JP3833961B2 - Write-once optical recording medium - Google Patents

Description

【００３０】
但し、上記シアニン色素の中でも、カウンターイオン（一般式〔化１〕中のＺ⁻）がＣｌＯ_４ ⁻である色素が特に分解特性が良好なため好ましい。何故ならば、この色素は、図４〔実線は減量率、破線はＤＴＡ（示差熱分析）の結果を表わす〕に示すように、明らかな分解を起す熱分解特性を有するためである（減量開始温度近傍で、大きな発熱反応を示す場合に相当する）。
一方、カウンターイオンがＢＦ_４ ⁻やＩ⁻であるシアニン色素は、図５、６〔実線は減量率、破線はＤＴＡ（示差熱分析）の結果を表わす〕に示すように、明らかな分解を起さない熱分解特性を有するためである（減量開始温度近傍で、発熱が小さいか又は吸熱反応である場合、更には減量率が著しく高い場合に相当する）。
また、一般式〔化１〕中の左右の複素環は、それ単独で３００ｎｍ以上に吸収ピークを有する分子・分子団であることが好ましい。
これによって、分解時の吸収係数の増加を、青色領域で大きく検出できる。
【００３１】
色素層の形成は、蒸着、スパッタリング、ＣＶＤ、溶剤塗布などの通常の手段によって行なうことができる。塗布法を用いる場合には、上記色素などを有機溶剤に溶解し、スプレー、ローラーコーティング、ディッピング、スピンコーティングなどの慣用のコーティング法で塗布すれよい。
用いられる有機溶剤としては、一般にメタノール、エタノール、イソプロパノールなどアルコール類；アセトン、メチルエチルケトン、シクロヘキサノンなどのケトン類；Ｎ，Ｎ−ジメチルアセトアミド、Ｎ，Ｎ−ジメチルホルムアミドなどのアミド類；ジメチルスルホキシドなどのスルホキシド類；テトラヒドロフラン、ジオキサン、ジエチルエーテル、エチレングリコールモノメチルエーテルなどのエーテル類；酢酸メチル、酢酸エチルなどのエステル類；クロロホルム、塩化メチレン、ジクロルエタン、四塩化炭素、トリクロルエタンなどの脂肪族ハロゲン化炭素類；ベンゼン、キシレン、モノクロルベンゼン、ジクロルベンゼンなどの芳香族類；メトキシエタノール、エトキシエタノールなどのセロソルブ類；ヘキサン、ペンタン、シクロヘキサン、メチルシクロヘキサンなどの炭化水素類などが挙げられる。
色素層の膜厚は、１００Å〜１０μｍ、好ましくは１００〜２０００Åが適当である。
【００３２】
カバー層は、高密度化を図るため高ＮＡのレンズを用いる場合に必要となる。
例えば高ＮＡ化すると、再生光が透過する部分の厚さを薄くする必要がある。これは、高ＮＡ化に伴い、光学ピックアップの光軸に対してディスク面が垂直からズレる角度（いわゆるチルト角、光源の波長の逆数と対物レンズの開口数の積の２乗に比例する）により発生する収差の許容量が小さくなるためであり、このチルト角が基板の厚さによる収差の影響を受け易いためである。
従って基板の厚さを薄くしてチルト角に対する収差の影響をなるべく小さくするようにしている。
そこで、例えば基板上に凹凸を形成して記録層とし、その上に反射膜を設け、更にこの上に、光を透過する薄膜である光透過性のカバー層を設けるようにし、カバー層側から再生光を照射して記録層の情報を再生するような光記録媒体や、基板上に反射膜を設け、その上に記録膜を形成して記録層とし、更にこの上に光透過性を有するカバー層を設けるようにし、カバー層側から再生光を照射して記録層の情報を再生するような光記録媒体が提案されている。
このようにすれば、カバー層を薄型化していくことで対物レンズの高ＮＡ化に対応可能である。つまり、薄いカバー層を設け、このカバー層側から記録再生することで、更なる高記録密度化を図ることができる。
なお、このようなカバー層は、ポリカーボネートシートや紫外線硬化型樹脂により形成するのが一般的である。
【００３３】
【実施例】
以下、実施例及び比較例により本発明を具体的に説明するが、本発明はこれらの実施例により限定されるものではない。
【００３４】
実施例１
溝深さ５０ｎｍの案内溝を有するポリカーボネート基板上に、スパッタ法により厚さ１００ｎｍのＺｎＳ・ＳｉＯ_２（変形抑制層。なお、ＳｉＯ_２の含有率は２０モル％）を設け、その上に下記一般式〔化２〕で示される色素からなる厚さ約６０ｎｍの有機材料層をスピンコート法によって形成し、更にその上に厚さ１０ｎｍのＳｉ（光吸収層）を設けて追記型光記録媒体を作成した。
なお、４０５ｎｍにおける下記〔化２〕の色素の複素屈折率は、１．４０７−ｉ０．０７６であり、従来の追記型の光記録媒体に用いる有機材料に要求される複素屈折率に対し、著しく劣った複素屈折率である（例えばＤＶＤ−Ｒに用いられている色素の、記録再生波長近傍での複素屈折率は、２．５−ｉ０．１０程度である）。
【００３５】
【化２】

【００３６】
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、下記の条件で記録を行なった結果、非常に明瞭な信号が得られ、ジッタ（σ／Ｔｗ）＝１０．２（％）が得られた。

更に、光記録媒体の光吸収層を剥がし、記録部分と未記録部分の色素をエタノールで溶かして、それぞれのスペクトルを測定した。
その結果、図１１に示すように、記録部分では吸収（吸収係数）の明らかな増加が認められ（記録はグル−ブ部のみに行なわれたため、記録部のスペクトルには多量の未記録部成分が存在する）、本発明の光記録媒体における記録原理を確認できた。
【００３７】
比較例１
溝深さ１５０ｎｍの案内溝を有するポリカーボネート基板上に、下記〔化３〕で示される色素からなる厚さ約１２０ｎｍの有機材料層をスピンコート法によって形成し、その上に厚さ１５０ｎｍのＡｇ反射層を設けて追記型光記録媒体を作成した（従来の層構成を青色領域でも適用した例）。
なお、４０５ｎｍにおける一般式〔化３〕の色素の複素屈折率は、２．２８５−ｉ０．０６９であり、従来の追記型光記録媒体に用いる有機材料に要求される複素屈折率に対し、比較的近い複素屈折率を有する（例えばＤＶＤ−Ｒに用いられている色素の、記録再生波長近傍での複素屈折率は、２．５−ｉ０．１０程
度である）。
【００３８】
【化３】

【００３９】
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、下記の条件で記録を行なった結果、長マークでは比較的大きな変調度が得られたが、短マークでは充分な信号が得られず、またマーク長にかかわらずノイズの多い信号であり、ジッタ（σ／Ｔｗ）は測定不能であった。

