JP3913014B2 - Information recording medium, manufacturing method thereof, and recording / reproducing method thereof - Google Patents

Description

【００６６】
表１において、ｎ_cは、サンプルの層が結晶相である場合の屈折率を示す。ｎ_aは、サンプルの層が非晶質相である場合の屈折率を示す。Δｎは、Δｎ＝ｎ_c−ｎ_aで表され、層が結晶相である場合と層が非晶質相である場合との屈折率の変化を示す。ｋ_cは、サンプルの層が結晶相である場合の消衰係数を示す。ｋ_aは、サンプルの層が非晶質相である場合の消衰係数を示す。Δｋは、Δｋ＝ｋ_c−ｋ_aで表され、層が結晶相である場合と層が非晶質相である場合との消衰係数の変化を示す。
【００６７】
表１に示すように、サンプルの層が結晶相であっても非晶質相であっても、（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁の消衰係数は、（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅および（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅の消衰係数よりも、約０．３小さかった。また、Ｓｂ₇₀Ｔｅ₃₀共晶組成近傍のＳｂ−Ｔｅ合金に元素Ｍ１を加えた組成である（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅、および（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅は、Ｇｅ−Ｓｂ−Ｔｅ３元系組成のＧｅをＳｎで置換した（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁と比較して、融点が約５０℃低く、また、屈折率の変化Δｎの絶対値が大きかった。
【００６８】
以上の結果から、第１の記録層４の材料には、消衰係数が小さいために透過率を大きくできるＧｅ−Ｓｂ−Ｔｅ３元系組成またはそれをベースとする組成を用いることが好ましい。また、第２の記録層１４の材料には、融点が低いため記録感度を高くでき、且つ屈折率変化Δｎが大きいため反射率変化を大きくできる（Ｓｂ−Ｔｅ）−Ｍ１系組成を用いることが好ましい。第１の記録層４／第２の記録層１４の具体的な組み合わせとしては、たとえば、Ｇｅ₆Ｓｂ₂Ｔｅ₉／（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅、Ｇｅ₈Ｓｂ₂Ｔｅ₁₁／（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅、Ｇｅ₈Ｓｂ₂Ｔｅ₁₁／（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅などが挙げられる。
【００６９】
第１の記録層４の厚さは、第１の情報層１１の透過率を高くして、第２の情報層２０の記録再生の際に必要なレーザ光量を第２の情報層２０に到達させるため、９ｎｍ以下であることが好ましく、５ｎｍ〜７ｎｍの範囲内であることがより好ましい。
【００７０】
第２の記録層１４の厚さは、第２の情報層２０の記録感度を高くするため、６ｎｍ〜１５ｎｍの範囲内であることが好ましい。第２の記録層１４が厚い場合における熱の面内方向への拡散による隣接領域への熱的影響と、第２の記録層１４が薄い場合における第２の情報層２０の反射率の低下とを考慮すると、第２の記録層１４の厚さは、８ｎｍ〜１２ｎｍの範囲内であることがより好ましい。
【００７１】
第１の反射層８および第２の反射層１８は、第１の記録層４または第２の記録層１４に吸収される光量を増大させるという光学的な機能を有する。また、これらの反射層は、第１の記録層４または第２の記録層１４で生じた熱を速やかに拡散させ、記録層を非晶質化しやすくするという熱的な機能も有する。さらに、これらの反射層は、使用する環境から多層膜を保護するという機能も有する。
【００７２】
第１の反射層８および第２の反射層１８の材料には、たとえばＡｌ，Ａｕ，Ａｇ，Ｃｕといった熱伝導率が高い単体金属を用いることができる。また、これらの金属元素の１つまたは複数を主成分とし、耐湿性の向上または熱伝導率の調整等のために１つまたは複数の他の元素を添加した合金を用いることもできる。具体的には、Ａｌ−Ｃｒ，Ａｌ−Ｔｉ，Ａｕ−Ｐｄ，Ａｕ−Ｃｒ，Ａｇ−Ｐｄ，Ａｇ−Ｐｄ−Ｃｕ，Ａｇ−Ｐｄ−Ｔｉ，Ａｇ−Ｒｕ−Ａｕ，またはＣｕ−Ｓｉといった合金を用いることができる。これらの合金は、いずれも耐食性に優れ且つ急冷条件を満足する優れた材料である。特にＡｇ合金は、熱伝導率が大きく、光の透過率も高いため、第１の反射層８の材料として好ましい。
【００７３】
第１の情報層１１の透過率ＴｃおよびＴａをできるだけ高くするため、第１の反射層８の厚さは、５ｎｍ〜１５ｎｍの範囲内であることが好ましく、８ｎｍ〜１２ｎｍの範囲内であることがより好ましい。第１の反射層８が５ｎｍより薄い場合には、その熱拡散機能が不十分となり、且つ第１の情報層１１の反射率が低下する。また、第１の反射層８が１５ｎｍより厚い場合には、第１の情報層１１の透過率が不十分となる。一方、第２の情報層２０は、高い透過率を必要としない。そのため、第２の反射層１８の厚さは、３０ｎｍ〜１５０ｎｍの範囲内であることが好ましく、７０ｎｍ〜９０ｎｍの範囲内であることがより好ましい。第２の反射層１８が３０ｎｍより薄い場合には、その熱拡散機能が不十分となり、第２の記録層１４が非晶質化しにくくなる。また、第２の反射層１８が１５０ｎｍより厚い場合には、その熱拡散機能が大きくなりすぎて第２の情報層２０の記録感度が低下する。
【００７４】
光学分離層２１は、第１の情報層１１のフォーカス位置と第２の情報層２０のフォーカス位置とを区別するために設けられる。光学分離層２１の材料としては、光硬化性樹脂または遅効性樹脂を用いることができる。光学分離層２１の材料は、記録再生に用いられるレーザビーム２３の波長における光吸収が小さいことが好ましい。光学分離層２１の厚さは、対物レンズの開口数ＮＡとレーザビーム２３の波長λによって決定される焦点深度ΔＺ以上であることが必要である。焦光点の強度の基準を無収差の場合の８０％と仮定した場合、ΔＺはΔＺ＝λ／｛２（ＮＡ）²｝で近似できる。λ＝４００ｎｍ、ＮＡ＝０．６のとき、ΔＺ＝０．５５６μｍとなり、±０．６μｍ以内は焦点深度内となる。そのため、この場合には、光学分離層２１の厚さは１．２μｍ以上であることが必要である。第１の情報層１１と第２の情報層２０との間の距離は、対物レンズを用いてレーザビーム２３を集光可能な範囲内にあることが必要である。したがって、光学分離層２１の厚さと第１の基板１の厚さとの合計は、対物レンズが許容できる基板厚さの公差内にすることが好ましい。このため、光学分離層２１の厚さは、１．２μｍ〜５０μｍの範囲内であることが好ましい。
【００７５】
実施形態１の情報記録媒体２２は、実施形態３で説明する方法によって製造できる。
【００７６】
（実施形態２）
実施形態２では、本発明の情報記録媒体について他の一例を説明する。実施形態２の情報記録媒体２６の一部断面図を図３に示す。情報記録媒体２６では、レーザビーム２３の照射によって記録再生が行われる。
【００７７】
図３を参照して、情報記録媒体２６は、光学分離層２１と、光学分離層２１を挟むように配置された第１の情報層２５および第２の情報層２０とを備える。
【００７８】
第１の情報層２５は、レーザビーム２３の入射側から順に配置された第１の基板１、透明層２４、第１の下側保護層２、第１の下側界面層３、第１の記録層４、第１の上側界面層５、第１の上側保護層６、第１の界面層７、第１の反射層８、第１の最上界面層９、および透過率調整層１０を備える。
【００７９】
第２の情報層２０は、レーザビーム２３の入射側から順に配置された第２の下側保護層１２、第２の下側界面層１３、第２の記録層１４、第２の上側界面層１５、第２の上側保護層１６、第２の界面層１７、第２の反射層１８、および第２の基板１９を備える。
【００８０】
以下の実施形態４で説明するように、情報記録媒体２６を製造する場合には、まず、第２の基板１９上に第２の反射層１８〜第２の下側保護層１２、光学分離層２１、透過率調整層１０〜第１の下側保護層２という順序で各層を積層する。そして、その後、透明層２４を用いて第１の下側保護層２と第１の基板１とを貼り合わせることによって情報記録媒体２６を形成できる。また、透明層２４を形成せずに、樹脂を塗布して硬化させることによって第１の基板１を形成してもよい。
【００８１】
光学分離層２１および透明層２４の材料としては、光硬化性樹脂または遅効性樹脂を用いて形成できる。この材料は、記録再生に用いるレーザビーム２３の波長における光吸収が小さいことが好ましい。光学分離層２１および透明層２４の厚さは、実施形態１で説明した理由により、それぞれ、１．２μｍ〜５０μｍの範囲内であることが好ましい。
【００８２】
光学分離層２１の表面のうち第１の情報層２５側の表面には、レーザビーム２３を導く案内溝が形成されていてもよい。実施形態１の情報記録媒体２２と同様に、レーザビーム２３は第１の基板１側から入射する。そして、第２の情報層２０においては、第１の情報層２５および光学分離層２１を透過したレーザビーム２３によって記録再生が行われる。
【００８３】
なお、第１の基板１、第１の下側保護層２、第１の下側界面層３、第１の記録層４、第１の上側界面層５、第１の上側保護層６、第１の界面層７、第１の反射層８、第１の最上界面層９、透過率調整層１０、第２の下側保護層１２、第２の下側界面層１３、第２の記録層１４、第２の上側界面層１５、第２の上側保護層１６、第２の界面層１７、第２の反射層１８、および第２の基板１９には、実施形態１で説明したものと同様のものを用いることができる。また、それらの形状および機能についても、実施形態１で説明した形状および機能と同様である。
【００８４】
（実施形態３）
実施形態３では、本発明の情報記録媒体２２の製造方法について説明する。
【００８５】
実施形態３の製造方法は、第１の情報層１１を形成する工程（工程（ａ））を含む。具体的には、まず、レーザビーム２３を導くための案内溝を形成した第１の基板１（厚さがたとえば０．１ｍｍ）を用意する。次に、第１の基板１を成膜装置内に配置し、第１の基板１上に第１の下側保護層２を成膜する。このとき、第１の基板１に案内溝が形成されている場合には、案内溝が形成されている側に第１の下側保護層２を成膜する。第１の下側保護層２は、Ａｒガスと反応ガスとの混合ガス雰囲気中で、第１の下側保護層２を構成する金属からなる母材を反応性スパッタリングすることによって形成できる。また、第１の下側保護層２は、Ａｒガス雰囲気中、またはＡｒガスと反応ガスとの混合ガス雰囲気中で化合物からなる母材をスパッタリングすることによっても形成できる。
【００８６】
続いて、第１の下側保護層２上に第１の下側界面層３を成膜する。第１の下側界面層３は、Ａｒガスと反応ガスとの混合ガス雰囲気中で、第１の下側界面層３を構成する金属からなる母材を反応性スパッタリングすることによって形成できる。また、第１の下側界面層３は、Ａｒガス雰囲気中、またはＡｒガスと反応ガスとの混合ガス雰囲気中で化合物からなる母材をスパッタリングすることによっても形成できる。
【００８７】
続いて、第１の下側界面層３上に第１の記録層４を成膜する。第１の記録層４は、その組成に応じて、Ｇｅ−Ｓｂ−Ｔｅ合金からなる母材、Ｇｅ−Ｓｂ−Ｔｅ−Ｍ２合金からなる母材、またはＧｅ−Ｓｂ−Ｔｅ−Ｍ３合金からなる母材を、一つの電源を用いて、スパッタリングすることによって形成できる。すなわち、第１の記録層４は、ＧｅとＳｂとＴｅとを含む母材を用いて形成できる。
【００８８】
スパッタリングの雰囲気ガス（スパッタリングガス）には、Ａｒガス、Ｋｒガス、Ａｒガスと反応ガス（酸素ガスおよび窒素ガスから選ばれる少なくとも１つのガス）との混合ガス、またはＫｒガスと反応ガスとの混合ガスを用いることができる。また、第１の記録層４は、Ｇｅ、Ｓｂ、Ｔｅ、Ｍ２、またはＭ３の各々の母材を複数の電源を用いて同時にスパッタリングすることによって形成することもできる。また、第１の記録層４は、Ｇｅ、Ｓｂ、Ｔｅ、Ｍ２、またはＭ３のうちいずれかの元素を組み合わせた２元系母材や３元系母材などを、複数の電源を用いて同時にスパッタリングすることによって形成することもできる。これらの場合でも、Ａｒガス雰囲気中、Ｋｒガス雰囲気中、Ａｒガスと反応ガスとの混合ガス雰囲気中、またはＫｒガスと反応ガスとの混合ガス雰囲気中でスパッタリングすることによって形成する。
【００８９】
第１の記録層４の成膜レートは、０．１ｎｍ／秒〜３ｎｍ／秒の範囲内であることが好ましい。実施形態１で説明したように、形成される第１の記録層４の厚さは、９ｎｍ以下（より好ましくは、７ｎｍ以下）であることが好ましい。成膜レートは電源の投入パワーで制御できる。成膜レートを下げすぎると、成膜時間が長くなり、また、雰囲気中のガスが必要以上に記録層中に混入してしまう。また、成膜レートを上げすぎると、成膜時間を短くできるが、記録層の厚さを正確に制御することが難しくなる。したがって、第１の記録層４の成膜レートは、０．１ｎｍ／秒〜３ｎｍ／秒の範囲内であることが好ましい。
【００９０】
続いて、第１の記録層４上に第１の上側界面層５を成膜する。第１の上側界面層５は、第１の下側界面層３と同様の方法で形成できる（以下の界面層についても同様である）。これらの界面層を形成する際に用いられる母材の組成は、界面層の組成およびスパッタリングガスに応じて選択される（他の層を形成する工程においても同様である）。すなわち、組成が同一の母材を用いてこれらの界面層を形成する場合もあるし、組成が異なる母材を用いてこれらの界面層を形成する場合もある（他の層を形成する工程においても同様である）。
【００９１】
続いて、第１の上側界面層５上に第１の上側保護層６を成膜する。第１の上側保護層６は、第１の下側保護層２と同様の方法で形成できる（以下の保護層についても同様である）。
【００９２】
続いて、第１の上側保護層６上に、第１の界面層７と第１の反射層８とを順に成膜する。第１の反射層８は、Ａｒガス雰囲気中で、第１の反射層８を構成する金属または合金からなる母材をスパッタリングすることによって形成できる。
【００９３】
続いて、第１の反射層８上に、第１の最上界面層９と透過率調整層１０とを順に成膜する。透過率調整層１０は、第１の下側保護層２と同様の方法で形成できる。
【００９４】
このようにして、第１の情報層１１を形成する。なお、必要に応じて、透過率調整層１０を成膜したのちに、第１の記録層４の全面を結晶化させる初期化工程を行ってもよい。第１の記録層４の結晶化はレーザビームを照射することによって行うことができる。
【００９５】
工程（ａ）の前後、または並行して、第２の情報層２０を形成する（工程（ｂ））。具体的には、まず、第２の基板１９（厚さがたとえば１．１ｍｍ）を用意する。そして、第２の基板１９を成膜装置内に配置し、第２の基板１９上に第２の反射層１８を成膜する。このとき、第２の基板１９に案内溝が形成されている場合には、案内溝が形成されている側に第２の反射層１８を成膜する。第２の反射層１８は、Ａｒガス雰囲気中で、第２の反射層１８を構成する金属または合金からなる母材を、スパッタリングすることによって形成できる。
【００９６】
続いて、第２の反射層１８上に、第２の界面層１７、第２の上側保護層１６、および第２の上側界面層１５を、この順序で成膜する。
【００９７】
続いて、第２の上側界面層１５上に第２の記録層１４を成膜する。第２の記録層１４は、Ｓｂ−Ｔｅ−Ｍ１合金からなる母材を、一つの電源を用いて、スパッタリングすることによって形成できる。すなわち、第２の記録層１４は、ＳｂとＴｅと元素Ｍ１とを含む母材を用いて形成できる。スパッタリングの雰囲気ガス（スパッタリングガス）には、Ａｒガス、Ｋｒガス、Ａｒガスと反応ガス（酸素ガスおよび窒素ガスから選ばれる少なくとも１つのガス）との混合ガス、またはＫｒガスと反応ガスとの混合ガスを用いることができる。また、第２の記録層１４は、Ｓｂ、ＴｅおよびＭ１の各々の母材を複数の電源を用いて同時にスパッタリングすることによって形成することもできる。また、第２の記録層１４は、Ｓｂ、Ｔｅ、およびＭ１のうちいずれかの元素を組み合わせた２元系母材などを、複数の電源を用いて同時にスパッタリングすることによって形成することもできる。これらの場合でも、Ａｒガス雰囲気中、Ｋｒガス雰囲気中、Ａｒガスと反応ガスとの混合ガス雰囲気中、またはＫｒガスと反応ガスとの混合ガス雰囲気中でスパッタリングを行う。
【００９８】
第２の記録層１４の成膜レートは、０．３ｎｍ／秒〜１０ｎｍ／秒の範囲内であることが好ましい。実施形態１で説明したように、第２の記録層１４の厚さは、６ｎｍ〜１５ｎｍの範囲内であることが好ましい。第２の記録層１４の成膜レートは、電源の投入パワーで制御できる。成膜レートを下げすぎた場合には、成膜時間が長くなることに加え、雰囲気中のガスが必要以上に記録層中に混入してしまう。また、成膜レートを上げすぎた場合には、成膜時間を短くできるが、層厚を正確に制御することが難しくなる。したがって、第２の記録層１４の成膜レートは、０．３ｎｍ／秒〜１０ｎｍ／秒の範囲内であることが好ましい。
【００９９】
続いて、第２の記録層１４上に、第２の下側界面層１３および第２の下側保護層１２を、この順序で成膜する。
【０１００】
このようにして第２の情報層２０を形成できる。なお、第２の下側保護層１２を形成したのちに、必要に応じて、第２の記録層１４の全面を結晶化させる初期化工程を行ってもよい。第２の記録層１４の結晶化はレーザビームを照射することによって行うことができる。
【０１０１】
最後に、第１の情報層１１と第２の情報層２０とを光学分離層２１を介して貼り合わせる。具体的には、まず、光学分離層２１の材料となる紫外線硬化性樹脂を透過率調整層１０上または第２の下側保護層１２上にスピンコートしたのち、第１の情報層１１と第２の情報層２０とを密着させる。その後、第１の情報層１１側から紫外線を照射して光学分離層２１を硬化させることによって、情報記録媒体２２が得られる。なお、光学分離層２１の材料として遅効性樹脂を用いる場合には、紫外線の照射は不要である。
【０１０２】
（実施形態４）
実施形態４では、情報記録媒体２６の製造方法について説明する。
【０１０３】
実施形態４の製造方法では、まず、第２の情報層２０を形成する（工程（ｂ））。具体的には、まず、第２の基板１９（厚さがたとえば１．１ｍｍ）を用意し、成膜装置内に配置する。
【０１０４】
続いて、第２の基板１９上に第２の反射層１８を成膜する。このとき、第２の基板１９に案内溝が形成されている場合には、案内溝が形成された側に第２の反射層１９を成膜する。そして、第２の反射層１８上に、第２の界面層１７、第２の上側保護層１６、第２の上側界面層１５、第２の記録層１４、第２の下側界面層１３、および第２の下側保護層１２を順に成膜する。これらの各層は、実施形態３で説明した方法で形成できる。
【０１０５】
このようにして第２の情報層２０を形成できる。なお、第２の下側保護層１２を成膜したのちに、必要に応じて、第２の記録層１４の全面を結晶化させる初期化工程を行ってもよい。
【０１０６】
続いて、第２の情報層２０の第２の下側保護層１２上に光学分離層２１を形成する（工程（ｃ））。光学分離層２１は、光硬化性樹脂または遅効性樹脂を第２の下側保護層１２上にスピンコートしたのち、樹脂を硬化させることによって形成できる。なお、光学分離層２１がレーザビームの入射側の表面に案内溝を備える場合には、溝が形成された基板（型）を硬化前の樹脂に密着させたのち、樹脂を硬化させ、その後、基板（型）をはがすことによって案内溝を形成できる。
【０１０７】
続いて、光学分離層２１上に第１の情報層２５を形成する（工程（ａ））。具体的には、まず、光学分離層２１上に、透過率調整層１０、第１の最上界面層９、第１の反射層８、第１の界面層７、第１の上側保護層６、第１の上側界面層５、第１の記録層４、第１の下側界面層３、および第１の下側保護層２をこの順序で成膜する。これらの各層は、実施形態３で説明した方法で形成できる。第１の下側保護層２を成膜したのちに、必要に応じて、第１の記録層４の全面を結晶化させる初期化工程を行ってもよい。
【０１０８】
最後に、透明層２４によって第１の下側保護層２と第１の基板１とを貼り合わせる。具体的には、まず、透明層２４の材料である紫外線硬化性樹脂を第１の基板１上または第１の下側保護層２上にスピンコートしたのち、第１の基板１と第１の下側保護層２とを密着させる。その後、第１の情報層２５側から紫外線を照射して樹脂を硬化させることによって、光学分離層２１上に配置された第１の情報層２５を形成できる。なお、透明層２４が遅効性樹脂からなる場合には、紫外線の照射は不要である。このようにして、情報記録媒体２６を製造できる。
【０１０９】
（実施形態５）
実施形態５では、実施形態１および２で説明した本発明の情報記録媒体の記録再生方法について説明する。
【０１１０】
本発明の記録再生方法に用いられる記録再生装置５０の一部の構成を図４に模式的に示す。図４を参照して、記録再生装置５０は、情報記録媒体５１を回転させるためのスピンドルモータ２７と、半導体レーザ２９を備える光学ヘッド３０と、半導体レーザ２９から出射されるレーザビーム２３を集光する対物レンズ２８とを備える。情報記録媒体５１は、実施形態１または２で説明した情報記録媒体であり、第１の記録層４と第２の記録層１４とを備える。対物レンズ２８は、レーザビーム２３を、第１の記録層４または第２の記録層１４上に集光する。
【０１１１】
対物レンズ２８の開口数ＮＡは、０．５以上１．１以下（より好ましくは、０．６以上１．０以下）であることが好ましい。レーザビーム２３の波長は、３５０ｎｍ以上５００ｎｍ以下（より好ましくは、３９０ｎｍ以上４３０ｎｍ以下）であることが好ましい。情報を記録する際の情報記録媒体の線速度は、３ｍ／秒以上３０ｍ／秒以下（より好ましくは、４ｍ／秒以上１５ｍ／秒以下）であることが好ましい。
【０１１２】
情報の記録は、レーザビーム２３のパワーを、高パワーのピークパワー（Ｐｐ（ｍＷ））と低パワーのバイアスパワー（Ｐｂ（ｍＷ））とに変調させることによって行う。ピークパワーのレーザビーム２３を照射することによって非晶質相が形成され、その非晶質相が記録マークとなる。記録マーク間では、バイアスパワーのレーザビーム２３が照射され、結晶相が形成される。
【０１１３】
第１の情報層１１または２５に対して記録を行う際には、レーザビーム２３の焦点を第１の記録層４に合わせて第１の記録層４に情報を記録する。再生は、第１の記録層４から反射してきたレーザビーム２３を用いて行う。第２の情報層２０に対して記録を行う際には、レーザビーム２３の焦点を第２の記録層１４に合わせ、第１の情報層１１または２５と光学分離層２１とを透過したレーザビーム２３によって情報を記録する。再生は、第２の記録層１４によって反射され、光学分離層２１と第１の情報層１１または２５とを透過してきたレーザビーム２３を用いて行う。
【０１１４】
なお、記録再生の対象となる情報記録媒体の第１の基板１、光学分離層２１および第２の基板１９のいずれかが溝（グルーブ）１ｂを備える場合には、情報は、溝１ｂに記録しても、ランド１ｃに記録してもよい。また、溝１ｂおよびランド１ｃの両方に情報を記録してもよい。第１の情報層１１または２５と第２の情報層２０とは、ともに同一の部分（溝、ランド、または、溝およびランド）に情報を記録してもよいし、異なる部分に情報を記録してもよい。
【０１１５】
（実施形態６）
実施形態６では、本発明の情報記録媒体についてその他の一例を説明する。実施形態６の情報記録媒体４１の一部断面図を図５に示す。情報記録媒体４１では、電気エネルギーの印加、具体的には電流パルスの印加によって情報の記録が行われる。
【０１１６】
図５を参照して、情報記録媒体４１は、基板３１と、基板３１上に順に積層された第１の電極３２と、第１の記録層３３と、中間電極３４と、第２の記録層３５と、第２の電極３６とを備える。第１の記録層３３は、第１の情報層を構成する。第２の記録層３５は第２の情報層を構成する。
【０１１７】
基板３１としては、ポリカーボネート等からなる樹脂からなる樹脂基板、ガラス基板、Ａｌ₂Ｏ₃等からなるセラミックからなるセラミック基板、Ｓｉ基板、または、さまざまな金属（たとえば銅）からなる金属基板を用いることができる。なお、基板３１が導電性を有する場合には、基板３１を第１の電極３２として用いてもよい。以下では、基板３１として絶縁性の基板を用いた場合について説明する。
【０１１８】
情報記録媒体４１は、基板３１上に、第１の電極３２、第１の記録層３３、中間電極３４、第２の記録層３５、および第２の電極３６を順に積層することによって製造できる。第１の記録層３３の組成および形成方法は、実施形態１および３で説明した第１の記録層４の組成および形成方法と同様である。第２の記録層３５の組成および形成方法は、実施形態１および３で説明した第２の記録層１４の組成および形成方法と同様である。第１の記録層３３および第２の記録層３５は、電流の印加により発生するジュール熱によって、結晶相と非晶質相との間で可逆的な相変化を起こす。
【０１１９】
第１の電極３２、中間電極３４、および第２の電極３６の材料としては、Ａｌ、Ａｕ、Ａｇ、Ｃｕ、Ｐｔ、Ｔｉ、Ｗといった単体金属を用いることができる。または、これらの金属元素のうちの１つまたは複数を主成分とし、耐湿性の向上あるいは熱伝導率の調整等のために１つまたは複数の他の元素を添加した合金材料を用いることもできる。第１の電極３２、中間電極３４、および第２の電極３６は、Ａｒガス雰囲気中で、これらの電極を構成する金属または合金からなる母材をスパッタリングすることによって形成できる。
【０１２０】
以下に、情報記録媒体４１を用いた記録再生方法について説明する。第１の電極３２と第２の電極３６の間、および中間電極３４と第２の電極３６の間には、スイッチ３９を介してパルス電源３７が接続されている。第１の電極３２と第２の電極３６との間には、スイッチ４０を介して抵抗測定器３８が接続されている。
【０１２１】
情報記録媒体４１では、第１の記録層３３と第２の記録層３５とを、それぞれ非晶質相と結晶相との間で相変化させることによって情報が記録される。また、情報の再生は、結晶相にある記録層の抵抗にくらべて非晶質相にある記録層の抵抗が高いことを利用して行われる。具体的には、第１の記録層３３および第２の記録層３５の抵抗値を測定することによって情報を再生する。
【０１２２】
非晶質相（高抵抗状態）にある第１の記録層３３を結晶相（低抵抗状態）に変化させる場合には、スイッチ３９を端子３９ａ側に閉じ（スイッチ４０は開）、第１の電極３２と第２の電極３６との間に電流パルスを印加する。このとき、第１の記録層３３の材料は、第２の記録層３５の材料に比べて結晶化温度が低く結晶化時間が長いため、印加する電流パルスの振幅やパルス幅を調整することによって、第１の記録層３３のみを相変化させることができる。
【０１２３】
また、非晶質相にある第２の記録層３５を結晶相に変化させる場合には、スイッチ３９を端子３９ｂ側に閉じ（スイッチ４０は開）、中間電極３４と第２の電極３６との間に電流パルスを印加する。記録層を、結晶相から再度非晶質相に戻す場合には、結晶化時よりも相対的に高い振幅（電流値）の電流パルスをより短い時間で印加する。
【０１２４】
具体的には、第１の記録層３３（または第２の記録層３５）を非晶質相から結晶相に変化させる際には、振幅がＩｃでパルス幅がｔｃの電流パルスを第１の記録層３３（または第２の記録層３５）に印加する。また、第１の記録層３３を結晶相から非晶質相に変化させる際には、振幅がＩａ１でパルス幅がｔａ１の電流パルスを第１の記録層３３に印加する。また、第２の記録層３５を結晶相から非晶質相に変化させる際には、振幅がＩａ２でパルス幅がｔａ２の電流パルスを第２の記録層３５に印加する。ここで、これらの振幅とパルス幅とは、Ｉｃ＜Ｉａ２＜Ｉａ１の関係、およびｔａ１≦ｔｃまたはｔａ２≦ｔｃの関係を満たすことが好ましい。
【０１２５】
第１の記録層３３および第２の記録層３５の抵抗値は、スイッチ４０を閉じて（スイッチ３９は開）、抵抗測定器３８によって測定する。第１の記録層３３および第２の記録層３５の抵抗値を測定することによって、記録された情報を読み出すことができる。
【０１２６】
この情報記録媒体４１をマトリクス的に多数配置することによって、大容量の書換型メモリが得られる。そのような情報記録媒体について、一例の構成を図６に模式的に示す。
【０１２７】
図６を参照して、情報記録媒体４２は、ストライプ状に配置された複数のワード線（ｗｏｒｄ ｌｉｎｅ）４３と、ストライプ状に配置された複数のビット線（ｂｉｔ ｌｉｎｅ）４４と、複数のメモリセル４５とを備える。ワード線４３およびビット線４４は、電流パルスの印加および抵抗の測定のための電気配線である。ワード線４３とビット線４４とは、直交するように配置されている。メモリセル４５は、ワード線４３とビット線４４との交点（図６中のハッチングで示す）において、ワード線４３とビット線４４との間に挟まれるように配置されている。メモリセル４５には、中間電極３４を省略した情報記録媒体４１を用いることができる。
【０１２８】
情報記録媒体４２では、ワード線４３とビット線４４との間の電圧を変化させてメモリセルに電流パルスを印加することによって、情報を記録することができる。
【０１２９】
以下に、中間電極３４を省略した場合の記録再生方法について説明する。第１の記録層３３を結晶相に変化させる際に、振幅がＩｃ１でパルス幅がｔｃ１の電流パルスを印加する。第２の記録層３５を結晶相に変化させる際に、振幅がＩｃ２でパルス幅がｔｃ２の電流パルスを印加する。第１の記録層３３を非晶質相に変化させる際に、振幅がＩａ１でパルス幅がｔａ１の電流パルスを印加する。第２の記録層３５を非晶質相に変化させる際に振幅がＩａ２でパルス幅がｔａ２の電流パルスを印加する。
【０１３０】
第１の記録層３３の材料が非晶質相から結晶相に変化する温度Ｔｘ１は、第２の記録層３５の材料が非晶質相から結晶相に変化する温度Ｔｘ２よりも低い（Ｔｘ１＜Ｔｘ２）。また、第１の記録層３３の材料が非晶質相から結晶相に変化する際に要する時間ｔｘ１は、第２の記録層３５の記録材料が非晶質相から結晶相に変化する際に要する時間ｔｘ２よりも長い（ｔｘ２＜ｔｘ１）。したがって、振幅Ｉｃ１、パルス幅ｔｃ１、振幅Ｉｃ２およびパルス幅ｔｃ２が、Ｉｃ１＜Ｉｃ２且つｔｃ１＞ｔｃ２を満たすようにすることによって、各記録層を選択的に結晶化できる。また、振幅がＩｃ２でパルス幅がｔｃ１の電流パルスを第１の記録層３３および第２の記録層３５に印加することによって、両方の記録層を同時に結晶化できる。
【０１３１】
また、第１の記録層３３の材料の融点は、第２の記録層３５の材料の融点よりも高い。したがって、ｔａ２を短くし、Ｉａ１＞Ｉａ２とすることによって、第２の記録層３５のみを非晶質化することができる。一方、パルス幅ｔａ１が短い場合、振幅がＩａ１でパルス幅がｔａ１の電流パルスを印加すると、２つの記録層が共に非晶質相になる。この場合、第２の記録層３５のみを結晶化することによって、第１の記録層３３のみを非晶質相にできる。
【０１３２】
以下に、各記録層の状態の判別方法について説明する。第１の記録層３３が非晶質相である場合の抵抗値Ｒａ１、第１の記録層３３が結晶相である場合の抵抗値Ｒｃ１、第２の記録層３５が非晶質相である場合の抵抗値Ｒａ２、および、第２の記録層３５が結晶相である場合の抵抗値Ｒｃ２とする。２つの記録層の抵抗値の合計は、２つの記録層の状態に応じてＲａ１＋Ｒａ２、Ｒａ１＋Ｒｃ２、Ｒｃ１＋Ｒａ２、またはＲｃ１＋Ｒｃ２となる。ここで、Ｒａ１とＲａ２とを異なる値とし、Ｒｃ１およびＲｃ２をそれらの値よりもずっと小さい値とすることによって、抵抗値から各記録層の状態を容易に判別することができる。このように、記録層の４つの異なる状態、すなわち２値の情報を抵抗値の一度の測定で検出することができる。
【０１３３】
【実施例】
以下に、実施例を用いて本発明をさらに詳細に説明する。
【０１３４】
（実施例１）
実施例１では、図１の情報記録媒体２２の第１の情報層１１の透過率を測定し、透過率調整層１０の効果について調べた。
【０１３５】
まず、透過率測定用のサンプルを作製した。具体的には、第１の情報層１１を作製し、光学分離層２１を介して第１の情報層１１と第２の基板１９とを貼りあわせることによってサンプルを作製した。
【０１３６】
一方、比較例として、透過率調整層１０がない場合のサンプルも作製し、透過率を測定した。この比較例のサンプルは以下のようにして製造した。まず、第１の基板１として、ポリカーボネート基板（直径１２０ｍｍ、厚さ０．６ｍｍ）を用意した。そして、そのポリカーボネート基板上に、第１の下側保護層２としてＺｎＳ−ＳｉＯ₂層（ＳｉＯ₂：２０ｍｏｌ％）、第１の下側界面層３としてＧｅＮ層（厚さ：５ｎｍ）、第１の記録層４として（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁層（厚さ：６ｎｍ）、第１の上側界面層５としてＧｅＮ層（厚さ：５ｎｍ）、第１の上側保護層６としてＺｎＳ−ＳｉＯ₂層（ＳｉＯ₂：２０ｍｏｌ％）、第１の界面層７としてＧｅＮ層（厚さ：５ｎｍ）、および、第１の反射層８としてＡｇ合金層（厚さ：１０ｎｍ）を順次スパッタリング法によって積層した。このようにして比較例のサンプルを製造した。
【０１３７】
透過率調整層１０を備えるサンプルを形成する場合には、第１の反射層８上に、さらに第１の最上界面層９としてＧｅＮ層（厚さ：３ｎｍ）、および、透過率調整層１０としてＺｎＳ−ＳｉＯ₂層（厚さ：約３０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）を順次スパッタリング法により積層した。そして、第２の基板１９に、光学分離層２１の材料である紫外線硬化性樹脂をスピンコートした。そして、樹脂の上に第１の情報層１１を密着させ、紫外線を照射して樹脂を硬化させた。以上のようにして、透過率測定用サンプルを製造した。
【０１３８】
ここで、第１の下側保護層２および第１の上側保護層６の厚さは、マトリクス法（たとえば、久保田 広著、「波動光学」、岩波書店、１９７１年、第３章を参照）に基づく計算により、厳密に決定された。具体的には、これらの厚さは、第１の記録層４が結晶相である場合と非晶質相である場合とで波長４０５ｎｍにおける反射光量の変化がより大きく、且つ第１の情報層１１の透過率がより大きく、且つ第１の記録層４の光吸収効率が大きくなるように決定された。また、透過率調整層１０の厚さは、第１の記録層４が結晶相である場合と非晶質相である場合との反射光量の差および第１の記録層４の光吸収効率を低下させることなく、第１の情報層１１の透過率がより大きくなるように厳密に決定された。
【０１３９】
このようにして得られたサンプルについて、最初に、第１の記録層４が非晶質相である場合の透過率Ｔａ（％）を測定した。その後、第１の記録層４を結晶化させる初期化工程を行い、第１の記録層４が結晶相である場合の透過率Ｔｃ（％）を測定した。測定には分光器を用い、波長４０５ｎｍにおける透過率の値を調べた。測定後、（Ｔｃ＋Ｔａ）／２の値を計算した。
【０１４０】
透過率の測定結果を表２に示す。ここで、表２中のサンプル２−１および２−３の第１の情報層１１は、記録層が結晶相である場合の反射率が、記録層が非晶質相である場合の反射率よりも高い。また、サンプル２−１および２−３は、記録層が結晶相である場合の反射率がほぼ同等である。サンプル２−２および２−４の第１の情報層１１は、記録層が非晶質相である場合の反射率が、記録層が結晶相である場合の反射率よりも高い。また、サンプル２−２と２−４とは、記録層が非晶質相である場合の反射率がほぼ同等である。
【０１４１】
【表２】

