SiC Schottky Diodes Research Articles

Epitaxial graphene/SiC Schottky ultraviolet photodiode with orders of magnitude adjustability in responsivity and response speed

A simple optical-electronic device that possesses widescale adjustability in its performance is specially required for realizing multifunctional applications as in optical communication and weak signal detectors. Here, we demonstrate an epitaxial graphene (EG)/n-type SiC Schottky ultraviolet (UV) photodiode with extremely widescale adjustability in its responsivity and response speed. It is found that the response speed of the device can be modulated over seven orders of magnitude from tens of nanoseconds to milliseconds by changing its working bias from 0 to −5 V, while its responsivity can be varied by three orders of magnitude. A 2.18 A/W responsivity is observed at −5 V when a 325 nm laser is irradiated on, corresponding to an external quantum efficiency over 800% ascribed to the trap induced internal gain mechanism. These performances of the EG/SiC Schottky photodiode are far superior to those based on traditional metal/SiC and indicate that the EG/n-type SiC Schottky diode is a good candidate for application in UV photodetection.

Comparison of SiC Voltage Source Inverters Using Synchronous Rectification and Freewheeling Diode

For power converters with inductive loads, a freewheeling path is needed for the current due to reactive power. The MOSFET synchronous rectification (SR) is widely used to reduce the conduction loss during the freewheeling period. Due to the wide band gap of silicon carbide (SiC), the intrinsic body diode of SiC MOSFET exhibits a high voltage drop. Hence, an antiparallel SiC Schottky diode is normally implemented to eliminate its conduction. However, the external SiC Schottky diode is not fully utilized as it only works during the dead time. In this paper, the hard-switching SR is investigated in an SiC three-phase inverter and compared with a conventional inverter using freewheeling diode (FWD). An improved power loss model for the two inverters has been developed. It is found that the inverter using SR has higher efficiency due to the smaller switching loss. A 7-kW prototype of SiC three-phase inverter is built, which achieves a peak efficiency of 98.8% ( $\pm$ 0.15%) and 98.5% ( $\pm$ 0.15%) at 40 kHz using SR and FWD, respectively. This paper confirms that the SiC MOSFET is an ideal candidate for the SR.

Диоды Шоттки графит/p-SiC, полученные методом переноса нарисованной пленки графита на SiC

AbstractGraphite/ p -SiC Schottky diodes are fabricated using the recently suggested technique of transferring drawn graphite films onto p -SiC single-crystal substrates. The current–voltage and capacitance–voltage characteristics are measured at different temperatures and at different frequencies of a small-signal AC signal, respectively. The temperature dependences of the potential-barrier height and of the series resistance of the graphite/ p -SiC junctions are measured and analyzed. The dominant mechanisms of the charge–carrier transport through the diodes are determined. It is shown that the dominant mechanisms of the transport of charge carriers through the graphite/ p -Si Schottky diodes at a forward bias are multi-step tunneling recombination and tunneling described by the Newman formula (at high bias voltages). At reverse biases, the dominant mechanisms of charge transport are the Frenkel–Poole emission and tunneling. It is shown that the graphite/ p -SiC Schottky diodes can be used as detectors of ultraviolet radiation since they have the open-circuit voltage V _oc = 1.84 V and the short-circuit current density I _sc = 2.9 mA/cm^2 under illumination from a DRL 250-3 mercury–quartz lamp located 3 cm from the sample.

Phase‐shift full bridge power supply based on SiC devices

In order to accurately obtain the switching characteristics of SiC MOSFET in practical application, a dual pulse test circuit is used to test the SiC MOSFET in this subject. By analysing the double pulse test circuit and taking into account the parasitic parameters, the effects of different gate resistances ( R g ) and the capacitance between gate and source ( C gs ) on the switching characteristics of the SiC MOSFET are summarised. Also, a phase-shifted full-bridge power supply based on SiC device is designed, which can be changed from 270 V direct current (DC) to 220 V alternating current (AC)/50 Hz, which consists of two stages. The first stage is the phase shifted full bridge ZVS DC/DC converter, which will boost the 270 V DC to the 350 V DC; the latter is a single-phase full bridge inverter, and the 350 V DC will be converted to the 220 V AC/50 Hz. The power supply uses the SiC MOSFET as the switch tube, which can reduce the switching loss, improve the switching frequency and reduce the volume of the transformer. A rectifier circuit using a SiC Schottky diode, with almost no reverse recovery process, greatly reduced the transformer side parasitic oscillation and improved the efficiency of the power supply. In this study, the design method of the parameters of the power supply is described in detail. Finally, the rationality of the design of the power supply parameters is verified by MATLAB/Simulink simulation and experimental prototypes.

