Fabrication of Low Frequency Split Micro Hemispherical Resonator Based on Positive Pressure Multiple-Step Blowing

This paper reports an innovative multiple-step blowing process based on positive pressure thermoforming, which reduces the substrate warpage of fused silica (FS) micro hemispherical resonator (MHRs) wafers by 85 % and effectively decreases the initial frequency split of the MHRs. Frequency split is a key factor affecting the signal-to-noise ratio (SNR) of the output signal of micro gyroscopes. Systematic research demonstrates that the multiple-step blowing process significantly reduce the warpage of 4-inch wafer substrates from$954 \mu \mathrm{m}$to$148 \mu \mathrm{m}$. Moreover, MHRs fabricated via the multiple-step blowing process exhibit better structural symmetry than those fabricated via the single-step blowing process. A total of 6 resonators were fabricated and experimentally characterized. Resonators manufactured multiple-step blowing achieve frequency split of less than 10 Hz in the$\mathrm{n}=2$mode.