【０１４２】
表２に示すように、透過率調整層１０を設けたサンプル２−３および２−４の第１の情報層１１では、透過率調整層１０がないサンプル２−１および２−２の第１の情報層１１と比較して、反射率を下げることなく（Ｔｃ＋Ｔａ）／２の値が２％〜６％程度向上した。従って、第１の情報層１１は、透過率調整層１０を含むことが好ましい。
【０１４３】
なお、図２の情報記録媒体２６の第１の情報層２５についても同様の方法で透過率を測定した結果、透過率調整層１０が同様の効果を持つことが確認できた。
【０１４４】
（実施例２）
実施例２では、第１の情報層１１の特性と第１の記録層４の厚さとの関係を調べた。具体的には、第１の記録層４の厚さを変化させて第１の情報層１１を作製し、光学分離層２１を介して第１の情報層１１と第２の基板１９とを貼り合わせたサンプルを作製した。形成したサンプルについて、第１の情報層１１の消去率、振幅対雑音比（Ｃａｒｒｉｅｒ ｔｏ Ｎｏｉｓｅ Ｒａｔｉｏ：ＣＮＲ）、および透過率を測定した。
【０１４５】
以下にサンプルの製造方法を説明する。まず、第１の基板１としてポリカーボネート基板（直径１２０ｍｍ、厚さ０．６ｍｍ）を準備した。そして、そのポリカーボネート基板上に、第１の下側保護層２としてＺｎＳ−ＳｉＯ₂層（厚さ：約４０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の下側界面層３としてＧｅＮ層（厚さ：５ｎｍ）、第１の記録層４として（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁層（厚さ：４ｎｍ〜１０ｎｍ）、第１の上側界面層５としてＧｅＮ層（厚さ：５ｎｍ）、第１の上側保護層６としてＺｎＳ−ＳｉＯ₂層（厚さ：約５ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の界面層７としてＧｅＮ層（厚さ：５ｎｍ）、第１の反射層８としてＡｇ合金層（厚さ：１０ｎｍ）、第１の最上界面層９としてＧｅＮ層（厚さ：５ｎｍ）、および、透過率調整層１０としてＺｎＳ−ＳｉＯ₂層（厚さ：約３０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）を、順次スパッタリング法によって積層した。その後、第１の記録層４の全面を結晶化させる初期化工程を行った。このようにして、第１の情報層１１を形成した。
【０１４６】
次に、光学分離層２１の材料である紫外線硬化性樹脂を第２の基板１９上にスピンコートした。そしてこの樹脂上に第１の情報層１１を密着させ、紫外線を照射することによって樹脂を硬化させた。以上のようにして、第１の記録層４の厚さが異なる複数のサンプルを作製した。
【０１４７】
作製したサンプルについて、実施例１と同様の方法によって、第１の情報層１１の透過率を測定した。また、作製したサンプルについて、図４に示した装置を用いて、第１の情報層１１の消去率およびＣＮＲを測定した。このとき、レーザビーム２３の波長は４０５ｎｍ、対物レンズ２８のＮＡは０．６５、測定時のサンプルの線速度は８．６ｍ／ｓ、最短マーク長は０．２９４μｍとした。また、情報はグルーブに記録した。
【０１４８】
ＣＮＲは、（８−１６）変調の３Ｔ信号を１０回記録したのち、スペクトラムアナライザーで測定した。消去性能は、３Ｔ信号を１０回記録して振幅を測定し、その上から１１Ｔ信号を１回重ね書きして再度３Ｔ信号の振幅を測定し、３Ｔ信号の減衰率を計算することによって評価した。以下、この３Ｔ信号の減衰率を消去率という。
【０１４９】
第１の情報層１１の消去率およびＣＮＲの測定結果、および（Ｔｃ＋Ｔａ）／２の計算結果を表３に示す。
【０１５０】
【表３】

