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Neutron single event effect (SEE) tolerance of SiC power MOSFETs with different drift region design were evaluated. The SEE is detected over the SEE threshold voltage (VSEE). The failure rate increases exponentially as the drain voltage increases above VSEE. The device with higher avalanche breakdown voltage has higher SEE threshold voltage. The neutron SEE tolerance of MOSFETs and PiN diodes of the same epitaxial structure were also evaluated. There was no significant difference in the neutron SEE tolerance of these devices.

The impact of cell size and JFET width reduction on static and dynamic device characteristics is investigated in 1.2-kV-class Schottky barrier diode (SBD)-embedded SiC metal–oxide–semiconductor field effect transistors (MOSFETs). We compare a conventional SBD-embedded MOSFET with improved SBD-embedded MOSFETs with smaller cell pitch and JFET width than the conventional SBD-embedded SiC MOSFET. The optimized SBD-embedded SiC MOSFETs achieve 39% lower on-resistance and 16% lower switching energy loss compared with the conventional design. We also investigate the tradeoff between R on A and short-circuit withstand time (t SC ). Although R on A reduction generally causes a decrease in short circuit withstand capability and reverse conduction capability, we demonstrate that the optimized SBD-embedded SiC MOSFETs have a lower forward voltage drop and short circuit withstand capability. These results show that it is possible to simultaneously reduce R on A and improve t SC with adequate optimization.

In the SBD-embedded SiC MOSFET, the operation of the parasitic PN diode that causes degradation of forward voltage of the diode is suppressed by the incorporated SBD. The aim of this study is to improve the maximum current at which the parasitic PN diode does not operate (I umax ). We confirmed the limitation of the existing equivalent circuit model used as a guideline to improve I umax , and then developed a new circuit model. In addition, a new guideline to improve I umax has been derived based on the equivalent circuit model. Utilizing this guideline, we have tried to improve I umax of 3.3 kV SBD-embedded SiC MOSFET experimentally. I umax at 200°C has been improved to 4.72 times that of the conventional device. Though it has been known that I umax decreases with temperature, this significant improvement in I umax is a promising result for future application of SBD-embedded SiC MOSFET above 175°C.

A novel compositional accommodation mechanism in perovskite (ABO3) SrNbO3 thin films was revealed by field-emission analytical electron microscopy (AEM). A new analytical methodology for estimating localized structures such as planar faults is also presented. The method was applied for investigating the compositional accommodation mechanism of B-ion-rich SrNbO3 epitaxial thin films. Two types of accommodation mechanism—formation of B-ion-rich amorphous phase and (110)-located high-density planar defects—were revealed. The latter mechanism is a new finding for B-ion-rich perovskites. Copyright © 2003 John Wiley & Sons, Ltd.

A heteroepitaxial BaTiO3 film with a thickness of 65 nm was prepared on SrRuO3/Pt/TiAlN/Si. The Ti0.91Al0.09N film was grown on Si substrate by DC sputtering in Ar/N2 ambient at 700°C. The BaTiO3, SrRuO3 and Pt films were deposited by radio-frequency magnetron sputtering at substrate temperatures ranging from 450°C to 600°C. The BaTiO3 film has a c-axis 1.6% longer (0.410 nm) than that of bulk, due to lattice misfit between SrRuO3 and BiTiO3. When positive and negative voltage pulses with an amplitude of 5 V were applied, a switching charge density, Q sw, of 40 μC/cm2 was obtained. No fatigue was observed after 1011 cycles of polarization switching even when an amplitude of 7 V was applied. Remanence of polarization for 4 hours was confirmed in a retention test. These results indicate that the heteroepitaxial BaTiO3 film capacitors on Si substrates can be used for ferroelectric nonvolatile memory applications.

Modification of ferroelectricity in heteroepitaxial Ba x Sr1-x TiO3(BST) films by making use of lattice misfit was investigated. Theoretical calculation suggested that application of two-dimensional compressive stress of 3 GPa to the ferroelectric crystal would result in Curie temperature increase by 270°C. This theoretical prediction was experimentally confirmed. Heteroepitaxial Ba0.6Sr0.4TiO3 films grown on SrRuO3/SrTiO3 substrates exhibited ferroelectric hysteresis at 200°C, even though the inherent Curie temperature is known to be 0°C. The possibility of heteroepitaxial BST films for ferroelectric non-volatile memory applications and their advantages were pointed out.

