4H-SiC Junction Barrier Schottky 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.

Novel design and modelling of SiC junction barrier Schottky diode with improved Baliga FOM under high-temperature applications

A novel 650 V/50 A 4H–SiC junction barrier Schottky diode (JBSD) featuring a stripe-square composite cell design (SSC-JBSD) is proposed in this paper to improve the high-temperature performance. A model of the resistance of the JBS (RJBS) is established to explain the mechanism. The particular cell design of the SSC-JBSD forms a circular current distribution, which can improve the forward current and suppress the degeneration of RJBS caused by the lower electron mobility at high temperatures. The combination of the stripe and square P+ regions achieves a high current and a lower power loss under high temperature while maintaining a high breakdown voltage. Specifically, the power loss of the SSC-JBSD with a forward current of 50 A only increases by 6.9 % under 450 K compared to that under 300 K, while that of the conventional JBS diode (Conv-JBSD) increases by 14.1 %. And the Baliga figure of merit (FOM) of the SSC-JBSD is 15.6 % higher than that of the Conv-JBSD under a temperature of 450 K. The on-state self-heating measurement shows that the temperature of the SSC-JBSD is approximately 30 K lower than that of the Conv-JBSD after 5 s of constant on-state operation with a forward current of 50 A. The proposed SSC-JBSD demonstrates superior performance at high temperatures, making it an available replacement for Conv-JBSD in harsh environments characterized by high temperatures and large currents.

Correlations between reverse bias leakage current, cathodoluminescence intensity and carbon vacancy observed in 4H-SiC junction barrier Schottky diode

Reverse bias currents of ten commercial junction barrier Schottky diodes were measured, and the dies were studied by scanning electron microscope (SEM) and cathodoluminescence (CL) after the de-capsulation of the diodes. Defect emissions (DEs) of 2.62 eV were observed in all the CL spectra. By comparing the SEM images, the integral CL intensity spatial mappings and the reverse bias leakage currents, correlations between the leakage current, the integral CL intensity and the Al-implantation process were established. The data of reverse bias leakage current against the reverse bias voltage taken at room temperature followed the Poole Frenkel emission from the Z 1/Z 2 carbon vacancy states to the conduction band. The DE at 2.62 eV is associated with the electronic transition from Z 1/Z 2 to the valence band. The current observation also opens up the feasibility of screening off SiC diodes with large leakage current during production by inspecting the CL intensity before the device fabrication is complete.

Development of 400 V-Tolerant Single-Event Effect Hardened 4H-SiC Schottky Diode With Linear Energy Transfer Upto 83.5 MeV⋅cm2/mg

A novel 4H-SiC junction barrier Schottky (JBS) with deep linear graded doping (DLGD) P junction structure is proposed and fabricated to enhance the radiation tolerance of Single-Event Effect (SEE). The radiation-hardened function of the proposed new structure is confirmed via two-dimensional numerical simulation and SEE experiment. The hardened device was tested under heavy ion irradiation with linear energy transfer (LET) up to 83.5 MeV·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /mg. Test results show that the single-event leakage current (SELC) threshold voltage of the hardened device is 400 V, which is the best SEE radiation-hardened performance reported so far for high-voltage 4H-SiC JBS. Compared with the state-of-the-art counterparts, this work is about 2 times improvement in SELC threshold voltage.