A fast-neutron detection detector based on fission material and large sensitive 4H silicon carbide Schottky diode detector.

Silicon carbide radiation detectors are attractive in the measurement of the total numbers of pulsed fast neutrons emitted from nuclear fusion and fission devices because of high neutron-gamma discrimination and good radiation resistance. A fast-neutron detection system was developed based on a large-area 4H-SiC Schottky diode detector and a 235U fission target. Excellent pulse-height spectra of fission fragments induced by mono-energy deuterium-tritium (D-T) fusion neutrons and continuous energy fission neutrons were obtained. The detector is proven to be a good candidate for pulsed fast neutron detection in a complex radiation field.

A V2O5/4H-SiC Schottky diode-based PTAT sensor operating in a wide range of bias currents

A proportional to absolute temperature sensor (PTAT) based on V2O5/4H-SiC (vanadium pentoxide/4H polytype of silicon carbide) Schottky diodes is presented. The linear dependence on temperature of the voltage difference appearing at the terminals of two constant-current forward-biased diodes has been used for thermal sensing in the wide temperature range from T=147K to 400K which extends down the state-of-the art of more than 80K. The proposed sensor shows a sensitivity of 307μV/K, a good reproducibility and a stable linear output also in case of deviation of the two bias currents from the best operating condition.

Silicon carbide of Ni/6H-SiC and Ti/4H-SiC type Schottky diode current-voltage characteristics modelling

On the base of the physical analytical models based on Poisson’s equation, drift–diffusion and continuity equations the forward current–voltage characteristics of 6H-SiC and 4H-SiC type Schottky diode with Ni and Ti Schottky contact have been simulated. It is shown on the base of analysis of current–voltage characteristics in terms of classical thermionic emission theory it is shown that the proposed simulation model of Schottky diode corresponds to the almost “ideal” diode with ideality factor n equals 1.1. Because of this it is determined that the effective Schottky barrier height φB equals 1.57 eV and 1.17 eV for Ni/6H and Ti/4H silicon carbide Schottky diode type, respectively.

Evaluation of SiC Schottky Diodes Using Pressure Contacts

The thermomechanical reliability of SiC power devices and modules is increasingly becoming of interest especially for high-power applications, where power cycling performance is critical. Press-pack assemblies are a trusted and reliable packaging solution that has traditionally been used for high-power thyristor-based applications in FACTS/HVDC, although press-pack IGBTs have become commercially available more recently. These press-pack IGBTs require antiparallel PiN diodes for enabling reverse conduction capability. In these high-power applications, paralleling chips for high current conduction capability is a requirement, hence, electrothermal stability during current sharing is critical. SiC Schottky diodes not only exhibit the advantages of wide bandgap technology compared to silicon PiN diodes, but they have significantly lower zero temperature coefficient (ZTC), meaning they are more electrothermally stable. The lower ZTC is due to the unipolar nature of SiC Schottky diodes as opposed to the bipolar nature of PiN diodes. This paper investigates the implementation and reliability of SiC Schottky diodes in press-pack assemblies. The impact of pressure loss on the electrothermal stability of parallel devices is investigated.

Radiation resistance of 4H-SiC Schottky diodes under irradiation with 0.9-MeV electrons

Degradation of the parameters of 4H-SiC Schottky diodes after irradiation with 0.9-MeV electrons is studied. A charge-carrier removal rate of 0.07–0.09 cm–1 is determined. The Schottky diodes under investigation are shown to retain rectifying current-voltage characteristics up to doses of ~1017 cm–2. The radiation resistance of SiC Schottky diodes is found to be much greater than that of Si p–i–n-diodes with the same breakdown voltage.

