N121-090 TITLE: Planar, Low Switching Loss, Gallium Nitride Devices for Power Conversion Applications

TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors, Electronics

ACQUISITION PROGRAM: Long Endurance Undersea Vehicle Propulsion FNC

OBJECTIVE: Develop a fast switching, low switching loss, 50 amp, 1KV normally-off Gallium Nitride (GaN) Transistor for efficient power conversion.

DESCRIPTION: Efficient power conversion and power conditioning devices significantly impact the mission capability and affordability of both the shipboard and airborne platforms through capacity considerations, generation cost, and size and weight-form factors. Switching devices are used to electrically drive a variety of mechanical loads. A key factor that determines the electrical-to-mechanical conversion-efficiency is the switching losses in the transistor. Fundamentally, this is a function of the switching speed and the properties of the material. Silicon is widely used for power conversion due to the technology maturity and low cost. GaN-based transistors have demonstrated significantly reduced switching losses in power conversion applications, and hence significantly improve energy efficiency. Applications such as Unmanned Undersea Vehicle (UUV) sonar transducers and propulsion are key opportunities to leverage highly efficient GaN technology to increase mission duration for power and space constrained platforms. A 1 kV blocking voltage device capability is required to begin to address this class of applications.

Current power technology for applications below 1 kV utilizes silicon-based technologies which are limited by inherently low switching speeds leading to conversion losses and inefficiency. GaN overcomes these switching losses and in many cases improves energy efficiency by several percentage points for buck converters. In load-driving applications, the improvement can be dramatic (20 percentage points). A GaN device does not currently exist at this voltage and current range.

The U.S. Navy is interested in developing a normally-off, GaN High-Electron mobility transistor (HEMT) that has a 1 kV blocking voltage and ultimately can switch 50 amps with low switching losses and at high power conversion frequencies (i.e., greater than 1 MHz). The goal is to improve overall efficiency for such applications as electroacoustic transducers and propulsion drives which will result in improved mission capability (e.g., range, endurance).

PHASE I: Provide an initial development effort that demonstrates scientific merit and feasibility of an approach to achieving normally-off device operation. The effort will demonstrate a device that provides a blocking voltage of 1000 V, a threshold voltage >1 V, with a specific on-resistance, Rsubscript(DS,ON-SP) of <20 Ohm-mm and low-gate and drain leakage of <1 �A/mm. For high efficiency switching, low output capacitance of <5 pF/mm must be achieved.

PHASE II: Demonstrate a device with 50 A continuous drain-current and an on-resistance of <50 milli-Ohm and Vsubscript(t)>1 V. Drain leakage at 1000 V not to exceed 5 mA. Gate leakage should not exceed 1 mA. Input and output capacitances must not exceed 1.5 nF and 150 pF, respectively, at 500 V drain bias. Must demonstrate > 5 MHz switching frequency in boost or buck converter test circuit with >90% conversion efficiency. In addition, the drain-current collapse, Rsubscript(AC)/Rsubscript(DC), at 600 V, will be <1.5. Device yield on-wafer should demonstrate > 50%.

PHASE III: Demonstrate manufacturability of a device with a 50 A drain-current with a blocking voltage > 1000 V, threshold voltage >1 V and reduced the on-resistance, of <40 milli-Ohm. Drain leakage at 1000V not to exceed 0.5 mA. Gate leakage should not exceed 0.1 mA over gate bias range of -10V to + 10V. Input and output capacitance must not exceed 1 nF and 100 pF, respectively, at 500 V drain bias. The drain current collapse, Rsubscript(AC)/Rsubscript(DC), at 600 V, must be reduced to <1.2. Advance on-wafer yield to > 90%.

Definitions:
Csubscript(OSS) (Output Capacitance) = Csubscript(DS) + Csubscript(GD)
Csubscript(ISS) (Input Capacitance) = Csubscript(GD) + Csubscript(GS)

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Electronic power converters and motor drive applications.

REFERENCES:
1. Yifeng Wu; Jacob-Mitos, M.; Moore, M.L.; Heikman, S.; "A 97.8% Efficient GaN HEMT Boost Converter With 300-W Output Power at 1 MHz," Electron Device Letters, IEEE, vol.29, no.8, pp.824-826, Aug. 2008.

2. Rongming Chu; Corrion, A.; Chen, M.; Ray Li; Wong, D.; Zehnder, D.; Hughes, B.; Boutros, K.; "1200-V Normally Off GaN-on-Si Field-Effect Transistors With Low Dynamic on-Resistance," Electron Device Letters, IEEE, vol.32, no.5, pp.632-634, May 2011.

KEYWORDS: Power efficiency; Gallium Nitride; GaN; converter; UUV

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