JP3645288B2 - Recording medium and recording method - Google Patents

Description

【００２０】
【化２】

【００２１】
【化３】

【００２２】
【化４】

【００２３】
上記一般式中、Ｂで示される色素骨格は同じものであっても、異なるものであってもよく、それぞれ用途に応じて適宜選択すればよい。色素骨格としては、例えば下記（Ｂ−１）〜（Ｂ−７９）などを挙げることができるが、特にこれらに限定されない。
【００２４】
【化５】

【００２５】
【化６】

【００２６】
【化７】

【００２７】
【化８】

【００２８】
【化９】

【００２９】
【化１０】

【００３０】
【化１１】

【００３１】
【化１２】

【００３２】
【化１３】

【００３３】
【化１４】

【００３４】
【化１５】

【００３５】
なお、これらの色素骨格は、適当な置換基でさらに置換されていてもよい。特に、水素結合性の置換基、例えば水酸基、カルボキシル基、アミド基、アミノ基、ウレタン基、または尿素基を導入した場合には、ドメイン構造においてＴｇが上昇しアモルファス状態がより安定化される。
上記一般式中、Ｘで示される連結基としては、例えば下記のようなものが挙げられる。
【００３６】
【化１６】

【００３９】
次に、本発明の記録媒体に対する書き込み、読み出しおよび消去の原理と、これらの動作を制御性よく実現するために記録媒体が満たすべき条件について説明する。
【００４０】
いま、電圧が印加された探針を記録層を構成する所定のドメインに接触させると、そのドメインに電荷が注入されて記録がなされる。このとき、下地導体層にイメージ電荷が誘起されて局所的にコンデンサが形成される。このコンデンサの容量Ｃ（Ｆ）は、ドメインの面積すなわちドメインと絶縁層との接触面積をＳ（ｎｍ² ）、ドメイン構造と下地導体層との間に存在する絶縁層の厚みをｄ（ｎｍ）、絶縁層の比誘電率をεとすると、
Ｃ＝８．８×１０^-21 ×εＳ／ｄ （２）
と表される。このとき注入された電荷の個数をｎとすると、静電エネルギーＥ_el（ｅＶ）は、
Ｅ_el＝１．６×１０^-19 ×ｎ² ／２Ｃ （３）
と表される。したがって、電荷の個数に応じて記録状態を設定するためには、注入された電荷数に対応する静電エネルギーの差が熱エネルギーよりも大きいことが必要となる。このための条件は、
１．６×１０^-19 ×１／２Ｃ≧０．０２６ （４）
と表される。この（４）式が、室温においてドメインへの電荷の注入すなわち書き込みを行い、かつ安定に電荷を蓄積するための条件となる。
【００４１】
次に、直流電圧または交流電圧が印加された探針をドメインと非接触な状態で走査してドメインに注入された電荷を、例えば探針−ドメイン間に働く静電力の大きさとして検出する。この場合、ドメインに注入された電荷数に対応する静電力の値が検出可能な大きさであることが重要になる。静電力の大きさＦ_elは、ドメインの表面電位をＶ_s （ｖｏｌｔｓ）、下地導体層に対する探針の電位をＶ（ｖｏｌｔｓ）としたとき、
Ｆ_el＝−Ａ（Ｖ−Ｖ_s ）² （５）
と表される。ここでＡは、探針のチップ先端の曲率半径、チップ−ドメイン間の距離、ドメイン構造をなす記録層を構成する材料の誘電率、および絶縁層の誘電率に依存した定数である。また、電荷が注入されたドメインでは、次式
ΔＶ＝１．６×１０^-19 ×ｎ／Ｃ （６）
で表されるΔＶ（ｖｏｌｔｓ）だけ表面電位がシフトする。
【００４２】
（５）式から明らかなように、この表面電位のシフトにより静電力の大きさが変化する。この表面電位のシフトまたはそれに起因した静電力の変化は、以下のようにして検出できる。例えば、探針電位を一定に保ったまま、探針を記録層表面から少し離して二次元的に走査することにより、直接的に静電力変化を検出することができる。また、探針に次式で表される周波数ωの交流電圧を印加した場合を考える。
【００４３】
Ｖ＝Ｖ₀ ＋Ｖ₁ ｓｉｎωｔ （７）
このとき、静電力Ｆ_elは次のように表される。