Innovative conception of SiC MOSFET-Schottky 3D power inverter module with double side cooling and stacking using silver sintering

In this paper, authors developed an innovative packaging for a power inverter SiC MOSFET-Schottky. The design, composed by 6 SiC-MOSFET and 6 SiC-Schottky diodes, places dice between 2 direct-bonding-copper substrates, it was optimized to equilibrate thermal repartition on the two DBC surfaces. We purpose to increase thermal dissipation of power modules by the use of two water-cooling blocks disposed on top and on the bottom of our power inverter; it permits to use both sides of power module to dissipate heat flux. According to Finite Element Method simulations performed with ANSYS®, double side cooling permits to enhance by up to two times thermal dissipation. Moreover solders are replaced by silver sintering and wire-bonds are suppressed by top substrate connections. We want to highlight that those improvements participates to increase reliability of power modules.

SiC power devices packaging with a short-circuit failure mode capability

The failure mode of press-pack-type packages dedicated to SiC devices is experimentally analyzed in order to investigate their use for HVDC applications. Single SiC Schottky diode samples have been submitted to short-circuit conditions and continuous current flow test. The samples have been then characterized with optical and scanning electronic microscopy. Results from the experiments reveal that the press-pack structure offers a short-circuit failure mode with SiC devices, as it does for Si devices. The metallurgy involved is, however, quite different. Cu, Ni, Ag or Al foils are found to be suitable interface material between the package and the die to achieve a stable a short-circuit failure mode, providing the die is properly attached to a substrate.

Product Development of High Power Electronics for High Reliability Applications

Abstract: The goal of this study was to achieve an improvement on power conversion based on SiC High Power Electronic devices at high temperature (+220°C). Two different devices (a SiC Schottky Diode & a Schottky Diode Bridge Rectifier) were studied using different substrates, die attach materials and die. Positive results were achieved; it was found a strong relationship between wire bond strength and die attach material; it was evident the two different die chosen for the study resulted in different electrical performance on the devices; and that, from the arrays of tests, there was no evident data to prefer one of the two substrates chosen for the study.

Design and Comparison of a 10-kW Interleaved Boost Converter for PV Application Using Si and SiC Devices

Grid-connected photovoltaic (PV) inverters have a dc/dc converter connected to the PV for executing the maximum power point tracking. The design of an interleaved boost converter (IBC) with three switching legs for a 10-kW PV inverter is presented in this paper. This paper shows how the use of silicon carbide (SiC) switches and powdered iron core inductors enables the operation of the converter at a higher switching frequency and when increasing the converter power density. The IBC is designed using a 1.2-kV SiC MOSFET and Schottky diodes and Kool Mμ powdered iron inductors. The design is compared with an IBC built with a silicon (Si) IGBT, fast recovery Si diodes, and ferrite cores. The use of SiC devices reduces the switching loses drastically and there are no reverse recovery losses, resulting in improved efficiency. The higher frequency and higher saturation flux density of the powdered iron core enable the reduction in core size by three times. A 10-kW prototype is built and tested for both the Si and SiC designs and compared with theoretical estimations.

A Multiphysics Modeling and Experimental Analysis of Pressure Contacts in Power Electronics Applications

This paper details a modeling and experimental assessment of the packaging process for a silicon carbide Schottky diode using pressure contacts. The work detailed in this paper is original, as it applies a combined electrothermomechanical modeling analysis to this packaging method supported by experimental validation. A key design objective for this packaging process is to identify suitable contact pad materials, heatsinks, and process variables such as clamping force to meet electrical, thermal, and reliability specifications. Molybdenum and aluminum graphite (ALG) have been identified as two suitable materials for the contact pads. Clamping forces ranging from 300 to 500 N and electric current ranging from 10 to 30 A have been investigated in terms of the resulting electrical and thermal contact resistances, temperatures, and stresses induced across the package. The performance of two heatsink designs with heat dissipation rates of 12 893 and 4991 W/ $\text{m}^{2}\text{k}$ has also been investigated. Both the modeling and initial experimental results detailed in this paper show that ALG provides better performance in terms of generating a lower average chip temperature. Both temperature and stress in the diode are predicted as a function of clamping force and load current. This will aid the packaging engineer to identify suitable process parameters to meet junction temperature requirements at different applied load currents.

