Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

A Survey of Wide Bandgap Power Semiconductor Devices

The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Gallium-nitride power transistor (GaN HEMT) and integrated circuit technologies have matured dramatically over the last few years, and many hundreds of thousands of devices have been manufactured and fielded in applications ranging from pulsed radars and counter-IED jammers to CATV modules and fourth-generation infrastructure base-stations. GaN HEMT devices, exhibiting high power densities coupled with high breakdown voltages, have opened up the possibilities for highly efficient power amplifiers (PAs) exploiting the principles of waveform engineered designs. This paper summarizes the unique advantages of GaN HEMTs compared to other power transistor technologies, with examples of where such features have been exploited. Since RF power densities of GaN HEMTs are many times higher than other technologies, much attention has also been given to thermal management-examples of both commercial “off-the-shelf” packaging as well as custom heat-sinks are described. The very desirable feature of having accurate large-signal models for both discrete transistors and monolithic microwave integrated circuit foundry are emphasized with a number of circuit design examples. GaN HEMT technology has been a major enabler for both very broadband high-PAs and very high-efficiency designs. This paper describes examples of broadband amplifiers, as well as several of the main areas of high-efficiency amplifier design-notably Class-D, Class-E, Class-F, and Class-J approaches, Doherty PAs, envelope-tracking techniques, and Chireix outphasing.

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A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs

Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

https://iopscience.iop.org/article/10.7567/JJAP.54.040103/pdf

Material science and device physics in SiC technology for high-voltage power devices

GaN high-electron-mobility-transistors (HEMTs) on SiC were fabricated with field plates of various dimensions for optimum performance Great enhancement in radio frequency (RF) current-voltage swings was achieved with acceptable compromise in gain, through both reduction in the trapping effect and increase in breakdown voltages When biased at 120 V, a continuous wave output power density of 322 W/mm and power-added efficiency (PAE) of 548% at 4 GHz were obtained using devices with dimensions of 055/spl times/246 /spl mu/m/sup 2/ and a field-plate length of 11 /spl mu/m Devices with a shorter field plate of 09 /spl mu/m also generated 306 W/mm with 496% PAE at 8 GHz Such ultrahigh power densities are a dramatic improvement over the 10-12 W/mm values attained by conventional gate GaN-based HEMTs

