Tomoaki Matsushima

Thin-Film Piezoelectric Materials For a Better Energy Harvesting MEMS

Ferroelectric PZT-based perovskite thin films are widely studied for fabrication of compact piezoelectric energy harvesting (EH) power microelectromechanical systems (MEMS) due to their large piezoelectric coefficients. Output energy of the piezoelectric EH power MEMS is chiefly governed by their energy conversion rate, κ2 and/or (e2/ε), where e and ε denote their piezoelectric coefficient and dielectric constant. The values of (e2/ε) are considered as figures of merit (FOM) for the piezoelectric EH power MEMS. At present nonferroelectric AlN thin films are considered as a candidate for a better piezoelectric EH power MEMS due to their high FOM values. These PZT-based thin films are mostly polycrystalline thin films of binary perovskite compounds, Pb(Zr, Ti)O3 (PZT). We have proposed single crystal thin films of PZT-based ternary perovskite compounds, Pb(Mn,Nb)O3-PZT (PMnN-PZT), instead of the binary perovskite PZT. The single crystal PMnN-PZT thin films have been successively fabricated by rf-magnetron sputtering. It is found that the FOM values of single c-domain/single crystal PMnN-PZT thin films are one order of magnitude higher than those of AlN thin films. This suggests output powers of the PMnN-PZT thin-film EH power MEMS are one order of magnitude higher than those of the AlN thin-film EH power MEMS.

Superconducting properties of Bi2Sr2CaCu2Oy/Bi2Sr2CuOx multilayer thin films

Abstract We have prepared Bi 2 Sr 2 CaCu 2 O y (BSCCO)/Bi 2 Sr 2 CuO x (BSCO) multilayer thin films using a multitarget RF magnetron sputtering technique. Our BSCO films exhibit a semiconductor-like transport property, and BSCCO/BSCO multilayers are supposed as superconductor/nonsuperconductor multilayers. The x-ray diffraction measurements showed that all of the multilayers with various thicknesses have the c-axis normal to the substrate surface. In the multilayer films with the constant BSCO layer thickness of 100A, an T c onset slightly decreases from 85 K to 75 K with decreasing the BSCCO layer thickness from 250A to 31A. From this result it seems that interlayer coupling in BSCCO/BSCO multilayers is weaker than in YBaCuO/PrBaCuO multilayers.

Highly polarized single-c-domain single-crystal Pb(Mn,Nb)O 3 -PZT thin films

In-plane unstrained single-c-domain/single-crystal thin films of PZT-based ternary ferroelectric perovskite, xPb(Mn,Nb)O₃-(1 - x)PZT, were grown on SrRuO₃/Pt/MgO substrates using magnetron sputtering followed by quenching. The sputtered unstrained thin films exhibit unique ferroelectric properties: high coercive field, E_c >; 180 kV/cm, large remanent polarization, P_r = 100 μC/cm², small relative dielectric constants, ε* = 100 to 150, high Curie temperature, T_c = ~600°C, and bulk-like large transverse piezoelectric constants, e_31,f = -12.0 C/m² for PZT(48/52) at x = 0.06. The unstrained thin films are an ideal structure to extract the bulk ferroelectric properties. Their micro-structures and ferroelectric properties are discussed in relation to the potential applications for piezoelectric MEMS.

Thin films of PZT-based ternary perovskite compounds for MEMS

Stress free heteroepitaxial thin films of PZT-based ternary perovskite, xPb(Mn,Nb)O₃-(1-x)PZT, were fabricated by magnetron sputtering on (001)MgO substrates and evaluated their crystal structure, ferroelectric and piezoelectric properties. The heteroepitaxial thin films showed single c-domain /single crystal structure and exhibit hard ferroelectric behavior with large Pr, Pr=60muC/cm², and high E_c, 2E_c=230kV/cm, at x=0.06. The PZT-based thin films exhibited high piezoelectric coupling factors k_t, k_t=70%, measured at GHz range FBAR structure. High values of mechanical quality factor Q_m, Q_m=185, were observed at 4Ghz range. The observed k_t and Q_m are, to our knowledge, the highest in the reported values. The figure of merit k_t ²Q_m is almost the same to piezoelectric AlN thin films. It is confirmed the PZT-based ternary perovskite thin films have a potential for a fabrication of FBAR and/or wide band filters at GHz range.

