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Radiation Hardness of 4H-SiC Devices and Circuits
KTH, School of Information and Communication Technology (ICT), Elektronics, Integrated devices and circuits.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Advances in space and nuclear technologies are limited by the capabilities of the conventional silicon (Si) electronics. Hence, there is a need to explore materials beyond Si with enhanced properties to operate in extreme environments. In this regards, silicon carbide (4H-SiC), a wide bandgap semiconductor, provides suitable solutions. In this thesis, radiation effects of 4H-SiC bipolar devices, circuits and dielectrics for SiC are investigated under various radiation types. We have demonstrated for the first time the radiation hardness of 4H-SiC logic circuits exposed to extremely high doses (332 Mrad) of gamma radiation and protons. Comparisons with previously available literature show that our 4H-SiC bipolar junction transistor (BJT) is 2 orders of magnitude more tolerant under gamma radiation to existing Si-technology. 4H-SiC devices and circuits irradiated with 3 MeV protons show about one order of magnitude higher tolerance in comparison to Si.

Numerical simulations of the device showed that the ionization is most influential in the degradation process by introducing interface states and oxide charges that lower the current gain. Due to the gain reduction of the BJT, the voltage reference of the logic circuit has been affected and this, in turn, degrades the voltage transfer characteristics of the OR-NOR gates.

One of the key advantages of 4H-SiC over other wide bandgap materials is the possibility to thermally grow silicon oxide (SiO2) and process device in line with advanced silicon technology. However, there are still questions about the reliability of SiC/SiO2 interface under high power, high temperature and radiation rich environments. In this regard, aluminium oxide (Al2O3), a chemically and thermally stable dielectric, has been investigated. It has been shown that the surface cleaning treatment prior to deposition of a dielectric layer together with the post dielectric annealing has a crucial effect on interface and oxide quality. We have demonstrated a new method to evaluate the interface between dielectric/4H-SiC utilizing an optical free carrier absorption technique to quantitative measure the charge carrier trapping dynamics. The radiation hardness of Al2O3/4H-SiC is demonstrated and the data suggests that Al2O3 is better choice of dielectric for devices in radiation rich applications.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 56
Series
TRITA-ICT ; 2017:04
Keyword [en]
Silicon carbide, radiation hardness, protons, gamma radiation, bipolar junction transistors, aluminium oxide, surface recombination.
National Category
Engineering and Technology
Research subject
Information and Communication Technology
Identifiers
URN: urn:nbn:se:kth:diva-199907ISBN: 978-91-7729-252-4 (print)OAI: oai:DiVA.org:kth-199907DiVA, id: diva2:1066193
Public defence
2017-02-17, Ka-Sal C (Sal Sven-Olof Öhrvik), KTH, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20170119

Available from: 2017-01-19 Created: 2017-01-17 Last updated: 2017-01-19Bibliographically approved
List of papers
1. Effects of 3-MeV Protons on 4H-SiC Bipolar Devices and Integrated OR-NOR Gates
Open this publication in new window or tab >>Effects of 3-MeV Protons on 4H-SiC Bipolar Devices and Integrated OR-NOR Gates
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2014 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 61, no 4, p. 1772-1776Article in journal (Refereed) Published
Abstract [en]

Radiation effects of 3-MeV protons on 4H-SiC bipolar devices and integrated OR-NOR gates have been investigated. The chips were irradiated from a fluence of 1 x 10(8) cm(-2) until 1 x 10(13) cm(-2). Up until a fluence of 1 x 10(11) cm-2, both the bipolar devices and the logic gates were found to be stable, but for higher fluence, they begin to degrade as a function of irradiation fluence. Using TCAD simulations, degradation of the transistor current gain has been found to be more dominated by surface states than bulk defects generated by the proton irradiation. Simulations of logic circuits using SPICE show that the gain degradation is the key contribution to the unstable performance of the circuits from the fluence of 1 x 10(12) cm(-2) and above.

