JP3844704B2 - Write-once type optical recording medium capable of multi-value recording and multi-value recording method - Google Patents

Description

【００２９】
上記光記録媒体に対し、パルステック工業（株）製の光ディスク評価装置ＤＤＵ−１０００（波長：４０５ｎｍ、ＮＡ：０．６５）を用いて、下記の記録条件で、記録時の記録パワーをある時間間隔で６．０（ｍＷ）と１０．０（ｍＷ）に切替えて記録を行った。
＜記録条件＞
記録線密度：１Ｔ＝０．０９１７（μｍ）
記録線速度：６．０（ｍ／ｓ）
記録ストラテジ：Ｂａｓｉｃ ｓｔｒａｔｅｇｙ（基本ストラテジー）
Ｔ_ｔｏｐ−Ｔ_ｍｐ＝１．４０−０．７５（Ｔ）
記録パワー：６．０（ｍＷ）、１０．０（ｍＷ）
記録パターン：８−１６変調信号
その結果、図２に示すように、記録パワーが６．０（ｍＷ）の時はＬｏｗ ｔｏ Ｈｉｇｈ記録が行え、記録パワーが１０．０（ｍＷ）の時はＨｉｇｈ ｔｏＬｏｗ記録が行えることが確認できた。
【００３０】
次いで、この記録が前述したような記録原理に基づいて行われているかどうかを確認するため、ＳｉＣと有機材料層界面の変形状態をＡＦＭ（アトミックフォースマイクロスコープ、Ａｔｏｍｉｃ ｆｏｒｃｅ ｍｉｃｒｏｓｃｏｐｅ）により測定した。
図３は、記録パワーが６．０（ｍＷ）の時に発生したＬｏｗ ｔｏ Ｈｉｇｈ記録部分の、ＳｉＣと有機材料層界面の変形状態を三次元で表した結果である（下側が基板である）。なお、図３では、濃淡によって高さを表し、色が薄い部分が高く、色が濃い部分が低い。
図４は、図３を二次元的に表した図（ａ）と、記録トラックの断面図（凹凸形状）を表した図（ｂ）である。
これらの図に示された結果から、記録パワーが６．０（ｍＷ）の時に発生したＬｏｗ ｔｏ Ｈｉｇｈ記録部分は、ＳｉＣと有機材料層界面が基板側へ変形（凹変形）していることが確認できた。
【００３１】
一方、図５は、記録パワーが１０．０（ｍＷ）の時に発生したＨｉｇｈ ｔｏＬｏｗ記録部分の、ＳｉＣと有機材料層界面の変形状態を三次元で表した結果である（下側が基板である）。なお、図５では、濃淡によって高さを表し、色が薄い部分が高く、色が濃い部分が低い。
図６は、図５を二次元的に表した図（ａ）と、記録トラックの断面図（凹凸形状）を表した図（ｂ）である。
これらの図に示された結果から、記録パワーが１０．０（ｍＷ）の時に発生したＨｉｇｈ ｔｏ Ｌｏｗ記録部分は、ＳｉＣと有機材料層界面が基板側とは反対方向へ変形（凸変形）していることが確認できた。
【００３２】
以上の結果から、本発明の追記型光記録媒体は、記録マーク長や振幅に加えて記録極性も変えて記録できることが明らかになり、この記録極性は、少なくともＳｉＣと有機材料層の界面形状の変形方向の差異によって生じていることが確認できた。
なお、この実施例ではＡＦＭ像を見易くするためランド部に記録を行ったが、本発明はランド記録に限定されるものではない。
また、変形形状の測定のし易さからＳｉＣと有機材料層の界面形状を測定したが、他の界面が同時に変形していても構わない。
更に、従来の有機材料を用いた光記録媒体では、有機材料層で熱を発生させる必要があったため、有機材料層を薄膜化できず、深い溝（例えば１５０〜１８０ｎｍ）を必要としていたが、本発明の記録原理によって、有機材料の薄膜化が可能となり、５０ｎｍという非常に浅い溝を有する基板を適用できることが確かめられた。このことは信頼性の高い光記録媒体を作製する上で、非常に大きなメリットとなる。
【００３３】
比較例１
実施例１における有機材料に代えてポリメチルメタクリレートを用いた点以外は、実施例１と同様の実験を行った。
その結果、６．０（ｍＷ）で記録した部分も、１０．０（ｍＷ）で記録した部分も記録極性が同一であり、また、ＳｉＣとポリマー層の界面は、図５〜図６と同様に基板と反対方向（凸変形）に変形していた。
これによって、実施例１においてＳｉＣと有機材料層の界面が基板側へ変形（凹変形）した現象は、有機材料の働きによるものであり、有機材料の状態変化（分解・爆発）がこの凹変形に寄与していることが裏付けられた。
【００３４】
実施例２
実際に記録部の変形方向や変形界面の位置（種類）を正確に測定することは非常に困難であるから（実施例１では、下引層と有機材料層の界面の状態のみを評価した）、ここでは光学シュミレーションによって、変形方向と変形界面の位置（種類）を変えることで、記録マーク長や振幅の違いに加えて記録極性も異なる再生信号が得られることを証明する。
下記の計算条件下で、次の（ｉ）〜（iv）のように記録条件を変えて、再生信号がどのように変化するかを計算した。
（ｉ）記録部分（ランド部又はグルーブ部）
（ii）有機材料層の形成状態〔有機材料層の表面形状が基板形状と同一（図８参照）、又は、有機材料層の表面形状はフラット（図９参照）〕
（iii）記録マーク形成界面〔下引層と有機材料層の界面のみが変形（図１０、１１、１４、１５参照）、又は、下引層／有機材料層の界面と有機材料層／上引層の界面が変形（図１２、１３、１６、１７参照）〕
（iv）記録マーク変形方向〔基板側へ凹変形（図１４〜１７参照）、又は、上引層側へ凸変形（図１０〜１３参照）〕
【００３５】
＜計算条件詳細＞
以下、長さ、大きさは記録再生波長λを単位として表した。
・ビーム形状：ガウス分布
・振幅が１／ｅとなる半径（ｘ方向、ｙ方向）：６０００λ、６０００λ
・対物レンズ開口半径：３０００λ
・対物レンズＮＡ（開口数）：０．６０
・対物レンズ焦点距離：５０００λ
・溝形状〔Ａ、Ｂ、Ｃ、Ｄ、ζ（図７参照）〕：（０．２λ、０．８λ、１．０λ、１．８５２５λ、０．１３７５λ）
・基板屈折率：１．６０（基板側入射）
・下引層複素屈折率：２．８１０−ｉ０．５６１、膜厚＝０．０２５λ
・有機材料層複素屈折率：１．５００−ｉ０．０５０、膜厚＝０．１５０λ
・上引層複素屈折率：０．１０７８−ｉ２．０４９５、膜厚＝０．２５０λ
・検出器：４分割ＰＤ
・検出器の半径（ｘ方向、ｙ方向）：３０００λ、３０００λ
・記録マーク長さ、幅、高さ：１．０λ、０．６０λ、±０．１０λ
【００３６】
計算の結果は、図２１〜図２４に示す通りである。
図２１は、グルーブに記録した場合で、有機材料層の形成状態は、図８に示すように、有機材料層の表面形状が基板形状と同一となるように形成されている場合の結果である。
なお、記録部の高さは±０．１０λとした（記録再生波長を４００ｎｍとした場合は±４０ｎｍとなる）。
凡例「＋４０ｎｍ−０，４」は、記録部が図１６であることを、凡例「−４０ｎｍ−０，４」は、記録部が図１２であることを、凡例「＋４０ｎｍ−０，２」は、記録部が図１４であることを、凡例「−４０ｎｍ−０，２」は、記録部が図１０であることを示す。
なお、以上の図ではグルーブ部に記録された状態が示されているが、ランド部の場合も、記録部の変形方向と変形界面の位置（種類）は同一である。
【００３７】
図２２は、ランドに記録した場合で、有機材料層の形成状態は、図８に示すように、有機材料層の表面形状が基板形状と同一となるように形成されている場合の結果である。
なお、記録部の高さは±０．１０λとした（記録再生波長を４００ｎｍとした場合は±４０ｎｍとなる）。
凡例「＋４０ｎｍ−０，４」は、記録部が図１６であることを、凡例「−４０ｎｍ−０，４」は、記録部が図１２であることを、凡例「＋４０ｎｍ−０，２」は、記録部が図１４であることを、凡例「−４０ｎｍ−０，２」は、記録部が図１０であることを示す。
【００３８】
図２３は、グルーブに記録した場合で、有機材料層の形成状態は、図９に示すように、有機材料層の表面形状がフラットとなるように形成されている場合の結果である。
なお、記録部の高さは±０．１０λとした（記録再生波長を４００ｎｍとした場合は±４０ｎｍとなる）。
凡例「＋４０ｎｍ−０，４」は、記録部が図１７であることを、凡例「−４０ｎｍ−０，４」は、記録部が図１３であることを、凡例「＋４０ｎｍ−０，２」は、記録部が図１５であることを、凡例「−４０ｎｍ−０，２」は、記録部が図１１であることを示す。
なお、以上の図ではグルーブ部に記録された状態が示されているが、ランド部の場合も、記録部の変形方向と変形界面の位置（種類）は同一である。
【００３９】
図２４は、ランドに記録した場合で、有機材料層の形成状態は、図９に示すように、有機材料層の表面形状がフラットとなるように形成されている場合の結果である。
なお、記録部の高さは±０．１０λとした（記録再生波長を４００ｎｍとした場合は±４０ｎｍとなる）。
凡例「＋４０ｎｍ−０，４」は、記録部が図１７であることを、凡例「−４０ｎｍ−０，４」は、記録部が図１３であることを、凡例「＋４０ｎｍ−０，２」は、記録部が図１５であることを、凡例「−４０ｎｍ−０，２」は、記録部が図１１であることを示す。
【００４０】
この図２１〜図２４の結果より、記録マークの変形方向と変形界面の位置（種類）を変えることで、記録極性を制御できるという考え方が、原理的に正しいことが証明された。
