International Rectifier (IR) is on target and is following a roadmap for the commercialization of GaN power switches first presented at last-year’s Electronica event. That roadmap includes both low-voltage (20-40V) and high-voltage (600V) devices. At last week’s Applied Power Electronics Conference, the company demonstrated its low-voltage devices as well as prototypes of the first-generation of high-voltage GaN FETs.
The low voltage devices have a figure of merit (FOM) of 30mΩ-nC compared with a FOM of 44mΩ-nC FOM of advanced low-voltage silicon FETs.
IR again presented a roadmap for improvement in the already-available 20-40V switches. Using the FOM described above, IR’s roadmap projects improvement from 30mΩ-nC for today’s devices down to about 2.5mΩ-nC by 2014.
The company demonstrated a point-of-load (PoL) converter prototype delivering 12A and switching at 5 MHz. The GaN PoL delivered an efficiency of 89% when converting from 12 to 1.8Vdc. When the switching frequency was pushed up to 10 MHz an efficiency of 85% was achieved.
IR is also on track to be in production with a 600V cascaded GaN switch in 2011. The normally off device will offer up to 10X better FOM than Si based equivalents. It is expected to have 20X lower Qrr compared to IGBT Copak devices and more than 200X less than Super Junction body diodes.
One of the problems that IR has overcome with the new 600V devices is dynamic Rds(on). In early prototype GaN devices, the Rds(on) transiently rose by as much as 250% after application of reverse voltage. For the new 600V devices, the dynamic Rds(on) is virtually non-existent out to 550V.
The Eoff switching losses for the 600V GaN device are expected to be 72% lower than for a Si IGBT. Compared with Si solutions, the high-voltage GaN switch will feature lower reverse recovery losses, lower Rds(on), lower Qg, lower EMI and will be in a smaller package.
