Feasibility of quasi-square-wave zero-voltage-switching bi-directional dc/dc converters with gan hemts

There are trade-offs for each power converter design which are mainly dictated by the switching component and passive component ratings. Recent power electronic devices such as Gallium Nitride (GaN) transistors can improve the application range of power converter topologies with lower conduction and switching losses. These new capabilities brought by the GaN High Electron Mobility Transistors (HEMTs) inevitably changes the feasible operation ranges of power converters. This paper investigates the feasibility of Buck and Boost based bi-directional DC/DC converter which utilizes Quasi-Square-Wave (QSW) Zero Voltage Switching (ZVS) on GaN HEMTs. The proposed converter applies a high-switching frequency at high output power to maximize the power density at the cost of high current ripple with high frequency of operation which requires a design strategy for the passive components. An inductor design methodology is performed to operate at 28 APP with a switching frequency of 450 kHz. In order to minimize the high ripple current stress on the output capacitors an interleaving is performed. Finally, the proposed bi-directional converter is operated at 5.4 kW with 5.24 kW/L or 85.9 W/in3 volumetric power density with air-forced cooling. The converter performance is verified for buck and boost modes and full load efficiencies are recorded as 97.7% and 98.7%, respectively

Technology and reliability of normally-off GaN HEMTs with p-type gate

open4siopenMeneghini, Matteo*; Hilt, Oliver; Wuerfl, Joachim; Meneghesso, GaudenzioMeneghini, Matteo; Hilt, Oliver; Wuerfl, Joachim; Meneghesso, Gaudenzi

ANALYSIS OF FAILURE MECHANISMS THAT IMPACT SAFE OPERATION OF ALGAN/GAN HEMTS

The reliability of AlGaN/GaN high electron mobility transistors (HEMTs) is tra- ditionally determined via thermal lifetime acceleration stress tests. More recently it has been proposed that electric field has a prominent role in limiting lifetimes. Multi- ple failure mechanisms have been proposed as a result of device degradation observed when stressed under high applied electric fields, as typical when the device is biased into the OFF-state. One potential reason for multiple mechanisms could be due to varying levels of quality and maturity of the GaN processes in the reported literature. The work presented in this dissertation seeks to provide clarity and understanding into the failure mechanism of AlGaN/GaN HEMT devices under high electric fields. The devices in this study were fabricated in a commercial GaN process, notable for exceptional ruggedness and industry leading 65V qualified operational bias for RF power amplifiers. A series of OFF-state, high electric field step-stress experiments, as described in literature, were performed to assess if any were applicable to this process. It was discovered that device degradation could only be induced when stressed close to the breakdown limits. This lead to the development of a unique stress method that enables the device to be held close to catastrophic breakdown, while avoiding an over stress event that would prevent the device from being studied at the conclusion of the experiment. It was discovered via careful electrical and optical analysis that failure was due to a localized degradation of the Schottky gate diode properties. The physical analysis found the failure inconsistent with the widely reported inverse piezoelectric effect. Instead the failures resemble recently proposed time dependent dielectric breakdown of the AlGaN barrier laye

The 2018 GaN power electronics roadmap

GaN is a compound semiconductor that has a tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

Innovative Approaches for AlGaN/GaN-based Technology

Gallium Nitride (GaN) has been proven to be a very suitable material for advanced power electronics on account of its outstanding material properties. Today, researchers are exploring GaN-based high electron mobility transistors (HEMTs) for conventional as well as high-end solutions in the range of 600 – 1200 V. However, thermal and power density limitations have impeded the achievement of the peak operational capability of AlGaN/GaN HEMTs. GaN-on-Diamond technology has proven to be a feasible solution to reduce thermal resistance and increase power density of AlGaN/GaN HEMTs for RF applications. The work presented in this thesis is focused on the realisation of high-voltage GaN-on-Diamond power semiconductor devices. This goal was achieved through extensive numerical simulations applied to device design, fabrication, and characterisation. The fabricated devices include conventional AlGaN/GaN HEMT design in circular and linear form with and without field plate engineering. The circular GaN-on-Diamond HEMTs with gate width of ~ 430 μm, gate length of 3 μm, gate-to-drain separation of 17 μm and source field plate length of 3 μm have shown breakdown voltage of ~ 1.1 kV. In this work a new concept of normally-off optically-controlled AlGaN/GaN-based power semiconductor device is proposed. A simulation study has been carried out in order to explore the DC characteristics, switching characteristics, breakdown voltage, and current gain of these novel devices. The typical structure comprises a 20 nm of undoped Al0.23Ga0.77N barrier layer, a 1.1 μm undoped-GaN buffer layer and a p-doped region (to locally deplete the electron channel and ensure a normally-off operation). The simulation study shows that the gain and the breakdown voltage of the device are highly dependent on the depth of the p-doped region. At a particular depth of the p-doped region of 500 nm the gain of the device is 970 (at light intensity of 7 W/cm2) and the breakdown voltage is ~ 350 V. The rise and fall times of the device is found to be 0.4 μsec and 0.3 μsec respectively. The simulation results show a significant potential of the proposed structure for high-frequency and high-power applications