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| 1.
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Wang, Z. P. ; Morimoto, Akiharu ; Kawae, Takeshi ; Ito, H. ; Masugata, Katsumi
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Preferentially-oriented aluminum nitride (AlN) films are grown directly on natively-oxidized Si (100) substrate by pulse
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d laser deposition (PLD) in nitrogen (N2) environment. The AlN preferential orientation changes from (002) to (100) with increasing N2 pressure. Such different behaviors are discussed in terms of deposition-rate-dependent preferential orientation, kinetic energy of depositing species and confinement of laser plume. Finally, sample deposited at 0.9 Pa is proved to have the highest (002) peak intensity, the lowest FWHM value, the highest deposition rate and a relatively low RMS roughness (1.138 nm), showing the optimal growth condition for c-axis-oriented AlN growth at this N2 pressure. © 2011 Elsevier B.V. All rights reserved.
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| 2.
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Nakata, Shunji ; Maeda, Ryoji ; Kawae, Takeshi ; Morimoto, Akiharu ; Shimizu, Tatsuo
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A thin-film structure comprising Al2O3/Al-rich Al2O3/SiO2 was fabricated on Si substrate. We used radio-frequency magnet
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ron co-sputtering with Al metal plates set on an Al2O3 target to fabricate the Al-rich Al2O 3 thin film, which is used as a charge storage layer for nonvolatile Al2O3 memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al2O3 is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 1018 cm-3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory. © 2011 Elsevier B.V. All rights reserved.
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| 3.
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Ukai, Yohei ; Yamazaki, Shuhei ; Kawae, Takeshi ; Morimoto, Akiharu
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BiFeO 3 (BNF) thin films were fabricated on SrRuO 3 (SRO)-coated (100) Nb-doped SrTiO 3 subtrates by pulsed laser deposi
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tion, and nondoped BiFeO 3 (BFO) thin films were also fabricated similarly for comparison. Then, Nd-doping effects on ferroelectric and photovoltaic properties were evaluated. Polarization-induced photovoltaic effects were observed in both the BFO and BNF solar cell structures with top and bottom electrodes under intense laser illumination. Using Au top electrodes, enhanced photovoltaic properties were observed in the BNF cell compared with the BFO cell. To improve the photovoltaic properties of the BNF cell, instead of the Au top electrodes, In-Sn-O (ITO) top electrodes were employed for the BNF cell. As a result, the photovoltaic properties were found to be markedly improved, resulting in an open circuit voltage of 0.81 V and a short circuit current density of 12.1 mA/cm2. © 2012 The Japan Society of Applied Physics.
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| 4.
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Nakata, Shunji ; Kato, Takashi ; Ozaki, Shinya ; Kawae, Takeshi ; Morimoto, Akiharu
概要:
Thin film Al2O3/Al-rich Al2O 3/SiO2 structures were fabricated on p-Si substrates. Radio-frequency magnetron co-sputteri
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ng was used to form Al-rich Al 2O3 thin film as the charge-trapping layer of nonvolatile Al2O3 memory. Capacitance-voltage measurements showed a large hysteresis due to charge trapping in the Al-rich Al2O 3 layer. The charge trap density was estimated to be 42.7 × 1018 cm- 3, which is the largest value ever reported for an Al-rich Al2O3 layer; it is six times larger than that of a conventional metal-nitride-oxide-silicon memory. Thermal annealing was found to reduce the leakage current of the Al2O3 blocking layer, thereby providing this structure with better data retention at room temperature than an as-deposited one. In addition, the annealed structure was found to exhibit good data retention even at 100 C. © 2013 Elsevier B.V. All rights reserved.
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| 5.
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Nomura, Yukihiro ; Tachi, Takashi ; Kawae, Takeshi ; Morimoto, Akiharu
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We applied Vopsaroiu's model to (Bi,Pr)(Fe,Mn)O3 (BPFM) and Pb(Zr,Ti)O3 (PZT) ferroelectric thin films fabricated by che
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mical solution deposition. The temperature dependences of the saturation polarization and the coercive field were measured in a low-temperature region from 100 to 200K. The saturation polarizations of BPFM thin films decreased on decreasing the measurement temperature due to the polarization pinning effect, while that of PZT thin film was almost unchanged over the temperature region. The coercive fields of all the thin films were increased linearly on decreasing the measurement temperature. The activation energies for polarization reversal in as-grown BPFM, postannealed BPFM, and PZT thin films were 1.18, 1.25, and 0.95eV, respectively. These results indicate that BPFM thin films have large activation energies for polarization reversal compared with PZT thin films. In addition, the postannealed BPFM thin film has a larger activation energy than the as-grown BPFM thin film. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 6.
