Junction Termination Structure Research Articles

Modulation of Diamond PN Junction Diode with Double-Layered n-Type Diamond by Using TCAD Simulation

This study proposed a novel double-layer junction termination structure for vertical diamond-based PN junction diodes (PND). The effects of the geometry and doping concentration of the junction termination structure on the PNDs’ electrical properties are investigated using Silvaco TCAD software (Version 5.0.10.R). It demonstrates that the electric performances of PND with a single n-type diamond layer are sensitive to the doping concentration and electrode location of the n-type diamond. To further suppress the electric field crowding and obtain a better balance between breakdown voltage and on-resistance, a double-layer junction termination structure is introduced and evaluated, yielding significantly improved electronic performances. Those results provide some useful thoughts for the design of vertical diamond PND devices.

Optimization of Two‐Zone Step‐Etched Junction Termination Structures for Vertical GaN Power Devices

Optimization of Two‐Zone Step‐Etched Junction Termination Structures for Vertical GaN Power Devices

Comparison in radiation tolerance between FLR planar junction termination and positive bevel edge termination for power diodes

In this paper, a coupled electro-thermal simulation model is established to investigate the single event burnout (SEB)-induced failure in power diode. The radiation tolerance of the two different termination structures, the field limiting ring (FLR) planar junction termination and the positive bevel edge termination, is revealed comparatively. Firstly, through the comparison in the SEB threshold voltage, our simulation results indicate that the positive bevel edge termination exhibits a stronger robustness to SEB. The difference in the anti-radiation performance can even reach 29.02% under the same ion incidence condition. Then, to fully understand why there is such a large difference in the radiation tolerance, we observed the entire failure process and obtained the SEB mechanism for the two termination structures. For the FLR planar junction termination, the edge of the main junction is the most sensitive region to SEB, since the high electric field here caused by the junction curvature effect can easily lead to the strong carrier multiplication and a large localized current density. By contrast, for the positive bevel edge termination, the electric field can be effectively reduced along the beveled surface, therefore, there is no electric field crowding at the edge of the pn junction. As a result, the positive bevel edge termination naturally exhibits a superior anti-radiation performance compared to the FLR planar junction termination structure.

Design of vertical diamond Schottky barrier diode with a novel beveled junction termination extension

In this paper, vertical diamond Schottky barrier diode with a beveled junction termination extension is designed by using Silvaco TCAD. We firstly investigate the effects of the pn junction termination extension on the electrical performances to optimize the doping concentration. In addition, the beveled structure with an angle of 45° decreases the current conduction path slightly, but it also enhances the reverse breakdown voltage effectively. By combining the junction termination extension and beveled structures, a new termination structure is proposed for the vertical diamond Schottky barrier diode. Under forward bias, the depletion region introduced by the pn junction hindrances the current conduction slightly and increases the on-resistance. However, the electric field crowding phenomenon is alleviated drastically under reverse bias, resulting in a more uniform electric field distribution and high breakdown voltage. Therefore, the beveled junction termination structure is promising to balance the on-resistance and the reverse breakdown voltage of the diamond Schottky barrier diode.

Hybrid Junction Termination Consisting of a Variation Lateral Doping Structure and a Spiral Polysilicon Resistive Field Plate

A hybrid junction termination structure consisting of a variation lateral doping (VLD) region and a spiral polysilicon resistive field plate (PRFP) is proposed in this brief. Surface electric fields of the VLD region are modulated by the PRFP and distribute more uniformly. Compared with the conventional VLD structure with the same size, its measured breakdown voltage increases by 11%. The breakdown voltage still has a positive temperature coefficient. And, the leakage current changes very little from −40 to 150 °C. Besides, it is more immune to the deviation of the VLD dosage. The deviation range of the VLD dosage increase from −20% - +20% to −50% - +60% when the breakdown voltage keeps above 90% of the maximum value. No extra masks or process steps are needed in power devices with a MOS gate structure, because the gate layer can be used to implement the spiral PRFP. At last, the hybrid termination is not detrimental to the switching characteristic of the device.

