Wear characteristics of large aspect ratio silicon microbearing systems

• High aspect ratio silicon journal microbearings were fabricated and tested.
• Wear morphology strongly indicative of adhesion or abrasion wear.
• Wear was measured using pixelated optical profiler images.
• Wear coefficients fell between polysilicon values at the macro- and microscale.

This paper addresses the wear characteristics of large aspect ratio (length-to-diameter) silicon microbearing systems using an enhanced experimental test rig. The test system is comprised of a rigid rotor which has been manually assembled onto a fixed hub to form the microbearing. CMOS-based lithographic and etching processes, including deep-reactive ion etching, are employed in the construction of the rotor and hub with length to diameter ratio of approximately 0.5 and radial clearance values in the range from 3.5 to 9.2 μm. The rotor is pneumatically driven by nitrogen gas at a constant supply pressure delivered through a rectangular microchannel.A new methodology for measuring wear was developed by digitizing optical microscope images of the rotor system, and the rotor load was calculated from CFD models of the entire rotor-hub system. It was found that the tested silicon microbearings have a wear coefficient (based on the well-known Archard relation) which falls within a relatively narrow band bounded by previously published values for polysilicon materials tested at the macroscale and microscale. The wear coefficient is also observed to be relatively unchanged during the wear process which is more characteristic of macroscale wear processes.