Influence of Scallops in Deep Reactive Ion Etching on Vertical Comb-Based Sensors/Actuators

The Bosch deep reactive ion etching (DRIE) is a critical bulk-silicon-micromachining (BSM) processing for vertical comb-based (VC-based) sensor/actuator fabrication. However, scallop in the Bosch process leads to undesirable VC gap varying. Herein, influence of scallops on performance of VC-based sensors/actuator is presented. Firstly, mathematical modeling of scallop distribution on VC sidewall is established. From this, capacitance of VCs and electrostatic force of VC-drive (VCD) actuators are derived, including for rotating and piston types. Then, finite element analysis (FEA) is used as modeling verification. Results indicate that the varying amplitude and period of VC capacitance are attributing to depth and period of scallops, respectively. Moreover, limitation of VCD actuators' positioning accuracy due to scallop is given.