14-05-2015 | | By Paul Whytock
Widespread adoption of Gallium Nitride (GaN) transistors as silicon MOSFET replacements is now an economic reality says California-based power semiconductor company Efficient Power Conversion (EPC). This bold proclamation follows the launch of its 60V EPC2035 and 100V EPC2036 eGaN power transistors which the company says outperforms silicon on both price and speed.
Cost has been a huge and at times prohibitive obstruction that GaN has had to overcome to secure the widespread application opportunities that would drive economy of scale in manufacturing terms that subsequently would result in a continued and sustainable price reduction of the technology.
The technical advantages of GaN have never been in question.
Its material and electronic properties provide a number of key performance advantages. Prime amongst these are high dielectric strength, high operating temperature, high current density, high speed switching and low on-resistance. It also cuts down heat sink requirements and offers an 80% reduction in system volume and weight.
So what is in the EPC GaN plan that has created this cost/performance competitiveness over silicon?
According to the company a device’s cost effectiveness starts with exploiting existing production infrastructures. EPC’s process begins with silicon wafers. Using existing silicon processing equipment, a thin layer of Aluminum Nitride (AlN) is grown on the silicon to isolate the device structure from the substrate. On top of this a thick layer of highly resistive GaN is grown.
This layer is what provides the foundation on which to build the GaN transistor. An electron generating material is applied to the GaN and this creates a GaN layer with a significant amount of electrons that is highly conductive. Further processing forms a depletion region under the gate. To enhance the transistor, a positive voltage is applied to the gate in the same manner as turning on an n-channel, enhancement mode power MOSFET. This structure is repeated many times to form a power device. The end result is a fundamentally simple, elegant, cost effective solution for power switching.
OK, but what power MOSFETS were used to make the all important price/performance comparisons with GaN FETs? The power MOSFETs that were compared to these new EPC GaN FETs were selected based on having comparable maximum rated on-resistance (RDS(on)) and having the same maximum rated breakdown voltage (VDS(max)). Note that the indicators of switching speed, QOSS, QGD, and QG, are shown in this table for comparison (lower values are better).
Capacitances are also significantly less for the new EPC2035 and EPC2036 devices than for their counterpart MOSFETs. Device area is also shown for comparison and it can be seen that the EPC2035 and EPC2036 are one-fortieth the area of their equivalent MOSFET component.
Development boards are available to support in-circuit performance evaluation of these eGaN FETs. They are in a half-bridge topology, featuring the eGaN FETs, onboard gate drives, supply and bypass capacitors.
And finally what about the all-important bottom line?
Pricing for the EPC2035 power transistors at 1K units is $0.36 each and $0.38 for the EPC2036. The 10K unit prices are $0.29 and $0.31 respectively and the EPC9049 and EPC9050 development boards are $104.40 each. These products are available from distribution company Digi-Key.