Format of Original
Institute of Electrical and Electronics Engineers
2012 IEEE 25th International Conference on Micro Electro Mechanical Systems (MEMS)
Original Item ID
This paper introduces an electrothermally actuated, piezoresistively detected, silicon-based tuning fork geometry as a suitable platform for resonant sensing applications in air. Operated at their fundamental tuning fork mode (fTF ≈ 400 kHz), in which the two tines oscillate with 180° phase shift to each other, the devices exhibit Q-factors of 4000-4200 in air. By properly choosing the locations of the integrated excitation resistors as well as the four piezoresistors forming a Wheatstone bridge, output signals stemming from low-frequency out-of-plane vibration modes of the microstructure are successfully suppressed. As a result, the tuning forks can be easily embedded into an amplifying feedback loop, achieving short-term frequency stabilities in air as low as 0.02 ppm (0.008 Hz) for gate times of 1 sec. Coated with a chemically sensitive polymer film, the tuning forks were used as mass-sensitive sensors with detection limits in the low-ppm range for toluene.