したがって、ロックインアンプを用いてω成分を検波することにより、電位シフトΔＶの大きさを求めることができる。あるいは、ω成分を検波し、ω成分がゼロとなるような直流電圧Ｖ₀ を探針に印加し、そのＶ₀ の値からΔＶの値を求めることも可能である。なおこの場合、表面電位の分解能は０．４ｍＶ程度と考えられており（横山ら、Ｍｏｌｅｃｕｌａｒ Ｅｌｅｃｔｒｏｎｉｃｓ ａｎｄ Ｂｉｏｅｌｅｃｔｒｏｎｉｃｓ，ｖｏｌ．３，Ｎｏ．２，ｐ．７９（１９９２））、極めて小さな表面電位の変化まで検出できる。いま、この分解能を１ｍＶとしたとき、電荷として単一の電子または正孔を検出するための条件は、
１．６×１０^-19 ×１／Ｃ≧０．００１ （９）
と表される。
【００４４】
本発明では、（４）式を満足すれば（９）式も満足することは明らかである。さらに（２）式を（４）式に代入すれば（１）式が得られる。すなわち、（１）式で表される条件を満たす記録媒体では、単一の電子・正孔を制御性よくドメインに注入でき、しかもドメインに注入された単一の電子・正孔を容易に検出できるので、注入された電荷の個数に応じた各記録状態を設定して多値記録などを行うことも可能となる。
【００４５】
なお、記録層を構成する材料としてドナー性分子を用いた場合には、正孔のみが注入され、正孔の個数を記録状態として用いる。一方、アクセプター性分子を用いた場合には、電子のみが注入され、電子の個数を記録状態として用いる。また、金属または半導体を用いた場合には、電子も正孔も注入されるので上記のような極性はなく、接触時の探針電位が正の場合に正孔の個数を、負の場合に電子の個数を記録状態として用いる。さらに本発明においては記録層の記録密度を高めるうえでＳ（ｎｍ² ）を１００００以下に設定することが好ましい。
【００４６】
【実施例】
以下、本発明の実施例を図面を参照して説明する。
実施例１
図１は本実施例において作製された記録媒体の断面図である。まず、下地導体層としての抵抗率１Ω・ｃｍのｐ型Ｓｉ基板１の表面に、熱酸化法により厚さ２０ｎｍのＳｉＯ₂ 膜２からなる絶縁層を形成した。次いで基板裏面のＳｉＯ₂ 膜を除去した後、基板裏面に厚さ２．５ｎｍのＣｒおよび厚さ５０ｎｍのＡｕを順次蒸着して下地電極３を形成した。その後、熱処理を施し、さらにヘキサメチルジシラザンの飽和蒸気圧下に約３日間放置し、基板表面のＳｉＯ₂ 膜２を疎水化した。
【００４７】
次に、このようにして形成されたＳｉ基板１表面のＳｉＯ₂ 膜２上に、ドナー性分子である１，１−ビス（Ｎ，Ｎ−ジトリルアミノフェニル）シクロヘキサン（以下、ジアミンと称する）を蒸着してドメイン構造をなす記録層４を形成した。ジアミンの分子構造を下記「化１７」に示す。このときの蒸着条件は、真空度１．３×１０^-4Ｐａ、基板温度２０℃、クヌーセンセルの加熱温度１８０℃であった。なおＳｉ基板の近傍に設置した水晶振動子によりジアミンの蒸着速度をモニターしたところ０．０２ｎｍ／ｓｅｃであった。本実施例においては、蒸着時間を約５０秒に設定して、厚さ１．０ｎｍに相当するジアミンを形成した。形成されたジアミンからなる記録層４の構造をＳＥＭで観察したところ、直径３２ｎｍ、高さ７ｎｍの液滴状のドメインが２．４×１０¹⁴ｍ^-2の密度で存在することが確認された。得られた記録媒体に関しては、ＳｉＯ₂ の比誘電率εが３．９であるので、ｄ／（Ｓε）の値は６．３８×１０^-3である。
【００４８】
【化１７】

