Vol.6 No.3 2014

Research paper : Development of diamond-based power devices (S. SHIKATA et al.)−156−Synthesiology - English edition Vol.6 No.3 (2013) Hitoshi UMEZAWAGraduated from the Faculty of Science and Engineering, Waseda University in 1998. Completed the master’s course at the Graduate School of Science and Engineering, Waseda University in 2000. Assistant at the Waseda Research Institute of Science and Engineering; assistant at the Research Institute for Advanced Science and Medical Care, Waseda University; and joined AIST in 2005. Currently, Senior Researcher at the Research Institute of Ubiquitous Energy Devices. Engages in R&D of synthesis technology, assessment, and device application of diamond material. Conferred doctorate at the Waseda University (Engineering). Member of Japan Society of Applied Physics and IEEE. After joining AIST, has been the main personnel in charge of this research. In this paper, was in charge of whole research except polishing.Discussions with Reviewers1 GeneralQuestion and comment (Naoto Kobayashi, Center for Research Strategy, Waseda University)This paper reports the results of the comprehensive research for superiority verification of diamond used in power semiconductor devices. It presents the general outcomes starting from the individual elemental technology that the authors have accumulated over the years to the actual verification, and it is a significant paper to be published in Synthesiology. Particularly, I think it can provide an effective guideline and direction to readers who may be working on the practical utilization and realization of diamond power devices. However, there are ambiguous expressions that are somewhat difficult to understand, and careful revision is necessary.Question and comment (Toshimi Shimizu, AIST)This research shows the result of the superiority verification of next-generation power semiconductor device that uses diamond materials which possess optimal performance among several substances. Its content is equivalent to Full Research as the four synthesis elements were solved along with the reference to breakthroughs. It is indeed appropriate as a Synthesiology paper. Although there is no major problem in the logical composition, I think you need to work on making it more understandable to the general reader. If this point is supplemented, it will be a more satisfying paper.2 Research scenario and specific applicationQuestion and comment (Naoto Kobayashi)Figure 3 shows the scenario (synthesiology tree diagram) for the superiority verification research of diamond power devices. This is the important main focus of this paper in terms of synthesiology. However, the meaning of the numbered items such as (1) electrical breakdown, (2) killer defect elimination, etc. and their relationships are hard to understand. There are some explanations in chapter 4, but it is unclear whether they show the passage of time or the order of research conducted, and you need some explanation in the text or in the caption of the figure.Answer (Shinichi Shikata)The numbers indicate the order in which the researches were ultimately conducted. I added a note in the figure. They more or less follow the basic plan that was created in December 2004, and combined with the wafer development for which the research was done concurrently, they lead up to the roadmap shown in Table 1. The future issues are the breakthroughs needed for practical use as shown in the upper left of Fig. 3, and we hope to accomplish them in Japan with cooperation from various organizations.Question and comment (Naoto Kobayashi)There is a brief description of the application of diamond power devices in chapter 1. Since this is the most important part for enabling practical use of the results of this paper, I recommend that it be discussed in detail by using a diagram (such as that you have shown on http://www.chubu.meti.go.jp/jisedai_jidoushiya/chiubu/pdf/sansoken/sansoken_8.pdf), which will help the readers’ understanding.Answer (Shinichi Shikata)I added the figure that I left out due to space limitations. I added the names of specific application devices. In the ENERGY OUTLOOK of IEA, 67 % of the CO2 reduction is accomplished by energy-saving technology, and I wish to attain practical use as soon as possible to meet this demand. Looking at the example of SiC, the Schottky diode that we took up as an exemplary device in this paper has more merit compared to the Si pn diode, and I think there is good possibility for the medium output devices. Also, diamond has excellent resistance to gamma rays and neutron rays, and I think there is potential in small current devices.3 Comparison of the performances of low-loss power devices and status of the R&D of the diamond deviceQuestion and comment (Toshimi Shimizu)You compare various property values for substances including diamond, SiC, GaN, and Si, but I would like to know the benchmark information of the devices to which such substances are actually implemented. In other words, in future power device applications, how will diamond exert its characteristics? What are the evidences and reasons for such claims? Please describe them. In the Synthesiology paper written by Kazuo Arai, “R&D of SiC semiconductor power devices and strategy towards their practical utilization - The role of AIST in developing new semiconductor devices” [Synthesiology English edition, Vol. 3, No. 4, p. 245-258 (2011)], there is a conceptual diagram that clearly shows the relationship between the application of power semiconductor and device performance in demand (p. 256). For easier understanding, I think you need to create a similar figure by superimposing the performance of diamond on this diagram.Answer (Shinichi Shikata)I created a new figure. I showed the specific applications according to the categories of current and voltage. In fact, by adding the cooling free and high temperature axes, it shows the characteristic merit of diamond that can be used without decreasing output.Question and comment (Naoto Kobayashi)In this paper, there are detailed explanations of the content and significance of the elemental technologies that the authors have accumulated over the years, but there is no explanation on the ongoing R&D in Japan and overseas, and this gives an obscure impression of the positioning of this research. I hope you address other R&Ds such as, for example, T. Iwasaki et al. [Appl. Phys. Express, 5, 091301 (2012)]. You should also cite the patent information, since your results have been utilized as patents.Answer (Shinichi Shikata)I added the prospects by citing the papers on transistors. The recent paper that you indicated is a research on the device based on pn junction, and ultra high breakdown voltage is assumed for its use. However, over 10 order improvement from nA to 100 A class is needed. In diamond, n+ doping has not been achieved, and further material research is necessary. Currently, I think the unipolar device that can be driven at low voltage will take the


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