Piezoelectric Fused Silica Resonators for Timing References
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There is a strong drive towards low size, weight, and power microelectromechanical system (MEMS) timing references to replace long-standing quartz-based timing units for applications in communication, defense, inertial sensors, and wearable electronics. To achieve this goal, notable improvements in resonator miniaturization, performance, and stability are required, necessitating investigation of alternate materials from the silicon devices sold commercially today. Fused silica, a purified amorphous silicon dioxide, is a viable alternative to silicon due to its excellent material and thermal properties for resonant devices and packaging.
This presentation provides a high level discussion of the design, characterization, and fabrication of fused silica MEMS resonators for use in timing references. Piezoelectric resonators with a fused silica substrate are demonstrated for the first time in reported literature, showing a high quality factor with low motional impedance. The major loss mechanisms in fused silica are also presented and investigated through simulation and experimental measurements, resulting in the proposal of a new form of loss for piezoelectric resonators. This loss, known as charge redistribution, is experimentally tested and the theory refined through the results.
Mitigation methods for the temperature sensitivity of fused silicon resonators are also presented. A number of compensation methods, including ovenization and passive compensation, are experimentally tested and results presented. From this, a method of providing ultra-stable devices is proposed using two resonant modes on a single device volume. Prototype dual mode devices are demonstrated using this technique and methods of oscillator implementation are introduced.