4H-SiC Junction Barrier Schottky Research Articles

Fabrication of a monolithic 4H-SiC junction barrier schottky diode with the capability of high current

There is a great interest in monolithic 4H-SiC Junction Barrier Schottky (JBS) diodes with the capability of a high forward current for industrial power applications. In this paper, we report large-area monolithic 4H-SiC JBS diodes fabricated on a 10 µm 4H-SiC epitaxial layer doped to 6×1015 cm−3. JBS diodes with an active area of 30 mm2 had a forward current of up to 330 A at a forward voltage of 5 V, which corresponds to a current density of 1100 A/cm2. A near ideal breakdown voltage of 1.6 kV was also achieved for a reverse current of up to 100 μA through the use of an optimum multiple floating guard rings (MFGR) termination, which is about 87.2% of the theoretical value. The differential specific-on resistance (R SP-ON) was measured to be 3.3 mΩ cm2, leading to a FOM (VB2/R SP-ON) value of 0.78 GW/cm2, which is very close to the theoretical limit of the tradeoff between the specific-on resistance and breakdown voltage for 4H-SiC unipolar devices.

Influence of Trench Structure on Reverse Characteristics of 4H-SiC JBS Diodes

We fabricated trench Junction Barrier Schottky (JBS) diodes, and investigated the effect on the reduction of leakage current and the device yield. First, by calculating of electric field at the Schottky contact interface (Es), we found that the trench JBS structure can reduce Es one digit smaller than the planar JBS structure, setting 80o < The bevel angle θ < 90o. Then, 600 V / 50 A trench JBS diodes are developed and characterized. The leakage current of a trench JBS diode at 600V is 10-2 times smaller than that of planar JBS diode by effectively reducing Es. This enables to reduce the number of low break down samples and raise the yield compared to the planar JBS structure.

Impact of Electron Irradiation on the ON-State Characteristics of a 4H–SiC JBS Diode

The ON-state characteristics of a 1.7-kV 4H–SiC junction barrier Schottky diode were studied after 4.5-MeV electron irradiation. Irradiation doses were chosen to cause a light, strong, and full doping compensation of an epitaxial layer. The diodes were characterized using Deep Level Transient Spectroscopy, $C$ – $V$ (T), and $I$ – $V$ measurements without postirradiation annealing. The calibration of model parameters of a device simulator, which reflects the unique defect structure caused by the electron irradiation, was verified up to 2000 kGy. The quantitative agreement between simulation and measurement requires: 1) the Shockley–Read–Hall model with at least two deep levels on the contrary to ion irradiation and 2) a new model for enhanced mobility degradation due to radiation defects. The diode performance at high electron fluences is shown to be limited by the doping compensation at the epitaxial layer.

Surge current capabilities and isothermal current–voltage characteristics of high-voltage 4H-SiC junction barrier Schottky rectifiers

Isothermal forward current–voltage characteristics of high-voltage 4H-SiC junction barrier Schottky rectifiers (JBS) have been studied for the first time. Isothermal characteristics were measured with JBS having a blocking voltage of 1700 V up to a current density j ≈ 4200 A cm−2 in the temperature range 297–460 K. Quasi-isothermal current–voltage characteristics of these devices were studied with injection of minority carriers (holes) up to j ≈ 7200 A cm−2 and ambient temperatures of 297 and 460 K. The isothermal forward current–voltage characteristics make it possible to numerically calculate (for example, by an iteration procedure) the overheating in an arbitrary operation mode.

Low‐leakage 4H‐SiC junction barrier Schottky rectifier with sandwich P‐type well

4H-SiC junction barrier Schottky (JBS) rectifier with sandwich P-type well (SPW JBS) is investigated by simulation. For this structure, the top and bottom of P+ grids are replaced by low-doped P (LDP) region based on the common JBS rectifier. The forward and reverse characteristics of SPW JBS rectifier have been compared with those of common JBS rectifier at different temperatures. The reverse current density of SPW JBS rectifier is about 2.4 × 10−5 times of common JBS rectifier at −800 V bias voltage. The upper LDP of SPW JBS is helpful to give a reduction in forward voltage drop. The spreading current and tunnelling current of SPW JBS rectifier are lower, because the depletion layer width in lower LDP is larger than that in P+ grid region at the same reverse voltage. As a result, the breakdown voltage of SPW JBS rectifier increases by 83.5% compared with that of common JBS rectifier. The on/off (1 V/ −500 V) current ratios of SPW JBS and common JBS rectifiers are 3.8 × 107 and 1.2 × 103, respectively. In addition, the figure of merit of SPW JBS rectifier is 347, which is two times larger than that of common JBS rectifier.

