Monolithic CMOS MEMS Oscillator Circuit for Sensing in the Attogram Range

This letter presents the design, fabrication, and demonstration of a CMOS/microelectromechanical system (MEMS) electrostatically self-excited resonator based on a submicrometer-scale cantilever with~1 ag/Hz mass sensitivity. The mechanical resonator is the frequency-determining element of an oscillator circuit monolithically integrated and implemented in a commercial 0.35-μm CMOS process. The oscillator is based on a Pierce topology adapted for the MEMS resonator that presents a mechanical resonance frequency of~6 MHz, a relative low quality factor of 100, and a large motional resistance of~25 MΩ. The MEMS oscillator has a frequency stability of~1.6 Hz resulting in a mass resolution of~1 ag (1 ag= 10- 18g) in air conditions.