なお、図２４に示す結果から、有機材料層の形成状態が、図９に示すように、有機材料層の表面形状がフラットとなるように形成されている場合には、ランド記録では記録極性の変化が現われ難いことが分る。
つまり、請求項６の「有機材料層と上引層の界面形状が、基板の溝形状と同一となるように形成されていることを特徴とする多値記録可能な光記録媒体」が、多値記録を可能にする有機材料を用いた光記録媒体として好ましいことが確認された。
但し、各層の複素屈折率や、記録による各層の複素屈折率の変化、或いは記録マークの高さ、形状によって記録極性が変化する条件が変るため、有機材料層の表面形状がフラットとなるように形成されている場合を否定するものではない。
【００４１】
【発明の効果】
本発明によれば、多値レベルの数を増やしながらも精度の高い多値記録が可能で、３５０〜５００ｎｍ程度の青色レーザ領域にも適用可能な追記型光記録媒体、及び多値記録方法を提供できる。
【図面の簡単な説明】
【図１】従来の光記録媒体の層構成を示す図。
【図２】本発明の記録媒体で記録極性の異なる記録マークが形成されたことを示す図。
【図３】本発明の記録媒体でＬｏｗ ｔｏ Ｈｉｇｈ記録が行われた部分をＡＦＭで観察した結果を示す図。
【図４】本発明の記録媒体でＬｏｗ ｔｏ Ｈｉｇｈ記録が行われた部分をＡＦＭで観察した結果を示す別の図。
（ａ） 図３を二次元的に表した図
（ｂ） 記録トラックの断面図（凹凸形状）
【図５】本発明の記録媒体でＨｉｇｈ ｔｏ Ｌｏｗ記録が行われた部分をＡＦＭで観察した結果を示す図。
【図６】本発明の記録媒体でＨｉｇｈ ｔｏ Ｌｏｗ記録が行われた部分をＡＦＭで観察した結果を示す別の図。
（ａ） 図５を二次元的に表した図
（ｂ） 記録トラックの断面図（凹凸形状）
【図７】実施例２で用いた溝形状のパラメータを説明するための図。
【図８】本発明の層構成を示す図であり、有機材料層の１形成形態を説明するための図。
【図９】本発明の層構成を示す図であり、有機材料層の他の１形成形態を説明するための図。
【図１０】有機材料層の形成形態と、記録マークの形成形態の一例を示す図。
【図１１】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１２】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１３】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１４】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１５】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１６】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１７】有機材料層の形成形態と、記録マークの形成形態の他の一例を示す図。
【図１８】有機材料の吸収係数の増加による記録原理を説明するための図。
【図１９】有機材料の吸収係数の増加による記録原理を実現し得る有機材料層の特性を説明するための図。
【図２０】有機材料の吸収係数の増加による記録原理を実現し得る有機材料層の特性を説明するための図。
【図２１】有機材料層が図８のように形成され、グルーブ部に記録が行われた場合の再生信号を計算した結果を示す図。
【図２２】有機材料層が図８のように形成され、ランド部に記録が行われた場合の再生信号を計算した結果を示す図。
【図２３】有機材料層が図９のように形成され、グルーブ部に記録が行われた場合の再生信号を計算した結果を示す図。
【図２４】有機材料層が図９のように形成され、ランド部に記録が行われた場合の再生信号を計算した結果を示す図。
【符号の説明】
Ａ ランドの上面端部と、隣接するグルーブの該ランドに近い方の底面端部との幅
Ｂ ランドの上面端部と、隣接するグルーブの該ランドから遠い方の底面端部との幅
Ｃ ランドの上面端部と、隣接するランドの、前記ランドに近い方の上面端部との幅
Ｄ ランドの上面端部と、隣接するランドの、前記ランドから遠い方の上面端部との幅
ζ ランドの高さ（溝の深さ）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a write-once type optical recording medium capable of performing multilevel recording by changing recording polarity in addition to recording mark length and amplitude according to recording data, a recording principle thereof, and a multilevel recording method.
[0002]
[Prior art]
In recent years, optical recording media have been required to have larger capacity and higher density. As one method for realizing an increase in capacity and density of an optical recording medium, there is multi-value recording.
Multi-level recording means that information is recorded / reproduced in association with three or more values, and is distinguished from binary recording in which recording / reproduction is performed in association with binary values “0” or “1”. Concept. Details of multilevel recording are described in, for example, Japanese Patent Laid-Open No. 6-76399.
In this conventional example, in the mark edge type recording / reproducing method, multi-value information is recorded by shifting the position of the edge of the recording mark stepwise from the reference position corresponding to the recording data. In this mark edge type multi-value recording, the greater the number of edge position shifts (the number of stages), the more advantageous for multi-value recording, that is, higher density.
However, if an attempt is made to increase the number of shifts of the edge position with respect to a limited reference clock cycle, it is necessary to precisely control the edge formation.
On the other hand, it is not easy to control the edge position of the recording mark formed by laser light irradiation.
[0003]
As another conventional example, the optical recording / reproducing method described in Japanese Patent Application Laid-Open No. 8-287468 realizes multi-value recording by the pit position method instead of the mark edge method as in the conventional example. .
In this case, multi-level recording is performed by shifting the center position of the recording mark stepwise with respect to the edge of the reference clock.
Still other multi-value recording techniques include the following.
