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

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°C and 320°C and exhibit temperature compensation as predicted by an analytical model. The DETFs exhibit peak temperature compensation near room temperature at 34°C and 38°C, respectively. Over a commercial temperature range from 0°C to 70°C, the devices display temperature sensitivities of 1.5 Hz/°C (7.4 ppm/°C) and 0.3 Hz/°C (1.7 ppm/°C), which is up to 17× 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.