【００４０】
比較例２
比較例１の溝深さ１５０ｎｍの案内溝を有するポリカーボネート基板に代えて、実施例１と同じ溝深さ５０ｎｍの案内溝を有するポリカーボネート基板を用い、この基板上に、上記一般式〔化３〕で示される色素からなる有機材料層をスピンコート法によって形成し、その上に厚さ１５０ｎｍのＡｇ反射層を設けて追記型光記録媒体を作成し、比較例１と同様の記録を行なったが、全く記録できなかった。
【００４１】
以上、本発明の実施例１と比較例１〜２から、本発明の追記型光記録媒体の層構成と記録原理が、青色レーザ波長対応の有機材料からなる追記型光記録媒体の実現に非常に有効であることが確認できた。
また、従来の有機材料を用いた追記型光記録媒体では、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。
【００４２】
実施例２
実施例１と同様にして、下記〔表１〕に記載したシアニン色素を有機材料層とする追記型光記録媒体を作製し、実施例１と同様の記録条件で記録を行なって記録特性の良否を判定した。
判定基準は、ジッタ（σ／Ｔｗ）が測定できるレベルで、１５％以下となったシアニン色素には「○」、そうでないシアニン色素には「×」を付けた。
また、表１には、各シアニン色素の熱重量分析における分解挙動（減量率、発／吸熱）のタイプを示した。
減量率のタイプについては、重量の減量の大小を記号Ｓ、Ｍ、Ｌで示し、減量の小さいものから順にＳ＜Ｍ＜Ｌと記した。
発／吸熱タイプは、分解時、即ち主減量過程が起ったときに発熱するか吸熱するかの状態を示すもので、発熱の場合は「＋」、吸熱の場合は「−」、発熱も吸熱も殆んど見られない場合は「０」と記した。
なお、主減量過程とは、減量率が減少する温度（過程）が複数存在する場合に最も大きな減量を示す過程を指し、例えば図４〜図６においては、実線で示される減量率が急激に減少している部分である。
表１の結果から、減量率のタイプ及び発／吸熱のタイプとカウンターイオンの種類は明らかな相関があり、また減量率のタイプ及び発／吸熱のタイプとジッタ（σ／Ｔｗ）にも同様な相関があることが分る。
即ち、カウンターイオンがＣｌＯ_４ ⁻であるシアニン色素の場合、主減量過程での減量率が比較的小さく発熱反応を示していることから、この主減量過程では単なる昇華等による減量でなく、分解による減量が起っていること、この分解が起るものほど良好なジッタ（σ／Ｔｗ）を示すことが分る。
【００４３】
【表１】

【００４４】
実施例３
従来のＤＶＤ−Ｒに用いることができる下記〔化４〕で示される色素の複素屈折率（屈折率ｎと吸収係数ｋ）、本発明で使用でき且つ従来のＤＶＤ−Ｒにも用いることができる色素（ＮＫ４３８２）の複素屈折率、及びＳｉの複素屈折率を測定した。
下記〔化４〕で示される色素の複素屈折率を図１２に、色素（ＮＫ４３８２）の複素屈折率を図１３に、Ｓｉの複素屈折率を図１４に示す。
これらの結果から、従来の有機（記録）材料に対し、記録再生波長を有機材料の吸収帯の長波長側に位置させるような従来の記録方法を適用した場合には、記録再生波長の変動に対し、屈折率ｎや吸収係数ｋが大きく変動することが確認できた。
一方、本発明では、従来の有機（記録）材料に対し、記録再生波長を有機材料の吸収帯から充分短波長側に位置させる記録方法であるため、記録再生波長の変動に対し、屈折率ｎや吸収係数ｋが殆んど変動しないことが確認できた。
また、光吸収層として用いるＳｉも、記録再生波長の変動に対して屈折率ｎや吸収係数ｋが大きく変動しないことが確認できた。
【００４５】
【化４】