【００４９】
一方、ＡＦＭ探針として、バネ定数０．５８Ｎ／ｍのＳｉＮ製のカンチレバー本体１１のチップ側の表面に、厚さ２ｎｍのＣｒおよび厚さ２０ｎｍのＡｕを順次蒸着して電極１２を形成したものを用意した。このカンチレバー先端のチップの曲率半径は１０ｎｍである。
【００５０】
次いで、得られた記録媒体に対して以下のようにして書き込みおよび読み出しを行った。まず、ＡＦＭ探針の電極１２にＶ_tip という電圧を印加した状態で、記録層を構成するジアミンドメインに約１秒間接触させ、探針からドメインへ電荷を注入して書き込みを行った後、ＡＦＭ探針とジアミンドメインとを引き離す。その後、ＡＦＭ探針とジアミンドメインとの距離を約１０ｎｍに保って、ＡＦＭ探針に交流電圧を印加し、静電力の電圧依存性から表面電位を評価することにより読み出しを行う。Ｖ_tip の値を０Ｖから徐々に増加させながら、この操作をくり返し行った。同一のドメインについて、接触時のＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を図２に示す。
【００５１】
この図からわかるように、表面電位Ｖ_s はＶ_tip が正の極性領域で階段状の変化を示す。すなわち、Ｖ_tip が０〜１．１Ｖの範囲ではＶ_s は０Ｖであるが、Ｖ_tip が１．１ＶのときＶ_s は不連続に増加して０．１１Ｖとなる。その後、Ｖ_tip が１．１〜２．２Ｖの範囲ではＶ_s は０．１１Ｖのまま変化せず、Ｖ_tip が２．２ＶでＶ_s は再度０．１１Ｖだけ不連続に増加して０．２２Ｖとなる。このようにＶ_tip が＋１．１Ｖだけ変化するごとに、Ｖ_s の不連続な増加とプラトー領域が周期的に現れた。なお、Ｖ_tip が負の極性領域では表面電位に変化は見られなかった。（６）式から、＋０．１１ＶというＶ_s の飛び（ΔＶ）は、ちょうど電荷（この場合ΔＶが正であるので正孔）１個分の変化に相当し、正孔１個がドメインに注入されたことによる表面電位の変化が検出されたことがわかる。
【００５２】
実施例２
実施例１とほぼ同様な方法を用いたが、蒸着時間を２５秒に設定し、厚さ０．５ｎｍに相当するジアミンを形成した。形成されたジアミンからなる記録層の構造をＳＥＭで観察したところ、直径１６ｎｍ、高さ４ｎｍの液滴状のドメインが３．５×１０¹⁴ｍ^-2の密度で存在することが確認された。得られた記録媒体に関しては、ｄ／（Ｓε）の値は２．５５×１０^-2である。
【００５３】
次いで、得られた記録媒体に対して実施例１と同様にして書き込みおよび読み出しを行った。このときの接触時のＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を図３に示す。この場合も表面電位Ｖ_s はＶ_tip が正の極性領域で階段状の変化を示すが、Ｖ_tip が＋４．５Ｖだけ変化するごとに、＋４５０ｍＶのＶ_s の飛びを示した。この場合も（６）式から、＋４５０ｍＶというΔＶの値は、正孔１個がドメインに注入されたことによる表面電位の変化に対応していることがわかる。
【００５４】
比較例
実施例１とほぼ同様な方法を用いたが、蒸着時間を１０００秒に設定し、厚さ２０ｎｍに相当するジアミンを形成した。形成されたジアミンからなる記録層の構造をＳＥＭで観察したところ、直径２２０ｎｍ、高さ７５ｎｍの液滴状のドメインが１．２×１０¹³ｍ^-2の密度で存在することが確認された。得られた記録媒体に関しては、ｄ／（Ｓε）の値は１．３５×１０^-4である。
【００５５】
次いで、得られた記録媒体に対して実施例１と同様にして書き込みおよび読み出しを行った。このときの接触時のＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を図４に示す。この場合、表面電位Ｖ_s はＶ_tip に対して連続的な変化を示し、階段状の変化は認められなかった。このように、この実施例では、正孔１個がドメインに注入されたことによる表面電位の変化は検出できなかった。
【００５６】
実施例３
記録層材料としてアクセプター性分子である下記「化１８」に示すＤＮＩＢＰＣを用い、図１と同様な構造の記録媒体を作製した。実施例１と同様に、Ｓｉ基板１の表面にＳｉＯ₂ 膜２を、裏面に下地電極３をそれぞれ形成し、ＳｉＯ₂ 膜２を疎水化処理した。次に、Ｓｉ基板１表面のＳｉＯ₂ 膜２上に、ＤＮＩＢＰＣを蒸着してドメイン構造をなす記録層４を形成した。このときの蒸着条件は、真空度１．３×１０^-4Ｐａ、基板温度２０℃、クヌーセンセルの加熱温度２２０℃であった。また、Ｓｉ基板の近傍に設置した水晶振動子によりＤＮＩＢＰＣの蒸着速度をモニターしたところ、０．０２ｎｍ／ｓｅｃであった。本実施例においては、蒸着時間を約１２５秒に設定して、厚さ２．５ｎｍに相当するＤＮＩＢＰＣを形成した。形成されたＤＮＩＢＰＣからなる記録層４の構造をＳＥＭで観察したところ、直径４０ｎｍ、高さ１０ｎｍの液滴状のドメインが２．０×１０¹⁴ｍ^-2の密度で存在することが確認された。得られた記録媒体に関しては、ｄ／（Ｓε）の値は４．０７×１０^-3である。
【００５７】
【化１８】