That is, a multi-value recording technique called SCIPER that shifts the edge of a pit corresponding to recording data in eight stages on the same read-only optical disk as a CD is, for example, “S. Kobayashi, JP De Kock, T. Horigome, H. Yamatsu and H. Oki, Tech. Dig. Of Optical Data Storage Conference, p. 130 (1994) ".
Although this technique has an advantage that the conventional disk structure can be used as it is, there is a problem that the signal processing circuit becomes very complicated.
[0004]
Further, an eight-level multilevel recording technique in which the pit depth is changed stepwise is disclosed in, for example, “S. Spielman, BV Johnson, GA McDermott, MP O'Neil, C.I. Pietrzyk, T. Shafaat, DK Warland and TL Wong, Proc. SPIE, 3109, p. 98 (1997).
This technique can suppress the complication of the signal processing circuit to some extent, but makes it difficult to manufacture a disk.
In addition, a quaternary recording technique for selectively causing magnetization reversal of each layer by introducing a plurality of magnetic recording films and switching the intensity of a recording magnetic field in a magneto-optical disk is, for example, “N. Saito, R. Sato, N. Kawamura and M. Kajiura, Jpn. J. Appl. Phys., 28, p. 343 (1989).
[0005]
In the magneto-optical disk, a four-value recording technique in which the magnetization reversal interval is changed stepwise by changing the period of the recording high-frequency magnetic field is, for example, “M. Arai and S. Kobayashi, Tech. Dig. Of”. Joint MORIS / ISOM, p. 32 (1997) ”.
In addition, in a phase change type optical disk, a multi-value recording technique in which the size of a recording mark is controlled by intensity modulation of a recording laser beam is described in, for example, “T. Ohta, K. Nishiuchi, K. Narumi, Y. Kitaoka, H. Ishibashi, N. Yamada and T. Kozaki, Jpn. J. Appl. Phys., 39, p. 770 (2000).
In a phase change type optical disc, a multi-value recording technique for performing 8-level recording by controlling a recording mark length by devising a recording pulse waveform using a dedicated phase change recording material is, for example, “MP. O'Neil and TL Wong, Tech.Dig.of Optical Data Storage Conference, p.170 (2000) ".
[0006]
[Problems to be solved by the invention]
To increase the density, it is necessary to increase the number of multi-levels. However, increasing the number of multi-levels makes it more difficult to judge multi-levels, so the playback reliability is greatly reduced. There is.
Conventionally, although a multi-value recording technique that can be applied to a read-only optical recording medium, a magneto-optical recording medium, or a phase change optical recording medium has been proposed, it is effective for a write-once optical recording medium using an organic material. Most multi-value recording techniques have not been proposed.
Therefore, the present invention solves the conventional problems as described above, is a multi-value recording technique effective for a write-once optical recording medium using an organic material, and highly accurate multi-value recording while increasing the number of multi-value levels. An object of the present invention is to provide a write-once optical recording medium that can be applied to a blue laser region of about 350 to 500 nm, a recording principle thereof, and a multi-value recording method.
[0007]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 11).
1) An organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength when unrecorded is placed on the substrate with an undercoat layer having a large refractive index difference from the organic material layer. An optical recording medium having a layer structure sandwiched between the undercoat layer and the undercoat layer or the overcoat layer having a light absorption function, and can change the deformation direction and the position (type) of the deformation interface during recording. Thus, a multi-level recordable write-once optical recording medium, wherein a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude is obtained.
2) An organic material layer that does not have an absorption function with respect to light having a recording / reproducing wavelength when unrecorded is placed on the substrate with an undercoat layer having a large refractive index difference from the organic material layer. An optical recording medium having a layer structure sandwiched between an undercoat layer and an undercoat layer or an overcoat layer having a light absorption function, wherein the undercoat layer is changed from an organic material layer to a change in state of the organic material in the organic material layer. The recording principle of recording mark formation by the pressure on the substrate or the pressure from the organic material layer to the overcoating layer and the recording principle of recording mark formation by the stress relaxation of the undercoating layer or the overcoating layer or the thermal expansion of the substrate In this case, the deformation direction of the recording mark portion and the position (type) of the deformation interface can be changed, whereby a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude can be obtained. A write-once optical recording medium capable of recording values.
3) An unrecorded main absorption band exists on the substrate on the long wavelength side with respect to the recording / reproducing wavelength via an undercoat layer, and has an absorption function for light of the recording / reproducing wavelength when not recorded. An optical recording medium having a layer structure in which an organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function Thus, it is possible to change the deformation direction and the position (type) of the deformation interface during recording, and in this way, reproduction signals having different recording polarities in addition to differences in recording mark length and amplitude can be obtained. A write-once optical recording medium capable of recording values.
4) An unrecorded main absorption band exists on the substrate on the longer wavelength side with respect to the recording / reproducing wavelength via an undercoat layer, and has an absorption function for light of the recording / reproducing wavelength when not recorded. An optical recording medium having a layer structure in which an organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function The recording principle of recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the undercoat layer accompanying the change in the state of the organic material in the organic material layer, Depending on the recording principle of recording mark formation by stress relaxation of the overcoat layer or thermal expansion of the substrate, the deformation direction of the recording mark portion and the position (type) of the deformation interface can be changed during recording, thereby the recording mark length And playback signals with different recording polarities in addition to amplitude differences A write-once optical recording medium capable of multi-value recording.
5) Recording / reproducing wavelength is 350nm more than 500nm Less than It is characterized by In any one of 1) to 4) Write-once type optical recording medium capable of multi-value recording as described.
6) The interface shape of the organic material layer and the overcoat layer is formed to be the same as the groove shape of the substrate. In any one of 1) to 5) Write-once type optical recording medium capable of multi-value recording as described.
7) An organic material layer that does not have an absorption function with respect to light of the recording / reproducing wavelength when unrecorded is placed on the substrate with an undercoat layer having a large refractive index difference from the organic material layer. For a write-once type optical recording medium that has a layer structure sandwiched between the underlayer and the undercoat layer or the overcoat layer has a light absorption function and is capable of multi-value recording, the direction of deformation and the position of the deformation interface (type) ) To obtain a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude.
8) An organic material layer that does not have an absorption function with respect to light of the recording / reproducing wavelength when not recorded is placed on the substrate with an undercoat layer having a large refractive index difference from the organic material layer. An organic layer with a change in the state of the organic material in the organic material layer with respect to the write-once type optical recording medium having a layer structure sandwiched between the underlayer and the undercoat layer or the overcoat layer having a light absorption function. Recording principle of recording mark formation by pressure from material layer to undercoat layer or pressure from organic material layer to overcoat layer, and recording mark formation by stress relaxation of undercoat layer or overcoat layer, or thermal expansion of substrate According to the recording principle, during recording, the deformation direction of the recording mark portion and the position (type) of the deformation interface are changed so that a reproduction signal having a different recording polarity in addition to the difference in recording mark length and amplitude can be obtained. A multi-value recording method characterized by that.
9) An unrecorded main absorption band exists on the substrate on the long wavelength side with respect to the recording / reproducing wavelength via an undercoat layer, and has an absorption function for light of the recording / reproducing wavelength when not recorded. Has a layer structure in which an organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function and can perform multi-value recording By changing the deformation direction and the position (type) of the deformation interface for a recordable optical recording medium, it is possible to obtain a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude. A multi-value recording method characterized by that.
10) The main absorption band at the time of unrecording exists on the substrate on the long wavelength side with respect to the recording / reproducing wavelength via the undercoat layer, and has an absorption function for the light at the recording / reproducing wavelength when not recorded. Has a layer structure in which an organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function and can perform multi-value recording Recording principle of recording mark formation on a write-once optical recording medium by pressure from the organic material layer to the undercoat layer or pressure from the organic material layer to the overcoat layer as the state of the organic material in the organic material layer changes And the recording principle of recording mark formation by the stress relaxation of the undercoat layer and the overcoat layer or the thermal expansion of the substrate, the deformation direction of the recording mark portion and the position (type) of the deformation interface are changed during recording, thereby Reproduced signals with different recording polarities in addition to recording mark length and amplitude A multi-value recording method characterized by comprising:
11) Recording / reproducing wavelength is 350 nm more than 500nm Less than It is characterized by 7) to any one of 10) The multi-value recording method described.
