を実現することができる。
【００４４】
【実施例】
以下、本発明の実施例を図面に基づいて説明する。但し、これら実施例や使用した初期化装置等については、本発明をなんら制限するものではない。
【００４５】
［実施例１］
図６には、この発明の相変化光記録媒体の一例としての相変化光ディスクの概略断面図を示す。相変化光ディスクは、レーザ光の案内溝が設けられた透明な１基板の上面に、第一保護層２、非晶質相と結晶相の可逆的相変化をする相変化記録層３、第二保護層４、硫化防止層５、反射層６、樹脂保護層７を備え、接着シートを介して貼り合せ用基板８を貼着してなる。
【００４６】
基板１は、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート製で、トラック（案内溝）ピッチ０．７４μｍである。第一保護層２は、厚さ６５ｎｍのＺｎＳ（８０ｍｏｌ％）−ＳｉＯ_２（２０ｍｏｌ％）からなる層である。相変化記録層３は、厚さ１７ｎｍのＧｅ_４Ｓｂ_６９Ｔｅ_２０Ｉｎ_５Ａｇ_２からなる層であり、前述のように初期結晶化後の結晶相が、以下の条件に示されるある特定の方向に、強く配向した状態であることに特徴がある。すなわち、面間隔が２．９〜３．３Åの結晶であり、基板１の上面に垂直である結晶面が、トラックの接線方向と３０±１５°の角度をなす。第二保護層４は、厚さ１４ｎｍのＺｎＳ（８０ｍｏｌ％）−ＳｉＯ_２（２０ｍｏｌ％）からなる層である。硫化防止層５は、厚さ４ｎｍのＳｉからなる層である。反射層６は、厚さ１４０ｎｍのＡｇからなる層である。貼り合せ用基板８は、基板１と同一の、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート製である。
【００４７】
まず、基板１の上に、スパッタリング法により、第一保護層２、相変化記録層３、第二保護層４、硫化防止層５、反射層６をこの順に成膜し、その上にスピンコート法により樹脂保護層７を成膜し、さらに、貼り合せ用基板８を接着シートで貼り合せると、相変化光ディスクとなる。
【００４８】
次に、この相変化光ディスクの初期化方法について説明する。
本実施例では、日立コンピュータ機器社製（ＰＯＰ２４０―Ｅ４）を用いて相変化光ディスクの初期化を行った（以下の実施例、比較例においても同じ装置で初期化した。）。また、繰り返し記録初期の特性の評価は、波長６６０ｎｍ、ＮＡ０．６５のピックアップを有する光ディスク評価装置（パルステック社製ＤＤＵ−１０００）を用いて記録線速度１４．０ｍ／ｓ、線密度０．２６７μｍ／ｂｉｔのもと、ＥＦＭ＋変調方式でランダム信号の繰り返し記録（２回）を行い、再生線速３．５ｍ／ｓ、再生パワー＝０．７ｍＷでＤＯＷ１特性（ジッター）を評価した。ここでジッターとは、ｄａｔａｔｏｃｌｏｃｋｊｉｔｔｅｒ（データ・ツー・クロック・ジッター）σを検出窓幅Ｔｗで規格化した値のことである。また保存信頼性については、上記ディスクを８０℃８５％ＲＨ恒温槽に３００時間放置したのち、再び記録特性を評価することで確認した。
【００４９】
下記表１に示すように、相変化光ディスクを照射光パワー密度１２．０ｍＷ／μｍ^２、照射光ビーム線速度９．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。その結果を下記表２に示す。
【００５０】
【表１】

【００５１】
【表２】

【００５２】
なお、評価基準は次の通りである。
（１）記録線速度１４ｍ／ｓにおけるＤＯＷ１特性について、ジッターが１０％以下の場合を「○」、１０％より大きい場合を「×」とした。
（２）保存信頼性については８０℃８５％ＲＨ恒温槽で３００時間放置した後のジッター変動が０．５％以内の場合を「○」、０．５％を超えてジッターが変動した場合を「×」、未評価のものを「−」とした。
【００５３】
本実施例では、ＤＯＷ１特性、及び保存信頼性の両項目において良好な結果を得ることができた。また、評価後に相変化記録層３のＸ線面内回折を測定したところ、結果は下記の回折条件を満たすものであった。（以下、実施例において、下記回折条件を満たした場合は○、満たさなかった場合は×で示した。）
回折条件：
図１及び図２で示すように、基板面に対しほぼ平行にＸ線を入射（入射角０．２〜０．５°）させ、回折したＸ線を基板面に対しほぼ平行に検出するＸ線面内回折測定（基板面に対して垂直な格子面を測定する方法）において、前述したように検出角を２θ＝２７〜３０°付近に固定し、結晶化した相変化記録層を持つ光記録媒体の反射層及び保護層を剥がした後、その試料を３６０度回転させながらＸ線回折強度を測定したとき、回転角（φ）が４５度、１３５度，２２５度、３１５度となるとき回折強度のピークが極大となること。
なお入射するＸ線の光源には銅のＫα線（λ＝１．５４Å）を用い、従ってＢｒａｇｇ条件より、検出角２θ＝２７〜３０°付近では面間隔ｄ＝２．９７〜３．３Åの結晶が測定されることになる。
【００５４】
［実施例２］
この例の相変化光ディスクは、相変化記録層３をＧｅ_３Ｓｂ_７１Ｔｅ_２１Ｉｎ_４Ａｇ_１で成膜する点以外は、実施例１と同様の構成、同様の製造方法であるので説明を省略する。そして、初期化方法は、表１に示すように、相変化光ディスクを照射光パワー密度１６．０ｍＷ／μｍ^２、照射光ビーム線速度１１．０ｍ／ｓとして、実施例１と同様の初期化装置で初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。表２に示すように、実施例１と同様にＤＯＷ１特性及び保存信頼性の両項目において良好な結果を得た。また、相変化記録層３のＸ線面内回折も、実施例１の回折条件を満たすものであった。
【００５５】
［実施例３］
この例の相変化光ディスクは、相変化記録層３をＧｅ_３Ｇａ_３Ｓｂ_７１Ｔｅ_１９Ｍｎ_４で成膜する点以外は、実施例１及び２と同様の構成であり、同様の製造方法であるので、説明を省略する。そして、表１に示すように、相変化光ディスクを照射光パワー密度１８．０ｍＷ／μｍ^２、照射光ビーム線速度１３．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。表２に示すように、実施例１及び２と同様にＤＯＷ１特性及び保存信頼性の両項目において良好な結果を得た。また、相変化記録層３のＸ線面内回折も、実施例１の回折条件を満たすものであった。
【００５６】
なお、実施例３においては他の実施例に比べ、初期化時に要する照射光パワー密度が比較的大きかったが、Ｍｎを添加したことで保存信頼性を損なわずに記録層材料の結晶化限界速度を速めることができ、記録線速度１７．５ｍ／ｓ以上（ＤＶＤの５倍速以上）でも良好な記録が可能であった。
【００５７】
［実施例４］
図７には、この発明の相変化光記録媒体の別の例としての相変化光ディスクの概略断面図を示す。相変化光ディスクは、レーザ光の案内溝が設けられた透明な１基板の上面に、第一保護層２、酸化物層９、非晶質相と結晶相の可逆的相変化をする相変化記録層３、第二保護層４、硫化防止層５、反射層６、樹脂保護層７を備え、接着シートを介して貼り合せ用基板８を貼着してなる。
【００５８】
基板１は、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート製で、トラック（案内溝）ピッチ０．７４μｍである。第一保護層２は、厚さ５５ｎｍのＺｎＳ（８０ｍｏｌ％）−ＳｉＯ_２（２０ｍｏｌ％）からなる層である。酸化層９は、厚さ３ｎｍの、８ｍｏｌ％のＹ_２Ｏ_３を含むＺｒＯ_２（８０ｍｏｌ％）−ＴｉＯ_２（２０ｍｏｌ％）からなる層である。相変化記録層３は、厚さ１１ｎｍのＧｅ_３Ｓｂ_７１Ｔｅ_２１Ｉｎ_４Ａｇ_１からなる層であり、前述のように初期結晶化後の結晶相が、以下の条件に示されるある特定の方向に、強く配向した状態であることに特徴がある。すなわち、面間隔が２．９〜３．３Åの結晶であり、基板１の上面に垂直である結晶面が、トラックの接線方向と３０±１５°の角度をなす。
【００５９】
第二保護層４は、厚さ１１ｎｍのＺｎＳ（８０ｍｏｌ％）−ＳｉＯ_２（２０ｍｏｌ％）からなる層である。硫化防止層５は、厚さ４ｎｍのＳｉからなる層である。反射層６は、厚さ１４０ｎｍのＡｇからなる層である。貼り合せ用基板８は、基板１と同一の、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート製である。
【００６０】
まず、基板１の上に、スパッタリング法により、第一保護層２、酸化物層９、相変化記録層３、第二保護層４、硫化防止層５、反射層６をこの順に成膜し、その上にスピンコート法により樹脂保護層７を成膜し、更に直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート基板を接着シートで貼り合せると、相変化光ディスクとなる。
【００６１】
そして、この相変化光ディスクを表１に示すように、照射光パワー密度１７．０ｍＷ／μｍ^２、照射光ビーム線速度１１．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。表２に示すように、実施例１〜３と同様にＤＯＷ１特性及び保存信頼性の両項目において良好な結果を得た。また、相変化記録層３のＸ線面内回折も、実施例１の回折条件を満たすものであった。
この例では、実施例２に比べてオーバーライト特性が一層改善され、また８０℃８５％ＲＨの恒温槽に放置後も特性の劣化は見られず、良好な保存信頼性を得ることができた。
【００６２】
なお、この例では、相変化光ディスクの第一保護層２と相変化記録層３との間に酸化物層９を備えたが、図８に示すように、相変化記録層３と第二保護層４との間に酸化物層９を備えてもよいし、図９に示すように、第一保護層２と相変化記録層３との間、及び相変化記録層３と第二保護層４との間に酸化物層９を備えてもよい。
【００６３】
［実施例５］
この例の相変化光ディスクは、酸化物層をＡｌ_２Ｏ_３で成膜する点以外は、実施例４と同様の構成であり、同様の製造方法であるので、説明を省略する。そして、表１に示すように、相変化光ディスクを照射光パワー密度１７．０ｍＷ／μｍ^２、照射光ビーム線速度１１．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。表２に示すように、実施例１〜４と同様にＤＯＷ１特性及び保存信頼性の両項目において良好な結果を得た。また、相変化記録層３のＸ線面内回折も、実施例１の回折条件を満たすものであった。実施例４と同様、実施例２に比べオーバーライト特性が一層改善され、また更に保存信頼性においても実施例４よりも良好な結果を得ることができた。
【００６４】
［比較例１］
この例は、実施例１と同様の相変化光ディスクを作製し、照射光パワー密度を９．０ｍＷ／μｍ^２、照射光ビーム線速度９．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。評価結果は、表２に示すように、ＤＯＷ１特性、保存信頼性とも特性が悪かった。また、相変化記録層３のＸ線面内回折は、実施例１の回折条件を満たすものではなかった。
