Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-01-19
2001-12-04
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C310S307000, C310S164000
Reexamination Certificate
active
06324748
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to microelectromechanical devices and, more particularly, to microelectromechanical devices that include thermal arched beam actuators and related fabrication methods.
BACKGROUND OF THE INVENTION
Microelectromechanical systems (MEMS) have recently been developed as alternatives for 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 may also be provided because MEMS devices can be much smaller than conventional electromechanical devices.
Many potential applications of MEMS technology utilize MEMS actuators. For example, many sensors, valves and positioners use actuators for movement. If properly designed, MEMS actuators can produce useful forces and displacement, while consuming reasonable amounts of power. Many configurations of MEMS actuators have been proposed. For example, U.S. Pat. No. 5,475,318 to Marcus et al. entitled “Microprobe”, discloses cantilever bimorph microprobes and doubly supported beam bimorph microprobes. In addition, an article entitled “Silicon Fusion Bonding and Deep Reactive Ion Etching; A New Technology For Microstructures”, by Erno H. Klaassen, et al. presented at the International Conference on Solid-Date Sensors and Actuators, Transducers '95 held in Stockholm, Sweden in June 1995 describes a thermal actuator having a pair of arched beams extending between a pair of supports. By current through the arched beams, the arched beams will expand so as to further arched. The thermal actuator of the Klaassen article can also a include a center post that connects the plurality of arched beams and serves to push against the workpiece. The Klaassen article also describes a capacitive accelerometer structure that utilizes the thermal actuators to vary the spacing between a number of interdigitated fingers.
Notwithstanding the MEMS actuators that have previously been proposed, a number of existing and contemplated MEMS systems, such as relays, actuators, valves and sensors, require more sophisticated actuators that provide useful forces and displacements while consuming reasonable amounts of power in an efficient manner. Since it is desirable that the resulting MEMS systems be fabricated with batch processing, it is also preferred that the microelectronic fabrication techniques for manufacturing the resulting MEMS systems be affordable, repeatable and reliable.
SUMMARY OF THE INVENTION
The MEMS devices of the present invention include a particularly advantageous MEMS actuator, as well as a family of other MEMS devices, such as relays, switching arrays and valves, that include one or more MEMS actuators. In addition, a method of fabricating a MEMS actuator is also provided according of the present invention.
According to the present invention, a MEMS structure, hereinafter referred to as a MEMS actuator, includes a microelectronic substrate, spaced apart supports on the substrate and a metallic arched beam extending between the spaced apart supports. The MEMS actuator also includes means for heating the arched beam to cause further arching of the beam. Preferably, the heating means includes a heater extending between first and second opposed ends which, in turn, are disposed upon the microelectronic substrate.
In order to effectively transfer heat from the heater to the metallic arched beam, the metallic arched beam extends over and is spaced, albeit slightly, from the heater such that the heat generated by the heater causes the metallic arched beam to further arch. As such, the MEMS actuator of this advantageous embodiment effectively converts the heat generated by the heater into mechanical motion of the metallic arched beam. As described herein, numerous MEMS devices can incorporate the MEMS actuator of the present invention in order to provide a controllable force and displacement without consuming significant amounts of power.
The heater preferably includes an at least partially conductive material having high resistivity, such as polysilicon, titanium or tungsten, surrounded by a dielectric material, such as silicon nitride or silicon dioxide. The dielectric material surrounding the at least partially conductive material cooperates with an air gap defined between the metallic arched beam and the heater to electrically isolate the metallic arched beam from the at least partially conductive material. In order to effectively transfer the thermal energy generated by the heater to the metallic arched beam, the air gap is preferably small, such as less than about 5 microns and, more preferably, between about 1 micron and 2 microns. Likewise, the dielectric material is also preferably relative thin and, in one advantageous embodiment, has a thickness of about 0.5 micron.
The MEMS actuator also preferably includes a lengthwise extending actuator member connected to the metallic arched beam and extending outwardly in a first direction. According to one advantageous embodiment, the heater underlies and is aligned with the actuator member in the first direction. As a result of this alignment, the heat generated by the heater of this embodiment is even more efficiently transmitted to the actuator member and, in turn, to the metallic arched beam so as to cause further arching of the arched beam.
A number of MEMS devices have also been developed according to the present invention that utilize one or more MEMS actuators for providing useful forces and displacements while consuming reasonable amounts of power. For example, a MEMS relay of the present invention includes a microelectronic substrate, a first pair of contacts on the substrate and a first MEMS actuator on the substrate for controllably establishing electrical contact between the pair of contacts. The actuator member of the MEMS actuator preferably includes a lengthwise extending portion coupled to the arched beam and an enlarged contact portion, responsive to movement of the lengthwise extending portion, for establishing contact with the first pair of contacts. According to one embodiment, the actuator member, including the lengthwise extending portion and the enlarged contact portion, is a unitary structures. According to another embodiment, however, the lengthwise extending portion and the enlarged contact portion of the actuator members are separate structures positioned such that the lengthwise extending portion will move into contact with the enlarged contact portion upon movement of the lengthwise extending portion in response to heating of the arched beams, thereby urging the enlarged contact portion into contact with the first pair of contacts.
Upon actuation of the MEMS relay of the present invention, the actuator member is moved between an open position in which the actuator member is spaced from the first pair of contacts and a closed position in which the actuator member contacts the first pair of contacts and establishes an electrical connection therebetween. In order to further reduce the power requirements of the MEMS relay, the MEMS relay preferably includes means for holding the actuator member in position following heating of the arched beam and movement of the actuator member. The holding means can include means for applying an electrostatic force between the actuator member and the substrate, thereby holding at least a portion of the actuator member against the substrate.
The MEMS relay can also include at least one retaining member on the substrate and positioned so as to underlie the actuator member once the actuator member has moved in response to heating of the arched beam. According to this advantageous embodiment, the actuator member also includes a lower surface facing the substrate that defines at least one recess for cooperably receiving a respective retaining member as the actuator member is held in position, such as by an electrostatic force.
Alternatively, the MEMS relay can include latch means for latching the actuator member in position following heating
Dhuler Vijayakumar R.
Mahadevan Ramaswamy
Wood Robert L.
JDS Uniphase Corporation
Myers Bigel & Sibley & Sajovec
Smith Sean
Young Lee
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