A Millimeter-Wave AlGaN/GaN HEMT Fabricated With Transitional-Recessed-Gate Technology for High-Gain and High- Linearity Applications

A high-linearity and high-gain AlGaN/GaN HEMTs with a 100-nm gate were demonstrated. The device employs transitional recessed gate (TRG) along the gate width for millimeter wave power application. The gradually changing gate recess depth was created using transitional dosed photoetching. Accurate etching ensured that the FET-elements have a continued $\text{V}_{\mathrm {ts}}$ offset in the local equivalent threshold voltage ( $\text{V}_{\mathrm {th}}$ ) in different areas. The device exhibits a high $\text{I}_{\mathrm {d,max}}$ of 1.12 A/mm and a high peak extrinsic $\text{g}_{\mathrm {m}}$ of 374 mS/mm with an improved gate swing >2.6 V, much higher than that of Fin-HEMT. Excellent RF performance was shown, including $\text{f}_{\mathrm {T}}/\text{f}_{\mathrm {max}} =61.8$ /148.8 GHz, $\text{G}_{\mathrm {as}}/\text{G}_{\mathrm {linear}} = {9.98}$ / 12dB at 30 GHz. To the best of our knowledge, this is the best associated gain and linearity performance reported to date for AlGaN/GaN HEMTs. This letter has great potential for high gain and linearity millimeter wave power applications, which are needed for future communication systems.