High-sensitivity parametrically amplified chemo-mechanical vapor sensors

In this paper we present a new kind of high sensitivity chemo-mechanical sensors. These devices consist of a torsional conductive see-saw paddle suspended by two torsional springs from a substrate with symmetric electrodes under each paddle wing. One of the wings is coated with a thin chemically sensitive polymer layer that swells when a specific compound vapor is absorbed. The absorption induced swelling thus causes wing bending and downward deflection proportional to the vapor concentration. Upon application of a fixed DC bias, the deflection is parametrically amplified causing a much larger deflection, and pull-in instability. A sufficiently large amplification results in unstable equilibrium of deflected paddle wing causing it to snap. This amplified drive mechanism does not consume any power, yet it can magnify the observed deflection by one or two orders of magnitude. This deflection is measured through a profilometer as well as a change in capacitance. We present the theory, fabrication and testing results of these sensors.