成果報告書詳細
管理番号20110000001373
タイトル*平成22年度中間年報 ナノエレクトロニクス半導体新材料・新構造ナノ電子デバイス技術開発 ナノギャップ不揮発性メモリ技術の研究開発
公開日2011/12/13
報告書年度2010 - 2010
委託先名国立大学法人京都大学 株式会社船井電機新応用技術研究所 独立行政法人産業技術総合研究所
プロジェクト番号P09002
部署名電子・材料・ナノテクノロジー部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等 本委託業務では、ナノメータースケールの間隙を有する2つの金属電極(ナノギャップ電極)の間に電圧を加えることにより発現する抵抗スイッチング現象(NGS: ナノギャップスイッチ)を利用する不揮発性メモリを開発し、その集積化(数Mb 級)を実現することを目的として、下記の研究開発を行っている。
(1) 平面先鋭型金属ナノギャップ素子およびその基本特性評価技術の開発(京都大学) 本年度は、フォーミング処理前の状態で先端曲率半径が10 nm以下(ギャップ長も10 nm以下)の電極構造を再現性よく作製するプロセスの確立、複雑な周辺構造変化を引き起こさないフォーミング処理法の確立、原子間力顕微鏡(AFM)および静電気力/ケルビンプローブ原子間力顕微鏡(EFM/KFM)によるギャップ近傍の構造変化および仕事関数変化の評価を実施した。
英文要約Title: Development of Nanoelectronic Device Technology, Development of Nanogap Nonvolatile Memory Technology (FY2009 - FY2011) FY2010 Annual Report
When an applied voltage between two metallic electrodes with the gap distance of a few nanometers exceeds a threshold voltage, the gap resistance suddenly changes, which is referred to as nano-gap switch (NGS) effect. The aim of this project is to develop nonvolatile integrated memory devices (megabit class) based on the NGS effect. (1) Reproducible fabrication process for metallic, tip-shaped NGS electrodes with a tip radius of 10 nm and a gap distance of 10 nm has been well-established by optimizing various process parameters related to the electron beam lithography as well as resist materials. In addition, the forming method was such improved that the forming process caused a negligible change of the gap peripheral structure, which is strongly related to the aging process of the NGS device. Furthermore, a nanometer-scale change of the structure and the electrical properties of the electrodes in close proximity of the gap before and that after the forming/switching processes were investigated by frequency-modulation atomic force microscopy, electrostatic force microscopy and Kelvin-probe force microscopy. (2) (a) New structures for the vertical type NGS element and the evaluation of their characteristics: We have developed two new structures of the vertical NGS element. They are referred to as improved Trench type II and dot type structures. Both were much improved in terms of the initial yield, the forming process and the rewriting performance and speed. In addition, they are more suitable for the mass production than the previous structure. The dot (Via hole) diameter was reduced to 40 nm, which is one of the final target specifications in this project. Single writing process from high- to low-resistance was successfully repeated for consecutive hundred cycles by constant-current pulse. These results are used for the 4k bits memory design. (b) Evaluation of NGS memory array: We evaluated the NGS arrays of the horizontal type and the vertical type elements. Although we found some difficulties in the vertical type array process, it was solved by adding one mask process. This check is useful for the 4k memory device because the same difficulties should lie in its fabrication. (3) To reduce the switching current below 20 uA, a nanogap junction having ultra-small electrode areas has been investigated. This nanogap junction was achieved using scanning tunneling microscope system. We also observed characteristic I-V curves which reflect the nanogap switch effect. Using this system, we successfully measured the switching current of about 10 uA. Secondly, we confirmed that the operation current and the voltage were suppressed by controlling oxygen gas pressure. The current and the voltage were successfully reduced to 1/10 and 1/3, respectively. Thirdly, the resistance switching in a Cu nanogap junction was investigated. The result exhibited a memory effect with a large on-off ratio of over 105, which implied that the nanogap switch effect also occurred using Cu, which is a popular wiring material for the integration circuit.
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