Polymer wicking to mass load cantilevers for chemical gravimetric sensors

Achieving size reduction with electrostatic capacitive detection in cantilever resonant gravimetric microsensors necessitates use of narrow gaps and beams, which are incompatible with polymer addition using techniques such as ink jet, spray coat, dip cast, and dip pen deposition. A method is introduced to wick controlled amounts of polymer onto narrow grooves. Polystyrene dissolved in toluene and xylene is deposited onto a target well area using drop-on-demand ink jetting. The solvent with polymer is wicked into a 2 /spl mu/m wide groove running the length of a 4 /spl mu/m wide cantilever. Sidewall 1 /spl mu/m-wide gaps to electrostatic actuation and sensing comb fingers remain free of polymer and operate as intended. The resonator with 410 pg of polymer and sensitivity of 76 fg/Hz is self-excited in a feedback oscillation loop. Initial measurements of saturated concentrations of acetone, ethanol and 2-propanol provide 20 Hz to 130 Hz shifts.