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A normally-off SiC-JFET/GaN-HEMT cascode device is recently proposed, featuring a cascode configuration that incorporates a high-voltage (HV, e.g., 1200 V) silicon-carbide (SiC) junction field effect transistor (JFET) delivering the HV blocking capability and a low-voltage (LV) enhanced-mode (E-mode) gallium-nitride (GaN) high electron mobility transistor (HEMT) providing the normally-off gate control. This all-wide-bandgap device exhibits superior thermal stability and high switching speed compared to its counterparts, e.g., the SiC/Si cascode device. In this article, we study short-circuit (SC) characteristics of a 1200-V/80-mΩ SiC/GaN cascode device by considering the interactions between the SiC and GaN devices. The single-event SC withstand time (SCWT) of the demonstrated SiC/GaN cascode device is tested to be ∼3 μs under a dc-bus voltage (Vdc) of 600 V when the turn-on gate voltage (VG-on) is set to 5 V. The SC failure occurs due to the formation of hot spots induced by thermal-runaway leakage currents inside the SiC JFET. The SCWT of the cascode device could be improved by applying a moderate VG-on (e.g., SCWT = ∼6.5 μs at VG-on = 3.5 V under v dc = 600 V) without affecting the on-state resistance (r on). However, it is identified that current oscillations tend to be triggered during the SC period when VG-on is too low (e.g., lower than 3 V). The oscillation behavior is attributed to the energy stored in the interconnection parts between the SiC and GaN devices. The harmful oscillations could be suppressed by applying higher VG-on, which drives the SiC JFET into low-transconductance mode by modulating the drain-to-source voltage (VDS-G) of the LV GaN HEMT. [ABSTRACT FROM AUTHOR]

A GaN on engineered bulk silicon (GaN-on-EBUS) power IC platform featuring an industry-standard 200-V GaN power HEMT epi-structure has been recently demonstrated, showing effective isolation and crosstalk suppression between the high-side (HS) and low-side (LS) GaN transistors in half-bridge configuration. In this work, we scale up the vertical breakdown voltage (BV) of the GaN film on the EBUS substrate to be over 600 V. Meanwhile, the built-in back-to-back PN junctions along the trench created in the Si substrate are employed to provide an overvoltage-protection scheme through their intrinsic avalanche capability for the overlaying GaN half-bridge circuit. [ABSTRACT FROM AUTHOR]

${p}$ -channel GaN field-effect transistors (FETs) with a SiNx/GaON gate stack have been demonstrated with enhanced stability within a wide range of voltage bias and temperature. In this letter, the gate leakage characteristics and reliability of this unconventional staggered gate stack are investigated. At relatively low gate voltages, the gate current is suppressed owing to the buried-channel structure and the presence of GaON that presents an effective hole barrier. With more negative gate biases, the gate leakage was found to be dominated by the transport of holes that spillover from the ${p}$ -channel through the SiNx via Poole-Frenkel emission. Based on this gate leakage mechanism at large gate bias, $\sqrt {{\mathrm {E}}} $ model was used for gate lifetime prediction. The maximum applicable ON-state gate voltage of −7.3 V is obtained for a 10-year lifetime with a 1% gate failure rate. [ABSTRACT FROM AUTHOR]

Hot electrons with high kinetic energy could be generated in the channel of GaN high-electron-mobility transistors (HEMTs) during hard switching operation. Those “lucky” hot electrons scattered to the vulnerable interface between the passivation and barrier layers could bombard the interface region and create new defects that would lead to degradation of the dynamic on-resistance (${R}_{ON}$) after long-term operations. In this work, we propose a solution to the hot-electron induced device degradation through channel engineering, i.e., deploying a double-channel structure in place of the conventional single-channel structure in ${p}$ -GaN gate HEMTs. It is revealed that hot electrons are mostly generated in the lower channel and thus the additional scattering interface can effectively deter the hot electrons from reaching the vulnerable surface. Dynamic ${R}_{ON}$ degradation induced by long-term stresses at “semi-on” states is shown to be substantially suppressed in the ${p}$ -GaN gate HEMT with the double-channel structure. [ABSTRACT FROM AUTHOR]

With a switching drain bias, the gate reliability of Schottky-type ${p}$ -GaN gate high-electron-mobility transistors (HEMTs) under AC positive gate bias stress has been systematically investigated. The mean-time-to-failure (MTTF) under such application-relevant stress is found to be prolonged compared to that extracted from static and AC gate bias stress tests with the absence of a switching drain bias and exhibits positive coefficients with frequency and OFF-state drain bias (${V} _{\text {DSQ}}$). Such results can be explained by the drain-induced hole insufficiency in the gate stack at large ${V} _{\text {DSQ}}$ , a physical mechanism that results in elevated energy band at ON-state when ${V} _{\text {DSQ}}$ is just switched to low voltage. This non-equilibrium transient status could suppress injection of electrons from the 2DEG channel to the ${p}$ -GaN gate, which in turn substantially weakens the hot-electron’s generation in the depleted ${p}$ -GaN layer and the subsequent bombardment to the gate-metal/ ${p}$ -GaN interface, and thus prolongs the gate lifetime. [ABSTRACT FROM AUTHOR]

