Oxide Electric Field-Induced Degradation of SiC MOSFET for Heavy-Ion Irradiation

Round 1

Reviewer 1 Report

This work by Liang et al. studied the effect of gate bias for the safe operation of SiC MOSFETs devices in space environment applications and the long-term device operation reliability and stability under the different heavy ion irradiated conditions (Cl, Ga ions etc.). The study presents the experimental results along with the TCAD simulation data. I find this work is well performed and indeed is warranted for publication in journal Electronics. Except for minor grammar issues that authors should consider modifying, I think the current version is warranted for publication as it is.

I find that minor English language editing and grammar check may be required.

Author Response

Our deepest gratitude goes to you for your careful work. We are sorry for the many errors in the manuscript, we have checked and corrected the article carefully

Reviewer 2 Report

The paper by Liang et al. is devoted to the evaluation of silicon carbide channel field effect transistors under artificial radiation emulating that in space. As it is recognised in the paper, the performance of SiC-based MOSFETs and resistance of its gate oxide against radiation has been studied in sufficient detail in conventional environments, the damaging effect in the gate oxide by heavy ion bombardment has initiated studies on the reliability of such devices under space radiation.

The paper is written in clear language and the hypothesis raised in the introductory part of the paper have been confirmed in the end, in terms of the damaging effect of the radiation. The goals of the study seem to be achieved, the extent of the damage in the gate oxide was recorded and described.

However, there is an issue that strongly reduces the scientific value of the paper. Namely, the devices tested in this paper were commercial SiC MOSFETs (CGE1M120060). This hardly describes the construction of the research object for a reader. There are at least two parameters, which must be revealed before the acceptance – the material and thickness of the gate oxide.

Author Response

We are grateful for the suggestion. A more detailed description of the device structure used in the study has been added in the experimental part of the manuscript. The oxide thickness of the device is 50 nm, and the SiC epitaxial layer thickness is 10 μm. Other parameters of the device are not available, but relevant information is given in the simulation, which can be found in Table 2.

Parameter	Value
N-Epi Doping/Depth	1×1016cm-3, 10 μm
N+ Substrate	1×1019cm-3
Body Doping/Depth	2×1017cm-3, 1.5 μm
N+ Drain Doping	1019cm-3
Oxide Thickness	50 nm
Ion Track Radius/Length	50 nm, 15 μm

Reviewer 3 Report

This paper is an experimental work for radiation effect of SiC MOSFET against heavy ions. Experiments were performed with various heavy ions sources with reasonable results. The explanation by TCAD simulations is also convincing. It deserves to be published. However, I still have the following comments for the authors:

1. Could you please define all the abbreviations when they appear for the first time?

2. Please check the consistency of Figure numbers in the text.

3. In Figure 3, could you provide the RMS values or other related values for the leakage current to evaluate and compare the fluctuation of the current for various radiation scenarios?

4. For Figure 6, could you provide the breakdown voltage of the device after irradiation?

5. Do you have an estimation of the environment in space application, such as radiation flux and fluence? How was that compared to your experiment?

The English is fine. Minor revision is required. 

Author Response

1. Could you please define all the abbreviations when they appear for the first time?

Response: Thank you for your precious comments and advice. I apologize for our carelessness. We have defined all abbreviations that appear for the first time in the manuscript.

2. Please check the consistency of Figure numbers in the text.

Response: Our deepest gratitude goes to you for your careful work. Sorry for the error in the number of some figures in the manuscript, it has been corrected.

3. In Figure 3, could you provide the RMS values or other related values for the leakage current to evaluate and compare the fluctuation of the current for various radiation scenarios?

Response: Thank you for your precious comments and advice. The leakage current values of the unirradiated devices in the figure are used as a reference, but the coordinates may not have been chosen appropriately to be observed. To address this issue, Figure 3 has been modified, as shown below. As can be seen from the figure, the leakage current of the unirradiated device is about 10^-10A, but the leakage current of the irradiated device increases.

Figure3. Variation of SiC MOSFET leakage current during irradiation

4. For Figure 6, could you provide the breakdown voltage of the device after irradiation?

We are grateful for the suggestion. We have marked the breakdown voltage of the gate oxide layer of the irradiated device for each condition in the figure6, as shown below.

Figure6. Variation of oxide breakdown voltage after heavy ion irradiation with different LET and biases

5. Do you have an estimation of the environment in space application, such as radiation flux and fluence? How was that compared to your experiment?

Thank you for your precious comments and advice. The figure below shows the flux of LET particles measured at different orbits, and the case of LET > 100 is usually not considered. Our experiment is a ground-based accelerated evaluation test, so the configurations are usually the worst conditions. The LET=75 used in our experiment is the maximum LET currently evaluated in commercial VDMOS, and the MIL-STD 750 standard usually does not require an flux, but rather an fluence of 10⁷. The total injection used in our experiment is 10⁶, which already covers most of the conditions.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper presents the measurement results on irradiated SiC MOSFET devices. The irradiation was done using Cl, Ge, and Ta ions, and the drain-source current and gate-source current were investigated as a function of gate voltage and irradiation time for different ions, LETs, and measurement conditions. In addition, TCAD simulations were performed to understand the potential distribution inside the device. The authors concluded that the degradation of the oxide reliability is influenced by LET, VGS, and VDS, as well as the defects generated by the ion irradiation under an electric field. 

