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.
We present a set of in-situ test structures for simultaneously determining residual stress (RS), Young's modulus (YM) and thermal expansion coefficient (TEC) of a film. Analytical models as functions of the displacement, geometry and material property of the test structures are theoretically derived for the task of extracting the film properties. This method utilizes available measurement apparatus and all the properties are identified and quantified on the same apparatus. The test structures consist of the measured film and the calibration film and are fabricated by a simple sacrificial-layer micromachining technique. The measured films made of undoped LPCVD polycrystalline silicon and the calibration film made of PECVD silicon nitride are used to demonstrate the effectiveness of the proposed method. The average calibrated residual stresses of undoped polysilicon films with deposition temperatures of 600°C and 620°C are 105± 5MPa and 240 ± 10MPa, respectively, and the corresponding Young's moduli are 170± 5GPa and 150 ± 5GPa. But the thermal expansion coefficient is approximately 2.7x 10-6 average.