8 December 2010

Panasonic develops blocking-voltage-boosting structure for GaN-on-Si power transistor

At the 56th annual IEEE International Electronic Devices Meeting (IEDM 2010) in San Francisco, CA, USA this week (6–8 December), Panasonic Corp of Osaka, Japan has reported the development of a new technique to increase the blocking voltage of a gallium nitride (GaN)-based power switching transistor on silicon (Si) substrates.

Graphic: Schematic of GaN power transistor on Si with BVB structure.

In a GaN transistor on a conductive Si substrate at high drain voltage, strong electric fields are formed in the vertical direction, says Panasonic. The blocking voltage is hence ideally determined by the sum of that due to the thickness of GaN and that due to the Si substrate.

However, experimentally observed values have been increased just by the GaN thickness, with no contribution from the blocking voltages of Si. Panasonic has hence investigated the mechanism and revealed that the increase is limited by leakage current at the interface between GaN and Si caused by electrons forming an inversion layer.

As a solution, Panasonic has proposed a new blocking-voltage-boosting (BVB) structure consisting of selectively formed p-type regions on the surface of the Si substrate, which prevent the inversion electrons from flowing as leakage current. The new structure hence allows the blocking voltage of the Si substrate to add to that of the GaN transistor.

A GaN transistor fabricated on Si with a BVB structure (with a total epitaxial thickness as small as 1.9 microns) has achieved a high breakdown voltage of 2200V. This is about five times that of a conventional GaN transistor on Si with the same epitaxial thickness of GaN. A further increase in epitaxial thickness will allow breakdown voltages of more than 3000V with existing epitaxial technologies, reckons the firm.

Panasonic says that the new GaN transistor on Si with a BVB structure should be applicable for increasing the operating voltages of various power switching systems, including inverters for industrial use and uninterruptible power supplies.

The firm has filed applications for 99 domestic and 64 overseas patents on the new technology.

See related items:

Panasonic claims GaN transistor power density record of 2.4W/mm at 60GHz

Tags: Panasonic GaN-on-Si power transistor

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