3. Radiation hardness of SiC devices

In this section, the change in the electrical characteristics of SiC transistors such as Static Induction Transistors (SITs), Metal-Semiconductor (MES) FETs and MOSFETs due to gammaray irradiation will be compared to Si MOS FETs from the point of view of the radiation hardness. Figure 7 shows ΔV2 for SiC SiTs [25], SiC MESFETs [26], C-coating+Dry SiC MOS-FETs and C-coating+Pyro SiC MOSFETs as a function of absorbed dose. All transistors were irradiated with gamma-rays at RT. During gamma-ray irradiation, no bias was applied to any electrodes of the transistors. For comparison, the results reported for Si MOSFETs are also plotted in the figure [9]. No significant change in ΔV2 for All SiC transistors is observed up to 10° Gy whereas the Si MOSFETs show obvious degradation in AV .. This indicates that those SiC transistors have extremely high radiation resistance compared to the Si MOSFETs. The value of △Vg for both the SiC MOSFETs shifts to the negative voltage side in high dose regions, and the shift for the C-coating+Dry ones is larger than that for the C-coating+Pyro ones. Thus, the C-coating+Pyro MOSFETs have higher radiation resistance than the C-coating+Dry MOSFETs. For the SiC MESFETs, the shift of AV2 to the negative voltage side increases with increasing in absorbed doses regions between 4×10° and the maximum shift of -0.75 V is observed at 2×106 Gy. However, the negative shift becomes smaller with increasing absorbed dose above 3×10€ Gy and the value of ΔVq becomes -0.27 V after irradiation at 10' Gy. For the SiC SITs, although the positive shift is observed for ΔΥη above 106 Gy, the value is relatively small (0.45V at 7×106 Gy) compared to other SiC transistors. Thus, it can be concluded that the radiation hardness of the SiC SITs and the MESFETs is higher than that of the SiC MOSFETs. Since SiTs and MESFETs do not have gate oxide, such high radiation resistance to gamma-rays can be observed. However, it should be noticed that the characteristics of SiC SITs and MESFETs are also affected by TID effects since the SiC SITs and the MESFETs is covered with a insulator (oxide) for the surface termination, and charge is trapped in such insulator. In addition, in such a high absorbed dose region, the displacement damage effect by Compton electrons also occurs and the characteristics of devices are degraded.

Next, the change in the electrical characteristics of the SiC SITs by gamma-ray irradiation is expressed. The SiC SITs have an on-resistance of 0.15 Ω and a blocking voltage of 900 V at V of -10 V before irradiation [27, 28]. Since the SiC SITs were developed as power devices, two Si power devices with similar current and voltage ratings, Si MOSFET (17N80C3) and Si IGBT (5/301), were also irradiated with gamma-rays for comparison. The SiC SiTs mounted in TO220 packages were irradiated with gamma-rays at absorbed dose rate of 8.8 kGy/h at RT. During irradiation, no bias was applied to electrodes. The shift of the breakdown voltage for the SiC SITs (squares), the Si MOSFETs (triangles) and the Si IGBT (upside-down triangles) as a function of absorbed dose is shown in Fig. 8. The blocking characteristics for the SiC SITs and the Si ones (IGBTs and MOSFETs) were measured under Vo at 10 V and 0V, respectively. No significant change in the breakdown voltage for the SiC SITs and the Si IGBT is observed up to 10' Gy. For the Si MOSFETs, the shift of the breakdown voltage increases with absorbed dose above 4×10° Gy, and the large shift of -500 V is observed at 10′ Gy. It was also reported [25] that no significant increase in the leakage current for the SiC SITs (of the order of 106 A) was observed where the leakage current for the Si MOSFETs increased to 10ª A level after irradiation 10º Gy.

Figure 7. Change in ΔV-for SiC SiC SiC (squares), SiC MESFETs (diamonds), C-coating+Dry SiC MOSFETs (triangles) and Ccoating+Pyro SiC MOSFETs (circles) as a function of absorbed dose. All transistors were irradiated with gamma-rays at RT. During gamma-ray irradiation, no bias was applied to any electrodes of the transistors. For comparison, the results reported for Si MOSFETs (upside-down triangles) are also plotted in the figure [9].

Figure 8. Shift of the breakdown voltage from the initial value for SiC SITs (squares), Si MOSFETs (triangles) and Si IGBT (upside-down triangles) as a function of absorbed dose. The blocking characteristics for SiC SITs and MOSFETs) were measured under Vg at 10 V and 0V, respectively.