A 650-V/84-mΩ normally-off GaN/SiC cascode device is demonstrated with systematic static and dynamic characterizations. The cascode device features a low-voltage enhancement-mode (E-mode) gallium nitride (GaN) high electron mobility transistor (HEMT) to enable normally-off gate control, and a 650-V normally-on silicon carbide (SiC) JFET provides the high-voltage blocking capability. The GaN/SiC cascode device exhibits many application-desired behaviors, including reverse conduction capability, avalanche breakdown capability, thermally stable threshold voltage, low input/output capacitances, no dynamic RON degradation, and negligible dynamic VTH shift. In addition, a customized double-pulse test board is built to evaluate the switching performance of this cascode device and other 650-V SiC-based power devices. This cascode device adopting low-voltage GaN HEMT has low QG×RON and exhibits excellent switching performance. The switching losses (EON and EOFF) are much smaller than that of the 650-V Si/SiC cascode device and comparable to that of the state-of-the-art 650-V SiC MOSFETs. [ABSTRACT FROM AUTHOR]

A cost-effective engineered bulk silicon (EBUS) substrate technology is presented, featuring p-n junction implemented on bulk Si substrates using mainstream ion implantation and thermal annealing processes. Standard p-GaN/AlGaN/GaN heterostructures are successfully grown on the EBUS substrate and used to fabricate 200-V enhancement-mode p-GaN gate HEMTs. By creating deep trenches in the EBUS substrate to isolate the local P+ silicon regions underneath the high-side (HS) and low-side (LS) power switches, adverse effects (e.g., back-gating and dynamic ON-resistance degradation) in the use of conventional bulk Si substrate are all eliminated. The mechanism of crosstalk suppression in the GaN-on-EBUS platform is revealed in comparison with conventional GaN-on-Si platform and verified by a series of designed tests. [ABSTRACT FROM AUTHOR]

The high-speed superiority of GaN power devices with silicon-based peripheral circuits is not yet fully leveraged, mainly due to the parasitic inductance of interconnections. In this article, we demonstrate a GaN-based gate driver with an overcurrent (OC) protection circuit and an undervoltage lockout (UVLO) circuit on a p-GaN gate power HEMT platform. The gate driver features a rail-to-rail output voltage, suppressed gate ringing, and tunable driving speed, all of which are highly desired in high-efficiency and high-speed GaN power systems. To offer timely but reliable protections, the OC protection and UVLO circuit are designed with reference to the switching speed and the threshold voltage of GaN power devices. The OC protection is implemented with a separated sensing branch and blanking time controller, and the response time to an OC event is reduced to 10 ns after the blanking time. The UVLO circuit has a fixed hysteresis of 0.5 V, and its threshold voltage is especially tailored for the GaN integrated circuits. [ABSTRACT FROM AUTHOR]

Although the gallium nitride (GaN) high-electron-mobility transistor/silicon carbide (SiC) junction field-effect transistor (JFET) cascode device exhibits certain performance advantages over the SiC metal–oxide–semiconductor field-effect transistor (MOSFET), its robustness in harsh operating conditions is unknown. In this work, the short-circuit (SC) robustness of 650-V GaN/SiC cascode devices is characterized, analyzed, and compared with that of several mainstream SiC MOSFETs. GaN/SiC cascode devices exhibit competitive SC capability. Different failure modes are observed: thermal runaway in the SiC JFET of the cascode device and gate-to-source breakdown in the SiC MOSFET. The difference is associated with the configuration of the dielectric above SiC in the JFET and the source pad layout. According to the waveforms in SC events, failure spots, and thermal simulation results, a thermal runaway in the SiC JFET is attributed to the positive feedback between the drain leakage current and the junction temperature in the local area (hotspot) without the source pad on the top. The SC withstand time of the cascode device can be extended by reduction of the active area without the source pad. [ABSTRACT FROM AUTHOR]

In this article, the impacts of the off-state gate bias (VGS,OFF) on dynamic on-resistance (RON) are systematically investigated in commercial Schottky-type p-GaN Gate high-electron-mobility transistors. Double-pulse tester and pulsed I–V system are adopted to evaluate the dynamic RON with various off-state gate and drain bias (VDS,OFF) under hard- and soft-switching conditions. More negative VGS,OFF can aggravate the dynamic RON degradation under both soft- and hard-switching, especially when switching with a high VDS,OFF. The impacts of VGS,OFF on switching transients and off-state stress are investigated separately to reveal the underlying mechanisms, which are found to be associated with the generation and movements of holes. The off-state gate bias of the voltage-driving scheme needs to be carefully considered according to the identified mechanisms in terms of dynamic on-resistance degradation. [ABSTRACT FROM AUTHOR]