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Nomura, Yukihiro ; Nomura, Keisuke ; Kinoshita, Koyo ; Kawae, Takeshi ; Morimoto, Akiharu
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(Bi0.9Pr0.1)(Fe0.97Mn0.03)O3 (BPFM) thin film was deposited on Pt-coated Si(100) substrate by chemical solution depositi
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on. Remnant polarization and coercive field in the BPFM film capacitor were 113 °C/cm2 and 630 kV/cm at the maximum electric field of 1000 kV/cm, respectively. Switching charge measured by a rectangular pulse measurement was 118 °C/cm2. Almost no polarization losses of BPFM film capacitor were observed even after retention time of 104 s at room temperature. Furthermore, the polarization loss at 450 °C was only 3.7% even after 104 s. These results indicate that BPFM film capacitor is suitable for non-volatile memory applications at high temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 7.
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Kawae, Takeshi ; Yasuda, T. ; Kim, S.-J. ; Nakajima, K. ; Yamashita, T.
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We have investigated the properties of submicron intrinsic Josephson junctions (IJJs) fabricated on Bi/sub 2/Sr/sub 2/Ca
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Cu/sub 2/O/sub 8+/spl delta// liquid phase epitaxy film. The IJJs with junction area S＜2 /spl mu/m/sup 2/ showed individual current-voltage curves, which have suppressed 1st branch and unsuppressed other branches. This suppression was observed systematically as an increase the ratio of charging energy and Josephson coupling energy. It is expected that such suppressions are due to charging effect in IJJs.
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| 8.
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Kawae, Takeshi ; Teraguchi, Yuki ; Nakajima, Takashi ; Okamura, Soichiro ; Morimoto, Akiharu
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金沢大学理工研究域電子情報学系<br />Pr and Mn co-substituted BiFeO3 (BFO) thin films were fabricated on a Pt-coated (100) SrTiO3 substr
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ates by pulsed laser deposition (PLD) method. X-ray diffraction patterns indicated that the formation of impurity phases was suppressed by Pr substitution in the BFO thin films. Furthermore, by combining with small amount of Mn substitution, Pr substitution was effective for reducing the leakage current density. The polarization vs electric field curves showed well-saturated hysteresis loops with measurement frequency of 20 kHz at room temperature. The remnant polarization at a maximum electric field of 1500 kV/cm was approximately 50–70 µC/cm2.
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| 9.
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Takahara, Seiichi ; Morimoto, Akiharu ; Kawae, Takeshi ; Kumeda, Minoru ; Yamada, Satoru ; Ohtsubo, Shigeru ; Yonezawa, Yasuto
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金沢大学理工研究域電子情報学系 金沢大学工学部<br />Fatigue-resistant epitaxial Pb(Zr,Ti)O3 capacitors on Pt electrode with ultra-thin SrTiO3 template layers<br />This article has not been published yet.
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Kawae, Takeshi ; Teraguchi, Y. ; Kumeda, Minoru ; Morimoto, Akiharu
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金沢大学理工研究域 電子情報学系<br />Polycrystalline BiFeO3 (BFO), Ti-doped BFO, Mn-doped BFO, and (Mn, Ti)-codoped BFO (BFMT) thin fil
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ms were fabricated on Pt/ SrTiO3 (100) substrate by pulsed laser deposition. Observed leakage current behavior in those ion-doped BFO films indicated the dominance of space-charge-limited current in the high electric field region. The leakage current of the BFMT film was much reduced in relation to the other films due to the formation of deep traps. In the BFMT film, well saturated P-E hysteresis curves were observed. Remanent polarization and coercive field for maximum electric field of 2100 kV/cm were 75 μC/ cm2 and 310 kV/cm, respectively. © 2009 American Institute of Physics.
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| 11.