【００５８】
次いで、得られた記録媒体に対して実施例１と同様にして書き込みおよび読み出しを行った。このときの接触時のＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を図５に示す。この場合実施例１と逆に、表面電位Ｖ_s はＶ_tip が負の極性領域で階段状の変化を示した。すなわち、Ｖ_tip が０〜−０．７２Ｖの範囲ではＶ_s は０Ｖであるが、Ｖ_tip が−０．７２ＶのときＶ_s は不連続に減少して−７２ｍＶとなる。その後、Ｖ_tip が−０．７２〜−１．４４Ｖの範囲ではＶ_s は−７２ｍＶのまま変化せず、Ｖ_tip が−１．４４ＶでＶ_s は再度−７２ｍＶだけ不連続に変化して−１４４ｍＶとなる。このようにＶ_tip が−０．７２Ｖだけ変化するごとに、Ｖ_s の不連続な減少とプラトー領域が周期的に現れた。なお、Ｖ_tip が正の極性領域では表面電位に変化は見られなかった。（６）式から、−７２ｍＶというΔＶの値は、ちょうど電荷（この場合ΔＶが負であるので電子）１個分の変化に相当し、電子１個がドメインに注入されたことによる表面電位の変化が検出されたことがわかる。
【００６１】
【発明の効果】
以上詳述したように本発明によれば、室温においてもドメイン構造を有する記録層に単一の電荷（電子および／または正孔）を制御性よく注入し、かつ注入された電荷を容易に検出でき、注入される電荷の個数に応じた記録状態を設定することが可能で、安定に動作する記録媒体を提供できる。
【図面の簡単な説明】
【図１】本発明に係る記録媒体の断面図。
【図２】本発明の実施例１における記録媒体について、ＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を示す特性図。
【図３】本発明の実施例２における記録媒体について、ＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を示す特性図。
【図４】本発明の比較例における記録媒体について、ＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を示す特性図。
【図５】本発明の実施例３における記録媒体について、ＡＦＭ探針電位Ｖ_tip とドメインの表面電位Ｖ_s との関係を示す特性図。
【符号の説明】
１…Ｓｉ基板、２…ＳｉＯ₂ 膜、３…下地電極、４…記録層、１１…カンチレバー本体、１２…電極。[0001]
[Industrial application fields]
The present invention relates to a recording medium and a recording method for the recording medium.
[0002]
[Prior art]
With the recent development of microfabrication technology, it has become possible to form micro tunnel junctions, and research on single-electron devices using the Coulomb blockade phenomenon caused by the particle nature of electrons has been actively conducted. In order to observe the single electron tunnel phenomenon, the change in electrostatic energy accompanying tunneling of one electron needs to be sufficiently larger than the thermal energy. In order to satisfy this condition, it is necessary to form a junction with a very small junction capacitance. However, a device capable of observing the single electron tunnel effect at room temperature from the limits of the current processing dimensions of semiconductors and metals should be formed. Is extremely difficult. For this reason, most of the single-electron tunneling phenomenon reported so far has been observed under extremely low temperature conditions.
[0003]
Needless to say, when the single electron effect is applied to the device, it is advantageous to operate at room temperature rather than at a very low temperature. Therefore, a report example of the single electron effect observed so far at room temperature will be described.
[0004]
(1) Yano et al. Have reported a memory using polysilicon grains as a channel (K. Yano et al., IEDM Tech. Digest, p. 541 (1993)). They anneal an amorphous silicon thin film to form a channel containing a large number of polysilicon grains having a thickness of 4 nm and a grain size of 10 nm, thereby fabricating a device having a gate length of 100 nm, a gate width of 100 nm, and a gate oxide film thickness of 150 nm. did. In this element, a discontinuous change in threshold voltage is detected as a result of one electron tunneled from the gate electrode to the polysilicon grain being trapped by a grain near the channel. This polysilicon grain has a very small capacity and is suitable for observing the Coulomb blockade phenomenon at room temperature. However, this device has a structure in which a large number of polysilicon grains are present in the channel, and it is uncertain to which grain the gate tunnels electrons from the gate electrode. In addition, since the region where single electrons are injected and the region where current flows are the same channel and are not spatially separated, the conduction channel formed in the polysilicon grain and one electron are trapped. The positional relationship with the grain is also uncertain. As a result, there is a problem that controllability and reproducibility of device characteristics such as a voltage value causing a single electron tunnel effect and a change width of a threshold voltage are lacking.
[0005]
(2) Nejoh et al. Have reported the observation of tunneling current through liquid crystal molecules using a scanning tunneling microscope (STM) probe (H. Nejoh, Nature 353, 640 (1991), Nejo et al., IEICE Technical Report, vol.93, No.524, p.25). They formed an island-shaped metal film on an insulating substrate, dropped liquid crystal molecule droplets on it, and formed a structure in which the liquid crystal molecules were arranged between the islands. A step-like current characteristic is observed by changing the electric potential by bringing the STM probe close to such a structure. In addition, when external electrodes are connected to both ends of the island-shaped metal film and driven at a constant current, it is confirmed that the voltage at both ends of the island-shaped metal film changes periodically by changing the potential of the STM probe. Yes. In this structure, the size of the metal islands, the distance between the islands and the islands, and the size of the liquid crystal molecules are all about 2 nm, and the liquid crystal molecules and the metal islands form a two-dimensional tunnel junction array. The Coulomb blockade observation at room temperature is considered possible. However, the distance between the electrodes at both ends of such a two-dimensional array is on the order of mm, and a large number of tunnel junctions are interposed therebetween. Since it is impossible in principle to control a large number of tunnel junctions with a single STM probe, the controllability of device characteristics is significantly deteriorated. In addition, it is impossible to specify which metal island or liquid crystal molecule the current flows through, and current characteristics are not reproducible.
[0006]
(3) Barrett et al. Have reported a study aimed at ultra-high density recording at the atomic and molecular level using an STM or an atomic force microscope (AFM) probe (J. Appl. Phys. 70). 2725 (1991)). They contact the structure of Si \ SiO ₂ \ SiN with a metal-coated AFM probe in a state where a voltage is applied to tunnel the charge from Si to SiN and write the charge to SiN. Is going. The obtained charge distribution is the smallest, the half width is 75 nm, and the density of charges trapped in SiN is 1.4 × 10 ¹³ cm ⁻² . This is equivalent to about 600 in terms of the number of charges, and the number of charges is on the order larger than in the case of the single electronic device described above. Therefore, in this structure, it is difficult in principle to control the number of charges to be written, and it is considered impossible to operate the element to set the recording state according to the number of charges.
