Demonstration of GaN‐Based HEMTs Using Extremely Thin h‐BN Passivation Layer and Air Spacer for the RF Performance Improvement

Abstract GaN‐based high electron mobility transistors (HEMTs) is demonstrated using an extremely thin (≈ 5 nm) h‐BN passivation layer and air spacer, for the first time. The h‐BN passivation layer is grown by metal–organic chemical vapor deposition on top of the AlGaN barrier, followed by GaN‐based HEMTs fabrication. To prohibit the loss and/or damage of the thin h‐BN passivation layer, the SiN is deposited as a protection layer during the device fabrication. When the device fabrication is finalized, the SiN protection layer is removed by buffered oxide etchant, introducing the air spacer under the head of the T‐gate electrode. The electrical properties of the GaN‐based HEMTs applying h‐BN passivation layer and air spacer are measured and compared to the h‐BN/SiN passivated and conventional SiN passivated GaN‐based HEMTs. The difference of the DC characteristics corresponding to the passivation layer in GaN‐based HEMTs is negligible. However, compared to the conventional SiN passivated GaN‐based HEMTs, the RF performance, such as current gain cut‐off frequency and maximum oscillation frequency is improved by 50.3% and 68.5%, respectively, since the parasitic capacitances is reduced by the air spacer formation in GaN‐based HEMTs using a thin h‐BN passivation layer.