Yasuhiro Hirao

Characteristics of AlN Thin Films Deposited by Electron Cyclotron Resonance Dual-Ion-Beam Sputtering and Their Application to GHz-Band Surface Acoustic Wave Devices

A (001) plane of hexagonal aluminum nitride (AlN) has been deposited on R-plane sapphire ((1 2)Al2O3) with inclination of about 26° against the substrate by electron cyclotron resonance (ECR) dual-ion-beam sputtering. A shear horizon (SH) wave as well as a modified Rayleigh wave could be excited on this AlN film. The phase velocities of the SH wave (V SH) and Rayleigh wave (V R) were 6000~6730 m/s and 5600~5950 m/s, respectively. V R has no effect on the propagation direction. However, V SH has considerable influence on the propagation direction, and becomes maximum at the propagation direction of 45 degrees against [120]AlN. The insertion loss and temperature coefficient of delay time (TCD) of the 1.21-GHz-band two-port-type resonator using SH waves were 7.5 dB and 35.4 ppm/°C, respectively. These values are acceptable for practical use.

New High-Phase-Velocity Leaky Surface Acoustic Wave Mode on LiTaO3 and LiNbO3

A new high-phase-velocity leaky surface acoustic wave (SAW) mode, which was predicted by computer simulation, was confirmed experimentally to exist on both LiTaO3 and LiNbO3. The Euler angles of the propagation direction are (90°, 90°, 31°) on LiTaO3 and (90°, 90°, 37°) on LiNbO3. One-port SAW resonators were produced to confirm these modes. The phase velocity of the mode on LiTaO3 (90°, 90°, 31°) is 6250 m/s, and that on LiNbO3 (90°, 90°, 37°) is 7170 m/s. The temperature coefficient of the resonance frequency on LiTaO3 (90°, 90°, 31°) is -30 ppm/°C, and that on LiNbO3 (90°, 90°, 37°) is -30 ppm/°C.

Small SAW filters using optimized high-reflection-coefficient reflectors

The dependence of the reflection coefficient on grating reflector parameters, such as electrode thickness, the reflector metallization ratio and Pi/Pr, was studied in detail. Pi and Pr are the electrode finger periods of interdigital transducers (IDTs) and reflectors, respectively. The maximum value of the reflection coefficient occurred at a metallization ratio of 75% and Pi/Pr of 0.990. Intermediate frequency (IF) surface acoustic wave (SAW) filters for the Advanced Mobile Phone Service (AMPS) system were made using these high-reflection-coefficient reflectors. As a result, package size was reduced from 11 mm/spl times/5 mm to 7 mm/spl times/5 mm. Their characteristics include a center frequency of 85.38 MHz, an insertion loss of 2.5 dB and a 3 dB-passband width of 54 kHz.