Repetitive-Avalanche-Induced Electrical Parameters Shift for 4H-SiC Junction Barrier Schottky Diode

The electrical parameters shift of 4H-SiC junction barrier Schottky diode under the repetitive avalanche current stress has been experimentally investigated. Using technical computer-aided design simulation and high resolution transmission electron microscopy analysis at atomic scale, it has been demonstrated that the forward voltage drop of the device has no variation during the stress due to the intactness of active area. However, the reverse breakdown voltage is gradually increased with the stress time, which results from hot electron injection and trapping into the SiO2 dielectric at the outer edge of p-type junction termination.

Fabrication and High Temperature Characterization of 1200V-15A 4H-SIC JBS Diode

1200V-15A 4H-SiC junction barrier schottky (JBS) diodes were designed and fabricated based on SiC epitaxy and device technology. By adopting the proper SBD metal,optimized structures and fabrication process, we succeeded in achieving good balance between blocking voltage and on-resistance, especially at high temperature to 200°C. Furthermore, the fabricated diode have a fast recovery time of 30ns, and its dynamic characteristics are constant at high temperature.

High-Voltage Large-Current 4H-SiC JBS Diodes

3.3kV and 4.5kV 4H-SiC junction barrier Schottky (JBS) diodes with floating guard rings edge termination have been fabricated. The 3.3kV device with 33μm 2.7E15 cm-3epilayer and 5.5Х5.5mm2schottky contact area has a blocking voltage (Vb) of 3.9 kV and a specificon-resistance (Ron) of 10.5 mΩ.cm2, with a forward current measured up to 50A at VF=3.0V. The 4.5kV device with 50 um 1.2E15 cm-3epilayer and 5.5Х5.5mm2schottky contact area has a blocking voltage (Vb) of 5.1 kV and a specificon-resistance (Ron) of 22.9 mΩ.cm2, with a forward current of 30A at VF=3.7V.

Experimental and numerical analyses of high voltage 4H-SiC junction barrier Schottky rectifiers with linearly graded field limiting ring

This paper describes the successful fabrication of 4H-SiC junction barrier Schottky (JBS) rectifiers with a linearly graded field limiting ring (LG-FLR). Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2 (about 80% of the theoretical value). Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termination, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.

Characterization of deep electron traps in 4H-SiC Junction Barrier Schottky rectifiers

Conventional deep level transient spectroscopy (DLTS) technique was used to study deep electron traps in 4H-SiC Junction Barrier Schottky (JBS) rectifiers. 4H-SiC epitaxial layers, doped with nitrogen and grown on standard n+−4H-SiC substrates were exposed to low-dose aluminum ion implantation process under the Schottky contact in order to form both JBS grid and junction termination extension (JTE), and assure good rectifying properties of the diodes. Several deep electron traps were revealed and attributed to impurities or intrinsic defects in 4H-SiC epitaxial layers, on the basis of comparison of their electrical parameters (i.e. activation energies, apparent capture cross sections and concentrations) with previously published results.

Investigation of Stacking Faults Affecting on Reverse Leakage Current of 4H-SiC Junction Barrier Schottky Diodes Using Device Simulation

We clarified the relationship between the enhanced leakage current of SiC Junction Barrier Schottky diodes and the stacking faults in the SiC crystal at the SiC and metal electrode interface by measuring the electrical and optical properties, and confirm by using the numerical simulations. Numerical simulation considering local lowering of Schottky barrier height, which is 0.8 eV lower than that of 4H-SiC well explained the 2-4 orders of magnitude higher reverse leakage current caused by the SFs. We concluded that the locally lowering of the Schottky barrier height at the 3C-SiC layer in the 4H-SiC surface is a main cause of the large reverse leakage current.

Development of 1000V SiC JBS Diodes

High voltage 4H-SiC Ni Schottky junction barrier schottky (JBS) diode with breakdown voltage of 1000V and forward current of 1A has been fabricated. A low reverse leakage current below 4.7×10-6A/cm2 at the bias voltage of-1000V has been obtained. The forward on-state current was 1A at VF = 2.2V. The chip is 1.3mm×1.3mm. The turn-on voltage is about 1.4V. The on-state resistance is 14.5mΩ·cm2. The doping and thickness of the N-type drift layer and the device structure have been performed by numerical simulations. The SiC JBS devices have been fabricated and the processes were in detail. The die was assembled in a SMB package. The thickness of the N-epilayer is 10μm, and the doping concentration is 4×1015cm3. A floating guard rings edge termination have been used to improve the effectiveness of the edge termination technique. By using WTi/Au multilayer metal structure, the double side Au process of 4H-SiC JBS diode is formed. We use the PECVD SixNy/SiO2 as the passivation dielectric and a non photosensitive polyamide as the passivation in the end.

