In this article, we report on the high dc and RF performance of AlGaN/GaN high electron mobility transistors that employ Ti/Au/Al/Ni/Au metallization stack with shallow trench etching ohmic contact (STEOC). An excellent ohmic contact performance including low contact resistance ( ${R}_{C}$ ) of $0.28~\Omega \cdot $ mm and smooth surface morphology have been achieved simultaneously. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (rms) roughness of 6.3 nm even after 810 °C high-temperature annealing (HTA), achieving an improvement of 79% as compared to the conventional Ti/Al/Ni/Au ohmic contact (COC). A high-resolution transmission electron microscope (HRTEM) showed a glossy morphology with a continuous and uniform TiN layer formed in the interface for the STEOC sample, while a bumpy morphology caused from the Ni-Al complexes balling up and TiN island penetrating into the AlGaN/GaN heterostructure were observed for the conventional sample. Consequently, the fabricated transistors with the STEOC process show a high output current of 1.52 A/mm and low ON-resistance ( ${R}_{ \mathrm{ ON}}$ ) of $2.09~\Omega $ mm. In addition, a high current cutoff frequency ( ${f}_{T}$ ) of 60 GHz and maximum oscillation frequency ( ${f}_{\text {max}}$ ) of 150 GHz were obtained for the STEOC HEMT with a gate length ( ${L}_{\text {g}}$ ) of 150 nm. Sub-6 GHz continuous-wave mode power sweep measurements deliver a high power-added-efficiency (PAE) of 67%. These results show the significant potential of the STEOC process to facilitate the development of GaN-based power amplifier (PA) applied for 5G.

中文翻译：

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通过 Ti/Au/Al/Ni/Au 浅沟槽蚀刻欧姆接触提高 AlGaN/GaN HEMT 的射频功率性能

在本文中，我们报告了采用 Ti/Au/Al/Ni/Au 金属化叠层和浅沟槽蚀刻欧姆接触 (STEOC) 的 AlGaN/GaN 高电子迁移率晶体管的高直流和射频性能。优异的欧姆接触性能，包括低接触电阻（ ${R}_{C}$ ） 的 $0.28~\Omega \cdot $ 毫米和光滑的表面形态已同时实现。原子力显微镜 (AFM) 显示出高度光滑的表面形态，即使在 810 °C 高温退火 (HTA) 后，均方根 (rms) 粗糙度仍为 6.3 nm，与传统 Ti/ Al/Ni/Au 欧姆接触 (COC)。高分辨率透射电子显微镜 (HRTEM) 显示出光滑的形态，在 STEOC 样品的界面中形成连续且均匀的 TiN 层，而由于 Ni-Al 复合物成球和 TiN 岛渗透到 AlGaN 中导致的凹凸形态对常规样品观察到 /GaN 异质结构。因此，采用 STEOC 工艺制造的晶体管显示出 1.52 A/mm 的高输出电流和低导通电阻（ ${R}_{ \mathrm{ ON}}$ ） 的 $2.09~\Omega $ 毫米。此外，高电流截止频率（ ${f}_{T}$ ) 的 60 GHz 和最大振荡频率 ( ${f}_{\text {max}}$ ) 的 STEOC HEMT 获得了 150 GHz 的栅极长度 ( ${L}_{\text {g}}$ ) 的 150 纳米。低于 6 GHz 的连续波模式功率扫描测量可提供 67% 的高功率附加效率 (PAE)。这些结果显示了 STEOC 工艺在促进用于 5G 的基于 GaN 的功率放大器 (PA) 的开发方面的巨大潜力。