【００４６】
以上の実施例により、本発明の層構成によって、記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化が少ない追記型光記録媒体を実現できることが確認できた。
【００４７】
【発明の効果】
本発明１〜３によれば、３５０〜５００ｎｍ程度の青色レーザ波長領域に対応可能であり、転写性のよい浅溝基板が利用でき、記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化が少なく、高密度化を図ることができる追記型の光記録媒体を容易に且つ安価に提供できる。
本発明４〜８によれば、更に記録再生特性を向上させることが可能となる。
本発明９によれば、本発明１〜８の追記型光記録媒体の各層の機能を最大限に活かすことができる。
【図面の簡単な説明】
【図１】従来の追記型光記録媒体の層構成を説明するための図である。
【図２】本発明の追記型光記録媒体の層構成例を説明するための図である。
【図３】本発明の追記型光記録媒体の別の層構成例を説明するための図である。
【図４】本発明の追記型光記録媒体に用いられる有機材料として好ましい熱分解特性の一例を説明するための図である。
【図５】本発明の追記型光記録媒体に用いられる有機材料として好ましくない熱分解特性の一例を説明するための図である。
【図６】本発明の追記型光記録媒体に用いられる有機材料として好ましくない熱分解特性の別の例を説明するための図である。
【図７】従来の追記型光記録媒体の記録原理を説明するための図である。
【図８】本発明の追記型光記録媒体の記録原理を説明するための図である。
【図９】本発明の追記型光記録媒体に用いられる有機材料の特性を説明するための図である。
【図１０】本発明の追記型光記録媒体に用いられる有機材料の特性を説明するための図である。
【図１１】実施例１で用いた色素の記録前後の吸収係数の変化を示す図である。
【図１２】実施例３で用いた色素の記録再生波長領域での複素屈折率変化を示す図である。
【図１３】色素（ＮＫ４３８２）の記録再生波長領域での複素屈折率変化を示す図である。
【図１４】本発明で用いるＳｉの複素屈折率変化を示す図である。
【符号の説明】
１ 基板
２ 変形抑制層
３ 有機材料層
４ 光吸収層
５ カバー層
６ 反射層
λ_１ 記録再生波長
λ_２ 有機化合物の主吸収帯
Ａ 分子や分子団が持っていた固有の吸収波長
Ｂ 分子や分子団が持っていた固有の吸収波長
Ｃ 個々の分子や分子団が持っていた固有の吸収帯が消滅、又は減衰した吸収スペクトル
ｎ 複素屈折率の実部
ｋ 複素屈折率の虚部（吸収係数）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a write once read many (WORM) optical recording medium, and more particularly to a write once optical recording medium capable of high density recording even in a blue laser wavelength region.
[0002]
[Prior art]
Development of blue lasers capable of ultra-high density recording is rapidly progressing, and write-once type optical recording media corresponding thereto are being developed.
In conventional write-once optical recording media, recording pits are formed by irradiating a recording layer made of an organic material with laser light and causing a change in refractive index mainly due to decomposition and alteration of the organic material. The optical constant and decomposition behavior of the organic material used are important factors for forming good recording pits.
Accordingly, it is necessary to select an organic material used for the recording layer that is suitable for optical properties and decomposition behavior with respect to the blue laser wavelength. In other words, the recording / reproducing wavelength has a large absorption band in order to increase the reflectivity when unrecorded, and to cause a large change in refractive index due to decomposition of the organic material by laser irradiation (this provides a large degree of modulation). It is selected so as to be located at the bottom of the long wavelength side.
This is because the skirt on the long wavelength side of the large absorption band of the organic material is a wavelength region having an appropriate absorption coefficient and a large refractive index.
[0003]
However, an organic material having an optical property with respect to a blue laser wavelength that is the same as the conventional value has not yet been found. In order to obtain an organic material having an absorption band in the vicinity of the blue laser wavelength, it is necessary to reduce the molecular skeleton or shorten the conjugated system, but this leads to a decrease in absorption coefficient, that is, a decrease in refractive index. Because.
That is, there are many organic materials having an absorption band near the blue laser wavelength, and the absorption coefficient can be controlled. However, since there is no large refractive index, a large degree of modulation cannot be obtained.
Examples of organic materials compatible with blue lasers are described in JP-A Nos. 2001-181524, 2001-158865, 2000-343824, 2000-343825, and 2000-335110. is there.
However, these publications only measure the spectra of the solution and the thin film even when looking at the examples, and there is no description regarding recording and reproduction.
[0004]
In JP-A-11-221964, JP-A-11-334206, and JP-A-2000-43423, although there is a description of recording in the examples, the recording wavelength is 488 nm, and the description regarding the recording conditions and recording density is as follows. There is only a statement that a good recording pit was formed.
In JP-A-11-58955, although there is a description of recording in the examples, the recording wavelength is 430 nm, and there is no description regarding recording conditions and recording density, and there is a description that a good degree of modulation was obtained. Only.
JP 2001-39034, JP 2000-149320, JP 2000-11504, JP 2000-108513, JP 2000-222772, JP 2000-218940, JP 2000-222771, In Japanese Laid-Open Patent Publication Nos. 2000-158818, 2000-280621, and 2000-280620, there are examples of recording with a recording wavelength of 430 nm and NA of 0.65, but the shortest pit is 0.4 μm. Density conditions (recording density equivalent to DVD).
In Japanese Patent Application Laid-Open No. 2001-146074, the recording / reproducing wavelength is 405 to 408 nm, but there is no specific description regarding the recording density, and the recording density is a low recording density condition of 14T-EFM signal recording.
[0005]
Further, the following technologies are disclosed regarding the layer configuration and recording method different from those of conventional CD and DVD optical recording media.
Japanese Patent Application Laid-Open No. 7-304258 discloses a technique for recording by changing the extinction coefficient (absorption coefficient in the present invention) of a saturable absorbing dye in a layer structure of substrate / saturable absorbing dye-containing layer / reflective layer. It is disclosed.
In JP-A-8-83439, recording is performed by discoloring or deforming a metal vapor deposition layer by heat generated by the light absorption layer in a layer configuration of substrate / metal vapor deposition layer / light absorption layer / protective sheet. Techniques to do are disclosed.
In JP-A-8-138245, recording is performed by changing the depth of the groove portion by changing the film thickness of the recording layer in a layer structure of substrate / dielectric layer / recording layer including light absorber / reflective layer. Technology is disclosed.
Japanese Patent Application Laid-Open No. H8-297838 discloses a technique for performing recording by changing the film thickness of the recording layer by 10 to 30% in a layer configuration of substrate / recording layer including a light absorber / metal reflective layer. Yes.
[0006]
Japanese Patent Application Laid-Open No. 9-198714 discloses that a substrate / a recording layer containing an organic dye / a metal reflective layer / a protective layer has a layer structure of 20 to 40% wider than the unrecorded portion. A technique for recording is disclosed.
Japanese Patent No. 2506374 discloses a technique for recording by forming a bubble by deforming a metal thin film with a layer structure of substrate / intermediate layer / metal thin film.
Japanese Patent No. 2591939 discloses a layer structure of substrate / light absorption layer / recording auxiliary layer / light reflecting layer, in which the recording auxiliary layer is deformed into a concave shape, and the light reflecting layer is made concave along the deformation of the recording auxiliary layer. A technique for recording by deforming is disclosed.
Japanese Patent No. 2591940 discloses a recording assist with a layer structure of substrate / light absorbing layer / porous recording auxiliary layer / light reflecting layer or substrate / porous recording auxiliary layer / light absorbing layer / light reflecting layer. A technique is disclosed in which recording is performed by deforming the layer into a concave shape and deforming the light reflecting layer into a concave shape along with the deformation of the recording auxiliary layer.
Japanese Patent No. 2591941 discloses a layer structure of substrate / porous light absorption layer / light reflection layer, in which the light absorption layer is deformed into a concave shape, and the light reflection layer is deformed into a concave shape along with the deformation of the light absorption layer. A technique for recording by performing the above is disclosed.
[0007]
Japanese Patent No. 2998925 discloses that the recording auxiliary layer and the organic dye are compatible with each other and the absorption spectrum of the organic dye is shifted to the short wavelength side in a layer configuration of substrate / recording layer containing organic dye / recording auxiliary layer. A technique for recording with the above is disclosed.
In Japanese Patent Laid-Open No. 9-265660, a composite functional layer having a function of a reflective layer and a recording layer and a protective layer are sequentially formed on a substrate, and recording is performed by forming bumps on the substrate and the composite functional layer. Techniques to do are disclosed. In addition, as a composite functional layer, there exists a prescription | regulation with metals, such as nickel, chromium, titanium, or those alloys.
Japanese Patent Laid-Open No. 10-134415 discloses a layer structure in which a metal thin film layer, a deformable buffer layer, a reflective layer, and a protective layer are sequentially formed on a substrate, and the substrate and the metal thin film layer are deformed at the same time. A technique for recording by reducing the thickness of the buffer layer is disclosed. In addition, as a metal thin film layer, there exists prescription | regulation with metals, such as nickel, chromium, titanium, or those alloys. In addition, as the buffer layer, there is a description that a resin that is easily deformable and has an appropriate fluidity is used, and a pigment may be contained in order to promote deformation.
[0008]
Japanese Patent Laid-Open No. 11-306591 discloses a layer structure in which a metal thin film layer, a buffer layer, and a reflective layer are sequentially laminated on a substrate, and the substrate and the metal thin film layer are deformed at the same time. A technique for recording by changing an optical constant is disclosed. In addition, as a metal thin film layer, there exists a description that metals, such as nickel, chromium, titanium, or those alloys are preferable. The buffer layer is made of a mixture of a dye and an organic polymer, and a dye having a large absorption band near the recording / reproducing wavelength is used.
Japanese Patent Laid-Open No. 10-124926 discloses a layer structure in which a metal recording layer, a buffer layer, and a reflective layer are sequentially stacked on a substrate, and the substrate and the metal recording layer are deformed at the same time. A technique for recording by changing an optical constant is disclosed. In addition, as a metal recording layer, there exists a description that metals, such as nickel, chromium, titanium, or those alloys are preferable. The buffer layer is made of a mixture of a dye and a resin, and a dye having a large absorption band near the recording / reproducing wavelength is used.
[0009]
As described above, the above-described conventional technologies are not aimed at realizing an optical recording medium in the blue laser wavelength region, and are not a layer configuration or a recording method effective in the blue laser wavelength region.
In particular, in the vicinity of 405 nm, which is the center of the oscillation wavelength of a blue semiconductor laser that is currently in practical use, most organic materials have an optical constant comparable to that required for the recording layer of conventional write-once type optical recording media. It does n’t exist. In addition, there are no examples in which recording conditions are clarified near 405 nm and recording is performed at a higher recording density than DVD.
Furthermore, many of the above-described prior art examples are experiments with a conventional disk configuration (see FIG. 1), and a configuration different from the conventional disk configuration has been proposed. However, there is no effective proposal for a layer structure, a recording principle, or a recording method that can easily realize a write-once optical recording medium made of an organic material in the blue laser wavelength region.
[0010]
In addition, in a write-once type optical recording medium using a conventional organic material, a large refractive index and a relatively small absorption coefficient (about 0.05 to 0.07) with respect to the recording / reproducing wavelength from the viewpoint of securing the degree of modulation and the reflectance. ) Can only be used.
That is, since the organic material does not have sufficient absorption capability for the recording light, it is impossible to reduce the film thickness of the organic material layer. Therefore, it is necessary to use a substrate having a deep groove. (Because the organic material layer is usually formed by spin coating, the organic material was buried in a deep groove to increase the thickness). Therefore, it becomes very difficult to form a substrate having a deep groove, which is a factor of deteriorating the quality as an optical recording medium.
Furthermore, in a write-once optical recording medium using a conventional organic material, the main absorption band of the organic material exists in the vicinity of the recording / reproducing wavelength, so the wavelength dependence of the optical constant of the organic material increases (the optical constant depends on the wavelength). Recording characteristics such as recording sensitivity, modulation factor, jitter, error rate, and reflectivity greatly change with respect to fluctuations in recording / reproducing wavelength due to individual differences of lasers, environmental temperature changes, etc. was there.
[0011]
[Problems to be solved by the invention]
An object of the present invention is to solve the above problems of the prior art and to realize an optical recording medium having the following characteristics.
(A) A write-once type optical recording medium having an organic material layer capable of recording and reproducing easily even in a blue laser wavelength region (about 350 to 500 nm), particularly in a wavelength region near 405 nm.
(B) A write-once optical recording medium having an organic material layer that can be easily recorded and reproduced even on a shallow groove substrate with good transferability.
(C) A write-once optical recording medium in which changes in recording characteristics such as recording sensitivity, modulation degree, jitter, error rate, and reflectivity are small with respect to fluctuations in the recording / reproducing wavelength.
[0012]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 9) (hereinafter referred to as the present inventions 1 to 9).
1) On the substrate, at least a deformation suppressing layer for suppressing deformation of the substrate, a main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength, and absorbs light of the recording / reproducing wavelength. Write-once type optical recording medium, characterized in that it has a structure in which an organic material layer not containing light and a light absorption layer are sequentially laminated.
2) At least a deformation suppressing layer that suppresses deformation of the substrate, a light absorption layer, and a main absorption band at the time of unrecording exist on the long wavelength side with respect to the recording / reproducing wavelength, and the light having the recording / reproducing wavelength On the other hand, a write-once type optical recording medium having a structure in which an organic material layer having no absorption function and a cover layer are sequentially laminated, and recording and reproduction are performed from the cover layer side.
3) Additional description according to 1) or 2), wherein the organic material layer is made of an organic material that changes its state due to heat generated by the light absorption function of the light absorption layer and increases an absorption coefficient at a recording / reproducing wavelength. Type optical recording medium.
4) Write-once type optical recording medium according to any one of 1) to 3), wherein n2> n1 where n1 is the refractive index of the organic material layer and n2 is the refractive index of the light absorption layer. .
5) The deformation suppressing layer is made of SiO.₂The write-once type optical recording medium according to any one of 1) to 4), comprising a material containing
6) The write-once optical recording medium according to any one of 1) to 5), wherein the light absorption layer is made of a material containing Si and / or Ge.
7) The write-once type optical recording medium according to any one of 1) to 6), wherein the organic material layer is made of an organic material that exhibits an exothermic reaction in the main weight loss process in the thermal decomposition characteristics.
8) Organic material layer is counter ion is ClO₄ ⁻The write-once type optical recording medium according to any one of 1) to 7), wherein the write-once optical recording medium is a cyanine dye.
9) The recordable optical recording medium according to any one of 1) to 8), wherein recording and reproduction are possible in a laser wavelength range of 350 to 500 nm.
[0013]
Hereinafter, the present invention will be described in detail.
The first aspect of the present invention provides a substrate side even in a blue laser wavelength or a short wavelength region where it is difficult to obtain an optical constant comparable to that required for a recording layer of a conventional write-once optical recording medium. Recording / reproduction can be achieved with high density, good recording / reproduction characteristics can be obtained, recording / reproduction can be easily performed even on a shallow groove substrate with good transferability, The present invention provides a layer structure of a write-once optical recording medium with little change in recording / reproducing characteristics.
The present invention 2 is characterized in that recording / reproduction is performed from the cover layer side, and provides a layer structure of a write-once type optical recording medium having the same effects as the present invention 1.
Invention 3 defines an organic material having suitable physical properties.
In the fourth aspect of the invention, suitable refractive indexes of the organic material layer and the light absorption layer are defined.
The present invention 5 defines a suitable material for the deformation suppressing layer.
The present invention 6 defines a suitable material for the light absorption layer.
The present invention 7 defines the thermal decomposition characteristics of a suitable organic material.
The present invention 8 defines a suitable organic material.
The present invention 9 provides a write-once type optical recording medium capable of recording / reproducing in a laser wavelength range of 350 to 500 nm.
[0014]
