Characterization of GaN-based HEMTs as Varactor Diode Devices

Varactors fabricated in 0.5 mu m and 0.15 mu m GaN HEMT technologies (National Research Council of Canada's GaN500 and GaN150 processes) are investigated. The devices were analyzed and characterized via DC and RF small-signal measurements up to 20 GHz. The drain and source terminals were connected, thus realizing a GaN-based heterojunction barrier varactor diode structure without changing the epitaxial masks and layers of the GaN processes. The CMAX/CMIN ratios are about 2.4 and 3.7, while the maximum cut-off frequencies are 419.2 GHz and 770.6 GHz for GaN500 and GaN150, respectively. The varactors are modeled by a simple physical equivalent circuit, and good agreement is obtained with measurements.