AlN epilayer slashes cost of GaN HEMT
Japan-based Fujitsu Laboratories has developed a low-cost manufacturing process that could propel GaN HEMT technology into commercial application.
By using substrates typically used for LED production, Fujitsu says that the devices can now be made at one third of the conventional cost.
The company made a big splash one year ago when it revealed a GaN HEMT amplifier that emitted 174 W at 63 V and which had a record drain efficiency (see related story).
One year on, Fujitsu says that it can make the HEMTs on a conducting SiC substrate rather than the more conventional "“ and much more expensive "“ semi-insulating SiC.
The new process uses hydride vapor phase epitaxy (HVPE) to deposit a 10 µm layer of aluminum nitride (AlN) on n-SiC. The GaN HEMT layer is then grown by MOCVD.
Devices made using the new process showed a maximum output power of 101 W, a power-added efficiency of 50% and a gain of 15.5 dB.
Fujitsu discovered that parasitic capacitance decreased when the AlN epilayer thickness was greater. The wider bandgap of AlN compared with GaN also helped to suppress leakage current to the conductive substrate, the company said.
Although GaN HEMTs are widely regarded as the superior chip technology for use in the power amplifier stage of 3G base stations, the high cost of the technology and its relative immaturity means that silicon LDMOS dominates the field.
However, Japan is thought to be the most likely place for GaN technology to catch on. Fujitsu says that it will implement the new production technology with commercial devices expected in one to two years.