 

The quality of the paper needs to be improved, and some essential information is missing. 

 

• The color legends of Figure 8/9/10 and the text in the figures (e.g., LET=20MeV/(mg/cm2), etc.) are not readable. Dimensions of the plot should be given.
• In Figure 4(b), the difference between un-irradiated/irradiated devices is not visible. To see a difference, the figure must be zoomed in on the y-axis to a range from 1400 to 1500 V. 
• For the TCAD simulation, even though the parameters and their values have been listed in Table 2, it is essential to give the physics models used in these simulations and the corresponding boundary conditions. 
• In Table 1, the units of "Flux" and "Fluence" are missing.
• Line 83 to line 85 is an incomplete sentence that is not understandable. 
• Does Keithley 2410 provide V_DS and measure I_DSS, and does Keithley 2636 provide V_GS and measure I_GSS? If so, there is a conflict to drawing V_DS/V_GS/I_DSS/I_GSS as independent blocks in Figure 2. The figure then needs to be changed to a format that makes sense.
• The overall writing could be better, and the manuscript needs to be reformulated in language. 

 

 

The overall writing could be improved significantly, and the manuscript needs to be reformulated in language.

Author Response

(1)The color legends of Figure 8/9/10 and the text in the figures (e.g., LET=20MeV/(mg/cm2), etc.) are not readable. Dimensions of the plot should be given.

Response: We are grateful for the suggestion. Coordinates have been added to Figures 8/9/10, and the dimensions of the simulated structure can be seen in the figures. Also, the resolution of the figures has been improved, and the color legend is now readable. The text in the plot is a brief description of the simulation conditions and is not related to the simulation results.

 

(2)In Figure 4(b), the difference between un-irradiated/irradiated devices is not visible. To see a difference, the figure must be zoomed in on the y-axis to a range from 1400 to 1500 V.

 

Response: Thank you for your precious comments and advice. Figure 4 shows the test results of the key electrical parameters of the device before and after irradiation. The graph is intended to convey that the selected biases are in the SEE safe operating area of the device and that no degradation of the electrical parameters of the device occurs. Therefore, there is indeed no difference between irradiated and unirradiated devices. The changes caused by irradiation are mainly reflected in the reliability experiments later in the article.

(3)For the TCAD simulation, even though the parameters and their values have been listed in Table 2, it is essential to give the physics models used in these simulations and the corresponding boundary conditions.

Response: Thank you for your suggestion. Information about the models used in the simulation has been added to the manuscript, in part as follows: "The models used in the simulations include drift-diffusion model for transport, the Shockley Read Hall model for generation-recombination, Doping Dependence model and High Field Saturation model for mobility. "

 

(4)In Table 1, the units of "Flux" and "Fluence" are missing.

Response: Our deepest gratitude goes to you for your careful work. The units of "Flux" and "Fluence" have been added in the table1.

Ions	Energy MeV	LET in SiC MeV/(mg/cm2)	Depth in SiC μm	Flux ions/cm2/s	Fluence ions/cm2	Irradiation Bias
Cl	110	15.89	20.31	104	106	VGS= 0V，VDS= 60V
Ge	210	39.6	20.19			VGS= 0V，VDS= 60V
181Ta	2005.5	78.7	79.29			VGS= 0V，VDS= 60V
						VGS= 0V，VDS= 30V
						VGS=-3V，VDS= 30V
						VGS=-5V，VDS= 30V

 

(5) Line 83 to line 85 is an incomplete sentence that is not understandable.

Response: Thank you for your comments. I apologize for the inconvenience caused by our carelessness. We have rewritten the sentence as follows: " Only one device can be irradiated at a time with this system, and to ensure the accuracy of the experimental results, three devices were irradiated for each bias condition in Table 1. "

 

(6) Does Keithley 2410 provide V_DS and measure I_DSS, and does Keithley 2636 provide V_GS and measure I_GSS? If so, there is a conflict to drawing V_DS/V_GS/I_DSS/I_GSS as independent blocks in Figure 2. The figure then needs to be changed to a format that makes sense.

Response: Thank you for your precious comments and advice. Theoretically, the rated voltage of the device is up to 1200 V and the V_GS is up to 20 V. Therefore, if the devices are not damaged, the leakage currents are in the nA. Because the flux and fluence are the same for all devices, the irradiation time is the same. So we plot the variation of I_DS with irradiation time for all irradiation conditions in (A) to observe the difference of I_DS during irradiation. The variation of I_GS with irradiation time is plotted in (B) to observe the difference in I_GS.

 

(7) The overall writing could be better, and the manuscript needs to be reformulated in language.

Response: We are grateful for the suggestion. The manuscript has been supplemented with content and grammatical corrections, and the article has been polished.

Round 2

Reviewer 2 Report

The paper manuscript has been revised and improved after the revision. The object studied has been described in more detail, as long as could be disclosed.

Reviewer 4 Report

Dear authors,

Thank you for answering all questions in the previous report and polishing the language of the submitted manuscript. The readability and quality of the paper have been improved significantly compared to the first version of the submission. I do not have further questions.