Page 281 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim
P. 281
MECHANICAL SENSORS 261
Further efforts have been made to fabricate a lateral resonant capacitive sensor
employing thin film polysilicon technology. Figure 8.30(a) shows a resonant capacitive
sensor fabricated in polysilicon along with its response (Figure 8.30(b)). The nonlinear
response is fitted using a high-order polynomial and temperature effects are
compensated for.
Here, the microstructure behaves as a nonlinear resonator and Equation (8.27) is
extended to describe a hard spring (Duffin's equation) so that
l
mx + b mx + k°x + k mx 3 = F x(t) (8.34)
Figure 8.30 (a) Lateral resonant capacitive pressure sensor based on the linear oscillation of a
strained surface micromachined structure; (b) its response to barometric pressure (from Welham
and coworkers (1996)); (c) current silicon process; and (d) latest device with piezoresistive pickup
(Welham et al. 2000)
