Aluminum-Nitride Power Semis at Darnell’s Energy Summit

Closing the morning plenary session at the 2014 edition of Darnell's Energy Summit, Baxter Moody, Director of Device Development at HexaTech, Inc. presented a path to commercialization for high-voltage power semiconductor devices fabricated with Aluminum-Nitride (AlN). The company is currently sampling its first-generation of UV-C LEDS on AlN and expects to expand its products to include Schottky rectifiers in 2016 with power switches to follow.

Hexatech manufactures its own AlN wafers and will migrate production to 2-inch wafers next year and 3-inch wafers the following year. HexaTech’s PVT process is considered ideal for high Al-percentage epitaxial layers. It has alow total dislocation density, ~1E2/cm2; no low angle grain boundaries; and a typical X-ray rocking curve FWHM < 20 arcsec. And, unlike SiC, there are no micropipes and no foreign polytypes in AlN.

“AlN offers a bandgap of 6.1eV, compared with bandgaps of 3.4eV for GaN and 3.3eV or 4H-SiC, giving AlN superior theoretical performance in terms of temperature limits and breakdown voltages.” Moody observed. “And it has a theoretical critical field limit of 15.9MV/cm, compared with corresponding limits of 3.0 and 2.2 for GaN and 4H-SiC, respectively, giving it the ability to offer superior combinations of breakdown voltage and on-resistance,” Moody continued.

“For example, at a specific on resistance of 10-3 Ohm•cm2, the Breakdown Voltage of silicon would be 100 V, for 4H-SiC it would be 4000 V, for GaN it would be 5000 V, while for AlN it would be 20000V! This indicates a more than 5:1 performance improvement over SiC and a 200:1 improvement over Si if the full potential of AlN is realized,” Moody observed.

Moody compared AlN high-voltage power devices to devices fabricated with SiC and claims that the AlN devices are produced with a blocking layer 65% to 75% thinner than that needed for SiC, making them more manufacturable, higher yielding, and lower cost. The AlN devices can operate faster than SiC GTOs and IGBTs since they are majority carrier devices and majority carrier devices are faster, particularly during turn off, which is delayed due to minority carrier storage. Resulting in the expectation that AlN devices will operate more efficiently than SiC GTOs and IGBTs since these bipolar devices will exhibit loss during the turn off due, again a result of minority carrier storage.

“AlN-based power devices provide: Exceptionally high breakdown voltage…Beyond 20 kV. Dramatically lower resistive losses, with increased efficiencies and greater energy savings. Switching frequencies above 20 kHz. Operation at higher junction temperatures. And lower cost. For example, in 20-kV diode application we estimate that an AlN device will be about 50% lower equivalent cost compared to either unipolar or bipolar SiC devices, while simultaneously delivering greater performance,” Moody concluded.