Testing and characterisation of electrothermal microgrippers with embedded microheaters

This paper presents our work on design, fabrication and characterisation of electrothermal microgrippers for micromanipulation and microassembly applications. The SU-8 based microgrippers were designed with embedded microheaters in the actuation structures of the grippers to improve thermal efficiency and to reduce the undesirable out of plane movement of the gripper tips. Electrothermal testing and characterisation have been conducted to determine the displacement between the gripper tips under an applied voltage. A measurement method based on an image tracking approach was used to measure gripper displacement. It has been shown that a displacement of 11 μm can be obtained at the actuation voltage of 0.65 V. The microheaters were also used as the sensors to determine the heater temperature by measurement of the resistance change at the applied voltage. The temperature coefficient of resistance (TCR) was determined independently and then used to calculate the heater temperature based on the measured resistance change. The values of TCR of the thin film chromium/gold microheaters were determined to be 0.00135/°C and 0.00147/°C which are significantly less than the value of 0.0034/°C for bulk gold material. Thus it is important to determine the TCR of the thin film microheaters for accurate calculation of the heater temperature at an applied actuation voltage.