[0008]
Hereinafter, the present invention will be described in detail.
(1) Summary (features) of the present invention
In the present invention, by performing multi-value recording by changing the deformation direction and the position (type) of the deformation interface during recording, it is possible to obtain a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude. . In the present invention, the recording principle of recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer accompanying the change in the state of the organic material in the organic material layer, Multi-level recording can be performed by using the recording principle of recording mark formation by stress relaxation of the drawing layer and the overcoat layer or thermal expansion of the substrate, and controlling this.
In other words, since the recording polarity is the same in the past (either so-called High to Low recording or Low to High recording), the number of multi-levels is increased. However, in the present invention, not only the recording mark length and the amplitude but also the reproduction signal having a different recording polarity is obtained. Therefore, a more reliable write once optical recording medium can be provided.
In the present invention, the “change in the state of the organic material” refers to melting, sublimation, decomposition, explosion, structural change, etc., but usually decomposition and explosion are the main, and in this case, it is the only requirement for the organic material. This is because the thermal decomposition characteristics (decomposition temperature, explosiveness, existence of a clear decomposition threshold, decomposition speed, decomposition amount, etc.) are excellent.
[0009]
(2) Explanation of the expression “change the deformation direction and the position (type) of the deformation interface”
The expression “changing the deformation direction and the position (type) of the deformation interface” in the present invention will be described.
The deformation direction means whether the deformation occurs in a convex shape or a concave shape when viewed from a certain reference side.
Also, the position (type) of the deformation interface refers to which layer interface has uneven deformation. The deformation interface includes the interface between the substrate and the undercoat layer, the interface between the undercoat layer and the organic material layer, the interface between the organic material layer and the overcoat layer, the overcoat layer and its upper layer (protective layer, cover layer, air layer, etc.) There is an interface with.
In the present invention, the deformation interface may be single or a plurality of the deformation interfaces may be combined. In short, the recording polarity and the contrast of the recording mark are changed according to the combination of the deformation interfaces, the deformation direction and the deformation amount of each interface.
In the present invention, the combination of the deformation interfaces and the deformation amount of each interface are controlled, and these can be changed depending on the film thickness of each layer, the magnitude of the absorption coefficient with respect to the recording wavelength, the thermal conductivity, and the hardness. The simplest is a method of controlling the combination of deformation interfaces and the deformation amount of each interface by controlling the recording power.
[0010]
In the present invention, the deformation direction of each interface is controlled, which is realized by giving the optical recording medium a different recording principle.
That is, the recording principle of recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer accompanying the change in the state of the organic material in the organic material layer, The deformation direction of each interface is controlled by combining the recording principle of recording mark formation by stress relaxation of the drawing layer or thermal expansion of the substrate.
For example, by using the recording principle of recording mark formation by pressure from the organic material layer to the undercoat layer accompanying the state change of the organic material in the organic material layer, the substrate or the undercoat layer can be seen from the front side when viewed from the substrate side. (It is expressed as a concave shape here). Further, by using the recording principle of recording mark formation by stress relaxation of the undercoat layer or thermal expansion of the substrate, the substrate and the undercoat layer can be deformed to the back side when viewed from the substrate side ( This is expressed as a convex shape).
An important feature of the present invention is that the direction of deformation is determined in one direction in the conventional recording principle using deformation, but in the present invention, the recording principle capable of making the direction of deformation variable is used.
[0011]
(3) Reason why “the organic material layer is sandwiched between the undercoat layer and the overcoat layer having a large refractive index difference from the organic material layer”
The present invention is characterized by having a “structure in which an organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer”.
With this structure, it is possible to improve the reflectance and signal quality, or the recording polarity in addition to the recording mark length and amplitude depending on the deformation direction and the position (type) of the deformation interface caused by recording. However, different reproduction signals can be generated efficiently.
The refractive index difference between the organic material layer, the undercoat layer, and the overcoat layer is usually 0.5 or more.
[0012]
(4) Requirements for organic materials used in organic material layers
In the present invention, in order to make the recording polarity variable, the deformation direction (convex deformation or concave deformation) of the recording mark is controlled.
In forming a recording mark by thermal expansion of a substrate, which is the basic deformation principle of a conventional optical recording medium (see FIG. 1), the substrate is always deformed in the direction of the organic material layer and not in the opposite direction. This is because the force due to the thermal expansion of the substrate is sufficiently large, and there is no force that obstructs this or a large force against it.
Therefore, the present inventor examined a means for generating a force in the direction opposite to the deformation direction due to the thermal expansion of the substrate, and as a result, the force accompanying the state change of the organic material (particularly decomposition / explosion force). Was found to be available.
However, in order to effectively use the force accompanying this state change, it is necessary to make the organic material in the vicinity of the interface between the organic material layer and the adjacent layer most likely to undergo the state change. In the configuration, since the central portion of the organic material layer has the highest temperature, the organic material in the vicinity of the interface between the organic material layer and the adjacent layer does not change sufficiently.
Therefore, in the present invention, in order to make the organic material in the vicinity of the interface between the organic material layer and the adjacent layer most likely to undergo a state change, a light absorption layer (a layer having a light absorption function) is adjacent to the organic material layer. (Slipping layer or overcoating layer).
[0013]
Since the absorption coefficient of the light absorption layer is set sufficiently larger than the absorption coefficient of the organic material layer (the light absorption layer has a light absorption function, the organic material layer has a light Naturally, it does not have an absorption function, so the organic material near the light-absorbing layer is at the highest temperature, and recording with the direction of deformation reversed can be performed by the force accompanying the state change of the organic material. It becomes.
By providing this light absorption layer, it is possible to separate the light absorption function from the conventional organic material layer having the functions of the recording layer and the light absorption layer.
As a result, severe optical constant conditions imposed on the organic material layer are relaxed, and the write-once type optical recording medium of the present invention can easily record even in the blue laser wavelength region of about 350 to 500 nm (conventional). In this layer configuration, since there are strict optical constant conditions in the organic material layer, there is almost no organic material that can cope with the blue laser wavelength region, and it is difficult to realize a write-once optical recording medium using the organic material. )
Further, in a write-once optical recording medium using a conventional organic material, it is necessary to generate heat in the organic material layer, so that the organic material layer cannot be thinned and a deep groove (for example, 150 to 180 nm) is required. However, the recording principle of the present invention makes it possible to reduce the thickness of the organic material, and it is possible to use a substrate having a shallow groove with excellent moldability. Therefore, it is possible to provide a highly reliable write once optical recording medium. Become.
[0014]
“Organic material layer in which the main absorption band at the time of unrecording exists on the longer wavelength side with respect to the recording / reproducing wavelength and does not have an absorption function for light of the recording / reproducing wavelength” used in the present invention, or “unrecorded In the expression “sometimes an organic material layer that does not have an absorption function for light at the recording / reproducing wavelength”, “it does not have an absorption function for light at the recording / reproducing wavelength” This means that the temperature does not reach the temperature at which the adjacent layer of the material layer is deformed or the state of the organic material itself changes (that is, it does not substantially perform the absorption function required as the light absorption layer). . Therefore, specifically, the case where the absorption coefficient of the organic material is small or the case where the film thickness is thin is pointed out.
