Research Review: TriQuint Ups GaN-on-silicon HEMT Efficiency
TriQuint claims that it has broken the power added efficiency (PAE) record for GaN onsilicon HEMTs operating at 10 GHz.
Transistors fabricated in the labs of this US chipmaker have delivered a PAE of 65 percent, a value that is very similar to that produced by the company’s commercial, state-of-the-art process on the superior platform of SiC.
Engineers at TriQuint point to improvements in epitaxy and device architecture for closing the PAE gap between GaN HEMTs on silicon and on SiC.
“Epitaxial material was designed to maximize the drain-source current while keeping a low leakage current and a high breakdown voltage," revealed corresponding author Deep Dumka. “Buffer growth was optimized to minimize RF loss."
Dumka told Compound Semiconductor that the device fabrication process was similar to the company’s production process for GaNon- SiC HEMTs. The GaN-on-silicon HEMTs were created by first growing a GaN/Al0.26Ga0.74N/GaN stack on 4-inch silicon (111). Reactive ion etching (RIE) created AlGaN/GaN mesa patterns, and evaporation and rapid thermal annealing formed Ti/Al-based ohmic contacts.
E-beam lithography, a RIE-based lowdamage nitride-etch process and evaporation of a Pt/Au metal stack defined 0.25 μm, T-shaped gates that inherently formed a field plate. A second field plate was added on top via optical lithography and Ti/Pt/Au metallization.
This pair of field plates cuts the peak electric field between drain and gate, leading to improved HEMT performance at high voltages.
At an input power of 20.8 dBm, TriQuint’s GaN-on-silicon transistor delivered a peak PAE of 65.6 percent, an output power of 33.9 dBm (6.1 W/mm) and a gain of 13.1 dB. This HEMT is also capable of producing 34.5 dBm (7.0W/mm), but this increase in output power comes at the expense of a reduction in PAE to just over 60 percent.
TriQuint’s GaN-on-silicon process is being developed with commercial interests in mind. “However, there is no firm date yet for production transfer of this process, since our GaN-on-SiC technology is meeting present demands" says Dumka.
D.C. Dumka et al. Electron. Lett. 46 946 (2010)