Precision curved micro hemispherical resonator shells fabricated by poached-egg micro-molding

This paper presents a new technique for the fabrication of high resolution non-planar precision microshells for hemispherical resonating gyros via a poached-egg micromolding (PEM) method. In PEM, precision ball lenses are used as starting molds. Hemispherical shells are formed on the lenses using five major steps: (1) isotropic coating with sacrificial and shell layers, (2) stencil transfer of coated lenses to substrate, (3) shell top removal by anisotropic etching, (4) sacrificial layer etching and (5) release of the ball lens molds. Using PEM, we fabricated posted sputtered ultra-low-expansion glass hemispherical shells of 1 mm diameter and 1.2 μm thickness. The microshells have better than 120 ppm uniformity in thickness and less than ±0.125 μm deviation from a perfect sphere. The measured microshell resonant frequency at 100 mTorr was 17.32 kHz and the Q was ~ 20,000.