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power electronics  industry


needed more space of its own, so in 2009 it moved into the basement of this building, assembling a fab just for itself. “We just share the central supply systems, like gases and clean water,” explains Sönmez.


Additional milestones for MicroGaN include the demonstration of 1000 V devices in 2007 and the establishment of intellectual property for three- dimensional devices the following year. “In 2009 we set up our 6-inch capability and in 2010 the initial prototypes of our switches went to customers,” adds Sönmez. “2011 will be the year of our fully featured prototype.”


Spreading the load


Despite having tremendous expertise in hetero-epitaxial deposition of nitride films, the founders of MicroGaN decided to outsource epi-growth. “You cannot do everything at the same time – our decision was to make close partnerships and jointly develop epi with our partners,” says Sönmez.


The only significant change to MicroGaN’s strategy over the years has been to switch its focus from RF devices to power devices. Sönmez reveals that the reason behind this move was an increase in the electrical field strength of GaN, which at one point was insufficient for making power devices. “Our RF technology was transferred to high-voltage technology after having the first high-voltage results from the epi.”


Today the firm is making products on 4-inch wafers. “In parallel, we are taking a close look at 6-inch, but for 600 V applications the critical field strength and homogeneity are tough requirements,” explains Sönmez. Device development is almost complete, and it will not be long before MicroGaN starts to demonstrate its products, both in-house and with lead customers.


The German outfit is already discussing the results of its prototype diodes and switches. Its 600 V Schottky barrier diode, which it claims to be ‘best in class’, turns on at 0.3 V and delivers 4 A at 1.2 V. This compares to a turn-on voltage for SiC diodes of over 0.9 V, a difference that accounts for the lower DC loss of the GaN-on- silicon product.


Meanwhile, the company’s 600 V, normally off switch


has an on-resistance of 320 mΩ – and at a gate-source voltage of 0 V, it has a drain current below 1 mA at a drain-source voltage of 600 V. Fix the drain-source voltage to 0.7 V, and drain current exceeds 2 A when the gate-source voltage hits just 3 V.


October 2011 www.compoundsemiconductor.net 17


Figure 2.The combination of a GaN HEMT and a silicon


Schottky diode allows the exceptional low-voltage characteristics of this diode to be transferred to higher voltages


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