Highly Efficient Floating Field Rings for SiC Power Electronic Devices - A Systematic Experimental Study

A systematic experimental study is conducted on floating field rings (FFR) incorporated into 4H-SiC junction barrier Schottky (JBS) diodes across four voltage ratings 650, 1200, 1700 and 3300V, in pursuit of highly efficient FFR designs. 30 designs of FFR in 3 categories are studied for each voltage rating, and the measured breakdown voltage (Vbr) of JBS divided by ring system width (W) is taken as the figure of merit (FOM) of each design. The influence of ring spacing, ring width and number of rings on Vbr is studied in detail. It is found that the initial ring spacing (S1) is critical in determining the highest Vbr achievable by a certain design, and its optimum value increases as voltage rating increases. TCAD simulation verifies the importance of S1. For designs with a small ring system width, subsequent ring spacing can also become important. Ring width does not have a definitive effect, and Vbr saturates beyond a certain ring number. The design with the highest Vbr may not render the highest FOM. Even style designs with appropriate ring spacings can be advantageous likely due to less susceptibility to variation of field oxide charge, and more tolerance to fabrication error, as well as ease of design.

Heavy Ion Induced Degradation Investigation on 4H-SiC JBS Diode with Different P+ Intervals

The heavy ion radiation response and degradation of SiC junction barrier Schottky (JBS) diodes with different P+ implantation intervals (S) are studied in detail. The experimental results show that the larger the S, the faster the reverse leakage current increases, and the more serious the degradation after the experiment. TCAD simulation shows that the electric field of sensitive points directly affects the degradation rate of devices with different structures. The large transient energy introduced by the heavy ion impact can induce a local temperature increase in the device resulting in lattice damage and the introduction of defects. The reverse leakage current of the degraded device is the same at low voltage as before the experiment, and is gradually dominated by space-charge-limited-conduction (SCLC) as the voltage rises, finally showing ballistic transport characteristics at high voltage.

Failure mechanism of 4H-SiC junction barrier Schottky diodes under harsh thermal cycling stress

The concern in the long-term reliability of the SiC power devies is raised lately in power electronic field due to its brief history and limited data. In this work, discrete 1200 V/20A SiC JBS diodes have been intensively investigated by HTRB, HAST, and TCT. 2 % samples have failed in the harsh thermal cycling test, showing that the failure mechanism is attributed to field-oxide cracking. The electrical and physical failure analysis pointed out that a gradual degradation occurred at the termination structure, causing non-recoverable damages and provoking a significant increase in the leakage current. The FIB cut and SEM analysis showed the delamination existence between field oxide layer and silicon carbide layer in the degraded devices. The observed leakage current after the TCT could be well correlated with the formation of the delamination, which created a current leaking path between active and termination region. These findings emphasize the importance of SiO2/SiC interface quality in the long-term highly reliable SiC power devices, and indicate further optimized design of SiO2 passivation layer or other alternative materials is urgently needed to overcome this structural weakness.

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.

The Optimization of 3.3 kV 4H-SiC JBS Diodes

The article reports a comprehensive study optimizing the OFF- and ON-state characteristics of 3.3 kV junction barrier Schottky (JBS) diodes made using nickel, titanium, and molybdenum contact metals. In this design, the same implants used in the optimized termination region are used to form the P-regions in the JBS active area. The width and spacing of the P-regions are varied to optimize both the ON- and OFF-state of the device. All the diodes tested displayed high blocking voltages and ideal turn-on characteristics up to the rated current of 2 A. However, the leakage current and the Schottky barrier height (SBH) were found to scale with the ratio of Schottky to p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions. Full Schottkys, without p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions, and those with very wide Schottky regions had the lowest SBH (1.61 eV for Ni, 1.11 eV for Mo, and 0.87 eV for Ti) and the highest leakage. Those diodes with the lowest Schottky openings of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 ~\mu \text{m}$ </tex-math></inline-formula> had the lowest OFF-state leakage, but they suffered severe pinching from the surrounding p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions, increasing their SBH. The best performing JBS diodes were Ni and Mo devices with the narrowest pitch, with the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> implants/Schottky regions both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 ~\mu \text{m}$ </tex-math></inline-formula> wide. These offered the best balanced device design, with excellent OFF-state performance, while the Schottky ratio guaranteed a relatively low forward voltage drop.

