SiC MOSFET and GaN FET in high voltage switching applications

For several decades, silicon-based semiconductor devices, such as Si MOSFETs have been the main choice for switching applications. However, their level of performance is approaching its maximum potential, and further development becomes increasingly challenging. As a result, semiconductor manufacturers and the electronics industry are exploring new technologies to meet current requirements. One promising option is the use of WBG (Wide Band Gap) devices, such as GaN FETs and SiC MOSFETs, which have gained attention due to their superior performance characteristics. Compared to traditional Si transistors, WBG devices can withstand higher voltages and tem-peratures, are faster, can be packed in smaller sizes, and are more efficient. This study aims to serve as a guide for designers seeking information on the technology and usage of WBG transistors, particularly in high voltage switching applications. The study in-cludes an examination of the structures of SiC MOSFETs and GaN FETs, as well as their most important electrical characteristics. Additionally, the efficiency of an LCC converter was measured to compare the performance of various FET types, with a specific interest in the use of WBG devices in soft switching applications. Scientific articles, application notes, and datasheets were investigated to provide a thorough understanding of the theory behind SiC MOSFETs and GaN FETs. According to resources, the primary SiC MOSFET and GaN FET technologies suitable for high voltage switching are planar SiC MOSFET, trench SiC MOSFET, p-GaN FET and GaN/Si cascode transistor. These devices are currently available with breakdown voltages of 1700 V (planar SiC MOSFET), 2000 V (trench SiC MOSFET), 650 V (p-GaN FET) and 900 V (GaN/Si cascode transistor). The efficiency of an LCC converter with a maximum output power of 40 W was measured using 1500 V Si MOSFET, 1700 V planar SiC MOSFET, 1700 V trench SiC MOSFET, and 900 V GaN/Si cascode transistor. A constant load of 1 A was used, and the input voltage was incre-mentally increased from 300 V to 900 V in 100 V steps. According to results, using planar and trench SiC MOSFETs, LCC converter had the highest efficiency, reaching up to 89,6 % while Si MOSFET exhibited slightly lower efficiency, which was 87,7 % at its best. GaN/Si cascode tran-sistors showed comparable efficiency to SiC MOSFETs at lower input voltages but fell signifi-cantly behind as the voltage increased, having eventually much worse efficiency than Si MOSFET.Useiden vuosikymmenien ajan pii-pohjaiset puolijohteet, kuten pii MOSFETit, ovat olleet pääasiallinen teknologia katkojasovelluksissa. Niiden suorituskyky lähestyy kuitenkin ylärajaa, ja niiden kehittäminen käy yhä vaikeammaksi. Tämän vuoksi puolijohdevalmistajat ja elektroniikkateollisuus etsivät uusia teknologioita täyttää nykyiset vaatimukset. Yksi lupaava teknologia ovat laajan energiavyön puolijohteet, kuten galliumnitridi FETit ja piikarbidi MOSFETit. Viime vuosina ne ovat herättäneet paljon huomiota niiden ylivoimaisten ominaisuuksien vuoksi. Verrattuna perinteisiin pii MOSFETeihin, laajan energiavyön transistorit kestävät suurempia jännitteitä ja lämpötiloja, ovat nopeampia ja ne voidaan pakata pienempään kokoon. Lisäksi ne ovat tehokkaampia. Tämä diplomityö pyrkii toimimaan oppaana elektroniikkasuunnittelijoille, jotka etsivät tietoa laajan energiavyön transistoreista ja niiden käytöstä erityisesti suurjännitekatkojasovelluksissa.Työssä tarkastellaan piikarbidi MOSFETien ja galliumnitridi FETien rakenteita sekä niiden tärkeimpiä sähköisiä ominaisuuksia. Lisäksi mitattiin kelaan ja kahteen kondensaattoriin perustuvan LCC resonanssiteholähteen hyötysuhde eri FET-tyypeillä, koska haluttiin saada tietoa laajan energiavyön transistorien käytöstä pehmeässä jännitteen katkonnassa. Tiedon keräämiseksi tutkittiin tieteellisiä artikkeleita, sovellusohjeita ja datalehtiä. Lähdeaineiston perusteella pääasialliset piikarbidi MOSFETien ja galliumnitridi FETien teknologiat suurjännitesovellusten alueella ovat planaarinen piikarbidi MOSFET, erityiseen kaivanto teknologiaan (trench) perustuva piikarbidi MOSFET, p-tyypin galliumnitridi FET ja galliumnitridi/pii kaskadi transistori. Tällä hetkellä näitä teknologioita on kaupallisesti saatavilla enimmillään 1700 V (planaarinen piikarbidi MOSFET), 2000 V (kaivanto piikarbidi MOSFET), 650 V (p-tyypin galliumnitridi FET) ja 900 V (galliumnitridi/pii kaskadi transistori) jännitteillä. Nimellisteholtaan 40 W LCC resonanssi teholähteen hyötysuhde mitattiin 1500 V pii MOSFETeilla, 1700 V planaarisilla piikarbidi MOSFETeilla, 1700 V kaivanto piikarbidi MOSFETeilla ja 900 V gallium-nitridi/pii kaskadi transistoreilla. Kuormana käytettiin 1 A vakiokuormaa ja tulojännitettä nostettiin asteittain 300 voltista 900 voltiin 100 voltin nostoin. Tulosten mukaan paras hyötysuhde oli 89,6 %, joka mitattiin planaarisella piikarbidi MOSFETilla ja kaivanto piikarbidi MOSFETilla. Pii MOSFETien tapauksessa hyötysuhde oli hieman huonompi, ollen parhaimmillaan 87,7 %. Alhaisilla jännitteillä galliumnitridi/pii kaskadi transistorien hyötysuhde oli verrattavissa piikarbidi MOSFETeihin, mutta hyötysuhde laski jännitettä nostettaessa, ollen lopulta merkittävästi huonompi kuin pii MOSFETeilla

