Magnetostatic MEMS relays which are capable of commutating the field windings of a DC brushless motor are presented. The commutation system based on these relays is less than 10% the mass and volume of the electronics it replaces, it eliminates all but two wires from the wiring harness, it requires no external control and it dissipates less than 1/1000 th the total motor power. Closure forces greater than 5 millinewton are generated in the relays providing four-wire contact resistance readings of less than 35 milliohms. Utilizing gold-to-gold contacts, hot switching of currents greater than 1 amp has been demonstrated. For lifetimes greater than 10 million cycles (greater than 50 hours of continuous motor operation), switched currents should be limited to less than 120 milliamp. At signal levels of less than 1 milliamp, no failure is seen after greater than half a billion cycles. No contact bounce is seen during make or break. Motor commutation in vacuum down to 5 microtorr and from room temperature down to -30/spl deg/C has been demonstrated.

A description is given of a functional silicon micromachined device that permits non-invasive, bidirectional, highly specific communication with cultured mammalian neurons. The heart of the system is a well structure that holds the cell in close proximity to a metal extracellular electrode while permitting normal outgrowth of axons and dendrites. An iterative approach is used to create a design that allows normal growth of the neurons while preventing their escape. An array of 16 such neurowells makes it possible to perform studies of biological neural network development and function with unprecedented detail.

A magnetostatic micromachined switch for commutation of DC brushless motors has been developed.Large contact closure forces (> 5 mN) are generated on a permalloy plate by strong perma nent magnets attached to the rotating motor shaft.Four point mea surements of the switch show a contact resistance of less than 35 milliohms.Commutation of a three-phase, four-pole DC brushless motor by three of the MEMS switches has been successfully demon strated.In hot-switched, resistive load lifetime testing, no failure is seen after greater than 500 million cycles at low currents ( < I mA) but at much higher currents (0.45 A), lifetime is reduced to less than I million cycles.

The design, fabrication and mechanical testing of a new types of silicon-micromachined structures for in vivo and in vitro extracellular stimulation and recording are presented. The novelty of these structures are neuron wells fabricated in a silicon membrane 20 μm thick, in which cultured neurons can be implanted and grown. Different kinds of neuron wells have been fabricated, but no difference in the survivability of implanted neurons has been observed. Neurons were successfully grown in various designs of neurowells as building elements of devices for both in vivo and in vitro applications. This approach should improve signal-to-noise ratio of the existing structures for extracellular recording.

A large-force, fully-integrated, electromagnetic actuator for microrelay applications is presented. Designed for high efficiency, the actuator integrates a cantilever beam and planar electromagnetic coil into a low-reluctance magnetic circuit using a combined surface and bulk micromachining process. Experimental testing shows that a coil current of 80 mA generates a 200 /spl mu/N actuation force. Theoretical extrapolation of the data indicates that an actuation force in the millinewton range can be produced by a coil current of 800 mA. The tested actuators have a footprint of less than 8 mm/sup 2/ and their fabrication is potentially compatible with CMOS processing technology.