Characteristics of the Wear Process of Side-Wall Surfaces in Bulk-Fabricated Si-MEMS Devices in Nitrogen Gas Environment

Wear is one of main obstacles to expand functions of microelectromechanical systems (MEMS). While the wear mechanism of surface-fabricated MEMS devices has been extensively investigated, the characteristics of bulk-fabricated Si-MEMS devices have hardly anywhere been reported. In this research, wear tests of bulk-fabricated Si-MEMS devices were carried out on a composite microtribology test system using out-of-chip loading and driving mechanisms. Wear evolution and the effects of initial topology, driving frequency and external normal load have been investigated over the running time from 5 s to 120 min. A transition from adhesive wear to abrasive wear has been observed, which is conceptually analogs to the wear process in surface-fabricated devices. The results of the experimental study indicate that plastic deformation of the silicon substrate down to nano-size and migration of the wear debris are the main characteristics of wear. When the normal load is >56 μN, wear particles can be grinded into pie or mud shape. At driving frequency higher than 2,000 Hz, the agglomerated wear debris can be thrown out of the contact zone, while at 100 Hz it remains on the rubbing surface and causes evolutionary damages. The energy consumption during wear has been estimated by tests at elevated temperatures, which is helpful to understand the poor wear resistance and the mechanical dominant mechanism of wear.