Sethu Saveda Suvanam

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… Mehr anzeigen

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 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. Weniger anzeigen

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 °C forms a thin interfacial layer of SiO2 between Al2O3 and SiC, which possibly improves the dielectric properties of the system by… Mehr anzeigen

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 °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 °C. Therefore, we propose that high-temperature post-oxide (Al2O3) deposition annealing of up to 1100 °C may be used in device processing, which can improve overall dielectric properties and consequently the device performance. Weniger anzeigen

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 dielectric-semiconductor 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 have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60s… Mehr anzeigen

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 dielectric-semiconductor 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 have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60s, 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 n-type 4H-SiC. From these shifts it was found that the as-deposited RCA cleaned sample had an oxide charge of 5.6×1013 q/cm-2, as compared to standard cleaned samples, having 4.6×1013 q/cm-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N2O, down to a value of 4×1013 q/cm-2. Weniger anzeigen

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 of all the samples were measured by an optical pump-probe… Mehr anzeigen

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 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 effective lifetime 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 2 000 000 cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 35 ?000 cm/s. Furthermore, the density of interface traps (Dit) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and Dits 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. Weniger anzeigen

In this paper, the effect of carbon (C), silicon (Si) and nitrogen (N) implantation on the interface properties of 4H-SiC/SiO2 and the implications for 4H-SiC bipolar junction transistors (BJT) passivation are discussed. 4H-SiC epi-layer have been implanted with 12C, 14N and 28Si ion at three different doses with energies of 3, 3.5 and 6 keV, respectively, resulting in a projected range of 8 nm for the three ions. Then metal oxide semiconductor (MOS) structures with SiO2 as dielectric have been… Mehr anzeigen

In this paper, the effect of carbon (C), silicon (Si) and nitrogen (N) implantation on the interface properties of 4H-SiC/SiO2 and the implications for 4H-SiC bipolar junction transistors (BJT) passivation are discussed. 4H-SiC epi-layer have been implanted with 12C, 14N and 28Si ion at three different doses with energies of 3, 3.5 and 6 keV, respectively, resulting in a projected range of 8 nm for the three ions. Then metal oxide semiconductor (MOS) structures with SiO2 as dielectric have been fabricated. Capacitance voltage measurements show an increase in the negative fixed charges for all the implanted samples as a function of implantation induced damage. Similarly, in the case of C and Si, the surface roughness increases as a function of dose and the mass of the ions. No reduction of Dits due to the implantations is seen for any of the ions. Furthermore, TCAD device simulations of npn bipolar junction transistors (BJT), using the interface and fixed charges extracted from CV measurements, show a way to further optimize current gain and breakdown properties for the BJT. Weniger anzeigen

Radiation effects of 3-MeV protons on 4H-SiC bipolar devices and integratedOR-NOR gates have been investigated. The chips were irradiated from a fluenceof 1X10^8 cm-2 until 1X10^13 cm-2 . Up until a fluence of 1X10^11 cm-2 , both the bipolar devices and the logic gates were found to bestable, but for higher fluence, they begin to degrade as a function of irradiationfluence. Using TCAD simulations, degradation of the transistor current gainhas been found to be more dominated by surface states… Mehr anzeigen

Radiation effects of 3-MeV protons on 4H-SiC bipolar devices and integratedOR-NOR gates have been investigated. The chips were irradiated from a fluenceof 1X10^8 cm-2 until 1X10^13 cm-2 . Up until a fluence of 1X10^11 cm-2 , both the bipolar devices and the logic gates were found to bestable, but for higher fluence, they begin to degrade as a function of irradiationfluence. Using TCAD simulations, degradation of the transistor current gainhas been found to be more dominated by surface states than bulk defects generatedby the proton irradiation. Simulations of logic circuits using SPICE showthat the gain degradation is the key contribution to the unstable performanceof the circuits from the fluence of 1X10^12 cm-2 and above. Weniger anzeigen

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… Mehr anzeigen

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. Weniger anzeigen