Thin film processing for high- Tc superconductors of the Bi-system

Basic thin film deposition processes for controlled deposition of the high- T c superconductors of the Bi-systems are described. The layered structures of Bi-oxide superconductors are fabricated by a multitarget sputtering process. The multitarget sputtering process realizes the controlled deposition of single phase Bi-oxide superconductors, Bi 2 O 2 · 2SrO · ( n −1)CaO · n CuO 2 for n = 1 to 5. The minimum thickness controlled by the multitarget sputtering is a half crystal unit-cell of around 15 A, and the superlattices comprising ( A k B k ) · m , where A and B denote the Bi-oxide superconductors with different numbers of Cu–O layers, could be fabricated for k > 1, although ion mixing takes place during the sputtering deposition due to the bombardment of the highly energetic sputtered adatoms. Multitarget sputtering will be available for the fabrication of the artificially-made layered oxide superconductors (ALOS).

Structure and Superconducting Properties of Bi-Sr-Ca-Cu-O Thin Films Annealed at Low Temperatures

Thin films of the Bi-Sr-Ca-Cu-O system were prepared at substrate temperatures between 550°C and 600°C. The film deposited at 570°C showed an X-ray diffraction pattern of the high-Tc phase without other phases and had a zero-resistance temperature Tc at 23 K. After annealing at 570°C under the oxygen pressure of 1 atm, the zero-resistance Tc increased to 47 K, but under the pressure of 0.1 atm, the crystal structure was changed and Ca-Cu-O phase appeared. On as-deposited films prepared by a low-temperature process, structure and superconducting properties are easily affected by low-temperature postannealing.

A highly sensitive Pb(Zr,Ti)O/sub 3/ thin film ultrasonic micro-sensor with a grooved diaphragm

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O3 (PZT) was 2.2 mum thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezoelectric ultrasonic sensor without the groove structure was 100 muV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 muV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure.

80 K Superconductivity in Bi-Sr-Cu-O Thin Films

High-Tc superconductivity near 80 K has been obtained in Bi-Sr-Cu-O thin films. Films were prepared by rf-magnetron sputtering onto heated MgO substrates and heat-treated. It was found that the Bi-based crystal structure with a c-axis length of 3.12 nm was formed in thin film. This film exhibited the superconducting transition with the onset temperature of about 80 K. The present superconducting phase in the Bi-Sr-Cu-O system is considered to be the isostructure with the conventional 80 K Bi2Sr2CaCu2Oy (2-2-1-2) phase.

Cross-Sectional Transmission Electron Microscopic Observation of Etch Hillocks and Etch Pits in LiTaO3 Single Crystal

Cross sections of etch hillocks and etch pits in LiTaO3 single crystal have been observed by transmission electron microscopy. The cross-sectional samples were prepared at their exact positions by the focused ion beam microfabrication method. Inverted polarized domains were observed both at the top of etch hillocks and at the bottom of etch pits, indicating that the etching figures originate in the inverted domain formed on the surface. Furthermore, some inverted domains that were pinned by lattice defects were also observed at the inner part of the crystal.

Ideal adiabatic structure LiTaO/sub 3/ pyroelectric microsensor fabricated by sandblasting technique

We have successfully developed a high performance LiTaO/sub 3/ microsensor with ideal adiabatic structure. A finite element method (FEM) was employed to design ideal structure with efficient temperature distribution. The FEM was also employed to reduce a stress concentration of the LiTaO/sub 3/ element. Four infrared detector segments were formed in the LiTaO/sub 3/ element. Each segment, with 500 /spl mu/m square, is thermally isolated by an 100 /spl mu/m wide slit penetrated around the segment using a sandblasting technique. The IR sensitivity per unit area of the developed sensor element is twice that of a conventional type element without slits. Furthermore this small sensor element enables to reduce a size of focusing multi-lens to one-fifth as large as that of the conventional multi-lens. The S/N ration of the developed sensor is five times as large as that of the conventional type pyroelectric sensors such as PZT sensor.