Silicon Carbide Schottky Research Articles

Experimental Demonstration of 1200V SiC-SBDs with Lower Forward Voltage Drop at High Temperature

The 1200V class silicon carbide Schottky barrier diodes were designed and fabricated. The drift layer resistance was reduced in order to realize low forward voltage drops. Since the low drift layer resistance led to the low breakdown voltage, the avalanche withstanding capability should be enhanced not to cause the destructive breakdown. By means of the optimized device design, we succeeded to realize the low forward voltage drop while maintaining the high avalanche withstanding capability. The forward voltage drops at 200A/cm2 were 1.35V at 25°C and 1.63V at 175°C, respectively. The avalanche withstanding capability was more than 3500mJ/cm2 at 25°C. By substituting SiC-SBDs for Si-pin diodes, the estimated total power loss of the module comprised by Si-IGBTs and the diodes was reduced by 35%. We could also confirm that no failures happened after long term reliability tests.

Evaluation of Correct Value of Richardson's Constant by Analyzing the Electrical Behavior of Three Different Diodes at Different Temperatures

Various attempts have been made to evaluate the correct value (A*=146 A/cm2.K2) ofRichardson's constant. In 2005 S. Ferrero et al. published their research in which they performedan analysis of electrical characterizations of twenty Ti/4H-SiC(titanium on silicon carbide) Schottkydiodes with the help of thermionic emission theory and evaluated the value of Richardson's constantto be 17±8 A/cm2.K2; which is very low as compared to the theoretical value of 146 A/cm2.K2.Wehave tried in this paper to evaluate the Richardson's constant's value by nearly same experimental tech-niques followed by S. Ferrero et al. and additionally, have applied Tung's theoretical approach whichdeals with the incorrect value of A* in the perspective of Schottky barrier inhomogeneities caused bythe presence of nanometer size low barrier patches present in the uniform high barrier of the Schottkydiode.We have fabricated two Ti/4H-SiC (titanium on silicon carbide) Schottky diodes with differentareas and oneMo/4H-SiC (molybdenumon silicon carbide) Schottky diode. In this paper we have pre-sented a comparative analysis of forward current-voltage characteristics of all three Schottky diodes.In all three cases we were successful in the evaluation of nearly correct value of Richardson's constant.This work emphasizes the effects of differentmetal-SiC combinations and laboratory environments onthe evaluation of Richardson's constant and the effective area involved in the current transport. As pre-dicted by Tung's model the effective area is seen to be substantially different from the geometric areaof the Schottky diode. Evaluated values of A*, with an error of ±2, come out to be 145.39, 148.33and 148.33 A/cm2.K2for Ti/4H-SiC(large area), Mo/4H-SiC and Ti/4H-SiC(small area) Schottkydiodes, respectively.

Barrier Inhomogeneities of a Medium Size Mo/4H-SiC Schottky Diode

Forward current-voltage characteristics of a medium sized (3.05mm2)Mo/4H-SiC (molyb-denum on silicon carbide) Schottky diode|fabricated for high power applications | are analysedwithin a temperature range of 125-450 K. Accurate theoretical modeling is carried out using Tung'smodel in which it is considered that numerous low barrier nanometer size patches, present in uniformhigh barrier, are responsible for the inhomogeneities in the Schottky barrier of SiC-based electronicdevices. A significant difference is observed between the effective area involved in the current trans-port and the geometric area of the Schottky contact along with a dependence of the ideality factor andhe barrier height on temperature. The obtained values of uniform Schottky barrier and Richardson'sconstant are seen to be in accordance with previous works. It is concluded that the above mentionedmodel can be used to describe the electrical behaviour of Mo/4H-SiC Schottky diodes.

Stability and performance analysis of a SiC-based cascode switch and an alternative solution

Wide band-gap semiconductors are most attractive as materials for power devices due to low losses, improved temperature capability and high thermal conductivity. Although silicon carbide Schottky diodes have been commercially available on the market for years, an active wide band-gap switch is still missing. Probably the best performance of upcoming devices is gained with normally-on concepts such as silicon-carbide JFETs and gallium-nitride HEMTs. However, the vast majority of power electronic topologies rely on normally-off switches. An alternative approach is the use of the cascode concept which combines a normally-on wide band-gap device with high blocking capability and a low-voltage normally-off silicon MOSFET. In this work, the performance and stability of such an arrangement is analyzed and an alternative solution is proposed.

