4H-SiC JBS Diodes Research Articles

Design and Optimization of High Performance Multi-Step Separated Trench 4H-SiC JBS Diode

In this paper, a novel 3300 V/40 A 4H-SiC junction barrier Schottky diode (JBS) with a multi-step separated trench (MST) structure is proposed and thoroughly investigated using TCAD simulations. The results show that the introduction of MST expands the Schottky contact area, resulting in a decrease in the forward voltage drop. Furthermore, the combination of the deep P+ shielded region and the central P+ region effectively reduces the leakage current, leading to a 43.7% increase in the blocking voltage compared to conventional 4H-SiC JBS. The effects of the step depth (ds) and the width of the central P+ region (wm) on the device performance are analyzed in depth. In addition, a multi-step trenched linearly graded field-limiting rings (MTLG-FLR) termination ensures a more uniform electric field distribution, and the terminal protection efficiency reaches up to 90%, which further enhances the reliability of the terminal structure.

Influence of Transport Mechanism and Defect Behavior on Leakage Current in 4H-SiC JBS Diodes After Neutron Irradiation

Influence of Transport Mechanism and Defect Behavior on Leakage Current in 4H-SiC JBS Diodes After Neutron Irradiation

Degradation mechanism of SiC diodes under thermal and irradiation stress

Abstract Silicon carbide (SiC)-based diodes are widely used due to their high temperature resistance. In this paper, breakdown voltage of 4H-SiC JBS diodes and capacitance-voltage of 4H-SiC MOS capacitors with identical interfacial structure were both measured at high temperature to study their interfacial properties. By analyzing the variation of interfacial properties, the correlation between thermal stress and failure mode of 4H-SiC JBS diodes was further established to reveal their degradation mechanism. During initial high temperature storage, interfacial negative effective charge density of 4H-SiC JBS diodes may increase, leading to the decrease of breakdown voltage. As storage time increases, interfacial charge density began reducing, resulting in the increase of breakdown voltage. Avalanche luminescence verifies that the variation of interfacial charge density under thermal stress led to the degradation of 4H-SiC JBS diodes and further affected their breakdown voltage. Finally, degradation mechanism of SiC-JBS, SiC-SBD and SiC-PIN diodes under irradiation stress was investigated. After irradiation, forward current of some SiC diodes increased at a small forward voltage. However, the reverse characteristics deteriorated obviously and even failed.

1.2-kV Low-Barrier 4H-SiC JBS Diodes by Virtue of P-Implants Across Dead Field of Current Flow

A low value of Schottky barrier height (SBH) ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{\textit{B}}\text{)}$</tex-math> </inline-formula> is highly desired to further reduce the power loss in 4H-SiC junction barrier Schottky (JBS) diodes; however, the reduced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{\textit{B}}$</tex-math> </inline-formula> results in serious leakage current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{R}}\text{)}$</tex-math> </inline-formula> when blocking high voltages. In this work, a tunable low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{\textit{B}}$</tex-math> </inline-formula> of 0.92–0.98 eV with an ideal factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{n}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 1.02–1.03 was first realized through effectual rapid thermal annealing (RTA) methods and combined with a trench-assisted stage-style p-type implants taking advantage of dead region for current flow to resolve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\text{R}}$</tex-math> </inline-formula> issue. Numerical simulation demonstrated the superiority of this promising strategy in alleviating the Schottky interface electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}_{\text{S}}\text{)}$</tex-math> </inline-formula> and suppressing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{R}}$</tex-math> </inline-formula> without constraining the forward current flow. Based on this practical strategy, the fabricated device achieved one order of magnitude less <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{R}}$</tex-math> </inline-formula> at 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C and 220% enhancement of breakdown voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{B}}\text{)}$</tex-math> </inline-formula> at 175 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C in contrast to the conventional low-barrier one. In addition, benefiting from the low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{\textit{B}}$</tex-math> </inline-formula> , the device achieved an ultralow turn-on voltage of 0.47 eV and a remarkable forward voltage drop ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{F}}\text{)}$</tex-math> </inline-formula> of 1.36 V extracted at 20 A, indicating 14% lower conduction loss than the titanium-based JBS diodes with the same device configuration. This novel device structure incorporating low-barrier Schottky contact metal and trench-assisted stage-style p-implants (SPs) in the dead region of current flow suggests a promising way to develop more advanced 4H-SiC JBS diodes in the future.

