Towards Understanding the Interaction Between Hydrogen Poisoning and Bias Stress in AlGaN/GaN MIS-HEMTs With SiNx Gate Dielectric

In this work, the interaction between hydrogen poisoning (HP) and bias stress in AlGaN/GaN MIS-HEMTs, which incorporate a SiNx gate dielectric, is investigated. The transfer characteristics show that a hydrogen-poisoned device exhibits a 1.15-V-negative threshold voltage (V
_th
) shift, a significant direct current (DC) ON-resistance (RON_DC) decrease, and a subthreshold swing (SS) decrease with respect to a fresh device, whereas the max-gm remains unchanged after excluding the effect of RON_DC. Moreover, the border trap energy distribution remains almost unaffected before and after HP, indicating that the border traps are insensitive to HP. The experimental results show that HP causes passivation in the interface states at the SiNx/AlGaN interface and introduces mobile H
⁺
ions in the bulk SiNx, resulting in the negative V
_th
shift, RON_DC decrease, and SS decrease. After applying a forward-bias stress on the gate, the H
⁺
ions in the bulk SiNx underneath the gate electrode drift toward the two-dimensional electron gas (2DEG) and annihilate with electrons, resulting in the irreversible positive V
_th
shift. The H
⁺
ions in the bulk SiNx beyond the gate electrode(gate-to-drain- and gate-to-source) remain unchanged, resulting in an unchanged RON_DC. This conclusion is significant for the AlGaN/GaN MIS-HEMT reliability optimization against HP, and it is particularly useful in spatial applications.