Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1999-11-12
2001-09-25
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C333S262000
Reexamination Certificate
active
06294847
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a micro-electromechanical switch and more particularly to a bistable micro-electromechanical switch having lateral transverse actuation.
BACKGROUND ART
Micro-electromechanical switches are used in a variety of applications and in particular for satellite communications systems with architecture that includes switching matrices and phased array antennas. It is desirable to have a switch having low-insertion loss, high isolation and high switching frequency.
Presently, the micro-electromechanical switches known in the prior art include a beam cantilevered from a switch base, or substrate. The beam acts as one plate of a parallel-plate capacitor. A voltage, known as an actuation voltage, is applied between the beam and an electrode on the switch base. In the switch-closing phase, or ON-state, the actuation voltage exerts an electrostatic force of attraction on the beam. As a result of the electrostatic force of attraction, the beam deflects and makes a connection with a contact on the switch base, closing the switch. Ideally, when the actuation voltage is removed, the beam will return to its natural state, breaking its connection with the contact electrode, thereby opening the switch.
The switch-opening phase, or OFF-state, is not directly controlled. It relies on the forces of nature embodied in the spring constant of the beam to effect the opening of the switch. Unfortunately, these forces are not always predictable and therefore unreliable.
For example, in some cases, once the actuation voltage is removed, stiction forces, (forces of attraction that cause the cantilevered beam to stick to the contact electrode), overcome the spring restoring force of the beam. The stiction force may cause the free end of the cantilevered beam to stick to the contact electrode and keep the switch closed when, in fact, it should be open.
Another problem associated with cantilever beam type switches is intrinsic to the beam's change of state from open to close. The operation of the beam is inherently unstable. When closing, the beam deforms gradually and predictably, up to a certain point, as a function of the actuation voltage being applied to the switch. Beyond that point, control is lost and the beam's operation becomes unstable, causing the beam to come crashing down onto the secondary electrode. This causes the beam to stick, or causes premature deterioration of the contact electrode. Both conditions impair the useful life of the switch and result in premature failure.
Prior art cantilever beam type switches require a trade-off between actuation voltage and isolation. For a low actuation voltage, the beam-to-substrate separation should be small. However, a small beam-to substrate separation results in a large parasitic capacitance, and thus a low isolation.
In addition, the maximum frequency at which the beam can deflect and relax is related to its geometry and material properties, such as length, bulk modulus, and density. Therefore, it may be impossible, in some applications, to achieve high switching frequencies at practical beam geometries.
SUMMARY OF THE INVENTION
The micro-electromechanical switch of the present invention exploits stiction forces to implement a bistable switch. The present invention has a detached segment of transmission line that is coerced into lateral transverse motion between two parallel plate capacitors in order to make, or break, a connection between transmission line segments.
The present invention has a substrate supporting two electrodes spaced a distance from each other and a transmission line located in between the electrodes. The transmission line has a detached segment, or a bridge, that moves laterally between the two electrodes. A beam is attached to the detached segment. The beam is transverse to the detached segment and is aligned with the direction of movement of the segment. The beam is a dielectric material and intrudes into both parallel plate capacitors so that when a voltage is applied to either capacitor, it affects the beam and initiates movement of the detached segment.
To actuate the switch a voltage is applied to one of the parallel plate capacitors. The dielectric beam is pulled in the direction of the capacitor having the voltage applied thereto. When the segment is pulled towards the parallel plate capacitor, the transmission line is broken and the switch is opened.
The switch of the present invention is bistable. When the voltage is removed from the parallel plate capacitor, the transmission line segment remains in its position and doesn't move until a voltage is applied to the opposite parallel plate capacitor, thereby drawing the segment back in line with the transmission line, closing the switch.
It is an object of the present invention to overcome the drawbacks associated with cantilever beam type switches. It is another object of the present invention to maintain indifference to resonant frequency.
It is a further object of the present invention to have a very low actuation voltage. It is yet a further object of the present invention to exhibit isolation that is not compromised by a low actuation voltage.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.
REFERENCES:
patent: 5578976 (1996-11-01), Yao
patent: 6069540 (2000-05-01), Berenz et al.
Ballato Josie
DeBeradinis Robert L.
Gudmestad Terje
The Boeing Company
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