【００６５】
［比較例２］
この例は、実施例４と同様の相変化光ディスクを作製し、照射光パワー密度を１７．０ｍＷ／μｍ^２、照射光ビーム線速度１１．０ｍ／ｓで初期化し、繰り返し初期の記録特性評価、及び保存信頼性の評価を行った。結果は、表２に示すように、ＤＯＷ１特性については良好であったが、保存信頼性が悪かった。また、相変化記録層３のＸ線面内回折は、実施例１の回折条件を満たすものであった。
【００６６】
なお、上述の全ての例において、日立コンピュータ機器社製（ＰＯＰ２４０―Ｅ４）を用いて相変化光ディスクの初期化を行ったが、この発明はこれに限定されるものではなく、どのような初期化装置を用いて光記憶媒体を初期化してもよい。
【００６７】
また、この発明は、成膜の順序が逆になる表面記録型の相変化光記録媒体や、ＤＶＤ系の相変化光記録媒体に見られるような貼り合せ用基板に代えて樹脂保護層を介し同一、又は異なる光記録媒体が互いに２枚貼り合わされた相変化光記録媒体の場合などに対しても適用しうる。
【００６８】
【発明の効果】
以上詳述したように、この発明によれば、相変化記録層の初期化後の結晶相にあって、面間隔が２．９〜３．３Å、かつ前記基板の上面に垂直である結晶面が、前記案内溝の接線方向と３０±１５°をなす角で配向するので、初期化後、最初に情報を記録する前の相変化記録層の結晶と、オーバーライト消去によって非晶質相を結晶化した結晶との結晶組織を均質化し、高線速記録における繰り返し記録初期の特性を改善することができ、オーバーライト回数に依らない良好な記録再生特性を有する相変化光記録媒体を提供することができる。
【００６９】
請求項２に係る発明によれば、相変化記録層がＧｅ_αＳｂ_βＴｅ_{（１−α―β）}からなり、その原子比率が０．０２≦α≦０．０７、０．６５≦β≦０．８０であるので、初期化後、最初に情報を記録する前の相変化記録層の結晶と、オーバーライト消去によって非晶質相を結晶化した結晶との結晶組織を一層均質化し、高線速記録における繰り返し記録初期の特性を改善することができ、オーバーライト回数に依らない一層良好な記録再生特性を有する相変化光記録媒体を提供することができる。
【００７０】
請求項３に係る発明によれば、相変化記録層が添加元素を原子比率で０．０１〜０．１０含み、添加元素として、Ｇａ、Ｉｎ、Ｔｌ、Ｐｂ，Ｓｎ、Ｂｉ、Ｃｄ，Ｈｇ、Ａｇ、Ｃｕ、Ｍｎ、Ｄｙのうち、少なくとも一種類を用いるので、ＤＶＤの４倍速（記録線速度１４ｍ／ｓ）以上の高線速記録においても、オーバーライト回数が１０回程度までに見られるジッターの上昇を抑え、オーバーライト回数に依らないさらに一層良好な記録再生特性を有し、保存信頼牲にも優れた相変化光記録媒体を提供することができる。
【００７１】
請求項４に係る発明によれば、照射光パワー密度が１０〜３０ｍＷ／μｍ^２であり、かつ照射光ビーム線速度が相変化記録層の結晶化限界速度に対し±２ｍ／ｓの範囲で初期化が行われるので、相変化記録層の初期化後の結晶相における、面間隔が２．９〜３．３Å、かつ基板の上面に垂直である結晶面が、案内溝の接線方向と３０±１５°をなす角で強く配向するように相変化光記録媒体を初期化することができ、一層、オーバーライト回数に依らない良好な記録再生特性を有する相変化光記録媒体を提供することができる。
【００７２】
請求項５に係る発明によれば、相変化記録層と第一保護層との間及び／又は相変化記録層と第二保護層との間に酸化物層を備えるので、酸化物層の低い熱伝導性によって初期化エネルギーを効率良く相変化記録層に伝達し、急熱、急冷が容易になり、一層オーバーライト特性に優れた相変化光記録媒体を提供することができる。
【００７３】
請求項６に係る発明によれば、酸化物層が、ＺｒＯ_２、Ａｌ_２Ｏ_３ＴｉＯ_２、ＳｉＯ_２、ＺｎＯ、Ｉｎ_２Ｏ_３、ＳｎＯ、ＰｂＯのうちの少なくとも一種類からなるので、さらに低い熱伝導性によって初期化エネルギーを一層効率良く相変化記録層に伝達し、急熱、急冷が一層容易になり、さらに一層オーバーライト特性に優れた相変化光記録媒体を提供することができる。
【００７４】
請求項７に係る発明によれば、酸化物層の膜厚が、８ｎｍ未満であるので、保存信頼性を劣化させることなく、オーバーライト特性に優れた相変化光記録媒体を提供することができる。
【図面の簡単な説明】
【図１】面内回折法による結晶面間隔及び配向の同定を示す説明図である。
【図２】面内回折法における側的の幾何学的条件を示す説明図である。
【図３】結晶化限界速度を示す説明図である。
【図４】初期化パワーとＤＯＷ１ジッタの関係を示す図である。
【図５】２θ＝２８．９°におけるＸ線面内回折のディスク回転角度依存度を示す図である。
【図６】この発明の一例としての相変化光ディスクの概略断面図である。
【図７】この発明の別の例の相変化光ディスクの概略断面図である。
【図８】この発明のさらに別の例の相変化光ディスクの概略断面図である。
【図９】この発明のまたさらに別の例の相変化光ディスクの概略断面図である。
【符号の説明】
１基板
２第一保護層
３相変化記録層
４第二保護層
５硫化防止層
６反射層
７樹脂保護層
８貼り合せ用基板
９酸化物層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a first protective layer, a phase change recording layer that performs a reversible phase change between an amorphous phase and a crystalline phase, a second protective layer, a reflective layer, on a transparent substrate provided with a laser light guide groove. The present invention relates to a phase-change optical recording medium having a layer and recording and / or reproducing information by irradiating the laser beam.
[0002]
[Prior art]
In recent years, with an increase in the amount of information, a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed has been demanded. A phase-change optical recording medium, which records and reproduces information by irradiating a light beam, particularly a phase-change optical disk, has high signal quality and can be made high-density, and one-beam overwriting is easy, so that high-speed access is possible. It is a recording medium with excellent properties.
A phase-change optical disc has a first protective layer, a phase-change recording layer that performs a reversible phase change between an amorphous phase and a crystalline phase, a second protective layer, on the upper surface of a transparent substrate provided with laser light guide grooves. A reflective layer made of metal is provided in this order, and a resin protective layer is further provided on the reflective layer. In the case of a bonded optical disk, the above-described configuration is used on one side, or the configuration is such that the reflective layers face each other on both sides via an adhesive layer and are bonded.
[0003]
The above-described phase-change optical disk is generally manufactured by forming a film by a vacuum process such as a sputtering method or a vacuum evaporation method, and the phase-change recording layer formed by these methods is in a state immediately after the film formation, that is, In the as-depo state, the material is often amorphous. An amorphous (mark) is also formed during overwriting, but in the as-depo state, the phase change recording layer has almost no crystal nuclei. Unlike amorphous to be formed, the time required for crystallization is very long. Therefore, after the phase change optical disc is manufactured, an initialization step for crystallizing the phase change recording layer before shipping is provided.
[0004]
Next, a procedure for recording information on the phase-change optical disk by the one-beam overwrite method will be described.