A Superior Reverse Characteristics of 1.2 kV 4H-SiC Planar JBS Diode Employing Channeling Implantation

This paper presents a study on improving the reverse characteristics of 1.2 kV 4H-SiC JBS diodes by employing a deep P+ grid structure. To achieve a deep junction with low implantation energy, channeling implantation was implemented. Diodes with different junction depths of the P+ grid were fabricated to compare the forward and reverse I-V characteristics; depth of 0.8 μm, 1.4 μm, and 2.2 μm. Almost identical forward I-V characteristics were achieved regardless of the P+ grid depth. However, the leakage current was significantly suppressed by the deeper P+ grid junction depth; 60 μA, 1.5 μA, and 1.7 nA (at 1200V for 0.8, 1.4, 2.2 μm deep P+ grids, respectively). Although the deep junction was implemented with channeling implantation, high breakdown voltages similar to that of the shallow junction are achieved in the proposed JBS diode. This is due to the relatively low doping concentration in the deep junction. Moreover, the edge termination structures with different main junction depths were discussed. For a near ideal breakdown voltage insensitive to the JTE dose, Hybrid-JTE was employed. It was demonstrated that the high breakdown voltage with the drastically reduced leakage current of the proposed JBS diodes, was achieved using identical edge termination technology to the conventional shallow junction. To better understand the effect of the deep junction, 2D simulation was conducted.

Effect of Schottky annealing temperature on reverse leakage current of 6500 V 4H-SiC JBS diodes

Annealing treatment has an important effect on the electrical properties of Schottky diodes. In this paper, the effect of Schottky annealing temperature on reverse leakage current of 6500 V 4H-SiC JBS diodes was studied. The reverse leakage current of the diode annealed at 500 °C is higher than that of the diode annealed at 450 °C. This is because the Schottky barrier height of the diode annealed at 500 °C is decreased by 0.08 eV, which leads to a large reverse leakage current. Meanwhile, the Schottky barrier height of the diode annealed at 500 °C is decreased more significantly with the increase of measurement temperature, therefore the reverse leakage current increases significantly.

Effect of overlap region for schottky metal and field oxide on the electrical characteristics of 6500 V/50A 4H-SiC JBS diodes

The effect of overlap region for schottky metal and field oxide (ORSMFO) of field limiting rings termination on the reverse breakdown voltage of 6500 V/50A 4H-SiC JBS diodes was studied. Two comparative diodes were designed and fabricated. The reverse breakdown voltage of diodes with 20 μm ORSMFO improved significantly, which was up to 7000 V at the reverse leakage current of 10 μA and yield was up to 73 %. The structure simulation implied that the difference of the ORSMFO influenced the electric field strongly. Compared with the simulative terminal structure with 3 μm and 0 μm ORSMFO, the electric field intensity of the simulative terminal structure with 20 μm ORSMFO reduced by about 30 %-50 % near the main junction and the first three field rings.

Reduced On-Resistance and Improved 4H-SiC Junction Barrier Schottky Diodes Performance by Laser Annealing on C-Face Ohmic Regions in Thin Structures

In this study, we investigated the characteristics of the n-type Ni/SiC ohmic contact using the laser annealing process on thin wafers. The electrical behavior of the ohmic contacts was tested in 4H-SiC JBS diode devices. As a result, a wafer thickness of 100 μm in the 4H-SiC JBS diode achieved a forward voltage of 1.33 V at 20 A with a laser annealing process using Ni silicide. Using a laser annealing process on a wafer thickness of 100 μm, an on-resistance decrease of almost 22% was demonstrated. Based on our experimental results, we suggest an alternative laser annealing fabrication scheme to obtain low on-resistance SiC power devices with thin structures after SiC grinding.

Analysis of Defects and Electrical Characteristics of Variable-Temperature Proton-Irradiated 4H-SiC JBS Diodes

The defects and electrical characteristics of 4H-SiC JBS diodes irradiated by 2 MeV protons under irradiation temperatures of 100–400 K were studied. Forward and reverse current–voltage (I–V), capacitance–voltage (C–V), and deep-level transient spectroscopy (DLTS) measurements were performed to study the changes in the characteristics of the device before and after variable-temperature proton irradiation. As the irradiation temperature increased from 100 to 400 K, the on-resistance decreased from 251 to 204 mΩ, and the carrier concentration gradually increased. The reverse current–voltage experiment results showed that the leakage current increased after proton irradiation at each irradiation temperature compared to before irradiation. The DLTS spectra analyses showed that proton irradiation mainly introduced a carbon vacancy related to the Z1/2 center (E0.68 and E0.72), which may have been the main reason for the changes in the forward and reverse electrical characteristics. The intensity of the DLTS spectrum decreased with the increasing irradiation temperature, indicating that the concentration of defects gradually decreased, due to the increase in the radius of the recombination of a vacancy with a related interstitial atom.

