Mechanism of Increased High-Frequency Channel Noise With PECVD SiN Passivation in AlGaN/GaN HEMTs

The effect of SiN surface passivation on high-frequency channel noise in AlGaN/GaN high-electron-mobility transistors on a high-resistivity Si substrate is investigated. It was observed that the channel noise increased after SiN surface passivation by plasma-enhanced chemical vapor deposition. The mean square of the channel noise voltage increased about three times at a bias of V_d = 12V and I_d = 120 A/mm. Based on the analysis on the noise source components in the channel region, it is believed that the channel noise increase is mainly due to the modification of the lateral electrical field profile by surface passivation. The modification of the lateral electrical field profile after passivation is verified by the 2-D numerical simulation and the observation that the gate leakage increases and the breakdown voltage decreases. The measured correlation coefficient between the channel noise and the gate noise agrees with the proposed mechanism of the electrical field profile modification by surface passivation.