Optimization of junction termination extension for ultrahigh voltage 4H-SiC planar power devices

Numerical simulations on the optimization of junction termination extension (JTE) have been performed. Various termination techniques have been applied and simulated in this paper, such as single-zone JTE (S-JTE), multi-zone JTE (M-JTE), and space-modulated JTE (SM-JTE). A completely novel and efficient method is demonstrated in this paper to determine total length of SM-JTE, and it is verified through simulation results. The simulation results show that the SM-JTE could provide a protection efficiency (defined in Section ) of 95.2%, which is much higher than that of M-JTE (82.4%) and S-JTE (64.7%). Based on the fabricated MOSFETs, the interface charge density is extracted and the approximate range of charge density has been determined. The influences of different interface charge densities have been investigated for the three termination techniques respectively. According to the previous reports, the JTE is quite sensitive to the implanted dose, so the blocking capability of each termination structure with different implanted doses is also simulated. The results show that when interface charge is considered, the SM-JTE always shows an enormous advantage over the other two junction termination structures, however the interface charge densities varied. The space-modulated JTE is also applicable to the power planar devices such as MOSFETs and IGBTs, which would provide a very promising lower fabrication cost.

Breakdown Characteristics of 15-kV-Class 4H-SiC PiN Diodes With Various Junction Termination Structures

15-kV-class 4H-SiC PiN diodes with various junction termination structures have been experimentally investigated. Employment of the space-modulated junction termination extension (SM-JTE) and the two-zone JTE have realized a breakdown voltage over 15 kV, corresponding to 93% of the parallel-plane breakdown voltage. The window of the implanted JTE dose to achieve the ultrahigh voltage has been enlarged, which indicates the robustness to the deviation of effective JTE dose. From the comparison of the experimental JTE-dose dependence of breakdown voltage with the numerical device simulation, a shift toward the heavier JTE-dose region was observed. To explain the phenomenon, effects of the charges at the SiO2/SiC interface are discussed.

Simulation and design of junction termination structures for diamond Schottky diodes

In this paper, the first step of the design of a junction termination structure usable on diamond Schottky diodes is introduced. Through the collaboration of AMPERE and LAAS laboratories, a study of junction termination structures using field plates and semi-resistive materials was carried out. Several results from simulations of p-type Schottky diodes protected by MESA etching and coated with several layers of dielectric materials are shown in this paper. The analysis of those simulations, conducted on pseudo-vertical diodes protected by a field plate on a semi-resistive layer deposited on top of a dielectric, shows a great efficiency of such junction termination structures.

Measurements of impact ionization coefficients of electrons and holes in 4H‐SiC and their application to device simulation

AbstractThis article is intended to review measurements and modeling of anisotropic impact ionization coefficients of electrons and holes in 4H‐SiC. Owing to the hexagonal crystal structure, the carrier transport in 4H‐SiC shows anisotropy, such as anisotropic mobility and anisotropic impact ionization coefficients. The anisotropy of impact ionization coefficients brings about the difference in the breakdown voltage of p+n diodes on Si‐face and A‐face. Experiments showed that the breakdown voltage of a p+n diode on A‐face is 62 percent of that on Si‐face. This difference in breakdown voltage corresponds to 81 percent of anisotropy in breakdown fields. The impact ionization coefficients parallel and perpendicular to c‐axis were extracted from measurements of the breakdown voltage and the multiplication factor of holes in high electric fields. The analytical model of the anisotropic impact ionization coefficients, which interpolates impact ionization coefficients parallel and perpendicular to c‐axis, was derived, considering the energy transport in the avalanche phenomena. The effects of anisotropic impact ionization coefficients on the avalanche breakdown in 4H‐SiC power devices are examined. We show that the avalanche breakdown voltage of a power device is affected by the anisotropy of impact ionization coefficients, because avalanche breakdown occurs at the field crowding point at peripheral edge of power device, where the lateral field dominates. Finally, we show that the optimized two‐zone junction termination structure suppresses the degradation of the breakdown voltage caused by anisotropy of the impact ionization coefficients. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bevel Mesa Combined with Implanted Junction Termination Structure for 10 kV SiC PiN Diodes

A 10 kV 4H-SiC PiN diode with an improved junction termination structure has been fabricated. An improved bevel mesa structure, nearly vertical side-wall at the edge of pn junction and rounded corner at mesa bottom, has been formed by reactive ion etching (RIE). The junction termination extension (JTE) region has been optimized by device simulation, and simulated breakdown voltage has been compared with experimental results. The locations of electric field crowding and diode breakdown have been discussed.