One of the most challenging issues in designing film bulk acoustic wave resonators (FBARs) is how to realize high-Q resonators. According to our experimental results, an acoustic leakage is the dominant loss factor at antiresonance frequency for FBARs with an aluminum bottom electrode. In this paper, we report simulation results obtained using the 2-dimensional finite element method (2D FEM), which was employed in order to confirm the above-mentioned acoustic loss mechanisms and optimize the design parameters of the resonator. As a result, optimizing the aluminum bottom electrode thickness and properly designing an attenuation structure that reflects the laterally propagating Lamb waves inside the resonator areas suppress the acoustical leakage significantly. Comparisons between FEM simulation and measured results in terms of the relationship between the Q-factors at antiresonance frequency and the structural parameters of the resonators are shown.

Crystal structure and magnetic properties in epitaxially grown Sr1−xBaxRuO3 on SrTiO3 substrates were determined. Epitaxial Sr1−xBaxRuO3 exhibits a simple perovskite structure in the whole region of the Ba/Sr ratio, in contrast to the complex hexagonal layered perovskite of Ba-rich bulk Sr1−xBaxRuO3, which has plane-sharing oxygen octahedra. Tetragonal deformation was enhanced from pseudocubic in SrRuO3 to a highly distorted tetragonal lattice in BaRuO3. Electronic properties such as conductivity and magnetization were examined. A metal–insulator transition was not observed in this system, and metallic conductivity was maintained in the whole region of Ba concentration. Ferromagnetic ordering at 160 K seen in bulk SrRuO3 was observed to be suppressed in the Sr1−xBaxRuO3 films with increasing tetragonal deformation and Curie temperatures decreased to 50 K in BaRuO3.

The selection of the bottom electrode materials for FBARs is a key issue in regard to the fabrication of highly c-axis oriented AlN thin films and high-Q resonators. In this paper, high-Q FBARs using aluminum electrodes are presented. An amorphous metal underlayer enables fabrication of highly -oriented Al thin films with XRD rocking curve FWHM of 0.6°. Using these high quality Al films, we have obtained highly c- axis oriented AlN films. These AlN films showed excellent crystallinity even at the initial stages of the AlN film deposition. The fabricated resonators showed good resonance characteristics, such as high-Q values (loaded-Q ~800) and high effective coupling constants (~6.7%). The impedance ratio (Zmax/Zmin) was more than 1500, corresponding to an FOM (Figure of merit) of 51.

Uniformity of lattice misfit strain was quantitatively evaluated in heteroepitaxial (Ba, Sr)TiO3 films which were deposited by radio-frequency magnetron sputtering on SrRuO3/SrTiO3 substrates. Due to lattice misfit strain, the (Ba, Sr)TiO3 films had a 3% longer c-axis than the inherent bulk of (Ba0.75Sr0.25)TiO3. As analyzed by Hall's theory, the uniformity of the strain was 0.3% of the c-axis (0.413 nm) and 9% of the elongation of the c-axis (0.015 nm). It was suggested by the comparative study of two specimens that there is a strong correlation between the quality of the ferroelectric hysteresis loop and the uniformity of the misfit strain in heteroepitaxial (Ba,Sr)TiO3 films.

The crystal structure and magnetic properties in epitaxially grown Sr1-xBaxRuO3 on SrTiO3 substrates were determined. Epitaxial Sr1-xBaxRuO3 exhibits a simple perovskite structure in the whole region of Ba/Sr ratio, in contrast to a complex hexagonal layered perovskite in the case of Ba-rich bulk Sr1-xBaxRuO3 which has plane-sharing oxygen octahedra. Tetragonal deformation was enhanced from the pseudo cubic structure of SrRuO3 to a highly distorted tetragonal lattice in BaRu03. Electronic properties such as conductivity and magnetization were examined and compared to the results of band calculation in which a tetragonal distortion was taken into account. A metal-insulator transition was not observed in this system either in the experiment or in the simulation, and metallic conductivity was maintained in the whole region of Ba content. The ferromagnetic ordering which occurs at 160K in pseudo-cubic bulk SrRuO3 was suppressed in Sr1-xBaxRuO3 films with increasing tetragonal deformation and Curie temperature decreased to 50K in BaRuO3.

The present invention is intended to provide a thin film bulk acoustic wave resonator, which has a resonant excitation portion free from damage caused by etching, a high electromechanical coupling coefficient k t 2 and a high quality coefficient Q value, and to provide a thin film bulk acoustic wave resonator having a plurality of different resonant frequencies, which can be formed on the same substrate without increasing number of lithography process. An internal cavity is provided in a semiconductor or insulative substrate such as crystal silicon. The thin film bulk acoustic wave resonator has a layered member comprising a first electrode film, a piezoelectric film and a second electrode film on a thin wall of e.g. single crystal over the internal cavity.

