Heterojunction PIN diode switch

This paper describes the development of a heterojunction AlGaAs/GaAs PIN diode as a replacement for the homojunction GaAs PIN diodes commonly used in microwave systems as a control element for commercial and military switch applications up through millimeter wave frequencies. In particular, a single heterojunction PIN diode, when simulated at a bias of 10 mA in a 50 ohm series configuration, indicates a potential reduction in insertion loss of 37% (Rs) with no degradation in isolation (Cj). This paper describes a switch topology of choice which uses a series-shunt element at the main junction, since it offers the widest bandwidth due to the low zero bias capacitance of the series diode. This simple structure has an upper frequency limitation that is dependent on the electrical distance due to the physical location of the series diode relative to the center of the actual device junction and the maximum isolation achievable by the Cj of a discrete diode. PIN switch circuits and RF probable test structures were processed through our GaAs wafer fab and later tested on-wafer for broadband RF performance from 50 MHz through 40 GHz. A comparison between simulated and empirical results for insertion loss, return loss and isolation demonstrates excellent agreement for isolation and a 10% offset for insertion loss and return loss.