[0007]
(4) In Japanese Patent Laid-Open No. 3-263633, an electric charge is injected into an island-shaped structure such as metal or a grain structure formed on a photoconductor using an STM probe, and this is used for a memory. It has been proposed. However, this proposal does not describe anything about the number of charges to be injected, and it is theoretically difficult to control the number of charges itself.
[0008]
[Problems to be solved by the invention]
As described above, the number of charges in the local region is controlled by the progress of microfabrication technology and the evaluation and operation technology using probes such as STM and AFM. Realization of an element whose operation principle is to be controlled is expected. However, at present, an element that operates at room temperature and has excellent controllability of operation has not been realized.
[0009]
It is an object of the present invention to set a recording state according to the number of injected charges, and to operate on a novel recording principle and recording method based on a novel operating principle that operates stably at room temperature and has excellent controllability Is to provide.
[0010]
[Means and Actions for Solving the Problems]
The recording medium of the present invention includes a base conductor layer, an insulating layer formed on the base conductor layer, and a recording layer made of a material capable of accumulating charges and having a domain structure formed on the insulating layer. It comprises.
[0011]
Here, the fact that the recording layer has a domain structure means that the recording layer is composed of a large number of island-like minute regions which are electrically separated. In the recording medium of the present invention, the thickness of the insulating layer is d (nm), the relative dielectric constant of the insulating layer is ε, and the contact area of each domain constituting the recording layer with the insulating layer is S (nm ² ). ,
d / (Sε) ≧ 2.86 × 10 ⁻³ (1)
It is characterized by satisfying the relationship.
[0012]
In the recording method of the present invention, a probe to which a voltage is applied is brought into contact with a predetermined domain constituting the recording layer of the recording medium according to the present invention, and electric charge is injected into the domain for recording. The probe is scanned in a non-contact state with the domain to detect the electric charge injected into the domain, and the probe to which a voltage having a polarity opposite to that at the time of recording is applied is brought into contact with the predetermined domain and injected into the domain. It is characterized by erasing the generated charges.
[0013]
The probe is equivalent to that used in STM and AFM, and has a shape in which a protrusion (tip) is provided at the tip of a cantilever made of an insulator, for example, Cr, Au on the tip side surface of the cantilever body It has the structure which formed the electrode which consists of conductors.
[0014]
Examples of the base conductor layer constituting the recording medium of the present invention include a substrate made of a semiconductor such as silicon or a metal, but are not particularly limited. In addition, you may form base electrodes, such as Cr and Au, further in the back surface of the base conductor layer which consists of semiconductors. Further, examples of the insulating layer include a silicon oxide film, but are not particularly limited.
[0015]
As the conditions of the material constituting the recording layer constituting the recording medium of the present invention, it is possible to form a domain structure and to have an electron level close to the work function of the electrode material on the probe surface. In other words, electrons or holes are injected from the probe into the electron level with good controllability and charge accumulation is possible.
[0016]
Suitable materials for the recording layer include, for example, organic molecules having a strong donor property or acceptor property. When the recording layer is composed of donor molecules, holes are injected from the probe into the highest occupied molecular orbital (HOMO). When the recording layer is made of an acceptor molecule, electrons are injected from the probe into its lowest unoccupied molecular orbital (LUMO). Here, the donor molecule is preferably a solid crystal or thin film having an ionization potential of 7 eV or less, and the acceptor molecule is preferably a solid crystal or thin film having an electron affinity of 1 eV or more.
[0017]
In order to form a recording layer having a domain structure using such organic molecules, a method of processing with an electron beam or an ion beam after the thin film is formed, or a thin film in a thin film thickness region where a two-dimensional film is not formed in the thin film formation process. A method of stopping growth is used. In particular, in the case of a donor molecule or an acceptor molecule that tends to be in a stable amorphous state, a large number of droplet-shaped domains with a small difference in diameter and height are formed in a film thickness region of several tens of nm or less. A recording layer having a uniform domain structure as a whole suitable for the recording medium of the invention can be obtained.
[0018]
Here, as a donor molecule or an acceptor molecule that is likely to be in a stable amorphous state, the following general formula A- (XB) n is used.
(In the formula, A is an aromatic skeleton or alicyclic skeleton, B is a dye skeleton, and a plurality of dye skeletons may be the same or different, n is an integer of 2 or more, X is a linking group, and a single bond Good.)
The thing represented by is mentioned.
In the above general formula, examples of the aromatic skeleton or alicyclic skeleton represented by A include (A-1) to (A-58) below, but are not particularly limited thereto.
[0019]
[Chemical 1]

