A new thermal switch design through CMOS MEMS fabrication process

The present study focuses on implementing a novel CMOS-MEMS thermal switch by using commercially available TSMC 0.35 μm two-poly four-metal (2P4M) CMOS process. There are two novel designs in this paper: first, the soft contact structure and post-processing fabrication; second, a new design of thermal actuator. To create the soft contact structure, residual stress effect has been utilized to make different bending curvatures. According to the experiments, the layer Metal1 has the largest residual stress [1] effect that can achieve the largest deflection in z-axis. Because the residual stress of the layer metal-1 is negative, the structure will bend down after release, the largest contact area which has been set up to get the lowest contact miss ability. In the post-processing fabrication, 0.3μm thickness gold will be patterned on the contact tips. Due to gold, rather than Aluminum, has no oxidation issue, it has more reliability on preventing the problem of oxidation than Aluminum. In the new thermal actuator design, we design a novel folded-flexure [2, 3] with the electrothermal excitation to turn the switch on or off. In the prototype, the device size is 500 μm * 400 μm and the gap between two contact pads is 9 μm in off-state. Depending on the simulation results, the switch can work stably at 3 volts, and the working temperature and operating bandwidth are individually 20-200°C.