Composite flexural-mode resonator with controllable turnover temperature

This paper presents the design and characterization of a flexural mode composite resonator whose inherent frequency sensitivity to temperature changes is reduced. The resonator is an encapsulated single anchor, double ended tuning fork (DETF) composed of single crystal silicon with a silicon dioxide coating. The frequency variation with temperature of the composite resonator exhibits a turnover temperature at which the frequency does not change with temperature. The turnover temperature can be controlled by varying the thickness of the silicon dioxide. This useful characteristic could be combined with active temperature compensation for more precise timing applications. The fabricated devices show a temperature sensitivity that is comparable to a quartz crystal tuning fork resonator.