Design and simulation of mass sensors based on horizontally actuated silicon cantilevers

Two designs for a mass sensor based on polysilicon cantilevers for hybrid integration with CMOS circuitry are introduced. The change of deposited mass on the cantilever is measured through the detection of frequency or settling-time shifts in the cantilever oscillation, which is horizontally produced by an interdigitated comb capacitor structure. Interdigitated comb actuators are preferred over parallel plates due to their larger displacement which is not a function of the gap between electrodes. Also, using the interdigitated comb as sensor port, the capacitive change is increased and the nonlinearity before pull-in effect is reduced. Therefore, the signal detection is improved, reducing readout electronics design effort. The preliminary results obtained are validated through finite element analysis and electrical simulations in SPICE. Mass-frequency changes of 3.43 pg/Hz and 6.71 pg/Hz are predicted for these designs with natural frequencies of 11.461 kHz and 8.465 kHz respectively. Also, settling time variations of 1.69 ms/ng and 0.7 ms/ng were obtained.