A chemical sensing microsystem utilizing an adaptive feedback circuit

For the first time, a chemical sensor utilizing optical MEMS with a novel adaptive feedback circuit is presented. This circuit implementation of a hill climbing feedback algorithm is capable of autonomously detecting resonant frequency shifts for a range of MEMS resonators. Eight different cantilever-based sensors (width = 0.6-1.4 mum, length = 40-75 mum, and thickness = 1.8 mum), resonating between 200 kHz to 600 kHz, have been measured. Additionally, the circuit has been used to track resonant frequency shifts due to isopropanol (IPA) adsorption on three different chemical sensors. The frequency detection range, measurement resolution, and sensitivity of the system have been evaluated.