Transphorm (United States)

In this talk, we present latest breakthrough in high-power GaN technologies: high-voltage rating up to 1200 V, high-current rating up to 170 A for a single die, short-circuit capability up to 5 μs, and monolithic bi-directional switches for novel, more compact circuit topologies for lighter, smaller, more efficient and more reliable power conversion systems for data-centers, artificial intelligence, transportation, and much more.

Transphorm Inc. is supplying N-polar GaN epitaxial wafers for ultra-high-performance RF and mm-wave electronics on sapphire and silicon carbide (SiC) substrates. In this work, we report on the manufacturing facility, epitaxial growth on both 100-mm sapphire and 100-mm SiC, and device electrical performance. Results show good material quality, a low 2DEG sheet resistance with good non-uniformity, and good dynamic behavior with no current dispersion at 60 V at both room temperature and high temperature (150°C).

900V GaN FETs are here. Their superior reliability allows them to handle 1000V transient voltage and 900V DC link with reduced lifetime. This paper is to demonstrate 900V 50m Ω GaN FETs in a 300 kHz, 2kW LLC converter bridging high voltage systems (500V to 900V), and low voltage systems (45V to 50V). As 900V GaN FETs can handle higher voltages, it becomes less necessary to design 3-level LLC converters with 600/650V devices. A 2-level half bridge using 900V 50m Ω GaN FETs enables high frequency LLC converters for a wide-range of high-input-voltages. And, the GaN FETs are compatible with classic gate drive circuits for Si MOSFETs. A prototype has been evaluated with input voltages ranging from 500V to 900V and output power up to 2kW.

Reliability related to the internal avalanche of GaN Cascode is addressed with optimum device design & confirmed with standard & over-voltage operation life tests. Further improvement in high-frequency resonant switching is achieved with inbuilt low-voltage MOSFET output charge matching.

Nitrogen polar (N-Polar) GaN high-electron-mobility transistors (HEMT) targeting high-voltage switching applications were fabricated on epi-layers grown by metal-organic chemical vapor deposition on sapphire substrates. Devices demonstrated a combination of high breakdown voltage and low dynamic ON-resistance. Breakdown voltages of over 2000 V were observed on transistors with ${L}_{G}=\text {1}\,\,\mu \text{m}$ , ${L}_{{\text {GS}}}=1\,\,\mu \text{m}$ , and ${L}_{{\text {GD}}}=28\,\,\mu \text{m}$ . These devices had a drain current density of ~ 575 mA/mm at ${V}_{{\text {GS}}}=1$ V, and the specific ON-resistance (active-area) was $ {4}~\text {m}\Omega \cdot \text {cm}^{2}~(10~\Omega \cdot \text {mm}$ ). Dynamic ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) was characterized $\text {5}~\mu \text{s}$ after the device was turned ON, with up to 575-V OFF-state stress. At ${V}_{{\text {DS}}, {Q}} = \text {575}$ V, the dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ was ~1.4 times the static ${R}_{ \mathrm{\scriptscriptstyle ON}}$ (40% increase). These transistors showed an ultra-low dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of ~5% when measured at 450-V stress. As one of the first demonstrations of N-Polar GaN HEMTs for power switching applications, the devices discussed in this letter achieve excellent ${V}_{ \mathrm{\scriptscriptstyle BR}}$ and dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ performance comparable to (and in most cases better than) the state-of-the-art Ga-Polar GaN HEMTs reported in the literature.

This letter reports on the dynamic $R_{\text{ON}}$ performance of large-area GaN vertical trench MOSFETs (OG-FETs) fabricated on bulk GaN substrates. OG-FETs demonstrated excellent DC performance with a breakdown voltage of 900 V and a $R_{\text{ON}}$ of 4.1 $\Omega$ (8.2 $\text{m}\Omega \cdot \text {cm}^{2}$ ). However, damage to the trench sidewalls caused by RIE dry etching led to poor dynamic $R_{\text{ON}}$ performance. An improved dynamic $R_{\text{ON}}$ performance was achieved by following the RIE dry etch with a TMAH wet etch. With this process combination, the dynamic $R_{\text{ON}}$ was reduced by more than 10 times compared with the dynamic $R_{\text{ON}}$ in devices fabricated by dry etch only.

Expert View High-voltage (HV) gallium nitride field-effect transistors (FETs) are becoming the next standard for power conversion. They provide cost competitive, easy-to-embed solutions that reduce energy loss by more than 50%, shrink system size by more than 40%, and simplify power converter/inverter design and manufacturing.

GaN devices have superior performance over Sibased devices, and high voltage normally-off GaN HEMTs with cascode structure have been available for industry application as they can be easily driven by mature commercial Si-MOSFET drivers. Due to the very fast switching speed, the PCB layout and driver circuit design should be very careful to keep the parasitic parameters as small as possible. Paralleling semiconductor devices is an effective and simple way for higher power application. It is very challenging to parallel GaN HEMTs in hard-switching bridge power converter application, especially for discrete leaded package devices. However, leaded packages are still dominant in industrial applications because of their simplicity for PCB assembly and capability for a wide variety of heat-sinking techniques. In this paper, a solution to paralleling GaN HEMTs for diode-free bridge power converters is proposed, and GaN device driver design is discussed. The partial phase method is also suitable for the low power application to improve the efficiency. Simulations of driving circuit and experimental results on a 5 kW half bridge operating in synchronous boost mode with 4 paralleling GaN HEMTs are provided for validation.

GaN-on-Si power devices have advantages in both performance and the potential for low cost and high volume production. Advances have been made in extended reliability tests exhibiting an intrinsic life time >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> hours for qualified 600-V GaN HEMT products. Experimental kV-class devices have shown CW operation at 800V with >99% efficiency at 100 kHz and a 2:1boost ratio. Both are exciting developments reaffirming the validity of the new power semiconductor technology.