Novel gate air cavity GaN HEMTs design for improved RF and DC performance

Abstract

Studies are performed to develop physical insights into the RF and DC behavior of GaN HEMTs. In purpose of improving the current gain cutoff frequency (fT) and power gain cutoff frequency (fmax), an air cavity structure was proposed, which efficiently decreases the gate–drain capacitance and gate–source capacitance. As a result, the proposed HEMTs with air cavity offers over 2× improvements in cutoff frequency comparing with the design without, which increases the fTand fmaxto 14.9 GHz and 33.1 GHz, respectively. It breaks through the performance bottleneck limited by the length of gate, realizing a relatively high scaling factor that Lg × fT= 20.86 GHz μm when compared with previous reports. Besides, in order to realize both DC and RF performance improvement we proposed another kind of air cavity design, the fTand fmaxcan be increased by 82% and 37.6% respectively. The maximum saturation drain current approximately increased by 50%, maximum transconductance (gm, max) raise from 209 to 237 mS/mm and the gate current leakage performance is improved to a certain extent. Furthermore, forth bias sweep C–V (capacitance–voltage) curves and current density are also extracted to discuss the mechanism accompany with the reported physical model, based on which 2 simplified capacitive networks are proposed.

Keywords

• Air cavity design
• AlGaN/GaN HEMT
• GaN TCAD modeling
• DC and RF characteristics
• Equivalent capacitive network