30-W/mm GaN HEMTs by field plate optimization

Field plate technologies have dramatically raised the benchmarks of GaN-based high-electron-mobility transistors (HEMTs). Greater than 30 W/mm power density was demonstrated with gate-connected field plates'. The drawback of additional feedback capacitances added by the field plates was then addressed using source-termination, achieving 21dB large-signal gain and 20-W/mm power density at 4 GHz"l. Recently, multiple field plates were pursued for further improvements""v I. Here we present double field-plated GaN HEMTs with increased power density and robustness. The devices in this study consisted of a Cree HPSI SiC substrate, a 2-4 ptm thick insulating GaN buffer, a thin AlN interlayer and an Al0.26Gao.74N barrier layer. The GaN buffer was doped with Fe for enhanced resistivity and the AlN interlay was included to achieve a high charge-mobility product without the complication of increasing the Al mole fraction of the top AlGaN layer. The device has a first field plate (FP1) integrated with the gate for both reduced gate resistance and elimination of electron trapping. The task of further tailoring the electric field and attaining a higher breakdown voltage is accomplished by a second field plate (FP2), placed on the drain side of the first field plate. FP2 is electrically connected to the source of the HEMT to minimize feedback capacitance. When designed properly, the double field-plated devices can offer a more optimal electric field distribution, improving performance and robustness. Targeting high-power operation at C band, the length of FP1 was set at LF1=0.3-0.5 ptm and FP2 at LF2=0.9-1.2 ptm. The SiN dielectric thickness under FP1 and FP2 was 100 nm and 200 nm, respectively. The device fabrication steps were similar to previous reports,"" except for the gate formation, where the integrated gate and FP1 were deposited on the SiN layer with a previously etched gate opening. Devices of four configurations were fabricated for a direct comparison. Device A had no field plate. Device B had double field plates, both connected to the gate. Device C had double field plates, FP, connected to the gate and FP2 connected to the source. Device D had a single field plate connected to the source. The gate length was about 0.55 ptm and gate-drain separation was 3.5 ptm. Typical devices showed -4 V pinch-off voltage and >1.2 A/mm full channel current. While circuit element extraction from S-parameters revealed practically the same current gain cut-off frequency of 30-35 GHz for the intrinsic devices, the maximum stable gains (MSG) varied based on the extrinsic parasitics. In particular, with LF1=0.3 pim and LF2=0.9 pim, MSG values at 10-GHz and 41 V for devices A, B, C and D were 15.6 dB, 11.2 dB, 16.7 dB and 17.1dB, respectively. It is expected that device B with both field plates connected to the gate has a high feedback capacitance, hence a much lower MSG than the non-field-pate device A. With FP2 connected to the source, however, device C actually exhibited higher MSG than the non-field-pate device. This is attributed to the Faraday shielding effect by the source field plate, which reduces the feedback capacitance. Although device D, with a single field plate connected to the source, showed 0.4-dB higher gain than device C, the less-optimum electric field distribution made it less robust and more prone to degradation at high operation voltages. Power measurements were performed with a load-pull system at 4 GHz. As intended, device C showed the best combination of output power, gain, power-added efficiency and robustness. A 246-pim-wide device with LF1=0.5 pim and LF2=1 .2 pim was able to be biased at 135 V and achieved a continuous-wave (CW) power density of 41.4 W/mm, along with 16-dB associated gain and 60% PAE. This is a significant improvement over previous result of 32.2 W/mm, 14 dB associated gain and 54.8% PAE by single-field-plated GaN HEMTs. Initial reliability tests showed that the double-fieldplated device had no degradation after 100-hour RF operation at 80 V while generating CW output power of 25 W/mm. In summary, a double-field-plate structure has been developed to extend the performance limit of microwave GaN HEMTs. The first field plate offers a high gate conductance and prevents the onset of trapping; while the 2nd field plate maximizes operation voltage without additional feedback capacitances. 41.4 W/mm CW power density was obtained, establishing a new state-of-the-art for microwave devices.

40-W/mm Double Field-plated GaN HEMTs

A 175-to-350 V hard-switched boost converter was constructed using a high-voltage GaN high-electron-mobility transistor grown on SiC substrate. The high speed and low on-resistance of the wide-band-gap device enabled extremely fast switching transients and low losses, resulting in a high conversion efficiency of 97.8% with 300-W output power at 1 MHz. The maximum efficiency was 98.0% at 214-W output power, well exceeding the state of the art of Si-based converters at similar frequencies.

A 97.8% Efficient GaN HEMT Boost Converter With 300-W Output Power at 1 MHz

A transistor comprising a plurality of active semiconductor layers on a substrate, with source and drain electrodes in contact with the semiconductor layers. A gate is formed between the source and drain electrodes and on the plurality of semiconductor layers. A plurality of field plates are arranged over the semiconductor layers, each of which extends from the edge of the gate toward the drain electrode, and each of which is isolated from said semiconductor layers and from the others of the field plates. The topmost of the field plates is electrically connected to the source electrode and the others of the field plates are electrically connected to the gate or the source electrode.

Wide bandgap transistors with multiple field plates

A semiconductor device, and particularly a high electron mobility transistor (HEMT), having a plurality of epitaxial layers and experiencing an operating (E) field. A negative ion region in the epitaxial layers to counter the operating (E) field. One method for fabricating a semiconductor device comprises providing a substrate and growing epitaxial layers on the substrate. Negative ions are introduced into the epitaxial layers to form a negative ion region to counter operating electric (E) fields in the semiconductor device. Contacts can be deposited on the epitaxial layers, either before or after formation of the negative ion region.

Marcia Moore

Papers

30-W/mm GaN HEMTs by field plate optimization

40-W/mm Double Field-plated GaN HEMTs

A 97.8% Efficient GaN HEMT Boost Converter With 300-W Output Power at 1 MHz

Wide bandgap transistors with multiple field plates

Robust transistors with fluorine treatment