Electricity: circuit makers and breakers – Electrostrictive or electrostatic
Reexamination Certificate
1999-03-30
2001-11-20
Friedhofer, Michael (Department: 2832)
Electricity: circuit makers and breakers
Electrostrictive or electrostatic
Reexamination Certificate
active
06320145
ABSTRACT:
TECHNOLOGICAL FIELD
The invention relates to miniaturization of electronic components and, in particular, to fabricating and using a micromachined magnetostatic relay or switch.
BACKGROUND
Manufacturers and users of electrical and electronic components strive to reduce the size and increase the reliability of these components and the systems in which they are used. Miniaturization of components leads to more compact and lightweight systems, which increases the range of uses for these systems and decreases the costs associated with transporting and using these systems. Improving component reliability lengthens the lifespan and enhances the performance of systems in which the components are used.
Miniaturization and reliability improvements are particularly important in areas such as space exploration and satellite communications. The cost of launching equipment from the Earth's surface is directly related to the size and weight of the equipment, and even modest reductions in equipment size produce large reductions in cost. Likewise, improving the reliability of components used in spaceborne systems extends and improves the performance of these systems, thus reducing the associated costs. In general, each newly developed generation of space oriented components and systems must meet or exceed the performance and cost standards set by previous generations.
One example of commonly used components for which size and reliability are particularly important is DC electric motors. DC motors are used widely as motive devices for linear and rotary drives in spaceborne applications. As gains have been made in the miniaturization of DC motors, the size, weight, and complexity of DC motor systems have become dominated by the commutation and control electronics that drive the motors. The disparity between the size of the motor and the size of its control electronics is particularly noticeable in a highly miniaturized motor, such as a commercially available 3-mm diameter motor, the commutation and control electronics of which are more than ten times larger than the motor itself. Even modest reductions in the power budget, complexity, mass, and volume of components such as these produce tremendous gains in the cost and reliability of spaceborne systems.
SUMMARY
In recognition of the above, the inventors have developed micromachined magnetostatic relays or switches that are highly miniaturized and highly reliable. The switches are made very small using micromachining fabrication techniques, and the materials are carefully selected to provide high reliability. The switches are useful in a wide variety of microelectronic mechanical system (MEMS) applications, particularly in the miniaturization of DC electric motors. For example, in one embodiment of the invention, the switches are used as relays in a MEMS circuit that replaces the conventional commutation and control electronics in a DC motor. This MEMS circuit is much smaller than the DC motor itself, so the size of the motor, not the size of the commutation electronics, is most critical in space constrained applications. The magnetostatic switch requires no biasing current or voltage and is useful in directly switching loads.
In one aspect, the invention features a magnetostatic switch having at least one substrate formed from a nonconductive or semiconductive material and a springing beam, such as a cantilever beam or a torsional beam, formed on the substrate. Two electrically conductive contacts define at least two switching states: (1) an open state in which the conductive contacts are physically separated from each other, and (2) a closed state in which the conductive contacts physically contact each other. One of the conductive contacts is formed on the springing beam. The springing beam includes a magnetic material which, in the presence of a magnetic field, creates an actuation force that causes the conductive contacts to switch from one of the switching states to another of the switching states.
In some embodiments, the springing beam includes a layer of material deposited onto the substrate. In other embodiments, the springing beam is formed from a portion of the substrate and is surrounded by a void left after etching away a portion of the substrate.
In some cases, one of the conductive contacts is formed on the substrate. In other cases, this conductive contact is formed on another substrate. In alternative embodiments, the springing beam is formed substantially from the magnetic material or from a nonconductive material or semiconductive material.
In other embodiments, the magnetic material is formed on a surface of the springing beam, and one of the conductive contacts is formed either on an opposing surface of the springing beam or on a surface of the magnetic material. Both normally open and normally closed versions of the switch are useful.
In another aspect, the invention involves the fabrication of a magnetostatic switch. A temporary layer of removable material is formed over a portion of a rigid substrate. A springing beam then is formed by depositing a layer of material over at least a portion of the temporary layer and over at least some portion of the substrate that is not covered by the temporary layer. The temporary layer then is removed to form a gap between the substrate and a portion of the springing beam.
In some embodiments, an electrically conductive contact layer is formed over at least a portion of the springing beam. Other embodiments include forming an electrically conductive contact layer over at least a portion of another rigid substrate, forming a patterned layer of material over a portion of the other substrate to serve as a spacing layer, and bending the two substrates to position the springing beam and the contact layer between the substrates.
Some embodiments include forming a layer of magnetic material, such as permalloy, on the springing beam. In other embodiments, the springing beam itself is formed from the magnetic material. In some of these embodiments, the electrically conductive material includes a metal, such as silver or gold, with good contact properties.
Still other embodiments include forming at least two electrically conductive areas, electrically isolated from each other, on a third substrate. The third substrate then is bonded to the other two substrates so that one of the conductive areas connects electrically to the springing beam and another of the conductive areas connects electrically to the contact layer. Electrically conductive pegs extend from the conductive areas on the third substrate and bond electrically to the other substrates.
Other embodiments and advantages will become apparent from the following description and from the claims.
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John Wright, et al.; Magnetostatic MEMS Relays for the Miniaturization of Brushless DC Motor Controllers; Jan. 1999; MEMS '99 Conference.
Tai Yu-Chong
Wright John A.
California Institute of Technology
Fish & Richardson P.C.
Friedhofer Michael
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