Look out, standard silicon MOSFETs: GaN is coming after you
Maintaining that progress in conventional silicon-based MOSFET switching devices has reached the point of diminishing returns, Alex Lidow, co-founder and CEO of Efficient Power Conversion (EPC) believes it is time for a new technology. Long associated with power-device leader International Rectifier (which has also announced its own GaN-based devices, see "IR introduces new GaN-based power devices at APEC"), Lidow's company has developed switching power devices based on gallium arsenide (GaN), which he maintains is a disruptive technology due to an order-of-magnitude improvement in on-resistance for a given device area—the primary figure of merit for such device--while also providing a 10x speed improvement, which minimizes switching losses.
Lidow's company is shipping enhancement-mode switches using this technology; depletion-mode switches, though easier to develop, are harder to use effectively, while enhancement-mode looks more like a standard MOSFET. The devices are targeting power supplies in server, data switches, hub, and even higher-power audio applications. Key to the cost-effective development is that these GaN-based devices, which are grown on top of silicon, can be built in standard CMOS fabs, and are thus priced like MOSFETs, not like GaN RF-signal transistors.
Packaging, also a key cost determinant for power devices, is also low cost with GaN, notes Lidow. Any heat sink (if needed) attaches directly to the die, since the process is self-isolating. Lack of a special package reduces thermal resistance, electrical resistance, and cost, of course.
Third-order Spice models are available for the GaN-based switching devices, along with reference designs and application notes, and are available via distributors. Lidow added that there are a few design-in differences when using this technology, which offers fT of 2 GHz for the larger units and fT of 5 GHz for the smaller ones: the GaN-based devices are fully enhanced at just 5 V, so you have to be careful you do not exceed 6 V at their gate. Noise and overshoot can therefore inadvertently trigger and turn on the switches, so it's the same design caution, once again: layout and attention to detail are critical. ♦