Panasonic Corp of Osaka, Japan says that it has developed gallium nitride (GaN) diodes that can not only operate at a high current of 7.6kA/cm2 - four times greater than that tolerated by conventional silicon carbide (SiC) diodes with a rated voltage of 1200V - but also operate at low voltages by virtue of their lower turn-on voltage (0.8V). Also, on-resistance (RonA) is approximately halved, to 1.3mΩcm2.
Production of the new diodes was enabled by a newly developed hybrid structure composed of separately embedded structure consisting of a low-voltage unit and a high-current-capable unit, in preparation for high-voltage conditions.
Conventional silicon diodes are limited with regard to reducing switching losses. On the other hand, diodes based on SiC and GaN require an increased chip area to achieve high-current operation, placing limitations on the reduction of switching losses and size due to the increased operating frequency, says Panasonic.
The new GaN diodes have achieved simultaneous high-current operations and low threshold voltage, and thus can handle high currents even with a small chip area. The capacitance of the chip can therefore be reduced to achieve lower switching losses, allowing the device to operate at higher frequencies. As a result, the use of GaN diodes in the voltage conversion circuits or inverter circuits of automotive or industrial equipment that requires high power can reduce system size due to high-frequency operation.
Panasonic says that the hybrid structure of the new diodes was created with a p-type GaN layer in which trenches are formed. The firm developed processing technology that can remove a p-type layer on an n-type layer in a selective way, to achieve not only high-current operations and a low turn-on voltage but also a breakdown voltage of 1.6kV.
To fabricate the new diodes, Panasonic used low-resistance conductive GaN substrates (which have been used commercially in LEDs and semiconductor lasers and are expected to be adopted in power devices in the future). The firm has also established technologies for epitaxial growth and processing on a GaN substrate. A structure in which currents flow in the vertical direction enables a smaller chip area and lower resistance, adds Panasonic.
The results of this development were presented at the 47th annual International Conference on Solid State Devices and Materials (SSDM 2015) in Sapporo, Japan (27-30 September). The work was partially supported by Japan's Ministry of Environment.
