A process-induced-frequency-drift resilient 32 kHz MEMS resonator

Abstract

This paper applies a frequency-drift resilient method for a 32 768 Hz lateral capacitive microelectromechanical system (MEMS) resonator design to make its resonant frequency insensitive to process-induced variation. The basic idea of the method is to synthesize the design of the supported springs and the releasing holes in the proof mass so that process-induced effective spring constant variation is approximately balanced by effective mass variation, and thus to keep their ratio and determined resonant frequency approximately unchanged. The 32 768 Hz MEMS resonator has been fabricated based on 30 µm silicon-on-insulator wafer for real-time clock application. The related testing results of more than 100 working devices from two different wafers show that the resonant frequencies are in the range of 32 102 ± 25 Hz and obey basically the normal distribution, and the drift from the designed value is less than 2.1%. The method is expected to significantly improve the reliability and fabrication yield of MEMS resonator, and can also be extended to other vibrating MEMS devices.