【０１５１】
表３中、Ａ〜Ｄは、（Ｔｃ＋Ｔａ）／２の値、ＣＮＲおよび消去率の値を示す。具体的には、（Ｔｃ＋Ｔａ）／２の値について、Ｄ＜３０％、３０％≦Ｃ＜４０％、４０％≦Ｂ＜５０％、５０％≦Ａである。ＣＮＲについては、４０（ｄＢ）≦Ｃ＜５０（ｄＢ）、５０（ｄＢ）≦Ｂである。消去率については、２０（ｄＢ）≦Ｃ＜３０（ｄＢ）、３０（ｄＢ）≦Ｂである。第１の情報層１１は、（Ｔｃ＋Ｔａ）／２の値が３０％以上であることが好ましく、４０％以上であることがより好ましい。また、ＣＮＲは、４０ｄＢ以上であることが好ましく、５０ｄＢ以上であることがより好ましい。また、消去率は、２０ｄＢ以上であることが好ましく、３０ｄＢ以上であることがより好ましい。
【０１５２】
表３に示すように、サンプル３−１（第１の記録層４の厚さ：４ｎｍ）では、透過率は十分であるがＣＮＲおよび消去率が不十分であった。サンプル３−４（第１の記録層４の厚さ：１０ｎｍ）では、ＣＮＲおよび消去率が高いが、透過率が３０％未満であった。サンプル３−２（第１の記録層４の厚さ：６ｎｍ）、およびサンプル３−３（第１の記録層４の厚さ：９ｎｍ）では、透過率が３５％〜４５％で、ＣＮＲが５０ｄＢ、消去率が３０ｄＢという良好な結果が得られた。以上の結果から、第１の記録層４の膜厚は、９ｎｍ以下であることが好ましい。
【０１５３】
なお、図２の情報記録媒体２６の第１の情報層２５についても同様の方法で消去率、ＣＮＲおよび透過率を測定した結果、同様の結果が得られた。
【０１５４】
（実施例３）
実施例３では、第１の情報層１１の特性と第１の記録層４の材料との関係を調べた。具体的には、第１の記録層４の組成を変化させて第１の情報層１１を作製し、光学分離層２１を介して第１の情報層１１と第２の基板１９とを貼り合わせたサンプルを作製した。形成したサンプルについて、第１の情報層１１のＣＮＲ、消去率および透過率を測定した。
【０１５５】
以下に、サンプルの製造方法について説明する。まず、第１の基板１としてポリカーボネート基板（直径：１２０ｍｍ、厚さ０．６ｍｍ）を準備した。そして、そのポリカーボネート基板上に、第１の下側保護層２としてＺｎＳ−ＳｉＯ₂層（厚さ：約４０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の下側界面層３としてＧｅＮ層（厚さ：５ｎｍ）、第１の記録層４（厚さ：６ｎｍ）、第１の上側界面層５としてＧｅＮ層（厚さ：５ｎｍ）、第１の上側保護層６としてＺｎＳ−ＳｉＯ₂層（厚さ：約５ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の界面層７としてＧｅＮ層（厚さ：５ｎｍ）、第１の反射層８としてＡｇ合金層（厚さ：１０ｎｍ）、第１の最上界面層９としてＧｅＮ層（厚さ：５ｎｍ）、および、透過率調整層１０としてＺｎＳ−ＳｉＯ₂層（厚さ：約３０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）を、順次スパッタリング法により積層した。ここで、第１の記録層４の材料としては、（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁、（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅、または（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅を用いた。透過率調整層１０を形成したのち、第１の記録層４の全面を結晶化させる初期化工程を行った。このようにして、第１の記録層４の組成が異なる３種類の第１の情報層１１を作製した。
【０１５６】
次に、光学分離層２１の材料である硬化前の紫外線硬化性樹脂を第２の基板１９上にスピンコートした。そしてこの樹脂上に第１の情報層１１を密着させ、紫外線を照射することによって樹脂を硬化させた。以上のようにして、第１の記録層４の組成が異なる複数のサンプルを作製した。
【０１５７】
作製したサンプルについて、実施例１と同様の方法で第１の情報層１１の透過率を測定した。また、これらのサンプルについて、実施例２と同様の方法で第１の情報層１１のＣＮＲおよび消去率を測定した。
【０１５８】
第１の情報層１１のＣＮＲおよび消去率、ならびに（Ｔｃ＋Ｔａ）／２の計算結果を表４に示す。
【０１５９】
【表４】

【０１６０】
表４中、Ｂ〜Ｄは、（Ｔｃ＋Ｔａ）／２の値、ＣＮＲおよび消去率の値を示す。具体的には、（Ｔｃ＋Ｔａ）／２の値について、３０％≦Ｃ＜４０％、４０％≦Ｂ＜５０％である。ＣＮＲについては、Ｄ＜４０（ｄＢ）、５０（ｄＢ）≦Ｂである。消去率については、２０（ｄＢ）≦Ｃ＜３０（ｄＢ）、３０（ｄＢ）≦Ｂである。
【０１６１】
表４に示すように、サンプル４−２および４−３は、透過率、ＣＮＲ、および消去率がともに不十分であった。一方、サンプル４−１では、透過率が４５％、ＣＮＲが５０ｄＢ、消去率が３０ｄＢという良好な結果が得られた。以上の結果から、上記サンプルの中では、組成式（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁で表される材料が、第１の記録層４の材料として好ましい。
【０１６２】
なお、図２の情報記録媒体２６の第１の情報層２５についても同様の方法で消去率、ＣＮＲおよび透過率を測定した結果、同様の結果が得られた。
【０１６３】
（実施例４）
実施例４では、第２の情報層２０の特性と第２の記録層１４の材料との関係を調べた。具体的には、第２の記録層１４の材料を変化させて第２の情報層２０を形成し、光学分離層２１を介して第１の基板１と第２の情報層２０とを貼りあわせたサンプルを作製した。形成したサンプルについて、第２の情報層２０の記録感度、ＣＮＲ、および反射率を測定した。
【０１６４】
以下に、サンプルの製造方法について説明する。まず、第２の基板１９としてポリカーボネート基板（直径１２０ｍｍ、厚さ０．６ｍｍ）を準備した。そして、そのポリカーボネート基板上に、第２の反射層１８としてＡｌ合金層（厚さ：８０ｎｍ）、第２の上側保護層１６としてＺｎＳ−ＳｉＯ₂層（厚さ：約１０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第２の上側界面層１５としてＧｅＮ層（厚さ：５ｎｍ）、第２の記録層１４（厚さ：１０ｎｍ）、第２の下側界面層１３としてＧｅＮ層（厚さ：５ｎｍ）、および、第２の下側保護層１２としてＺｎＳ−ＳｉＯ₂層（厚さ：約６０ｎｍ）を、順次スパッタリング法によって積層した。ここで、第２の記録層１４としては、（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁、（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅、または（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅を用いた。
【０１６５】
第２の下側保護層１２および第２の上側保護層１６の厚さは、マトリクス法に基づく計算により、波長４０５ｎｍにおいて、第２の記録層１４が結晶相のときの反射光量が第２の記録層１４が非晶質相のときの反射光量よりも大きく、且つ第２の記録層１４が結晶相のときと非晶質相のときとで反射光量の変化がより大きく、且つ第２の記録層１４の光吸収効率が大きくなるように厳密に決定した。
【０１６６】
次に、第２の記録層１４の全面を結晶化させる初期化工程を行った。次に、光学分離層２１の材料である紫外線硬化性樹脂を第１の基板１上にスピンコートした。そして、この樹脂上に第２の情報層２０を密着させ、紫外線を照射して樹脂を硬化させた。以上のようにして、第２の記録層１４の組成が異なる複数のサンプルを形成した。
【０１６７】
形成したサンプルについて、基板の鏡面部における反射率を測定した。また、これらのサンプルについて、図４の装置を用いて、第２の情報層２０の記録感度およびＣＮＲを測定した。このとき、レーザビーム２３の波長は４０５ｎｍ、対物レンズ２８のＮＡは０．６５、測定時のサンプルの線速度は８．６ｍ／ｓ、最短マーク長は０．２９４μｍとした。また、情報はグルーブに記録した。ここで、記録感度とは、振幅（ｄＢｍ）の飽和値から３ｄＢｍだけ低い振幅を与えるピークパワーＰｐ（ｍＷ）の１．３倍のピークパワーＰｐ（ｍＷ）で定義される値である（以下の実施例においても同様である）。記録感度の値が小さいほど、より低いレーザパワーで記録が可能であることを示す。なお、第１の情報層１１の透過率の平均値（Ｔｃ＋Ｔａ）／２が４０％程度であり、第１の基板１に入射する半導体レーザ２９の最大パワーは約１２ｍＷ程度であるので、第２の情報層２０に到達するレーザパワーは約５ｍＷである。このため、第２の情報層２０の記録感度は５ｍＷ以下であることが好ましい。
【０１６８】
第２の情報層２０の記録感度、ＣＮＲ、および第２の記録層１４が結晶相である場合の反射率の測定結果を表５に示す。
【０１６９】
【表５】

【０１７０】
表５中、Ｂ〜Ｄは、記録感度、ＣＮＲ、および反射率の値を示す。具体的には、記録感度について、５（ｍＷ）＜Ｄ、Ｂ≦５ｍＷである。ＣＮＲについては、５０（ｄＢ）≦Ｂである。反射率については、１０％≦Ｃ＜２０％、２０％≦Ｂ＜３０％である。第２の情報層２０では、ＣＮＲが４０ｄＢ以上であることが好ましく、５０ｄＢ以上であることがより好ましい。また、反射率が１０％以上であることが好ましく、反射率が２０％以上であることがより好ましい。
【０１７１】
表５に示すように、サンプル５−１では、５ｍＷ以下の記録レーザパワーでＣＮＲが飽和せず記録感度が十分でないこと、および反射率が不十分であることがわかった。また、低融点材料である（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅または（Ｓｂ_0.7Ｔｅ_0.3）₉₀Ａｇ₅Ｉｎ₅を用いたサンプル５−２および５−３では、５ｍＷ以下の記録感度と高いＣＮＲとを両立できることがわかった。
【０１７２】
なお、図３に示した情報記録媒体２６の第２の情報層２０についても同様の方法で記録感度を測定した結果、同様の結果が得られた。
【０１７３】
（実施例５）
実施例５では、実施例３および実施例４の結果に基づき、図１の情報記録媒体２２を製造した。そして、製造した情報記録媒体２２について、第１の情報層１１の透過率、ＣＮＲおよび消去率と、第２の情報層２０の記録感度、反射率およびＣＮＲとを測定した。
【０１７４】
実施例５では、第１の記録層４および第２の記録層１４の組成は、（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁または（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅とした。第１の記録層４の厚さは６ｎｍ、第２の記録層１４の厚さは１０ｎｍとした。
【０１７５】
第１の情報層１１は、各層を成膜した後に、初期化工程を行った。第１の情報層１１について、初期化工程の前後で透過率を測定した。第２の情報層２０も、成膜後に初期化工程を行った。その後、光学分離層２１の材料である硬化前の紫外線硬化性樹脂を第２の下側保護層１２の上にスピンコートし、第１の情報層１１と第２の情報層２０とを密着させた。そして、紫外線を照射して樹脂を硬化させた。このようにして第１の情報層１１と第２の情報層２０とを備えるサンプル（情報記録媒体２２）を製造した。なお、記録層および光学分離層以外の構成および製造条件は、実施例３および４と同様である。
【０１７６】
このようにして得られたサンプルについて、第１の情報層１１のＣＮＲおよび消去率を測定した。また、第２の情報層２０の記録感度、反射率およびＣＮＲを測定した。これらの測定は、上記実施例で説明した方法と同様の方法で行った。測定結果を表６に示す。
【０１７７】
【表６】