Keyword
4H-SiC, bipolar integrated circuits, emitter couple logic (ECL), OR-NOR gates, proton radiation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-156460 (URN)10.1109/TNS.2014.2310293 (DOI)000343928100038 ()2-s2.0-84906780937 (Scopus ID)
Conference
European Conference on Radiation and its Effects on Components and Systems (RADECS), SEP 23-27, 2013, Oxford, ENGLAND
Funder
Swedish Foundation for Strategic Research
Note

QC 20141201

Available from: 2014-12-01 Created: 2014-11-28 Last updated: 2017-12-05Bibliographically approved
2. Total Dose Effects on 4H-SiC Bipolar Junction Transistors
Open this publication in new window or tab >>Total Dose Effects on 4H-SiC Bipolar Junction Transistors
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2017 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Material science Forum, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-199903 (URN)10.4028/www.scientific.net/MSF.897.579 (DOI)2-s2.0-85020007905 (Scopus ID)
Conference
European Conference on Silicon Carbide and Related Materials 2016 (ECSCRM-16)
Note

QC 20170201

Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2017-10-23Bibliographically approved
3. High Gamma Ray Tolerance for 4H-SiC Bipolar Circuits
Open this publication in new window or tab >>High Gamma Ray Tolerance for 4H-SiC Bipolar Circuits
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2016 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578Article in journal (Refereed) Published
Abstract [en]

A high gamma radiation hardness of 4H-SiC circuits is performed. The OR NOR circuits are based on emitter coupled logic (ECL), using integrated bipolar NPN transistors. Gain degradation in individual bipolar junction transistors (BJT) is minimal up to a dose of 38 Mrad (SiO2), but for the dose of 332 Mrad (SiO2) a degradation of 52% is observed. The SiC BJTs show higher radiation hardness than existing Si-technology and high stability under temperature stress. It is proposed that the oxide charge-dominated recombination is the key base current recombination mechanism contributing to gain degradation. An improvement in the gain is seen after annealing at 400 °C for 1800 s due to the possible annealing of some of the oxide defects contributing to the oxide charge.

Place, publisher, year, edition, pages
IEEE Press, 2016
Keyword
Ionization radiation, 4H-SiC, Bipolar Junction Transistors, Gamma rays, Logic Circuits
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-199901 (URN)10.1109/TNS.2016.2642899 (DOI)000396813400012 ()2-s2.0-85014561700 (Scopus ID)
Note

Qc 20170118

Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2017-06-09Bibliographically approved
4. 4H-silicon carbide-dielectric interface recombination analysis using free carrier absorption
Open this publication in new window or tab >>4H-silicon carbide-dielectric interface recombination analysis using free carrier absorption
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2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 10, article id 105309Article in journal (Refereed) Published
Abstract [en]

In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre-and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (tau(eff)) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to tau(eff) from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2 x 10(6) cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5 x 10(4) cm/s. Furthermore, the density of interface traps (D-it) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and D(it)s extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-164450 (URN)10.1063/1.4914521 (DOI)000351442900065 ()2-s2.0-84924859308 (Scopus ID)
Note

QC 20150423

Available from: 2015-04-23 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
5. Improved Interface and Electrical Properties of Atomic Layer Deposited Al2O3/4H-SiC
Open this publication in new window or tab >>Improved Interface and Electrical Properties of Atomic Layer Deposited Al2O3/4H-SiC
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(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-199905 (URN)
Note

QC 20170118

Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2017-01-23Bibliographically approved
6. Stoichiometry of the ALD-Al2O3/4H-SiC interface by synchrotron-based XPS
Open this publication in new window or tab >>Stoichiometry of the ALD-Al2O3/4H-SiC interface by synchrotron-based XPS
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2016 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 25, article id 255308Article in journal (Refereed) Published
Abstract [en]

The interface of Al2O3 with 4H-SiC is investigated with synchrotron-based high-resolution x-ray photoelectron spectroscopy to clarify the effect of post-dielectric deposition annealing processes (rapid thermal annealing (RTA) and furnace annealing (FA)) involved in device fabrication. Our results show that post-deposition annealing of Al2O3/4H-SiC up to 1100 degrees C forms a thin interfacial layer of SiO2 between Al2O3 and SiC, which possibly improves the dielectric properties of the system by reducing oxide charges and near-interface traps. Moreover, the formation of SiO2 at the interface gives additional band offset to the dielectric system. We have also observed that the RTA and FA processes have similar results at a high temperature of 1100 degrees C. Therefore, we propose that high-temperature post-oxide (Al2O3) deposition annealing of up to 1100 degrees C may be used in device processing, which can improve overall dielectric properties and consequently the device performance.

