Microelectromechanical switches are used in a variety of applications and in particular for satellite communication 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 microelectromechanical 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 large enough to overcome the stiffness of the beam. As a result of the electrostatic force of attraction, the beam deflects and makes a connection with a contact, electrode 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 and opening the switch.
The switch-opening phase, or OFF-state, is not directly controlled, however, and relies on the forces of nature embodied in the spring constant of the beam to effect the opening of the switch. However, the forces of nature 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 beam to stick to the contact electrode), between the beam and the contact electrode overcome the spring restoring force of the beam. This results in the free end of the beam sticking to the contact electrode and keeping the switch closed when, in fact, it should be open. Prior art cantilever beam type switches have no mechanism to overcome stiction forces upon switching to the ON-state.
Another problem associated with the cantilever beam type switch is a problem 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 as described above, or causes premature deterioration of the contact electrode. Both conditions impair the useful life of the switch and result in premature failure.
There is a need for a microelectromechanical switch that overcomes the problems associated with prior art cantilevered beam-type switches.