Sr(Ti1-x ,Ru x )O3 (STRO) epitaxial thin films were deposited on single-crystal SrTiO3(100) substrates using the inductive-coupling-plasma-induced RF magnetron sputtering method without oxygen. The electrical conductivity of STRO films increases with Ru concentration and levels of the Ru 4d states are observed in the band gap of SrTiO3 by X-ray photoelectron spectroscopy (XPS) analysis. These results are consistent with those obtained by first-principles calculations. Thermodynamic stability increases with the decrease of Ru concentration, and STRO (x2 atmosphere at 600°C. This high resistance against reductive processes indicates that STRO (x

Ferroelectric properties were investigated using SrRuO3/(Ba x , Sr1-x )TiO3(BSTO)/SrRuO3 all-perovskite heteroepitaxial capacitors on strontium titanate substrates. The dielectric film had a composition with a Ba content of x=0 to 1, i.e., the whole composition of the SrTiO3–BaTiO3 solid-solution system. The c-axis of the BSTO film was elongated depending on the Ba content, and reached 0.441 nm at the BaTiO3 composition, which was 8.6% larger than the bulk c-axis. A peak relative dielectric constant of 870 and maximum remanent polarization (2P r) of 58 µC/cm2 were obtained depending on the Ba content at a dielectric thickness of 20 nm. These are the highest storage capacitance capacitor and the thinnest ferroelectric capacitor reported so far. Possibilities for deep submicron ferroelectric and dielectric memory applications are also discussed.

Epitaxial titanium aluminum nitride, Ti1-x Al x N(100) (0≦x2 + ion beam irradiation with 100 eV energy and Ti and Al simultaneous evaporation. The epitaxial relationship was confirmed to be Ti1-x Al x N(100)//Si(100), Ti1-x Al x N//Si by X-ray diffraction (XRD) and in situ reflection high-energy electron diffraction (RHEED). Although the electrical resistivity increased exponentially with x, the values remained on the order of 10-4 Ω·cm. Using the Ti1-x Al x N buffer layer, we have successfully fabricated a capacitor with an epitaxial (Ba, Sr)TiO3 film on a Si substrate.

Asymmetric ferroelectricity and conduction of anomalous leakage current were observed in heteroepitaxial BaTiO3 thin films grown by rf magnetron sputtering at 600° C on three different electrode/substrate combinations: SrRuO3/SrTiO3, Pt/MgO and Nb doped SrTiO3. The voltage shift of hysteresis loops of the capacitance was a linear function of the thickness of the BaTiO3 films and became as large as 10 V in the film with a thickness of 410 nm. The asymmetry did not disappear even after a heat treatment carried out at 800° C in air. On the other hand, a steep increase in the leakage current was observed in the heteroepitaxial films when a positive voltage was applied. The origin of both the asymmetric hysteresis and the anomalous conduction is discussed in terms of asymmetric crystal structure caused by misfit dislocations introduced in heteroepitaxial growth.

Heteroepitaxial Ba0.6Sr0.4TiO3 thin films with thicknesses from 26 nm to 97 nm were grown on SrRuO3 bottom electrode films on SrTiO3 single crystal substrates. Although the films have a paraelectric composition, ferroelectric hysteresis was observed in displacement versus electric field (D–E) loops. The ferroelectricity is considered to be developed as a result of bi-axial stress, caused by lattice mismatch between the dielectric films and the bottom electrodes. The maximum difference in the displacement was over 0.4 C/m2, even when the thickness of the film was reduced to 26 nm. The hysteresis loops showed an asymmetric characteristic at a polarity of applied voltage. The asymmetry was discussed in terms of an asymmetrical deformation of the crystal structure, which is probably introduced during the heteroepitaxial growth.

Epitaxial TiN(111) films were grown on Si(111) substrates by low energy reactive ion beam deposition using N2 ion beam irradiation and Ti evaporation. TiN epitaxial film formation was investigated as a function of the substrate temperature (T s) and the kinetic energy of the ion beam (E b). Using X-ray diffraction (XRD) and in-situ reflection high-energy electron diffraction (RHEED), the epitaxial relationship was found to be TiN(111)|| Si(111), TiN|| Si above substrate temperature of 400° C. Cross-sectional bright-field transmission electron microscope (TEM) observation has shown that the interface is quite flat and sharp and that four TiN lattice spacings match three spacings of the Si lattice. A lowest resistivity value of 18 µΩ· cm (T s=600° C, E b=100 eV) was obtained.

Reactive ion beam epitaxy with an extra-low energy N2 + ion beam and a Ti molecular beam has been employed to grow hetero-epitaxial TiN films on MgO substrates. The TiN film quality drastically depends on the N2 + kinetic energy. Epitaxial TiN films with a low resistivity about 16 µΩ·cm were obtained at a kinetic energy of 50 eV/atom even at room substrate temperature, which is the lowest epitaxial temperature so far. At an elevated temperature, epitaxial growth was observed at a wide kinetic energy range. Epitaxial growth mechanisms in low energy reactive ion beam deposition are discussed.