SiC Power Diodes Research Articles

Investigation of Two High-Temperature Bipolar Phenomena and Characteristics of 1.2-kV SiC Power Diodes for High-Temperature Applications

Investigation of Two High-Temperature Bipolar Phenomena and Characteristics of 1.2-kV SiC Power Diodes for High-Temperature Applications

Proton Irradiation‐Induced Displacement Damage in 650 V Si and SiC Power Diodes

A comparison of the displacement damage effects in Si and silicon carbide (4H‐SiC) commercial diodes due to 6 MeV proton irradiation is presented. The devices chosen for this study are rated at 650 V/8 A, making them technological alternatives of each other. It is found that Si diodes degrade ≈4.6 times faster than the SiC counterparts under forward biasing. In addition, the leakage current for the SiC diode in reverse mode decreases due to proton irradiation, whereas it increases for the Si diode under the same conditions. The difference in the behavior of both the diodes, as a result of the irradiation process, is discussed in terms of the induced deep‐level defects. The results show that SiC diodes are more resistant to displacement damage caused by proton irradiation than Si devices, with the same specifications.

Carrier removal rates in 4H–SiC power diodes – A predictive analytical model

An analytical model for predicting the proton and neutron radiation-induced carrier removal in silicon carbide (4H–SiC) diodes, is developed. It is primarily aimed towards a fast calculation of the carrier removal rates (ηe) and critical fluence (above which the diode drift layer is fully compensated), for a wide range of particle energies and diode ratings. The model utilizes the NIEL (non-ionizing energy loss) concept along with the actual carrier removal rate values for SiC available in the literature. A comparison to Si power devices is also made. The results from the predictive model suggest that diodes with a lower voltage rating can sustain a higher particle fluence and displacement damage before their drift layers are fully compensated. This provides radiation hardening guidelines for 4H–SiC power diodes at a device engineering level, which can help improve the reliability of circuits in harsh environment applications, such as space. The model is validated through TCAD simulations incorporating the proton-induced defects, as well as experimentally by irradiating SiC diodes with 2 MeV protons. The extracted compensation levels are in good agreement with those predicted by the analytical model, validating its potential in predicting carrier removal rate of SiC diodes for radiation prone environments.

Investigation of Electrically Active Defects in SiC Power Diodes Caused by Heavy Ion Irradiation

Deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) are used to investigate electrically active defects in commercial SiC Schottky power diodes after heavy-ion microbeam irradiation at different voltages. The DLTS and MCTS spectra of pristine samples are analysed and compared to devices showing or not signatures of Single Event Leakage Current (SELC) degradation. An additional peak labelled ‘C’ with an activation energy of 0.17 eV below the conduction band edge is observed in the DLTS spectra of a sample degraded with SELC.

Morphological and electrical properties of Nickel based Ohmic contacts formed by laser annealing process on n-type 4H-SiC

This work reports on the morphological and electrical properties of Ni-based back-side Ohmic contacts formed by laser annealing process for SiC power diodes. Nickel films, 100 nm thick, have been sputtered on the back-side of heavily doped 110 µm 4H-SiC thinned substrates after mechanical grinding. Then, to achieve Ohmic behavior, the metal films have been irradiated with an UV excimer laser with a wavelength of 310 nm, an energy density of 4.7 J/cm2 and pulse duration of 160 ns. The morphological and structural properties of the samples were analyzed by means of different techniques. Nanoscale electrical analyses by conductive Atomic Force Microscopy (C-AFM) allowed correlating the morphology of the annealed metal films with their local electrical properties. Ohmic behavior of the contacts fabricated by laser annealing have been investigated and compared with the standard Rapid Thermal Annealing (RTA) process. Finally, it was integrated in the fabrication of 650V SiC Schottky diodes.

(Invited) GaN, SiC Power Devices are Competing with Si Insulated Gate Bipolar Transistors

