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| 1.
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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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Morimoto, Akiharu ; Takezawa, Katsuhito ; Minamikawa, Toshiharu ; Yonezawa, Yasuto ; Shimizu, Tatsuo
概要:
金沢大学工学部<br />The effect of ambient gas on the preparation of YBa2Cu3Ox (YBCO) high-Tc superconducting thin films by puls
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ed laser ablation was explored in gas mixtures of argon+oxygen, argon+nitrous oxide, and nitrous oxide+oxygen. These experiments revealed that a reducing environment for the preparation of YBCO films enhances the film growth with the high temperature phase (trilayered perovskite YBCO) rather than the low temperature phase (cubic YBCO). This phenomenon is explained in terms of thermodynamic phase diagram. The effect of nitrous oxide on the thermodynamic phase diagram is far smaller than that of oxygen by a factor of two to three orders of magnitude.
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| 8.
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Morimoto, Akiharu ; Shigeno, Hideki ; Morita, Shinya ; Yonezawa, Yasuto ; Shimizu, Tatsuo
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金沢大学工学部<br />The effect of ambient N2 gas on the preparation of Ti0.9Al0.1N (TAN) thin films for ferroelectric capacitor
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s by pulsed laser ablation (PLA) using ArF and KrF excimer lasers was explored. The TAN films were prepared on (100)Si substrates heated at 620°C in various N2 pressures ranging from vacuum to 130 Pa. The TAN crystal growth was found to be influenced by the content of unintentionally incorporated O which was found to be controlled by the introduction of N2 gas into the deposition chamber. The O content for films prepared by KrF was found to be smaller than that for films prepared by ArF. This was due to the smaller optical absorption cross-section of KrF excimer laser for residual O2 or H2O molecules in the chamber and/or the higher deposition rate. The TAN film prepared by KrF excimer laser was found to be nearly epitaxial Si with a cube-on-cube crystallographic orientation.
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| 9.
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Yonezawa, Yasuto ; Matsuda, Kazuko ; Morimoto, Akiharu ; Shimizu, Tatsuo
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金沢大学工学部<br />Bi-iron garnet(BIG) firms were prepared using Bi-substituted Y-iron-garnet(Bi:YIG) template layer on platin
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ized Si. First, Bi:YIG template layer was prepared on the platinized (100)Si (Pt/Ti/Sio2/Si) by PLA deposition and successive rapid thermal annealing (RTA). Then Bi3Fe5O12 firm was grown on the template layer by PLA. The Bi3Fe5O12 firm deposited was found to have a garnet (BIG) phase by X-ray diffraction measurement. For the BIG firm, the saturated magnetization and the Faraday rotation were characterized and discussed.
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| 10.
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Morimoto, Akiharu ; Asada, K. ; Minamikawa, T. ; Yonezawa, Y. ; Shimizu, T.
概要:
金沢大学工学部<br />YBa2Cu3Ox (YBCO) films were prepared in nitrous oxide (N2O) gas by pulsed laser ablation (PLA) using Kantha
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l hot filament of approximately 1000°C for cracking the N2O gas. The crystal orientation was changed from the a-axis to c-axis by turning on the filament. The possible origin of this result is a rise of surface temperature of the substrate by thermal radiation from the hot filament and/or generation of oxygen-related radicals produced by cracking of N2O. Temperature measurements revealed that the change of crystal orientation caused by the hot filament could be partly explained by the substrate heating effect. Mass-analysis revealed that N2O gas was really cracked by the hot filament, supporting the possible change of the crystal orientation by the cracking effect of N2O.
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