Magnetically actuated microrelay uses
micromachining for batch production

Researchers at the Georgia Institute of Technology (Atlanta, GA) have developed a magnetically actuated microrelay that can be batch-produced in groups of a hundred or more using established micromachining techniques. Traditional magnetically actuated relays are produced from discrete parts one at a time.

According to the relay's developer, William Taylor, “The advantage is that every step you take uses photolithographic techniques to build 100 or 500 relays on a wafer, which can be cut up like semiconductor chips. This provides some real economies of scale and should help lower production costs.” Because the techniques used in fabricating the new devices are compatible with standard microelectronic processing, the microrelay can be integrated–in varying configurations–onto circuit boards in normally-open (NO), normally-closed (NC), and multipole configurations.

The relay ranges in size from 3 x 4 mm up to 7 x 8 mm, and measures less than 200 µm high. Although small, its 1.2-A switching current capability and contact resistance of less than 100 milliohm sets a new record for microrelays, according to the institute.

Using a magnetically actuated microrelay as opposed to an electrostatic microrelay allows a larger air gap. The larger air gap enables the device to hold off larger voltages and switch higher voltages. While typical electrostatic relays require high actuation voltages, this device uses a 5-V supply voltage and can be driven by digital logic circuits.

Unlike traditional such devices that are produced one at time,
this magnetically actuated microrelay can be batch-produced
in groups of 100 or more using established micromachining techniques.

The microrelay is fabricated using standard polyimide-mold electroplating techniques in which an integrated planar meander coil and one or more pairs of contacts are positioned above the coil. A mobile nickel-iron magnetic plate is then surface micromachined above the contacts. Applying current to the coil generates a magnetic flux, which pulls the nickel-iron plate onto the contacts and closes an NO circuit.

Relays that are designed to operate in an NC position work in the opposite way. They use a permanent magnet to maintain their NC position and are opened when a current is applied to their coil. Because a permanent magnet for this type of relay has yet to be made with micromachining techniques, it must be added during the fabrication process.

This relay is fabricated with an oxidized silicon wafer that has a seed layer deposited on it. The magnetic core is then electroplated directly above an insulating polymer mold. Remaining fabrication is done by alternating the polymer mold deposition and electroplating steps.

Because of the planar nature of the design, additional contacts can be added by increasing the size of the electromagnet, adding another pair of contacts, and redesigning the coil. The microrelays manufactured using the Georgia Tech process have been tested through more than 850,000 operating cycles without failure. For more information, contact John Toon of the Georgia Institute of Technology at 404-894-6986 or e-mail john.toon@edi.gatech.edu.