[0020]
[Chemical formula 2]

[0021]
[Chemical 3]

[0022]
[Formula 4]

[0023]
In the above general formula, the dye skeletons represented by B may be the same or different, and may be appropriately selected depending on the application. Examples of the dye skeleton include (B-1) to (B-79) below, but are not particularly limited thereto.
[0024]
[Chemical formula 5]

[0025]
[Chemical 6]

[0026]
[Chemical 7]

[0027]
[Chemical 8]

[0028]
[Chemical 9]

[0029]
[Chemical Formula 10]

[0030]
Embedded image

[0031]
Embedded image

[0032]
Embedded image

[0033]
Embedded image

[0034]
Embedded image

[0035]
These dye skeletons may be further substituted with an appropriate substituent. In particular, when a hydrogen bonding substituent such as a hydroxyl group, a carboxyl group, an amide group, an amino group, a urethane group, or a urea group is introduced, Tg increases in the domain structure and the amorphous state is further stabilized.
In the above general formula, examples of the linking group represented by X include the following.
[0036]
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[0039]
Next, the principles of writing, reading and erasing from the recording medium of the present invention and the conditions that the recording medium should satisfy in order to realize these operations with good controllability will be described.
[0040]
Now, when a probe to which a voltage is applied is brought into contact with a predetermined domain constituting the recording layer, charge is injected into that domain and recording is performed. At this time, an image charge is induced in the underlying conductor layer to locally form a capacitor. The capacitance C (F) of this capacitor is the domain area, that is, the contact area between the domain and the insulating layer, S (nm ² ), and the thickness of the insulating layer existing between the domain structure and the underlying conductor layer is d (nm). If the dielectric constant of the insulating layer is ε,
C = 8.8 × 10 ⁻²¹ × εS / d (2)
It is expressed. If the number of charges injected at this time is n, the electrostatic energy E _el (eV) is
E _el = 1.6 × 10 ⁻¹⁹ × n ² / 2C (3)
It is expressed. Therefore, in order to set the recording state according to the number of charges, it is necessary that the difference in electrostatic energy corresponding to the number of injected charges is larger than the thermal energy. The condition for this is
1.6 × 10 ⁻¹⁹ × 1 / 2C ≧ 0.026 (4)
It is expressed. This equation (4) is a condition for injecting charge into the domain, that is, writing at room temperature and stably storing the charge.
[0041]
Next, the probe to which a DC voltage or an AC voltage is applied is scanned in a non-contact state with the domain, and the electric charge injected into the domain is detected as, for example, the magnitude of the electrostatic force acting between the probe and the domain. In this case, it is important that the value of the electrostatic force corresponding to the number of charges injected into the domain has a detectable magnitude. Size F _el of electrostatic force, the surface potential of the domain V _s (volts), when the probe of the potential relative to the underlying conductor layer was V (volts),
F _el = −A (V−V _s ) ² (5)
It is expressed. Here, A is a constant depending on the radius of curvature of the tip of the probe, the distance between the tip and the domain, the dielectric constant of the material constituting the recording layer forming the domain structure, and the dielectric constant of the insulating layer. In the domain into which charges are injected, ΔV = 1.6 × 10 ⁻¹⁹ × n / C (6)
The surface potential is shifted by ΔV (volts) represented by
[0042]
As is clear from the equation (5), the magnitude of the electrostatic force changes due to the shift of the surface potential. This shift in surface potential or the change in electrostatic force resulting therefrom can be detected as follows. For example, the electrostatic force change can be directly detected by scanning the probe in a two-dimensional manner with a slight separation from the recording layer surface while keeping the probe potential constant. Consider a case where an AC voltage having a frequency ω expressed by the following equation is applied to the probe.
[0043]
V = V ₀ + V ₁ sin ωt (7)
At this time, the electrostatic force F _el is expressed as follows.

