Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
1999-06-30
2001-05-08
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C361S207000
Reexamination Certificate
active
06229683
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microelectromechanical switch and relay structures, and more particularly to electrostatically activated high voltage switch and relay structures.
BACKGROUND OF THE INVENTION
Advances in thin film technology have enabled the development of sophisticated integrated circuits. This advanced semiconductor technology has also been leveraged to create MEMS (Micro Electro Mechanical System) structures. MEMS structures are typically capable of motion or applying force. Many different varieties of MEMS devices have been created, including microsensors, microgears, micromotors, and other microengineered devices. MEMS devices are being developed for a wide variety of applications because they provide the advantages of low cost, high reliability and extremely small size.
Design freedom afforded to engineers of MEMS devices has led to the development of various techniques and structures for providing the force necessary to cause the desired motion within microstructures. For example, microcantilevers have been used to apply rotational mechanical force to rotate micromachined springs and gears. Electromagnetic fields have been used to drive micromotors. Piezoelectric forces have also been successfully been used to controllably move micromachined structures. Controlled thermal expansion of actuators or other MEMS components has been used to create forces for driving microdevices. One such device is found in U.S. Pat. No. 5,475,318, which leverages thermal expansion to move a microdevice. A micro cantilever is constructed from materials having different thermal coefficients of expansion. When heated, the bimorph layers arch differently, causing the micro cantilever to move accordingly. A similar mechanism is used to activate a micromachined thermal switch as described in U.S. Pat. No. 5,463,233.
Electrostatic forces have also been used to move structures. Traditional electrostatic devices were constructed from laminated films cut from plastic or mylar materials. A flexible electrode was attached to the film, and another electrode was affixed to a base structure. Electrically energizing the respective electrodes created an electrostatic force attracting the electrodes to each other or repelling them from each other. A representative example of these devices is found in U.S. Pat. No. 4,266,399. These devices work well for typical motive applications, but these devices cannot be constructed in dimensions suitable for miniaturized integrated circuits, biomedical applications, or MEMS structures.
Micromachined MEMS electrostatic devices have been created which use electrostatic forces to operate electrical switches and relays. Various MEMS relays and switches have been developed which use relatively rigid cantilever members separated from the underlying substrate in order to make and break electrical connections. Typically, contacts at the free end of the cantilever within these MEMS devices move as the cantilever deflects, so that electrical connections may be selectively established. As such, when the contacts are connected in these MEMS devices, most of the cantilever remains separated from the underlying substrate. For instance, U.S. Pat. Nos. 5,367,136, 5,258,591, and 5,268,696 to Buck, et al., U.S. Pat. No. 5,544,001 to Ichiya, et al., and U.S. Pat. No. 5,278,368 to Kasano, et al. are representative of this class of microengineered switch and relay devices.
Another class of micromachined MEMS switch and relay devices include curved cantilever-like members for establishing electrical connections. For instance, U.S. Pat. Nos. 5,629,565 and 5,673,785 to Schlaak, et al., describe a microcantilever that curls as it separates from the fixed end of the cantilever and then generally straightens. The electrical contact is disposed at the generally straight free end of the microcantilever. When electrostatically attracted to a substrate electrode, the Schlaak devices conform substantially to the substrate surface except where the respective electrical contacts interconnect. In addition, a technical publication by Ignaz Schiele et al., titled
Surface-Micromachined Electrostatic Microrelay
, also describes micromachined electrostatic relays having a curled cantilever member. The Schiele cantilever initially extends parallel to the underlying substrate as it separates from the fixed end before curling away from the substrate. While the cantilever member having a contact comprises a multilayer composite, flexible polymer films are not used therein. As such, the Schiele devices do not describe having the cantilever member conform substantially to the underlying substrate in response to electrostatic actuation thereof.
MEMS electrostatic switches and relays are used advantageously in various applications because of their extremely small size. Electrostatic forces due to the electric field between electrical charges can generate relatively large forces given the small electrode separations inherent in MEMS devices. However, problems may arise when these miniaturized devices are used in high voltage applications. Because MEMS devices include structures separated by micron scale dimensions, high voltages can create electrical arcing and other related problems. In effect, the close proximity of contacts within MEMS relays and switches multiplies the severity of these high voltage problems. Further, relatively high electrostatic voltages are required to switch high voltages. The air gap separation between the substrate electrode and moveable cantilever electrode affects the electrostatic voltage required to move the cantilever electrode and operate the switch or relay. A relatively large air gap is beneficial for minimizing high voltage problems. However, the larger the air gap, the higher the voltage required to operate the electrostatic switch or relay. As such, traditional MEMS electrostatic switch and relay devices are not well suited for high voltage switching applications.
It would be advantageous to switch high voltages using MEMS devices operable with relatively low electrostatic voltages. In addition, it would be advantageous to provide MEMS electrostatic switching devices that overcome at least some of the arcing and high voltage operational problems. There is still a need to develop improved MEMS devices for switching high voltages while leveraging electrostatic forces. Existing applications for MEMS electrostatic devices could be better served. In addition, advantageous new devices and applications could be created by leveraging the electrostatic forces in new MEMS structures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide MEMS electrostatic switches and relays that can switch high voltages while using relatively lower electrostatic voltages.
In addition, it is an object of the present invention to provide MEMS electrostatic switches and relays actuators that overcome at least some of the arcing and other problems related to high voltage.
Further, it is an object of the present invention to provide improved MEMS electrostatic switches and relays.
The present invention provides improved MEMS electrostatic devices that can operate as high voltage switches or relays. Further, a method for using a MEMS electrostatic device according to the present invention is provided. The present invention solves at least some of the problems noted above, while satisfying at least some of the listed objectives.
A MEMS device driven by electrostatic forces according to the present invention comprises a microelectronic substrate, a substrate electrode, a substrate contact, a moveable composite, a composite contact, and an insulator. A microelectronic substrate defines a planar surface upon which the MEMS device is constructed. The substrate electrode forms a layer on the surface of the microelectronic substrate. The moveable composite overlies the substrate electrode. In cross section, the moveable composite comprises an electrode layer and a biasing layer. The moveable composite across its length comprises a fixed portion attached to
Alston & Bird LLP
MCNC
Sherry Michael J.
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