Noise and sensitivity in polysilicon piezoresistive cantilevers

Piezoresistive cantilevers with dimensions of 200 x 50 x 1.8 mum(3) have be en fabricated from polycrystalline silicon using reactive ion etching (RIE) and back etching processes. Full Wheatstone bridges have been designed sym metrically on-chip, with two resistors placed on the cantilevers and two re sistors on the substrate. The differential measurements of the two cantilev ers can reduce the thermal shift of the signal in the system and the extern al noise in the laboratory. The characteristics of the fabricated cantileve rs have been analysed by measuring the noise and the sensitivity. The measu red noise spectra show that the 1/f noise is the dominant noise source at l ow frequencies. With the linear relation between 1/f noise and bias voltage s, the Hooge factor (alpha) was calculated to be 0.0067. The 1/f noise was explained in terms of a lattice scattering model, which occurs in the deple tion region of the grains. The displacement sensitivity of the cantilevers (DeltaR/Rz(-1)) was calculated to be 1 x 10(-6)nm(-1) by measuring the resi stance change and the vertical deflection of the cantilever. The gauge fact or of the piezoresistive cantilever was calculated to be 19. At a 3V bias v oltage and 1000 Hz measurement bandwidth, I mn of minimum detectable deflec tion has been obtained.