In the present invention, the basic principle of recording is to change the state of the organic material of the organic material layer by the heat generation of the light absorption layer and increase the absorption on the shorter wavelength side than the main absorption band of the organic material.
However, not only the state of the organic material of the organic material layer is changed by the heat generation of the light absorption layer, but also the substrate or the like may be greatly deformed. In particular, when the light absorption layer is in contact with the substrate, the deformation of the substrate and the light absorption layer becomes large.
This large deformation of the substrate and the light absorption layer may lead to deterioration of the crosstalk, or the recording characteristics may be different from the recording polarity due to an increase in the absorption coefficient due to the change in the state of the organic material. The recording polarity to be changed varies depending on the groove shape of the substrate, the deformed shape of the substrate, etc.).
Here, the difference in recording polarity means that the recording polarity due to an increase in the absorption coefficient due to a change in the state of the organic material is high to low, while the deformation of the substrate or the light absorption layer is caused. This means that the resulting recording polarity is Low to High.
Therefore, in the present invention, the deformation of the substrate and the light absorption layer is suppressed in order to sufficiently generate the degree of modulation due to the increase in the absorption coefficient due to the change in the state of the organic material. That is, the substrate is not in contact with the light absorption layer, and the deformation suppressing layer is provided on the substrate that is easily deformed. As a result, a sufficient degree of modulation can be generated and crosstalk can be suppressed.
[0015]
In the conventional write-once type optical recording medium, the absorption coefficient at the recording / reproducing wavelength is lowered by the decomposition and alteration of the organic material, and the degree of modulation is generated by utilizing the large refractive index change (see FIG. 7, horizontal axis). The arrow below indicates the recording / reproducing wavelength).
In contrast, the write-once type optical recording medium of the present invention has conventionally functioned as a heat generation layer with a light absorption function and a recording layer with a change in refractive index (real part of complex refractive index) caused by decomposition and alteration. The feature is that the function of the heat generation layer by the light absorption function is separated from the organic material layer and a light absorption layer different from the organic material layer is provided.
Then, the state of the organic material is decomposed by the heat generated in the light absorption layer, and recording is performed by increasing the absorption coefficient of the organic material layer in the blue laser wavelength region of about 350 to 500 nm, for example. I do.
That is, the change in the state of the organic material causes the absorption of the molecules and molecular groups constituting the organic material (increase the absorption coefficient on the shorter wavelength side than the large absorption band), and By setting the absorption wavelength band and the recording / reproducing wavelength so as to overlap, the absorption coefficient at the recording / reproducing wavelength is increased to generate the degree of modulation (see FIG. 8).
As a result, the organic material layer has no refractive index limitation and does not have to have a light absorption capability with respect to the recording / reproducing wavelength.
[0016]
The “change in the state of the organic material” in the present invention refers to melting, sublimation, decomposition, explosion, structural change, etc. Among them, “decomposition, explosion” is important, and in that case, the only requirement for the organic material is What is done is that the thermal decomposition characteristics (decomposition temperature, explosiveness, existence of a definite decomposition threshold, decomposition speed, decomposition amount, etc.) are excellent.
Therefore, even when recording / reproduction is performed in the blue laser wavelength region, the organic material has a large absorption band in the red laser wavelength region, does not have a large absorption band in the blue laser wavelength region, and has excellent decomposition characteristics. For example, a dye for CD-R or DVD-R can be used.
Conventionally, it has been necessary to use a complicated substituent or a dye having high synthesis difficulty as a recording layer for wavelength control. However, in the organic material layer of the present invention, such complicated wavelength control is necessary. Therefore, it is possible to select an organic material with a low cost.
[0017]
The above-mentioned recording principle will be explained 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 the absorption spectra A and B in FIG. 9) possessed by the molecule or molecular group, and the intrinsic absorption possessed by each molecule or molecular group. The band has an absorption spectrum in which the band disappears or attenuates (corresponding to the absorption spectrum C in FIG. 10).
For such an organic material, when λ1 as shown in FIG. 10 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. 9), absorption at λ1 also increases, and a recording portion can be formed by a change in absorption coefficient.
Therefore, a molecule in which only a small molecule or molecular group is bonded and a conjugated system does not form a spread is in the state shown in FIG. 10, 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.
[0018]
Further, in the conventional write-once type optical recording medium, the organic material layer combines the function of the recording layer and the function of the light absorption / conversion layer. Therefore, a large refractive index n and a relatively small absorption coefficient k with respect to the recording / reproducing wavelength. Therefore, in order to reach the temperature at which the organic material is decomposed, a relatively thick film thickness is required (and the substrate is different from the phase-change-type write-once optical recording medium). The groove depth of was very deep).
However, in the recording medium of the present invention, since the light absorption function and the recording function are separated, the film thickness of the organic material layer can be made thinner than before.
In addition, since the organic material layer can be made thinner, it is possible to use a substrate with a shallow groove depth with excellent transferability (formability), which greatly improves the signal quality of write-once optical recording media. In addition to the improvement, the substrate can be manufactured (molded) easily and at a lower cost than the conventional one.
[0019]
Furthermore, since the light absorption layer of the present invention can use a material whose refractive index shows normal dispersion, the organic material layer has a main absorption band of the organic material sufficiently longer than the recording / reproducing wavelength. In the vicinity of a large absorption band, the refractive index exhibits anomalous dispersion and the refractive index varies greatly depending on the wavelength. The rate shows normal dispersion and shows a gradual change with respect to the wavelength), recording sensitivity, modulation degree, jitter, error rate, etc., with respect to fluctuations in the recording / reproducing wavelength due to individual differences in the laser, changes in the environmental temperature, etc. The conventional problem that the recording characteristics, reflectivity, etc. change greatly can be solved.
In the expression “an organic material layer that does not have an absorption function with respect to light of a recording / reproducing wavelength” used in the present invention, “not having an absorption function” means that the organic material layer alone has an organic layer. It means that the temperature does not change the state of the material itself (that is, it means that the material does not substantially perform the absorption function necessary for 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.
[0020]
Further, as described above, the present invention utilizes the recording principle that increases the absorption on the shorter wavelength side than the main absorption band of the organic material, so there is no limitation on the range of the recording / reproducing wavelength, and from the red region. The present invention can be applied to a write-once type optical recording medium corresponding to a wide range of recording / reproducing wavelengths up to the blue region and further to a region having a shorter wavelength than the blue region.
Then, by selecting organic materials containing molecules and molecular groups that have an appropriate absorption band according to the laser wavelength used for recording / reproduction of the target medium, a medium that supports a wide range of recording / reproduction wavelengths can be created. can do.
However, for the following reasons (1) to (3), the recording / reproducing wavelength range to which the present invention is applied is preferably 500 nm or less (currently, about 350 to 500 nm in view of the wavelength of available laser light. Is).
(1) In the wavelength region exceeding 500 nm, since the molecular skeleton becomes large, there are many dye materials having excellent decomposition characteristics.
(2) The absorption wavelength of molecules and molecular groups generated by the decomposition of the dye should be approximately 500 nm or less.
(3) The absorption coefficient (and refractive index) of SiC, Si, or Ge used in the light absorption layer decreases as the wavelength increases (in the red laser region, SiC, Si, or Ge functions sufficiently as the light absorption layer). Disappear).
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 shows an example of a layer structure for realizing a write-once type optical recording medium corresponding to a blue laser wavelength, and has a structure in which a deformation suppression layer, an organic material layer, and a light absorption layer are sequentially provided on a substrate.
Due to the presence of the deformation suppression layer, the heat of the light absorption layer can be transmitted to the substrate and the substrate can be prevented from being greatly deformed. For the deformation suppression layer, it is preferable to use a material that hardly absorbs at a recording / reproducing wavelength and has a high hardness.
In this structure, normal recording / reproduction is performed from the substrate side, the light absorption layer is heated by laser light irradiation from the substrate side, and this heat induces a state change of the organic material, thereby increasing the absorption coefficient at the recording / reproduction wavelength. To record.
[0022]
FIG. 3 shows another example of a layer structure that realizes a write-once type optical recording medium corresponding to a blue laser wavelength. A deformation suppressing layer, a light absorbing layer, an organic material layer, and a cover layer are sequentially provided on a substrate. It has a structure.
Due to the presence of the deformation suppression layer, it is possible to suppress the heat of the light absorption layer from being transferred to the substrate and greatly deforming the substrate. It is preferable to use a material having high hardness for the deformation suppressing layer.
In this structure, normal recording / reproduction is performed from the cover layer side, the light absorption layer is heated by laser light irradiation from the cover layer side, and this heat induces a change in the state of the organic material, resulting in an absorption coefficient at the recording / reproduction wavelength. Increase and record.
In both cases of FIGS. 2 and 3, a light absorbing layer and an organic material layer are used in order to improve the reflectivity when not recorded, reduce the load on the recording / reproducing apparatus, and improve the recording / reproducing characteristics. It is preferable to increase the difference in refractive index (normally 0.5 or more).
In the organic material of the present invention, since the main absorption band is located on the long wavelength side of the recording / reproducing wavelength, the refractive index of the organic material at the recording / reproducing wavelength is small. Therefore, it is preferable to make the refractive index of the light absorption layer larger than that of the organic material layer.
[0023]
The principle of recording information on the optical recording medium of the present invention as shown in FIG. 2 or FIG. 3 will be described as follows.
For example, when a laser having a wavelength of 350 to 500 nm is used as the light source and the optical recording medium is irradiated with a power of about 5 to 15 mW, the light absorption layer absorbs light, raises the temperature, and releases heat.
This heat is transferred to the organic material layer and induces a state change of the organic material. Due to this change in state, the organic material is divided into individual molecules and molecular groups constituting the organic material, and the intensity of absorption bands of these individual molecules and molecular groups is increased.
The recorded pits formed by increasing the intensity of the absorption bands of these individual molecules and molecular groups produce a large difference in reflectance from the unrecorded part, so they can be clearly detected by irradiating with a reproduction laser. It becomes possible.
In addition, in order to prevent the deformation of the substrate due to the heat of the light absorption layer and increase in crosstalk, and to efficiently generate the degree of modulation due to the increase in the absorption coefficient accompanying the change in the state of the organic material, the substrate is formed on the substrate. A deformation suppressing layer for suppressing deformation is provided. This deformation suppression layer can also function as an interference layer (a layer for optimizing interference) for optimizing the reflectance and the modulation factor when not recorded.
[0024]
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.
[0025]
For the light absorption layer, a material having a large refractive index difference from the organic material layer (usually 0.5 or more) and a relatively low thermal conductivity compared to Ag or Au is suitable.
A large refractive index difference from the organic material layer is effective for increasing the reflectivity and improving the quality of the recording / reproducing signal (it is preferable that the light absorption layer can also be used as the light reflection layer). Also, having a relatively low thermal conductivity as compared with Ag and Au is necessary for changing the state of the organic material efficiently (with low recording power).
Furthermore, in order to cause a change in the state of the organic material with low recording power, it is preferable to use a material having a large absorption coefficient at the recording wavelength (preferably 0.2 or more) as the material of the light absorption layer.
From the above points, it is preferable to use a material containing Si and / or Ge for the light absorption layer. Specific examples thereof include, for example, Si, Ge, Si_xGe_1-x, Mg₂Ge, Mg₂Si, SiC, etc. are mentioned.
A preferable film thickness range of the light absorption layer is 5 to 50 nm.
[0026]
For the deformation suppressing layer, it is preferable to use a material having a relatively small refractive index difference from the organic material layer and a high hardness and a small absorption coefficient with respect to the recording / reproducing wavelength.
Moreover, it is preferable to set a film thickness sufficient to suppress the deformation of the substrate.
High hardness and a small absorption coefficient at the recording / reproducing wavelength are necessary to suppress substrate deformation. A relatively small refractive index difference from the organic material layer may cause deformation of the substrate, etc. Even when a deformation occurs at the interface between the layer or the deformation suppressing layer and the organic material layer, the deformation is hardly detected optically, which is effective for improving the quality of the recording / reproducing signal.
However, this is not the case when the substrate deformation is small enough not to affect recording / reproduction, or when the recording polarity due to substrate deformation is the same as the recording polarity due to the state change of the organic material. The difference in refractive index can be increased.
In addition, when recording / reproduction is performed from the cover layer side and the deformation suppression layer is present on the back side of the light absorption layer with respect to the incident laser light, the refractive index of the deformation suppression layer is not limited.
[0027]
Considering the above points, the material of the deformation suppression layer is Al.₂O₃, MgO, BeO, ZrO₂, UO₂, ThO₂Simple oxide based oxides such as SiO₂2MgO · SiO₂, MgO / SiO₂, CaO · SiO₂, ZrO₂・ SiO₂3Al₂O₃・ 2SiO₂2MgO · 2Al₂O₃・ 5SiO₂, Li₂O ・ Al₂O₃・ 4SiO₂Silicate oxides such as Al₂TiO₅, MgAl₂O₄, Ca₁₀(PO₄)₆(OH)₂, BaTiO₃LiNbO₃, PZT [Pb (Zr, Ti) O₃], PLZT [(Pb, La) (Zr, Ti) O₃], Double oxide oxides such as ferrite; Si₃N₄, Si_6-ZAl_ZO_ZN_8-ZNon-oxides of nitrides such as AlN, BN, TiN; SiC, B₄Non-oxides of carbides such as C, TiC and WC; LaB₆TiB₂, ZrB₂Non-oxides of borides such as CdS, MoS₂Sulfide non-oxide such as MoSi₂Non-oxides of silicides such as ZnS / SiO₂SiO₂And a mixture with a material other than an oxide containing as a main component; carbon-based non-oxides such as amorphous carbon, graphite, and diamond.
Among them, SiO₂And ZnS / SiO₂SiO₂A material containing is preferred. “Contained” here means to occupy 10 mol% or more of the entire material.
The thickness of the deformation suppression layer is preferably 20 to 2000 mm.
[0028]
As a material used for the organic material layer, for example, a dye is preferable.
The dyes include polymethine, naphthalocyanine, phthalocyanine, squarylium, croconium, pyrylium, naphthoquinone, anthraquinone (indanthrene), xanthene, triphenylmethane, azulene, tetrahydrocholine, phenanthrene And triphenothiazine dyes, and metal complex compounds.
For example, a cyanine dye represented by the following general formula [Chemical Formula 1], which is known to have a decomposition behavior in which the methine chain that bonds the left and right heterocycles is cleaved and tarized by heat and the left and right heterocycles remain, is suitable for the present invention This is an example of a pigment.
[0029]
[Chemical 1]