【０１７８】
表６中、Ｂ〜Ｄは、各測定の結果を示す。（Ｔｃ＋Ｔａ）／２の値については、３０％≦Ｃ＜４０％、４０％≦Ｂ＜５０％である。ＣＮＲについては、Ｄ＜４０（ｄＢ）、４０（ｄＢ）≦Ｃ＜５０（ｄＢ）、５０（ｄＢ）≦Ｂである。消去率については、２０（ｄＢ）≦Ｃ＜３０（ｄＢ）、３０（ｄＢ）≦Ｂである。記録感度については、１２（ｍＷ）＜Ｄ、Ｂ≦１２（ｍＷ）である。表６の反射率とは第２の記録層１４が結晶相である場合の第２の情報層２０の反射率であり、１０％≦Ｃ＜２０％、２０％≦Ｂ＜３０％である。
【０１７９】
サンプル６−１は、第１の記録層４および第２の記録層１４の組成が、ともに（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁である。サンプル６−２は、第１の記録層４の組成が（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁であり、第２の記録層１４の組成が（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅である。サンプル６−３は、第１の記録層４および第２の記録層１４の組成が、ともに（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅である。
【０１８０】
表６に示すように、サンプル６−１では、実施例４の結果と同様に、第２の情報層２０の記録感度および反射率が十分でなかった。また、サンプル６−３では、実施例３の結果と同様に、透過率、ＣＮＲおよび消去率が不十分であり、且つ第１の情報層１１の透過率が十分でないために第２の情報層２０の記録感度、反射率およびＣＮＲが低下した。これに対して、サンプル６−２では、第１の情報層１１および第２の情報層２０がともに、ＣＮＲが５０ｄＢ以上で、消去率が３０ｄＢ以上であるという良好な結果が得られた。
【０１８１】
以上、情報をグルーブに記録した場合について説明した。さらに、ランドに情報を記録した場合と、ランドとグルーブの両方に情報を記録した場合とについて同様の測定を行ったところ、同様の結果が得られた。
【０１８２】
（実施例６）
実施例６では、実施形態４の製造方法で図３の情報記録媒体２６を製造した。そして、製造した情報記録媒体２６について、第１の情報層２５のＣＮＲおよび消去率、ならびに第２の情報層２０の消去率およびＣＮＲを測定した。
【０１８３】
以下に、サンプルの製造方法について説明する。まず、第２の基板１９としてポリカーボネート基板（直径１２０ｍｍ、厚さ１．１ｍｍ）を準備した。そして、そのポリカーボネート基板上に、第２の反射層１８としてＡｌ合金層（厚さ：８０ｎｍ）、第２の上側保護層１６としてＺｎＳ−ＳｉＯ₂層（厚さ：約１０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第２の上側界面層１５としてＧｅＮ層（厚さ：５ｎｍ）、第２の記録層１４として（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅層（厚さ：１０ｎｍ）、第２の下側界面層１３としてＧｅＮ層（厚さ：５ｎｍ）、および、第２の下側保護層１２としてＺｎＳ−ＳｉＯ₂層（厚さ：約６０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）を、順次スパッタリング法によって積層した。その後、第２の記録層１４の全面を結晶化させる初期化工程を行った。
【０１８４】
続いて、第２の下側保護層１２上に紫外線硬化性樹脂をスピンコートし、その上に案内溝を形成した基板をかぶせ、樹脂を硬化させた後に基板をはがした。この工程によって、レーザビーム２３を導く案内溝が第１の情報層２５側に形成された光学分離層２１を形成した。
【０１８５】
その後、光学分離層２１の上に、透過率調整層１０としてＺｎＳ−ＳｉＯ₂層（厚さ：約３０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の最上界面層９としてＧｅＮ層（厚さ：３ｎｍ）、第１の反射層８としてＡｇ合金層（厚さ：１０ｎｍ）、第１の界面層７としてＧｅＮ層（厚さ：５ｎｍ）、第１の上側保護層６としてＺｎＳ−ＳｉＯ₂層（厚さ：約５ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）、第１の上側界面層５としてＧｅＮ層（厚さ：５ｎｍ）、第１の記録層４として（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁層（厚さ：６ｎｍ）、第１の下側界面層３としてＧｅＮ層（厚さ：５ｎｍ）、および、第１の下側保護層２としてＺｎＳ−ＳｉＯ₂層（厚さ：約４０ｎｍ、ＳｉＯ₂：２０ｍｏｌ％）を、順次スパッタリング法により積層した。その後、第１の記録層４の全面を結晶化させる初期化工程を行った。
【０１８６】
次に、第１の基板１としてポリカーボネート基板（直径１２０ｍｍ、厚さ０．１ｍｍ）を準備した。そして、透明層２４の材料である紫外線硬化性樹脂を、第１の基板１上にスピンコートした。その後、その樹脂上に第１の下側保護層２を密着させ、紫外線を照射して樹脂を硬化させた。以上のようにして、サンプル（情報記録媒体２６）を製造した。
【０１８７】
製造したサンプルについて、図４の装置を用いて、第１の情報層２５および第２の情報層２０のＣＮＲおよび消去率を測定した。このとき、レーザビーム２３の波長は４０５ｎｍ、対物レンズ２８のＮＡは０．８５、測定時の情報記録媒体２６の線速度は５．０ｍ／ｓ、最短マーク長は０．２０６μｍとした。情報は、グルーブに記録した。その結果、第１の情報層２５および第２の情報層２０は共に、ＣＮＲが５０ｄＢ以上で消去率が３０ｄＢ以上という良好な結果が得られた。
【０１８８】
（実施例７）
第２の記録層１４の材料に、Ｍ１として、Ａｇ、ＩｎおよびＧｅの代わりにＳｎ、Ｓｅ、Ｂｉ、ＡｕまたはＭｎを添加した場合について、実施例４、５および６と同様の測定を行った。その結果、実施例４、５および６と同様の効果が得られた。
【０１８９】
（実施例８）
実施例８では、図５の情報記録媒体４１を製造し、電気エネルギー（電流パルス）の印加による記録層の相変化を確認した。
【０１９０】
まず、基板３１として、表面を窒化処理したＳｉ基板を用意した。そして、そのＳｉ基板上に、第１の電極３２としてＡｕ層（面積：１．０ｍｍ×１．０ｍｍ、厚さ：０．１μｍ）、第１の記録層３３として（Ｇｅ_0.74Ｓｎ_0.26）₈Ｓｂ₂Ｔｅ₁₁層（面積：０．６ｍｍ×０．６ｍｍ、厚さ：０．５μｍ）、中間電極３４としてＡｕ層（面積：０．６ｍｍ×０．６ｍｍ、厚さ０．１μｍ）、第２の記録層３５として（Ｓｂ_0.7Ｔｅ_0.3）₉₅Ｇｅ₅層（面積：０．２ｍｍ×０．２ｍｍ、厚さ：０．５μｍ）、および、第２の電極３６としてＡｕ層（面積：０．２ｍｍ×０．２ｍｍ、厚さ：０．１μｍ）を、順次スパッタリング法により積層した。
【０１９１】
その後、第１の電極３２、中間電極３４、および第２の電極３６にＡｕからなるリード線をボンディングした。第１の電極３２と第２の電極３６との間、および中間電極３４と第２の電極３６との間には、パルス電源３７をスイッチ３９を介して接続した。第１の記録層３３および第２の記録層３５の相変化による抵抗値の変化は、第１の電極３２と第２の電極３６との間にスイッチ４０を介して接続した抵抗測定器３８によって検出した。
【０１９２】
第１の記録層３３および第２の記録層３５が共に高抵抗状態（非晶質相）のときに、第１の電極３２と第２の電極３６との間に振幅５０ｍＡ、パルス幅１００ｎｓの電流パルスを印加したところ、２つの記録層がともに、低抵抗状態（結晶相）に変化した。次に、第１の電極３２と第２の電極３６との間に、振幅１５０ｍＡ、パルス幅５０ｎｓの電流パルスを印加したところ、第２の記録層３５のみが低抵抗状態から高抵抗状態に変化した。また、第１の記録層３３および第２の記録層３５がともに低抵抗状態のときに、第１の電極３２と第２の電極３６との間に振幅２００ｍＡ、パルス幅５０ｎｓの電流パルスを印加したところ、２つの記録層が共に低抵抗状態から高抵抗状態に変化した。さらに、第１の記録層３３および第２の記録層３５がともに高抵抗状態のときに、中間電極３４と第２の電極３６の間に振幅５０ｍＡ、パルス幅１００ｎｓの電流パルスを印加したところ、第２の記録層３５のみが高抵抗状態から低抵抗状態に変化した。
【０１９３】
以上のように、図５の情報記録媒体４１では、第１の記録層３３および第２の記録層３５のそれぞれを、電気的に結晶相と非晶質相との間で可逆的に変化させることことができた。その結果、４つの状態、すなわち、第１の記録層３３と第２の記録層３５が共に高抵抗の状態、第１の記録層３３が低抵抗で第２の記録層３５が高抵抗の状態、第１の記録層３３が高抵抗で第２の記録層３５が低抵抗の状態、第１の記録層３３と第２の記録層３５が共に低抵抗の状態を実現できた。
【０１９４】
以上、本発明の実施の形態について例を挙げて説明したが、本発明は、上記実施の形態に限定されず本発明の技術的思想に基づき他の実施形態に適用することができる。
【０１９５】
【発明の効果】
以上のように本発明の情報記録媒体およびその製造方法によれば、２層の記録層を有し且つ記録・消去性能が良好な情報記録媒体が得られる。
【０１９６】
また、本発明の記録再生方法によれば、高密度の記録が可能である。
【図面の簡単な説明】
【図１】 本発明の情報記録媒体について一例を示す一部断面図である。
【図２】 本発明の情報記録媒体について他の一例を示す一部断面図である。
【図３】 本発明の情報記録媒体についてその他の一例を示す一部断面図である。
【図４】 本発明の記録再生方法に用いられる記録再生装置について構成の一部を模式的に示す図である。
【図５】 本発明の情報記録媒体のその他の一例、およびその記録再生装置の一例について構成を模式的に示す図である。
【図６】 本発明の情報記録媒体のその他の一例について構成の一部を模式的に示す図である。
【符号の説明】
１，１ａ 第１の基板
１ｂ 溝（グルーブ）
１ｃ ランド
２ 第１の下側保護層
３ 第１の下側界面層
４，３３ 第１の記録層
５ 第１の上側界面層
６ 第１の上側保護層
７ 第１の界面層
８ 第１の反射層
９ 第１の最上界面層
１０ 透過率調整層
１１，１１ａ，２５ 第１の情報層
１２ 第２の下側保護層
１３ 第２の下側界面層
１４，３５ 第２の記録層
１５ 第２の上側界面層
１６ 第２の上側保護層
１７ 第２の界面層
１８ 第２の反射層
１９，１９ａ 第２の基板
２０，２０ａ 第２の情報層
２１ 光学分離層
２２，２２ａ，２６，４１，４２ 情報記録媒体
２３ レーザビーム
２４ 透明層
２７ スピンドルモータ
２８ 対物レンズ
２９ 半導体レーザ
３０ 光学ヘッド
３１ 基板
３２ 第１の電極
３４ 中間電極
３６ 第２の電極
３７ パルス電源
３８ 抵抗測定器
３９，４０ スイッチ
４３ ワード線
４４ ビット線
４５ メモリセル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium for optically or electrically recording, erasing, rewriting and reproducing information, a manufacturing method thereof, and a recording / reproducing method thereof.
[0002]
[Prior art]
There is a phase change information recording medium as an information recording medium for recording, erasing, rewriting, and reproducing information using a laser beam. For recording, erasing, and rewriting information on the phase change information recording medium, a phenomenon in which the recording layer reversibly changes between a crystalline phase and an amorphous phase is used. In general, when information is recorded, information is recorded with an irradiated portion in an amorphous phase by irradiating a laser beam to melt and quench the recording layer. On the other hand, when erasing information, the previous information is erased by irradiating a laser beam having a lower power than that at the time of recording to raise the temperature of the recording layer and gradually cooling the irradiated portion as a crystal phase. Therefore, in the phase change information recording medium, new information is recorded while erasing the recorded information by irradiating the recording layer with a laser beam whose power is modulated between a high power level and a low power level. Or, it can be rewritten (for example, Yoshito Tsunoda et al. “Basics and Applications of Optical Disk Storage”, edited by the Institute of Electronics, Information and Communication Engineers, 1995, Chapter 2).
[0003]
In recent years, various techniques have been studied as techniques for increasing the capacity of information recording media. For example, the spot diameter of the laser beam can be made smaller by using a short wavelength blue-violet laser, or by using a lens with a large numerical aperture NA by reducing the thickness of the substrate on which the laser beam is incident. Therefore, a technique for performing high-density recording is being studied. In addition, a technique for recording and reproducing two information layers using a laser beam incident from one side of an information recording medium having two information layers has been studied (see Japanese Patent Laid-Open No. 12-36130). In this technique, the recording density can be almost doubled by using two information layers.
[0004]
In an information recording medium that records and reproduces two information layers from one side (hereinafter sometimes referred to as a two-layer information recording medium), a laser that has passed through an information layer on the incident side of a laser beam (hereinafter referred to as a first information layer) Recording and reproduction of an information layer (hereinafter referred to as a second information layer) opposite to the laser beam incident side is performed using the beam. Accordingly, the transmittance of the first information layer is preferably 40% or more. On the other hand, the second information layer is desired to have high recording sensitivity (recording marks can be formed even with a low-power laser beam) in terms of recording characteristics, and high reflectivity in terms of reproduction characteristics.
[0005]
In order to increase the transmittance of the laser beam to the first information layer to 40% or more, it is necessary to reduce the thickness of the first recording layer to about 6 nm. However, when the recording layer is thinned, the crystal nuclei formed are reduced when the recording layer is crystallized, and the distance that atoms can move is shortened. For this reason, even in the recording layer made of the same material, the crystallization speed tends to be relatively lowered in the thin recording layer. Therefore, the thinner the recording layer, the harder the crystal phase is formed, and the erasure rate decreases.
[0006]
Conventionally, as a recording layer material (phase change material), a GeSbTe-based material having a high crystallization speed, excellent rewrite performance, and high reliability has been used. Using this material, optical discs for computer data recording and video recording have been commercialized. Among GeSbTe-based materials, GeTe-Sb₂Te_ThreeThe quasi-binary composition on the line has the fastest crystallization rate. The inventors conducted a recording / reproducing experiment using a red laser having a wavelength of 660 nm. As a result, in recording at a high linear velocity of 9 m / s, GeTe-Sb₂Te_ThreeEven when the thickness of the recording layer made of was reduced to 6 nm, a good erasure rate of 30 dB was obtained. With this technology, the feasibility of a two-layer information recording medium using a red laser has been found.
[0007]
In addition, an information recording medium in which a recording layer made of a phase change material is phase-changed by applying a current has been conventionally studied. In this information recording medium, the recording layer is sandwiched between two electrodes. In this information recording medium, when a current is gradually passed through the recording layer in an amorphous phase, the recording layer changes into a crystalline phase at a certain threshold current, and the electric resistance rapidly decreases. To do. Further, by applying a large current pulse with a short pulse width to the recording layer in the crystalline phase state, the recording layer can be melted and rapidly cooled to return to the high resistance amorphous phase. Since the difference in electrical resistance can be easily detected by ordinary electrical means, a rewritable information recording medium can be obtained by using such a recording layer.
[0008]
[Problems to be solved by the invention]
In order to increase the capacity of the information recording medium, it is desired to put to practical use a two-layer information recording medium that performs recording and reproduction using a short wavelength blue-violet laser. By using a short-wavelength laser beam or an objective lens having a large numerical aperture, the spot diameter of the laser beam can be reduced, and higher-density recording becomes possible. In order to perform recording using a laser beam with a short wavelength, an information recording medium capable of forming a small recording mark in a good shape is necessary. When a blue-violet laser is used, the time for which the recording layer is irradiated with the laser beam becomes relatively short. Therefore, in order to form a small recording mark, it is necessary to form the recording layer with a material having a high crystallization speed. Become. Further, in order to obtain a sufficient signal amplitude even with a small recording mark, it is desirable to form the recording layer using a material having a large change in optical characteristics between the crystalline phase and the amorphous phase.
[0009]
In the experiments by the inventors, when a conventional two-layer information recording medium using a red laser is applied as it is as an information recording medium for a blue-violet laser, recording marks formed in the first information layer and the second information layer are recorded. As a result, a sufficient signal amplitude could not be obtained. Further, regarding the first information layer, when the thickness of the recording layer was set to about 6 nm in order to ensure sufficient transmittance, the erasure rate was an insufficient value of less than 15 dB. In order to obtain a large signal amplitude, GeTe-Sb₂Te_ThreeIt has been found by the inventors' experiments that the ratio of GeTe should be increased in the quasi-binary composition on the line. However, since the melting point of the material tends to increase as the proportion of GeTe increases, the laser power (recording power) for forming the amorphous phase increases as the proportion of GeTe increases. The output of currently available blue-violet lasers is smaller than that of red lasers. For this reason, when a composition containing a large amount of GeTe is applied to the second information layer for recording / reproducing with the laser beam transmitted through the first information layer, a signal amplitude that is saturated due to insufficient recording power is obtained. I could not.
[0010]
As described above, in the two-layer information recording medium using the blue-violet laser, it was found that securing the erasure rate of the first information layer and increasing the recording sensitivity of the second information layer are important issues. .
[0011]
For practical use of a two-layer information recording medium using a blue-violet laser, a first information layer having a high transmittance and a good recording / erasing performance, and a good recording / erasing performance having a high reflectance and recording sensitivity A second information layer is required. Therefore, for practical use, it is necessary to consider the materials of the first and second recording layers and the configurations of the first and second information layers.
[0012]
In addition, as a material for the recording layer that causes a phase change by applying a current, a material mainly composed of Te has been put into practical use. However, the time required for crystallization of the conventional material is as long as μs. In addition, an electrical phase change information recording medium having good recording / erasing performance and having two recording layers has not yet been put into practical use.
[0013]
It is an object of the present invention to provide an information recording medium having two recording layers and good recording / erasing performance, a manufacturing method thereof, and a recording / reproducing method thereof.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, an information recording medium of the present invention is an information recording medium comprising a first information layer and a second information layer, wherein the first information layer is irradiated with a laser beam. Or a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by application of current, and the second information layer is formed by irradiation with the laser beam. Or a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by the application of the current, and the first recording layer is made of a first material. The second recording layer is made of a second material, and the first material and the second material are different. According to the information recording medium of the present invention, good recording / reproducing characteristics can be obtained in each information layer.
[0015]
In the information recording medium of the present invention, the first material includes Ge, Sb, and Te, and the second material is at least one selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn. It may be composed of two elements M1, Sb, and Te. According to this configuration, with respect to a recording medium for recording information using a laser beam (hereinafter sometimes referred to as an optical information recording medium), the first information layer having a high transmittance and erasing rate, the reflectance and the recording An information recording medium comprising a second information layer with high sensitivity is obtained. In particular, this optical information recording medium is suitable for high-density recording using a blue-violet laser. In addition, regarding a recording medium for recording information using an electric current (hereinafter sometimes referred to as an electrical information recording medium), the first recording layer, the second recording layer, or both are selectively used as a crystalline phase. The phase can be easily changed between the amorphous phase.
[0016]
In the information recording medium of the present invention, the first material has a composition formula.
Ge_aSb_bTe_{3 + a}
(However, 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
It may be represented by According to this configuration, good recording / reproducing characteristics can be obtained even when the first recording layer is extremely thin.
[0017]
In the information recording medium of the present invention, the first material has a composition formula.
(Ge-M2)_aSb_bTe_{3 + a}
(However, M2 is at least one element selected from Sn and Pb, and 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
It may be represented by According to this configuration, Sn or Pb substituted with Ge having a Ge—Sb—Te ternary composition improves the crystallization ability, and a sufficient erasure rate can be obtained even when the first recording layer is extremely thin.
[0018]
In the information recording medium of the present invention, the first material has a composition formula.
(Ge_aSb_bTe_{3 + a})_100-cM3_c
(However, M3 is Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ta, W, Os, Ir. , Pt, Au and Bi, and 0 <a ≦ 10, 1.5 ≦ b ≦ 4, 0 <c ≦ 20)
It may be represented by According to this configuration, the element M3 added to the Ge—Sb—Te ternary composition increases the melting point and the crystallization temperature of the recording layer, thereby improving the thermal stability of the recording layer.
[0019]
In the information recording medium of the present invention, the second material has a composition formula.
(Sb_xTe_100-x)_100-yM1_y
(However, 50 ≦ x ≦ 95, 0 <y ≦ 20)
It may be represented by According to this configuration, since the melting point of the second recording layer is low and the refractive index difference between the crystalline phase and the amorphous phase is large, the recording sensitivity is high and the reflectance difference between the crystalline phase and the amorphous phase is high. A large second information layer is obtained.
[0020]
In the information recording medium of the present invention, the first and second recording layers are layers that cause a reversible phase change upon irradiation with the laser beam, and the first information layer is the second information layer. The melting point of the second material may be lower than the melting point of the first material. According to this configuration, a second information layer with high recording sensitivity can be obtained.
[0021]
In the information recording medium of the present invention, the first and second recording layers are layers that cause a reversible phase change upon irradiation with the laser beam, and the first information layer is the second information layer. It may be arranged closer to the incident side of the laser beam. According to this configuration, an optical information recording medium can be obtained.
[0022]
In the optical information recording medium, the thickness of the first recording layer may be 9 nm or less. According to this configuration, it is easy to increase the transmittance of the first information layer so that the amount of laser light necessary for recording / reproduction of the second information layer reaches the second information layer.
[0023]
In the optical information recording medium, the thickness of the second recording layer may be in the range of 6 nm to 15 nm. According to this configuration, the recording sensitivity of the second recording layer can be particularly increased. By setting the thickness to 6 nm or more, the amount of light absorption in the recording layer can be increased. By setting the thickness to 15 nm or less, it is possible to reduce the volume of the portion to be melted when forming the recording mark, so that it is possible to prevent a decrease in recording sensitivity.
[0024]
In the optical information recording medium, the transmittance Tc (%) of the first information layer when the first recording layer is in a crystalline phase, and the case where the first recording layer is in an amorphous phase The transmittance Ta (%) of the first information layer of the laser beam having a wavelength of 390 nm or more and 430 nm or less,
40 ≦ (Tc + Ta) / 2
May be satisfied. According to this configuration, particularly good recording / erasing characteristics can be obtained for the second information layer.
[0025]
The optical information recording medium further includes an optical separation layer disposed between the first information layer and the second information layer, and the first information layer includes the first substrate and the first information layer. A second lower protective layer, a second upper protective layer, and a second reflective layer. The lower protective layer, the first upper protective layer, and the first reflective layer are further included. And a second substrate, the first substrate, the first lower protective layer, the first recording layer, the first upper protective layer, the first reflective layer, and the optical The separation layer, the second lower protective layer, the second recording layer, the second upper protective layer, the second reflective layer, and the second substrate are separated from the incident side of the laser beam. They may be arranged in order. According to this configuration, the reflectivity, recording sensitivity, erasing sensitivity, and transmittance (particularly the first information layer) of the first and second information layers are optimized in accordance with the recording / erasing / reproducing conditions. Can be Further, the first information layer and the second information layer can be optically separated by the optical separation layer.
[0026]
The optical information recording medium may further include a transparent layer disposed between the first substrate and the first lower protective layer.
[0027]
The optical information recording medium is at least selected from the interface between the first lower protective layer and the first recording layer, and the interface between the first upper protective layer and the first recording layer. You may further provide the interface layer arrange | positioned at one interface. The optical information recording medium is selected from the interface between the second lower protective layer and the second recording layer, and the interface between the second upper protective layer and the second recording layer. It may further comprise an interface layer disposed on at least one interface. The optical information recording medium is selected from an interface between the first upper protective layer and the first reflective layer, and an interface between the second upper protective layer and the second reflective layer. You may further provide the interface layer arrange | positioned at an at least 1 interface. According to these structures including the interface layer, atomic diffusion between adjacent layers can be prevented, and an information recording medium having particularly high characteristics and reliability can be obtained.
[0028]
The optical information recording medium may further include a transmittance adjusting layer for adjusting the transmittance of the first information layer between the first reflective layer and the optical separation layer. According to this configuration, the transmittance of the first information layer can be particularly increased.
[0029]
The optical information recording medium may further include an interface layer disposed between the first reflective layer and the transmittance adjusting layer. According to this configuration, atomic diffusion between the first reflective layer and the transmittance adjusting layer can be prevented, and an information recording medium with particularly high reliability can be obtained.
[0030]
In the optical information recording medium, the thickness of the first substrate may be in the range of 10 μm to 800 μm. According to this configuration, by changing the numerical aperture (NA) of the objective lens, the length, width, and interval of the recording mark are optimized in accordance with the groove shape of the first substrate and the recording / erasing / reproducing conditions. Can be For example, when the thickness of the first substrate is 100 μm, good recording / erasing performance was obtained at NA = 0.85. When the thickness of the first substrate was 600 μm, good recording / erasing performance was obtained with NA = 0.6.
[0031]
In the optical information recording medium, the thickness of the second substrate may be in the range of 400 μm to 1300 μm. According to this configuration, by changing the NA of the objective lens, the length, width, and interval of the recording mark can be optimized according to the groove shape of the second substrate and the recording / erasing / reproducing conditions. When the thickness of the first substrate is about 100 μm, the thickness of the second substrate is about 1100 μm, and when the thickness of the first substrate is about 600 μm, the thickness of the second substrate is about 600 μm. Thus, it is preferable to select the thicknesses of the first and second substrates so that the thickness of the information recording medium is about 1200 μm.
[0032]
The information recording medium of the present invention further includes first and second electrodes, wherein the first and second recording layers are layers that cause a reversible phase change by the application of the current. The first recording layer, the second recording layer, and the second electrode may be laminated in this order on the electrodes. According to this configuration, an electrical information recording medium can be obtained.
[0033]
The electrical information recording medium may further include an intermediate electrode disposed between the first recording layer and the second recording layer. According to this configuration, since atomic diffusion between the first recording layer and the second recording layer can be prevented, it is possible to improve the repetition characteristics and the reliability. Further, according to this configuration, a current can be applied to only one of the first recording layer and the second recording layer.
[0034]
The manufacturing method of the present invention is a method of manufacturing an information recording medium comprising a first information layer and a second information layer,
(A) forming the first information layer;
(B) forming the second information layer,
The first information layer includes a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of a laser beam or by application of a current,
The second information layer includes a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of the laser beam or by application of the current. ,
The step (a) includes a step of forming the first recording layer using a base material containing Ge, Sb, and Te,
In the step (b), the second recording layer is formed using a base material containing at least one element M1, Sb and Te selected from Ag, In, Ge, Sn, Se, Bi, Au and Mn. A step of forming. According to this manufacturing method, the information recording medium of the present invention can be easily manufactured.
[0035]
In the manufacturing method of the present invention, the first and second recording layers may be formed by a sputtering method using a sputtering gas containing argon gas or krypton gas. The sputtering gas may further include at least one gas selected from nitrogen gas and oxygen gas. According to this configuration, an information layer having excellent repeated recording performance can be manufactured.
[0036]
In the manufacturing method of the present invention, the thickness of the first recording layer is 9 nm or less, and in the step (a), the first recording layer is formed at a film formation rate in the range of 0.1 nm / second to 3 nm / second. The recording layer may be formed. According to this configuration, an optical information recording medium including the first recording layer with little variation in thickness can be manufactured with high productivity.
[0037]
In the manufacturing method of the present invention, the thickness of the second recording layer is in the range of 6 nm to 15 nm, and in the step (b), the film formation rate is in the range of 0.3 nm / second to 10 nm / second. The second recording layer may be formed. According to this configuration, an optical information recording medium including the second information layer with high recording sensitivity can be manufactured with high productivity.
[0038]
In the production method of the present invention, the step (b) is performed before the step (a), and after the step (b) and before the step (a),
(C) further comprising a step of forming an optical separation layer on the second information layer;
In the step (a), the first information layer may be formed on the optical separation layer.
[0039]
Further, the first method of the present invention for recording / reproducing information recording medium is that the information recording medium is the information recording medium of the present invention, and the first information layer of the information recording medium is Information is recorded / reproduced by a laser beam incident from the first information layer side, and information is recorded / reproduced by the laser beam transmitted through the first information layer with respect to the second information layer of the information recording medium. The wavelength of the laser beam is not less than 390 nm and not more than 430 nm. According to the first recording / reproducing method, it is possible to perform recording / reproduction with high density and reliability with respect to the first and second information layers of the optical information recording medium.
[0040]
In the first recording / reproducing method of the present invention, the linear velocity of the information recording medium when information is recorded / reproduced may be 3 m / sec or more and 30 m / sec or less.
[0041]
In the first recording / reproducing method of the present invention, the laser beam may be a laser beam condensed by an objective lens, and the numerical aperture NA of the objective lens may be 0.5 or more and 1.1 or less. According to this configuration, the length, width, and interval of the recording mark can be optimized according to the thickness of the first and second substrates, the shape of the groove, and the recording / reproducing conditions.
[0042]
In addition, in a second method of the present invention for recording / reproducing an information recording medium, the information recording medium is the information recording medium of the present invention, and the first and second recording layers of the information recording medium are A layer that undergoes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by application of a current, wherein the first or second recording layer changes from an amorphous phase to a crystalline phase; The amplitude Ic and the pulse width tc of the current pulse applied to the first or second recording layer, and the first recording layer when the first recording layer is changed from a crystalline phase to an amorphous phase. The amplitude Ia1 and pulse width ta1 of the current pulse applied to the layer, and the amplitude Ia2 and pulse of the current pulse applied to the second recording layer when changing the second recording layer from the crystalline phase to the amorphous phase The width ta2 is Ic <Ia2 <Ia1 Engagement, and characterized by satisfying the relation ta1 ≦ tc or ta2 ≦ tc. According to the second recording / reproducing method, in the electrical information recording medium, the first recording layer, the second recording layer, or both are selectively changed into a crystalline phase or an amorphous phase. Can do. In addition, since the electrical information recording medium of this invention produces the change of the electrical resistance by a phase change, it can also be used as a component of the programmable circuit which can be changed.
[0043]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiment is an example, and the present invention is not limited to the following embodiment. In the following embodiments, the same portions may be denoted by the same reference numerals and redundant description may be omitted.
[0044]
(Embodiment 1)
In the first embodiment, an example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 22 of Embodiment 1 is shown in FIG. In the information recording medium 22, recording / reproduction is performed by irradiation with the laser beam 23.
[0045]
With reference to FIG. 1, the information recording medium 22 includes an optical separation layer 21, and a first information layer 11 and a second information layer 20 disposed so as to sandwich the optical separation layer 21. The first information layer 11 is disposed closer to the incident side of the laser beam 23 than the second information layer 20.
[0046]
The first information layer 11 includes a first substrate 1, a first lower protective layer 2, a first lower interface layer 3, a first recording layer 4, which are arranged in order from the incident side of the laser beam 23. A first upper interface layer 5, a first upper protective layer 6, a first interface layer 7, a first reflective layer 8, a first uppermost interface layer 9, and a transmittance adjusting layer 10 are provided.
[0047]
The second information layer 20 includes a second lower protective layer 12, a second lower interface layer 13, a second recording layer 14, and a second upper interface layer arranged in order from the incident side of the laser beam 23. 15, a second upper protective layer 16, a second interface layer 17, a second reflective layer 18, and a second substrate 19. In the names of the interface layer and the protective layer, the lower side means the incident side of the laser beam 23 from the recording layer, and the upper side is the opposite side of the recording layer from the incident side of the laser beam 23. It means that.
[0048]
The laser beam 23 is incident from the first substrate 1 side. The second information layer 20 is recorded and reproduced by the laser beam 23 that has passed through the first information layer 11 and the optical separation layer 21.
[0049]
The first substrate 1 and the second substrate 19 are transparent and disk-shaped substrates. The first substrate 1 and the second substrate 19 can be formed using, for example, a resin such as polycarbonate, amorphous polyolefin, or PMMA, or glass. The first substrate 1 may be formed by applying a resin on the first lower protective layer 2 and then curing the resin.
[0050]
Guide grooves for guiding a laser beam may be formed on the inner surfaces (on the optical separation layer 21 side) of the first substrate 1 and the second substrate 19 as necessary. The outer surface of these substrates is preferably smooth. These substrates preferably have a small optical birefringence in a short wavelength region. As a material for these substrates, polycarbonate is particularly useful because of its excellent transferability and mass productivity and low cost. The thickness of the 1st board | substrate 1 exists in the range of 10 micrometers-800 micrometers (preferably 50 micrometers-150 micrometers or 550 micrometers-650 micrometers), for example. The thickness of the second substrate 19 is, for example, in the range of 400 μm to 1300 μm (preferably 550 μm to 650 μm or 1050 μm to 1150 μm).
[0051]
An example of an information recording medium in which a groove for guiding a laser beam is formed on both the first substrate 1 and the second substrate 19 is shown in FIG. In the information recording medium 22a of FIG. 2, the first information layer 11a includes the first substrate 1a, and the second information layer 20a includes the second substrate 19a. Grooves (grooves) 1b are formed in the first substrate 1a and the second substrate 19a. In the information recording medium 22a, information may be recorded in a portion of the groove 1b which is a groove surface on the incident side of the laser beam 23, or a portion between the grooves 1b (a groove far from the incident side of the laser beam 23). Or may be referred to as a land 1c). Information may be recorded on both the groove 1b and the land 1c.
[0052]
The first lower protective layer 2, the first upper protective layer 6, the second lower protective layer 12, and the second upper protective layer 16 are all made of a dielectric. These protective layers have the function of adjusting the optical distance to increase the light absorption efficiency of the recording layer and the function of increasing the change in the amount of reflected light before and after recording to increase the signal amplitude. These protective layers include, for example, SiO._x(X is 0.5 to 2.5), Al₂O_Three, TiO₂, Ta₂O_Five, ZrO₂An oxide such as ZnO or Te-O can be used. Further, a nitride such as Si—N, Al—N, Ti—N, Ta—N, Zr—N, or Ge—N can be used. Further, a sulfide such as ZnS or a carbide such as SiC can also be used. A mixture of the above materials can also be used. Among these, ZnS and SiO₂ZnS-SiO which is a mixture with₂Is particularly excellent as a material for the protective layer. ZnS-SiO₂Is an amorphous material, has a high refractive index, a high deposition rate, and good mechanical properties and moisture resistance.
[0053]
The thickness of the first lower protective layer 2 and the first upper protective layer 6 is such that the amount of reflected light varies between when the first recording layer 4 is in a crystalline phase and when it is in an amorphous phase. It can be determined strictly so that the transmittance of the first information layer 11 is large and the light absorption efficiency of the first recording layer 4 is large. Specifically, these thicknesses can be determined using calculations based on, for example, a matrix method.
[0054]
Similarly, the thicknesses of the second lower protective layer 12 and the second upper protective layer 16 are also different in the amount of reflected light when the second recording layer 14 is in the crystalline phase and when it is in the amorphous phase. It can be determined strictly so that the change is large and the light absorption efficiency of the second recording layer 14 is increased. The first lower protective layer 2, the first upper protective layer 6, the second lower protective layer 12, and the second upper protective layer 16 may be formed of different materials and compositions, or the same material -You may form with a composition.
[0055]
The transmittance adjusting layer 10 has a function of adjusting the transmittance of the first information layer 11. The transmittance adjusting layer 10 allows the transmittance Tc (%) of the first information layer 11 when the first recording layer 4 is in a crystalline phase and the case where the first recording layer 4 is in an amorphous phase. Both the transmittance Ta (%) of the first information layer 11 can be increased. Specifically, in the information recording medium 22 including the transmittance adjusting layer 10, the transmittance of the first information layer 11 is increased by about 2% to 6% as compared with the case where the transmittance adjusting layer 10 is not provided. The transmittance adjusting layer 10 can be formed of the material described for the protective layer. In the information recording medium 22, it is preferable that 40 ≦ (Tc + Ta) / 2 (more preferably 45 ≦ (Tc + Ta) / 2) (the same applies to the information recording medium 26 of the second embodiment).
[0056]
The first lower interface layer 3, the first upper interface layer 5, the second lower interface layer 13, and the second upper interface layer 15 are respectively the first lower protective layer 2 and the first recording layer. Layer 4, between the first upper protective layer 6 and the first recording layer 4, between the second lower protective layer 12 and the second recording layer 14, and second upper protective layer The substance is prevented from moving between 16 and the second recording layer 14. These interfacial layers in particular prevent mass transfer caused by repeated recording. These interface layers can be formed of nitrides such as Si—N, Al—N, Ti—N, Ta—N, Zr—N, and Ge—N, nitride oxides including these, or carbides such as SiC. . Among these, Ge—N is particularly preferable. Ge-N is easy to form by reactive sputtering and has excellent mechanical properties and moisture resistance. If the interface layer is thick, the reflectivity and absorptance of the information layer will change greatly, affecting the recording / erasing performance. Therefore, the thickness of the interface layer is preferably in the range of 1 nm to 10 nm, and more preferably in the range of 2 nm to 5 nm.
[0057]
The first interface layer 7, the first uppermost interface layer 9, and the second interface layer 17 are respectively disposed between the first upper protective layer 6 and the first reflective layer 8, and between the transmittance adjusting layer 10 and the second interface layer 17. The material is prevented from moving between the first reflective layer 8 and between the second upper protective layer 16 and the second reflective layer 18. These interfacial layers prevent mass transfer caused by recording, particularly in high temperature and high humidity environments. These interface layers can be formed of the materials described for the first lower interface layer 3, the first upper interface layer 5, the second lower interface layer 13, and the second upper interface layer 15. The thickness of these interface layers is preferably in the range of 1 nm to 10 nm, and more preferably in the range of 2 nm to 5 nm.
[0058]
The first recording layer 4 is made of a material that causes a reversible phase change between a crystalline phase and an amorphous phase when irradiated with a laser beam. The first recording layer 4 can be formed of a material containing, for example, Ge, Sb, and Te. Specifically, the first recording layer 4 has a composition formula Ge._aSb_bTe_{3 + a}It can form with the material represented by these. In the case of a = 0, this material has a very stable crystal phase and lacks the stability of the amorphous phase. On the other hand, when 10 <a, the signal amplitude increases, but the melting point increases and the crystallization speed decreases. Therefore, a preferably satisfies the relationship 0 <a ≦ 10, and more preferably satisfies the relationship 1 ≦ a ≦ 9. Further, this material has a very stable crystal phase and lacks the stability of the amorphous phase when b <1.5. On the other hand, when 4 <b, the signal amplitude increases, but the crystallization speed decreases. Therefore, b preferably satisfies the relationship of 1.5 ≦ b ≦ 4, and more preferably satisfies the relationship of 1.5 ≦ b ≦ 3.
[0059]
The first recording layer 4 has a composition formula (Ge-M2)._aSb_bTe_{3 + a}(However, M2 may be formed of a material represented by at least one element selected from Sn and Pb). This composition formula means that Ge and the element M2 are contained in total by 100 · a / (3 + 2a + b) atomic%. The composition of this material is the composition formula Ge_aSb_bTe_{3 + a}A composition in which a part of Ge of the material represented by the formula is substituted with the element M2. When this material is used, since the element M2 substituted with Ge improves the crystallization ability, a sufficient erasure rate can be obtained even when the first recording layer 4 is very thin. As the element M2, Sn is more preferable because of no toxicity. Also when using this material, it is preferable that 0 <a ≦ 10 (more preferably 1 ≦ a ≦ 9) and 1.5 ≦ b ≦ 4 (more preferably 1.5 ≦ b ≦ 3). .
[0060]
The first recording layer 4 has a composition formula (Ge_aSb_bTe_{3 + a})_100-cM3_c(However, M3 is Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ta, W, Os, It may be formed of a material represented by at least one element selected from Ir, Pt, Au, and Bi. The composition of this material is the composition formula Ge_aSb_bTe_{3 + a}The element M3 is added to the material represented by In this case, since the added element M3 increases the melting point and the crystallization temperature of the recording layer, the thermal stability of the recording layer can be improved, and as a result, the recording / reproducing performance of the first information layer 11 can be improved. This material preferably has 0 <c ≦ 20, more preferably 2 ≦ c ≦ 10, since the crystallization rate is insufficient when 20 <c. Further, it is preferable that 0 <a ≦ 10 (more preferably 1 ≦ a ≦ 9) and 1.5 ≦ b ≦ 4 (more preferably 1.5 ≦ b ≦ 3).
[0061]
The second recording layer 14 is made of a material that causes a reversible phase change between a crystalline phase and an amorphous phase when irradiated with a laser beam. The second recording layer 14 is formed of a material different from the material of the first recording layer 4. The second recording layer 14 is preferably made of a material having a lower melting point than the material of the first recording layer 4.
[0062]
The second recording layer 14 can be formed of a material composed of at least one element M1, Sb, and Te selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn. Specifically, the composition formula (Sb_xTe_100-x)_100-yM1_yIt can form with the material represented by these. This material is Sb₇₀Te₃₀It is obtained by adding the element M1 to the Sb—Te alloy near the eutectic composition. When x and y satisfy 50 ≦ x ≦ 95 and 0 <y ≦ 20, respectively, this material has a low melting point and a high refractive index. Therefore, by forming the second recording layer 14 using a material having a composition in this range, the second information layer 20 having high recording sensitivity and high reflectance can be obtained.
[0063]
In the case of 65 ≦ x, the crystallization speed is particularly fast, and a particularly good erasure rate can be obtained. In addition, in the case of x ≦ 85, it is possible to suppress the appearance of a plurality of phases, and thus it is possible to suppress deterioration of characteristics due to repeated recording. Therefore, it is more preferable that 65 ≦ x ≦ 85. In order to obtain good recording / reproducing performance, it is preferable to add the element M1 for adjusting the crystallization speed. y is more preferably 1 ≦ y ≦ 10. In the case of y ≦ 10, it is possible to suppress the appearance of a plurality of phases, and thus it is possible to suppress deterioration of characteristics due to repeated recording.
[0064]
Where (Ge_0.74Sn_0.26)₈Sb₂Te₁₁, And (Sb_0.7Te_0.3)₉₅Ge_Five, (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveTable 1 shows the results of examining the refractive index, the extinction coefficient, and the melting point. The refractive index and extinction coefficient were obtained by measuring with a spectroscope a sample in which a 10 nm thick layer made of the above material was formed on a quartz substrate. The melting point was measured by a differential scanning calorimeter (DSC method).
[0065]
[Table 1]