Optimization of Schottky-contact process on 4H-SiC Junction Barrier Schottky (JBS) Diodes

SiC Junction Barrier Schottky (JBS) Rectifier is a kind of unipolar power diode with low threshold voltage and high reverse blocking voltage. And the Schottky barrier Φ BN is a main technology parameter, which could greatly affect the forward conduction power and reverse leakage current in the JBS rectifiers. Therefore, it is necessary to balance the influence of Φ BN on the electrical characteristics of JBS rectifiers. In this paper, physical properties at the metal-semiconductor at the Schottky-contact could be optimized by the improvement of Schottky-contact process. And this optimization could significantly decrease Φ BN to reduce the on-state voltage drop V F and minimize negative impact on its reverse characteristics. After the completion of Silicon carbide JBS diodes, the static parameter electrical test was carried out on the wafer by using Keysight B1505A Power Device Analyzer/Curve Tracer. The test results show that the Schottky barrier height Φ BN of JBS Schottky rectifier manufactured by the modified Schottky foundation technology decreased from 1.19eV to 0.99eV and I R increased from 1.08μA to 3.73μA (reverse blocking voltage V R=1200V). It indicated that the power consumption of Schottky barrier junction in JBS rectifiers could be significantly reduced by about 25%, and I R could effectively be limited to less than 10μA.

Analysis of Floating Limiting Rings Termination Under Repetitive Avalanche Current Stress for 4H-SiC JBS Rectifiers

The reverse breakdown characteristics of 4H-SiC Junction Barrier Schottky (JBS) rectifiers adopting the different floating limiting rings (FLRs) termination structures are experimented and analyzed under the repetitive avalanche current stress. The experimental results indicate that the breakdown voltage (BV) shift of the device after the repetitive avalanche current stress is highly dependent on the FLRs design, which determines the distributions of the surface electric field and avalanche current at avalanche condition. It is proved that the uniform surface electric field distribution of the FLRs structure at avalanche condition is helpful for the device achieve to achieve better BV shift robustness on the repetitive avalanche current stress. Additionally, the FLRs structure, which has smaller S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and enough N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , can present both higher BV and excellent BV shift robustness on the repetitive avalanche current stress.

Design and Fabrication of 1.2 kV/10A 4H-SiC Junction Barrier Schottky Diodes with High Current Density

This paper presents an overall optimization procedure and the electrical performances of 1.2 kV/10 A 4H-SiC junction barrier Schottky (JBS) diodes with high current density. To achieve high current density, the epi-layer, the design parameters for active region including p-grid width and cell pitch, and the field limiting ring for edge termination were optimized with analytic calculation to estimate forward electrical performances and with Silvaco atlas™ simulator to estimate reverse electrical performances. Based on the systematic design, the JBS diodes were fabricated and electrically characterized. The experimental results showed that the breakdown voltage (BV) of JBS diode was significantly sensitive to field limiting ring (FLR) space and that the JBS diode with the ratio of pure Schottky contact area to total active area of 0.75 and the FLR space of 1.25 μm had optimum electrical performances such as a forward current density of 370 A/cm2, a reverse leakage current below 20 μA at the reverse anode voltage of 1.2 kV, and the BV of 1400 V. These were in coincidence with the simulation results within 10% error.

High Single-Event Burnout Resistance 4H-SiC Junction Barrier Schottky Diode

This paper presents a single-event burnout (SEB) resistance method for 4H-SiC Junction Barrier Schottky Diode (JBS) under high bias voltage and linear energy transfer (LET) conditions. The method is validated via two-dimensional numerical simulations. The analysis and comparison of conventional 4H-SiC JBS and 4H-SiC Multi-Buffer Layer JBS (MBL-JBS) diodes verify the resistance tolerance of the latter device to SEB. Silvaco TCAD simulation results prove that the 4H-SiC MBL-JBS modulates the drift region's electric field distribution and disperses the high-peak electric field at the N-/N+ junction. Moreover, it reduces the impact generation rate at the Schottky, PN and N-/N+ junctions to achieve SEB tolerance. The device's SEB performance is optimized by adjusting the 4H-SiC MBL-JBS structure parameters, and the SEB threshold voltage is significantly improved compared with the traditional structure.

