CMOS chemical microsensors based on resonant cantilever beams

We present a chemical gas sensor based on a resonating cantilever beam in CMOS MEMS technology. The sensor is actuated employing electrothermal actuation. Thus, for a 300 mu m long beam vibration amplitudes of 6.5 nm per mW heating power are achieved. The vibrations are detected with piezoresistors in a Wheatstone bridge scheme. Detection sensitivities above 200 mu V per mW heating power are measured with the bridge biased at 5 V. The beams have quality factors of up to 600. The static power dissipation that goes along with the electrothermal actutation scheme leads to a small temperature elevation of 0.3 K/mW of the sensitive area. The beams are coated with poly(etherurethane) (PEUT) as the sensitive layer. The layer thickness was determined by the change of the initial resonance frequency. Concentrations of octane, ethanol and toluene in synthetic air were measured. For toluene, concentrations as low as 250 ppm can be detected.