Design and Fabrication of Non-Uniform Spacing Multiple Floating Field Limiting Rings for 6500V 4H-SiC JBS Diodes

Designed for 6500V 4H-SiC JBS diodes, a highly-efficient termination structure of a non-uniform multiple floating field limiting rings (MFFLR) featuring with a non-uniform ring spacing and a multiple region division is studied and purposed. For each region, ring spacing is modulated independently by a multiplication factor and a linear increment factor. The non-uniform MFFLR structure is simulated and optimized for a better electric field distribution and a higher breakdown voltage. Based on the simulation results, 4H-SiC JBS diodes with the optimized non-uniform termination designs are fabricated. Experimental results show that the SiC JBS diode with optimized non-uniform MFFLR termination structure can achieve a breakdown voltage of up to 7800 V, and its termination efficiency is about 94% of an ideal parallel-plane junction’s. Our results demonstrate that the optimized non-uniform MFFLR termination structure is capable for SiC JBS diodes with breakdown voltage of 6500V and above. Our results can provide a valuable design methodology of edge termination structures for other high-voltage SiC devices.

Effect of the Field Oxidation Process on the Electrical Characteristics of 6500V 4H-SiC JBS Diodes

The effect of the field oxidation process on the electrical characteristics of 6500V 4H-SiC JBS diodes is studied. The oxide thickness and field plate length have an effect on the reverse breakdown voltage of the SiC JBS diode. According the simulation results, we choose the optimal thickness of the oxide layer and field plate length of the SiC JBS diode. Two different field oxide deposition processes, which are plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD), are compared in our paper. When the reverse voltage is 6600V, the reverse leakage current of SiC JBS diodes with the field oxide layer obtained by LPCVD process is 0.7 μA, which is 60% lower than that of PECVD process. When the forward current is 25 A, the forward voltage of SiC JBS diodes with the field oxide layer obtained by LPCVD process is 3.75 V, which is 10% higher than that of PECVD process. There should be a trade-off between the forward and reverse characteristics in the actual high power and high temperature applications.

Temperature Dependence of the Bipolar Activation and the Leakage Currents of 10 kV 4H-SiC JBS-Diodes

The activation of bipolar conduction was investigated for two 4H-SiC 10 kV JBS-diodes which differ in the area ratio between p-doped and n-doped regions (Ws/WPin). Quasi-static measurements at low electric current densities (j &lt; 2.5 Acm-2) were performed in a temperature range between 25°C and 500°C. The lower ratio (Ws/WPin) leads to a higher threshold voltage. On the other hand lower electric power density is neccessary to trigger temperature enhanced bipolar activation. Moreover, the lower ratio improves the leakage currents in blocking direction. Dynamic surge current investigations were performed in a temperature range between 25°C and 250°C. The turning voltages, which indicate the transition from unipolar to bipolar conduction, are lower for the diode with smaller ratio (Ws/WPin) but the self-heating of the device is more severe in comparison to the other diode with the larger ratio. Both devices are stable under extreme conditions (high temperatures/ surge current) and exhibit special benefits for different applications.

On the design of the channel region in 4H-SiC JBS diode through an analytical model of the potential barrier

In this paper, we propose a tool for the design of 4H-polytype Silicon Carbide Junction Barrier Schottky, JBS, diodes, which are promising devices for their low on-state resistance and their high blocking voltage. Our tool calculates the width of the channel region in terms of the geometrical and physical parameters and of the doping concentration in order that the device shows forward electrical characteristics similar to that of Schottky Barrier Diode. Their operating principle is defined by the control of the flow of electron carriers through a potential barrier, which is located in the n-type region under the Schottky metal contact surrounded by the p+-type regions. Indeed, if the electric fields of the p+-n junctions extend for the whole channel region under equilibrium conditions, the height of the induced potential barrier can be higher than that of the conventional Schottky built-in potential and can affect the electrical characteristics of the device, for example increasing the turn-on voltage. Although they have been firstly developed in Silicon technology, 4H-SiC JBS diodes are easier to fabricate because the electric fields of 4H-SiC p–n junctions have a wider space charge region for the same values of the doping concentrations with respect to Si JBS devices, resulting in a more relaxed design constrain of the channel geometry. Our analytical model can calculate the potential barrier height as function of the geometrical and physical parameters of the device and can evaluate the maximum channel width for which the potential barrier is higher than Schottky built-in voltage. The analytical results are compared through numerical simulations obtained from ATLAS Silvaco software.