The high breakdown voltage, good thermal properties, and (in case of GaN) a higher field effect mobility compared to Si make the expected performance of GaN and SiC based power devices to be potentially vastly superior to that of the today leading power device technology - Si Insulated Gate Bipolar Power Transistors (Si IGBTs). After many year of development, commercial SiC power diodes and MOSFETs now outperform recent Si IGBTs and are poised to compete in the renewable energy and electrical vehicle markets. The recent generation of the hybrid SiC-Si IGBT modules combine the best features of both competing technologies.. These device hybrid modules handle powers up to 350 kW range at voltages well over 1 kV and have several times higher switching speed than the recent generations of Si IGBTs. SiC power technology is more mature than GaN power technology. However, the GaN enhancement mode High Electron Mobility Transistor (E-HEMT) on Si technology reached power ratings over 10 kW operating at 200 kHz with lower switching losses than Si MOSFETs and SiC MOSFETs. GaN devices already take about 20% of the RF power market with expectations of reaching 40% by 2025. Still, the existing device designs are not fully taking advantages of the superior materials properties of GaN. The lateral-vertical designs for a higher breakdown voltage; quantum well channel designs limiting high electron injection into the buffer layers; a low conducting passivation making the electric field distribution in the gate-to-drain spacing more uniform and therefore increasing the breakdown voltage, improving reliability, and increasing lifetime; perforated channel designs for decreasing the effect of the parasitic resistances and increasing the switching speeds are the innovative design features poised to improve the competitive edge of SiC and GaN technologies. For ultimate performance, the Si substrate in the GaN on Si technology should be replaced by SiC or even diamond, even though in a short run it would be hard for such technologies to be cost competitive. In a more distant feature, even diamond by itself might emerge as superior high power material. In a more near future, AlInN/AlN/GaN on Si technology could become a leading technology for high power applications.

Leakage Current Mechanisms in Reverse Biased High-Voltage 4H-SiC Power Diodes

Today’s commercial 4H-SiC power diodes contain an abundance of threading screw dislocations (TSDs) and threading edge dislocations (TEDs). It is not clear exactly how these crystal defects manifest on the performance and reliability of high-voltage power devices. In this paper, extensive current-voltage (I-V) and capacitance-voltage (C-V) measurements of 600V, 1200V and 1700V commercial SiC power diodes at temperatures ranging from 22ºC to 250ºC will be reported. Detailed analysis of leakage current mechanisms is performed and it is shown that space charge limited current (SCLC) is a significant contributor to diode leakage current especially at increased electric fields. The static I-V data will be correlated with defect delineation using in-situ hard X-rays and it is shown that TSDs get excited first under high field stress conditions.

Analysis of neutron-induced single-event burnout in SiC power MOSFETs

The triggering mechanism of single-event burnout (SEB) in SiC power MOSFETs was studied by white neutron irradiation experiments and device simulations. Electron–hole pairs generated along a recoil ion trajectory resulted in a highly localized SEB current. This dynamic current led to an increase in the electron density in the vicinity of the n−/n+ interface, which resulted in a shift in the peak electric field strength. Finally, a local short-circuit occurred between the drain and source electrodes by punch-through of the electric field in the n+ source diffusion region.A cross-sectional view of the SEB damage showed that melting of the SiC occurred and cracks were formed in the n− drift region due to the highly localized SEB current. This indicates that the maximum lattice temperature reached the sublimation temperature of SiC. The location of the simulated peak lattice temperature agreed closely with the position of the observed SEB damage. This demonstrated that the main mechanism triggering SEB in SiC power MOSFETs is not parasitic npn-transistor action, but a shift in the peak electric field and the punch-through in the n+ source diffusion region, similar to the case for SiC power diodes.

Characterization and modeling of laser-induced single-event burn-out in SiC power diodes

We present results of laser testing of radiation-induced single event burn-out (SEB) in two 600V Silicon Carbide Schottky power diodes using two-photon absorption at blue wavelength. Transient currents and destructive events are observed and analyzed. A simple physical model of the laser induced current in the tested devices is proposed to evaluate the impact of experimental parameters on the occurrence of an SEB.

A Simplified Model for SiC Power Diode Modules for Implementation in Spice Based Simulators

A simplified model for SiC Power diodes has been developed and implemented in Spice simulator in order to get the advantages of a modular and hierarchical structure that can be easily used for modeling of power semiconductor modules. The proposed approach is based on the lumped charge technique. One of the main targets for the proposed model is the implementation of a modeling structure starting from the evaluation and simplification of the semiconductor equations. The paper will show the implementation of the model along with an experimental evaluation of the proposed method.

Terrestrial Neutron-Induced Single-Event Burnout in SiC Power Diodes

Tolerance against single-event burnout (SEB) caused by terrestrial neutrons is one of the urgent issues in practical application of SiC power devices. This paper presents evaluation results of neutron-induced SEB in SiC power diodes and differences between SiC and Si devices from the SEB standpoint.

