A GaN Approach to Schottky Diodes

The G²REC program aims to create a new generation of energy-efficient power devices for high-volume applications over 250V.

The greater electronics industry has an urgent need for fast-switching, high-voltage, energy-efficient and cost-competitive rectifiers.

Rectifiers (which convert AC to DC) are comprised of diodes, components that ensure electricity flows in just one direction. For certain high-volume applications such as power factor correction (PFC) in computer server power supplies and motor control in large appliances, the diodes need to: switch on very fast at low voltage; handle high voltage spikes; and switch off very fast and completely. They also need to be cost-competitive and suited to high-volume production.

For applications under 250V that require fast switching, this is handled by silicon-based Schottky diodes. For fast-switching needs in the 250-1500V range, however, the choice is currently limited to a range of much more complex and expensive components, most of which are notorious wasters of energy.

The €30 million G²REC project aims to develop a new generation of highly energy-efficient GaN-based Schottky diodes for the 250-1500V range, which will be competitively priced and well-suited to high-volume production. The target market is approaching $1 billion, and set to double over the next five years.

This new generation of Schottky diodes requires a thick (›6μ) epitaxially grown GaN layer on 6” silicon substrates – as opposed to today’s 2” and 4” substrates – enabling significant economies of scale.

Other advantages to the GaN approach include:

• Very fast recovery time, so very low dissipation.
• Low R_ON, very low leakage current, and high electron mobility.
• Smaller passive components and packaging, easy integration with other modules, and operational at ›150°C.
• The simplified circuitry (requiring no snubber network) makes them well suited to high-volume applications in PFC or motor control.

STMicroelectronics is leading the G²REC project, with partners: Picogiga, OMMIC, the French national labs of CHREA Sophia Antipolis and LMP Tours, and NOVASiC. The project has recently been granted funding, and is scheduled to produce a commercial solution within the next three years.