1200-V 4H-SiC Merged p-i-n Schottky Diodes With High Avalanche Capability

In this article, the avalanche capability of the 1.2-kV 4H-SiC junction barrier Schottky (JBS) and merged p-i-n Schottky (MPS) diodes is investigated through simulation and experiments. For MPS diodes, the width of the wide P+ region (W) is found to have great effects on the device avalanche capability. MPS diodes with varied W-values (3-20 μm) and JBS diode are designed and fabricated, and their avalanche energy/current capability is tested with unclamped inductive switching tests. The experimental results show that the MPS diode has an optimized avalanche capability at W = 8-μm design. Simulation study reveals that the avalanche current is mainly distributed at the edges of the P+ regions in the JBS/MPS diodes as a result of the curvature-effect-induced electric field crowding. The localized current crowding and unbalanced current distribution in the avalanche mode contribute to a reduced effective power dissipation area and a weaker avalanche capability. The current nonuniformity coefficient (k) is used to characterize the severity of the current unbalance, and it is found that kdeclines as Wincreases when W = 3-8 μm and then gets increased when W exceeds 8 μm. Both the experimental and simulation results indicate that the MPS diode is superior to the JBS diode in avalanche capability, and the width of the wide P+ region in the MPS diode has an optimal design (8 μm in this article) which corresponds to the alleviated current crowding issue and 9%-19% improvement of the avalanche capability.

Origin and anomalous behavior of dominant defects in 4H-SiC studied by conventional and Laplace deep level transient spectroscopy

Several deep level defects were observed by conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS (LDLTS) in n-type 4H-SiC junction barrier Schottky diodes. We have shown that the broad DLTS peak labeled Z1/2 has, in fact, two components, Z1 and Z2, with activation enthalpies for electron emission of 0.63 eV and 0.68 eV, respectively. The reorientation process between these two components was observed. A combination of double-correlated DLTS and LDLTS demonstrated an anomalous reduction of the emission rate and an increase of the activation enthalpy of Z2 with an increase of the reverse bias applied to the diode. The possible explanation of this phenomenon could be correlated with a tensile stress in epitaxial SiC layers. The results observed are discussed in the frame of the model that correlates Z1 and Z2 with carbon vacancies (VC), located at hexagonal (h) and cubic (k) lattice sites, respectively. We also discussed the origin of other traps E0–E5 with particular emphasis on a N-related shallow donor level located at 0.04 eV below the conduction band, which has never been previously reported by DLTS studies.

High-Performance Temperature Sensors Based on Dual 4H-SiC JBS and SBD Devices.

Schottky diode-based temperature sensors are the most common commercially available temperature sensors, and they are attracting increasing interest owing to their higher Schottky barrier height compared to their silicon counterparts. Therefore, this paper presents a comparison of the thermal sensitivity variation trend in temperature sensors, based on dual 4H-SiC junction barrier Schottky (JBS) diodes and Schottky barrier diodes (SBDs). The forward bias current–voltage characteristics were acquired by sweeping the DC bias voltage from 0 to 3 V. The dual JBS sensor exhibited a higher peak sensitivity (4.32 mV/K) than the sensitivity exhibited by the SBD sensor (2.85 mV/K), at temperatures ranging from 298 to 573 K. The JBS sensor exhibited a higher ideality factor and barrier height owing to the p–n junction in JBS devices. The developed sensor showed good repeatability, maintaining a stable output over several cycles of measurements on different days. It is worth noting that the ideality factor and barrier height influenced the forward biased voltage, leading to a higher sensitivity for the JBS device compared to the SBD device. This allows the JBS device to be suitably integrated with SiC power management and control circuitry to create a sensing module capable of working at high temperatures.