[0030]
However, among the above cyanine dyes, counter ions (Z in the general formula [Chemical Formula 1]⁻) Is ClO₄ ⁻Is particularly preferred because of its good decomposition characteristics. This is because this dye has a thermal decomposition characteristic that causes obvious decomposition as shown in FIG. 4 (the solid line represents the weight loss rate, and the broken line represents the result of DTA (differential thermal analysis)) (the start of weight loss). This corresponds to a case where a large exothermic reaction is exhibited near the temperature).
On the other hand, the counter ion is BF₄ ⁻And I⁻This is because the cyanine dye as shown in FIGS. 5 and 6 (the solid line represents the weight loss rate and the broken line represents the result of DTA (differential thermal analysis)) has a thermal decomposition characteristic that does not cause obvious decomposition ( In the vicinity of the weight loss starting temperature, when the exotherm is small or the reaction is endothermic, it corresponds to the case where the weight loss rate is extremely high).
In addition, the left and right heterocycles in the general formula [Chemical Formula 1] are preferably molecules / molecular groups each having an absorption peak at 300 nm or more.
Thereby, an increase in the absorption coefficient at the time of decomposition can be detected largely in the blue region.
[0031]
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 pigment or the like may be dissolved in an organic solvent and applied 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; and 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.
The film thickness of the dye layer is 100 to 10 μm, preferably 100 to 2000 mm.
[0032]
The cover layer is necessary when using a lens with a high NA in order to increase the density.
For example, when the NA is increased, it is necessary to reduce the thickness of the portion through which the reproduction light is transmitted. This is due to the angle at which the disk surface deviates from the optical axis of the optical pickup as the NA increases (so-called tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens). This is because the allowable amount of generated aberration is reduced, and this tilt angle is easily affected by the aberration due to the thickness of the substrate.
Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.
Therefore, for example, an unevenness is formed on the substrate to form a recording layer, a reflective film is provided thereon, and a light-transmitting cover layer, which is a thin film that transmits light, is further provided on the recording layer. An optical recording medium that reproduces information on the recording layer by irradiating the reproducing light, or a reflective film on the substrate, and a recording film is formed thereon to form a recording layer, which is further light transmissive. There has been proposed an optical recording medium in which a cover layer is provided and information on the recording layer is reproduced by irradiating the reproducing light from the cover layer side.
In this way, the NA of the objective lens can be increased by reducing the thickness of the cover layer. That is, it is possible to further increase the recording density by providing a thin cover layer and recording / reproducing from the cover layer side.
Such a cover layer is generally formed of a polycarbonate sheet or an ultraviolet curable resin.
[0033]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.
[0034]
Example 1
On a polycarbonate substrate having a guide groove with a groove depth of 50 nm, a ZnS · SiO film with a thickness of 100 nm is formed by sputtering.₂(Deformation suppression layer.₂And an organic material layer having a thickness of about 60 nm made of a dye represented by the following general formula [Chemical Formula 2] is formed thereon by spin coating, and a thickness of 10 nm is further formed thereon. A write-once optical recording medium was prepared by providing Si (light absorption layer).
The complex refractive index of the following [Chemical Formula 2] dye at 405 nm is 1.407-i0.076, which is significantly higher than the complex refractive index required for organic materials used in conventional write-once optical recording media. The complex refractive index is inferior (for example, the complex refractive index in the vicinity of the recording / reproducing wavelength of the dye used in DVD-R is about 2.5-i0.10).
[0035]
[Chemical 2]

