Evaluation of linearity at 30 GHz for N-polar GaN deep recess transistors with 10.3 W/mm of output power and 47.4% PAE

Abstract

The advantage of GaN is the capability of producing amplifiers with high output power and efficiency. At microwave frequencies, this performance has been achieved; however, when transitioning device design into mm-wave frequencies, the output power and efficiency of GaN HEMTs decrease. Traditionally, the approach taken to develop Ka-band (30–40 GHz) GaN devices has been to modify a device designed for a lower frequency. By contrast, this work modified a N-polar GaN deep recess HEMT developed for W-band power performance (94 GHz), for improved performance in the Ka-band. In this Letter, we first report on improvement in the 30 GHz continuous-wave (CW) power density through modification of the W-band device with the demonstration of 10.3 W/mm at 47.4% power-added efficiency (PAE). We then report on the two-tone linearity performance of the device when measured under the same bias and matching conditions. While the evaluation of GaN HEMTs has traditionally focused on the use of one-tone CW power measurements, with the increasing adoption of GaN transistors into communication systems, such as mm-wave 5 G cellular communication, simply demonstrating high power density and efficiency does not provide a sufficient understanding of the device as high linearity is required to transmit data using complex modulation schemes. Under two-tone stimulus, the device demonstrates an OIP3 to PDC ratio greater than 6.7 dB and a C/IM3 ratio of greater than 37 dBc under backoff conditions greater than 10 dB from the peak one-tone PAE.