In addition, “an organic material layer in which the main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength and does not have an absorption function for light at the recording / reproducing wavelength” or “recording / reproducing at the time of unrecorded” The reason why the “organic material layer that does not have an absorption function with respect to light of a wavelength” is an important component of the optical recording medium of the present invention is that the present invention has a light absorption function that is used in a conventional write-once optical recording medium. This is because, by using an undercoat layer or an overcoat layer having a relatively large absorption coefficient instead of the organic material, the absorption function in the organic material layer can be reduced to improve the reflectance.
[0015]
Further, as described above, in addition to the difference in recording mark length and amplitude, the recording polarity differs depending on the improvement in reflectivity, the improvement in signal quality, or the difference in deformation direction and deformation interface position (type) caused by recording. In order to generate a signal efficiently, a structure in which the organic material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer is suitable. For this purpose, the refractive index of the organic material layer is suitable. It is more advantageous to select a material for the undercoat layer and the overcoat layer if the value is set low.
This is because, for example, a substrate / undercoat layer (light absorption layer) / organic material layer / overcoat layer (reflective layer) can be cited as a preferred layer structure of the present invention. The refractive index of the layer is usually very small at about 0.1, and the refractive index of the light absorption layer is, for example, about 2.0 to 4.0, and the difference in refractive index between the organic material layer and the light absorption layer tends to be small. . Therefore, it is important to increase this difference in refractive index. For that purpose, if the refractive index of the organic material layer is set low, the refractive index difference between the organic material layer and the light absorption layer is increased, and the light absorption layer This is because the range of choices can be expanded.
[0016]
Therefore, “an organic material layer in which the main absorption band at the time of unrecording exists on the longer wavelength side with respect to the recording / reproducing wavelength and does not have an absorption function for light at the recording / reproducing wavelength” or “recording / reproducing at the time of unrecording” It is possible to lower the refractive index of the organic material layer by making the organic material layer having no absorption function for light of a wavelength, that is, by greatly shifting the maximum absorption band of the organic material and the recording / reproducing wavelength. Become.
In addition, when the recording / reproducing wavelength is 500 nm or more, for example, in the vicinity of 650 nm which is the recording / reproducing wavelength of the DVD-based optical recording medium or near 780 nm which is the recording / reproducing wavelength of the CD-based optical recording medium, It is sufficient to satisfy the “organic material layer that does not have an absorption function with respect to light of the recording / reproducing wavelength”, and the magnitude relationship between the wavelength of the main absorption band of the organic material and the recording / reproducing wavelength hardly poses a problem.
[0017]
However, when the recording / reproducing wavelength is set to a blue laser region of about 350 to 500 nm, for example, near 400 nm, the main absorption band when not recorded exists on the short wavelength side with respect to the recording / reproducing wavelength, and the recording / reproducing wavelength In a state that does not have an absorption function for light, it means that the molecular size of the organic material is very small, and this is subtracted from the organic material layer as the state of the organic material changes. This means that the pressure on the layer or the pressure from the organic material layer to the overcoat layer is significantly reduced, which is not preferable for the write-once type optical recording medium using the recording principle of the present invention.
Therefore, when the recording / reproducing wavelength is set to 350 to 500 nm, for example, in the vicinity of 400 nm, the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer accompanying the state change of the organic material is set. In order to generate sufficiently, an organic material with a large molecular skeleton is selected, the main absorption band when not recorded exists on the long wavelength side with respect to the recording / reproducing wavelength, and the light absorption function with respect to the light of the recording / reproducing wavelength It is preferable to use an organic material layer that does not include
[0018]
(5) Reason for forming the interface shape of the organic material layer and the overcoat layer to be the same as the groove shape of the substrate
The thickness of the organic material layer is arbitrary, and the formation form is also arbitrary.
The formation form refers to the shape of the surface shape of the organic material layer (interface shape between the organic material layer and the overcoat layer). For example, the surface shape of the organic material layer is the same as the substrate shape (see FIG. 8) or the surface shape of the organic material layer may be flat (see FIG. 9).
In the present invention, the surface shape of the organic material layer has been found to be important as one of the conditions where the change in recording polarity is relatively likely to occur. The surface shape of the organic material layer is the same as the substrate shape ( In the case of (see FIG. 8), it has been found that the change in recording polarity is likely to occur (the condition for changing the recording polarity is relaxed).
However, here, the meaning of the phrase “form to be the same” means
Not only the case where they are literally the same, but also when the interface shape of the organic material layer and the overcoat layer is formed substantially following the groove shape of the substrate, that is, each layer is formed on the substrate by a normal film forming method such as sputtering. In this case, it is assumed that each layer is formed substantially following the groove shape of the substrate, although there is some variation in film thickness.
The write-once type optical recording medium of the present invention may be provided with various layers such as a conventionally known intermediate layer and back coat layer in addition to the above layers.
[0019]
(6) Combination of other recording principles
In the present invention, in addition to the recording principle described above, a state change occurs in the organic material layer due to heat generation of the undercoat layer or the overcoat layer due to laser light irradiation, and recording is performed by increasing the absorption coefficient at the recording / reproducing wavelength due to the state change. The principle may be used in combination.
However, in this recording principle, unless the refractive index or film thickness of the organic material layer changes significantly, the recording polarity becomes High to Low. Therefore, this recording principle is used in combination with the recording principle by the deformation described above. Only when High to Low.
The recording principle by increasing the absorption coefficient of the organic material layer will be described with reference to FIGS.
When an organic material having an unrecorded absorption spectrum as shown in FIG. 18 is selected and this organic material changes its state (especially decomposition or explosion), the absorption of the molecules or molecular groups constituting the organic material by decomposition is performed. Occurs. Since this absorption is usually shorter than the absorption of the organic material before decomposition or explosion, the absorption coefficient on the shorter wavelength side of the large absorption band of the original organic material increases (see the absorption spectrum in the recorded state). ). If the range in which the change in the absorption wavelength on the short wavelength side is large and the recording / reproducing wavelength (for example, the position of the arrow in the figure) are combined, the absorption coefficient at the recording / reproducing wavelength after recording can be increased. Can be generated.
[0020]
To explain this recording principle in more detail, the organic material used in the present invention is an organic material in which a small molecule or molecular group is bonded, or a complex or aggregate is formed to form a large conjugated system, It has a large absorption band on the longer wavelength side than the intrinsic absorption wavelength (corresponding to absorption spectra A and B in FIG. 19) possessed by the molecule or molecular group, and the intrinsic absorption band possessed by each molecule or molecular group Has an absorption spectrum that disappears or is attenuated (corresponding to the absorption spectrum C in FIG. 20).
For such an organic material, when λ1 as shown in FIG. 20 is selected as the recording / reproducing wavelength, a large molecule was formed by decomposition, explosion, etc. from a state where absorption at λ1 was small when unrecorded. Intrinsic absorption of molecules and molecular groups increases (see FIG. 19), absorption at λ1 also increases, and a recording portion can be formed by a change in absorption coefficient.
Accordingly, a molecule in which only a small molecule or molecular group is bonded and a conjugated system does not form a spread is in a state as shown in FIG. 20, that is, the intrinsic absorption that the molecule or molecular group has. Since a state in which the band disappears or attenuates and a new large sharp absorption band is formed is not realized, the change in the absorption coefficient before and after recording does not increase, and a recording pit cannot be formed.
[0021]
(7) Material of each layer
As a material of the substrate, there are special restrictions as long as it has excellent thermal and mechanical properties, and has excellent light transmission characteristics when recording / reproducing is performed from the substrate side (through the substrate). Absent.
Specific examples include polycarbonate, polymethyl methacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate and the like, and polycarbonate and amorphous polyolefin are preferred.
The thickness of the substrate varies depending on the application and is not particularly limited.
[0022]
A material having a relatively low thermal conductivity is suitable for the undercoat layer or the overcoat layer that functions as a light absorption layer that absorbs light and generates heat. The reason for selecting a material having a relatively low thermal conductivity is to efficiently deform the interface of each layer (with low recording power), and to change the state of the organic material efficiently (with low recording power). It is.