(Invited) Emerging Role of Silicon Carbide and Gallium Nitride Based Power Electronics in Power and Transportation Sectors

Free fuel-based energy sources (solar and wind) are pointing towards a future in which sustainable energy is affordable, abundant and deployed with high energy efficiency. Driven by advancements in the technology of lithium batteries and the availability of low-cost sustainable clean electric power, the electrification of transportation is going through fundamental disruptive transformation. Without any doubt, both power and transportation sectors will provide phenomenal growth of power electronics in the 21st century. Recently, both SiC and GaN are drawing the attention as potential replacement of Si-based power electronics. These may open some new markets where Si based power electronics cannot function either due to power or temperature limitations. In this paper we have identified the WBG based key power electronics products that should be focused to see their high growth

Smart Power Devices and ICs Using GaAs and Wide and Extreme Bandgap Semiconductors

We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively review the recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before large-scale commercialization commences

Power electronics based on wide-bandgap semiconductors: opportunities and challenges

The expansion of the electric vehicle market is driving the request for efficient and reliable power electronic systems for electric energy conversion and processing. The efficiency, size, and cost of a power system is strongly related to the performance of power semiconductor devices, where massive industrial investments and intense research efforts are being devoted to new wide bandgap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN). The electrical and thermal properties of SiC and GaN enable the fabrication of semiconductor power devices with performance well beyond the limits of silicon. However, a massive migration of the power electronics industry towards WBG materials can be obtained only once the corresponding fabrication technology reaches a sufficient maturity and a competitive cost. In this paper, we present a perspective of power electronics based on WBG semiconductors, from fundamental material characteristics of SiC and GaN to their potential impacts on the power semiconductor device market. Some application cases are also presented, with specific benchmarks against a corresponding implementation realized with silicon devices, focusing on both achievable performance and system cost

Gallium-Nitride Efficacy for High-Reliability Forward Converters in Spacecraft

Gallium Nitride (GaN) devices show particular promise for space-rated power conversion applications that rely on MOSFET technology whose performance is severely limited by the radiation hardening processes. Though GaN failure mode classification and radiation hardened device variety is limited, the current space-rated selection pool can still yield significant efficiency and power density improvements. However, the context of GaN research is often future oriented such that the application of GaN to common, proven, space-rated converter designs is rare. The presented work quantifies the performance benefits of market available, space-rated GaN HEMTs over radiation hardened MOSFETs for a synchronous forward converter, which remains an extremely popular topology for isolated, medium power, DC-DC conversion on NASA satellite systems. Two 75-Watt, space-rated forward converters were designed, implemented, and benchmarked, with the power switch technology being the single variable of change. By forming pareto-optimal fronts of the key device metrics, optimal Rad-hard MOSFETs were chosen so that the baseline converter performance was considered best-case. The frequency limitations of common, available, Rad-hard PWM controllers limited power density in the GaN and Si converter alike, however, efficiency gains proved sizeable. The GaN based converter saw a peak efficiency of 86%, which was a 4.54% improvement over the Si baseline. Detailed efficiency and loss differential plots are presented which show the GaN converter’s reduced sensitivity to input voltage. Extreme similarity between the waveforms and functional characteristics of the two converters verified the design of the experiment. Furthermore, the performance of the baseline Si converter proved very similar to that of a large sampling of space-rated forward converters, making the experimental results have a high degree of utility for manufacturers

