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Research paper : Development of diamond-based power devices (S. SHIKATA et al.)−152−Synthesiology - English edition Vol.6 No.3 (2013) the Al2O3 insulating film as the field relaxing structure. As shown in Fig. 11(a), this is a structure in which the Al2O3 was set around the Schottky electrode. The prototype of the first ampere class device is shown in Fig. 11(b).[28]For the high-speed operation property, joint research was done with Professor Funaki of the Graduate School of Engineering, Osaka University. The switching characteristics of the diamond diode was measured, as the recovery of the diamond Schottky diode was measured using the “double pulse method” after constructing the driving circuit using the Si MOSFET. Figure 12 shows the switching property. This corresponds to (8) in the synthesiology tree in Fig. 3.For the high-speed switching of (8), the high-speed switching of 0.01 sec and small reverse recovery current (low loss) of 40 A/cm2 were confirmed for the high-speed operation at 225 °C in small vertical diode that was our first prototype. The operation at 250 °C was achieved in a 1 A class device.[28][31]By demonstrating that the diamond diode could operate in high temperature at high speed and with low loss in a structure that is actually used, even in a small vertical device, it can be said that Phase 1 (superiority verification) of this research was cleared.5 Future prospects and roadmapFirst of all, the main issue is the growth of epitaxial film with low defects. While we were able to eliminate the killer defects, it is known that the leakage current increases significantly if the device size is increased,[32]-[34] and the most important issue is to decrease the defects. At present, we have started to work on identifying the defect types, effects on the device characteristics, and the ways to reduce them. The research from this perspective has not been done intensively for diamond, and it is necessary to return to basic research. Currently, through various analysis such as x-ray topography, the presence of edge dislocation and mixed type dislocation (a) Schematic diagram of vertical device structure using field plate as the field termination(b) Example of forward-biased property of diodesp+ 300 µmp 12 µm00-8-7-6-5-4-3-2-1-0.2-0.4-0.6-0.8-1RT150 ℃250 ℃Forward bias VF(V)Forward-biased current IF(A)Ohmic electrode(Ti/Pt/Au)Schottky electrode(Mo/Au)φ30-1,000 µmField plate(AI2O3, 1.8 µm)(a)(b) Comparison at various temperatures (show same recovery property)(a) Comparison at various current levels (show same high-speed recovery property)-80-400040801200.020.04Time (μs)Time (μs)Current density (A/cm2)Current density (A/cm2)-80-400040801200.02-0.02-0.04-0.06-0.02-0.04-0.06-0.080.04200 ℃100 ℃25 ℃Fig. 11 Ampere class diamond Schottky diode with field relaxing structure(From Reference [28] H. Umezawa et al.)Fig. 12 Recovery property of the diamond Schottky diode(From Reference [29] K. Kodama et al.)

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