Investigation of a New Concept in Semiconductor Microwave Oscillators: The Contiguous Domain Oscillator

Abstract

Abstract : The contiguous domain oscillator (CDO) is a resistive-gate GaAs FET which functions as a voltage-controlled millimeter-wave oscillator. The structure is compatible with planar processing and can be incorporated with standard GaAs FET in the form of monolithic millimeter-wave integrated circuits (MMICs). The device was first proposed by Cooper and Thornber in 1983, and has been under investigation at Purdue since 1985. Conventional microwave oscillators (such as the IMPATT, BARITT, and Gunn diodes) generate microwave power by using a mechanism which depends strongly on electric field (e.g. avalanche multiplication or negative differential mobility) to create charge packets or domains. The conventional devices all employ a two-terminal geometry and hence are diodes. Since the internal electrostatic geometry is one dimensional, once a charge packet is introduced, it alters the electric field throughout the device in such a way as to turn off the generation mechanism. The single charge packet then drifts across the device and is extracted by the anode. Once the charge packet has drifted out of the device, the internal field returns to it's original value and the generation process begins again. The entire process is therefore a series of repeated transients, with the oscillation frequency determined by the inverse of the generation time plus the transit time. Clearly, once the device has been built, the transit time (and hence the oscillation frequency) is fixed. In addition, for millimeter-wave operation the drift distance must be made very short, typically less than 1 micrometer.