Junction field effect microwave switch fabricated with electron beam exposure and ion implantation doping

Abstract

In recent electronically scanned radar systems, pin diodes are used extensively as phase shifting elements. However, to obtain the proper range of dynamic impedance, a relatively large dc current is usually required for each diode. In a large array this control current is the source of numerous problems, caused by heat, weight and cost of driver circuitry. Following some experimental work originated by R. Tang, a new field effect switch has been developed which decreases the control current to a minimum and thus reduces the above-mentioned problems. This switch is fabricated in the following manner. The gate of the device is formed by the p+substrate material on which an n-type epitaxial channel layer is grown. Interleaving diffused source and drain bus bars pIaced with 23 micron spacing comprise the major current distribution network for the device. The channel conductance is then greatly increased by using a high resolution scanning electron microscope to expose the finely spaced interdigitated source and drain regions between adjacent bus bars. These regions are doped by means of phosphorus ion implantation to avoid lateral spread otherwise introduced by diffusion. The resultant source and drains are each one micron wide and about 10 microns long, while the center to center spacing is 3 microns. This extremely high channel conductance provided by the scanning electron microscope exposure and ion implantation doping allows the use of this device in a microwave phase shifting application. Characteristics of this device including microwave performance will be given.