The reversible phase change between the amorphous phase and the crystalline phase of the phase change recording layer is performed by a pulsed focused laser beam having three output levels. The laser beam having the highest output level is used for melting the phase change recording layer, and the laser beam having an intermediate output level is used for heating the phase change recording layer to a temperature just below the melting point and higher than the crystallization temperature. The lowest level laser beam is used to control the heating or cooling of the phase change recording layer.
[0005]
In order to record information on a phase change optical disk, a laser beam having the highest output level is irradiated to a desired portion, and the phase change recording layer is rapidly heated and melted, and then rapidly cooled. Then, the phase change recording layer is fixed while the atomic arrangement is disturbed, and becomes amorphous or microcrystalline, and the reflectance is reduced to become a recording mark. On the other hand, a portion other than the desired portion is irradiated with a laser beam having an intermediate output level, gradually cooled, and gradually cooled to return the atomic arrangement of the phase change recording layer to the original state, thereby making the phase change recording layer crystalline. As a result, a crystalline region and an amorphous region are created in the phase change recording layer, and information is recorded.
Further, the case of rewriting the information of the phase change optical disc on which the information is recorded with new information is the same as the recording method described above.
[0006]
In order to reproduce a phase-change optical disc on which information has been recorded or rewritten in this way, a laser beam for reproduction is irradiated, and the phase-change recording layer usually undergoes a reversible amorphous-crystal phase change phenomenon. Reproduction is performed using the accompanying reflectance difference or reflected light phase difference.
[0007]
The phase change optical recording medium is expected to expand its application to high-density image recording in the future. Therefore, it is required to increase the capacity and density of the recording medium, so that high linear velocity recording is indispensable. However, when high linear velocity recording is performed by the one-beam overwriting method as described above, the erasing rate at the beginning of repetitive recording (from the number of overwrites of about 1 to about 10) is low. There is a problem that a stable erasing rate cannot be obtained unless the operation is repeated once or twice, and a technique has been disclosed to solve the problem (for example, Patent Document 1).
[0008]
[Patent Document 1]
Japanese Patent No. 2830336
[0009]
[Problems to be solved by the invention]
One of the causes of the decrease in the erasing rate occurring at the beginning of such repetitive recording is that the crystal state of the phase change recording layer after the initialization is different from the crystal state obtained by overwriting and erasing the amorphous mark. As a result, the reflectance may become non-uniform, and as a result, jitter may increase. On the other hand, the reason why the erasing rate is stabilized after the number of overwrites is about 10 is that the crystal state after the initialization is completely shifted to the crystal state after overwriting and erasing the amorphous mark by the number of overwrites 10 times. It is considered that the reflectance becomes uniform.
[0010]
Accordingly, an object of the present invention is to provide a phase change optical recording medium having good recording / reproducing characteristics irrespective of the number of times of overwriting.
[0011]
[Means for Solving the Problems]
For this reason, the first aspect of the present invention provides a phase change recording in which a first protective layer and a reversible phase change between an amorphous phase and a crystalline phase are formed on the upper surface of a transparent substrate provided with a laser light guide groove. A phase-change optical recording medium comprising a layer, a second protective layer, and a reflective layer for recording and / or reproducing information by irradiating the laser beam;
In the crystal phase after the initialization of the phase change recording layer, a crystal plane having a plane interval of 2.9 to 3.3 ° and perpendicular to the upper surface of the substrate is 30 ± 15 with respect to the tangential direction of the guide groove. It is characterized by being oriented at an angle forming an angle of °.
