Junction Barrier Schottky Rectifiers Research Articles

Mg-implanted vertical GaN junction barrier Schottky rectifiers with low on resistance, low turn-on voltage, and nearly ideal nondestructive breakdown voltage

Vertical GaN junction barrier Schottky (JBS) diodes with superior electrical characteristics and nondestructive breakdown were realized using selective-area p-type doping via Mg ion implantation and subsequent ultra-high-pressure annealing. Mg-ion implantation was performed into a 10 μm thick Si-doped GaN drift layer grown on a free-standing n-type GaN substrate. We fabricated the JBS diodes with different n-type GaN channel widths Ln = 1 and 1.5 μm. The JBS diodes, depending on Ln, exhibited on-resistance (RON) between 0.57 and 0.67 mΩ cm2, which is a record low value for vertical GaN Schottky barrier diodes (SBDs) and high breakdown (BV) between 660 and 675 V (84.4% of the ideal parallel plane BV). The obtained low RON of JBS diodes can be well explained in terms of the RON model, which includes n-type GaN channel resistance, spreading current effect, and substrate resistance. The reverse leakage current in JBS diodes was relatively low 103–104 times lower than in GaN SBDs. In addition, the JBS diode with lower Ln exhibited the leakage current significantly smaller (up to reverse bias 300 V) than in the JBS diode with large Ln, which was explained in terms of the reduced electric field near the Schottky interface. Furthermore, the JBS diodes showed a very high current density of 5.5 kA/cm2, a low turn-on voltage of 0.74 V, and no destruction against the rapid increase in the reverse current approximately by two orders of magnitude. This work demonstrated that GaN JBS diodes can be strong candidates for low loss power switching applications.

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.

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.

Experimental study and characterization of an ultrahigh-voltage Ni/4H–SiC junction barrier Schottky rectifier with near ideal performances

Abstract An ultra-high voltage SiC JBS (silicon carbide junction barrier Schottky) rectifier utilizing a novel area-efficient multi-zone gradient modulated field limiting ring (MGM-FLR) technique have been fabricated, measured, and analysed in this paper. Ni-Schottky metal with a high barrier height is used to achieve a better trade-off between the on-resistance and the breakdown voltage. MGM-FLR, which is implanted simultaneously with the P+ grids within the active area of the device, forms a similar variation of lateral doping to mitigate the electric field crowding caused by junction curvature effect and obtains a maximum blocking voltage with minimally sized edge termination area. The fabricated device is tested to obtain a specific on-resistance is 140 mΩ cm2 and a reverse breakdown voltage of 14 kV with the leakage current of 10 μA, which is quite close to the theoretical value of parallel plane junction calculated using the device parameter of drift region 100 μm and the concentration 5 × 1014 cm−3. The highest Baliga's figure-of-merit (BFOM) 5.6 GW/cm2 was obtained for the proposed devices. Furthermore, the distribution of the extracted barrier height versus ideality factor on the wafer are demonstrated using I–V method. Impacts of ring spacing and zone of MGM-FLR termination on SiC device reverse blocking performance are also investigated in detail.

A charge-based model of Junction Barrier Schottky rectifiers

A new charge-based model of the electric field distribution for Junction Barrier Schottky (JBS) diodes is presented, based on the description of the charge-sharing effect between the vertical Schottky junction and the lateral pn-junctions that constitute the active cell of the device. In our model, the inherently 2-D problem is transformed into a simple but accurate 1-D problem which has a closed analytical solution that captures the reshaping and reduction of the electric field profile responsible for the improved electrical performance of these devices, while preserving physically meaningful expressions that depend on relevant device parameters. The validation of the model is performed by comparing calculated electric field profiles with drift-diffusion simulations of a JBS device showing good agreement. Even though other fully 2-D models already available provide higher accuracy, they lack physical insight making the proposed model an useful tool for device design.

