A micromachined surface stress sensor with electronic readout

A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and filtered resulting in a dc output voltage proportional to the change in differential surface stress. The differential surface stress change of the Au(111) coated silicon sensors due to chemisorbed alkanethiols is Δ s ≈-0.42±0.0028 N m-1 for 1-dodecanethiol (DT) and Δ s ≈-0.14±0.0028 N m-1 for 1-butanethiol (BT). The estimated measurement resolution (1 Hz bandwidth) is ≈0.12 mN m-1 (DT: 0.2 pg mm-2 and BT: 0.8 pg mm-2) and as high as ≈3.82 μN m-1 (DT: 8 fg mm-2 and BT: 24 fg mm-2) with system optimization.