[0012]
According to a second aspect of the present invention, in the phase change optical recording medium according to the first aspect, the phase change recording layer is made of Ge. _α Sb _β Te _(1-α-β) Wherein the atomic ratio is 0.02 ≦ α ≦ 0.07 and 0.65 ≦ β ≦ 0.80.
[0013]
The invention according to claim 3 is the phase change optical recording medium according to claim 1 or 2, wherein the phase change recording layer contains an additive element in an atomic ratio of 0.01 to 0.10. At least one of Ga, In, Tl, Pb, Sn, Bi, Cd, Hg, Ag, Cu, Mn, and Dy is used.
[0014]
According to a fourth aspect of the present invention, in the phase change optical recording medium according to the second or third aspect, the irradiation light power density is 10 to 30 mW / μm. ² And the initialization is performed within the range of ± 2 m / s in the irradiation light beam linear velocity with respect to the crystallization limit velocity of the phase change recording layer.
[0015]
According to a fifth aspect of the present invention, in the phase change optical recording medium according to any one of the first to fourth aspects, between the phase change recording layer and the first protective layer and / or between the phase change recording layer and the first protection layer. An oxide layer is provided between the second protective layer and the second protective layer.
[0016]
The invention according to claim 6 is the phase change optical recording medium according to claim 5, wherein the oxide layer is made of ZrO. ₂ , Al ₂ O ₃ TiO ₂ , SiO ₂ , ZnO, In ₂ O ₃ , SnO, and PbO.
[0017]
According to a seventh aspect of the present invention, in the phase-change optical recording medium according to the fifth or sixth aspect, the oxide layer has a thickness of less than 8 nm.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the above-mentioned invention is explained concretely.
The phase-change optical recording medium according to the present invention is, for example, a phase-change recording method in which a first protective layer and a reversible phase change between an amorphous phase and a crystalline phase are formed on an upper surface of a transparent substrate provided with a guide groove for laser light. Layer, a second protective layer, and a reflective layer.
The crystal structure of the phase change recording layer after initialization largely depends on the initialization method. Therefore, the present inventors focused on this fact, performed initialization under various conditions, and performed the crystal state of the phase change recording layer and the recording characteristics at the beginning of repeated recording (recording when the number of overwrites was about 1 to 10 times). Investigation of the relationship between the characteristics and the "initial characteristics of repetitive recording") revealed that when a crystal plane of a specific crystal was strongly oriented in a specific direction with respect to a crystal plane perpendicular to the substrate surface. It was found that the characteristics at the beginning of repeated recording were improved.
Here, “a specific crystal” means a crystal having a plane spacing of 2.9 to 3.3 °, and “a specific direction” means that a crystal plane perpendicular to the substrate is in a track tangential direction. It refers to a direction forming an angle of 30 ± 15 °.
[0019]
The following can be considered as reasons why the characteristics at the initial stage of repeated recording can be improved when many crystals satisfying such conditions exist in the phase change recording layer. That is, when an amorphous mark is re-formed into a crystal by overwriting and erasing, the crystal is oriented in a specific direction around the amorphous mark along the direction of crystallization (laser scanning direction = track direction). When there is a large number of layers, epitaxial growth is likely to occur with the structure around the mark as a base, and the crystal structure of the phase-change recording layer after crystallization by initialization and the crystal structure of the crystal formed by overwriting and erasing the amorphous mark It is considered that the non-uniformity between them is eliminated.
Further, even when fine crystal grain boundaries are present in the crystal phase, which is considered to be one of the causes of noise generation, it is possible to avoid the crystal grains (crystal faces) being aligned in a certain direction. can do.
[0020]
The phase-change recording layer provided in the phase-change optical recording medium of the present invention has a characteristic intensity distribution in the in-plane diffraction measurement result of the phase-change recording layer crystallized by initialization as described later. And
The plane having this characteristic orientation is a plane having a diffraction peak at a diffraction angle 2θ = 27 to 30 degrees (a crystal having a plane interval of 2.9 to 3.3 °). The sample is rotated by 360 ° with respect to this plane. When the change in intensity is measured, there is a local maximum value of a specific crystal plane at φ = 45 ° and 225 °, and it is characterized in that there is little orientation other than this direction.
[0021]
Specifically, as shown in FIGS. 1 and 2, the rotation angle (φ) of the sample is set to φ = 0 ° for convenience when the incident direction of the X-rays and the tangential direction of the track on the substrate are parallel to each other. When the sample is rotated with the detector fixed at about θ = 27 to 30 ° and the emitted X-ray diffraction intensity is measured, peaks of the X-ray diffraction intensity are observed at φ = 45 ° and 225 °. Means that. This means that the crystal plane is oriented at an angle of about 30 ° with the track tangent direction (30 ± 15 ° in the present invention) from the principle of X-ray diffraction. Means.
[0022]
As a phase change recording material capable of realizing the above-mentioned crystalline state, an Sb-Te binary alloy having a composition in the vicinity of Sb0.7Te0.3, in which crystallization proceeds due to heterogeneous nucleation, is used as a mother phase, and essential to this. Ge is contained as an element, and at least one element selected from Ga, In, Tl, Pb, Sn, Bi, Cd, Hg, Ag, Cu, Mn, and Dy has an atomic ratio of 0.01 to 0.10. The added phase change recording material is preferably used.
[0023]
Here, crystallization by uniform nucleation refers to crystallization that occurs by crystal nucleation occurring first at a relatively low temperature and then by growing the crystal at a relatively high temperature around the nucleus formed. . Crystallization by heterogeneous nucleation means that nucleation hardly occurs, and crystallization proceeds by crystal growth from the interface between an existing crystal region and an amorphous (mark) region. In the present invention, the crystallization proceeds due to the formation of heterogeneous nuclei, so that the present invention has an effect.
[0024]
Hereinafter, the optimum composition range of each element constituting the phase change recording layer of the present invention will be described. An Sb-Te binary alloy having a composition in the vicinity of Sb70Te30, in which the molar ratio of Sb to Te is 7: 3, is a phase change recording material in which composition segregation due to overwriting hardly occurs and excellent in repetitive recording characteristics. The crystallization limit speed, which will be described later, can be adjusted by changing the mixing ratio of Sb and Te. When the Sb ratio is increased, the crystallization limit speed is increased, and the transfer speed can be increased. In the phase change optical recording medium to which the present invention is applied, the optimum composition range of Sb is such that the atomic ratio of Sb is 0.65 or more and 0.80 or less. This is because if the atomic ratio of Sb is less than 0.65, the increase in jitter due to overwriting becomes large and it becomes difficult to improve the recording characteristics. This is because the formation speed is rapidly increased to make it difficult to form a mark and storage reliability is deteriorated.
[0025]
On the other hand, Ge is an essential additive element because the storage reliability of the phase-change optical recording medium can be drastically improved by adding a small amount without increasing the crystallization temperature as compared with Ga. When the atomic ratio of Ge added at this time is 0.02 or more, the effect of improving the amorphous stability of the recording layer with a high crystallization rate appears, and the effect increases as the amount of addition increases. The upper limit needs to be set to 0.07 in atomic ratio because adverse effects such as an increase in jitter due to overwriting are caused.
[0026]
Further, since Ga has the effect of increasing the crystallization limit speed and the crystallization temperature of the recording layer material with a small amount of addition, it is possible to provide a phase change optical recording medium having excellent stability of amorphous marks. is there. However, if the addition amount of Ga is too large, the crystallization temperature becomes too high, and it becomes difficult to obtain a uniform crystal phase at the time of initialization. Therefore, the composition range of Ga is preferably set to 0.10 or less in atomic ratio. .
