Study On Residual Stress And Film Thickness Uniformity Of Hemispherical Resonator Metallization Coating

As a high-precision,long-life and low-power inertial navigation device,the hemispherical resonator gyro(HRG)has a broad prospect in many applications including aerospace and strategic weapons.The hemispherical resonator is the core component of the hemispherical resonator gyro.The high Q-value and low frequency difference characteristics ensure the working accuracy of the hemispherical resonator gyro.Metallization coating on the surface of the resonator is an important process in the fabrication of hemispherical resonators.The film residual stress and film thickness uniformity have a critical influence on the Q-value and frequency difference of the resonator.In this paper,we presented a theoretical study of the effects of spherical film residual stress and film thickness uniformity on the harmonic Q-value and frequency difference after metallization coating on the surface of the hemispherical resonator.Based on the analysis,the uneven film will cause the natural frequency of the resonator to change.The residual stress in the film causes the internal friction of the resonator,then decrease its Q value by increasing the frequency difference.The classification of the residual stress in film and the generation mechanism of various residual stresses were studied.The thermal stress of the two-layer thin film system composed of Au and Cr was theoretically modeled.According to the model,the thermal stress values of the films were unrelated to other layers.And the neutral axis of this two-layer film system located at the position where the substrate is 2/3 of the base thickness from the lower end free surface.The thermal stress of the film was simulated at different substrate temperatures and the optimal theoretical value of the substrate temperature was determined.The simulation results showed that the intrinsic stress in the residual stress was much larger than the thermal stress.For the non-contact measurement of the residual stress of the ultra-thin film,Curvature substrate method,X-ray conventional method and X-ray grazing incidence method were carried out.Based on these experiments,the ductility of Au and Cr materials caused that the residual stress value measured by the curvature substrate method was smaller than its true value.The residual stress of the film in this paper can only be analyzed qualitatively by using conventional Xray method.Although the X-ray grazing incidence is suitable for the residual stress test of the ultra-thin film,the diffraction peak of the received film material was incomplete because the degree of freedom in the measurement process was limited.This paper presented the patch method to measure the uniformity of the spherical film thickness.The spherical metallization coating experiment was carried out by magnetron sputtering and electron beam evaporation respectively.It was found that a spherical metal film with good uniformity can be achieved by the electron beam evaporation coating.According to the Lambert's law,the thickness distribution and uniformity of the harmonic oscillator were simulated by ZEMAX.The simulation results were basically consistent with the film thickness uniformity test.The effects of the motion mode of the resonator hemisphere during the coating process on the film thickness distribution and uniformity were analyzed.