Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
1999-11-08
2001-07-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
Reexamination Certificate
active
06262512
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electromechanical systems, and more particularly to microelectromechanical systems.
BACKGROUND OF THE INVENTION
Microelectromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of microelectronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
A major breakthrough in MEMS devices is described in U.S. Pat. No. 5,909,078 entitled Thermal Arched Beam Microelectromechanical Actuators to Wood et al., the disclosure of which is hereby incorporated herein by reference. Disclosed is a family of thermal arched beam microelectromechanical actuators that includes an arched beam which extends between spaced apart supports on a microelectronic substrate. The arched beam expands upon application of heat thereto. Means are provided for applying heat to the arched beam to cause further arching of the beam as a result of thermal expansion thereof, to thereby cause displacement of the arched beam.
When used as a microelectromechanical actuator, thermal expansion of the arched beam can create relatively large displacement and relatively large forces while consuming reasonable power. A coupler can be used to mechanically couple multiple arched beams. Thermal arched beams can be used to provide actuators, relays, sensors, microvalves and other MEMS devices. Other thermal arched beam microelectromechanical devices and associated fabrication methods are described in U.S. Pat. No. 5,994,816 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Devices and Associated Fabrication Methods, the disclosure of which is hereby incorporated herein by reference.
Notwithstanding the above-described advances, there continues to be a need to further increase the thermal efficiency of MEMS devices. By increasing the thermal efficiency of MEMS devices, lower power, larger deflection, higher forces and/or higher speed operations may be provided.
SUMMARY OF THE INVENTION
It therefore is an object of the present invention to provide improved microelectromechanical structures.
It is another object of the present invention to provide improved thermal arched beam microelectromechanical devices.
It is yet another object of the present invention to provide microelectromechanical devices that can have higher thermal efficiency.
It is still another object of the present invention to provide thermal arched beam devices that can have higher thermal efficiency.
These and other objects may be provided, according to the present invention, by microelectromechanical structures that include a microelectronic substrate, at least one support on the microelectronic substrate and a beam that extends from the at least one support and that expands upon application of heat thereto, to thereby cause displacement of the beam. Application of heat to the beam also creates a thermal conduction path from the beam, through the at least one support and into the substrate. A thermal isolation structure in the heat conduction path reduces thermal conduction from the beam through the at least one support and into the substrate, compared to absence of the thermal isolation structure. The thermal isolation structure preferably has lower thermal conductivity than the beam and the at least one support. The heat that remains in the beam thereby can be increased. Higher thermal efficiency may be obtained, to thereby obtain lower power, larger deflection, higher force and/or higher speed operation.
Microelectromechanical structures according to the present invention preferably comprise a microelectronic substrate and spaced apart supports on the microelectronic substrate. A beam extends between the spaced apart supports and expands upon application of heat thereto, to thereby cause displacement of the beam between the spaced apart supports. The application of heat to the beam creates a thermal conduction path from the beam through the spaced apart supports and into the substrate. A thermal isolation structure in the heat conduction path reduces thermal conduction from the beam, through the spaced apart supports and into the substrate, compared to absence of the thermal isolation structure. The thermal isolation structure preferably has lower thermal conductivity than the beam and the at least one support. The heat that remains in the beam thereby can be increased.
The thermal isolation structure may comprise a thermally insulating structure at each end of the beam, between the beam and the spaced apart supports, to thereby thermally isolate the beam from the supports and the substrate. Alternatively, or in addition, the thermal isolation structure may comprise a thermally insulating structure in each spaced apart support, between the beam and the substrate, to thereby thermally isolate the beam from at least a portion of the supports and from the substrate. Alternatively, or in addition, the thermal isolation structure may comprise a thermally insulating structure in the substrate adjacent each spaced apart support, to thereby thermally isolate the beam and the supports from at least a portion of the substrate. Alternatively, or in addition, the thermal isolation structure can include at least one thermally insulating structure in the beam, to thermally isolate a portion of the beam from remaining portions of the beam, from the supports and from the substrate.
The beam may be heated externally by an external heater, or internally by passing current through the beam. When current is passed through the beam, and the thermal isolation structure includes a thermally insulating structure at each end of the beam, an electrically conductive structure also may be provided on each of the thermally insulating structures, to provide an electrically conductive path from the beam to the spaced apart supports. A thermally insulating structure in each spaced apart support may be provided when it is difficult to thermally isolate a portion of the beam. For example, when the beam comprises metal, a silicon nitride tether may be provided in each spaced apart support, between the metal beam and the substrate. Finally, a thermally insulating structure in the substrate may comprise an insulator-containing trench, such as an oxide-filled trench, in the substrate beneath each spaced apart support.
In all of the above embodiments, a trench also may be provided in the microelectronic substrate beneath the beam, to provide increased spacing between the beam and the surface of the substrate beneath the beam. The heat that remains in the beam thereby may be increased by providing an increased air gap between the beam and the substrate, to thereby allow reduced thermal conduction and/or convection directly from the beam to the substrate through the air gap.
Microelectromechanical structures according to the present invention preferably are employed with thermal arched beams as described in the above-cited U.S. patents, that comprise an arched beam that is arched in a predetermined direction and that further arches in the predetermined direction upon application of heat thereto. The predetermined direction preferably extends generally parallel to the face of the microelectronic substrate. A valve plate, coupler, capacitor plate, relay contact and/or other structure may be mechanically coupled to the thermal arched beam, for example as described in the above-cited patents.
One preferred embodiment of microelectromechanical structures according to the present invention includes an arched silicon beam that extends between spaced apart supports on a microelectronic substrate. The arched silicon beam is arched in a predetermined direction and further arches in the predetermined direction upon application of heat thereto, to thereby cause displacement of the arched silicon beam in the predetermined direction. A silicon dioxide link is provided at each end of the arched
Dougherty Thomas M.
JDS Uniphase Inc.
Myers Bigel & Sibley & Sajovec
LandOfFree
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