Characterization of GaN-based HEMTs as varactor diode devices

Varactors fabricated in 0.5 μm and 0.15 μm 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.