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Wang, Z. P. ; Morimoto, Akiharu ; Kawae, Takeshi ; Ito, H. ; Masugata, Katsumi
概要:
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
概要:
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
概要:
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
概要:
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
概要:
(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.
概要:
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
概要:
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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| 10.
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Kawae, Takeshi ; Teraguchi, Y. ; Kumeda, Minoru ; Morimoto, Akiharu
概要:
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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