Vol.6 No.3 2014

Research paper−147−Synthesiology - English edition Vol.6 No.3 pp.147-157 (Dec. 2013) in output at high temperature, and this property can be used to create an innovative device module without a cooling system unit. Figure 2 shows the correlation between the on-resistance and the breakdown voltage of the Schottky diode at room temperature and at 250 °C. For the property of SiC, the incremental effect of the drift layerTerm 2 due to temperature increase was applied to the optimal structure at room temperature.[5] In diamond, the increase in carrier due to temperature increase supplements the decrease in mobility due to scattering. The current increases to about 200 °C and becomes low on-resistance, and become constant to about 250 °C. Therefore, in case of the diamond, low-loss, high-current, high-voltage, and ultra downscaling are realizable as long as the device that has reached high temperature due to self-heating is not “cooled on purpose.”[6] This property can be applied to power devices such as electrical vehicles, trains, and vessels, as well as industrial devices and for power distribution. Compared to SiC, the CO2 reduction of 2.34 million ton/year (2040) and 4.93 million ton/year (2050) can be expected. It is mentioned as one of the ultimate devices that may support power electronics in the Cool Earth Innovative Energy Technology PlanNote) of the Japan Ministry of Economics, Trade and Industry.Because it is composed entirely of carbon, diamond has a major advantage that there is no natural resource problem such as raw material procurement and remaining reserves. It is also highly safe, as it can be synthesized using safe gases such as methane and CO2, is extremely stable all the way to high temperature, and does not emit harmful substances upon combustion, and is safe at nano size.In conducting the fundamental researches and various application researches for diamond, in February 2005, we 1 Objective of the research and its outcomeDiamond is a material with the highest performance among all materials in terms of heat conductivity and electrical breakdown field. It can be called the “super material.” Although there are several applications for diamond, it is best known as the material for wide-gap semiconductors. For power semiconductor devices, its expectation as low-loss power conversion device surpassing SiC is high.[1]-[4] The related material parameters are shown in Fig. 1. The thermal conductivity is one order higher than Si, overwhelmingly higher than AlN, Cu, Al and other heat spreader materials commonly used. It can be easily inferred that diamond may alter the fundamental thermal management of a device. The electrical breakdown field is one order higher compared to other materials, and high breakdown voltage is expected. The high hole mobility is advantageous for high-speed and high-output operations. Also, with increased carrier at self-heating temperatures of 200~250 °C, there is no decrease - Verification of its superiority as the ultimate power device-Diamond is expected to be an excellent material exceeding SiC for producing low loss power devices because of its superior material characteristics. We have developed series of elemental technologies including killer-defect free epitaxial growth, refractory Schottky contact, Schottky barrier height control associated with low leakage current and termination structure. As a result, we have developed a refractory Schottky barrier diode with fast switching capability, which can operate for over 300,000 hours at 250 °C. R&D of large scale wafers and large power devices are required to realize low-loss devices with a new concept of “cooling system free.”Development of diamond-based power devicesKeywords : Diamond, power switching device, refractory, low loss, Schottky diode[Translation from Synthesiology, Vol.6, No.3, p.152-161 (2013)]Shinichi Shikata* and Hitoshi UmezawaDiamond Research Laboratory, AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568, Japan *E-mail: (current affiliation: Research Institute for Ubiquitous Energy Devices, AIST 1-8-31 Midorigaoka, Ikeda 563-8577, Japan)Original manuscript received August 28, 2012, Revisions received January 16, 2013, Accepted February 7, 2013Diamond02468101214161820Dielectric constantMobility (cm2/Vs)Thermal conductivity (W/cmK)Electrical breakdown field (MV/cm)02468101214161820010002000024620SiSiCGaNSiSiCGaNp DiamondSiSiCDiamondGaNSiSiCGaNDiamondFig. 1 Comparison of parameters of various materials that affect the power device(Mobility for diamond is p type)


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