A Micromachined Robust Planar Triggered Sparkgap Switch for High Power Pulse Applications

Abstract

High voltage (HV) switches capable of operating at high speeds with high current levels are used in a variety of applications in commercial and government systems. Examples of HV switches include triggered sparkgap, dielectric breakdown, and mercury vapor switches. The triggered sparkgap switch is a three-element, gas-filled, ceramic-to-metal, hermetically sealed, pressurized switch that operates in an arc discharge mode. Triggered sparkgaps have been in use for many years, providing precision timing and activation of in-flight functions such as missile stage separation. These applications involve the activation of electro-explosive devices such as an exploding bridge-wire [EBW] or an exploding foil initiator [EFI]. This paper discusses the fabrication and characterization of a novel high voltage planar discharge switch using micromachining techniques. The switch provides a low cost alternative to conventional triggered sparkgaps. The switch is designed for direct integration into the strip-line geometries used in a conventional capacitive discharge unit (CDU). The geometry of the device was selected to minimize parasitic impedances associated with conventional firing circuits. The switch design is microfabricated on an alumina substrate utilizing a patterned electron-beam deposited metallic stack. A polyimide layer selectively deposited over the metal stack provides dielectric isolation and passivation for the switch electrodes. A similar methodology was utilized to fabricate sample EFIs for switch validation tests with insensitive secondary high explosive (HE) pellets. The discharging of the HV capacitor through the patterened bridgefoil of an EFI results in rapid vaporization of the metal stack. The high pressure gas formed by the vaporized metal accelerates the adjacent polyimide layer to high velocity. The polyimde layer then impacts the HE pellet, inducing a shock wave, which results in prompt detonation of the material. Thus, this device is a type of MEMS actuator with a very specialized use. Design, fabrication and test data are presented and discussed.