[0036]
As a result of recording on the optical recording medium under the following conditions using an optical disk evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd., the result is very clear. A signal was obtained, and jitter (σ / Tw) = 10.2 (%) was obtained.

Further, the light absorbing layer of the optical recording medium was peeled off, and the dyes in the recorded part and the unrecorded part were dissolved in ethanol, and the respective spectra were measured.
As a result, as shown in FIG. 11, a clear increase in absorption (absorption coefficient) was observed in the recorded portion (since recording was performed only in the groove portion, a large amount of unrecorded portion components were recorded in the recorded portion spectrum. The recording principle of the optical recording medium of the present invention was confirmed.
[0037]
Comparative Example 1
On a polycarbonate substrate having a guide groove having a groove depth of 150 nm, an organic material layer having a thickness of about 120 nm made of a dye represented by the following [Chemical Formula 3] is formed by a spin coating method, and Ag reflection having a thickness of 150 nm is formed thereon. A write-once type optical recording medium was prepared by providing a layer (an example in which the conventional layer structure was applied to the blue region).
The complex refractive index of the dye of the general formula [Chemical Formula 3] at 405 nm is 2.285-i0.069, which is a comparison with the complex refractive index required for the organic material used for the conventional write-once type optical recording medium. Have a complex refractive index close to the target (for example, the complex refractive index in the vicinity of the recording / reproducing wavelength of the dye used in DVD-R is about 2.5-i0.10.
Degrees).
[0038]
[Chemical Formula 3]

