Four electrode MEMS switch for higher reliability in power systems
Rather than using two electrodes that can be damaged, Assistant Professor of Mechanical Engineering Sherry Towfighian and graduate student Mark Pallay created a microelectromechanical switch with three electrodes on the bottom and one electrode parallel to the others. The two bottom electrodes on the right and left side are charged while the middle and top electrodes are grounded.
“This type of MEMS switch is normally closed, but the side electrodes provide a strong upward force that can overcome the forces between the two middle electrodes and open the switch,” said Prof Towfighian. This electrostatic levitation is currently not available with the two-electrode system and prevents permanent damage of the device after continuous use and enables a reliable bi-directional switch.
A MEMS cantilever with a parallel plate electrode configuration is pulled-in by applying a voltage above the pull-in threshold. An electrode is fixed to the substrate on each side of the beam to allow electrostatic levitation. Large voltage pulses upwards of 100 V are applied to the side electrodes to release the pulled-in beam, which is needed to overcome the strong parallel plate electrostatic force and stiction forces that hold the beam in its pulled-in position.
“For power lines, this type of MEMS switch would be useful when voltage goes beyond a limit and we want to open the switch. The design allows us to have more reliable switches to monitor unusual spikes in voltage, like those caused by an earthquake, that can cause danger to public safety,” she said.