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Liu, Chen ; Kawae, Takeshi ; Tsukada, Yoshinori ; Morimoto, Akiharu ; Naganuma, Hiroshi ; Nakajima, Takashi ; Okamura, Shoichiro ; 森本, 章治
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金沢大学理工研究域電子情報通信学系<br />We report the preparation of (Bi,Pr)(Fe,Mn)O 3(BPFM)/SrRuO 3 (SRO)-Pt/CoFe 2O 4(CFO) layered film
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structure on (100) SrTiO 3 substrate by pulsed laser deposition method and their structural and electrical properties. Favorable ferroelectric properties of BPFM were observed in the layered film structure with (100)-oriented growth of BPFM, SRO, and CFO. Variation of polarization vs electric field loops of BPFM by applying DC magnet field was observed, and the remnant polarization was found to increase by 3% with increasing the applied magnetic field from 0 to 10 kOe. The magnetoelectric coefficient in the present structure was estimated to be 1.5 V/(cmOe). © 2012 American Institute of Physics.
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| 12.
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Nomura, Keisuke ; Kondo, Yuki ; Kawae, Takeshi ; Morimoto, Akiharu ; 川江, 健 ; 森本, 章治
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金沢大学理工研究域電子情報通信学系<br />We investigated the effects of a SrRuO3 (SRO) layer on the retention properties of (Bi, Pr)(Fe, M
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n)O3 (BPFM) film capacitors under high temperature conditions. The dielectric constant of the BPFM film capacitor was increased by the introduction of the SRO layer. In addition, the Pt/BPFM/SRO/Pt capacitor showed polarization losses of only 6.4% in both polarization directions after a retention time of 104 s at 400°C, resulting in symmetrical switching behavior. These results imply that the introduction of the SRO layer is effective in suppression of the formation of an interfacial layer between BPFM and Pt. © 2015 The Electrochemical Society.
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| 13.
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川江, 健 ; Kawae, Takeshi
概要:
ダイヤモンドはワイドギャップ半導体としての優れた性能に加えて高濃度不純物添加により超伝導が発現する事が知られている。当該分野の将来の発展と現状の打破を目指し、強誘電体(Bi,Pr)(Fe,Mn)O3（BPFM）の巨大分極を利用した表面キャリ
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ア制御を提案する。ダイヤモンド・BPFM間において良好な界面構造を確認した。また、BPFMの良好な強誘電性を示した。一方、現在までにソース・ドレインを形成したMFISダイヤモンドFET構造の動作特性に関して、BPFMの自発分極に対するダイヤモンドチャネル層のキャリア変調は達成されていないが、ダイヤモンドチャネルの欠陥抑制により改善され得るものと考える。<br />It is known to the diamond that superconductivity develops by highly-concentrated impurities addition in addition to the superior performance as the wide gap semiconductor. Aiming at the future development of the field concerned and the present defeat, I suggest surface carrier control using a huge polarization of ferroelectric (Bi,Pr)(Fe,Mn)O3(BPFM).I confirmed good interface structure without the interdiffusion between diamond, and BPFM. In addition, I showed good ferroelectricity of BPFM. On the other hand, about movement properties of the MFIS diamond FET structure that formed a source drain, enough abnormality of the drain electric current of the class of diamond channels for the spontaneous polarization of BPFM is not accomplished to date, but think that this can be improved by the defect restraint of the diamond channel.<br />研究課題/領域番号:24656380, 研究期間(年度):2012-04-01 - 2014-03-31
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| 14.
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川江, 健 ; Kawae, Takeshi
概要:
極限環境動作を目指した新規強誘電体不揮発性メモリデバイスの実現を目指し、ワイドギャップ半導体ダイヤモンド上に高キュリー温度非鉛強誘電体BiFeO3(BFO)を堆積した積層構造の作製と特性評価を行った。ボロン添加した導電性ダイヤモンド層上にB
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FOが結晶化可能である事および良好な強誘電性を示す事が確認された。また、同構造試料の高温特性を検証したところ、最大200℃まで安定的に動作可能である事が確認された。以上の結果より、本研究課題が掲げるBFO/ダイヤモンド積層構造を用いた極限環境動作型強誘電体メモリデバイスの実現に向けて、当該構造の形成プロセスの確立および今後の展開に対する有用性が立証されたものと言える。<br />As an integration of Pb-free ferroelectrics with wide-gap semiconductors, (Pr, Mn)-codoped BiFeO_3 (BPFM)/B-doped diamond layered structure was fabricated on a diamond substrate. B-doped diamond films were homoepitaxially grown on diamond substrate using microwave plasma-enhanced chemical vapor deposition. Then, BPFM thin films were deposited on the B-doped diamond layer by pulsed laser deposition. BPFM thin films were polycrystalline with random orientations on the B-doped diamond layer. Fabricated heterostructure showed saturated P-E hysteresis curves with 2P_r : 90℃/cm^2 and 2E_c : 740kV/cm for maximum electric field of 900kV/cm at room temperature. P-E hysteresis curves without influences of leakage current were observed even when the measurement temperature was increased to 200 ℃.<br />研究課題/領域番号:21760233, 研究期間(年度):2009-2010
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| 15.