Characteristic and Robustness of Trench Floating Limiting Rings for 4H-SiC Junction Barrier Schottky Rectifiers

In this letter, planar floating limiting rings (FLRs) and trench FLRs with different trench depths for the 4H-SiC junction barrier Schottky (JBS) rectifiers are analyzed and compared with simulations and experiments. Compared with the planar FLRs, the experimental results present that the first ring spacing window that termination efficiency exceeds 80% of the parallel plane breakdown voltage (BV) can be widened and termination area can be reduced at the same BV by adopting the trench FLRs. The simulations also indicate that there is an optimal trench depth for the trench FLRs and a smaller sidewall angle can achieve better device performance. Additionally, the repetitive avalanche current stress measurements imply that the trench FLRs has better robustness regarding the BV shift, achieving better device reliability.

Reverse-Bias Stress-Induced Electrical Parameters Instability in 4H-SiC JBS Diodes Terminated Nonequidistance FLRs

In this article, the breakdown voltage ( ${V}_{\text {BR}}$ ) shift of 4H-SiC Junction Barrier Schottky (JBS) diodes terminated by optimum nonequidistant field limiting rings (FLRs) subject to reverse-bias stress (RBS) has been investigated, and the corresponding mechanisms are studied in-depth. It can be observed that ${V}_{\text {BR}}$ gradually increases with increasing stress time, but there is no obvious shift of the forward voltage ( ${V}_{F}$ ). The increment in the magnitude of ${V}_{\text {BR}}$ induced by RBS testing is shown to depend strongly on the degree of applied reverse-bias voltage. The physical mechanism of ${V}_{\text {BR}}$ shift has been investigated and explained by means of numerical technical computer-aided design (T-CAD) simulations. Our analysis shows that the hole injection and trapping into SiO2 at the FLR terminal area are identified to be the main cause, resulting in the increase of ${V}_{\text {BR}}$ . Besides, a simple model is proposed to explain the behavior of ${V}_{\text {BR}}$ instability.

Degradation in electrothermal characteristics of 4H-SiC junction barrier Schottky diodes under high temperature power cycling stress

The electrothermal characteristics and degradation mechanism of 4H-SiC JBS under high temperature power cycling (HTPC) stress were investigated based on thermal structure function, failure analysis and electrothermal simulation. Results show that, the HTPC stress at different temperature conditions (maximum junction temperature Tjmax = 150 °C and Tjmax = 200 °C) have different effects on the reverse breakdown voltage (Vbr), reverse leakage current and the on-resistance (Ron-sp). It was that the increased reverse leakage currents with HTPC stress are due to the Schottky barrier lowering at the beginning. However, as the heat concentration effect increased at the metal/4H-SiC interface, the contribution of tunneling to leakage current is the major components. So the heat flux path and thermal distribution are very crucial to the reliability of chip and package. It can be concluded that the degradations of die-attach, die surface and metal/SiC interface are the main reliability limiting factors of SiC JBS diodes under high temperature applications.

Influence of Trench Design on the Electrical Properties of 650V 4H-SiC JBS Diodes

This work presents a design study of customized p+ arrays having influence on the electrical properties of manufactured 4H-SiC Junction Barrier Schottky (JBS) diodes with designated electrical characteristics of 5 A forward and 650 V blocking capabilities. The effect of the Schottky area consuming p+ grid on the forward voltage drop, the leakage current and therefore the breakdown voltage was investigated. A recessed p+ implantation, realized through trench etching before implanting the bottom of the trenches, results in a more effective shielding of the electrical field at the Schottky interface and therefore reduces the leakage current. Customizing the p+ grid array in combination with the trench structure, various JBS diode variants with active areas of 1.69 mm2 were fabricated whereas forward voltage drops of 1.58 V @ 5 A with blocking capabilities up to 1 kV were achieved.