2GHz GaN-on-Silicon PA For Mobile Communications
The new gallium nitride-on silicon amplifier achieves a conversion efficiency rating of 70%
Mitsubishi Electric has developed a prototype high-output, high-efficiency 2GHz power amplifier for mobile communications base stations.
The amplifier, which features a GaN transistor on a silicon substrate instead of more costly SiC, achieves a conversion efficiency rating of 70%. This, says the firm, is unprecedented among 2GHz power amplifiers with outputs of 150W or higher.
The amplifier is expected to lead to the development of smaller and more power-efficient base station transmitters. The installation of such equipment in tighter spaces will help expand wireless network coverage to accommodate increasing wireless traffic due to smartphone proliferation.
While amplifiers that use GaN transistors consume less power and have a higher output than amplifiers made with silicon transistors, they typically require a more robust substrate made SiC, which elevates the cost.
Initial efforts to develop a GaN transistor using a silicon substrate were hampered by deformation between the GaN layer and Si substrate, which led to increased loss and decreased power conversion efficiency. Eventually, however, the company designed a high-performance transistor by optimising the GaN crystal structure and inserting a buffer layer between the GaN layer and silicon substrate.
Could this buffer be aluminium nitride? Mitsubishi has remained tight-lipped about this but it is known from literature, that using this material as a buffer layer can minimise wafer bow and strain in the full structure of GaN-on silicon devices.
Optimised crystal structure of GaN-on-Silicon substrate
Mitsubishi Electric's new GaN power amplifiers made with cheap silicon substrates achieve a power conversion efficiency of 70% at 2.1GHz, largely improving upon the 58% conversion efficiency of silicon transistor amplifiers currently available commercially.
Comparison of new and current amplifiers
Moving forward, Mitsubishi Electric expects to further downsize the power amplifier and its power supply and cooling units to enable even smaller mobile communications base stations.