Vertical GaN Junction Barrier Schottky Rectifiers by Selective Ion Implantation

This letter demonstrates vertical GaN junction barrier Schottky (JBS) rectifiers fabricated with novel ion implantation techniques. We used two different methods to form the lateral p-n grids below the Schottky contact: 1) Mg implantation into n-GaN to form p-wells and 2) Si implantation into p-GaN to form n-wells. Specific differential ON-resistances ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) of 1.5–2.5 $\text{m}\Omega ~\cdot $ cm2 and 7–9 $\text{m}\Omega ~\cdot $ cm2 were obtained in the Mg-implanted and Si-implanted JBS rectifiers, respectively. A breakdown voltage of 500–600 V was achieved in both devices, with a leakage current at high reverse biases at least 100-fold lower than conventional vertical GaN Schottky barrier diodes. The impact of n-well and p-well widths on the ${R}_{ \mathrm{\scriptscriptstyle ON}}$ and BV was investigated. Fast switching capability was also demonstrated. This letter shows the feasibility of forming patterned p-n junctions by novel ion implantation techniques, to enable high-performance vertical GaN power devices.

Isothermal current–voltage characteristics of high-voltage 4H-SiC junction barrier Schottky rectifiers

The forward-pulse isothermal current–voltage characteristics of 4H-SiC junction barrier Schottky rectifiers (JBSs) with a nominal blocking voltage of 1700 V are measured in the temperature range from–80 to +90°C (193–363 K) up to current densities j of ~5600 A/cm2 at–80°C and 3000 A/cm2 at +90°C. In these measurements, the overheating of the structures relative to the ambient temperature, ΔT, did not exceed several degrees. At higher current densities, the effective injection of minority carriers (holes) into the base of the structures is observed, which is accompanied by the appearance of an S-type differential resistance. The pulsed isothermal current–voltage characteristics are also measured at a temperature of 77 K.

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.

1.4 kV Junction barrier Schottky rectifier with mixed trench structure

Junction barrier Schottky (JBS) rectifier with mixed trench structure on 4H-SiC for improving the electrical performance is proposed. The device shows the increasing forward current density compared to the common JBS rectifier on 4H-SiC because of the larger Schottky contact area without considerable degradation of breakdown voltage. This work is solely based on simulations with Silvaco TCAD tool. The forward current density of this device with 1.5 µm Schottky region depth of the trench structure is 102 A/cm2 at the forward voltage drop of 3 V while the current density of the common JBS is 70 A/cm2. The proposed structure improves the forward voltage drop at 100 A/cm2 effectively by 23%. The reverse characteristic and output capacitance of this device are similar to common JBS rectifier. In addition, in this work the forward and reverse characteristic of the proposed device at room and high temperatures is simulated.

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.

High Voltage SiC JBS Diodes with Multiple Zone Junction Termination Extension Using Single Etching Step

A novel variation of lateral etching junction termination extension (VLE-JTE) for Silicon carbide (SiC) power junction barrier Schottky rectifier (JBS) using a single mask is proposed and investigated. Simulation results shows that the breakdown voltage of JBS terminated with VLE-JTE can achieve 6500V, reaching up to more than 95% of parallel-plane junction bulk breakdown. Moreover, it implements a single mask with window areas varying laterally away from the main junction instead of extra ion implantation or etching steps to achieve multiple-zone JTE, making it easier to be implemented in applications.

Junction barrier Schottky rectifier with an improved P-well region

A junction barrier Schottky (JBS) rectifier with an improved P-well on 4H—SiC is proposed to improve the VF—IR trade-off and the breakdown voltage. The reverse current density of the proposed JBS rectifier at 300 K and 800 V is about 3.3×10−8 times that of the common JBS rectifier at no expense of the forward voltage drop. This is because the depletion layer thickness in the P-well region at the same reverse voltage is larger than in the P+ grid, resulting in a lower spreading current and tunneling current. As a result, the breakdown voltage of the proposed JBS rectifier is over 1.6 kV, that is about 0.8 times more than that of the common JBS rectifier due to the uniform electric field. Although the series resistance of the proposed JBS rectifier is a little larger than that of the common JBS rectifier, the figure of merit (FOM) of the proposed JBS rectifier is about 2.9 times that of the common JBS rectifier. Based on simulating the values of susceptibility of the two JBS rectifiers to electrostatic discharge (ESD) in the human body model (HBM) circuits, the failure energy of the proposed JBS rectifier increases 17% compared with that of the common JBS rectifier.