[0039]
Using the optical disk evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd., recording was performed on the above optical recording medium under the following conditions. Although a large degree of modulation was obtained, a sufficient signal could not be obtained with a short mark, and it was a noisy signal regardless of the mark length, and jitter (σ / Tw) could not be measured.

[0040]
Comparative Example 2
Instead of the polycarbonate substrate having a guide groove with a groove depth of 150 nm in Comparative Example 1, a polycarbonate substrate having the same guide groove with a groove depth of 50 nm as in Example 1 was used. A write-once type optical recording medium was prepared by forming an organic material layer made of a dye represented by the above by a spin coating method and providing an Ag reflective layer having a thickness of 150 nm thereon, and recording was performed in the same manner as in Comparative Example 1. , Could not record at all.
[0041]
As described above, from Example 1 of the present invention and Comparative Examples 1 and 2, the layer structure and recording principle of the write-once optical recording medium of the present invention are extremely suitable for realizing a write-once optical recording medium made of an organic material corresponding to the blue laser wavelength. It was confirmed that it was effective.
Further, in a write-once type 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 was confirmed that a substrate having a very shallow groove of 50 nm can be applied.
[0042]
Example 2
In the same manner as in Example 1, a write-once type optical recording medium having a cyanine dye described in [Table 1] below as an organic material layer was produced, and recording was performed under the same recording conditions as in Example 1. Was judged.
The criterion for determination was a level at which jitter (σ / Tw) could be measured, and “C” was assigned to cyanine dyes that were 15% or less, and “X” was assigned to cyanine dyes that were not.
Table 1 shows the types of decomposition behavior (weight loss rate, heat generation / endotherm) in thermogravimetric analysis of each cyanine dye.
Regarding the type of weight loss rate, the magnitude of weight loss is indicated by symbols S, M, and L, and S <M <L in order from the smallest weight loss.
The exothermic / endothermic type indicates the state of heat generation or endotherm at the time of decomposition, that is, when the main weight loss process occurs. “+” For heat generation, “-” for heat absorption, and heat generation When little endotherm was observed, it was marked “0”.
The main weight loss process refers to a process showing the largest weight loss when there are a plurality of temperatures (processes) at which the weight loss rate decreases. For example, in FIGS. It is a decreasing part.
From the results in Table 1, there is a clear correlation between the type of weight loss rate and the type of heat generation / endotherm and the type of counter ion, and the same applies to the type of weight loss rate and the type of heat generation / endotherm and jitter (σ / Tw). You can see that there is a correlation.
That is, the counter ion is ClO₄ ⁻In the case of the cyanine dye, the weight loss rate in the main weight loss process is relatively small and indicates an exothermic reaction, so in this main weight loss process, weight loss due to decomposition is occurring, not simply weight loss due to sublimation, It can be seen that the more this decomposition occurs, the better the jitter (σ / Tw).
[0043]
[Table 1]

