A sensitive electronic capacitance measurement system to measure the comb drive motion of surface micromachined MEMS devices

Abstract

We have developed a method to measure the displacement of a MEMS comb drive using a probe station, by monitoring the minute capacitance changes between the fingers due to the motion. Probe station measurements of the capacitance changes of small comb drives are usually hampered by the relatively large parasitic capacitances present. This can be reduced by using a proper measurement layout design for minimal on-chip capacitance, in combination with a resonant LCR-circuit to counteract the effect of the probe station cable capacitance. The method results in a measurement that, after averaging, enables us to see the motion of a MEMS comb drive with 4 nm peak-to-peak noise sensitivity, corresponding to a capacitance change around 10 aF. Both the effect of comb drive lateral motion and that of levitation are observed.

Microscale Friction Reduction by Normal Force Modulation in MEMS

“…The actual normal and lateral positions of the slider with respect to the countersurface are measured by monitoring the capacitance change of a second set of comb drive fingers with attofarad accuracy (indicated as 'measurement combs' in Fig. 1) [34].…”

The Leiden MEMS Tribometer: Real Time Dynamic Friction Loop Measurements With an On-Chip Tribometer

“…In order to obtain accurate position readings, we have developed a method to obtain the capacitance changes of moving comb drives with high resolution in the presence of large, non-constant parasitic on-chip and cable capacitance [32]. The comb drive motion is intended to be fully in plane, but in practice it also has a small out-of plane component (levitation, first discussed by Tang et al [33]).…”

Capacitive displacement sensor for detecting planar submicrometer motion

“…[9][10][11][12] Recent applications of nano scale capacitive sensors demonstrate great variety of designs and performances. 4,[13][14][15][16][17] Authors in Ref. 14 built a comb actuator with a motion range of 2 µm with capacitance resolution of approximately 5 fF.…”