[0027]
In has the same effect as Ga, but does not increase the crystallization temperature as much as Ga. Therefore, considering the problem of initialization, it is effective to use Ga as an element to supplement Ga. Further, in addition to Ga and In, Tl, Pb, Sn, Bi, Cd, and Hg also have the effect of increasing the crystallization limit speed. The reason why the addition of these elements increases the crystallization limit speed is unknown, but if the crystallization of the Sb-Te alloy is promoted, the same valence as Sb among these elements is obtained. Ga, In, and Bi, which can easily take numbers, are more preferable, and Sn, which has the closest atomic number to Sb and is considered to have high affinity with Sb, is also preferable. However, if the added amount is too large, it is expected that deterioration of reproduction light and deterioration of characteristics at the initial stage of repetitive recording will be caused. In addition, according to the investigation by the present inventors, it has been found that Mn and Dy also have the same effect as In as an additive element. In particular, Mn accelerates the crystallization rate and decreases the amount of Ge added. It has also been found that it is an additive element that does not need to be increased and has excellent storage reliability.
Further, it is desirable that Cu and / or Au be contained together with the above-mentioned additional element. Since Cu and Au are additive elements that have an effect on storage reliability, a desired high linear velocity optical recording medium can be realized by combining them appropriately with the above-mentioned additive elements, and the reflectance after initialization and the reflectivity can be reduced. It is possible to design a recording material that can easily eliminate the nonuniformity of the light reflectance.
[0028]
The thickness of the phase change recording layer is preferably in the range of 8 to 20 nm. If the thickness is less than 8 nm, the repetitive recording characteristics deteriorate significantly. When the thickness is more than 20 nm, it is difficult to uniformly initialize the phase change recording layer, and the light transmittance is insufficient, so that a high reflectance cannot be obtained and the degree of modulation is reduced.
[0029]
The amorphous state (as-depo state) immediately after the initialization of the phase change recording layer also changes depending on the film forming conditions. In the as-depo state, atoms are randomly arranged on the substrate, and the greater the degree of disorder, the longer it takes to initialize and the more difficult it is to obtain a desired crystal state. However, the sputtered particles flying on the substrate in the film formation by the sputtering method at a low gas pressure and a high voltage are considered to have a larger kinetic energy than the sputtered particles in normal sputtering, and to some extent An ordered alignment film is easily formed, and a desired crystal state is easily obtained after initialization. Therefore, it is preferable to employ a sputtering method at a low gas pressure and a high voltage when forming the phase change recording layer.
[0030]
Note that the present inventors can easily obtain a desired crystal state by providing an oxide layer between the phase change recording layer and the first protective layer and / or between the phase change recording layer and the second protective layer. I also understood. This is because ZnS-SiO which has been conventionally used as a protective layer is used. ₂ In general, the thermal conductivity of the oxide layer is lower than that of the oxide layer, and it is considered that the initialization energy is efficiently absorbed by the phase change recording layer. Such an effect can be expected even when the oxide layer is provided, for example, in a thickness of about 1 nm. However, when the thickness is increased, a problem occurs in that the storage reliability of the recording medium is deteriorated. It is necessary to prevent the deterioration of storage reliability by reducing the thickness to less than, preferably about 2 to 4 nm.
[0031]
The oxide layer is made of ZrO ₂ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , ZnO, In ₂ O ₃ , SnO, and PbO. Among them, especially ZrO ₂ Has extremely excellent mechanical strength, so that not only the characteristics at the initial stage of repeated recording are improved, but also the recording characteristics are not degraded even after overwriting 1000 times or more. In addition, since the thermal conductivity is extremely low, the recording layer reaching temperature at the time of recording is ZnS-SiO ₂ It is higher than a conventional recording medium having only a protective layer, and a quenching structure required for forming a mark is realized, so that sensitivity can be improved.
[0032]
Furthermore, ZrO ₂ The oxide layer mainly composed of ZrO ₂ In addition, it is preferable to include titanium oxide, and further to include a rare earth oxide or a Group IIa oxide other than beryllium. This means that the addition of titanium oxide can further reduce the thermal conductivity of the oxide layer, and is effective in adjusting optical characteristics and reducing reliability deterioration. For oxides or Group IIa oxides except beryllium, ZrO ₂ This has the effect of reducing the volume change with respect to the temperature, and improving the stability with respect to the temperature change during initialization and recording.
[0033]
In order to obtain such an effect, the content of titanium oxide should be 60 mol% or less of the whole oxide layer material, and the content of rare earth oxides or Group IIa oxides except beryllium should be ZrO. ₂ Is desirably 1 to 10 mol% with respect to The content of titanium oxide is not necessarily limited to this range, but if it exceeds 60 mol%, ZrO ₂ The above range is suitable because the effect of the oxide layer containing ambiguity becomes unclear. Preferred examples of rare earth oxides or Group IIa oxides other than beryllium include oxides of Y, Mg, Ca and the like. ZrO ₂ In the case of an oxide layer in which an oxide such as Y, Mg, Ca or the like is dissolved as a solid solution, the storage reliability of the recording medium is significantly deteriorated. ₂ It is desirable to add it in combination with an oxide such as.
[0034]
Other oxide materials Al ₂ O ₃ , TiO ₂ , SiO ₂ , ZnO, In ₂ O ₃ , SnO and PbO, ZrO ₂ It is known that it has almost the same effect as.
Of these, Al ₂ O ₃ Is ZrO ₂ Since the storage reliability is not significantly impaired as compared with a recording medium in which is used as an interface layer material, this is an optimal material for a recording medium in which storage stability is a problem.
[0035]
Next, a method for initializing a phase-change optical recording medium having the above-described phase-change recording layer will be described.
Irradiation light power density is 10 to 30 mW / μm ² Then, the irradiation light beam linear velocity is initialized within a range of ± 2 m / s with respect to the crystallization limit velocity of the phase change recording layer.
[0036]
When the recording layer material with a high crystallization limit speed is used for high linear velocity recording, the irradiation light power density becomes difficult to initialize as the crystallization limit speed of the recording layer material increases, and high output power is required. In addition, even with a high output power, the irradiation light power density is 10 to 30 mW / μm when the linear velocity and the feed width are constant. ² In this case, the characteristics at the initial stage of repetitive recording (especially, the recording characteristics of the first overwriting operation, hereinafter referred to as "DOW1") were further improved, so that the irradiation light power density was 10 to 30 mW / μm. ² Was decided.
[0037]
In addition, the present inventors investigated the relationship between the initial characteristics of repetitive recording and the beam linear velocity during high linear velocity recording in the irradiation light power density range, and found that the crystallization limit of the phase change recording layer was determined. Since the recording medium initialized within the linear velocity range of ± 2 m / s with respect to the speed had good characteristics at the initial stage of repeated recording, the recording medium was reduced to ± 2 m / s with respect to the crystallization limit velocity of the phase-change recording layer. Were determined.
[0038]
The “crystallization limit speed” is a physical property value that indicates the characteristics of the recording layer material defined and devised based on the experience of the present inventors. When the dependence of the reflectivity on the irradiation light beam linear velocity (that is, the rotational speed of the optical disk) (however, the linear velocity dependence in the recording / reproducing system) is evaluated, the sharp decrease in the reflectivity as shown in FIG. 3 starts. Means linear velocity. This is based on the assumption that "DC light of constant power" is regarded as an intermediate output laser pulse (erase pulse) based on the above-described recording principle, and to which linear velocity when the irradiation light beam linear velocity of the recording / reproducing system is increased. This is an evaluation method focusing on whether (erasing) is possible.
