Sanken Claims First GaN-on-silicon Inverter
Sanken Electric has produced what it says is the first ever power supply circuit to use GaN-on-silicon transistors, which were produced using its own epitaxial expertise. 
The Japanese company has produced normally-off field effect transistors (FET) with a 157 mm gate width, a 1 V threshold voltage and on-resistance of 72 mΩ.
“Gate leakage current is about four orders of magnitude smaller than conventional normally-on type FETs," Hirokazu Goto, manager of Sanken s GaN development group, told compoundsemiconductor.net.
The company has exploited its GaN FET s 800 V breakdown voltage in a demonstration inverter circuit, proving its effectiveness for power applications.
Goto says that these devices are still in development, with the aim of reducing the chip size to one-seventh that of silicon MOSFETs, but are targeted for commercialization in the near future. Immediate problems that need solving include current collapse and long-term reliability.
Sanken deposits material on the 5-inch silicon wafers by MOCVD, with multiple GaN/AlN buffer layers easing tensile stress on the final GaN film.
“We successfully produced non-pitted and crack-free epilayers," Goto said. “The thickness of the total epitaxial layers could be increased to more than 5 ?m."
To make the FET normally-off, Goto said that the key innovation came in forming a recess under a gate electrode made from p-type material.
The team s GaN-on-silicon epitaxial expertise derives from an LED manufacturing approach that Sanken developed as long ago as 2002.
It is now using GaN s high breakdown electric field to make chips smaller and with lower power losses than silicon competitors.
Most other companies working on exploiting the advantages of GaN for power devices are using SiC or sapphire substrates, which are more expensive than silicon.
However, in recent months a number of groups have announced progress in GaN-on-silicon technologies and may be able to challenge Sanken s inverter claim. These include US power electronics giant International Rectifier, European research center IMEC and GaN device development startup Velox Semiconductor.
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