We propose the Ti/Al/Ni/Ti ohmic contacts to improve the breakdown voltage (V _BD ) of GaN-based high electron mobility transistors (HEMTs). Using the same photolithography process, the first Ti/Al metal stack and the second Ni/Ti metal stack were achieved by electron beam (EB) evaporation and magnetron sputter, respectively. Attributed to the better particle filling on the sidewall by magnetron sputtering, the second Ni/Ti metal stack completely wraps the first Ti/Al metal stack and extends to both sides after a lift-off process. Even after high temperature annealing (HTA), the Ti/Al/Ni/Ti metal stack can keep smooth edge acuity and surface morphology, resulting in a uniform electric-field distribution near the ohmic contacts. Compared with Ti/Al/Ni/Au ohmic contacts, HEMTs with Ti/Al/Ni/Ti ohmic contacts have higher V _BD and can improve the uniformity as well as repeatability of V _BD .

中文翻译：

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具有Ti / Al / Ni / Ti欧姆接触的硅上高击穿电压GaN基HEMT

我们建议使用Ti / Al / Ni / Ti欧姆接触来提高击穿电压（V _BD GaN基高电子迁移率晶体管（HEMT）。使用相同的光刻工艺，分别通过电子束（EB）蒸发和磁控溅射实现了第一Ti / Al金属叠层和第二Ni / Ti金属叠层。由于通过磁控溅射在侧壁上更好地填充了颗粒，第二个Ni / Ti金属叠层完全包裹了第一个Ti / Al金属叠层，并在剥离工艺之后延伸到两侧。即使经过高温退火（HTA），Ti / Al / Ni / Ti金属叠层仍可以保持光滑的边缘锐度和表面形态，从而在欧姆接触附近产生均匀的电场分布。与Ti / Al / Ni / Au欧姆接触相比，具有Ti / Al / Ni / Ti欧姆接触的HEMT具有更高的V _BD并可以改善V 的均匀性和可重复性 _BD 。