Ryoichi Ohara

P2G-4 Suppression of Acoustic Energy Leakage in FBARs with Al Bottom Electrode: FEM Simulation and Experimental Results

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.

Electrical Properties and Thermodynamic Stability of Sr(Ti1-x,Rux)O3 Thin Films Deposited by Inductive-Coupling-Plasma-Induced RF Magnetron Sputtering

Sr(Ti1-x,Rux)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 (x<0.50) is free from degradation under annealing H2 atmosphere at 600°C. This high resistance against reductive processes indicates that STRO (x<0.50) is one of the most suitable candidates for conductive oxide electrodes of oxide capacitors.

Ferroelectric properties of epitaxial barium titanate thin film capacitors on silicon substrate

Abstract 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.

High-q thin film bulk acoustic wave resonator using highly [111]-oriented aluminum electrode

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.