An on-chip test structure for studying the frictional behavior of deep-RIE MEMS sidewall surfaces

In this paper, an on-chip micro-mechanical test structure has been developed to investigate the frictional behavior of Deep-RIE sidewall contacting surfaces of single crystal silicon which is most widely used in micromechanical systems (MEMS). The test structure is fabricated on Silicon on Insulator (SOI) wafer using standard MEMS process. Two orthogonally placed electrostatic comb-drive actuators are adopted, one comb drive is used to align a contact with the friction surfaces under a certain normal load and another one is used to generate the tangential motion on contacted sidewall surfaces. To assess the frictional behavior, both static and dynamic friction coefficients were observed on the contacted surfaces during the experiment with different DRIE process parameters. Through experiments, it was found that with the increment of normal forces, the static friction coefficient is no longer a constant value and it has less effect on dynamic friction coefficient. DRIE process parameters greatly influence the frictional properties on both static and dynamic friction coefficients.