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^-18 g) in air conditions.