Characterization of a MEMS tribogauge

Abstract

A MEMS tribogauge was used for on-chip and in-situ characterization of nano-tribological phenomena (stiction, friction, and wear). The measurements were made on the sidewall surfaces on the tribogauge at the third structural polysilicon layer in the device. The device consists of two orthogonally oriented comb-drive mechanisms that are used for both actuation and sensing functions. One actuator applies a normal load (Fn) to a contacting surface, while the other actuator induces a tangential load (FT). A LabVIEW controlled AD7747 capacitance sensor is used to measure the position of the interacting surfaces. This data is converted into adhesive force information. The spatial resolution of the characterization apparatus is ±10nm. Experiments were conducted with tribogauges with and without a self-assembled monolayer (SAM) coating. The SAM coatings being explored have a fluorocarbon tail group. The tribogauge with no SAM coating is UV/Ozone cleaned to remove organic contaminants. The tribogauge characterization includes: measurement of baseline stiction force FbaselineFOTS, static (FS) and dynamic (FD) coefficient of friction, and induced stiction force FinducedFOTS. The UV/Ozone treated tribogauge was used to measure the baseline stiction force. Additional experiments showed that the induced stiction force increases in proportion to the increase in the number of load cycles, indicating degradation of the SAM coating and inducing surface topographical changes to the interacting surfaces.