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Takeshi Kanashima,Koji Ikeda,Masanori Okuyama,Masayuki Sohgawa,Taizo Tada 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
High-k HfO2 thin lms have been prepared mainly at 400 C in O2 atmosphere by pulsed laser deposition (PLD), and defects in the lm have been characterized by electron spin resonance (ESR). Two ESR peaks are found at g ' 2:003 and 2:006. The g ' 2:006 peak intensity is higher in the sample deposited at target-sample distance of 45 mm than in that deposited at 60 mm. This is because part of the substrate and the lm are exposed to high-energy particles ablated during deposition and are hence damaged. Moreover, the peak at g ' 2:006 is related to the interface state density calculated from the high-frequency C V curve. On the other hand, the peak at g ' 2:003 is related to the thickness of the interfacial layer, and thus may be attributed to defects in the interfacial layer.
Takeshi Kanashima,Hyun Lee,Masanori Okuyama 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
HfO2 thin .lms were prepared by using photoassisted MOCVD with Hf(O-t-C4H9)4 (HTB) and various oxidants. HTB and the oxidizing reagent were supplied alternately. The °at-band shift voltage of the C-V characteristic is about ¡0:3 V in the case of an HfO2 .lm deposited from HTB and H2O2 and is larger than the value for a sample deposited from HTB and H2O. The surface potential (As) of the samples was measured by using photore°ectance spectroscopy. The value of As for the sample deposited from HTB and H2O is a little larger than the value for the sample deposited from HTB and H2O2. This indicates that the amounts of .xed charge in these .lms may be a little large, and that the quality of the .lm is not improved by using H2O2 as an oxidant. On the other hand, the quality was improved by using NH4OH as an oxidant. In this case, the C-V hysteresis is very small and a large accumulation capacitance is observed. The leakage current density is about 1 £ 10¡7 A/cm2 at Vg = 1 V.
T. Kanashima,M. Okuyama,H. Kanda,K. Ikeda,M. Sohgawa 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
High-k thin lms of ZrO2, PrOx of 10 nm thickness have been prepared by pulsed laser deposition, and characterized in microscopic structure and electrical properties. Crystallization is promoted in ZrO2 lms deposited above 400 C, but a signicant XRD peak was not observed in the ZrO2 lm grown below 400 C. The leakage current is decreased by increasing growth temperature, but an equivalent-oxide thickness (EOT) obtained from accumulation capacitance of C .. V characteristics becomes large. The lms deposited at 400 C were annealed at 400 C in O2 gas to reduce the leakage. The leakage current change to be small, but the EOTs become large. Oxygen radical annealing is carried out to reduced the leakage, and is eective for ZrO2 thin lm. On the other hand, only small improvement is observed in the PrOx lms.
박정민,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima,김경만,이재열,이희영 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31
Epitaxial 0.7BiFeO_3-0.3.BaTiO_3 solid solution thin films were grown on La doped SrTiO_3 (001) substrates by using pulsed laser deposition (PLD). The XRD pattern and the pole figure showed peaks corresponding to (001) planes. The capacitance-voltage (C-V) measurement showed dielectric constant and loss values of 70 and 0.07, respectively. The polarization hysteresis (P-E) was obtained at room temperature with remnant polarization (2P_r) and coercive field (2E_c) values of 23 μC/cm^2 and 508 kV/cm, respectively. The magnetization hysteresis (M-H) loop showed a linear behavior of a typical paramagnetic nature.
Air Damping Effect on the Air-based CMUT Operation
Bu-sang Cha,Takeshi Kanashima,Seung-Mok Lee,Masanori Okuyama 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.3
The vibration amplitude, damping ratio and viscous damping force in capacitive micromachinedultrasonic transducers (CMUTs) with a perforated membrane have been calculated theoretically and compared with the experimental data on its vibration behavior. The electrical bias of the DC and the AC voltages and the operation frequency conditions influence the damping effect because leads to variations in the gap height and the vibration velocity of the membrane. We propose a new estimation method to determine the damping ratio by the decay rate of the vibration amplitudes of the perforated membrane plate are measured using a laser vibrometer at each frequency, and the damping ratios were calculated from those results. The influences of the vibration frequency and the electrostatic force on the damping effect under the various operation conditions have been studied.
