Robot Leg Motion in a Planarized-SOI, Two-Layer Poly-Si Process

With the ultimate goal of creating autonomous microrobots, we developed a five-mask process that combines two polysilicon structural layers with 50- -thick SOI structures and a backside substrate etch. The polysilicon layers provide three-dimensional (3-D) hinged structures, high compliance structures, and electrical wiring. The SOI structural layer yields much stronger structures and large-force actuators. This process was developed as a part of a three-chip solution for a solar-powered 10-mg silicon robot. Here, we describe the fabrication of this planarized-SOI, two-layer poly-Si process (henceforth called the SOI/poly process), basic modules in the design of robot legs in this process, and lastly, the results of fabricated robot legs. In designing the leg structures, we developed guidelines and test structures to provide a better understanding of the robot leg performance. These guidelines include understanding the relationship between the lateral etch depth to the actuator spacing and performing static friction tests of polysilicon flaps to more accurately model the frictional forces of the linkages. Last, we report on the performance of the robot legs and inchworm motors. On an 8 mm 3 mm robot, we have demonstrated a 1 degree-of-freedom (DOF) robot leg, 1 mm in length, which demonstrates up to 60 of vertical leg force with an angular deflection of almost 30 . A two-DOF robot leg, also 1 mm in length, operated with at least 90 of angular deflection, and each inchworm motor demonstrated a shuttle displacement of 400 with speeds up to 6.8 mm/s. In addition to robot legs, a bidirectional inchworm motor that produces equivalent forces in both directions was also fabricated in this SOI/poly process. This motor uses an additional set of gap-closing-actuator (GCA) arrays to prebias the drive frame.