Here, the relatively low thermal conductivity means that the thermal conductivity reaches such a temperature that the state of the organic material is locally changed by recording.
From the above points, it is preferable to use ceramics such as SiC, semimetals such as Si, metals such as Ge, or a mixture thereof for the undercoat layer and the overcoat layer that function as the light absorption layer. Further, the thickness of the undercoat layer and the overcoat layer is usually 20 to 500 mm.
[0023]
As ceramics used as the material for the undercoat layer and the overcoat layer, Al ₂ O ₃ , MgO, BeO, ZrO ₂ , UO ₂ , ThO ₂ Simple oxide based oxides such as SiO ₂ 2MgO · SiO ₂ , MgO / SiO ₂ , CaO / SiO ₃ , ZrO ₂ ・ SiO ₂ 3Al ₂ O ₃ ・ 2SiO ₂ 2MgO · 2Al ₂ O ₃ ・ 5SiO ₂ , Li ₂ O ・ Al ₂ O ₃ ・ 4SiO ₂ Silicate oxides such as Al ₂ TiO ₅ , MgAl ₂ O ₄ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , BaTiO ₃ LiNbO ₃ , PZT [Pb (Zr, Ti) O ₃ ], PLZT [(Pb, La) (Zr, Ti) O ₃ ], Double oxide oxides such as ferrite; Si ₃ N ₄ , Si _6-Z Al _Z O _Z N _8-Z Non-oxides of nitrides such as AlN, BN, TiN; SiC, B ₄ Non-oxides of carbides such as C, TiC and WC; LaB ₆ TiB ₂ , ZrB ₂ Non-oxides of borides such as CdS, MoS ₂ Sulfide non-oxide such as MoSi ₂ Silicide-based non-oxides such as amorphous carbon, graphite, diamond and other carbon-based non-oxides can be used.
As the metal, Au, Al, Ag, Cu, Pd, Pt, Ti, Ta, Cr, Ni, Fe, and alloys thereof can be used.
[0024]
As the organic material used for the organic material layer, a so-called dye is preferable. In order to sufficiently deform the undercoat layer and the overcoat layer, a dye having a high sublimation property or decomposition / explosive property, or a dye into which a substituent having a high sublimation property or decomposition / explosive property is introduced is preferable.
In order to ensure high decomposition and explosive properties, an organic material having a large molecular skeleton is preferable. Further, a dye that causes a volume change due to a structural change can also be used.
The dyes that satisfy the above requirements include polymethine dyes, naphthalocyanine series, phthalocyanine series, squarylium series, croconium series, pyrylium series, naphthoquinone series, anthraquinone (indanthrene) series, xanthene series, triphenylmethane series, and azulene series. , Tetrahydrocholine-based, phenanthrene-based, triphenothiazine-based dyes, metal complex compounds, and the like.
The film thickness of the dye layer is 100 to 10 μm, preferably 100 to 2000 mm.
[0025]
The dye layer can be formed by ordinary means such as vapor deposition, sputtering, CVD, and solvent coating. In the case of using the coating method, the above-described dye or the like can be dissolved in an organic solvent, and the coating can be performed by a conventional coating method such as spraying, roller coating, dipping, or spin coating.
As the organic solvent to be used, alcohols such as methanol, ethanol and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylacetamide and N, N-dimethylformamide; sulfoxide such as dimethyl sulfoxide Ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; aliphatic halogenated carbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane; Aromatics such as benzene, xylene, monochlorobenzene and dichlorobenzene; cellosolves such as methoxyethanol and ethoxyethanol; hexane, pentane, Cyclohexane, and hydrocarbons such as methylcyclohexane.
[0026]
As the undercoating layer or the overcoating layer that does not function as a light absorbing layer, a metal or a ceramic is preferable.
For the metal or ceramic, it is preferable to use a material having a refractive index difference from the organic material layer in order to improve the reflectance or the recording / reproducing characteristics.
Of the undercoat layer and the overcoat layer, when the layer on the near side with respect to the incident laser beam has a light absorption capability, in order to improve the reflectance or the recording / reproduction characteristics, The side layer is preferably a metal.
On the other hand, if the back layer of the undercoat layer and the overcoat layer has a light absorption capability with respect to the incident laser beam, the incident laser beam is used to improve the reflectance or the recording / reproduction characteristics. On the other hand, the near layer is preferably a ceramic having a small absorption coefficient (about 0.02 or less) with respect to the recording / reproducing wavelength.
As the metal, a metal selected from the group consisting of Au, Al, Cu, Cr, Ag, Ti and alloys thereof is preferable, and ceramics having a small absorption coefficient with respect to the recording / reproducing wavelength (here, near the blue region). Is the above-mentioned ceramics or ZnS · SiO ₂ Etc. are preferred.
These materials are generally formed to a thickness of 50 to 5000 mm, preferably 50 to 3000 mm, by vacuum deposition or sputtering.
[0027]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited at all by these Examples.
[0028]
Example 1
(Embodiment for clarifying that the write-once type optical recording medium of the present invention can provide a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude, and confirming the recording principle)
An undercoating layer (SiC) having a thickness of 10 nm functioning as a light absorption layer is provided by sputtering on a polycarbonate substrate having a guide groove with a groove depth of 50 nm, and an organic material represented by the following [Chemical Formula 1] is provided thereon. Was formed by spin coating (film thickness of about 60 nm), and an overcoat layer (Ag) with a film thickness of 100 nm was further provided thereon to produce an optical recording medium.
[Chemical 1]

[0029]
Using the optical disk evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. for the above optical recording medium, the recording power during recording for a certain time under the following recording conditions Recording was performed by switching between 6.0 (mW) and 10.0 (mW) at intervals.
<Recording conditions>
Recording linear density: 1T = 0.0917 (μm)
Recording linear velocity: 6.0 (m / s)
Recording strategy: Basic strategy
T _top -T _mp = 1.40-0.75 (T)
Recording power: 6.0 (mW), 10.0 (mW)
Recording pattern: 8-16 modulation signal
As a result, as shown in FIG. 2, it can be confirmed that when the recording power is 6.0 (mW), Low to High recording can be performed and when the recording power is 10.0 (mW), High to Low recording can be performed. It was.
[0030]
Next, in order to confirm whether or not this recording was performed based on the recording principle as described above, the deformation state of the interface between the SiC and the organic material layer was measured by an AFM (Atomic Force Microscope).
FIG. 3 shows a three-dimensional representation of the deformation state of the interface between SiC and the organic material layer in the Low to High recording portion generated when the recording power is 6.0 (mW) (the lower side is the substrate). In FIG. 3, the height is represented by shading, where the light color portion is high and the dark color portion is low.
FIG. 4 is a diagram (a) representing the two-dimensional representation of FIG. 3 and a diagram (b) representing a cross-sectional view (uneven shape) of the recording track.
From the results shown in these figures, it is found that the interface between SiC and the organic material layer is deformed (concavely deformed) toward the substrate side in the Low to High recording portion generated when the recording power is 6.0 (mW). It could be confirmed.
[0031]
On the other hand, FIG. 5 shows a three-dimensional representation of the deformation state of the interface between SiC and the organic material layer in the High to Low recording portion generated when the recording power is 10.0 (mW) (the lower side is the substrate). . In FIG. 5, the height is represented by shading, where the light color portion is high and the dark color portion is low.
6A and 6B are a two-dimensional view of FIG. 5A and a cross-sectional view (uneven shape) of the recording track.
