Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
1999-05-03
2001-04-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
C257S415000
Reexamination Certificate
active
06218762
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microelectromechanical actuator structures, and more particularly to thermally actuated microelectromechanical actuator structures and arrays capable of scalable displacement in multiple dimensions.
BACKGROUND OF THE INVENTION
Microelectromechanical structures (MEMS) and other microengineered devices are presently being developed for a wide variety of applications in view of the size, cost and reliability advantages provided by these devices. Many different varieties of MEMS devices have been created, including microgears, micromotors, and other micromachined devices that are capable of motion or applying force. These MEMS devices can be employed in a variety of applications including hydraulic applications in which MEMS pumps or valves are utilized and optical applications which include MEMS light valves and shutters.
MEMS devices have relied upon various techniques to provide the force necessary to cause the desired motion within these microstructures. MEMS devices are driven by electromagnetic fields, while other micromachined structures are activated by piezoelectric or electrostatic forces. Recently, MEMS devices that are actuated by the controlled thermal expansion of an actuator or other MEMS component have been developed. For example, U.S. patent application Ser. Nos. 08/767,192; 08/936,598, and 08/965,277 which are assigned to the assignee of the present invention, describe various types of thermally actuated MEMS devices. The contents of each of these applications are hereby incorporated by reference herein. Thermal arched beam (TAB) actuators as described in these applications comprise arched beams formed from silicon or metallic materials that further arch or otherwise deflect when heated, thereby creating motive force. These applications also describe various types of direct and indirect heating mechanisms for heating the beams to cause further arching. The aforementioned thermal actuators are designed to move in one direction, i.e., in one dimension. Further, arrays of thermal actuators are typically used to increase the amount of actuation force provided. While these thermally actuated MEMS devices may be used in a variety of MEMS applications, such as MEMS relays, valves and the like, some applications for MEMS thermal actuators require other types of displacement, such as motion in two or three dimensions.
Thermally actuated MEMS devices capable of motion in two or three dimensions have been developed. For example, Lucas NovaSensor of Fremont, Calif. has developed a variety of thermally actuated MEMS devices capable of moving in either two or three dimensions. The devices capable of movement in two dimensions typically comprise one or more arched beams that deflect within a plane in response to thermal actuation. The devices capable of movement in three dimensions are disposed within a plane parallel to the substrate when not thermally actuated. Once thermally actuated, these devices are moved out of this plane, such as by rotating or lifting out of the plane. Another class of thermally actuated devices designed for out of plane movement are disposed out of plane when not thermally actuated. For example, these devices include the thermally actuated devices described by U.S. Pat. No. 5,796,152 to Carr et al., and U.S. Pat. No. 5,862,003 to Saif et al. These devices typically have one end affixed to the substrate and another end free to move in response thermal actuation. Because of this design, the relative amount of movement out of plane is limited. In addition, while all the aforementioned devices can be disposed in an array, the amount of movement produced by the array is not increased proportionately to the number of devices that have been combined into the array.
While thermally activated MEMS structures able to move in one, two, and three dimensions have been developed, it would still be advantageous to develop devices better optimized for increased amounts of movement in these directions. For example, it would be advantageous to provide thermally actuated MEMS devices that could be scalably arrayed so as to correspondingly combine the displacement of individual devices within the array, thereby providing much greater displacement than conventional MEMS devices. Further, it would be advantageous to provide improved thermally actuated MEMS devices that could move along more than one dimension in response to thermal actuation thereof. For example, improved thermally actuated MEMS devices capable of relatively large displacement both in plane and out of plane are needed both for new applications and to better serve existing applications.
SUMMARY OF THE INVENTION
The present invention includes several thermally actuated microelectromechanical structures providing scalable movement in one or more dimensions that collectively address the shortcomings noted above with respect to conventional MEMS devices. In particular, the MEMS structures of the present invention are not only capable of movement in two and three dimensions, but when arrayed are also capable of significantly greater ranges of displacement than conventional thermally actuated MEMS devices.
As such, one embodiment according to the present invention provides a thermally actuated microelectromechanical structure comprising a microelectronic substrate, at least one anchor, and a pair of arched beams. The microelectronic substrate serves as the base upon which the thermally actuated microelectromechanical structure is disposed. In this regard, at least one anchor is affixed to the microelectronic substrate while the remainder of the MEMS structure is suspended from the anchor over the substrate. Each arched beam of the pair has a medial portion and two end portions. The opposed end portions of the pair of arched beams are operably interconnected. Further, the medial portion of one arched beam in the pair is connected to at least one anchor, such that the pair of arched beams extends from at least one anchor in a cantilever configuration overlying the microelectronic substrate. The pair of arched beams further arch once thermal actuation is applied thereto, thereby causing the pair of arched beams to correspondingly move along a predetermined path with respect to the microelectronic substrate. As such, the MEMS structure of this embodiment can provide movement along a one dimensional or two dimensional path, parallel to a plane defined by the microelectronic substrate.
The MEMS structure of this embodiment can also include a crossbeam disposed between the pair of arched beams so as to operably interconnect the opposite ends of the pair of arched beams. The crossbeam is preferably adapted to be heated less than the pair of arched beams when the microelectromechanical structure is thermally actuated. By tying the ends of the arched beams together with the crossbeam, the MEMS structure of the embodiment can provide significantly more displacement than conventional MEMS devices.
In one embodiment, the pair of arched beams are arranged such that concave portions of the pair of arched beams face one another, thereby defining a generally diamond shaped structure adapted to expand in response to thermal actuation. Alternatively, another embodiment is arranged such that convex portions of the pair of arched beams face one another, thereby defining a generally bowtie shaped structure adapted to compress in response to thermal actuation. A thermally actuated microelectromechanical array is further provided by the present invention, wherein the aforementioned thermally actuated microelectromechanical structures comprise cells within the array in order to provide even greater displacement.
One embodiment of the present invention provides a thermally actuated structure comprising a microelectronic substrate, at least one anchor affixed thereto, an arched beam, and a crossbeam. The arched beam has a medial portion and two end portions. The crossbeam operably connects the opposed end portions of the arched beam such that the separation of the medial portion from
Dhuler Vijayakumar R.
Hill Edward A.
Dougherty Thomas M.
MCNC
Myers Bigel & Sibley & Sajovec
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