W- And G-Band GaN Voltage-Controlled Oscillators with High Output Power and High Efficiency

This article presents W- and G-band voltage-controlled oscillators (VCOs) fabricated in a 60 nm GaN high electron-mobility transistor (HEMT) process with $f_{T}/f_{\mathrm {MAX}}$ of 190/250 GHz. Two W-band fundamental VCOs (VCO1 and VCO2) are designed without and with a varactor, respectively. In addition, a G-band push-push VCO (VCO3) is designed to demonstrate feasibility of a GaN power source in the sub-terahertz band. The measurement shows that VCO1 and VCO2 exhibit output power of 22.5 and 22.6 dBm and dc-to-RF efficiency of 14.7% and 16.8% at 87.5 and 86.5 GHz, respectively. The power and efficiency are the highest values among the previously reported GaN VCOs operating beyond 50 GHz. Furthermore, VCO2 achieves a wide tuning range of 9.0 GHz (77.5-86.5 GHz). The VCO3 exhibits high output power of 9.3 dBm at 180.6 GHz. To the best of the authors' knowledge, this is the first demonstration of a G-band VCO in a GaN technology. The W- and G-band VCOs occupy compact chip areas of 0.48 and 0.32 mm2, respectively.