Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

This paper reviews the basic physical mechanisms of the interactions of ionizing radiation with MOS oxides, including charge generation, transport, trapping and detrapping, and interface trap formation. Device and circuit effects are also discussed briefly.

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Total ionizing dose effects in MOS oxides and devices

Electronic devices in space environments can contain numerous types of oxides and insulators. Ionizing radiation can induce significant charge buildup in these oxides and insulators leading to device degradation and failure. Electrons and protons in space can lead to radiation-induced total-dose effects. The two primary types of radiation-induced charge are oxide-trapped charge and interface-trap charge. These charges can cause large radiation-induced threshold voltage shifts and increases in leakage currents. Two alternate dielectrics that have been investigated for replacing silicon dioxide are hafnium oxides and reoxidized nitrided oxides (RNO). For advanced technologies, which may employ alternate dielectrics, radiation-induced voltage shifts in these insulators may be negligible. Radiation-induced charge buildup in parasitic field oxides and in SOI buried oxides can also lead to device degradation and failure. Indeed, for advanced commercial technologies, the total-dose hardness of ICs is normally dominated by radiation-induced charge buildup in either parasitic field oxides and/or SOI buried oxides. Heavy ions in space can also degrade the oxides in electronic devices through several different mechanisms including single-event gate rupture, reduction in device lifetime, and large voltage shifts in power MOSFETs.

Radiation Effects in MOS Oxides

We report electron spin resonance (ESR) measurements of E′‐center (a ‘‘trivalent silicon’’ center in SiO2) density as well as capacitance versus voltage (C‐V) measurements on γ‐irradiated metal/oxide/silicon (MOS) structures. We also report a considerable refinement of earlier ESR measurements of the dependence of radiation‐induced Pb ‐center (a ‘‘trivalent silicon’’ center at the Si/SiO2 interface) occupation as a function of the Fermi level at the Si/SiO2 interface. These measurements indicate that the Pb centers are neutral when the Fermi level is at mid‐gap. Since the Pb centers are largely responsible for the radiation‐induced interface states, one may take ΔVmg Cox/e (where ΔVmg is the ‘‘mid‐gap’’ C‐V shift, Cox is the oxide capacitance, and e is the electronic charge) as the density of holes trapped in the oxide. We find that radiation‐induced E′ density equals ΔVmg Cox/e in oxides grown in both stream and dry oxygen. Etch‐back experiments demonstrate that the E′ centers are concentrated very near the Si/SiO2 interface (as are the trapped holes). Furthermore, we have subjected irradiated oxide structures to a sequence of isochronal anneals and find that the E′ density and ΔVmg annealing characteristics are virtually identical. We conclude that the E′ centers are largely responsible for the deep hole traps in thermal SiO2 on silicon. This observation coupled with observations regarding the Pb center indicates that two intrinsic centers, both involving silicon atoms lacking one bond to an oxygen atom, are largely responsible for the two electrically significant aspects of radiation damage in MOS devices: charge buildup in the oxide and interface‐state creation at the Si/SiO2 interface.

Hole traps and trivalent silicon centers in metal/oxide/silicon devices

An empirical model of radiation-induced interface states at the SiO2/Si interface in SiO2 MOS capacitors is developed. The formulation explicitly addresses the time-dependent two stage nature of the buildup process, and it gives the mathematical dependencies of the experimentally observed buildup on time, field, temperature, and dose. The model is applied to both wet and dry grown oxides. The implications of the empirical model for microscopic mechanisms involved in the buildup are discussed. In particular, it is argued that the experimental observations can best be understood in terms of a positive ion (probably H+) release in the SiO2 bulk and the subsequent transport of the liberated ions to the SiO2/Si interface (for positive gate bias). The induced interface states result from an interaction of the ions at the interface.

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A Framework for Understanding Radiation-Induced Interface States in SiO2 MOS Structures

The interface‐state buildup in wet‐oxide MOS capacitors under positive bias was studied as a function of time following pulsed e‐beam irradiation. The buildup was found to be a two‐stage process. The first stage, which occurs during the time required for holes to transport to the SiO2/Si interface, determines the final or saturation value of interface states and was found to be field dependent and temperature independent. The second stage, which begins after the holes have reached the SiO2/Si interface and continues for several thousand seconds, determines the time scale for the buildup and was found to be both field and temperature dependent.

Two‐stage process for buildup of radiation‐induced interface states

Dependence of Interface-State Buildup on Hole Generation and Transport in Irradiated MOS Capacitors

Combined simulation and experimental analyses are performed to characterize the 4H-silicon carbide (SiC) lateral metal-oxide-semiconductor field-effect transistor (MOSFET). Using a quasi-two-dimensional depth dependent Coulomb mobility model for scattering due to interface and oxide charge, along with existing models for other scattering mechanisms, and an in-house drift diffusion device simulator tailored for SiC MOSFETs, we have extracted values for interface trap density of states for 4H-SiC MOSFETs. Characterization shows that the interface trapped charge in 4H-SiC MOSFETs is responsible for mobility degradation and reduction in mobile inversion charge, and therefore reduced current. Its effect on mobility degradation decreases at higher gate voltages due to increased screening. Our results show that at high gate voltages, surface roughness plays the major role in surface mobility degradation in 4H-SiC MOSFETs. Results indicate that due to high Coulomb scattering near the interface, current density is...

Numerical and experimental characterization of 4H-silicon carbide lateral metal-oxide-semiconductor field-effect transistor

Total dose and neutron-induced displacement damage effect studies are reported for n-channel, 2- mu m channel length, depletion mode junction-field-effect-transistors (JFETs) fabricated on 6H-silicon carbide. Very little effect was observed on device characteristics for total dose ionizing radiation for doses up to 100 Mrads(Si), but the devices were significantly degraded after a neutron fluence of 10/sup 16/ n/cm/sup 2/. A value of 4.5+or-0.5 carriers/cm/sup 3//neutrons/cm was obtained for the carrier removal rate from neutron irradiation. The results offer promise for SiC devices to be used in applications which combine high-temperature and radiation environments, where the use of Si and GaAs technologies is limited. >

Silicon carbide JFET radiation response

A detailed analysis of silicon-carbide (SiC) metal–oxide–semiconductor field-effect-transistor (MOSFET) physics is performed Measurements of current–voltage characteristics are taken A device simulator is developed based on the drift–diffusion equations The model accounts for incomplete ionization Comprehensive mobility and interface state models are developed for SiC MOSFETs The mobility model accounts explicitly for bulk transport, as well as for interface states, surface phonons and surface roughness Agreement between simulated and measured terminal characteristics is obtained The results provide values for interface state occupation as a function of energy and position along the surface Results giving values for surface mobility as a function of position along the channel indicate that interface states have an especially strong effect on SiC operation Our investigation indicates that substantial reduction of interface states can give rise to a fivefold increase in transconductance

J.M. McGarrity

Papers

Two‐stage process for buildup of radiation‐induced interface states

Dependence of Interface-State Buildup on Hole Generation and Transport in Irradiated MOS Capacitors

Numerical and experimental characterization of 4H-silicon carbide lateral metal-oxide-semiconductor field-effect transistor

Silicon carbide JFET radiation response

Physics-based numerical modeling and characterization of 6H-silicon-carbide metal–oxide–semiconductor field-effect transistors