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm2 with a total active area of 2.46 × 10−3 cm2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250°C in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9 × 10−5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

4.5kV SiC JBS Diodes

High voltage 4H-SiC junction barrier schottky (JBS) diode with breakdown voltage higher than 4.5 kV has been fabricated. The doping level and thickness of the N-type drift layer and the device structure have been performed by numerical simulations. The thickness of the device epilayer is 50 μm, and the doping concentration is 1.2×1015 cm3. A floating guard rings edge termination has been used to improve the effectiveness of the edge termination technique. The diodes can block a reverse voltage of at least 4.5 kV, and the on-state current density was 80 A/cm2 at VF =4 V.

Application of 1200V-8A SiC JBS Diodes in the Motor System

1200V-8A 4H-SiC junction barrier schottky (JBS) diodes were designed and fabricated based on in-house SiC epitaxy and device technology. As a free-wheeling diode for the IGBT in inverter of motor system, the 1200V SiC JBS diode was compared to the Si ultra-fast diode from Fairchild Co. Ltd. The SiC diode achieved 88% recovery loss reduction and corresponding IGBT showed 35% lower turn-on loss. So, it will promote the application of motor system in high frequency and high efficiency.

Effect of Stacking Faults in Triangular Defects on 4H-SiC Junction Barrier Schottky Diodes

The relationship between stacking faults and the position of the leakage current inside a triangular defect was analyzed. Triangular defects are categorized into two types on the basis of the current–voltage (I–V) characteristics. It was found that stacking faults (SFs) of the 3C structure inside a triangular defect increase leakage current at a reverse bias voltage as well as forward current at a low bias voltage, while SFs of the SF(4,2) structure inside a triangular defect do not lead to deterioration of device performance in this case.

Reverse Leakage Currents in High-Voltage 4H-SiC Schottky Diodes

High-voltage 4H-SiC Schottky Barrier Diodes (SBDs) and Junction Barrier Schottky (JBS) diodes have been fabricated and evaluated. Current-voltage (I-V) characteristics were measured in a wide temperature range. All diodes fabricated showed nearly ideal forward behavior. For SBDs with Schottky Barrier Height (SBH) of 1.12 eV, the reverse I–V characteristics are described well by the thermionic emission model (at voltages varying from several mV to 2 kV and temperatures ranging from 361 to 470 K) if barrier lowering with increasing band bending is taken into account. For SBDs with SBH of 1.53 eV, no thermionic current was detected in reverse direction at temperatures below ~500 K. The leakage currents appeared only at high reverse voltages and elevated temperatures. The analysis of reverse I-V characteristics allowed to propose dislocation related mechanism of current flow due to the local injection of electrons from metal to semiconductor. It is shown that defect related leakage currents can be significantly reduced by JBS-structure.

Temperature-dependent characteristics of 4H—SiC junction barrier Schottky diodes

The current—voltage characteristics of 4H—SiC junction barrier Schottky (JBS) diodes terminated by an offset field plate have been measured in the temperature range of 25–300 °C. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H—SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.

High Temperature Capability of High Voltage 4H-SiC JBS

This paper presents the high blocking capability of the 4H-SiC tungsten Schottky and junction barrier Schottky (JBS) diodes at room temperature as well as at high operating temperature. First, we present the design of the proposed devices and the process employed for their fabrication. In a second part, their forward and reverse characteristics at room temperature will be presented. Our rectifiers exhibit blocking capability up to 9kV at room temperature. Then, we investigate the reverse current behaviour at 5kV from room temperature to 250°C under vacuum. JBS and Schottky devices that are capable to block 8kV at room temperature, show leakage current inferior to 100µA at 250°C when reverse biased at 5kV. It confirms the capability of Silicon Carbide to produce devices capable of operation at temperatures and voltages above the Silicon limits.

Study of the effect of lithography deviation on 4H-SiC floating junction junction barrier Schottky diode

The breakdown voltage of 4H-SiC junction barrier schottky diode with floating junction is larger than that of traditional junction barrier Schottky diode under the condition of the same fixed on-resistance. It is a crucial technology that the alignment of lithography between p+ region of floating junction and main junction. The simulation results obtained using two-dimensional simulator ISE show that the breakdown voltage obviously drops with the deviation of lithography increasing. Although the breakdown characteristics of the dislocation and the alignment structure are similar, the series resistance of the dislocation structure is larger than the latter when the forward voltage is larger than 2 V.