SiC ショットキーバリアダイオードの特性と電力損失低減効果の確認

SiC ショットキーバリアダイオードの特性と電力損失低減効果の確認

Comparative investigation of SiC and Si power electronic devices operating at high switching frequency

Comparative investigation of SiC and Si power electronic devices operating at high switching frequencyThe paper presents results of measurements of the reverse recovery current and dynamic forward voltage of the silicon carbide (SiC) Schottky diodes operating at a 500 A/μs current slope. These data were compared with the corresponding parameters determined for ultrafast silicon (Si) diodes. Results of power losses measurement in SiC Schottky diodes operating at switching frequency range of (10-200) kHz are presented and compared with corresponding data of ultrafast Si diodes. Also, results of power losses measurements in transistors of dc voltage switch are shown. Investigations were conducted with a SiC and the ultrafast Si freewheeling diode at the transistor switching frequency of 100 kHz. The results of measuring power losses dissipated in the dc converter with a SiC Schottky diode and the ultrafast silicon diode are also presented.

High temperature long term stability of SiC Schottky diodes

Reliability of Silicon Carbide (SiC) power devices is still an open problem, preventing a wider application of such a promising technology. Moreover, specific reliability assessment procedures must be developed for SiC devices, as they are designed to work at temperatures well beyond those of standard Silicon devices. A detailed investigation about the reliability of 600V, 6A Silicon Carbide Schottky diodes is accomplished along this paper. It is based on an extensive set of high temperature reverse bias endurance tests, performed on devices featuring different packages. Only small forward voltage drop and reverse current drifts have been recorded after a 1000h long test, confirming the parametric stability and the reliability level reached by last generation SiC Schottky diodes. Moreover, devices assembled in TO220 package without flame retardant components in the molding compound performed better than devices assembled in other TO220 packages, or assembled in hermetic TO3 package, pointing out the role played by the interface between the green molding compound and the top passivation layer in the long term parametric stability.

Nonlinear Characterization of Varactors for Tunable Networks by Active Source–Pull and Load–Pull

Varactors are key components in the realization of tunable networks, for instance, in high-efficiency power-amplifier architectures. This paper presents a method to measure the varactor quality factor (Q-factor) in the presence of nonlinear distortion. The importance of correctly choosing the loading condition at the second harmonic is illustrated by multiharmonic active source- and load-pull measurements. Furthermore, the method also allows for accurate extraction of the bias-dependent series resistance without the need of area consuming resonant structures. The proposed method is applied to characterize a silicon-carbide (SiC) Schottky diode varactor at 3 GHz. The measured results reemphasize that varactors are not linear tunable, but inherently nonlinear components that require proper consideration of the higher order harmonics.

SiC Schottky Diodes for Harsh Environment Space Applications

This paper reports on the fabrication technology and packaging strategy for 300-V 5-A silicon carbide Schottky diodes with a wide temperature operation range capability (between -170 °C and 300 °C). These diodes have been designed for harsh environment space applications such as inner Solar System exploration probes. Different endurance tests have been performed to evaluate the diode behavior when working at a high temperature and under severe thermal cycling conditions (ranged from -170 °C to 270 °C). The radiation hardness capability has been also tested. It has been found that the hermeticity of the package in a neutral atmosphere is a key aspect to avoid an electrical parameter drift. Moreover, the use of gold metallization and gold wire bonds on the anode allows reducing the diode surface and bonding degradation when compared to Al-containing technology. On the back-side cathode contact, the Ti/Ni/Au metallization and AuGe combination have shown a very good behavior. As a result, the manufactured diodes demonstrated high stability for a continuous operation at 285 °C.

The thermally induced limitations of SiC SBDs operation conditions

In the paper, the DC current–voltage characteristics of silicon carbide Schottky barrier diodes are analyzed, with special attention paid to the critical current and junction temperature estimation. The self-heating phenomenon, interpreted as an electro-thermal positive feedback, is taken into account. The measurements of isothermal and non-isothermal I–V characteristics, as well as adequate calculations, are shown and discussed. The electro-thermal models, based on various descriptions of temperature-dependent series resistance of the device, are proposed. It is also shown that the shapes of I–V characteristics depend on the current range and on the heat-sink size.

