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Mitsubishi Electric Develops High-output, High-efficiency GaN Power Amplifier on Si Substrate for Mobile Communications Base Stations

Tokyo, June 20, 2012 - Mitsubishi Electric Corporation (TOKYO: 6503) announced today it has developed a prototype high-output, high-efficiency 2GHz power amplifier for mobile communications base stations. The amplifier, which features a gallium nitride (GaN) transistor on a silicon (Si) substrate instead of a more costly silicon carbide (SiC), achieves a conversion efficiency rating of 70%, 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 of silicon carbide, which elevates the cost. Initial efforts to develop a GaN transistor using a Si 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 optimizing the GaN crystal structure and inserting a buffer layer between the GaN layer and Si substrate.
Optimized crystal structure of GaN on Si Substrate
Mitsubishi Electric's new GaN power amplifier made with affordable silicon substrate achieves a power conversion efficiency of 70% at 2.1GHz, largely improving upon the 58% conversion efficiency of Si transistor amplifiers currently available commercially.

Going 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.
Comparison of new and current amplifiers

Frequency Output Power Conversion Efficiency Size
Mitsubishi Electric
prototype GaN transistor amplifier
2.14GHz 170W 70% 23mm x 10mm x
Si transistor
amplifier currently
available commercially
2.17GHz 150W 58% 21mm x 10mm x