Keyword
4H-SiC, Al2O3, atomic layer deposition, annealing, interface, synchrotron radiation, XPS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-189801 (URN)10.1088/0022-3727/49/25/255308 (DOI)000378089600020 ()2-s2.0-84976394351 (Scopus ID)
Funder
Swedish Research Council, D0674701Swedish Foundation for Strategic Research
Note

QC 20160721

Available from: 2016-07-21 Created: 2016-07-15 Last updated: 2017-11-28Bibliographically approved
7. Interface analysis of p-type 4H-SiC/Al2O3 using synchrotron-based XPS
Open this publication in new window or tab >>Interface analysis of p-type 4H-SiC/Al2O3 using synchrotron-based XPS
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2016 (English)In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015, Trans Tech Publications Ltd , 2016, p. 693-696Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, the interface between Al2O3 and p-type 4H-SiC is evaluated using x-ray photoelectron spectroscopy (XPS) measurements. These studies are made on dielectricsemiconductor test structures with Al2O3 as dielectric with different pre- and post-deposition treatments. XPS measurements on the as-deposited samples with two different pre-surface cleaning methods have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60 s, a SiO2 interlayer is formed. The surface band bending was determined from Si 2p core level peak shifts measured using XPS. These results suggest that Al2O3 deposited on the p-type 4H-SiC have a net positive oxide charge which is complementary to that of Al2O3 on n-type 4H-SiC. From these shifts it was found that the asdeposited RCA cleaned sample had an oxide charge of 5.6×1013 cm-2, as compared to standard cleaned samples, having 4.6×1013 cm-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N2O, down to a value of 4×1013 cm-2.

Place, publisher, year, edition, pages
Trans Tech Publications Ltd, 2016
Keyword
Al2O3, Band bending, P-type 4H-SiC, X-ray photoelectron spectroscopy (XPS), Aluminum, Core levels, Deposition, Photoelectrons, Photons, Rapid thermal annealing, Silicon carbide, Silicon oxides, Surface cleaning, Bandbending, Core-level peaks, Interface analysis, Post deposition treatment, Rapid thermal annealing (RTA), Surface band bending, XPS measurements, X ray photoelectron spectroscopy
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-195522 (URN)10.4028/www.scientific.net/MSF.858.693 (DOI)2-s2.0-84971570052 (Scopus ID)9783035710427 (ISBN)
Conference
4 October 2015 through 9 October 2015
Note

QC 20161125

Available from: 2016-11-25 Created: 2016-11-03 Last updated: 2017-01-17Bibliographically approved
8. A comparison of free carrier absorption and capacitance voltage methods for interface trap measurements
Open this publication in new window or tab >>A comparison of free carrier absorption and capacitance voltage methods for interface trap measurements
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2013 (English)In: Silicon Carbide and Related Materials 2012, Trans Tech Publications Inc., 2013, Vol. 740-742, p. 465-468Conference paper, Published paper (Refereed)
Abstract [en]

This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing Al2O3 and SiO2 dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar+ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using Matlab to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (Dit) and a comparison was made. It is observed that SiO2 samples show a large rise of SRVs, from 0.5×104 cm/s for a reference sample to 8×104 cm/s for a fluence of 1×1012 cm-2, whereas Al2O3 samples show more stable SRV, changing from 3×104 cm/s for the un-irradiated reference sample to 6×104 cm/s for a fluence of 1×1012 cm-2. A very similar trend is observed for Dit values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2013
Series
Materials Science Forum, ISSN 0255-5476 ; 740-742
Keyword
4H-SiC, FCA, High-k dielectrics, Interface trap density, Radiation hardness, SRV
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-127228 (URN)10.4028/www.scientific.net/MSF.740-742.465 (DOI)000319785500109 ()2-s2.0-84874098513 (Scopus ID)978-303785624-6 (ISBN)
Conference
9th European Conference on Silicon Carbide and Related Materials, ECSCRM 2012; St. Petersburg; Russian Federation; 2 September 2012 through 6 September 2012
Note

QC 20130829

Available from: 2013-08-29 Created: 2013-08-28 Last updated: 2017-01-17Bibliographically approved

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Citation style
  • apa
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