Simulation, Design, Fabrication, and Testing of a MEMS Resettable Circuit Breaker

We describe a novel concept for a microelectromechanical systems (MEMS) resettable circuit breaker. The concept involves fabricating the circuit breaker and the reset switch using a single microcantilever. The MEMS resettable circuit breaker consists of a microcantilever that is pulled toward the bottom electrode by electrostatic actuation. The MEMS cantilever also has a thermal heater, and when a current passes through the heater, it overcomes the electrostatic actuation force thereby disconnecting the circuit. A detailed finite element analysis using thermal-electric-structural multiphysics phenomena was studied. Electrostatic-structural coupled-field analysis shows the circuit breaker switch has a pull-in voltage of about 31 V for a singlecrystal Si cantilever with a thickness of 2 μm, a length of 1000 μm, and a width of 500 μm. Thermal-electric coupledfield analysis shows the switch maximum temperature is 80.5 °C at a 50-mA current flow. Thermal-electric-structural sequential analysis shows the cantilever tip has a maximum upward displacement of 0.3 μm, which is just enough to open the switch. The impact of the initial film stress in the SiO
₂
insulation layer was also simulated, and the results show that the film stress has a significant impact on the initial cantilever position after release. Fabrication of the chips was done using two wafers, a silicon-on-insulator (SOI) wafer, and a double-side polished silicon wafer. The SOI wafer device silicon layer was selected as cantilever material. Platinum was selected as heater material and chrome-gold was selected for bonding, trace, and electrostatic electrodes. Electrical testing results confirmed the proposed and simulated operation principle of the MEMS resettable circuit breaker. The results showed that the switch achieved good contact at an electrostatic switch-ON voltage of about 55 V. The measured circuit breaker current threshold is in the range of 45-55 mA.