An Ultra High-Q Micromechanical In-plane Tuning Fork

This work presents a micromechanical in-plane tuning fork with internal vibration amplification ability that can be used as an ultra-sensitive MEMS gyroscope. The structure is designed to incorporate a thermal-piezoresistive energy pump for one of the vibration modes leading to significant amplification of vibration amplitude with the same actuation force. Up to 473X vibration amplitude enhancement has been demonstrated leading to a measured effective quality factor (Q) of 10.4x10(6) for the vibration mode with intrinsic mechanical Q of 22,097. This was achieved by applying a bias current of only 1.607mA to the piezoresistor embedded within the structure. The internal thermal-piezoresistive amplification is caused by coupling of mechanical strain and Joule's heating in the piezoresistor biased with a DC current. Measured effective Q values as a function of bias current agree with the theoretical predication. Theoretically there is no upper limit on the achievable effective Q provided that the bias current can be controlled with adequate precision.