From the results shown in these figures, in the High to Low recording portion generated when the recording power is 10.0 (mW), the interface between the SiC and the organic material layer is deformed in the direction opposite to the substrate side (convex deformation). It was confirmed that
[0032]
From the above results, it becomes clear that the recordable optical recording medium of the present invention can be recorded by changing the recording polarity in addition to the recording mark length and amplitude, and this recording polarity is at least of the interface shape between SiC and the organic material layer. It was confirmed that it was caused by the difference in deformation direction.
In this embodiment, recording is performed on the land portion in order to make the AFM image easy to see. However, the present invention is not limited to land recording.
Moreover, although the interface shape of SiC and an organic material layer was measured from the ease of measurement of a deformation | transformation shape, the other interface may be deform | transforming simultaneously.
Furthermore, in the conventional optical recording medium using an organic material, since it was necessary to generate heat in the organic material layer, the organic material layer could not be thinned, and a deep groove (for example, 150 to 180 nm) was required. The recording principle of the present invention makes it possible to reduce the thickness of the organic material, and it has been confirmed that a substrate having a very shallow groove of 50 nm can be applied. This is a great advantage in producing a highly reliable optical recording medium.
[0033]
Comparative Example 1
The same experiment as in Example 1 was performed except that polymethyl methacrylate was used instead of the organic material in Example 1.
As a result, the portion recorded at 6.0 (mW) and the portion recorded at 10.0 (mW) have the same recording polarity, and the interface between the SiC and the polymer layer is the same as in FIGS. It was deformed in the opposite direction (convex deformation) to the substrate.
As a result, the phenomenon in which the interface between the SiC and the organic material layer is deformed (concave deformation) toward the substrate side in Example 1 is due to the action of the organic material, and the state change (decomposition / explosion) of the organic material is caused by the concave deformation. It was proved that it contributed to.
[0034]
Example 2
Actually, it is very difficult to accurately measure the deformation direction of the recording portion and the position (type) of the deformation interface (in Example 1, only the interface state between the undercoat layer and the organic material layer was evaluated). In this example, it is proved that a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude can be obtained by changing the deformation direction and the position (type) of the deformation interface by optical simulation.
Under the following calculation conditions, the recording conditions were changed as in the following (i) to (iv) to calculate how the reproduction signal changes.
(I) Recording part (land part or groove part)
(Ii) Formation state of the organic material layer [the surface shape of the organic material layer is the same as the substrate shape (see FIG. 8), or the surface shape of the organic material layer is flat (see FIG. 9))
(Iii) Recording mark forming interface (only the interface between the undercoat layer and the organic material layer is deformed (see FIGS. 10, 11, 14, and 15), or the interface between the undercoat layer / organic material layer and the organic material layer / overcoating) Layer interface is deformed (see FIGS. 12, 13, 16, and 17)
(Iv) Deformation direction of recording mark [concave deformation toward the substrate (see FIGS. 14 to 17) or convex deformation toward the overcoat layer (see FIGS. 10 to 13)]
[0035]
<Details of calculation conditions>
Hereinafter, the length and size are expressed in units of the recording / reproducing wavelength λ.
-Beam shape: Gaussian distribution
Radius with amplitude 1 / e (x direction, y direction): 6000λ, 6000λ
Objective lens aperture radius: 3000λ
Objective lens NA (numerical aperture): 0.60
Objective lens focal length: 5000λ
Groove shape [A, B, C, D, ζ (see FIG. 7)]: (0.2λ, 0.8λ, 1.0λ, 1.8525λ, 0.1375λ)
・ Substrate refractive index: 1.60 (substrate side incidence)
Undercoat layer complex refractive index: 2.810-i0.561, film thickness = 0.025λ
Organic material layer complex refractive index: 1.500-i0.050, film thickness = 0.150λ
・ Upper layer complex refractive index: 0.1078-i2.0495, film thickness = 0.250λ
・ Detector: 4-section PD
Detector radius (x direction, y direction): 3000λ, 3000λ
Recording mark length, width, height: 1.0λ, 0.60λ, ± 0.10λ
[0036]
The calculation results are as shown in FIGS.
FIG. 21 shows a case where recording is performed on a groove, and the formation state of the organic material layer is a result when the surface shape of the organic material layer is formed to be the same as the substrate shape as shown in FIG. .
The height of the recording portion was ± 0.10λ (when the recording / reproducing wavelength is 400 nm, the height is ± 40 nm).
The legend “+40 nm-0, 4” indicates that the recording part is FIG. 16, the legend “−40 nm-0, 4” indicates that the recording part is FIG. 12, and the legend “+40 nm-0, 2” The legend “−40 nm−0, 2” indicates that the recording unit is shown in FIG. 10.
In the above drawings, the state recorded in the groove portion is shown, but also in the land portion, the deformation direction of the recording portion and the position (type) of the deformation interface are the same.
[0037]
FIG. 22 shows the result when recording is performed on a land, and the organic material layer is formed so that the surface shape of the organic material layer is the same as the substrate shape as shown in FIG. .
The height of the recording portion was ± 0.10λ (when the recording / reproducing wavelength is 400 nm, the height is ± 40 nm).
The legend “+40 nm-0, 4” indicates that the recording part is FIG. 16, the legend “−40 nm-0, 4” indicates that the recording part is FIG. 12, and the legend “+40 nm-0, 2” The legend “−40 nm−0, 2” indicates that the recording unit is shown in FIG. 10.
[0038]
FIG. 23 shows a result of recording in the groove, and the organic material layer is formed in a state where the surface shape of the organic material layer is flat as shown in FIG.
The height of the recording portion was ± 0.10λ (when the recording / reproducing wavelength is 400 nm, the height is ± 40 nm).
The legend “+40 nm-0, 4” indicates that the recording portion is FIG. 17, the legend “−40 nm-0, 4” indicates that the recording portion is FIG. 13, and the legend “+40 nm-0, 2” indicates The legend “−40 nm−0, 2” indicates that the recording unit is FIG. 11.
In the above drawings, the state recorded in the groove portion is shown, but also in the land portion, the deformation direction of the recording portion and the position (type) of the deformation interface are the same.
[0039]
FIG. 24 shows the result when recording is performed on a land, and the organic material layer is formed so that the surface shape of the organic material layer is flat as shown in FIG.
The height of the recording portion was ± 0.10λ (when the recording / reproducing wavelength is 400 nm, the height is ± 40 nm).
The legend “+40 nm-0, 4” indicates that the recording portion is FIG. 17, the legend “−40 nm-0, 4” indicates that the recording portion is FIG. 13, and the legend “+40 nm-0, 2” indicates The legend “−40 nm−0, 2” indicates that the recording unit is FIG. 11.
[0040]
The results shown in FIGS. 21 to 24 prove that the idea that the recording polarity can be controlled by changing the deformation direction of the recording mark and the position (type) of the deformation interface is theoretically correct.
From the results shown in FIG. 24, when the organic material layer is formed so that the surface shape of the organic material layer is flat as shown in FIG. It turns out that change is difficult to appear.
In other words, the “multi-level recordable optical recording medium characterized in that the interface shape between the organic material layer and the overcoat layer is the same as the groove shape of the substrate” in claim 6 is provided. It was confirmed that the optical recording medium using an organic material that enables value recording is preferable.
However, since the condition for changing the recording polarity depends on the complex refractive index of each layer, the change of the complex refractive index of each layer due to recording, or the height and shape of the recording mark, the surface shape of the organic material layer should be flat. It does not deny the case where it is formed.
[0041]
【The invention's effect】
According to the present invention, there is provided a write-once type optical recording medium and a multi-value recording method capable of high-precision multi-value recording while increasing the number of multi-value levels and applicable to a blue laser region of about 350 to 500 nm. Can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a layer structure of a conventional optical recording medium.
FIG. 2 is a diagram showing that recording marks having different recording polarities are formed on the recording medium of the present invention.
FIG. 3 is a view showing a result of observing a portion where Low to High recording is performed on the recording medium of the present invention by AFM.