[0066]
In Table 1, n_cIndicates the refractive index when the sample layer is in the crystalline phase. n_aIndicates the refractive index when the sample layer is in an amorphous phase. Δn is Δn = n_c-N_aAnd shows a change in refractive index between the case where the layer is a crystalline phase and the case where the layer is an amorphous phase. k_cIndicates the extinction coefficient when the sample layer is in the crystalline phase. k_aIndicates the extinction coefficient when the sample layer is in an amorphous phase. Δk is Δk = k_c-K_aThe change in the extinction coefficient between the case where the layer is a crystalline phase and the case where the layer is an amorphous phase is shown.
[0067]
As shown in Table 1, whether the sample layer is crystalline or amorphous, (Ge_0.74Sn_0.26)₈Sb₂Te₁₁The extinction coefficient of (Sb_0.7Te_0.3)₉₅Ge_FiveAnd (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveIt was about 0.3 smaller than the extinction coefficient. Sb₇₀Te₃₀This is a composition in which the element M1 is added to the Sb—Te alloy near the eutectic composition (Sb_0.7Te_0.3)₉₅Ge_Five, And (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveSubstituted Ge with Ge—Sb—Te ternary composition with Sn (Ge_0.74Sn_0.26)₈Sb₂Te₁₁The melting point was lower by about 50 ° C. and the absolute value of the refractive index change Δn was larger.
[0068]
From the above results, it is preferable to use a Ge—Sb—Te ternary composition or a composition based on the Ge—Sb—Te ternary composition that can increase the transmittance because the extinction coefficient is small. Further, as the material of the second recording layer 14, a (Sb-Te) -M1 composition in which the recording sensitivity can be increased because the melting point is low and the reflectance change can be increased because the refractive index change Δn is large is used. preferable. As a specific combination of the first recording layer 4 / second recording layer 14, for example, Ge₆Sb₂Te₉/ (Sb_0.7Te_0.3)₉₅Ge_Five, Ge₈Sb₂Te₁₁/ (Sb_0.7Te_0.3)₉₅Ge_Five, Ge₈Sb₂Te₁₁/ (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveEtc.
[0069]
The thickness of the first recording layer 4 increases the transmittance of the first information layer 11 so that the amount of laser light necessary for recording / reproducing of the second information layer 20 reaches the second information layer 20. Therefore, it is preferably 9 nm or less, and more preferably in the range of 5 nm to 7 nm.
[0070]
The thickness of the second recording layer 14 is preferably in the range of 6 nm to 15 nm in order to increase the recording sensitivity of the second information layer 20. When the second recording layer 14 is thick, the thermal effect on the adjacent region due to the diffusion of heat in the in-plane direction, and when the second recording layer 14 is thin, the reflectance of the second information layer 20 is decreased. In consideration of the above, the thickness of the second recording layer 14 is more preferably in the range of 8 nm to 12 nm.
[0071]
The first reflective layer 8 and the second reflective layer 18 have an optical function of increasing the amount of light absorbed by the first recording layer 4 or the second recording layer 14. These reflective layers also have a thermal function of quickly diffusing heat generated in the first recording layer 4 or the second recording layer 14 and making the recording layer amorphous. Furthermore, these reflective layers also have a function of protecting the multilayer film from the environment in which it is used.
[0072]
For the material of the first reflective layer 8 and the second reflective layer 18, a single metal having a high thermal conductivity such as Al, Au, Ag, Cu can be used. In addition, an alloy containing one or more of these metal elements as a main component and one or more other elements added for the purpose of improving moisture resistance or adjusting thermal conductivity can also be used. Specifically, an alloy such as Al—Cr, Al—Ti, Au—Pd, Au—Cr, Ag—Pd, Ag—Pd—Cu, Ag—Pd—Ti, Ag—Ru—Au, or Cu—Si is used. Can be used. These alloys are all excellent materials that have excellent corrosion resistance and satisfy rapid cooling conditions. In particular, an Ag alloy is preferable as a material for the first reflective layer 8 because of its high thermal conductivity and high light transmittance.
[0073]
In order to make the transmittances Tc and Ta of the first information layer 11 as high as possible, the thickness of the first reflective layer 8 is preferably in the range of 5 nm to 15 nm, and in the range of 8 nm to 12 nm. Is more preferable. When the first reflective layer 8 is thinner than 5 nm, its thermal diffusion function is insufficient, and the reflectance of the first information layer 11 is lowered. Further, when the first reflective layer 8 is thicker than 15 nm, the transmittance of the first information layer 11 is insufficient. On the other hand, the second information layer 20 does not require high transmittance. Therefore, the thickness of the second reflective layer 18 is preferably in the range of 30 nm to 150 nm, and more preferably in the range of 70 nm to 90 nm. When the second reflective layer 18 is thinner than 30 nm, its thermal diffusion function is insufficient, and the second recording layer 14 is difficult to become amorphous. On the other hand, when the second reflective layer 18 is thicker than 150 nm, the thermal diffusion function becomes too large and the recording sensitivity of the second information layer 20 is lowered.
[0074]
The optical separation layer 21 is provided to distinguish between the focus position of the first information layer 11 and the focus position of the second information layer 20. As the material of the optical separation layer 21, a photocurable resin or a delayed action resin can be used. The material of the optical separation layer 21 preferably has small light absorption at the wavelength of the laser beam 23 used for recording and reproduction. The thickness of the optical separation layer 21 needs to be not less than the depth of focus ΔZ determined by the numerical aperture NA of the objective lens and the wavelength λ of the laser beam 23. Assuming that the intensity standard of the focal point is 80% of the case of no aberration, ΔZ is ΔZ = λ / {2 (NA)²}. When λ = 400 nm and NA = 0.6, ΔZ = 0.556 μm, and within ± 0.6 μm is within the depth of focus. Therefore, in this case, the thickness of the optical separation layer 21 needs to be 1.2 μm or more. The distance between the 1st information layer 11 and the 2nd information layer 20 needs to exist in the range which can condense the laser beam 23 using an objective lens. Therefore, the sum of the thickness of the optical separation layer 21 and the thickness of the first substrate 1 is preferably within the tolerance of the substrate thickness that the objective lens can tolerate. For this reason, the thickness of the optical separation layer 21 is preferably in the range of 1.2 μm to 50 μm.
[0075]
The information recording medium 22 of the first embodiment can be manufactured by the method described in the third embodiment.
[0076]
(Embodiment 2)
In Embodiment 2, another example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 26 of Embodiment 2 is shown in FIG. In the information recording medium 26, recording / reproduction is performed by irradiation with the laser beam 23.
[0077]
With reference to FIG. 3, the information recording medium 26 includes an optical separation layer 21, and a first information layer 25 and a second information layer 20 disposed so as to sandwich the optical separation layer 21.
[0078]
The first information layer 25 includes a first substrate 1, a transparent layer 24, a first lower protective layer 2, a first lower interface layer 3, and a first layer arranged in order from the incident side of the laser beam 23. A recording layer 4, a first upper interface layer 5, a first upper protective layer 6, a first interface layer 7, a first reflective layer 8, a first uppermost interface layer 9, and a transmittance adjusting layer 10 are provided. .
[0079]
The second information layer 20 includes a second lower protective layer 12, a second lower interface layer 13, a second recording layer 14, and a second upper interface layer arranged in order from the incident side of the laser beam 23. 15, a second upper protective layer 16, a second interface layer 17, a second reflective layer 18, and a second substrate 19.
[0080]
As will be described in Embodiment 4 below, when the information recording medium 26 is manufactured, first, the second reflective layer 18 to the second lower protective layer 12 and the optical separation layer are formed on the second substrate 19. 21. The layers are laminated in the order of the transmittance adjusting layer 10 to the first lower protective layer 2. Then, the information recording medium 26 can be formed by bonding the first lower protective layer 2 and the first substrate 1 using the transparent layer 24. Alternatively, the first substrate 1 may be formed by applying and curing a resin without forming the transparent layer 24.
[0081]
As a material for the optical separation layer 21 and the transparent layer 24, a photo-curing resin or a slow-acting resin can be used. This material preferably has small light absorption at the wavelength of the laser beam 23 used for recording and reproduction. The thicknesses of the optical separation layer 21 and the transparent layer 24 are preferably in the range of 1.2 μm to 50 μm, respectively, for the reason described in the first embodiment.
[0082]
A guide groove for guiding the laser beam 23 may be formed on the surface of the optical separation layer 21 on the first information layer 25 side. Similar to the information recording medium 22 of Embodiment 1, the laser beam 23 is incident from the first substrate 1 side. In the second information layer 20, recording / reproduction is performed by the laser beam 23 transmitted through the first information layer 25 and the optical separation layer 21.
[0083]
Note that the first substrate 1, the first lower protective layer 2, the first lower interface layer 3, the first recording layer 4, the first upper interface layer 5, the first upper protective layer 6, the first 1 interface layer 7, first reflective layer 8, first uppermost interface layer 9, transmittance adjustment layer 10, second lower protective layer 12, second lower interface layer 13, second recording layer 14, the second upper interface layer 15, the second upper protective layer 16, the second interface layer 17, the second reflective layer 18, and the second substrate 19 are the same as those described in the first embodiment. Can be used. Further, the shape and function thereof are the same as those described in the first embodiment.
[0084]
(Embodiment 3)
In Embodiment 3, a method for manufacturing the information recording medium 22 of the present invention will be described.
[0085]
The manufacturing method of Embodiment 3 includes a step of forming the first information layer 11 (step (a)). Specifically, first, a first substrate 1 (having a thickness of, for example, 0.1 mm) having a guide groove for guiding the laser beam 23 is prepared. Next, the first substrate 1 is placed in a film forming apparatus, and the first lower protective layer 2 is formed on the first substrate 1. At this time, when the guide groove is formed on the first substrate 1, the first lower protective layer 2 is formed on the side where the guide groove is formed. The first lower protective layer 2 can be formed by reactive sputtering of a base material made of a metal constituting the first lower protective layer 2 in a mixed gas atmosphere of Ar gas and reactive gas. The first lower protective layer 2 can also be formed by sputtering a base material made of a compound in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.
[0086]
Subsequently, a first lower interface layer 3 is formed on the first lower protective layer 2. The first lower interface layer 3 can be formed by reactive sputtering of a base material made of a metal constituting the first lower interface layer 3 in a mixed gas atmosphere of Ar gas and reactive gas. The first lower interface layer 3 can also be formed by sputtering a base material made of a compound in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.
[0087]
Subsequently, the first recording layer 4 is formed on the first lower interface layer 3. The first recording layer 4 has a base material made of a Ge—Sb—Te-M2 alloy, a base material made of a Ge—Sb—Te—M3 alloy, or a base made of a Ge—Sb—Te—M3 alloy, depending on the composition. The material can be formed by sputtering using a single power source. That is, the first recording layer 4 can be formed using a base material containing Ge, Sb, and Te.
[0088]
The sputtering atmosphere gas (sputtering gas) includes Ar gas, Kr gas, a mixed gas of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas), or a mixture of Kr gas and reactive gas. Gas can be used. The first recording layer 4 can also be formed by simultaneously sputtering each base material of Ge, Sb, Te, M2 or M3 using a plurality of power supplies. Further, the first recording layer 4 is formed by simultaneously using a plurality of power sources with a binary base material or a ternary base material combining any element of Ge, Sb, Te, M2, or M3. It can also be formed by sputtering. Even in these cases, sputtering is performed in an Ar gas atmosphere, a Kr gas atmosphere, a mixed gas atmosphere of Ar gas and a reactive gas, or a mixed gas atmosphere of Kr gas and a reactive gas.
[0089]
The film formation rate of the first recording layer 4 is preferably in the range of 0.1 nm / second to 3 nm / second. As described in Embodiment 1, the thickness of the formed first recording layer 4 is preferably 9 nm or less (more preferably 7 nm or less). The film formation rate can be controlled by turning on the power. If the film formation rate is lowered too much, the film formation time becomes longer, and the gas in the atmosphere is mixed in the recording layer more than necessary. If the film formation rate is increased too much, the film formation time can be shortened, but it becomes difficult to accurately control the thickness of the recording layer. Therefore, the film formation rate of the first recording layer 4 is preferably in the range of 0.1 nm / second to 3 nm / second.
[0090]
Subsequently, a first upper interface layer 5 is formed on the first recording layer 4. The first upper interface layer 5 can be formed by the same method as the first lower interface layer 3 (the same applies to the following interface layers). The composition of the base material used when forming these interface layers is selected according to the composition of the interface layer and the sputtering gas (the same applies to the steps of forming other layers). That is, the interface layer may be formed using a base material having the same composition, or the interface layer may be formed using a base material having a different composition (in the process of forming another layer). Is the same).
[0091]
Subsequently, a first upper protective layer 6 is formed on the first upper interface layer 5. The first upper protective layer 6 can be formed by the same method as the first lower protective layer 2 (the same applies to the following protective layers).
[0092]
Subsequently, a first interface layer 7 and a first reflective layer 8 are sequentially formed on the first upper protective layer 6. The first reflective layer 8 can be formed by sputtering a base material made of a metal or an alloy constituting the first reflective layer 8 in an Ar gas atmosphere.
[0093]
Subsequently, the first uppermost interface layer 9 and the transmittance adjusting layer 10 are sequentially formed on the first reflective layer 8. The transmittance adjusting layer 10 can be formed by the same method as the first lower protective layer 2.
[0094]
In this way, the first information layer 11 is formed. If necessary, an initialization step for crystallizing the entire surface of the first recording layer 4 may be performed after forming the transmittance adjusting layer 10. The crystallization of the first recording layer 4 can be performed by irradiating a laser beam.
[0095]
Before or after the step (a) or in parallel, the second information layer 20 is formed (step (b)). Specifically, first, a second substrate 19 (having a thickness of 1.1 mm, for example) is prepared. Then, the second substrate 19 is placed in the film formation apparatus, and the second reflective layer 18 is formed on the second substrate 19. At this time, when the guide groove is formed in the second substrate 19, the second reflective layer 18 is formed on the side where the guide groove is formed. The second reflective layer 18 can be formed by sputtering a base material made of a metal or an alloy constituting the second reflective layer 18 in an Ar gas atmosphere.
[0096]
Subsequently, the second interface layer 17, the second upper protective layer 16, and the second upper interface layer 15 are formed in this order on the second reflective layer 18.
[0097]
Subsequently, the second recording layer 14 is formed on the second upper interface layer 15. The second recording layer 14 can be formed by sputtering a base material made of an Sb—Te—M1 alloy using one power source. That is, the second recording layer 14 can be formed using a base material containing Sb, Te, and the element M1. The sputtering atmosphere gas (sputtering gas) includes Ar gas, Kr gas, a mixed gas of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas), or a mixture of Kr gas and reactive gas. Gas can be used. The second recording layer 14 can also be formed by simultaneously sputtering each base material of Sb, Te and M1 using a plurality of power supplies. The second recording layer 14 can also be formed by simultaneously sputtering a binary base material combining any element of Sb, Te, and M1 using a plurality of power supplies. Even in these cases, sputtering is performed in an Ar gas atmosphere, a Kr gas atmosphere, a mixed gas atmosphere of Ar gas and a reactive gas, or a mixed gas atmosphere of Kr gas and a reactive gas.
[0098]
The film forming rate of the second recording layer 14 is preferably in the range of 0.3 nm / second to 10 nm / second. As described in the first embodiment, the thickness of the second recording layer 14 is preferably in the range of 6 nm to 15 nm. The film formation rate of the second recording layer 14 can be controlled by the power-on power. When the film formation rate is lowered too much, the film formation time becomes longer and gas in the atmosphere is mixed in the recording layer more than necessary. If the film formation rate is increased too much, the film formation time can be shortened, but it becomes difficult to accurately control the layer thickness. Therefore, the film formation rate of the second recording layer 14 is preferably in the range of 0.3 nm / second to 10 nm / second.
[0099]
Subsequently, the second lower interface layer 13 and the second lower protective layer 12 are formed in this order on the second recording layer 14.
[0100]
In this way, the second information layer 20 can be formed. Note that, after forming the second lower protective layer 12, an initialization step of crystallizing the entire surface of the second recording layer 14 may be performed as necessary. Crystallization of the second recording layer 14 can be performed by irradiating a laser beam.
[0101]
Finally, the first information layer 11 and the second information layer 20 are bonded together via the optical separation layer 21. Specifically, first, an ultraviolet curable resin as a material of the optical separation layer 21 is spin-coated on the transmittance adjusting layer 10 or the second lower protective layer 12, and then the first information layer 11 and the first information layer 11 are formed. The two information layers 20 are brought into close contact with each other. Thereafter, the optical recording layer 22 is obtained by curing the optical separation layer 21 by irradiating ultraviolet rays from the first information layer 11 side. Note that when a slow-acting resin is used as the material of the optical separation layer 21, irradiation with ultraviolet rays is not necessary.
[0102]
(Embodiment 4)
In the fourth embodiment, a method for manufacturing the information recording medium 26 will be described.
[0103]
In the manufacturing method of Embodiment 4, first, the second information layer 20 is formed (step (b)). Specifically, first, a second substrate 19 (having a thickness of, for example, 1.1 mm) is prepared and placed in a film forming apparatus.
[0104]
Subsequently, the second reflective layer 18 is formed on the second substrate 19. At this time, when the guide groove is formed on the second substrate 19, the second reflective layer 19 is formed on the side where the guide groove is formed. Then, on the second reflective layer 18, the second interface layer 17, the second upper protective layer 16, the second upper interface layer 15, the second recording layer 14, the second lower interface layer 13, And the 2nd lower side protective layer 12 is formed in order. Each of these layers can be formed by the method described in Embodiment 3.
[0105]
In this way, the second information layer 20 can be formed. Note that, after forming the second lower protective layer 12, an initialization process for crystallizing the entire surface of the second recording layer 14 may be performed as necessary.
[0106]
Subsequently, the optical separation layer 21 is formed on the second lower protective layer 12 of the second information layer 20 (step (c)). The optical separation layer 21 can be formed by spin-coating a photocurable resin or a slow-acting resin on the second lower protective layer 12 and then curing the resin. In the case where the optical separation layer 21 includes a guide groove on the laser beam incident side surface, the substrate (mold) on which the groove is formed is brought into close contact with the resin before curing, and then the resin is cured, The guide groove can be formed by peeling off the substrate (mold).
[0107]
Subsequently, the first information layer 25 is formed on the optical separation layer 21 (step (a)). Specifically, first, on the optical separation layer 21, the transmittance adjusting layer 10, the first uppermost interface layer 9, the first reflective layer 8, the first interface layer 7, the first upper protective layer 6, The first upper interface layer 5, the first recording layer 4, the first lower interface layer 3, and the first lower protective layer 2 are formed in this order. Each of these layers can be formed by the method described in Embodiment 3. After the first lower protective layer 2 is formed, an initialization process for crystallizing the entire surface of the first recording layer 4 may be performed as necessary.
[0108]
Finally, the first lower protective layer 2 and the first substrate 1 are bonded together by the transparent layer 24. Specifically, first, an ultraviolet curable resin, which is a material of the transparent layer 24, is spin-coated on the first substrate 1 or the first lower protective layer 2, and then the first substrate 1 and the first substrate 1 are coated. The lower protective layer 2 is adhered. Then, the 1st information layer 25 arrange | positioned on the optical separation layer 21 can be formed by irradiating an ultraviolet-ray from the 1st information layer 25 side and hardening resin. In addition, when the transparent layer 24 consists of a slow-acting resin, irradiation of an ultraviolet-ray is unnecessary. In this way, the information recording medium 26 can be manufactured.
[0109]
(Embodiment 5)
In the fifth embodiment, the recording / reproducing method of the information recording medium of the present invention described in the first and second embodiments will be described.
[0110]
FIG. 4 schematically shows a partial configuration of the recording / reproducing apparatus 50 used in the recording / reproducing method of the present invention. Referring to FIG. 4, the recording / reproducing apparatus 50 focuses the spindle motor 27 for rotating the information recording medium 51, the optical head 30 including the semiconductor laser 29, and the laser beam 23 emitted from the semiconductor laser 29. Objective lens 28. The information recording medium 51 is the information recording medium described in the first or second embodiment, and includes the first recording layer 4 and the second recording layer 14. The objective lens 28 condenses the laser beam 23 on the first recording layer 4 or the second recording layer 14.
[0111]
The numerical aperture NA of the objective lens 28 is preferably 0.5 or more and 1.1 or less (more preferably, 0.6 or more and 1.0 or less). The wavelength of the laser beam 23 is preferably 350 nm to 500 nm (more preferably 390 nm to 430 nm). The linear velocity of the information recording medium when recording information is preferably 3 m / sec or more and 30 m / sec or less (more preferably 4 m / sec or more and 15 m / sec or less).
[0112]
Information recording is performed by modulating the power of the laser beam 23 into a high power peak power (Pp (mW)) and a low power bias power (Pb (mW)). By irradiating the laser beam 23 with the peak power, an amorphous phase is formed, and the amorphous phase becomes a recording mark. Between the recording marks, a laser beam 23 with a bias power is irradiated to form a crystal phase.
[0113]
When recording is performed on the first information layer 11 or 25, information is recorded on the first recording layer 4 with the focus of the laser beam 23 being aligned with the first recording layer 4. Reproduction is performed using the laser beam 23 reflected from the first recording layer 4. When recording is performed on the second information layer 20, the laser beam 23 is focused on the second recording layer 14 and transmitted through the first information layer 11 or 25 and the optical separation layer 21. 23, information is recorded. The reproduction is performed by using a laser beam 23 reflected by the second recording layer 14 and transmitted through the optical separation layer 21 and the first information layer 11 or 25.
[0114]
In addition, when any of the first substrate 1, the optical separation layer 21, and the second substrate 19 of the information recording medium to be recorded / reproduced includes a groove 1b, information is recorded in the groove 1b. Alternatively, it may be recorded on the land 1c. Information may be recorded on both the groove 1b and the land 1c. Both the first information layer 11 or 25 and the second information layer 20 may record information in the same part (groove, land, or groove and land), or record information in different parts. May be.
[0115]
(Embodiment 6)
In Embodiment 6, another example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 41 of Embodiment 6 is shown in FIG. In the information recording medium 41, information is recorded by applying electrical energy, specifically, by applying a current pulse.
[0116]
Referring to FIG. 5, an information recording medium 41 includes a substrate 31, a first electrode 32, a first recording layer 33, an intermediate electrode 34, and a second recording layer that are sequentially stacked on the substrate 31. 35 and a second electrode 36. The first recording layer 33 constitutes a first information layer. The second recording layer 35 constitutes a second information layer.
[0117]
As the substrate 31, a resin substrate made of a resin such as polycarbonate, a glass substrate, Al₂O_ThreeIt is possible to use a ceramic substrate made of ceramic, etc., a Si substrate, or a metal substrate made of various metals (for example, copper). Note that the substrate 31 may be used as the first electrode 32 when the substrate 31 has conductivity. Hereinafter, a case where an insulating substrate is used as the substrate 31 will be described.
[0118]
The information recording medium 41 can be manufactured by sequentially laminating the first electrode 32, the first recording layer 33, the intermediate electrode 34, the second recording layer 35, and the second electrode 36 on the substrate 31. The composition and formation method of the first recording layer 33 are the same as the composition and formation method of the first recording layer 4 described in the first and third embodiments. The composition and formation method of the second recording layer 35 are the same as the composition and formation method of the second recording layer 14 described in the first and third embodiments. The first recording layer 33 and the second recording layer 35 cause a reversible phase change between the crystalline phase and the amorphous phase by Joule heat generated by application of current.
[0119]
As materials for the first electrode 32, the intermediate electrode 34, and the second electrode 36, single metals such as Al, Au, Ag, Cu, Pt, Ti, and W can be used. Alternatively, an alloy material containing one or more of these metal elements as a main component and one or more other elements added for improving moisture resistance or adjusting thermal conductivity can also be used. . The first electrode 32, the intermediate electrode 34, and the second electrode 36 can be formed by sputtering a base material made of a metal or an alloy constituting these electrodes in an Ar gas atmosphere.
[0120]
Hereinafter, a recording / reproducing method using the information recording medium 41 will be described. A pulse power source 37 is connected between the first electrode 32 and the second electrode 36 and between the intermediate electrode 34 and the second electrode 36 via a switch 39. A resistance measuring device 38 is connected between the first electrode 32 and the second electrode 36 via a switch 40.
[0121]
In the information recording medium 41, information is recorded by changing the phase of the first recording layer 33 and the second recording layer 35 between an amorphous phase and a crystalline phase, respectively. Information is reproduced by utilizing the fact that the resistance of the recording layer in the amorphous phase is higher than the resistance of the recording layer in the crystalline phase. Specifically, information is reproduced by measuring the resistance values of the first recording layer 33 and the second recording layer 35.
[0122]
When the first recording layer 33 in the amorphous phase (high resistance state) is changed to the crystal phase (low resistance state), the switch 39 is closed to the terminal 39a side (the switch 40 is open), A current pulse is applied between the electrode 32 and the second electrode 36. At this time, since the material of the first recording layer 33 has a lower crystallization temperature and a longer crystallization time than the material of the second recording layer 35, the amplitude and pulse width of the applied current pulse are adjusted. Only the first recording layer 33 can be phase-changed.
[0123]
When the second recording layer 35 in the amorphous phase is changed to the crystalline phase, the switch 39 is closed to the terminal 39b side (the switch 40 is opened), and the intermediate electrode 34 and the second electrode 36 are connected. A current pulse is applied between them. When the recording layer is returned from the crystalline phase to the amorphous phase again, a current pulse having a relatively higher amplitude (current value) than that during crystallization is applied in a shorter time.
[0124]
Specifically, when the first recording layer 33 (or the second recording layer 35) is changed from an amorphous phase to a crystalline phase, a current pulse having an amplitude Ic and a pulse width tc is applied to the first recording layer 33 (or the second recording layer 35). Applied to the recording layer 33 (or the second recording layer 35). Further, when the first recording layer 33 is changed from the crystalline phase to the amorphous phase, a current pulse having an amplitude Ia1 and a pulse width ta1 is applied to the first recording layer 33. Further, when the second recording layer 35 is changed from the crystalline phase to the amorphous phase, a current pulse having an amplitude Ia2 and a pulse width ta2 is applied to the second recording layer 35. Here, it is preferable that these amplitudes and pulse widths satisfy the relationship of Ic <Ia2 <Ia1 and the relationship of ta1 ≦ tc or ta2 ≦ tc.
[0125]
The resistance values of the first recording layer 33 and the second recording layer 35 are measured by the resistance measuring device 38 with the switch 40 closed (the switch 39 opened). By measuring the resistance values of the first recording layer 33 and the second recording layer 35, the recorded information can be read out.
[0126]
A large capacity rewritable memory can be obtained by arranging a large number of information recording media 41 in a matrix. An example of the configuration of such an information recording medium is schematically shown in FIG.
[0127]
Referring to FIG. 6, information recording medium 42 includes a plurality of word lines 43 arranged in stripes, a plurality of bit lines 44 arranged in stripes, and a plurality of memories. Cell 45. The word line 43 and the bit line 44 are electric wirings for applying a current pulse and measuring resistance. The word line 43 and the bit line 44 are arranged so as to be orthogonal to each other. The memory cell 45 is disposed so as to be sandwiched between the word line 43 and the bit line 44 at the intersection (indicated by hatching in FIG. 6) between the word line 43 and the bit line 44. An information recording medium 41 in which the intermediate electrode 34 is omitted can be used for the memory cell 45.
[0128]
In the information recording medium 42, information can be recorded by changing the voltage between the word line 43 and the bit line 44 and applying a current pulse to the memory cell.
[0129]
The recording / reproducing method when the intermediate electrode 34 is omitted will be described below. When changing the first recording layer 33 to the crystalline phase, a current pulse having an amplitude of Ic1 and a pulse width of tc1 is applied. When changing the second recording layer 35 to the crystalline phase, a current pulse having an amplitude of Ic2 and a pulse width of tc2 is applied. When the first recording layer 33 is changed to an amorphous phase, a current pulse having an amplitude Ia1 and a pulse width ta1 is applied. When the second recording layer 35 is changed to an amorphous phase, a current pulse having an amplitude Ia2 and a pulse width ta2 is applied.
[0130]
The temperature Tx1 at which the material of the first recording layer 33 changes from the amorphous phase to the crystalline phase is lower than the temperature Tx2 at which the material of the second recording layer 35 changes from the amorphous phase to the crystalline phase (Tx1 < Tx2). The time tx1 required for the material of the first recording layer 33 to change from the amorphous phase to the crystalline phase is the time tx1 required when the recording material of the second recording layer 35 changes from the amorphous phase to the crystalline phase. It is longer than the required time tx2 (tx2 <tx1). Therefore, each recording layer can be selectively crystallized by making the amplitude Ic1, the pulse width tc1, the amplitude Ic2 and the pulse width tc2 satisfy Ic1 <Ic2 and tc1> tc2. Also, by applying a current pulse having an amplitude of Ic2 and a pulse width of tc1 to the first recording layer 33 and the second recording layer 35, both the recording layers can be crystallized simultaneously.
[0131]
The melting point of the material of the first recording layer 33 is higher than the melting point of the material of the second recording layer 35. Therefore, by shortening ta2 and satisfying Ia1> Ia2, only the second recording layer 35 can be made amorphous. On the other hand, when the pulse width ta1 is short, when a current pulse having an amplitude of Ia1 and a pulse width of ta1 is applied, the two recording layers are both in an amorphous phase. In this case, only the first recording layer 33 can be made into an amorphous phase by crystallizing only the second recording layer 35.
[0132]
A method for determining the state of each recording layer will be described below. Resistance value Ra1 when the first recording layer 33 is in an amorphous phase, resistance value Rc1 when the first recording layer 33 is in a crystalline phase, and when the second recording layer 35 is in an amorphous phase And the resistance value Rc2 when the second recording layer 35 is in the crystalline phase. The sum of the resistance values of the two recording layers is Ra1 + Ra2, Ra1 + Rc2, Rc1 + Ra2, or Rc1 + Rc2, depending on the state of the two recording layers. Here, by making Ra1 and Ra2 different values and making Rc1 and Rc2 values much smaller than those values, the state of each recording layer can be easily determined from the resistance value. Thus, four different states of the recording layer, that is, binary information can be detected by a single measurement of the resistance value.
[0133]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0134]
Example 1
In Example 1, the transmittance of the first information layer 11 of the information recording medium 22 of FIG. 1 was measured, and the effect of the transmittance adjusting layer 10 was examined.
[0135]
First, a sample for measuring transmittance was prepared. Specifically, the first information layer 11 was prepared, and the sample was prepared by bonding the first information layer 11 and the second substrate 19 with the optical separation layer 21 interposed therebetween.
[0136]
On the other hand, as a comparative example, a sample without the transmittance adjusting layer 10 was also prepared, and the transmittance was measured. The sample of this comparative example was manufactured as follows. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. Then, on the polycarbonate substrate, ZnS-SiO as the first lower protective layer 2 is formed.₂Layer (SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the first lower interface layer 3, and (Ge) as the first recording layer 4_0.74Sn_0.26)₈Sb₂Te₁₁Layer (thickness: 6 nm), GeN layer (thickness: 5 nm) as the first upper interface layer 5, and ZnS-SiO as the first upper protective layer 6₂Layer (SiO₂: 20 mol%), a GeN layer (thickness: 5 nm) as the first interface layer 7, and an Ag alloy layer (thickness: 10 nm) as the first reflective layer 8 were sequentially laminated by sputtering. Thus, the sample of the comparative example was manufactured.
[0137]
When a sample including the transmittance adjusting layer 10 is formed, a GeN layer (thickness: 3 nm) is further formed as the first uppermost interface layer 9 on the first reflective layer 8, and the transmittance adjusting layer 10 is formed. ZnS-SiO₂Layer (thickness: about 30 nm, SiO₂: 20 mol%) were sequentially laminated by a sputtering method. Then, the second substrate 19 was spin-coated with an ultraviolet curable resin that is a material of the optical separation layer 21. And the 1st information layer 11 was stuck on resin, and ultraviolet rays were irradiated and the resin was hardened. A transmittance measurement sample was manufactured as described above.
[0138]
Here, the thickness of the first lower protective layer 2 and the first upper protective layer 6 is determined by a matrix method (see, for example, Hiroshi Kubota, “Wave Optics”, Iwanami Shoten, 1971, Chapter 3) It was strictly determined by calculation based on. Specifically, these thicknesses are such that the change in the amount of reflected light at a wavelength of 405 nm is larger between the case where the first recording layer 4 is in the crystalline phase and the case where it is in the amorphous phase, and the first information layer 11 is larger, and the light absorption efficiency of the first recording layer 4 is determined to be larger. Further, the thickness of the transmittance adjusting layer 10 determines the difference in the amount of reflected light between the case where the first recording layer 4 is in the crystalline phase and the case where it is in the amorphous phase, and the light absorption efficiency of the first recording layer 4. It was determined strictly so that the transmittance of the first information layer 11 was increased without being lowered.
[0139]
With respect to the sample thus obtained, first, the transmittance Ta (%) when the first recording layer 4 was in an amorphous phase was measured. Thereafter, an initialization process for crystallizing the first recording layer 4 was performed, and the transmittance Tc (%) when the first recording layer 4 was in a crystalline phase was measured. A spectroscope was used for measurement, and the transmittance value at a wavelength of 405 nm was examined. After the measurement, a value of (Tc + Ta) / 2 was calculated.
[0140]
Table 2 shows the measurement results of transmittance. Here, in the first information layers 11 of Samples 2-1 and 2-3 in Table 2, the reflectance when the recording layer is a crystalline phase is the reflectance when the recording layer is an amorphous phase. Higher than. Samples 2-1 and 2-3 have substantially the same reflectivity when the recording layer is in a crystalline phase. In the first information layer 11 of Samples 2-2 and 2-4, the reflectance when the recording layer is in an amorphous phase is higher than the reflectance when the recording layer is in a crystalline phase. Samples 2-2 and 2-4 have substantially the same reflectance when the recording layer is in an amorphous phase.
[0141]
[Table 2]

