High-Q GaAs varactor diodes

A double epitaxial gallium arsenide tuning diode has been developed for TV varactor tuners. The capacitance variation ratio is 6.0 and is large enough to cover the UHF TV broadcasting band. Diode series resistance is 0.18 Ω (
Q = 200
) at 470 MHz, and at a capacitance of 9 pF. This resistance is 4.4 times smaller than Si diodes in its mean value. Contribution of each resistance component to the total diode resistance was studied. The result shows that package loss is 0.11 Ω, RF skin-effect resistance is 0.05 Ω, and the undepleted epitaxial layer resistance is 0.048 Ω. Therefore, a diode with a 0.075-Ω (
Q = 480
) series resistance at 470 MHz could be developed, if package loss and RF skin-effect resistance are improved.