Design and fabrication of an electro-thermal microactuator with multidirectional in-plane motion

We present a new electro-thermal microactuator with multidirectional in-plane motion by selectively applying a single potential across two of four contacts. The design principle is based on the asymmetrical thermal expansion of the structure with 1. different lengths and widths of the beams, 2. varying resistivities of the beams by selectively doping, and 3. rigorous control of the thermal boundary conditions. Analytical models are derived to describe the electro-thermo-mechanical performances of the actuator. The commercial finite element package ANSYS is used to demonstrate the feasibility of the design, to verify the analytical results, and to characterize the actuator in details under complex heat transfer conditions. The design parameters that significantly affect the performance of the actuator are discussed, including the structural dimension, selective doping, and heat transfer condition. Conventional silicon-based micromachining techniques compatible with IC processes are used to fabricate the microactuator. The phosphorous-doped polycrystalline silicon film by low pressure chemical vapor deposition (LPCVD) is used to demonstrate the effectiveness of the microactuator. In conclusion, it is found that input voltages 7 V are required for the microactuator to achieve the maximum displacement in 8 µm and the maximum tip force in 8 µN with the operating temperature below 300 °C, the power as low as 10 mW, and the response time about 30 msec in average.