SiC Schottky Diode Rectifier Bridge Represented as Diffusion-Welded Stack

We considered the prototype of a SiC Schottky diode Rectifier Bridge made on the basis of commercial SiC Schottky diodes by diffusion welding (DW). Vertical integration for four diode chips in combination with molybdenum electrodes can improve the overall weight and dimensions of the module performance and increase device durability to radiation exposure. Our DW prototype, in contrast to commercial bridges, completely preserved the initial characteristics after irradiation by electrons with an energy of 0.9 MeV and density of 3 x 1016 cm-2

Degradation of 600-V 4H-SiC Schottky Diodes under Irradiation with 0.9 MeV Electrons

In this paper investigation of degradation 4H SiC Schottky diodes parameters after irradiation by electrons with an energy of 0.9 MeV was doine. It was determined the carrier removal rate (Vd), which amounted to 0.07 - 0.09 cm-1. It is shown that the investigated Schottky diodes retained rectifying current-voltage characteristics of up to doses ~ 1017 cm-2. It is concluded that the radiation resistance of SiC Schottky diodes is much greater than the radiation resistance of Si p-i-n diodes with the same breakdown voltages

Design of Active Contact Area, Reduced Leakage Current 4H–SiC Schottky Diodes Using Epi-Regrowth

Design of Active Contact Area, Reduced Leakage Current 4H–SiC Schottky Diodes Using Epi-Regrowth

SiC Detector for Sub-MeV Alpha Spectrometry

4H-SiC silicon carbide (SiC) Schottky diodes, with a 25 μm thick n-type epitaxial active layer and a very thin front electrode contact are studied and proposed for the detection of low energetic ions. For a first evaluation of the detection properties of the SiC detectors, a standard alpha emitting radiation source was used obtaining an energy resolution of 0.85% at 5.15 MeV energy. Then the devices were employed to monitor low energetic alpha particles. From these tests it was found that the 4H-SiC diodes are able to monitor the alpha particles backscattered by different single and multilayers metallic targets (Au, Ag, Cu on Si substrates) in the energy range between 300 keV and 600 keV. In this energy range a linear energy response and a good energy resolution, close to those of a traditional commercial silicon detector, were obtained. The possibility to use these detectors for material analysis and for plasma monitoring is also discussed.

Investigations of mutual thermal coupling between SiC Schottky diodes situated in the common case

PurposeThis paper aims to present the results of measurements and calculations illustrating mutual thermal coupling between power Schottky diodes made of silicon carbide situated in the common case.Design/methodology/approachThe idea of measurements of mutual transient thermal impedances of the investigated device is described.FindingsThe results of measurements of mutual transient thermal impedances between the considered diodes are shown. The experimentally verified results of calculations of the internal temperature waveforms of the considered diodes obtained with mutual thermal coupling taken into account are presented and discussed. The influence of mutual thermal coupling and a self-heating phenomenon on the internal temperature of the considered diodes is pointed out.Research limitations/implicationsThe presented methods of measurements and calculations can be used for constructing the investigated diodes made of other semiconductor materials.Originality/valueThe presented results prove that mutual thermal coupling between diodes mounted in the common case must be taken into account to calculate correctly the waveforms of the device internal temperature.

Forward current-voltage characteristics simulation of 4H-SiC silicon carbide Schottky diode for power electronics

Forward current-voltage characteristics of 4H-SiC Schottky diode with Ni Schottky contact have been simulated based on in the physical analytical models based on Poisson’s equation, drift-diffusion and continuity equations. On the base of analysis of current-voltage characteristics in terms of classical thermionic emission theory it is established that the proposed simulation model of Schottky diode corresponds to the “ideal” diode with average ideality factor n»1.1 at low temperature ~300 K. It is determined that effective Schottky barrier height equals 1.1 eV for Ni/4H-SiC Schottky diode.