Passive Substrate Temperature Compensation of Doubly Anchored Double-Ended Tuning Forks

摘要

While microdevices have shown a number of key advantages over similar macrosize sensors including size, cost, and sensitivity, a key challenge has centered on reducing drift and error due to changes in temperature. This paper proposes a novel substrate temperature compensation mechanism for microelectromechanical systems double-ended tuning forks (DETFs). The device layer and substrate layer are purposefully made from differing materials. This mismatch induces thermal strains that cancel changes in the frequency due to a shift in the modulus of elasticity. Two polycrystalline silicon carbide DETFs of different physical dimensions are fabricated on single-crystalline silicon substrates. The devices are tested between 5 $^{circ}hbox{C}$ and 320 $^{circ}hbox{C}$ and exhibit temperature compensation as predicted by an analytical model. The DETFs exhibit peak temperature compensation near room temperature at 34 $^{circ}hbox{C}$ and 38 $^{circ}hbox{C}$, respectively. Over a commercial temperature range from 0 $^{circ}hbox{C}$ to 70 $^{circ}hbox{C}$, the devices display temperature sensitivities of 1.5 $hbox{Hz}/^{circ}hbox{C}$ (7.4 $hbox{ppm}/^{circ}hbox{C}$) and 0.3 $hbox{Hz}/^{circ}hbox{C}$ (1.7 $hbox{ppm}/^{circ}hbox{C}$), which is up to 17$times$ better than a similar epitaxial silicon device. This work is broadly applicable to tuning-fork-based sensing systems such as strain gauges, pressure sensors, accelerometers, and gyroscopes.$hfill$ [2012-0034]