MEMS -> MEMS switch uses magnetic actuation

MEMS switch uses magnetic actuation

MEMS switch uses magnetic actuation
By Jun Shen, Chandler, Ariz., jshen@microlab.net, Charles Wheeler, Vice Pres and CTO, Microlab Inc., Chandler, Ariz., Meichun Ruan, Sr. Device Engineer, Microlab Inc., Chandler, Ariz., EE Times
July 12, 2001 (7:43 p.m. EST)
URL: http://www.eetimes.com/story/OEG20010712S0078

MEMS RF switches have distinct advantages over solid-state switches. They provide much lower insertion loss, higher isolation, better linearity, use lower power and are potentially cheaper. They also outdo conventional electromechanical switches and relays in terms of switching speed, integration capabilities, power and cost.

However, most MEMS RF work has focused on electrostatic actuation, presumably because other actuation mechanisms, such as magnetic and thermal actuation, consume much power and thus are not suitable for many applications.

Microlab and Arizona State University have demonstrated a magnetic latching and switching mechanism that eliminates the need for the static power supply and that can latch on or off with zero power required to hold this state. The switch is nonvolatile and bistable. Because of the long-range magnetic forces, the switch-it has been named MagLatch-requires low operation voltage (less than 5 V) .

The design consists of a cantilever, an embedded planar coil, a permanent magnet and the necessary electrical contacts. As an electrical switch, the cantilever is a two-layer composite consisting of a soft magnetic material NiFe permalloy on its topside and a highly conductive material, such as gold, at the bottom surface. The cantilever is supported by torsion flexures from the two sides. The contact end to the right of the cantilever can be deflected up or down by applying a current through the coil. When down, the cantilever makes electrical contact with the bottom conductors and the switch is on, or closed; when the contact end is up, or opened, the switch is off. The permanent magnet holds the cantilever up or down after switching, making the device a latching relay. Single-pole-double-throw and RF switches can be designed. Latching optical switches can be made based on similar principles.

The principle behind the latching characteristics is the preferential magnetization of a cantile ver made of soft magnetic material (for example, permalloy). In a constant, nearly perpendicular magnetic field, a cantilever can have a clockwise or a counter-clockwise torque depending on the angle between the cantilever and the field, which leads to the bistability. To switch the relay, a second magnetic field, in this case generated by a short current pulse through a coil, realigns the magnetization of the cantilever causing it to flip. A static external magnetic field instantly latches the switch in the closed or open position, respectively. The switch maintains this state until the next switching signal realigns the cantilever. The relay consumes no power to maintain the latched state.