Magnetic actuation is key to high power microrelay

Magnetic actuation is key to high power microrelay“The significant issue in using a magnetically-actuated relay is that you can achieve larger contact forces and a greater air gap between contacts when compared to electrostatic relays…”. Steve Bush. A low actuation voltage magnetically-actuated microrelay that can be batch-produced using established micromachining techniques has been developed at Georgia Institute of Technology. “The significant issue in using a magnetically-actuated relay is that you can achieve larger contact forces and a greater air gap between contacts when compared to electrostatic relays,” explained William Taylor, who developed the devices, “The larger gap allows the relay to control higher voltage signals than would be permitted with other types of microrelays.” Really small relays… These microrelays, less than 8mm across and 200?m high, switch currents up to 1.2A, operate at 5V and have contact resistance under 100mOhm. Microrelay technologies tend to use electrostatic forces to move the contacts. These require higher actuation voltages than magnetically operated relays, though they consume less actuating current. The magnetic and electrostatic approaches offer advantages that depend on the specific application, said Taylor. The Georgia Tech microrelays can be controlled by a 5V signal, have contact resistance under 100mOhm and handle contact currents of up to 1.2A, claimed to be unmatched in microrelays. The relays range in size from 3 x 4mm up to 7 x 8mm, and are less than 200 microns in height. Between 100 and 500 can be made at once. Prototypes have been tested through more than 850,000 operating cycles without failure. Making microrelays The microrelay fabrication is based on standard polyimide mould electroplating techniques and consists of an integrated magnetic plate, made of a magnetic nickel-iron material, which is surface micromachined above a set of contacts. Magnetic flux from current applied to the coil, pulls the nickel-iron plate down until it touches the contacts, closing the circuit. For normally-closed operation, a permanent magnet holds the actuating plate down and the contacts closed. Current pulls the plate off of the contacts, opening the circuit. The permanent magnet for this type of relay is not currently made through micromachining techniques and is added during the fabrication process. Fabrication begins with a silicon wafer that has been oxidised. The researchers then deposit a seed layer and electroplate a lower magnetic core, adding an insulating polymer mould above that. Then a coil is electrodeposited and coated with an insulator. The remainder of the fabrication is completed by alternating steps of polymer mould deposition and electroplating. “By doing it in this way, many devices can be built on the same wafer at the same time, so there is no need for hybrid assembly,” said developer William Taylor, “Everything is assembled on the same wafer.”


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