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 106 cycles, and long retention time. [ABSTRACT FROM AUTHOR]

Recently, a GaN reverse-conducting high-electron-mobility transistor (RC-HEMT) has been demonstrated. The RC-HEMT features built-in distributive Schottky contacts, which provide a low-loss freewheeling path. The RC-HEMT offers the same functionality as an HEMT/Schottky barrier diode (SBD) pair, but consumes much less chip area, thus its ${R}_{ \mathrm{\scriptscriptstyle ON}}$ (ON-resistance $\times $ total device width) is significantly reduced. Theoretically, ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of the RC-HEMT can approach that of an HEMT. In practice, due to certain geometry limitations, ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of an RC-HEMT lies between an HEMT/SBD pair and a single HEMT. This work investigates the factors that influence ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of the RC-HEMT using both experimental measurements and numerical simulations. It is found that ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of the RC-HEMT is strongly affected by the geometry of the source and channel regions, where HEMT sections and SBD sections are interdigitally distributed. With coarse patterning of these regions, ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of the RC-HEMT is close to the HEMT/SBD pair. Through proper geometry scaling, ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of RC-HEMT is reduced and approaches that of HEMT. [ABSTRACT FROM AUTHOR]

The short circuit (SC) behavior of a newly developed GaN-HEMT/SiC-JFET cascode device is investigated in this work. The reverse leakage current through the drain-side PN junction (IR) of the SiC JFET under SC conditions is measured simultaneously during the SC event. IR of the SiC JFET increases to 6.4 A at the end of a 5-μs nondestructive SC pulse. The increase of IR during the SC pulse induces a turning point in the SC current waveform and a dramatic negative threshold voltage shift (>30 V) in the SiC JEFT, resulting in high transient drain-to-source voltage in the GaN HEMT. The underlying mechanism is associated with the increase of local potential in the P-type layer of the SiC JFET with inevitable spread resistance (RSPD). It is suggested that reducing RSPD can improve SC capability and high IR should be considered in SC failure mechanism analysis and the design of external gate resistance of the SiC JFET. [ABSTRACT FROM AUTHOR]

GaN ${p}$ -channel field-effect transistors (${p}$ -FETs) are essential components for implementing the energy-efficient complementary logic circuitry for monolithic GaN power integration. This letter reports the threshold voltage (${V}_{\mathrm {TH}}$) instability of ${p}$ -channel GaN MOSFETs with Al2O3 as the gate dielectric. When the gate-to-source bias sweeps toward the negative direction, the ${V}_{\mathrm {TH}}$ exhibits a shift toward more negative values. The impacts of such ${V}_{\mathrm {TH}}$ instability on GaN complementary logic circuits are characterized using logic inverters and ring oscillators. It is shown that impacts on circuit functions are limited with an operating voltage swing below 5 V. However, the propagation delay could be gradually prolonged, as a result of the drifting ${V}_{\mathrm {TH}}$. [ABSTRACT FROM AUTHOR]

Short circuit (SC) capability of 650-V Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) under single and repetitive tests is characterized in this article. The investigated devices exhibit strong capability under a single SC test, but weak capability under repetitive SC tests with a bus voltage of 400 V and a gate drive voltage of 6 V. The failure mechanism under repetitive SC tests is revealed through electrothermal simulation and microscale failure spot analysis. Thermal fatigue cracks are formed due to the high temperature spike and local temperature fluctuations in the narrow GaN channel and buffer layers, leading to weak repetitive SC capability. The unique heat confinement effect in the GaN layer plays an important role in the formation of high temperature spike and fatigue cracks. The withstand time in a single SC test is several hundred microseconds due to fast drain current drop that results from high temperature and, to a lesser degree, the dynamic threshold voltage shift during the SC transient. The device failure in a single-event SC test is related to heat diffusion to a wider region. Some guidelines are proposed for handling and improving the repetitive SC capability. [ABSTRACT FROM AUTHOR]

A closely coupled double-channel (DC) structure realized on an 8-inch GaN-on-Si wafer is utilized to fabricate GaN high-electron-mobility-transistors (HEMTs) with enhanced RF linearity. The strong channel-to-channel coupling from this DC structure enables efficient transport of electrons between the two parallel channels to accommodate balanced carrier concentration and current density between the two channels. Consequently, the nonlinearity of source resistance under high current operations and the external bias dependence of cut-off frequencies could be substantially mitigated, leading to device linearity enhancement. Meanwhile, the DC structure enables simple top gate control that favors a high-yield planar process. Two-tone measurements at 4 GHz show that the DC GaN HEMT delivers an output 3rd-order intermodulation point (OIP3) that is improved by 5.2 dB over a single-channel GaN HEMT. [ABSTRACT FROM AUTHOR]