[0044]
Example 3
The complex refractive index (refractive index n and absorption coefficient k) of the dye represented by the following [Chemical Formula 4] that can be used in a conventional DVD-R, can be used in the present invention, and can also be used in a conventional DVD-R. The complex refractive index of the dye (NK4382) and the complex refractive index of Si were measured.
The complex refractive index of the dye represented by the following [Chemical Formula 4] is shown in FIG. 12, the complex refractive index of the dye (NK4382) is shown in FIG. 13, and the complex refractive index of Si is shown in FIG.
From these results, when the conventional recording method in which the recording / reproducing wavelength is positioned on the long wavelength side of the absorption band of the organic material is applied to the conventional organic (recording) material, the fluctuation of the recording / reproducing wavelength is On the other hand, it was confirmed that the refractive index n and the absorption coefficient k fluctuate greatly.
On the other hand, the present invention is a recording method in which the recording / reproducing wavelength is positioned sufficiently shorter than the absorption band of the organic material relative to the conventional organic (recording) material. It was confirmed that the absorption coefficient k hardly fluctuated.
It was also confirmed that Si used as the light absorption layer did not vary greatly in refractive index n or absorption coefficient k with respect to fluctuations in the recording / reproducing wavelength.
[0045]
[Formula 4]

[0046]
According to the above embodiment, the write-once type optical recording medium has little change in recording characteristics such as recording sensitivity, modulation degree, jitter, error rate, and reflectivity with respect to fluctuations in the recording / reproducing wavelength by the layer structure of the present invention. It was confirmed that can be realized.
[0047]
【The invention's effect】
According to the first to third aspects of the present invention, it is possible to use a shallow groove substrate that can cope with a blue laser wavelength region of about 350 to 500 nm and has good transferability. In addition, a write-once type optical recording medium that has a small change in recording characteristics such as error rate, reflectance, and the like and can achieve high density can be provided easily and inexpensively.
According to the present invention 4 to 8, it is possible to further improve the recording / reproducing characteristics.
According to the ninth aspect of the present invention, the functions of the respective layers of the write-once optical recording media of the first to eighth aspects of the present invention can be utilized to the maximum extent.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a layer structure of a conventional write-once type optical recording medium.
FIG. 2 is a diagram for explaining a layer configuration example of a write-once type optical recording medium of the present invention.
FIG. 3 is a diagram for explaining another example of the layer structure of the write-once type optical recording medium of the present invention.
FIG. 4 is a diagram for explaining an example of a thermal decomposition characteristic preferable as an organic material used in the write-once type optical recording medium of the present invention.
FIG. 5 is a diagram for explaining an example of a thermal decomposition characteristic which is not preferable as an organic material used in the write-once type optical recording medium of the present invention.
FIG. 6 is a diagram for explaining another example of thermal decomposition characteristics that are not preferable as an organic material used in the write-once type optical recording medium of the present invention.
FIG. 7 is a diagram for explaining the recording principle of a conventional write-once type optical recording medium.
FIG. 8 is a diagram for explaining the recording principle of the write-once type optical recording medium of the present invention.
FIG. 9 is a diagram for explaining the characteristics of an organic material used in the write-once type optical recording medium of the present invention.
FIG. 10 is a diagram for explaining the characteristics of an organic material used in the write-once type optical recording medium of the present invention.
11 is a graph showing changes in absorption coefficient before and after recording of the dye used in Example 1. FIG.
12 is a diagram showing a change in complex refractive index in the recording / reproducing wavelength region of the dye used in Example 3. FIG.
FIG. 13 is a diagram showing a change in complex refractive index of a dye (NK4382) in a recording / reproducing wavelength region.
FIG. 14 is a diagram showing a change in complex refractive index of Si used in the present invention.
[Explanation of symbols]
1 Substrate
2 Deformation suppression layer
3 Organic material layer
4 Light absorption layer
5 Cover layer
6 Reflective layer
λ₁  Recording / reproducing wavelength
λ₂  Main absorption band of organic compounds
A Intrinsic absorption wavelength of molecules and molecular groups
B Unique absorption wavelength of molecules and molecular groups
C Absorption spectrum in which the intrinsic absorption band of each molecule or molecular group disappeared or was attenuated
n Real part of complex refractive index
k Imaginary part of complex refractive index (absorption coefficient)

Claims (9)

On the substrate, at least a deformation suppression layer that suppresses deformation of the substrate, a main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength, and has an absorption function for light of the recording / reproducing wavelength. A write-once optical recording medium having a structure in which an organic material layer and a light absorption layer that are not stacked are sequentially laminated. On the substrate, at least a deformation suppressing layer that suppresses deformation of the substrate, a light absorption layer, a main absorption band at the time of unrecording exist on the long wavelength side with respect to the recording / reproducing wavelength, and for light of the recording / reproducing wavelength A write-once type optical recording medium having a structure in which an organic material layer having no absorption function and a cover layer are sequentially laminated, and recording / reproduction is performed from the cover layer side. 3. The write-once light according to claim 1, wherein the organic material layer is made of an organic material that changes its state due to heat generated by the light absorption function of the light absorption layer and increases an absorption coefficient at a recording / reproducing wavelength. recoding media. 4. The write-once type optical recording medium according to claim 1, wherein n2> n1, where n1 is a refractive index of the organic material layer and n2 is a refractive index of the light absorption layer. The write-once type optical recording medium according to claim 1, wherein the deformation suppressing layer is made of a material containing SiO ₂ . The write-once type optical recording medium according to claim 1, wherein the light absorption layer is made of a material containing Si and / or Ge. The write-once type optical recording medium according to any one of claims 1 to 6, wherein the organic material layer is made of an organic material that exhibits an exothermic reaction in a main weight loss process in thermal decomposition characteristics. The write-once type optical recording medium according to claim 1, wherein the organic material layer comprises a cyanine dye whose counter ion is ClO ₄ ^— . 9. The write-once type optical recording medium according to claim 1, wherein recording / reproduction is possible in a laser wavelength range of 350 to 500 nm.

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