A MEMS Device for Studying the Friction Behavior of Micromachined Sidewall Surfaces

A microelectromechanical system device fabricated by deep reactive ion etching for friction characterization was developed with single-crystal silicon in this paper. Two orthogonally placed electrostatic comb-drive actuators were adopted to apply the normal load and generate the tangential motion. A sensing plate for sliding contact and a driving plate with two bumps designed for the Hertzian contact are included in the testing device. With an image processing technique developed, experimental displacement data were extracted from the captured video frames. A quasi-static stick-slip model was developed to predict the transitions between static and kinetic friction at the contacting sidewall surfaces. Both static and kinetic friction coefficients can be determined by using this model, and these measured results are shown to be insensitive to errors in the calculation of the electrostatic forces. The measured displacements of the driving and sensing plates are in good agreement with the trend predicted by the model. Based on the Hertz theory, the contact silicon interface has been found to be in an elastic regime at the scale of the designed bumps. With the aid of the quasi-static stick-slip model, a saturation phenomenon of the kinetic friction at the sidewall surfaces was observed while the normal load was increased.