Therefore, the magnitude of the potential shift ΔV can be obtained by detecting the ω component using a lock-in amplifier. Alternatively, it is also possible to detect the ω component, apply a DC voltage V ₀ such that the ω component becomes zero to the probe, and obtain the value of ΔV from the value of V ₀ . In this case, the resolution of the surface potential is considered to be about 0.4 mV (Yokoyama et al., Molecular Electronics and Bioelectronics, vol. 3, No. 2, p. 79 (1992)), up to a very small change in the surface potential. It can be detected. Now, when this resolution is 1 mV, the condition for detecting a single electron or hole as a charge is:
1.6 × 10 ⁻¹⁹ × 1 / C ≧ 0.001 (9)
It is expressed.
[0044]
In the present invention, it is clear that if the expression (4) is satisfied, the expression (9) is also satisfied. Further, if the expression (2) is substituted into the expression (4), the expression (1) is obtained. That is, in a recording medium that satisfies the condition expressed by equation (1), single electrons / holes can be injected into the domain with good controllability, and single electrons / holes injected into the domain can be easily detected. Therefore, it is possible to perform multi-value recording by setting each recording state according to the number of injected charges.
[0045]
When donor molecules are used as the material constituting the recording layer, only holes are injected and the number of holes is used as the recording state. On the other hand, when acceptor molecules are used, only electrons are injected and the number of electrons is used as a recording state. In addition, when metals or semiconductors are used, electrons and holes are injected, so there is no polarity as described above, and when the probe potential at the time of contact is positive, the number of holes is negative. The number of electrons is used as the recording state. Furthermore, in the present invention, it is preferable to set S (nm ² ) to 10,000 or less in order to increase the recording density of the recording layer.
[0046]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 is a cross-sectional view of a recording medium manufactured in this example. First, an insulating layer made of a SiO ₂ film 2 having a thickness of 20 nm was formed on the surface of a p-type Si substrate 1 having a resistivity of 1 Ω · cm as a base conductor layer by a thermal oxidation method. Next, after removing the SiO ₂ film on the back surface of the substrate, 2.5 nm thick Cr and 50 nm thick Au were sequentially deposited on the back surface of the substrate to form the base electrode 3. Thereafter, heat treatment was performed, and the substrate was left under a saturated vapor pressure of hexamethyldisilazane for about 3 days to hydrophobize the SiO ₂ film 2 on the substrate surface.
[0047]
Next, 1,1-bis (N, N-ditolylaminophenyl) cyclohexane (hereinafter referred to as diamine), which is a donor molecule, is formed on the SiO ₂ film 2 on the surface of the Si substrate 1 thus formed. Was deposited to form a recording layer 4 having a domain structure. The molecular structure of diamine is shown in “Chemical Formula 17” below. The deposition conditions at this time were a degree of vacuum of 1.3 × 10 ⁻⁴ Pa, a substrate temperature of 20 ° C., and a Knudsen cell heating temperature of 180 ° C. When the deposition rate of diamine was monitored by a quartz oscillator placed in the vicinity of the Si substrate, it was 0.02 nm / sec. In this example, the deposition time was set to about 50 seconds, and a diamine corresponding to a thickness of 1.0 nm was formed. When the structure of the recording layer 4 made of diamine was observed with an SEM, it was confirmed that a droplet-like domain having a diameter of 32 nm and a height of 7 nm was present at a density of 2.4 × 10 ¹⁴ m ⁻² . . Regarding the obtained recording medium, since the relative dielectric constant ε of SiO ₂ is 3.9, the value of d / (Sε) is 6.38 × 10 ⁻³ .
[0048]
Embedded image

[0049]
On the other hand, as an AFM probe, an electrode 12 is formed by sequentially depositing Cr having a thickness of 2 nm and Au having a thickness of 20 nm on the surface of the tip of the SiN cantilever body 11 having a spring constant of 0.58 N / m. Prepared. The radius of curvature of the tip of the cantilever tip is 10 nm.
[0050]
Next, writing and reading were performed on the obtained recording medium as follows. First, in a state where a voltage V _tip is applied to the electrode 12 of the AFM probe, contact is made with the diamine domain constituting the recording layer for about 1 second, and charge is injected from the probe into the domain for writing. Pull the probe away from the diamine domain. Thereafter, the distance between the AFM probe and the diamine domain is maintained at about 10 nm, an AC voltage is applied to the AFM probe, and reading is performed by evaluating the surface potential from the voltage dependence of the electrostatic force. This operation was repeated while gradually increasing the value of V _tip from 0V. FIG. 2 shows the relationship between the AFM probe potential V _tip at the time of contact and the surface potential V _s of the domain for the same domain.
[0051]
As can be seen from this figure, the surface potential V _s shows a step-like change in the positive polarity region of V _tip . That is, V _s is 0 V in the range of V _tip from 0 to 1.1 V, but V _s increases discontinuously to 0.11 V when V _tip is 1.1 V. Thereafter, V _s is in the range V _tip is 1.1~2.2V does not change from 0.11V, V _s in V _tip is 2.2V is increased discontinuously by 0.11V again 0. 22V. Thus, every time V _tip changes by +1.1 V, a discontinuous increase in V _s and a plateau region appear periodically. Note that no change was observed in the surface potential in the negative polarity region of V _tip . From equation (6), the jump of V _s (ΔV) of + 0.11V corresponds to the change of just one charge (in this case, since ΔV is positive), one hole is injected into the domain. It can be seen that a change in surface potential due to the detection was detected.
[0052]
Example 2
The same method as in Example 1 was used, but the deposition time was set to 25 seconds and a diamine corresponding to a thickness of 0.5 nm was formed. When the structure of the formed recording layer made of diamine was observed with an SEM, it was confirmed that droplet-like domains having a diameter of 16 nm and a height of 4 nm were present at a density of 3.5 × 10 ¹⁴ m ⁻² . For the recording medium obtained, the value of d / (Sε) is 2.55 × 10 ⁻² .
[0053]
Next, writing and reading were performed on the obtained recording medium in the same manner as in Example 1. FIG. 3 shows the relationship between the AFM probe potential V _tip and the domain surface potential V _s during contact at this time. Also in this case, the surface potential V _s shows a step-like change when V _tip is in the positive polarity region, but every time V _tip changes by +4.5 V, a jump of V _s of +450 mV is shown. Also in this case, it can be seen from the equation (6) that the value of ΔV of +450 mV corresponds to the change in the surface potential due to the injection of one hole into the domain.
[0054]
Comparative Example The same method as in Example 1 was used, but the deposition time was set to 1000 seconds and a diamine corresponding to a thickness of 20 nm was formed. When the structure of the formed recording layer made of diamine was observed by SEM, it was confirmed that droplet-like domains having a diameter of 220 nm and a height of 75 nm were present at a density of 1.2 × 10 ¹³ m ⁻² . For the obtained recording medium, the value of d / (Sε) is 1.35 × 10 ⁻⁴ .
[0055]
Next, writing and reading were performed on the obtained recording medium in the same manner as in Example 1. FIG. 4 shows the relationship between the AFM probe potential V _tip and the domain surface potential V _s during contact at this time. In this case, the surface potential V _s showed a continuous change with respect to V _tip , and no step-like change was observed. Thus, in this example, the change in the surface potential due to the injection of one hole into the domain could not be detected.
[0056]
Example 3
A recording medium having the same structure as that shown in FIG. 1 was prepared using DNIBPC represented by the following “chemical formula 18” which is an acceptor molecule as a recording layer material. In the same manner as in Example 1, the SiO ₂ film 2 was formed on the surface of the Si substrate 1, the base electrode 3 was formed on the back surface, and the SiO ₂ film 2 was hydrophobized. Next, a recording layer 4 having a domain structure was formed on the SiO ₂ film 2 on the surface of the Si substrate 1 by depositing DNIBPC. The deposition conditions at this time were a degree of vacuum of 1.3 × 10 ⁻⁴ Pa, a substrate temperature of 20 ° C., and a Knudsen cell heating temperature of 220 ° C. In addition, when the deposition rate of DNIBPC was monitored by a quartz resonator placed in the vicinity of the Si substrate, it was 0.02 nm / sec. In this example, the deposition time was set to about 125 seconds, and DNIBPC corresponding to a thickness of 2.5 nm was formed. When the structure of the formed recording layer 4 made of DNIBPC was observed with an SEM, it was confirmed that a droplet-like domain having a diameter of 40 nm and a height of 10 nm was present at a density of 2.0 × 10 ¹⁴ m ⁻² . . For the obtained recording medium, the value of d / (Sε) is 4.07 × 10 ⁻³ .
[0057]
Embedded image