[0142]
As shown in Table 2, in the first information layer 11 of samples 2-3 and 2-4 provided with the transmittance adjusting layer 10, the first of samples 2-1 and 2-2 having no transmittance adjusting layer 10 is provided. Compared with the information layer 11, the value of (Tc + Ta) / 2 was improved by about 2% to 6% without lowering the reflectance. Therefore, the first information layer 11 preferably includes the transmittance adjustment layer 10.
[0143]
As a result of measuring the transmittance of the first information layer 25 of the information recording medium 26 of FIG. 2 by the same method, it was confirmed that the transmittance adjusting layer 10 had the same effect.
[0144]
(Example 2)
In Example 2, the relationship between the characteristics of the first information layer 11 and the thickness of the first recording layer 4 was examined. Specifically, the first information layer 11 is produced by changing the thickness of the first recording layer 4, and the first information layer 11 and the second substrate 19 are bonded via the optical separation layer 21. Combined samples were made. With respect to the formed sample, the erasure rate of the first information layer 11, the amplitude to noise ratio (CNR), and the transmittance were measured.
[0145]
A sample manufacturing method will be described below. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. Then, on the polycarbonate substrate, ZnS-SiO as the first lower protective layer 2 is formed.₂Layer (thickness: about 40 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the first lower interface layer 3, and (Ge) as the first recording layer 4_0.74Sn_0.26)₈Sb₂Te₁₁Layer (thickness: 4 nm to 10 nm), GeN layer (thickness: 5 nm) as the first upper interface layer 5, and ZnS-SiO as the first upper protective layer 6₂Layer (thickness: about 5 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the first interface layer 7, Ag alloy layer (thickness: 10 nm) as the first reflective layer 8, and GeN layer (thickness as the first uppermost interface layer 9) And: ZnS-SiO as the transmittance adjusting layer 10₂Layer (thickness: about 30 nm, SiO₂: 20 mol%) were sequentially laminated by a sputtering method. Thereafter, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed. In this way, the first information layer 11 was formed.
[0146]
Next, an ultraviolet curable resin that is a material of the optical separation layer 21 was spin-coated on the second substrate 19. And the 1st information layer 11 was stuck on this resin, and resin was hardened by irradiating with ultraviolet rays. As described above, a plurality of samples having different thicknesses of the first recording layer 4 were produced.
[0147]
About the produced sample, the transmittance | permeability of the 1st information layer 11 was measured by the method similar to Example 1. FIG. Further, the erasure rate and CNR of the first information layer 11 were measured for the manufactured sample using the apparatus shown in FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.65, the linear velocity of the sample during measurement was 8.6 m / s, and the shortest mark length was 0.294 μm. Information was recorded in the groove.
[0148]
CNR was measured with a spectrum analyzer after recording (8-16) modulated 3T signal 10 times. The erasure performance was evaluated by recording the 3T signal 10 times, measuring the amplitude, overwriting the 11T signal once, measuring the amplitude of the 3T signal again, and calculating the attenuation rate of the 3T signal. . Hereinafter, the attenuation rate of the 3T signal is referred to as an erasure rate.
[0149]
Table 3 shows the measurement results of the erasure rate and CNR of the first information layer 11 and the calculation result of (Tc + Ta) / 2.
[0150]
[Table 3]

