High Power-Added-Efficiency AlGaN/GaN E-Mode HEMTs for Low-Supply-Voltage RF Terminal Applications

In this paper, an enhancement-mode (E-mode) GaN high electron mobility transistors (HEMTs) with an innovational inverted trapezoidal recessed-gate is successfully fabricated by using a developed variable pressure gate etching process, which contributes to a 0.41 V positive threshold voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(\mathrm{V}_{\text {TH }}\right)$</tex> and a significant saturation output current density (IDMAX) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.94 ~\mathrm{A} / \text{mm}$</tex>. the device employing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.2-\mu \mathrm{m}$</tex> T-gate length exhibits a high peak transconductance (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$G_{\text {mmax }}$</tex>) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$577.6 \text{mS} / \text{mm}$</tex> and a power gain cut-off frequency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{\text {max }}$</tex>) of 138 GHz. At 18 GHz, a record power-added-efficiency (PAE) of 70 % associated with a high output power density of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.22 ~\mathrm{W} / \text{mm}$</tex> is realized in a continuous-wave (CW) mode at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text {DS }}=12 ~\mathrm{V}$</tex>. Compared with others E-mode structure, the improved E-mode GaN HEMTs demonstrates a great potential in Low-Supply-Voltage RF terminal applications.