Evaluation of Power and Linearity at 30 GHz in AlGaN/GaN HEMT Fabricated by Integrating Transistors With Multiple Threshold Voltages

In this work, using the multiple threshold voltages (multi- $\textit{V}_{\text{Ths}}\text{)}$ coupling technology introduces an innovative approach to leverage AlGaN/GaN-based high-electron-mobility transistor (AlGaN/GaN HEMT) for high linearity millimeter-wave (mm-W) applications. As a result of optimizing the etching depth of the recessed trench ( $\textit{H}_\textit{R}$ ), the fabricated composite HEMT demonstrated a remarkably flat transconductance ( $\textit{G}_\textit{m}$ ) plateau, and well-maintained profile of small-signal characteristics as a function of gate voltage. As a consequence, at a biased drain voltage of 10 V and a frequency of 30 GHz, the composite HEMT achieved the highest ratio of output third-order intercept point (OIP3) to DC power consumption ( $\textit{P}_{\text{DC}}\text{)}$ , denoted as (OIP3/ $\textit{P}_{\text{DC}}\text{)}$ , measuring $\sim$ 9.3 dB. Simultaneously optimizing the bias conditions, the devices showcased a remarkable combination of high one-tone saturated output power density reaching 6.5 W/mm and two-tone OIP3/ $\textit{P}_{\text{DC}}$ of $\sim$ 6.1 dB, achieved at a biased drain voltage of 25 V. The experimental results provide compelling evidence of the attractiveness of the multi- $\textit{V}_{\text{Ths}}$ coupling technique for millimeter wave RF transmitters.