Micromachined thermal switch

Abstract

A monolithic micromachined temperature switch obviates the necessity of assembling discrete components and also allows the temperature switch to be disposed in a relatively small package. In one embodiment of the invention, the temperature switch includes a bimetallic element operatively coupled to a pair of electrical contacts. In order to minimize contact wear due to contact arcing, a biasing force such as an electrostatic force is applied to the switch which provides snap action of the electrical contacts in both the opening and closing directions which enables the temperature set point to be adjusted by varying electrostatic force biasing voltage. In an alternate embodiment of the invention, the biasing force for providing the snap action effect can be eliminated by substituting the movable contacts with a field effect transistor with a movably mounted gate terminal. With such an arrangement since little or no current would normally flow through the gate terminal, the need to reduce contact arcing normally resulting from contact bounce would thus be eliminated. Thus, in such an embodiment, a biasing force such as an electrostatic biasing force is not necessary unless a snap action with hysteresis is desired. In alternate embodiments of the invention, the temperature switch may be formed with an integral power transistor for switching relatively large currents. The temperature switch may also be provided with an integrally formed capacitor for reducing the effects of switching inductive loads, such as relays and the like.