[0039]
Taking FIG. 3 as an example, satisfactory crystallization cannot be realized if the initialization is performed at a high linear velocity exceeding 2 m / s with respect to the crystallization limit velocity (thick line in the figure) of the recording layer material. When the initialization is performed at a linear velocity lower than 2 m / s with respect to the crystallization limit velocity of the material, the initialization process takes a long time and is not practical, and it is difficult to solve the problem of the characteristic deterioration at the initial stage of repetitive recording. You can see that.
[0040]
FIG. 4 shows the dependency of the DOW1 jitter on the initialization power. FIG. 5 shows the initialization condition (Pi = 9.3 mW / μm) at which the DOW1 jitter indicated by A in FIG. ² ) And initialization conditions (Pi = 12 mW / μm) at which the DOW1 jitter indicated by B is reduced. ² ) Shows the measurement results of the in-plane X-ray diffraction of the phase change recording layer in the case of initialization.
[0041]
According to FIG. 5, the peaks of the X-ray diffraction intensity observed at φ = 45 ° and 225 ° were obtained under the initializing condition in which the DOW1 jitter was lower than in the initializing condition in which the DOW1 jitter was higher. It can be seen that the case of initialization is more remarkable. That is, the initialization condition (Pi = 12 mW / μm ² The phase change recording layer initialized in ()) has an initialization condition (Pi = 9.3 mW / μm) in which the DOW1 jitter is high. ² The crystal is more strongly oriented at an angle of 30 ± 15 ° with the track tangent direction as compared with the phase change recording layer initialized in the step (1), and the recording characteristics of the phase change recording layer can be improved.
[0042]
Although the peak of the X-ray diffraction intensity was observed even at an angle of φ = 135 ° or 315 °, this was because the Sb—Te binary eutectic alloy constituting the phase change recording layer was cubic. Due to certain properties, as the number of crystals whose crystal planes are oriented at an angle of 30 ± 15 ° with the track tangent direction increases (or grows larger), the angle shifts from 45 ° to 90 °, 135 ° and 225 ° to 90 °. It is considered that the peak of the X-ray diffraction intensity was similarly observed at 315 °.
[0043]
As described above, if an appropriate initialization condition is selected so that “a crystal structure satisfying a certain condition” is maximized in the phase change recording layer in the above range, an optical recording medium having excellent initial characteristics of repetitive recording can be obtained. Can be realized.
[0044]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments and the used initialization device.
[0045]
[Example 1]
FIG. 6 is a schematic sectional view of a phase change optical disk as an example of the phase change optical recording medium of the present invention. The phase-change optical disc has a first protective layer 2, a phase-change recording layer 3 that undergoes a reversible phase change between an amorphous phase and a crystalline phase, It is provided with a protective layer 4, an anti-sulfuration layer 5, a reflective layer 6, and a resin protective layer 7, and has a bonding substrate 8 adhered thereto via an adhesive sheet.
[0046]
The substrate 1 is made of polycarbonate having a diameter of 12 cm and a thickness of 0.6 mm, and has a track (guide groove) pitch of 0.74 μm. The first protective layer 2 is made of ZnS (80 mol%)-SiO having a thickness of 65 nm. ₂ (20 mol%). The phase change recording layer 3 is a 17 nm thick Ge ₄ Sb ₆₉ Te ₂₀ In ₅ Ag ₂ Which is characterized in that, as described above, the crystal phase after the initial crystallization is strongly oriented in a specific direction indicated by the following conditions. That is, the crystal is a crystal having a plane spacing of 2.9 to 3.3 °, and a crystal plane perpendicular to the upper surface of the substrate 1 forms an angle of 30 ± 15 ° with the tangential direction of the track. The second protective layer 4 is made of ZnS (80 mol%)-SiO having a thickness of 14 nm. ₂ (20 mol%). The sulfuration prevention layer 5 is a layer made of Si having a thickness of 4 nm. The reflection layer 6 is a layer made of Ag having a thickness of 140 nm. The bonding substrate 8 is made of the same polycarbonate as the substrate 1 and has a diameter of 12 cm and a thickness of 0.6 mm.
[0047]
First, a first protective layer 2, a phase-change recording layer 3, a second protective layer 4, an anti-sulfuration layer 5, and a reflective layer 6 are formed in this order on a substrate 1 by a sputtering method. When a resin protective layer 7 is formed by a method and a bonding substrate 8 is bonded with an adhesive sheet, a phase change optical disk is obtained.
[0048]
Next, a method for initializing this phase change optical disk will be described.
In the present embodiment, the phase change optical disk was initialized using Hitachi Computer Equipment Co., Ltd. (POP240-E4) (the same device was used in the following examples and comparative examples). The evaluation of the characteristics at the beginning of the repetitive recording was performed by using an optical disk evaluation apparatus (DDU-1000 manufactured by Pulstec) having a pickup with a wavelength of 660 nm and NA of 0.65, a recording linear velocity of 14.0 m / s and a linear density of 0.267 μm. / Bit, a random signal was repeatedly recorded (two times) by the EFM + modulation method, and the DOW1 characteristic (jitter) was evaluated at a reproduction linear velocity of 3.5 m / s and a reproduction power of 0.7 mW. Here, the jitter is a value obtained by standardizing data to clock jitter (σ) with the detection window width Tw. The storage reliability was confirmed by leaving the disk in an 80 ° C. and 85% RH constant temperature bath for 300 hours and then evaluating the recording characteristics again.
[0049]
As shown in Table 1 below, the phase change optical disk was irradiated with an irradiation light power density of 12.0 mW / μm. ² Initialization was performed at an irradiation light beam linear velocity of 9.0 m / s, and the recording characteristics at the initial stage of repetition and the storage reliability were evaluated. The results are shown in Table 2 below.
[0050]
[Table 1]

[0051]
[Table 2]

[0052]
The evaluation criteria are as follows.
(1) Regarding the DOW1 characteristics at a recording linear velocity of 14 m / s, the case where the jitter was 10% or less was evaluated as “○”, and the case where the jitter was greater than 10% was evaluated as “X”.
(2) Regarding the storage reliability, “」 ”indicates that the jitter fluctuation after being left in a constant temperature bath at 80 ° C. and 85% RH for 300 hours is within 0.5%, and that the jitter fluctuation exceeds 0.5%. “×” and those not evaluated were “−”.
[0053]
In this example, good results were obtained in both items of DOW1 characteristics and storage reliability. After the evaluation, the in-plane X-ray diffraction of the phase change recording layer 3 was measured, and the result satisfied the following diffraction conditions. (Hereinafter, in the examples, the case where the following diffraction conditions were satisfied was indicated by ○, and the case where they were not satisfied was indicated by ×)
Diffraction conditions:
As shown in FIGS. 1 and 2, X-rays are incident (into an incident angle of 0.2 to 0.5 °) substantially parallel to the substrate surface and diffracted X-rays are detected substantially parallel to the substrate surface. In the in-line diffraction measurement (method of measuring a lattice plane perpendicular to the substrate surface), as described above, the detection angle is fixed at around 2θ = 27 to 30 °, and the light having the crystallized phase change recording layer is used. When the X-ray diffraction intensity is measured while rotating the sample 360 degrees after peeling off the reflective layer and the protective layer of the recording medium, when the rotation angles (φ) are 45 degrees, 135 degrees, 225 degrees, and 315 degrees The peak of the diffraction intensity is maximized.
