Fabrication of 0.25 μm T-Gate AlInGaN/AlN/GaN HEMTs by I-Line Optical Lithography

In this report, we demonstrate an optical lithography process to fabricate T-gate AlInGaN/AIN/GaN high electron mobility transistors (HEMTs) on Si substrates with gate length down to 0.25 mu m. The gate foot is defined by backfilling and etching a SiNx layer with a 0.6 mu m wide window. The backfilled SiNx layer serves not only as the spacer layer that results in a reduced gate foot, but also as a passivation layer for reducing surface trap states. The fabricated AlInGaN/AIN/GaN HEMTs exhibit IDss of 537 mA/mm, transconductance of 439 mS/mm, current gain cut-off frequency (f(T)) of 58 GHz, and power gain cut-off frequency (f(max)) of 73 GHz.