The concept of "collapsed electrodes" for glassblown spherical resonators demonstrating 200:1 aspect ratio gap definition

We report a technique for defining high aspect ratio electrostatic gaps in micromachined glassblown spherical resonators. The approach is based on intentionally allowing a physical contact between the resonator and electrode structure, hence “collapsed electrodes”, then releasing and metalizing the electrodes and resonator. We utilized 500 um SOI electrodes in the glassblowing fabrication process, allowing to define narrow (2 um) and thick (400 um) electrostatic actuators (200:1 aspect ratio). We demonstrated a spherical resonator integrated with electrodes, blurring the boundary in complexity of fabricating conventional (2D) and glassblown (3D) resonators. The test resonator demonstrated 866kHz, 1.46MHz and 1.59MHz for N=1, N=2, and N=3 modes and the corresponding Q-factors of 1500, 1300 and 1600, all in vacuum of 0.4mT.