Electrical characteristics of Mo/4H-SiC Schottky diodes having ion-implanted guard rings: temperature and implant-dose dependence

The electrical characteristics of ion-implanted guard rings for molybdenum (Mo) Schottky diodes on 4H-SiC are analyzed on the basis of the standard thermionic emission model and the assumption of a Gaussian distribution of the barrier height. For edge termination, high-resistivity guard rings manufactured by carbon and aluminum ion-implanted areas were used. Extractions of barrier heights of molybdenum on silicon carbide (4H-SiC) Schottky diodes have been performed on structures with various gate metallization, using both current–voltage–temperature (I–V–T) and capacitance–voltage (C–V) measurements. Characteristic features of the Schottky barrier height (SBH) are considered in relation to the specific dose of the carbon- or aluminum-implanted guard ring. Contacts showed excellent Schottky behavior ideality factors between 1.02 and 1.24 in the range of 303–473 K. The measured SBHs were between 0.92 and 1.17 eV in the same temperature range from I–V–T characteristics. The variations in the barrier height, which is significantly temperature- and implantation-dose-dependent, are well fitted to a single Gaussian distribution function. Experimental results agree reasonably well by using this approach, particularly for carbon implantation dose of 1.75 × 1014 cm−2, and a mean barrier height () of 1.22 eV and zero bias standard deviation σ0 = 0.067 V have been obtained. Furthermore, the modified Richardson plot according to the Gaussian distribution model resulted in a mean barrier height () and a Richardson constant (A*) of 1.22 eV and 148 A cm−2 K−2, respectively. The A* value obtained from this plot is in very close agreement with the theoretical value of 146 A cm−2 K−2 for n-type 4H-SiC. Therefore, it has been concluded that the temperature dependence of the forward (I–V) characteristics of the Mo/4H-SiC contacts can be successfully explained on the basis of a thermionic emission conduction mechanism with Guassianly distributed barriers.

Thermal stability of SiC Schottky diode anode and cathode metalisations after 1000 h at 350 °C

The thermal stability of two commercially available silicon carbide Schottky diode types has been evaluated following a 1000 h non-biased storage test under vacuum at 350 °C. The Ti-based Schottky (Anode) contact shows excellent stability over the duration of the test with less than 5% change in either extracted Schottky barrier height or ideality values. The Al die attach metalisation on the anode also shows no evidence of degradation after the test. However, a considerable change in series resistance was observed for both diode types, with up to a factor of 100 measured for one of the diodes. The primary early failure mode is related to degradation of the NiAg Ohmic (cathode) die attach metalisation. Demixing of the NiAg alloy, leading to Ag agglomeration is proposed to be the underlying degradation mechanism involved resulting in delamination of the die attach metalisation and the corresponding series resistance increase.

DC characteristics of the SiC Schottky diodes

The isothermal and non-isothermal characteristics of silicon carbide Schottky diodes in the wide range of currents and ambient temperatures are investigated in this paper. The measurements of the diodes characteristics have been performed with the use of a pulse method, with fast registration of measurement points after the diode current turning on, or with the use of a fully static method, in which the self-heating phenomenon is taken into account. Apart from the measurements, the series of numerical experiments, giving the isothermal and non-isothermal characteristics as a result, were executed. The complex, accurate numerical procedures as well as simplified analytical calculations were implemented. A good conformity of all calculation and measurement results have been obtained. In the presented investigations, for relatively high currents and ambient temperatures, the influence of self-heating on the SiC Schottky diodes static characteristics is significant. The large (even 4 V for the ambient temperature 300◦C ) values of voltages corresponding to the nominal diode currents have been observed.

Novel Bridgeless PFC Converters with Low Inrush Current Stress and High Efficiency

This paper presents novel bridgeless power factor correction circuits that achieve both high reliability and high efficiency. The proposed circuits can protect silicon carbide Schottky barrier diodes, MOSFETs, and body diodes against flowing high inrush current without impairing efficiency. This paper introduces the principle of operation including the control scheme and the simulation and experimental results.

Electrical characterization of Au/3C-SiC/ n-Si/Al Schottky junction

High temperature silicon carbide Schottky diode was fabricated with Au deposited on poly 3C-SiC thin film grown on n-type Si(1 0 0) using atmospheric pressure chemical vapor deposition. The charge transport mechanism of the diode was studied in the temperature range of 300–550 K. The forward and reverse bias currents of the diode increase strongly with temperature and the diode shows a non-ideal behavior due to the series resistance and the interface states associated with 3C-SiC. The charge transport mechanism is a temperature activated process, in which, the electrons passes over of the low barriers and in turn, the diode has a large ideality factor. The electrical parameters of the Au/3C-SiC/ n-Si/Al Schottky diode were explained on the basis of the thermionic emission theory with double Gaussian distribution of the barrier heights due to the barrier height inhomogeneities at metal/semiconductor interface. The interface state density of the diode was determined by the conductance–frequency method and it was of order of 9.18 × 10 10 eV −1 cm −2.

