SPICE modeling of polysilicon thermal actuators

This paper reports on modeling the behavior of micromachined polysilicon thermal actuators. The thermal actuators used in this research were fabricated using the DARPA-sponsored Multi-User MEMS Processes (MUMPs). Data collected in both air and vacuum demonstrates that thermal actuators can be controlled and positioned using a pulsed input with a period much less than the thermal time constant of the device. Both pulse width and pulse amplitude modulation have been successfully employed to position lateral actuators, lateral actuator arrays, and piston micro-mirrors. In order to better exploit the power averaging characteristics of thermal actuators, SPICE models for polysilicon thermal actuators were developed using relationships between resistance, deflection, and average power. These models incorporate the polysilicon thermal actuator's electrical load and transient characteristics necessary for predicting actuator performance and developing CMOS drive circuits. The SPICE models exhibit good agreement with theory and measured performance of the polysilicon thermal actuators.