An SOI process for fabrication of solar cells, transistors and electrostatic actuators

We have developed a new process for fabricating integrated, solar-powered microelectromechanical systems (MEMS) on a silicon-on-insulator (SOI) wafer. The intended applications for this process are autonomous microsystems, such as microrobots and distributed sensor networks. Two versions of the process have been created. The first combines solar cells and MEMS devices with NMOS transistors utilizing metal gates. This version has yielded solar cell efficiencies greater that 11%, a 200 cell array with an output of 88.5 V and transistor breakdown voltages above 25 V. Using this process, a fully integrated device has been demonstrated consisting of an electrostatic, gap-closing actuator being powered by an on-board buffer consisting of an NMOS inverter. The only external connections were ground and a 5 V control signal. A second version has also been developed which provides better solar cell performance and CMOS circuits utilizing polysilicon gates. This version has yielded solar cell efficiencies greater than 14%, a 90 cell array with an output over 50 V, and NMOS and PMOS devices with breakdown voltages greater than 50 V.