Panasonic develops GaN power transistor on silicon with blocking voltage boosting structure

According to the company, the blocking voltage of the Si substrate can be added to that of the GaN transistor by the new structure, which enables the blocking voltage over 3000V. The new GaN transistor is said to extend the operating voltages of a variety of power switching systems including inverters for industrial use and uninterruptible power supply. The technique works by forming strong electric fields along the vertical direction in the GaN transistor on a conductive Si substrate at high drain voltage. As a result, the blocking voltage is determined by the sum of that by the thickness of GaN and that by the Si substrate. However, experimentally observed values have been increased just by the thickness of GaN, where the blocking voltages of Si have never contributed to those. Panasonic investigated the mechanism and discovered that the increase was limited by leakage current at the interface between GaN and Si caused by electrons formed as an inversion layer. As a solution, the company has proposed a new technology called blocking voltage boosting (BVB) structure which consists of selectively formed p-type regions on the surface of the Si substrates. The p-type regions are said to prevent the inversion electrons from flowing as leakage current. The fabricated GaN transistor on Si with the BVB structure has been optimised to achieve high breakdown voltage of 2200V, with the total epitaxial thickness said to be as small as 1.9m. According to Panasonic, this value is said to be five times higher than that in the conventional GaN transistor on Si with the same thickness of GaN. Further increase of the epitaxial thickness is said to enable the break down voltages over 3000V with existing epitaxial technologies.