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

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Abstract
A (001) plane of hexagonal aluminum nitride (AlN) has been deposited on R-plane sapphire ((1 1̄·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 [12·0]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.