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GaN-based Transistors for Power Electronics

• Authors: D. Piedra, B. Lu, M. Sun, H.-S. Lee, Y. Zhang, T. Palacios
• Sponsorship: SRC/FCRP MSD, SRC-FCRP IFC, ADEPT ARPA-E, DOE GIGA, MIT-MTL GaN Energy Initiative

Wide band-gap III-nitride semiconductors have excellent potential for next-generation power electronics systems.  AlGaN/GaN high-electron-mobility transistors (HEMTs) have attracted great interest due to their high breakdown electric field and high electron mobility.  InAlN/GaN HEMTs also show great promise for high-performance power electronic switches, due to the very high sheet charge density induced by the polarization difference between InAlN and GaN. Transistors built from GaN could theoretically have 3 orders of magnitude reduction in on-resistance compared to Si power devices.  With lower conduction loss and higher switching frequency, they can improve the efficiency and reduce the size of many power electronics systems.

Wide-periphery AlGaN/GaN transistors with W_g=80 mm have been designed and successfully fabricated, as Figure 1 shows.  These devices were flip-chip solder-bumped and placed in a power converter circuit (designed by Professor Perreault’s group) resulting in 92.72% efficiency at 25 W.  To ensure that the device did not suffer from breakdown or dramatic dynamic on-resistance during the converter operation, passivation and field-plate structures were optimized.  Work is ongoing to integrate the enhancement mode tri-gate technology^[1] with these wide-periphery devices.

InAlN/GaN devices with an off-state breakdown voltage of 3000V and a low specific on-resistance of 4.25 mΩ∙cm² were also fabricated^[2].  In order to suppress sub-threshold current leakage, an AlGaN back-barrier was used to better confine the channel electrons in these devices, as shown in Figure 2.

Finally, the thermal characteristics of lateral AlGaN/GaN HEMTs and vertical MOSFET power transistors were analyzed using a self-consistent electro-thermal simulation.  It was found that although the lateral device structure offers better performance for breakdown voltage below 200 V, the vertical transistors have the potential (although at a substantially higher cost) for higher power density at or above 600 V^[3].



Figure 1: AlGaN/GaN multi-finger device with Wg=80 mm with layout designed for solder ball, flip-chip packaging.



Figure 2: Schematic cross section of the fabricated InAlN/GaN HEMT with AlGaN back-barrier and corresponding breakdown voltage data.




1. B. Lu, E. Matioli, and T. Palacios, “Tri-Gate Normally-Off GaN Power MISFET,” IEEE Electron Device Letters, vol. 33, no.3, Mar. 2012. [↩]
2. H.-S. Lee, D. Piedra, M. Sun, X. Gao, S. Guo, and T. Palacios, “3000V 4.3mΩcm² InAlN/GaN MOSHEMTs With AlGaN Back Barrier,” IEEE Electron Device Letters, vol. 33, no. 7, July 2012. [↩]
3. Y. Zhang, M. Sun, T. Fujishima, K. Bagnall, Z. Liu, E. Wang, and T. Palacios, “Thermal Performance of GaN Vertical and Lateral Power Transistors,” International Workshop on Nitride Semiconductors, Sapporo, Japan, 2012. [↩]