AlGaN/GaN HEMT with LPCVD deposited SiN and PECVD deposited SiCOH low-k passivation

This paper reports AlGaN/GaN HEMT with 20 nm LPCVD deposited SiN and 200 nm PECVD deposited SiCOH low-k passivation layer. The capacitance–voltage (C–V) measurement indicates that LPCVD deposited SiN results in a better interface quality compared with the PECVD method. PECVD SiCOH with a dielectric constant lower than 2.2 helps to reduce the parasitic capacitance while providing mechanical support for field plate and protection of passivation layer. The thin and dense LPCVD SiN film passivates the interface. Meanwhile, low-k material results in reduction of C GS + C GD by over 20% and an increased cutoff frequency (f T) compared with SiO2/SiN passivated device.