Fabrication of highly homogeneous metal films for hemispherical resonators by a 3D mask based on a sputter-coating process

Abstract

The metal film of fused silica resonators is critical for electrostatic driving and detection in hemispherical resonator gyroscope (HRG). The circumferential and radial inhomogeneities of the deposited metal film considerably reduce the homogeneity of the resonator damping, leading to an inhomogeneous Q-factor in the HRG. In this paper, we propose a high-uniformity coating method for fused silica HRG based on a magnetron sputtering coating process combined with a 3D mask. First, the deposition rate of the metal film on the HRG is modeled and the simulation results are presented. A 3D mask is then designed based on the simulation results to improve the homogeneity of the metal film on the inner surface of the resonator by adjusting the passage rate of the sputtered atoms. Subsequently, a hemispherical device is designed to measure the film thickness and the theoretical model is tested. The radial inhomogeneity of the resonator film deposition is reduced from 11.9 % to 3.5 %. Finally, the damping parameters of the hemispherical resonator are tested. Compared to the conventional coating process, the damping inhomogeneity of the hemispherical resonator generated by the sputtering coating process is increased by only 0.5 %, while the Q-factor loss is 18.1 % less than that of the conventional process.