[0058]
Next, writing and reading were performed on the obtained recording medium in the same manner as in Example 1. FIG. 5 shows the relationship between the AFM probe potential V _tip and the domain surface potential V _s during contact at this time. In this case, contrary to Example 1, the surface potential V _s showed a step-like change in the negative polarity region of V _tip . That is, V _s is 0 V in the range of V _tip from 0 to −0.72 V, but V _s decreases discontinuously to −72 mV when V _tip is −0.72 V. Thereafter, when V _tip is in the range of −0.72 to −1.44 V, V _s remains −72 mV, V _tip remains −1.44 V, and V _s changes discontinuously by −72 mV again − It becomes 144 mV. Thus, every time V _tip changes by −0.72 V, a discontinuous decrease in V _s and a plateau region appear periodically. It should be noted that no change was observed in the surface potential in the region where V _tip is positive. From the equation (6), the value of ΔV of −72 mV corresponds to a change of one charge (in this case, since ΔV is negative), and the surface potential due to the injection of one electron into the domain. It can be seen that a change has been detected.
[0061]
【The invention's effect】
As described above in detail, according to the present invention, a single charge (electrons and / or holes) is injected with good controllability into a recording layer having a domain structure even at room temperature, and the injected charge is easily detected. The recording state can be set according to the number of injected charges, and a recording medium that operates stably can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a recording medium according to the present invention.
FIG. 2 is a characteristic diagram showing the relationship between an AFM probe potential V _tip and a domain surface potential V _s for the recording medium in Example 1 of the present invention.
FIG. 3 is a characteristic diagram showing the relationship between an AFM probe potential V _tip and a domain surface potential V _s for a recording medium in Example 2 of the present invention.
FIG. 4 is a characteristic diagram showing a relationship between an AFM probe potential V _tip and a domain surface potential V _s for a recording medium according to a comparative example of the present invention.
FIG. 5 is a characteristic diagram showing the relationship between the AFM probe potential V _tip and the surface potential V _{s of the} domain for the recording medium in Example 3 of the present invention.
[Explanation of symbols]
1 ... Si substrate, 2 ... SiO ₂ film, 3 ... underlying electrode, 4 ... recording layer, 11 ... cantilever body, 12 ... electrode.

Claims (3)

Comprising: a base conductor layer; an insulating layer formed on the base conductor layer; and a recording layer made of a material capable of charge accumulation formed in a domain structure on the insulating layer, The recording layer is made of donor organic molecules or acceptor organic molecules, the insulating layer thickness is d (nm), the insulating layer has a relative dielectric constant ε, and the area of each domain constituting the recording layer is S ( nm ² )
d / (Sε) ≧ 2.86 × 10 ⁻³
A recording medium characterized by satisfying the relationship:   A probe to which a voltage is applied is brought into contact with a predetermined domain constituting a recording layer of a recording medium according to claim 1 and charges are injected into the domain for recording. It scans in a contact state to detect the charge injected into the domain, and the probe applied with a voltage of the opposite polarity to that in recording is brought into contact with the predetermined domain to erase the charge injected into the domain. And a recording method. The recording method according to claim 2 , wherein a recording state corresponding to the number of charges injected into the domain is set.

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