Mitsubishi Electric developed an amplifier made of gallium nitride semiconductor for mobile phone base stations of the 2.14 GHz band. The new amplifier has a structure that gallium nitride is formed on the silicon substrate, and the production cost is about one thirtieth of that of the convention chip. It has an output of 170 W with currently world’s highest power conversion efficiency of 70%. If it is put into practical use, a unit complete with this amplifier and a power circuit will be 30% smaller than the existing unit. The company wishes to upgrade the new amplifier to make it effective for the 2.5 GHz band in 2013.
The new semiconductor sandwiches a buffer of a micrometer size between the silicon substrate and the gallium nitride layer. Because silicon and gallium nitride have different crystal structures, distortion is generated from the gallium nitride layer. The company decreased the distortion that affects the performance of a transistor and improved the performance by devising the higher harmonic wave processing circuit. Two kinds of amplifiers exist. One is made of silicon alone, and the other is made of either a silicon substrate or a silicon carbide substrate with gallium nitride on it. An amplifier made entirely of silicone has an output of 150 W with power conversion efficiency of 58%, while an amplifier made of silicon substrate or a silicon carbide substrate with gallium nitride on it has an output of 200 W with power conversion efficiency of 68%. Because the latter is much higher in performance than the former, a technology to produce the latter at a lower cost has been desired.