Note that a copper Kα ray (λ = 1.54 °) is used as a light source for the incident X-rays. Therefore, according to the Bragg condition, the surface interval d = 2.97 to 3.3 ° near the detection angle 2θ = 27 to 30 °. The crystals will be measured.
[0054]
[Example 2]
In the phase change optical disk of this example, the phase change recording layer 3 is ₃ Sb ₇₁ Te ₂₁ In ₄ Ag ₁ Except for the point that the film is formed, the configuration and the manufacturing method are the same as those of the first embodiment, and the description is omitted. Then, as shown in Table 1, the initialization method uses the irradiation light power density of 16.0 mW / μm ² With the irradiation light beam linear velocity set to 11.0 m / s, initialization was performed using the same initialization apparatus as in Example 1, and the recording characteristics and storage reliability at the initial stage were repeatedly evaluated. As shown in Table 2, similar to Example 1, good results were obtained in both items of DOW1 characteristics and storage reliability. Further, the in-plane X-ray diffraction of the phase change recording layer 3 also satisfied the diffraction condition of Example 1.
[0055]
[Example 3]
In the phase change optical disk of this example, the phase change recording layer 3 is ₃ Ga ₃ Sb ₇₁ Te ₁₉ Mn ₄ The structure is the same as in Examples 1 and 2, except that the film is formed by the method described in Example 1. Since the manufacturing method is the same, the description is omitted. Then, as shown in Table 1, the phase change optical disk was irradiated with the irradiation light power density of 18.0 mW / μm. ² Initialization was performed at an irradiation light beam linear velocity of 13.0 m / s, and the recording characteristics at the initial stage of repetition and the storage reliability were evaluated. As shown in Table 2, as in Examples 1 and 2, good results were obtained in both items of DOW1 characteristics and storage reliability. Further, the in-plane X-ray diffraction of the phase change recording layer 3 also satisfied the diffraction condition of Example 1.
[0056]
In Example 3, the irradiation light power density required at the time of initialization was relatively large as compared with the other examples, but the addition of Mn did not impair the storage reliability, and the crystallization limit speed of the recording layer material was not impaired. , And good recording was possible even at a recording linear velocity of 17.5 m / s or more (5 times the speed of DVD or more).
[0057]
[Example 4]
FIG. 7 is a schematic sectional view of a phase change optical disk as another example of the phase change optical recording medium of the present invention. The phase-change optical disc has a first protective layer 2, an oxide layer 9, and a phase-change recording in which a reversible phase change between an amorphous phase and a crystalline phase is formed on an upper surface of a transparent substrate provided with a laser light guide groove. It is provided with a layer 3, a second protective layer 4, an anti-sulfuration layer 5, a reflective layer 6, and a resin protective layer 7, and is attached with a bonding substrate 8 via an adhesive sheet.
[0058]
The substrate 1 is made of polycarbonate having a diameter of 12 cm and a thickness of 0.6 mm, and has a track (guide groove) pitch of 0.74 μm. The first protective layer 2 is made of ZnS (80 mol%)-SiO having a thickness of 55 nm. ₂ (20 mol%). The oxide layer 9 has a thickness of 3 nm and 8 mol% of Y. ₂ O ₃ ZrO containing ₂ (80mol%)-TiO ₂ (20 mol%). The phase change recording layer 3 is made of 11 nm thick Ge. ₃ Sb ₇₁ Te ₂₁ In ₄ Ag ₁ Which is characterized in that, as described above, the crystal phase after the initial crystallization is strongly oriented in a specific direction indicated by the following conditions. That is, the crystal is a crystal having a plane spacing of 2.9 to 3.3 °, and a crystal plane perpendicular to the upper surface of the substrate 1 forms an angle of 30 ± 15 ° with the tangential direction of the track.
[0059]
The second protective layer 4 is made of ZnS (80 mol%)-SiO having a thickness of 11 nm. ₂ (20 mol%). The sulfuration prevention layer 5 is a layer made of Si having a thickness of 4 nm. The reflection layer 6 is a layer made of Ag having a thickness of 140 nm. The bonding substrate 8 is made of the same polycarbonate as the substrate 1 and has a diameter of 12 cm and a thickness of 0.6 mm.
[0060]
First, a first protective layer 2, an oxide layer 9, a phase change recording layer 3, a second protective layer 4, an anti-sulfuration layer 5, and a reflective layer 6 are formed on the substrate 1 in this order by a sputtering method. When a resin protective layer 7 is formed thereon by a spin coating method, and a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm is bonded with an adhesive sheet, a phase change optical disk is obtained.
[0061]
Then, as shown in Table 1, the irradiation light power density was 17.0 mW / μm ² Initialization was performed at an irradiation light beam linear velocity of 11.0 m / s, and the recording characteristics and the storage reliability were evaluated repeatedly at the initial stage. As shown in Table 2, similar to Examples 1 to 3, good results were obtained in both items of DOW1 characteristics and storage reliability. Further, the in-plane X-ray diffraction of the phase change recording layer 3 also satisfied the diffraction condition of Example 1.
In this example, the overwrite characteristics were further improved as compared with Example 2, and no deterioration of the characteristics was observed even after being left in a constant temperature bath at 80 ° C. and 85% RH, so that good storage reliability could be obtained. .
[0062]
In this example, although the oxide layer 9 was provided between the first protective layer 2 and the phase change recording layer 3 of the phase change optical disk, as shown in FIG. An oxide layer 9 may be provided between the first protective layer 2 and the phase change recording layer 3 and between the first protective layer 2 and the phase change recording layer 3 and between the phase change recording layer 3 and the second protective layer as shown in FIG. 4, an oxide layer 9 may be provided.
[0063]
[Example 5]
The phase change optical disk of this example has an oxide layer of Al ₂ O ₃ The structure is the same as that of the fourth embodiment except that the film is formed by the method described in Example 4. Since the manufacturing method is the same, the description is omitted. Then, as shown in Table 1, the irradiation light power density was 17.0 mW / μm ² Initialization was performed at an irradiation light beam linear velocity of 11.0 m / s, and the recording characteristics and the storage reliability were evaluated repeatedly at the initial stage. As shown in Table 2, similar to Examples 1 to 4, good results were obtained in both items of DOW1 characteristics and storage reliability. Further, the in-plane X-ray diffraction of the phase change recording layer 3 also satisfied the diffraction condition of Example 1. As in the case of Example 4, the overwrite characteristics were further improved as compared with Example 2, and a better result was also obtained in the storage reliability than in Example 4.
[0064]
[Comparative Example 1]
In this example, a phase change optical disk similar to that of Example 1 was manufactured, and the irradiation light power density was 9.0 mW / μm. ² Initialization was performed at an irradiation light beam linear velocity of 9.0 m / s, and the recording characteristics at the initial stage of repetition and the storage reliability were evaluated. As shown in Table 2, as shown in Table 2, both the DOW1 characteristics and the storage reliability were poor. Further, the in-plane X-ray diffraction of the phase change recording layer 3 did not satisfy the diffraction conditions of Example 1.
