1. Field of the Invention
The present invention relates generally to a capacitive microelectromechanical switch based on utilization of the Lorentz force.
2. Description of the Related Art
There now exists a small but growing number of microelectromechanical systems (MEMS) including micro-actuators; examples of which are switches, resonant magnetometers, micro mirrors, micro valves, etc. A typical MEMS shunt switch 10, as illustrated in
where ε0=8.854×10−12 C2/N−m2, where C is coulombs and N is Newtons. As the gap 16 decreases, the electrostatic force increases. When the deflection is greater than approximately ⅓ of the initial gap 16, this force exceeds the restoring force of the bridge and causes the switch to snap closed. The minimum voltage that causes this to happen (pull-down voltage, Vp) is given by the following equation:
where k is the spring constant.
Accordingly, to actuate a MEMS-based switch having the gap 16 of from 1.5 to 5 micrometers, typically it is required that a pull-down voltage be from 30 to 90 V. In the context of MEMS, these voltages are high enough to create problems associated with energy losses, processing and reliability.
A need therefore exists for a MEMS-based switch actuateable by a relatively low pull-down voltage.
This need is met by an MEMS-based capacitive switch of the present invention utilizing the Lorentz force, which is produced as a result of coupling between magnetic and electric fields applied across the switch. Accordingly, since the switch actuation is a function of the Lorentz force combined with an actuation voltage, as the Lorentz force increases, the actuation electrostatic pull-down voltage decreases.
Structurally, the MEMS-based switch of the present invention is configured with a source generating a magnetic field across the switch, and an electrical conductor carrying a current and extending transversely to the magnetic field. Coupling the electric and magnetic fields produces the Lorentz force sufficient to assist in displacement of the electrical conductor between two positions corresponding to the on- and off-states of the switch in accordance with a direction of current flow through the electrical conductor.
The above and other features, as well as advantages and objects of this invention will become more readily apparent from the following description of the preferred embodiment accompanied by the attached drawings, in which:
Referring to
To provide the bridge 22 with the desired flexibility, only its opposite ends 34, 36 are supported by the substrate 26, whereas an inner span 38 of the bridge is separated from the substrate by, for example, undercutting or underetching. As a consequence, the unsupported span 38 of the bridge 22 is capable of flexing towards the substrate 26 to contact the pull-down electrode 24 and, thus, to define the on-state of the device 20 once a voltage applied to the switch overcomes the restoring force of the bridge 22.
In accordance with the present invention, the bridge 22 is juxtaposed with an electrical conductor 28 made from flexible conducting or semi-conducting materials and coupled to an electric field generating source 40 to conduct a current I (
The source 40 is preferably an electric pulse generator, which is coupled to a pulse duration modulator 42 operative to control the duration of pulses, which are preferably relatively short to minimize Joule heating that, if not controlled, can lead to overheating of the bridge 22 and the pull-down electrode 24. The source 33 generating the magnetic field B may include permanent magnets capable of generating high magnetic fields, a coil or a thin film deposited on the substrate 26.
Referring to
While the conductor 68 does not necessarily have to contact the bridge 62 directly, preferably, the latter provides a support top surface 70 (
The Lorentz force generated by a current in a magnetic field B, which is applied in the plane of and perpendicular to the longitudinal direction of the bridge, is given by the following equation:
FL=B×I×L (III)
where I is the current, B is the magnetic field and L is the length of the conductor. The direction of the force is defined by the direction in which the current flows. Alternatively, the direction of the force may be controlled by changing the direction of the magnetic field if the latter is generated by an external source, provided, of course, that such a structure would meet the local requirements.
The magnetic fields required to produce forces comparable to electrostatic pull-down forces in the bridge of 300 μm length in the range of 1–100×10−6 N with drive currents of 0.5, 1.0, and 5.0 A are shown in
Thus, in the switch of the present invention, which can be integrated in, for example, micromotors, microvalves, mechanical resonators, etc., the Lorentz force is used to reduce the gap between the bridge and the pull-down electrode of the switch from its “full up” position, as shown in
It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting the scope of the invention, but merely as exemplifications of the preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.
This application claims the benefit of U.S. Provisional Application No. 60/411,377, filed Sep. 17, 2002, the contents of which are incorporated herein by reference.
Number | Name | Date | Kind |
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4169999 | Kishel | Oct 1979 | A |
4841834 | Gruden | Jun 1989 | A |
5322258 | Bosch et al. | Jun 1994 | A |
5847474 | Gruden et al. | Dec 1998 | A |
5872384 | Gabara | Feb 1999 | A |
6657525 | Dickens et al. | Dec 2003 | B1 |
Number | Date | Country | |
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20040108195 A1 | Jun 2004 | US |
Number | Date | Country | |
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60411377 | Sep 2002 | US |