Katsuhiko Tanaka

A micromachined vibrating gyroscope

Abstract A vibrating microgyroscope with a thin polysilicon resonator fabricated by silicon surface micromachining is described. The 400 μm × 800 μm resonator is driven in a lateral direction by electrostatic force, and the angular rate is detected as the capacitance change between the resonator and its substrate. Mechanical Q -factors for the driving mode and the detecting mode of the polysilicon resonator are 2800 and 16 000, respectively, at pressures below 0.1 Pa. Methods are presented for modifying the difference between the resonance frequencies of the driving and detecting modes. The test device shows a noise-equivalent rate of 2° s −1 .

Multilayer Ceramic Capacitors with Thin (Ba,Sr)TiO3 Layers by MOCVD

Barium strontium titanate ((Ba,Sr)TiO3; BST) thin films were prepared on platinum-coated MgO substrates at 650°C by metalorganic chemical vapor deposition (MOCVD). Perovskite single phased BST thin films were obtained. Dielectric constant at 1 kHz–100 mV was 1000. Multilayer ceramic capacitor with twelve BST dielectric layers of 0.26 μm thick was formed on the MgO substrate. Capacitance and dissipation factor (tanδ) at 1 kHz–100 mV were 32 nF and 1.5% respectively. Capacitance per unit volume of 33 μF/mm3 provided 10 to 20 times larger volumetric efficiency than the conventional multilayer ceramic capacitors. Temperature coefficient of capacitance was −4000 ppm/°C. The leakage current at 1 V was 2.3×10-9 A that yielded an acceptable CR product of 12.8 MΩ-μF. MOCVD was proposed as one of the promising manufacturing technologies for multilayer ceramic capacitors of high performance with sub-micron thick dielectric layers.

Characterization of piezoelectric properties of PZT thin films deposited on Si by ECR sputtering

Abstract Ferroelectric lead zirconate titanate (PZT) thin films are deposited at a low substrate temperature (530–590 °C) by an electron cyclotron resonance (ECR) sputtering method using two targets: a ceramic PZT and a lead metal target. Si wafers are employed as substrates. The piezoelectric constant e31 is 2.1 C m−2 without poling treatment for a PZT film deposited at 550 °C.

Preparation of piezoelectric Pb(Zr,Ti)O3–Pb(Zn1/3Nb2/3)O3 thick films on ZrO2 substrates using low-temperature firing

Abstract Thick films of Pb(Zr,Ti)O3–Pb(Zn1/3Nb2/3)O3 (PZT–PZN) with additional PbO-TiO2-ZrO2-SiO2-Bi2O3 glass-ceramics were fabricated using a sequential process of screen-printing, drying, pressing, and firing. PZT–PZN paste containing the glass-ceramics was formed into thick films by firing it at temperatures above 700xa0°C, where the glass-ceramics enhanced the densification of the films by liquid-phase sintering. Press-treatment of the printed film done before firing also enhanced the densification. Dielectric constant, remnant polarization, and coercive field of the films were investigated as a function of the firing temperature, which ranged from 700 to 950xa0°C. The best properties were obtained for films fired at 800–850xa0°C. Piezoelectric actuations were demonstrated using unimorph cantilevers made from the films fired above 700xa0°C.

Crystallinity and Surface Morphology of Epitaxial (Sr,Ba)Nb 2 O 6 Thin Film Prepared by Pulsed Laser Deposition with Two-Step Growth Sequence

We have prepared epitaxially grown SBN thin film with c-axis orientation by an ArF pulsed laser deposition on SrTiO 3 (100). Pole figures show that the SBN film has a twin structure aligned at ±18.4: with the a-axis of SrTiO 3 . The epitaxial relationship of SBN //SrTiO 3 is determined. The lattice mismatch between SBN and SrTiO 3 is approximately 0.9%, which contributes to the desirable crystallinity of the SBN thin film. Furthermore, we have tried to form the SBN film with a two-step growth sequence in order to improve surface morphology. The amorphous initial growth region of 5 monolayers (2 nm thickness) is prepared with no substrate heating followed by post-annealing treatment at 720°C and additional growth on the initially crystallized layer. RHEED patterns of the SBN film with the two-step growth sequence have remained streaky throughout the film formation, compared with spotty patterns observed from films prepared by a conventional sequence. Atomic force microscope (AFM) images show that both the initial stage and final stage have extremely flat surfaces of rms≦ lnm which is a remarkably improved figure compared with the roughness rms ≧3nm for the film deposited at 720°C from the initial stage. These results suggest that the two-step growth sequence makes it possible to improve surface morphology to a nanometer level.

Application of HTS / Dielectric Multilayered Thin Films for Microwave Devices

A new concept of resonator with an electrode structure consisting of YBa2Cu3O7-δ (YBCO)/MgO multilayered films has been proposed [1]. Toward its realization of this concept, in the present study, epitaxial growth of YBCO / MgO / YBCO trilayered film on LaA1O3 (100) substrate is obtained and its properties are compared with bi- and mono-layered films. The monolayer YBCO films show a good transport and microwave properties and a crystalline quality. The quality of the crystal structure of the film tended to degrade with increasing the number of layer.