SiC JFETs for Power Module Applications

Starting with the production of Infineon´s first silicon carbide (SiC) Schottky diodes in 2001, a lot of progress was achieved during recent years. Currently, a 3rd generation of MPS (merged pn Schottky) diodes is commercially available combining tremendous improvements with respect to surge current capability and reduced thermal resistance. In this work we present the implementation of SiC switches in power modules and a comparison of these units with the corresponding Si-based power modules. Also the frequency dependence of the total losses of the 1200V configurations using Si-IGBTs or SiC-JFETs as active device is shown, indicating that modules solution with a state of the art SiC JFET outperforms all other options for switching frequencies of 20 kHz and beyond. Additionally a total loss vs. frequency study will be presented. Furthermore, it is show that the switching losses of JFET based modules can be further reduced by reducing the internal distributed gate resistivity.

Simulation and Analysis of Si Schottky Diode Family in DC-DC Converter

The unipolar-based devices, silicon schottky (Si) and silicon carbide schottky (SiC) power diodes are investigated for their reverse recovery transient responses and the effects on the switching losses of the FET in the DC-DC converter. Two inductive load chopper circuits are simulated with different test diodes using PSpice software to determine the effectiveness and superiority in each of the devices. All parameter settings are consistent for both converter circuits. The results have shown that the SiC diode has higher energy savings of more than 73.13 % in turn-off switching losses. This eventually corresponds to the reduction of 96.16 % in FET turn-on peak power dissipation of SiC converter. However, there is a minor drawback in drain voltage overshoot of the converter. Some detailed analyses are presented in the paper.

Light ions response of 4H-SiC Schottky diodes with different dopant concentration

Silicon Carbide (SiC) Schottky diodes of different dopant concentration have been used to detect 12 C ions at 14.2, 28.1 and 37.6 MeV incident energies. The relation between the applied reverse bias and the thickness of the depleted epitaxial region is studied for different dopant concentrations. The results show that SiC diodes with lower dopant concentration require lower reverse bias values to deplete the same thickness. Moreover, the radiation damage, produced by irradiating SiC diodes with 16 O ions at 35.2 MeV, was evaluated by measuring the degradation of both the signal pulse-height and the energy resolution as a function of the 16 O fluence. Diodes having a factor 20 lower dopant concentration show a radiation hardness reduced by 60%.

Accelerated Life Test for SiC Schottky Blocking Diodes in High-Temperature Environment

This paper reports on the life tests of silicon carbide Schottky diodes with high-temperature operation capability (up to 270degC). These 300-V-3-A diodes have been designed to meet the BepiColombo requirements, a European Space Agency mission to Mercury. The life test consisted in a dc current stress of 5 A applied to these diodes at 270degC for 600 h or more. Different diode technologies have been tested and compared. On typical Ti or Ni Schottky diodes with thick aluminum metal layer, these reliability tests revealed degradation at both the Schottky interface and the diode top surface due to aluminum diffusion. The use of W as Schottky metal allows eliminating the forward voltage drift producing stable metal-semiconductor interface properties. The use of thick gold metallization allows reducing the surface and bonding degradation. The final diodes demonstrated high stability at 270degC.

Epitaxial Layer Parameters Estimation Approach of Silicon Carbide Schottky Diodes

Silicon-carbide Schottky diode is seen as one of the newest devices deployed in sensor application. Temperature sensors using these highly developed devices have been introduced. The linearity of the output signal versus temperature of the silicon-carbide Schottky diode is demonstrated. From a modeling point of view, accurate simulations are necessary for checking sensor behavior. These simulations tend to rely on component models and associated confidential epitaxial parameters. Therefore, this paper sets out to extract accurate parameters of the silicon-carbide Schottky diode. In pursuit of this end, a systematic approach is developed and a physically based model is introduced. This model is run for many devices, giving directly epitaxial layer parameters. A contrastive study between experimental and simulation is undertaken, resulting in good agreement.