High-Performance Junction Barrier Schottky Rectifier With Optimized Structure

Junction barrier Schottky (JBS) rectifiers with p-well on 4H-SiC for improving the electrical performance are proposed. Compared with the common JBS rectifier, the devices show an increasing breakdown voltage due to a uniform electric field. Forward and reverse characteristics have been verified at room and elevated temperatures. As a result, the breakdown voltage of 1.9 kV was obtained for the JBS rectifier with the P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> grids on the p-well (POP), and that of the JBS rectifier with the P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> grids in the p-well (PIP) is about 1.6 kV. The forward voltage drops of the POP and PIP JBS rectifiers at a current density of 100 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are 3 and 3.2 V, respectively. The POP and PIP JBS rectifiers have more than 3.3 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> and 5.4 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> on/off (1 V/ -500 V) current ratios, respectively. In addition, the output capacitance of the POP JBS rectifier at -3 V reduces about 15% relative to that of the common JBS rectifier. In addition, the figures of merit of the POP and PIP JBS rectifiers are about 4.1 times and 2.9 times that of the common JBS rectifier, respectively.

Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region

This paper proposes a double epi-layers 4H–SiC junction barrier Schottky rectifier (JBSR) with embedded P layer (EPL) in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage (BV) and low specific on-resistance (Ron,sp). The influences of device parameters, such as the depth of the embedded P+ regions, the space between them and the doping concentration of the drift region, etc., on BV and Ron,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga's figure of merit (BFOM) is increased by 67.9% compared to a conventional 4H–SiC JBSR.

Advanced High-Voltage 4H-SiC Schottky Rectifiers

This paper presents advanced 4H-SiC high-voltage Schottky rectifiers with improved performance when compared to conventional 4H-SiC Schottky rectifiers. Two types of 4H-SiC junction barrier Schottky (JBS) rectifiers have been explored. These rectifiers offer Schottky-like ON-state and fast switching characteristics, while their OFF-state characteristics have a low leakage current similar to that of the PiN junction rectifier. Planar 4H-SiC JBS rectifiers, with more than 1-kV blocking capability and orders of magnitude lower reverse leakage current than that of conventional SiC Schottky rectifiers, have been demonstrated. In addition, a novel device structure, called lateral channel JBS rectifier, was designed and experimentally demonstrated in 4H-SiC with up to 1.5-kV blocking capability and pinlike reverse characteristics.

Analytical Modeling of High-Voltage 4H-SiC Junction Barrier Schottky (JBS) Rectifiers

We develop a new analytical model for the junction barrier Schottky (JBS) rectifier and apply it to high-voltage 4H-SiC JBS rectifiers. This model uses a novel method to approximate the electric field at the Schottky contact, which is together with the Fowler-Nordheim tunneling equation to accurately calculate the reverse leakage current of a high-voltage 4H-SiC JBS rectifier. The forward on-resistance of a high-voltage 4H-SiC JBS rectifier consists of several components, which are dominated by the spreading resistances in the drift layer. Moreover, this model has been verified by comparing the simulation and experimental results, and they are shown to be in good agreement.

Design, fabrication, and characterization of low forward drop, low leakage, 1-kV 4H-SiC JBS rectifiers

The 1-kV 4H-SiC planar junction barrier Schottky (JBS) rectifiers were designed, fabricated, and characterized. Different p+ implantation dosages and activation anneal methods were used to determine an optimum baseline process. Using the optimized process, the forward drop of our JBS rectifiers is <1.5 V while the reverse leakage current density is <1/spl times/10/sup -5/ A/cm/sup -2/. Blocking voltage>1 kV was achieved using a single-zone junction termination extension termination. It was shown experimentally that 4-/spl mu/m p-type implantation window spacing gives an optimum tradeoff between forward drop voltage and leakage current density for these rectifiers, yielding a specific on-resistance of 3 m/spl Omega//spl middot/cm/sup 2/.