Introduction of Carbon Nanotubes as Heat Dissipating Material in Amplifier Transistors for Mobile Base Station by Fujitsu
With expectation that 4G (IMT-Advanced) mobile communication systems in near future would be capable of handling large volume of data in order of 50Mbps to 1Gbps with a high frequency transmission all within single transmission, forcing the wireless base station that serve as a link to mobile phones and data to become capable of transmitting in high frequency and handling large volume of data as well , along with high-power output of in 100W class in order to cover the wide area coverage for mobile phones.
Two key technical challenges in achieving such a high frequency and high-output amplifiers are mainly, the electrical interconnection methods that are required to ensure that amplification rates do not drop at high frequencies and the other is the heat dissipation methods that are required to control heat in achieving high power output. The existing conventional electrical interconnection method uses long metallic wires where at the high frequencies the amplification rates tend to drop due to the length of the wires. Furthermore, with the conventional method, making the transistor chip smaller does not allow a sufficient chip size for heat dissipation, making the practical miniaturization of the transistors extremely challenging. In response to these challenges, Fujitsu Laboratories made an announcement on introduction of carbon nanotubes acting as a heat-dissipating material for amplifier transistors for next generation mobile base stations. Fujitsu has become the first company in achieving the successful operation of high frequency, high power (100W-class) flip-chip amplifiers. The company has achieved the high frequency, high output and high amplification in the amplifiers through development of “dual-side heat-dissipation” technology where the heat is dissipated through both sides of the transistors chip, which is the source of the amplifier’s heat output. This has been done by employing a structure called a flip-chip structure featuring an excellent high-frequency characteristics. The newly developed technology will increase the heat-dissipation by a factor of 1.5 times in comparison to the conventional methods. Furthermore, applying the new technology will result in transistor chip size reduction by approximately 2/3 that of existing transistor chips, a stepping stone in amplifiers miniaturization.
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