Novel TCAD oriented definition of the off-state breakdown voltage in Schottky-gate FETs: a 4H SiC MESFET case study

Physics-based breakdown voltage optimization in Schottky-barrier power RF and microwave field-effect transistors as well as in high-speed power-switching diodes is today an important topic in technology computer-aided design (TCAD). OFF-state breakdown threshold criteria based on the magnitude of the Schottky-barrier leakage current can be directly applied to TCAD; however, the results obtained are not accurate due to the large uncertainty in the Schottky-barrier parameters and models arising above all in advanced wide-gap semiconductors and to the need of performing high-temperature simulations to improve the numerical convergence of the model. In this paper, we suggest a novel OFF-state breakdown criterion, based on monitoring the magnitude (at the drain edge of the gate) of the electric field component parallel to the current density. The new condition is shown to be consistent with more conventional definitions and to exhibit a significantly reduced sensitivity with respect to physical parameter variation

Diamond power devices: State of the art, modelling and figures of merit

With its remarkable electro-thermal properties such as the highest known thermal conductivity (~22W/cmbold dotK at room temperature) of any material, high hole mobility (> 2000cm2/Vbold dots), high critical electric field (>10MV/cm), and large bandgap (5.47eV), diamond has overwhelming advantages over silicon and other wide bandgap semiconductors (WBG) for ultra-high- voltage and high temperature applications (>3kV and >450 K, respectively). However, despite their tremendous potential, fabricated devices based on this material have not delivered yet the expected high-performance. The main reason behind this is the absence of shallow donor and acceptor species. The second reason is the lack of consistent physical models and design approaches specific to diamond-based devices that could significantly accelerate their development. The third reason is that the best performances of diamond devices are expected only when the highest electric field in reverse bias can be achieved, something that has not been widely obtained yet. In this context, high temperature operation and unique device structures based on the 2DHG formation represent two alternatives which could alleviate the issue of the incomplete ionization of dopant species. Nevertheless, ultra-high temperature operations and device parallelization could result in severe thermal management issues and affect the overall stability and long-term reliability. Additionally, problems connected to the reproducibility and the long-term stability of 2DHG based-devices still need to be resolved. This review paper aims at addressing these issues by providing the power device research community with a detailed set of physical models, device designs and challenges associated to all the aspects of the diamond power device value chain, from the definition of figures of merits, the material growth and processing conditions, to packaging solutions and targeted applications. Finally, the paper will conclude with suggestions on how to design power converters with diamond devices and will provide the roadmap of diamond devices development for power electronics.This work was supported by the U.K. Engineering and Physical Sciences Research Council for the University of Cambridge Centre for Doctoral Training under Grant EP/M506485/1 and by the French ANR Research Agency under grant ANR-16-CE05-0023 #Diamond-HVDC. The research leading to these results has been performed within the GREENDIAMOND project and received funding from the European Community's Horizon 2020 Programme (H2020/2014–2020) under grant agreement no. 640947

Beta-Ga2O3 MOSFETs with near 50 GHz fMAX and 5.4 MV/cm average breakdown field

This letter reports high-performance $\mathrm{\beta} Ga2O3 thin channel MOSFETs with T-gate and degenerately doped source/drain contacts regrown by MOCVD. Gate length scaling (LG= 160-200 nm) leads to a peak drain current (ID,MAX) of 285 mA/mm and peak trans-conductance (gm) of 52 mS/mm at 10 V drain bias with 23.5 Ohm mm on resistance (Ron). A low metal/n+ contact resistance of 0.078 Ohm mm was extracted from TLM measurement. Ron is dominated by interface resistance between channel and regrown layer. A gate-to-drain breakdown voltage of 192 V is measured for LGD = 355 nm resulting in average breakdown field (E_AVG) of 5.4 MV/cm. This E_AVG is the highest reported among all sub-micron gate length lateral FETs. RF measurements on 200 nm Silicon Nitride (Si3N4) passivated device shows a current gain cut off frequency (f_T) of 11 GHz and record power gain cut off frequency (f_MAX) of 48 GHz. The f_T.V_Br product is 2.11 THz.V for 192 V breakdown voltage. The switching figure of merit exceeds that of silicon and is comparable to mature wide-band gap devices

The 2018 GaN Power Electronics Roadmap

Gallium nitride (GaN) is a compound semiconductor that has 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