Design and fabrication of high performance 4H-SiC TJBS diodes

Abstract In this paper, high performance 4H-SiC trench junction barrier Schottky diodes (TJBS) have been successfully designed and fabricated. For making a larger design window that enables good reverse blocking and forward conduction capabilities at the same time in TJBS, trench profile, especially bevel angle (θ) of a tapered trench sidewall, are further studied. The optimal design is verified by the experimental results measured from the fabricated 4H-SiC JBS and TJBS diodes. Experimental results show that the reverse leakage current (Ir) of the TJBS is only 1.62 × 10−7 A/cm2 at Vr of 1200 V, which is about one order of magnitude less than that of planar JBS (PJBS) fabricated at the same time. The figure of merit (FOM) of TJBS is improved by 56.3% when compared with that of the PJBS.

Effect of P+ region design on the fabrication of 6500 V 4H-SiC JBS diodes

We studied the effect of P+ region design on the simulation and fabrication of 6500 V 4H-SiC JBS diodes. There existed a deviation of 0.9 μm in P+ region design between theoretical simulation and actual device during the fabrication. We mainly attributed this change of P+ region design to the implantation spreading and the mask etching processes. The simulation fitted well with the measured results considering the broadening of 0.9 μm of P+ region. According to the analysis, we calibrated the simulation and successfully fabricated the 6500 V/40A 4H-SiC JBS diodes. The simulation fitted very well with the performance of fabricated device.

On the Development of 1700V SiC JBS Diodes in a 6-Inch Foundry

This paper presents the development of 1700V-rated 4H-SiC JBS diodes in the state-of-the-art 6-inch SiC-dedicated foundry, NY-PEMC (New York- Power Electronics Manufacturing Consortium). The critical considerations in developing the SiC JBS diode including the cell optimization, edge termination design, process flow, and unit process developments are discussed in this paper. Static device performances such as forward conduction and reverse blocking behaviors of fabricated 1700V, 20A-rated JBS diode are presented.

Change in the Parameters of Electron-Irradiated 4H-SiC Schottky Diodes as a Function of the Time during Low-Temperature Isothermal Annealing

In the present work, the kinetics of low-temperature annealing (400 °C) of 4H-SiC JBS diodes irradiated by electrons with an energy of 0.9 MeV and with a dose of 1E16 cm-2 was studied. The dynamics of changes in I-V, C-V characteristics, as well as DLTS spectra are shown. In the course of the work, a thermal cycling effect was discovered, i.e., effect of multiple rapid cooling to the temperature of liquid nitrogen and heating of the samples. As a result of thermal cycling, the barrier capacity increases and the on-resistance (Rs) decreases. In the DLTS spectrum, a level of - 0.38 eV appears, absent in the as-irradiated diodes.

Surge Driven Evolution of Schottky Barrier Height on 4H-SiC JBS Diodes

In this paper we will present the results of repetitive surge stress carried out on six 3.3 kV-5A Ti/Ni 4H-SiC JBS diodes. Repetitive current peaks between 10 A and 24 A have been applied and some diodes were able to endure 100,000 cycles while others failed before. The causes of failure have not been determined but a correlation between peak surge current and physical parameters evolution rate has been proven. Simulations show that contact temperature during surge can reach 300 °C, which is very close to Schottky contact annealing temperatures.

Comparison of the Effects of Electron and Proton Irradiation on 4H-SiC and Si Device Structures

The change in the current-voltage characteristics and in Nd-Na values in the base of 4H-SiC Schottky diodes and JBS diodes under irradiation with 0.9 MeV electrons and 15 MeV protons has been studied. The carrier removal rate for the diodes irradiated with electrons was 0.07-0.15 cm-1, and that in the case of protons, 50-70 cm-1. It was shown that the devices under study retain rectifying current-voltage characteristics up to electron doses of ~1017 cm-2. It was found that the radiation resistance of the SiC-based devices significantly exceeds that of silicon p-i-n-diodes with similar breakdown voltages. The simultaneous effect of high temperature and proton irradiation on the characteristics of 4H-SiC pn structures was examined.

Modeling of Inhomogeneous 4H-SiC Schottky and JBS Diodes in a Wide Temperature Range

This paper presents a study of the Schottky barrier evolution on SBD and JBS diodes over a wide range of temperatures from 80 to 500 K. We show that inhomogeneities of the Schottky contact have a strong impact on the dependence of barrier characteristics with temperature, especially below 200 K. Analysis of the reverse bias current of such diodes at low temperature show that the barrier height depends on temperature but also on voltage.