AlGaN/GaN high electron mobility transistor with Al 2 O 3 +BCB passivation

In this paper, A12O3 ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al2O3+BCB passivation. For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of fmax reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The fmax/ft ratio (≥ 4) is also improved after Al2O3+BCB passivation. The capacitance–voltage (C–V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states (on the order of magnitude of 1010 cm−2) than that obtained at commonly studied SiN HEMT.