[0151]
In Table 3, A to D indicate values of (Tc + Ta) / 2, CNR, and erasure rate. Specifically, for the value of (Tc + Ta) / 2, D <30%, 30% ≦ C <40%, 40% ≦ B <50%, 50% ≦ A. Regarding CNR, 40 (dB) ≦ C <50 (dB) and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B. The first information layer 11 preferably has a value of (Tc + Ta) / 2 of 30% or more, and more preferably 40% or more. Moreover, it is preferable that CNR is 40 dB or more, and it is more preferable that it is 50 dB or more. Further, the erasure rate is preferably 20 dB or more, and more preferably 30 dB or more.
[0152]
As shown in Table 3, in Sample 3-1, the thickness of the first recording layer 4 was 4 nm, the transmittance was sufficient, but the CNR and the erasure rate were insufficient. In Sample 3-4 (thickness of the first recording layer 4: 10 nm), the CNR and the erasure rate were high, but the transmittance was less than 30%. In Sample 3-2 (the thickness of the first recording layer 4: 6 nm) and Sample 3-3 (the thickness of the first recording layer 4: 9 nm), the transmittance is 35% to 45% and the CNR is Good results of 50 dB and an erasure rate of 30 dB were obtained. From the above results, the film thickness of the first recording layer 4 is preferably 9 nm or less.
[0153]
Note that the same results were obtained for the first information layer 25 of the information recording medium 26 of FIG. 2 as a result of measuring the erasure rate, CNR, and transmittance by the same method.
[0154]
(Example 3)
In Example 3, the relationship between the characteristics of the first information layer 11 and the material of the first recording layer 4 was examined. Specifically, the first information layer 11 is produced by changing the composition of the first recording layer 4, and the first information layer 11 and the second substrate 19 are bonded together via the optical separation layer 21. A sample was prepared. For the formed sample, the CNR, erasure rate, and transmittance of the first information layer 11 were measured.
[0155]
Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter: 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. Then, on the polycarbonate substrate, ZnS-SiO as the first lower protective layer 2 is formed.₂Layer (thickness: about 40 nm, SiO₂: 20 mol%), the GeN layer (thickness: 5 nm) as the first lower interface layer 3, the first recording layer 4 (thickness: 6 nm), and the GeN layer (thickness: 5 nm) as the first upper interface layer 5. 5 nm), ZnS-SiO as the first upper protective layer 6₂Layer (thickness: about 5 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the first interface layer 7, Ag alloy layer (thickness: 10 nm) as the first reflective layer 8, and GeN layer (thickness as the first uppermost interface layer 9) And: ZnS-SiO as the transmittance adjusting layer 10₂Layer (thickness: about 30 nm, SiO₂: 20 mol%) was sequentially laminated by a sputtering method. Here, the material of the first recording layer 4 is (Ge_0.74Sn_0.26)₈Sb₂Te₁₁, (Sb_0.7Te_0.3)₉₅Ge_FiveOr (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveWas used. After forming the transmittance adjusting layer 10, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed. In this way, three types of first information layers 11 having different compositions of the first recording layer 4 were produced.
[0156]
Next, an uncured ultraviolet curable resin, which is a material of the optical separation layer 21, was spin-coated on the second substrate 19. And the 1st information layer 11 was stuck on this resin, and resin was hardened by irradiating with ultraviolet rays. As described above, a plurality of samples having different compositions of the first recording layer 4 were produced.
[0157]
About the produced sample, the transmittance | permeability of the 1st information layer 11 was measured by the method similar to Example 1. FIG. For these samples, the CNR and erasure rate of the first information layer 11 were measured in the same manner as in Example 2.
[0158]
Table 4 shows the CNR and erasure rate of the first information layer 11 and the calculation result of (Tc + Ta) / 2.
[0159]
[Table 4]