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川江, 健 ; Kawae, Takeshi
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ダイヤモンド超伝導体ジョセフソン接合の作製を目指し、高濃度ボロン添加ダイヤモンド薄膜の作製および微細加工プロセスの確立を試みた。マイクロ波プラズマCVD法を用いた高濃度ボロン添加ダイヤモンド薄膜作製に関して、Si(111)およびダイヤモンド
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(111)基板上に超伝導転移温度4〜6Kの超伝導ダイヤモンド薄膜の作製を実現した。特にSi(111)基板上でのダイヤモンド超伝導体薄膜のヘテロエピ成長は世界的にも初めての成功例であり、当該材料を用いた今後のデバイス応用を検討する上で有用な成果と言える。また、デバイス作製に向けたダイヤモンド薄膜の微細加工としてO_2プラズマRIEを用いたダイヤモンド基板上の段差加工およびホモエピ成長したダイヤモンド超伝導体薄膜のエッチングを試み、段差基板上にウィークリン型接合形成を実現した。上記の各種プロセスにより作製された接合試料の基礎特性を評価した結果、観測温度2Kにおいてジョセフソン接合的な振る舞いを確認した。今後は試料の超伝導転移温度の更なる向上と微小接合を用いたトンネル分光による詳細な各種接合特性の評価が求められる。以上の結果より、本研究課題が掲げるダイヤモンド超伝導体ジョセフソン接合実現に向けたダイヤモンド超伝導薄膜作製および接合作製用微細加工プロセスの基礎がほぼ確立されたものと言える。<br />研究課題/領域番号:19760213, 研究期間(年度):2007-2008<br />出典：「高濃度ボロン添加ダイヤモンド超伝導体薄膜を用いたジョセフソンデバイスの開発」研究成果報告書 課題番号19760213（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-19760213/19760213seika/)を加工して作成
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| 16.
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川江, 健 ; Kawae, Takeshi
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金沢大学理工研究域電子情報通信学系<br />本研究では、ワイドギャップ半導体ダイヤモンドに対し、強誘電体をゲートとした電界効果トランジスタ（FeFET）構造を形成し、従来型パワーデバイスに比する優位性について検証を行った。強誘電体ゲートを
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用いたダイヤモンドチャネルの電圧変調において、電流ON/OFF比10E+8を実証するに至った。また、強誘電体ゲートの残留分極を利用したダイヤモンドFeFETの疑似ノーマリオフ動作に関して、現在までに最長70時間に至るオフ状態の保持を実証した。以上の結果は、強誘電体をゲートにより実現したパワーFETの新動作原理を示したものであり、今後、当該構造を利用したパワーデバイス開発に資するものと考える。<br />In this study, for wide-gap semiconductor diamond, we proposed the creation of field-effect transistor structure with a ferroelectric gate (FeFET), and investigated its superiority to conventional power devices.We have demonstrated a current ON/OFF ratio of 10E+8 of diamond channel due to the modulation of huge amount of carrier by applying the gate voltage. In addition, about the pseudo normally-off operation of diamond FeFET using the remnant polarization of the ferroelectric gate, it has been demonstrated that the off-state can be maintained for up to 70 hours.The above results indicate the new operating principle of a power FET realized by a ferroelectric gate, and are considered to contribute to the development of power devices using this structure in the future.<br />研究課題/領域番号:17H03248, 研究期間(年度):2017-04-01 - 2020-03-31<br />出典：「強誘電体の巨大分極を利用した超低損失ダイヤモンドパワーFETの創出」研究成果報告書 課題番号17H03248（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-17H03248/17H03248seika/)を加工して作成
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