Physical Modeling of SiC Power Diodes with Empirical Approximation

This article presents the development of a model for SiC power diodes based on the physics of the semiconductor. The model is able to simulate the behavior of the dynamics of the charges in the N- region based on the stored charge inside the SiC power diode, depending on the working regime of the device (turn-on, on-state, and turn-off). The optimal individual calculation of the ambipolar diffusion length for every phase of commutation allows for solving the ambipolar diffusion equation (ADE) using a very simple approach. By means of this methodology development a set of differential equations that models the main physical phenomena associated with the semiconductor power device are obtained. The model is developed in Pspice with acceptable simulation times and without convergence problems during its implementation.

Carrier-Removal Comparison (n/p) and Functional Testing of Si and SiC Power Diodes

Commercial Si and 4H-SiC Schottky barrier power diodes were irradiated in the mixed neutron and gamma-ray radiation field of The Ohio State University research reactor (OSURR). The forward I-V characteristics were measured before and immediately after each successive irradiation, and the carrier-removal rates were compared, on the basis of NIEL, to a previous study, for which the same diode models were irradiated with a 203 MeV proton beam. In addition, a number of SiC Schottky barrier diodes were also irradiated in the OSURR and subsequently functionally tested in half-wave rectifier circuits, for which the voltage and current waveforms in the circuit were recorded. The results from the functional testing of these half-wave rectifier circuits were analyzed using results from I-V characterization, PSpice simulations, and an analytical formulation.

Fundamental physical limitations on the blocking voltage of SiC rectifier diodes

The problem of expedient limitations on the blocking voltage of SiC rectifier diodes is considered, with a full set of nonlinear physical phenomena responsible for the energy loss in semiconductor structures taken into account. The physical nature of the limitations on the blocking voltage is analyzed. It is shown that Auger recombination is the most important physical effect that restricts the blocking capability of high-voltage SiC diodes. It is demonstrated that the advisability of using a single diode or several in-series-connected diodes depends on the W/L ratio (W is the base width, and L is the ambipolar diffusion length) and temperature. A method that can be used to determine the optimal parameters of SiC power diode structures is suggested.

Sic Power Diodes Improvement by Fine Surface Polishing

AbstractSurface treatment is a key technological parameter in the microelectronics technology and especially for SiC devices since high temperatures must be used for implanted impurities annealing and crystal damage recovery. In this work we take profit of a novel fine polishing process developed by NOVASIC to improve the electrical characteristics of Boron and Aluminium implanted Schottky diodes, which are surface quality highly sensitive devices. The mentioned fine polishing process allows to remove a layer thickness of 100nm to 3000nm on the surface of a processed SiC wafer, reducing the surface roughness to RMS of 1Å. The impact of this process on the electrical properties of the samples shows a general improvement of characteristics reproducibility, reduction of leakage current and improvement of breakdown of Boron implanted diodes.

SiC power Schottky and PiN diodes

The present state of SiC power Schottky and PiN diodes are presented in this paper. The design, fabrication, and characterization of a 130 A Schottky diode, 4.9 kV Schottky diode, and an 8.6 kV 4H-SiC PiN diode, which are considered to be significant milestones in the development of high power SiC diodes, are described in detail. Design guidelines and practical issues for the realization of high-power SiC Schottky and PiN diodes are also presented. Experimental results on edge termination techniques applied to newly developed, extremely thick (e.g., 85 and 100 /spl mu/m) 4H-SiC epitaxial layers show promising results. Switching and high-temperature measurements prove that SiC power diodes offer extremely low loss alternatives to conventional technologies and show the promise of demonstrating efficient power circuits. At sufficiently high on-state current densities, the on-state voltage drop of Schottky and PiN diodes have been shown to be comparable to those offered by conventional technologies.

Electrical noise used as a tool for assessing the defectivity of SiC Schottky diodes

We report the observation of random telegraph signals (RTS) occurring in the forward regime of silicon carbide Schottky diodes. RTS noise is attributed to the modulation of the conductivity either by the trapping/detrapping of a single electron or by the switching of a bistable defect, in the neighbourhood of a localized current path. Noise measurement is therefore a convenient and non-destructive method for assessing the defectivity of SiC power diodes.

Note on charge conservation in the transient semiconductor equations

A modification of the continuity equations for electrons and holes in materials with deep donors or acceptors is presented. The modification is necessary in order to prevent violation of charge conservation in transient simulations. The influence of incomplete ionization of dopants on the transient characteristics of a SiC power diode is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>