The on-state characteristics were measured under *V*G at +2.5 V for the SiC SITs and at +15 V for the Si transistors (IGBTs and MOSFETs). Then, the on-voltage was defined as the value of *V*D at *I*D of 10 A. Figure 9 shows the shift of the on-voltage for the SiC SITs (squares), the Si MOSFETs (triangles) and the Si IGBT (upside-down triangles) as a function of absorbed +/!^z\$!z/\$%"0z+"z+\*w2+(0#!z"+.z0\$!z%z /z\* z0\$!z%z
/z 1!z0+z#))w.5z%.. %¥ ation shows a very stable behavior up to 107 Gy, whereas the on-voltage for the Si IGBTs remarkably increases after irradiation at 8×105 z5z c".+)z E^Fz 0+z)+.!z 0\$\*z ECzd^z 0z3/z .!¥ ported [29] that the displacement damage effect induced by Compton electrons degrades the gain for Si bipolar transistors. So, the result obtained from the Si IGBT is interpreted in terms +"z 0\$!z)&+.%05z..%!.z.!)+2(z%\*z 0\$!z .%"0z.!#%+\*z c(+3z +,%\*#z.!#%+\*dz 1!z 0+z 0\$!z %/,(!¥ ment damage effect. For the SiC SITs and the Si MOSFETs, since the doping concentration in the drift region is not low, the displacement damage effect might not be observed and as a result, on-voltage shows almost constant values up to 107 z5^z(0\$+1#\$z 0\$!z/0(!z+\*w2+(0¥ age behavior is obtained for the SiC MOSFETs, the large fluctuation of *V*<sup>T</sup> was reported due to the TID effect. Considering gamma-ray irradiation effects on the breakdown voltage, the on-voltage, and *V*T, the characteristics of only the SiC SITs show the stable behaviors up to 107 MGy. Thus, we can conclude that the SiC SITs have extremely high radiation resistance, they have an enough potential for electronic devices used in harsh radiation environments such as nuclear power plants, space, and so on.

4. Charge induced in SiC diodes by Ion irradiation

ous studies [35-40].

%\*!z !/0.10%2!z+.u\* z\*+\*w !/0.10%2!z)("1\*0%+\*/z((! z/z+1./z%\*z!(!0.+\*%z !2%¥ ces by charge (electron-hole pairs) generated by charged particle incidence, especially heavy %+\*/^z\$!z/z+\*z/!)%+\* 10+.z !2%!/z.!z+\*!z+"z0\$!z)+/0z)&+.z%//1!/z"+.z/,!z,,(%¥ tions. On the other hand, for high energy physics using accelerators with high luminosity, such as J-PARC and Super-LHC, Rad-hard particle detectors are expected to be developed. For the development of Rad-hard particle detectors as well as Rad-hard devices for space ,,(%0%+\*/\_z%0z%/z%),+.0\*0z0+z(.%"5z0\$!z!\$2%+.z+"z\$.#!z#!\*!.0! z%\*z !2%!/z5z\$.#¥ ed particle incidence. In a previous study [30f\_z2z!0z(^z.!,+.0! z0\$0z0\$!z\$.#!z+((!¥ tion Efficiency (CCE) obtained from 4H-SiC Schottky diodes by alpha particle incidence was estimated to be 100 %. It was also reported that 4H-SiC Schottky diodes could detect X-rays from radio isotopes [31,32]. Besides, the neutron detection by SiC diodes was investigated previously [33, 34]. As for light ions and X-rays irradiation into SiC, relatively large number of studies has been already reported. On the other hand, from the point of view of SEEs, study of ion irradiation on electronic devices using heavy ions is important. In this section, \$.#!z%\* 1! z%\*z%z %+ !/z5z\$!25z%+\*z%\*% !\*!z%/z.!2%!3! z+\*z0\$!z/%/z+"z+1.z,.!2%¥

Radiation Response of Silicon Carbide Diodes and Transistors

http://dx.doi.org/10.5772/51371

391

Figure 10. Schematic set-up of the TIBIC system installed at JAEA Takasaki and photo of the TIBIC system.

0\$!z !.!/!z%\*z+((!0! z\$.#!z 1.%\*#z -

 \*z +. !.z 0+z +0%\*z 0\$!z %\*"+.)0%+\*z +\*z \$.#!z %\* 1! z %\*z !(!0.+\*%z !2%!/\_z +\*z -

duced Charge (IBIC) measurements is thought to be one of the useful methods. However,

1.0!z !2(10%+\*z +"z \$.#!z%\* 1! z 5z%+\*z !)/\_z /%\*!z 0\$!z !2%!z \$.0!.%/0%/z .!z !¥ graded by radiation damage created in samples by ion incidence [41]. Therefore, single-ion hit Transient Ion Beam Induced Current (TIBIC) was developed at JAERI Takasaki in order to realize the evaluation of ion-induced current with minimizing the influence of damage

 z)!/1.!)!\*0/z/\$+1( z!z+\*/% !.! z"+.z0\$!z¥

!)z \*¥

Figure 9. Shift of the on-voltage from the initial value for SiC SITs (squares), Si MOSFETs (triangles) and Si IGBT (upsidedown triangles) as a function of absorbed dose.
