Design and characterization of a CMOS MEMS capacitive resonant sensor array

Resonant sensing has been used to detect various physical or chemical quantities, however many reported sensing systems are still bulky and expensive as they rely on external instruments to conduct measurements. For practical applications, it is often desirable to have a low-cost miniaturized sensor chip with multiple sensing devices. This paper presents the first attempt to implement a capacitive resonant sensor array in a complementary metal oxide semiconductor process. The damping loss of all sensors is compensated by placing them in an oscillator loop that contains a phase-locked loop (PLL) driving circuit. The inclusion of a PLL is beneficial for sustaining the oscillation of various resonant frequencies due to the manufacturing tolerance and detected quantity within the PLL capture range. The fabricated micromechanical resonators have a resonant frequency near 200 kHz. To evaluate the sensor performance, a parylene-D thin film was deposited on microstructures and the corresponding frequency shift of 12 devices was on average 33.87 kHz. The resolution for mass detection was estimated to be 23 pg. (paper)