[0065]
[Comparative Example 2]
In this example, a phase change optical disk similar to that of Example 4 was manufactured, and the irradiation light power density was 17.0 mW / μm. ² Initialization was performed at an irradiation light beam linear velocity of 11.0 m / s, and the recording characteristics and the storage reliability were evaluated repeatedly at the initial stage. As shown in Table 2, the DOW1 characteristics were good, but the storage reliability was poor. The in-plane X-ray diffraction of the phase change recording layer 3 satisfied the diffraction conditions of Example 1.
[0066]
In all the above examples, the initialization of the phase change optical disk was performed using Hitachi Computer Instruments (POP240-E4). However, the present invention is not limited to this, and any initialization may be performed. The optical storage medium may be initialized using the device.
[0067]
In addition, the present invention provides a resin-protective layer instead of a bonding substrate such as a surface-recording type phase-change optical recording medium in which the order of film formation is reversed or a DVD-based phase-change optical recording medium. The present invention can also be applied to a phase change optical recording medium in which two identical or different optical recording media are bonded to each other.
[0068]
【The invention's effect】
As described above in detail, according to the present invention, in the crystal phase after the initialization of the phase change recording layer, the crystal plane having a plane distance of 2.9 to 3.3 ° and perpendicular to the upper surface of the substrate However, since it is oriented at an angle of 30 ± 15 ° with the tangential direction of the guide groove, after initialization, the crystal of the phase change recording layer before the first recording of information and the amorphous phase by overwrite erasing are used. Provided is a phase-change optical recording medium which can homogenize a crystal structure with a crystallized crystal, improve characteristics at the time of repeated recording at high linear velocity recording, and have good recording / reproducing characteristics regardless of the number of overwrites. be able to.
[0069]
According to the invention of claim 2, the phase change recording layer is made of Ge. _α Sb _β Te _(1-α-β) Since the atomic ratios are 0.02 ≦ α ≦ 0.07 and 0.65 ≦ β ≦ 0.80, the crystal of the phase change recording layer after the initialization and before the first information is recorded, The crystal structure of the amorphous phase crystallized by overwrite erasure can be further homogenized to improve the initial characteristics of repetitive recording at high linear velocity recording. A phase change optical recording medium having characteristics can be provided.
[0070]
According to the invention according to claim 3, the phase change recording layer contains an additive element in an atomic ratio of 0.01 to 0.10, and includes Ga, In, Tl, Pb, Sn, Bi, Cd, Hg, Since at least one of Ag, Cu, Mn, and Dy is used, even at a high linear velocity recording of 4 × speed (recording linear velocity of 14 m / s) or more of DVD, the jitter which can be seen up to about 10 times of overwriting times. It is possible to provide a phase-change optical recording medium which has an even better recording / reproducing characteristic independent of the number of overwrites, and which has excellent storage reliability.
[0071]
According to the invention of claim 4, the irradiation light power density is 10 to 30 mW / μm. ² And the initialization is performed within a range of ± 2 m / s of the irradiation light beam linear velocity with respect to the crystallization limit velocity of the phase change recording layer. Therefore, the plane spacing in the crystal phase after the initialization of the phase change recording layer is performed. Initializing the phase-change optical recording medium such that the crystal plane perpendicular to the upper surface of the substrate is oriented at an angle of 30 ± 15 ° with respect to the tangential direction of the guide groove. Thus, it is possible to provide a phase-change optical recording medium having good recording / reproducing characteristics irrespective of the number of overwrites.
[0072]
According to the invention according to claim 5, since the oxide layer is provided between the phase change recording layer and the first protective layer and / or between the phase change recording layer and the second protective layer, the oxide layer is low. Initialization energy is efficiently transmitted to the phase change recording layer by thermal conductivity, rapid heating and rapid cooling are facilitated, and a phase change optical recording medium having more excellent overwrite characteristics can be provided.
[0073]
According to the invention according to claim 6, the oxide layer is made of ZrO. ₂ , Al ₂ O ₃ TiO ₂ , SiO ₂ , ZnO, In ₂ O ₃ , SnO, and PbO, the initialization energy is transmitted to the phase-change recording layer more efficiently due to lower thermal conductivity, rapid heating and rapid cooling are further facilitated, and overwriting characteristics are further improved. It is possible to provide a phase change optical recording medium which is excellent in quality.
[0074]
According to the invention of claim 7, since the thickness of the oxide layer is less than 8 nm, it is possible to provide a phase-change optical recording medium having excellent overwrite characteristics without deteriorating storage reliability. .
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing identification of crystal plane spacing and orientation by an in-plane diffraction method.
FIG. 2 is an explanatory diagram showing lateral geometric conditions in an in-plane diffraction method.
FIG. 3 is an explanatory diagram showing a crystallization limit speed.
FIG. 4 is a diagram showing a relationship between initialization power and DOW1 jitter.
FIG. 5 is a diagram showing the disc rotation angle dependence of X-ray in-plane diffraction at 2θ = 28.9 °.
FIG. 6 is a schematic sectional view of a phase change optical disk as an example of the present invention.
FIG. 7 is a schematic sectional view of a phase change optical disk according to another example of the present invention.
FIG. 8 is a schematic sectional view of a phase change optical disk according to still another example of the present invention.
FIG. 9 is a schematic sectional view of a phase change optical disk according to still another example of the present invention.
[Explanation of symbols]
1 substrate
2 First protective layer
3 Phase change recording layer
4 Second protective layer
5 Anti-sulfuration layer
6 Reflective layer
7 Resin protective layer
8 Lamination substrate
9 Oxide layer

Claims

On the upper surface of the transparent substrate provided with a guide groove for laser light, a first protective layer, a phase change recording layer that performs a reversible phase change of an amorphous phase and a crystalline phase, a second protective layer, a reflective layer, In a phase change optical recording medium for recording and / or reproducing information by irradiating the laser beam,
In the crystal phase after the initialization of the phase change recording layer, a crystal plane having a plane interval of 2.9 to 3.3 ° and perpendicular to the upper surface of the substrate is 30 ± 15 with respect to the tangential direction of the guide groove. A phase-change optical recording medium characterized by being oriented at an angle forming an angle of °.

And wherein the phase change recording layer is made of _{_{_{Ge α Sb β Te (1-}}} α-β), the atomic ratio is 0.02 ≦ α ≦ 0.07,0.65 ≦ β ≦ 0.80 The phase change optical recording medium according to claim 1.

The phase change recording layer contains an additive element in an atomic ratio of 0.01 to 0.10, and the additive element includes Ga, In, Tl, Pb, Sn, Bi, Cd, Hg, Ag, Cu, Mn, and Dy. 3. The phase-change optical recording medium according to claim 1, wherein at least one type is used.

The initialization is performed when the irradiation light power density is 10 to 30 mW / μm ² and the irradiation light beam linear velocity is within ± 2 m / s of the crystallization limit velocity of the phase change recording layer. The phase-change optical recording medium according to claim 2 or 3, wherein:

5. An oxide layer is provided between the phase change recording layer and the first protective layer and / or between the phase change recording layer and the second protective layer. 3. The phase-change optical recording medium according to claim 1.

The oxide _{_{_{_{_layer, ZrO 2, Al 2 O 3}}}} TiO 2, SiO 2, ZnO, In 2 O 3, SnO, phase change optical according to claim 5, characterized in that it consists of at least one of PbO recoding media.

7. The phase change optical recording medium according to claim 5, wherein the thickness of the oxide layer is less than 8 nm.