[0160]
In Table 4, B to D show values of (Tc + Ta) / 2, CNR, and erasure rate. Specifically, for the value of (Tc + Ta) / 2, 30% ≦ C <40% and 40% ≦ B <50%. Regarding CNR, D <40 (dB) and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B.
[0161]
As shown in Table 4, Samples 4-2 and 4-3 had insufficient transmittance, CNR, and erasure rate. On the other hand, in Sample 4-1, good results were obtained with a transmittance of 45%, a CNR of 50 dB, and an erasure rate of 30 dB. From the above results, the composition formula (Ge_0.74Sn_0.26)₈Sb₂Te₁₁Is preferable as the material of the first recording layer 4.
[0162]
Note that the same results were obtained for the first information layer 25 of the information recording medium 26 of FIG. 2 as a result of measuring the erasure rate, CNR, and transmittance by the same method.
[0163]
(Example 4)
In Example 4, the relationship between the characteristics of the second information layer 20 and the material of the second recording layer 14 was examined. Specifically, the second information layer 20 is formed by changing the material of the second recording layer 14, and the first substrate 1 and the second information layer 20 are bonded together via the optical separation layer 21. A sample was prepared. With respect to the formed sample, the recording sensitivity, CNR, and reflectance of the second information layer 20 were measured.
[0164]
Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the second substrate 19. Then, on the polycarbonate substrate, an Al alloy layer (thickness: 80 nm) as the second reflective layer 18, and ZnS—SiO as the second upper protective layer 16.₂Layer (thickness: about 10 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the second upper interface layer 15, second recording layer 14 (thickness: 10 nm), and GeN layer (thickness: as the second lower interface layer 13). 5 nm), and ZnS-SiO as the second lower protective layer 12₂Layers (thickness: about 60 nm) were sequentially stacked by a sputtering method. Here, as the second recording layer 14, (Ge_0.74Sn_0.26)₈Sb₂Te₁₁, (Sb_0.7Te_0.3)₉₅Ge_FiveOr (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveWas used.
[0165]
The thicknesses of the second lower protective layer 12 and the second upper protective layer 16 are calculated based on the matrix method, and the reflected light amount when the second recording layer 14 is in the crystalline phase at the wavelength of 405 nm is the second amount. The amount of reflected light is greater when the recording layer 14 is in the amorphous phase, the change in reflected light amount is greater when the second recording layer 14 is in the crystalline phase and in the amorphous phase, and the second The recording layer 14 was determined strictly so as to increase the light absorption efficiency.
[0166]
Next, an initialization process for crystallizing the entire surface of the second recording layer 14 was performed. Next, an ultraviolet curable resin that is a material of the optical separation layer 21 was spin-coated on the first substrate 1. And the 2nd information layer 20 was stuck on this resin, and ultraviolet rays were irradiated and the resin was hardened. As described above, a plurality of samples having different compositions of the second recording layer 14 were formed.
[0167]
About the formed sample, the reflectance in the mirror surface part of a board | substrate was measured. For these samples, the recording sensitivity and CNR of the second information layer 20 were measured using the apparatus shown in FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.65, the linear velocity of the sample during measurement was 8.6 m / s, and the shortest mark length was 0.294 μm. Information was recorded in the groove. Here, the recording sensitivity is a value defined by a peak power Pp (mW) that is 1.3 times the peak power Pp (mW) that gives an amplitude that is 3 dBm lower than the saturation value of the amplitude (dBm) (the following). The same applies to the examples). A smaller value of recording sensitivity indicates that recording is possible with a lower laser power. The average value (Tc + Ta) / 2 of the transmittance of the first information layer 11 is about 40%, and the maximum power of the semiconductor laser 29 incident on the first substrate 1 is about 12 mW. The laser power reaching the information layer 20 is about 5 mW. For this reason, the recording sensitivity of the second information layer 20 is preferably 5 mW or less.
[0168]
Table 5 shows the measurement results of the recording sensitivity, CNR, and reflectance when the second recording layer 14 is in the crystalline phase.
[0169]
[Table 5]

[0170]
In Table 5, B to D indicate values of recording sensitivity, CNR, and reflectance. Specifically, the recording sensitivity is 5 (mW) <D and B ≦ 5 mW. Regarding CNR, 50 (dB) ≦ B. The reflectances are 10% ≦ C <20% and 20% ≦ B <30%. In the second information layer 20, the CNR is preferably 40 dB or more, and more preferably 50 dB or more. Moreover, it is preferable that a reflectance is 10% or more, and it is more preferable that a reflectance is 20% or more.
[0171]
As shown in Table 5, it was found that in Sample 5-1, the CNR was not saturated at a recording laser power of 5 mW or less, the recording sensitivity was not sufficient, and the reflectance was insufficient. Moreover, it is a low melting point material (Sb_0.7Te_0.3)₉₅Ge_FiveOr (Sb_0.7Te_0.3)₉₀Ag_FiveIn_FiveIt was found that Samples 5-2 and 5-3 using the recording medium can achieve both a recording sensitivity of 5 mW or less and a high CNR.
[0172]
Note that the recording sensitivity of the second information layer 20 of the information recording medium 26 shown in FIG. 3 was measured by the same method, and the same result was obtained.
[0173]
(Example 5)
In Example 5, based on the results of Examples 3 and 4, the information recording medium 22 of FIG. 1 was manufactured. And about the manufactured information recording medium 22, the transmittance | permeability, CNR, and erasure rate of the 1st information layer 11, and the recording sensitivity, reflectance, and CNR of the 2nd information layer 20 were measured.
[0174]
In Example 5, the composition of the first recording layer 4 and the second recording layer 14 is (Ge_0.74Sn_0.26)₈Sb₂Te₁₁Or (Sb_0.7Te_0.3)₉₅Ge_FiveIt was. The thickness of the first recording layer 4 was 6 nm, and the thickness of the second recording layer 14 was 10 nm.
[0175]
The first information layer 11 was subjected to an initialization process after forming each layer. The transmittance of the first information layer 11 was measured before and after the initialization process. The second information layer 20 was also subjected to an initialization process after film formation. Thereafter, an uncured ultraviolet curable resin, which is a material of the optical separation layer 21, is spin-coated on the second lower protective layer 12, and the first information layer 11 and the second information layer 20 are brought into close contact with each other. It was. And ultraviolet rays were irradiated and the resin was hardened. In this way, a sample (information recording medium 22) including the first information layer 11 and the second information layer 20 was manufactured. The configuration and manufacturing conditions other than the recording layer and the optical separation layer are the same as those in Examples 3 and 4.
[0176]
For the sample thus obtained, the CNR and erasure rate of the first information layer 11 were measured. Further, the recording sensitivity, reflectance, and CNR of the second information layer 20 were measured. These measurements were performed in the same manner as described in the above examples. Table 6 shows the measurement results.
[0177]
[Table 6]

[0178]
In Table 6, B to D show the results of each measurement. The values of (Tc + Ta) / 2 are 30% ≦ C <40% and 40% ≦ B <50%. Regarding CNR, D <40 (dB), 40 (dB) ≦ C <50 (dB), and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B. The recording sensitivity is 12 (mW) <D and B ≦ 12 (mW). The reflectance in Table 6 is the reflectance of the second information layer 20 when the second recording layer 14 is in a crystalline phase, and 10% ≦ C <20% and 20% ≦ B <30%.
[0179]
In Sample 6-1, the compositions of the first recording layer 4 and the second recording layer 14 are both (Ge_0.74Sn_0.26)₈Sb₂Te₁₁It is. In Sample 6-2, the composition of the first recording layer 4 is (Ge_0.74Sn_0.26)₈Sb₂Te₁₁And the composition of the second recording layer 14 is (Sb_0.7Te_0.3)₉₅Ge_FiveIt is. In Sample 6-3, the compositions of the first recording layer 4 and the second recording layer 14 are both (Sb_0.7Te_0.3)₉₅Ge_FiveIt is.
[0180]
As shown in Table 6, in the sample 6-1, similarly to the result of Example 4, the recording sensitivity and the reflectance of the second information layer 20 were not sufficient. Further, in the sample 6-3, similarly to the result of the third example, the transmittance, the CNR, and the erasure rate are insufficient, and the transmittance of the first information layer 11 is not sufficient. The recording sensitivity, reflectance, and CNR of 20 decreased. On the other hand, in Sample 6-2, both the first information layer 11 and the second information layer 20 had a good result that the CNR was 50 dB or more and the erasure rate was 30 dB or more.
[0181]
The case where information is recorded in the groove has been described above. Furthermore, when the same measurement was performed for the case where information was recorded on the land and the case where information was recorded on both the land and the groove, similar results were obtained.
[0182]
(Example 6)
In Example 6, the information recording medium 26 of FIG. 3 was manufactured by the manufacturing method of Embodiment 4. Then, for the manufactured information recording medium 26, the CNR and erasure rate of the first information layer 25 and the erasure rate and CNR of the second information layer 20 were measured.
[0183]
Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter 120 mm, thickness 1.1 mm) was prepared as the second substrate 19. Then, on the polycarbonate substrate, an Al alloy layer (thickness: 80 nm) as the second reflective layer 18, and ZnS—SiO as the second upper protective layer 16.₂Layer (thickness: about 10 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the second upper interface layer 15, and (Sb_0.7Te_0.3)₉₅Ge_FiveLayer (thickness: 10 nm), GeN layer (thickness: 5 nm) as the second lower interface layer 13, and ZnS—SiO as the second lower protective layer 12₂Layer (thickness: about 60 nm, SiO₂: 20 mol%) were sequentially laminated by a sputtering method. Thereafter, an initialization process for crystallizing the entire surface of the second recording layer 14 was performed.
[0184]
Subsequently, an ultraviolet curable resin was spin-coated on the second lower protective layer 12, and a substrate on which guide grooves were formed was placed thereon, and after the resin was cured, the substrate was peeled off. By this step, the optical separation layer 21 in which the guide groove for guiding the laser beam 23 was formed on the first information layer 25 side was formed.
[0185]
Thereafter, ZnS-SiO2 is formed on the optical separation layer 21 as the transmittance adjusting layer 10.₂Layer (thickness: about 30 nm, SiO₂20 mol%), GeN layer (thickness: 3 nm) as the first uppermost interface layer 9, Ag alloy layer (thickness: 10 nm) as the first reflective layer 8, and GeN layer (thickness as the first interface layer 7) The first upper protective layer 6 is ZnS-SiO.₂Layer (thickness: about 5 nm, SiO₂: 20 mol%), GeN layer (thickness: 5 nm) as the first upper interface layer 5, and (Ge_0.74Sn_0.26)₈Sb₂Te₁₁Layer (thickness: 6 nm), GeN layer (thickness: 5 nm) as the first lower interface layer 3, and ZnS—SiO as the first lower protective layer 2₂Layer (thickness: about 40 nm, SiO₂: 20 mol%) was sequentially laminated by a sputtering method. Thereafter, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed.
[0186]
Next, a polycarbonate substrate (diameter 120 mm, thickness 0.1 mm) was prepared as the first substrate 1. Then, an ultraviolet curable resin that is a material of the transparent layer 24 was spin-coated on the first substrate 1. Then, the 1st lower side protective layer 2 was stuck on the resin, and ultraviolet rays were irradiated and the resin was hardened. A sample (information recording medium 26) was manufactured as described above.
[0187]
About the manufactured sample, CNR and the erasure rate of the 1st information layer 25 and the 2nd information layer 20 were measured using the apparatus of FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.85, the linear velocity of the information recording medium 26 at the time of measurement was 5.0 m / s, and the shortest mark length was 0.206 μm. Information was recorded in the groove. As a result, both the first information layer 25 and the second information layer 20 had good results with a CNR of 50 dB or more and an erasure rate of 30 dB or more.
[0188]
(Example 7)
In the case where Sn, Se, Bi, Au, or Mn was added to the material of the second recording layer 14 instead of Ag, In, and Ge as M1, the same measurement as in Examples 4, 5, and 6 was performed. . As a result, the same effects as in Examples 4, 5 and 6 were obtained.
[0189]
(Example 8)
In Example 8, the information recording medium 41 of FIG. 5 was manufactured, and the phase change of the recording layer due to the application of electric energy (current pulse) was confirmed.
[0190]
First, as the substrate 31, a Si substrate whose surface was nitrided was prepared. On the Si substrate, an Au layer (area: 1.0 mm × 1.0 mm, thickness: 0.1 μm) is formed as the first electrode 32, and (Ge) is formed as the first recording layer 33._0.74Sn_0.26)₈Sb₂Te₁₁Layer (area: 0.6 mm × 0.6 mm, thickness: 0.5 μm), Au layer (area: 0.6 mm × 0.6 mm, thickness 0.1 μm) as the intermediate electrode 34, second recording layer 35 (Sb_0.7Te_0.3)₉₅Ge_FiveLayer (area: 0.2 mm × 0.2 mm, thickness: 0.5 μm), and Au layer (area: 0.2 mm × 0.2 mm, thickness: 0.1 μm) as the second electrode 36, Lamination was performed sequentially by sputtering.
[0191]
Thereafter, lead wires made of Au were bonded to the first electrode 32, the intermediate electrode 34, and the second electrode 36. A pulse power source 37 was connected between the first electrode 32 and the second electrode 36 and between the intermediate electrode 34 and the second electrode 36 via a switch 39. The change in the resistance value due to the phase change of the first recording layer 33 and the second recording layer 35 is caused by a resistance measuring device 38 connected between the first electrode 32 and the second electrode 36 via the switch 40. Detected.
[0192]
When both the first recording layer 33 and the second recording layer 35 are in a high resistance state (amorphous phase), the amplitude between the first electrode 32 and the second electrode 36 is 50 mA and the pulse width is 100 ns. When a current pulse was applied, both recording layers changed to a low resistance state (crystalline phase). Next, when a current pulse having an amplitude of 150 mA and a pulse width of 50 ns is applied between the first electrode 32 and the second electrode 36, only the second recording layer 35 changes from the low resistance state to the high resistance state. did. When both the first recording layer 33 and the second recording layer 35 are in the low resistance state, a current pulse having an amplitude of 200 mA and a pulse width of 50 ns is applied between the first electrode 32 and the second electrode 36. As a result, the two recording layers both changed from the low resistance state to the high resistance state. Furthermore, when both the first recording layer 33 and the second recording layer 35 are in a high resistance state, a current pulse having an amplitude of 50 mA and a pulse width of 100 ns is applied between the intermediate electrode 34 and the second electrode 36. Only the second recording layer 35 changed from the high resistance state to the low resistance state.
[0193]
As described above, in the information recording medium 41 in FIG. 5, each of the first recording layer 33 and the second recording layer 35 is electrically reversibly changed between a crystalline phase and an amorphous phase. I was able to. As a result, there are four states, that is, the first recording layer 33 and the second recording layer 35 are both in a high resistance state, the first recording layer 33 is in a low resistance state, and the second recording layer 35 is in a high resistance state. The first recording layer 33 has a high resistance and the second recording layer 35 has a low resistance, and both the first recording layer 33 and the second recording layer 35 have a low resistance.
[0194]
Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.
[0195]
【The invention's effect】
As described above, according to the information recording medium and the manufacturing method thereof of the present invention, an information recording medium having two recording layers and good recording / erasing performance can be obtained.
[0196]
Also, according to the recording / reproducing method of the present invention, high-density recording is possible.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing an example of an information recording medium of the present invention.
FIG. 2 is a partial cross-sectional view showing another example of the information recording medium of the present invention.
FIG. 3 is a partial cross-sectional view showing another example of the information recording medium of the present invention.
FIG. 4 is a diagram schematically showing a part of the configuration of a recording / reproducing apparatus used in the recording / reproducing method of the present invention.
FIG. 5 is a diagram schematically showing the configuration of another example of the information recording medium of the present invention and an example of the recording / reproducing apparatus thereof.
FIG. 6 is a diagram schematically showing a part of the configuration of another example of the information recording medium of the present invention.
[Explanation of symbols]
1,1a First substrate
1b Groove
1c land
2 First lower protective layer
3 First lower interface layer
4,33 First recording layer
5 First upper interface layer
6 first upper protective layer
7 First interface layer
8 First reflective layer
9 First top interface layer
10 Transmittance adjustment layer
11, 11a, 25 First information layer
12 Second lower protective layer
13 Second lower interface layer
14, 35 Second recording layer
15 Second upper interface layer
16 Second upper protective layer
17 Second interface layer
18 Second reflective layer
19, 19a Second substrate
20, 20a Second information layer
21 Optical separation layer
22, 22a, 26, 41, 42 Information recording medium
23 Laser beam
24 Transparent layer
27 Spindle motor
28 Objective lens
29 Semiconductor laser
30 Optical head
31 substrates
32 first electrode
34 Intermediate electrode
36 Second electrode
37 Pulse power supply
38 Resistance measuring instrument
39, 40 switches
43 word lines
44 bit line
45 memory cells

Claims (13)

A method for manufacturing an information recording medium comprising a first information layer and a second information layer,
(A) forming the first information layer;
(B) forming the second information layer,
The first information layer includes a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of a laser beam or by application of a current,
The second information layer includes a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of the laser beam or by application of the current. ,
The step (a) includes the step of forming the first recording layer using a base material containing Sn, Ge, Sb, and Te,
In the step (b), the second recording layer is formed using a base material containing at least one element M1, Sb and Te selected from Ag, In, Ge, Sn, Se, Bi, Au and Mn. A method for manufacturing an information recording medium, comprising the step of forming. The composition of the first recording layer formed in step (a) is formula _{(Ge- Sn) a Sb b Te} 3 + a
(However, 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
The manufacturing method of the information recording medium of Claim 1 represented by these. The composition of the second recording layer formed in the step (b) has a composition formula (Sb _x Te _100-x ) _100-y M1 _y
(However, 50 ≦ x ≦ 95, 0 <y ≦ 20)
The manufacturing method of the information recording medium of Claim 1 or 2 represented by these.   4. The method of manufacturing an information recording medium according to claim 1, wherein the first and second recording layers are formed by a sputtering method using a sputtering gas containing an argon gas or a krypton gas. 5.   The method of manufacturing an information recording medium according to claim 4, wherein the sputtering gas further includes at least one gas selected from nitrogen gas and oxygen gas. The first recording layer has a thickness of 9 nm or less;
6. The method of manufacturing an information recording medium according to claim 4, wherein in the step (a), the first recording layer is formed at a film formation rate within a range of 0.1 nm / second to 3 nm / second. The thickness of the second recording layer is in the range of 6 nm to 15 nm;
The information recording medium according to any one of claims 4 to 6, wherein in the step (b), the second recording layer is formed at a film formation rate within a range of 0.3 nm / second to 10 nm / second. Manufacturing method. The step (b) is performed before the step (a), and after the step (b) and before the step (a),
(C) further comprising a step of forming an optical separation layer on the second information layer;
The method for manufacturing an information recording medium according to claim 1, wherein in the step (a), the first information layer is formed on the optical separation layer. An information recording medium recording / reproducing method comprising:
The information recording medium is an information recording medium manufactured using the manufacturing method according to claim 1,
Recording / reproducing information with respect to the first information layer of the information recording medium by a laser beam incident from the first information layer side,
Recording / reproducing information with respect to the second information layer of the information recording medium by the laser beam transmitted through the first information layer;
The information recording medium recording / reproducing method, wherein the laser beam has a wavelength of 390 nm to 430 nm.   10. The information recording medium recording / reproducing method according to claim 9, wherein the information recording medium has a linear velocity of 3 m / sec or more and 30 m / sec or less when information is recorded / reproduced. The laser beam is focused by an objective lens,
10. The information recording medium recording / reproducing method according to claim 9, wherein the numerical aperture NA of the objective lens is 0.5 or more and 1.1 or less. An information recording medium recording / reproducing method comprising:
The information recording medium is an information recording medium manufactured using the manufacturing method according to claim 1,
The first and second recording layers of the information recording medium are layers that cause a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by application of current;
The amplitude Ic and pulse width tc of the current pulse applied to the first or second recording layer when the first or second recording layer is changed from an amorphous phase to a crystalline phase, and the first recording layer The amplitude Ia1 and pulse width ta1 of the current pulse applied to the first recording layer when the layer is changed from the crystalline phase to the amorphous phase, and the second recording layer is changed from the crystalline phase to the amorphous phase. The amplitude Ia2 and the pulse width ta2 of the current pulse applied to the second recording layer when satisfying the relationship satisfy the relationship of Ic <Ia2 <Ia1 and the relationship of ta1 ≦ tc or ta2 ≦ tc. A recording / reproducing method for a recording medium.   2. The method of manufacturing an information recording medium according to claim 1, wherein the first information layer is disposed closer to the laser beam incident side than the second information layer.

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