FIG. 4 is another diagram showing a result of observing a portion where Low to High recording is performed on the recording medium of the present invention by AFM.
(A) A two-dimensional representation of FIG.
(B) Cross section of recording track (uneven shape)
FIG. 5 is a view showing a result of observing a portion where High to Low recording is performed on the recording medium of the present invention by AFM.
FIG. 6 is another diagram showing a result of observing a portion where High to Low recording is performed on the recording medium of the present invention by AFM.
(A) A two-dimensional representation of FIG.
(B) Cross section of recording track (uneven shape)
7 is a diagram for explaining parameters of a groove shape used in Example 2. FIG.
FIG. 8 is a diagram showing a layer structure of the present invention, and is a diagram for explaining one form of forming an organic material layer.
FIG. 9 is a diagram showing a layer structure of the present invention, and is a view for explaining another form of forming an organic material layer.
FIGS. 10A and 10B are diagrams illustrating an example of a form of forming an organic material layer and a form of forming a recording mark.
FIGS. 11A and 11B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark. FIGS.
FIGS. 12A and 12B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark.
FIG. 13 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.
FIGS. 14A and 14B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark.
FIGS. 15A and 15B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark. FIGS.
FIGS. 16A and 16B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark. FIGS.
FIGS. 17A and 17B are diagrams showing another example of the formation form of the organic material layer and the formation form of the recording mark. FIGS.
FIG. 18 is a diagram for explaining a recording principle by increasing an absorption coefficient of an organic material.
FIG. 19 is a diagram for explaining the characteristics of an organic material layer that can realize the recording principle by increasing the absorption coefficient of the organic material.
FIG. 20 is a diagram for explaining the characteristics of an organic material layer that can realize the recording principle by increasing the absorption coefficient of the organic material.
FIG. 21 is a view showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 8 and recording is performed on a groove portion;
FIG. 22 is a view showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 8 and recording is performed on a land portion.
FIG. 23 is a view showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 9 and recording is performed on a groove portion;
FIG. 24 is a view showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 9 and recording is performed on a land portion.
[Explanation of symbols]
A Width of the top surface end of the land and the bottom surface end of the adjacent groove closer to the land
B Width between the top surface end of the land and the bottom surface end of the adjacent groove far from the land
C Width of the upper surface end of the land and the upper surface end of the adjacent land closer to the land
D Width between the upper surface edge of the land and the upper surface edge of the adjacent land far from the land
ζ Land height (groove depth)

Claims (11)

  An organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength when not recorded is provided on the substrate via an undercoat layer. The undercoat layer and the overcoat layer have a large refractive index difference from the organic material layer. Is an optical recording medium in which the undercoat layer or the overcoat layer has a light absorption function, and the deformation direction and the position (type) of the deformation interface can be changed during recording. A write-once type optical recording medium capable of multi-value recording, characterized in that a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude can be obtained.   An organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength when not recorded is provided on the substrate via an undercoat layer. The undercoat layer and the overcoat layer have a large refractive index difference from the organic material layer. Is an optical recording medium in which the undercoat layer or the overcoat layer has a light absorption function, and the organic material layer changes from the organic material layer to the undercoat layer in accordance with the state change of the organic material in the organic material layer. When recording, the recording principle of recording mark formation by pressure or pressure from the organic material layer to the overcoating layer and the recording principle of recording mark formation by stress relaxation of the undercoating layer or overcoating layer or thermal expansion of the substrate In addition, it is possible to change the deformation direction of the recording mark portion and the position (type) of the deformation interface, thereby obtaining a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude. Possible write-once optical recording medium.   An organic layer that has a main absorption band when not recorded on the long wavelength side with respect to the recording / reproducing wavelength and has no absorption function for light of the recording / reproducing wavelength when not recorded on the substrate via an undercoat layer An optical recording medium having a layer structure in which a material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function. The multi-value recording is characterized in that, during recording, the deformation direction and the position (type) of the deformation interface can be changed, whereby a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude can be obtained. Possible write-once optical recording medium.   An organic layer that has a main absorption band when not recorded on the long wavelength side with respect to the recording / reproducing wavelength and has no absorption function for light of the recording / reproducing wavelength when not recorded on the substrate via an undercoat layer An optical recording medium having a layer structure in which a material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function. The recording principle of recording mark formation by the pressure from the organic material layer to the undercoating layer or the pressure from the organic material layer to the overcoating layer as the state of the organic material in the organic material layer changes, and the undercoating layer and the overcoating layer Depending on the recording principle of recording mark formation by layer stress relaxation or thermal expansion of the substrate, the deformation direction of the recording mark portion and the position (type) of the deformation interface can be changed during recording, thereby the recording mark length and amplitude In addition to the difference between the above, it is possible to obtain playback signals with different recording polarities Value recordable write-once optical recording medium. The write-once type optical recording medium capable of multi-value recording according to any one of claims 1 to 4, wherein a recording / reproducing wavelength is 350 nm or more and 500 nm or less . 6. The multi-value recordable additional recording according to claim 1 , wherein an interface shape of the organic material layer and the overcoat layer is formed to be the same as a groove shape of the substrate. Type optical recording medium.   An organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength when not recorded is provided on the substrate via an undercoat layer. The undercoat layer and the overcoat layer have a large refractive index difference from the organic material layer. For the write-once type optical recording medium capable of multi-value recording, in which the undercoating layer or the overcoating layer has a light absorption function, the deformation direction and the position (type) of the deformation interface are recorded. A multi-value recording method characterized in that, by changing, a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude is obtained.   An organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength when not recorded is provided on the substrate via an undercoat layer. The undercoat layer and the overcoat layer have a large refractive index difference from the organic material layer. Organic material layer with a change in the state of the organic material in the organic material layer with respect to a write-once type optical recording medium having a layer structure sandwiched between and an undercoat layer or an overcoat layer having a light absorption function The recording principle of recording mark formation by the pressure from the undercoat layer or the pressure from the organic material layer to the overcoat layer, and the recording of the recording mark formation by the stress relaxation of the undercoat layer and the overcoat layer, or the thermal expansion of the substrate The principle is to change the deformation direction of the recording mark part and the position (type) of the deformation interface during recording, so that a reproduction signal with different recording polarity in addition to the difference in recording mark length and amplitude can be obtained. A characteristic multi-value recording method.   An organic layer that has a main absorption band when not recorded on the long wavelength side with respect to the recording / reproducing wavelength and has no absorption function for light of the recording / reproducing wavelength when not recorded on the substrate via an undercoat layer Additional recording capable of multi-value recording having a layer structure in which a material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function By changing the deformation direction and the position (type) of the deformation interface for a recording optical recording medium, it is possible to obtain a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude. A characteristic multi-value recording method.   An organic layer that has a main absorption band when not recorded on the long wavelength side with respect to the recording / reproducing wavelength and has no absorption function for light of the recording / reproducing wavelength when not recorded on the substrate via an undercoat layer Additional recording capable of multi-value recording having a layer structure in which a material layer is sandwiched between an undercoat layer and an overcoat layer having a large refractive index difference from the organic material layer, and the undercoat layer or the overcoat layer has a light absorption function Recording principle of recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer with respect to the type optical recording medium, with the change in the state of the organic material in the organic material layer, Depending on the recording principle of recording mark formation by stress relaxation of the undercoat layer or overcoat layer or thermal expansion of the substrate, the deformation direction of the recording mark portion and the position (type) of the deformation interface are changed during recording, thereby recording mark In order to obtain playback signals with different recording polarities in addition to differences in length and amplitude Multilevel recording method, comprising and. The multi-value recording method according to any one of claims 7 to 10, wherein a recording / reproducing wavelength is 350 nm or more and 500 nm or less .

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