In this article, we experimentally investigate the degradation mechanisms of GaN high-electron mobility transistors (HEMTs) with p-type gate during long-term high-temperature reverse bias (HTRB) stress and negative bias temperature instability (NBTI) stress. Based on a number of stress/recovery experiments, we demonstrate that HTRB stress could lead to hole emission in the p-GaN layer, making threshold voltage (Vth) positively shift, while NBTI stress could result in detrapping at the AlGaN/GaN interface or the AlGaN layer and make Vth negatively shift. It is also found that the temperature rise can suppress the positive Vth shift and accelerate its recovery process in HTRB experiments.

CMOS technology dominates the semiconductor industry, and the reliability of MOSFETs is a key issue. To optimize chip design, trade-offs between reliability, speed, power consumption, and cost must be carried out. This requires modeling and prediction of device instability, and a major source of instability is device aging, where defects gradually build up and eventually cause malfunction of circuits. This paper first gives an overview of the major aging processes and discusses their relative importance as CMOS technology developed. Attentions are then focused on the negative and positive bias temperature instabilities (NBTI and PBTI), mainly based on the early works of the authors. The aim is to present the As-grown-Generation (AG) model, which can be used not only to fit the test data but also to predict long-term BTI at low biases. The model is based on an in-depth understanding of the different types of defects and the experimental separation of their contributions to BTI. The new measurement techniques developed to enable this separation are reviewed. The physical processes responsible for BTI are explored, and the reasons for the failure of the early models in predicting BTI are discussed.

In this article, the degradation behavior of the electrical characteristics of AlGaN/GaN HEMTs subjected to radio frequency (RF) overdrive stress has been studied. Trap analysis based on low-frequency noise (LFN) and electroluminescence (EL) characterizations was carried out for AlGaN/GaN HEMTs before and after RF stress. The experimental results show that drain-to-source current of AlGaN/GaN HEMTs after RF stress is obviously lower than that of the fresh devices. The maximum change of drain-to-source current was up to 79 mA in the saturation zone. The threshold voltage drifted forward and gate-lag characteristic became worse for the AlGaN/GaN HEMTs after RF stress. The EL characterizations also showed the nonuniformity of channel illumination intensity, which indicates the distribution of electron of the channel nonuniform. Trap analysis was performed by using the LFN method, and the LFN results showed that the trap density increased by about one order of magnitude in the AlGaN/GaN HEMTs after RF stress, which would lead to more depletion of the channel two-dimensional electron gas (2DEG) electrons. The mechanism of increasing trap density could be attributed to defects induced by RF stress at AlGaN surface and AlGaN barrier layer. The experimental results may offer a useful reference in the design and application of RF of AlGaN/GaN HEMTs.

In this paper, the degradation behavior of the electrical characteristics was investigated, and trap analysis based on low-frequency noise (LFN) was carried out for the commercial 1.2-kV/30-A silicon carbide (SiC) power MOSFETs under repetitive short-circuit (SC) stress. The experiment results show that the on-state resistance (Rdson) and threshold voltage (Vth) increase significantly. Meanwhile, the drain-source current (Ids) decreases obviously with the increase of the SC cycles. Furthermore, the gate-source leakage current (Igss) of the SiC power MOSFETs increase greatly and the blocking characteristics deteriorated after 1000 SC cycles. The positive shift was observed on the gate-capacitance versus gate-voltage (Cg-Vg) curve, which shows that the damage region could be in channel along the SiC/SiO2 interface after repetitive SC stress. In order to obtain the trap information, trap characterization was performed by using LFN method, and the LFN results show that the trap density increases with the SC cycles. The physical mechanism could be attributed to electrically active traps generated at SiC/SiO2 interface and oxide layer due to the peak ionization rate, the perpendicular electrical field and high temperature during SC stress. The study may be useful to provide reference for converters design and fault protection of SiC power MOSFETs.

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.

Non-filament 3D vertical random access memory (VRRAM) is a promising technology for emerging high-density memory applications, which can significantly improve system performance by simplifying memory hierarchy. Reliability issue is one of the most challenging concerns precluding the commercial application of RRAM. The bulk of RRAM reliability papers focus on the electric stress, while the effect of moisture stress from ambient environment has seldomly been studied. In this brief we examine the aging kinetics of moisture stress through statistical measurements on state-of-the-art 8-layer 3D VRRAMs. The results reveal that RHRS and on/off window declines significantly while RLRS remains unaltered in terms of the average value of multiple devices. Meanwhile, reset current Ireset increase obviously. Moreover, different layers exhibit the same aging kinetics. We speculate the observed degradation is due to the moisture stress introduces defects at HfO2/TaOx interface and brings down the barrier.