박정민,Fumiya Gotoda,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
Polycrystalline BiFeO_3 thin film has been prepared on indium tin oxide (ITO)-coated glass substrate at 520^oC by pulsed laser deposition (PLD). The XRD pattern shows a polycrystalline perovskite phase and (010) preferred orientation. Higher deposition temperature for BFO thin film on ITO substrate was required for crystallization, compared to that of BFO thin film grown on Pt substrate. Grain size becomes smaller than that of the BFO thin film on Pt substrate and leakage current density is decreased. Optical transmittance is about 80 % around 780 nm and the direct band gap (E_g) is 2.72 ± 0.03 eV. P-E hysteresis loop of the BFO thin film on ITO substrate was obtained at RT and polarization difference at zero electric field (2P_(ro)), corresponding to the double remanent polarization was 140 μ/cm^2. The M-H hysteresis loop was obtained at RT and antiferromagnetic behavior is little affected by difference of the substrate.
박정민,Masayuki Sohgawa,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
Epitaxial BiFeO<sub>3</sub> (BFO) thin films have been prepared on La-doped (001) SrTiO<sub>3</sub> substrates (La-STO) by using magnetic-field-assisted pulsed laser deposition. X-ray diffraction patterns of the epitaxial BFO thin films prepared under magnetic fields of 0, 0.1, and 0.4 T show only (00l) diffraction peaks without secondary phases. From the results of reciprocal space mapping for all epitaxial BFO thin films, (003) reflections show splitting spots, and asymmetric spots of (−103) and (103) reflections exhibit a rhombohedral structure. The microstructure of the epitaxial thin films was modified by the strength of magnetic field, and a columnar structure was shown in the film prepared under a high deposition rate for a magnetic field of 0.4 T. The polarization versus electric field hysteresis loops were obtained at room temperature (RT) in all the epitaxial films; in particular, the remanent polarization for the epitaxial film prepared under a magnetic field of 0.1 T was 46 μC/cm<sup>2</sup> at RT while the current density was reduced in comparison with those of other epitaxial films.
Le Van Hai,Takeshi Kanashima,Masanori Okuyama 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
Fast annealing was used to improve the electronic properties of ferroelectric and buffer layers in Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures. Damage of the SiO2 layer due to SBT constituent diffusion was reduced significantly as annealing time at high temperature of the ferroelectric SBT can be reduced from 1 − 2 hours to few minutes. Leakage currents through both the SiO2 buffer and the SBT ferroelectric layers were decreased in the sample prepared by using fast annealing. The C-V and the I-V characteristics also show electronic improvement at the interface and reduced of thermal diffusion of constituent elements. It is shown by SEM and atomic force microscopy(AFM) images revealed that the SBT thin film with fast annealing had a gets better surface morphology. The retention time of a capacitor with a MFIS structure in the ON and the OFF states was improved, and the maximum is retention time was longer than 23 days. Fast annealing was used to improve the electronic properties of ferroelectric and buffer layers in Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures. Damage of the SiO2 layer due to SBT constituent diffusion was reduced significantly as annealing time at high temperature of the ferroelectric SBT can be reduced from 1 − 2 hours to few minutes. Leakage currents through both the SiO2 buffer and the SBT ferroelectric layers were decreased in the sample prepared by using fast annealing. The C-V and the I-V characteristics also show electronic improvement at the interface and reduced of thermal diffusion of constituent elements. It is shown by SEM and atomic force microscopy(AFM) images revealed that the SBT thin film with fast annealing had a gets better surface morphology. The retention time of a capacitor with a MFIS structure in the ON and the OFF states was improved, and the maximum is retention time was longer than 23 days.