J.M. McGarrity

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

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.

Enhanced Flatband Voltage Recovery in Hardened Thin MOS Capacitors

The short-term recovery of hardened pyrogenic SiO2 MOS capacitors exposed to pulsed electron-beam irradiation was studied as a function of oxide thickness between 200 and 1000 Å. Two sets of samples were studied: one set grown to a single thickness and then etched back to various thicknesses, and the other set grown for different lengths of time to varying thicknesses. In both cases, the recovery time was observed to vary approximately as the fourth power of oxide thickness. This anomalous superlinear dependence of recovery time on the SiO2 thickness agrees with the predictions of the stochastic model of hole transport based on a continuous-time random walk. Combining the highly field activated character of hole transport in SiO2 with the thickness dependence reported here demonstrates that very significant gains in the short-term recovery speed can be made by reducing the oxide thickness and/or increasing the oxide field.

Analysis of neutron damage in high-temperature silicon carbide JFETs

Neutron-induced displacement damage effects in n-channel, depletion-mode junction-field-effect transistors (JFETs) fabricated on 6H-silicon carbide are reported as a function of temperature from room temperature (RT) to 300/spl deg/C. The data are analyzed in terms of a refined model that folds in recently reported information on the two-level ionization energy structure of the nitrogen donors. A value of 5/spl plusmn/1 cm/sup -3/ per n/cm/sup 2/ is obtained for the deep-level defect introduction rate induced by the neutron irradiation. Due to partial ionization of the donor atoms at RT, the carrier removal rate is a function of temperature, varying from 3.5 cm/sup -1/ at RT to 4.75 cm/sup -1/ at 300/spl deg/C. The relative neutron effect on carrier mobility varies with temperature approximately as T/sup -7/2/, dropping by an order of magnitude at 300/spl deg/C compared with the RT effect. The results offer further support for the use of SiC devices in applications which combine high-temperature and severe radiation environments, where the use of Si and GaAs technologies is limited. >

Determining 4H silicon carbide electronic properties through combined use of device simulation and metal–semiconductor field-effect-transistor terminal characteristics

A two-dimensional numerical device simulator has been developed specially for the recessed gate 4H silicon carbide(4H-SiC) metal–semiconductor field-effect-transistor (MESFET). By combining numerical techniques, material physics, and measured device characteristics, we are able to use the simulator to extract more information about the new material 4H-SiC, including the mobility, velocity-field curves, and the Schottky barrier height. We have also enabled and used the new simulator to investigate breakdown voltage and thus predict operation limitations of the 4H-SiC device. Simulations indicate that impact ionization is relatively small in 4H-SiC, thereby leading to a very high breakdown voltage of 125 V in a 0.7 μm gate MESFET.

Radiation Effects in Commercial 1200 V 24 A Silicon Carbide Power MOSFETs

In 2011, after many years of research and development SiC power MOSFETs became available in the commercial marketplace. This paper presents the results of Co60 total ionizing dose (TID) effects for the new high power-high current 24 A SiC devices irradiated at room temperature and 125°C. These commercially available components remained operational after a radiation dose of more than 100 krad. However, gamma ray irradiation gave rise to changes in current-voltage and capacitance-voltage characteristics. Specifically, threshold voltage decreased, resulting in increased current drive. We also observed rises in interface state densities, as well as input, output and reverse transfer capacitances with increasing accumulated doses.

Modeling the temperature response of 4H silicon carbide junction field-effect transistors

The electrical characteristics of 4H-SiC depletion-mode junction field-effect transistors (JFETs) have been measured over an extended temperature range from 218 to 673 K. A basic model has been applied to predict I–V characteristics for SiC JFETs over this extended temperature range using the standard abrupt-junction long-channel JFET equations. The model employs a two-level donor ionization structure using ionization energies of 0.050 and 0.080 eV and assumes a two-step inverse power law dependence of mobility on temperature based on recently published Hall measurement data. The modeled I–V characteristics are in good agreement with the experimental data over the temperature range from 273 to 673 K. The deviations between the experimental data and the response model at the temperature extremes are attributed to increased substrate resistivity at 218 K and increased device leakage currents at 673 K.

Modeling the electrical characteristics of n‐channel 6H–SiC junction‐field‐effect transistors as a function of temperature

The electrical characteristics of buried‐gate, n‐channel junction‐field‐effect transistors (JFETs) fabricated in epitaxial layers grown on 6H–SiC wafers have been measured as a function of temperature, from 218 to 773 K (−55 to 500 °C). The data are in good agreement with predictions of a model that uses standard abrupt‐junction, long‐channel JFET device equations for which the carrier concentration is calculated based on a two‐level ionization structure for the nitrogen donor. An inverse power‐law dependence of carrier mobility on temperature is assumed based on recent measurements of Hall mobility in epitaxial films of comparable doping. The only free parameter of the model is the compensation density, which is chosen by fitting the calculated saturated drain current to the measured value at room temperature. There are some deviations between the calculated and measured I–V characteristics at both temperature extremes (218 and 773 K), which are attributed to increased substrate resistivity at 218 K and ...

Silicon carbide FETs for high temperature nuclear environments

SiC transistors can operate at very high temperatures and survive very high radiation doses. These characteristics make SiC potentially the ideal technology for nuclear power applications. In this paper we report, for the first time, on the active in-core irradiation of 6H-SiC depletion-mode junction field-effect transistors (IFETs) at 25/spl deg/ and 300/spl deg/C in a nuclear reactor operated at 200 kW. No significant degradation in the device characteristics was observed until the total neutron fluence exceeded 10/sup 15/ n/cm/sup 2/ for irradiation at 25/spl deg/C, and no significant changes were observed even at 5/spl times/10/sup 15/ n/cm/sup 2/ at 300/spl deg/C. The results of this experiment may also indicate exciting evidence for the anneal of neutron displacement damage for devices irradiated at 300/spl deg/C.

Single Event Effects in Si and SiC Power MOSFETs Due to Terrestrial Neutrons

Experimental investigation of neutron induced single event failures and the associated device cross sections as well as low altitude failure-in-time (FIT) curves in silicon (Si) and silicon carbide (SiC) power MOSFETs at room temperature are reported along with possible explanation of failure mechanisms in SiC devices. Neutrons are found to give rise to significantly fewer failures in SiC power MOSFETs compared to their Si equivalents; however, SiC power MOSFETs do exhibit catastrophic failures when exposed to neutrons that simulate the terrestrial spectrum.

A SiC JFET amplifier for operation in high temperature and high radiation environments

A SiC high temperature amplifier circuit has been developed using discrete SiC depletion mode transistors. The amplifier open loop gain decreases by only 4 dB over the temperature range of 298 to 573 K at 1 kHz. From radiation effects results on the discrete devices included in this paper it is expected that this amplifier could survive a severe radiation environment to a total dose of 100 Mrad and neutron fluence exceeding 1015 n/cm2. The radiation results also suggest that the amplifier will be less susceptible to radiation at high temperatures.