Simulation and Experimental Study on the Junction Termination Structure for High-Voltage 4H-SiC PiN Diodes

Designing and fabrication of 10-kV 4H-SiC PiN diodes with an improved junction termination structure have been investigated. An improved bevel mesa structure and a single-zone junction termination extension (JTE) have been employed to achieve a high breakdown voltage (ges 10 kV). The improved bevel mesa structure, nearly a vertical sidewall at the edge of the p-n junction and a gradual slope at the mesa bottom, has been fabricated by reactive ion etching. The effectiveness of the improved bevel mesa structure has been experimentally demonstrated. The JTE region has been optimized by device simulation, and the JTE dose dependence of the breakdown voltage has been compared with experimental results. A 4H-SiC PiN diode with a JTE dose of 1.1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> has exhibited a high blocking voltage of 10.2 kV. The locations of electric field crowding and breakdown are also discussed.

Characterization and TCAD modelling of termination structures for silicon radiation detectors

We have recently proposed a novel junction termination structure for silicon radiation detectors, featuring all-p-type multiguard and scribe-line implants, with metal field-plates completely covering the gap between the implanted rings. The structure is intended for detector long-term stability enhancement even in adverse ambient conditions and for fabrication-process simplification. A thorough static characterization, including stability measurements in varying humidity conditions, has been carried out on a variety of samples fabricated at ITC-irst. Comparisons with diodes featuring an n-type implant along the border—or no edge structure at all—have been performed. The new structures show stable behaviour at relatively high bias (∼200 V) , also in the presence of wide humidity changes (1–90%). A good qualitative agreement has been obtained between experimental results and simulation predictions, allowing to gain deep insight into the physical behaviour of the device.

An improved termination structure for silicon radiation detectors with all-P-type multiguard and cut-line implants

A junction termination structure for silicon radiation detectors is investigated, featuring all-p-type multiguard and scribe-line implants, with metal field-plates providing complete coverage of the oxide upper surface above nonimplanted regions. The sensitive interface between oxide and n-type substrate is thus electrostatically screened from the external environment, resulting in improved long-term stability of the device and excellent insensitivity to ambient conditions both before and after X-ray and neutron irradiations. Careful design of the multiguard layout enables high-voltage operation to be achieved. With respect to a previously proposed structure, the adoption of alternate outward and inward field plates between adjacent rings allows a significant improvement in the voltage handling capability.

Design of junction termination structures for GaN Schottky power rectifiers

Junction termination extension (JTE) structures for GaN power Schottky rectifiers were investigated using a quasi-three-dimensional simulator. The use of single JTE edge termination was found to produce an almost fivefold increase in reverse breakdown voltage ( V B) over an unterminated rectifier fabricated on the same bulk GaN substrate. The use of p + guard rings or planar junction termination with oxide field plates also offers significant enhancements in V B relative to unterminated rectifiers. V B was found to be a strong function of the JTE doping concentration and the p + guard-ring spacing.

Investigation of efficient termination structure for improved breakdown properties of semiconductor radiation detectors

Efficiency of a new junction termination structure for improvement of breakdown properties of semiconductor radiation detectors is investigated. The structure consists of a diffused resistor winding around the active junction in a spiral fashion. The current flow through the spiral enables controlled potential distribution along the spiral turns and thus controlled depletion spreading from the main junction, efficiently preventing premature avalanche breakdown. Both, multiple guard-ring structures and spiral junction termination structures have shown good breakdown properties typically three to five times higher than breakdown voltages of diodes without junction termination. The breakdown voltages of spiral junction termination structures are only weakly influenced by changes in substrate doping concentration caused by neutron irradiation. They can thus be considered for termination of future semiconductor radiation detectors.

Spiral junction termination

A new junction termination structure composed of a decreasing width spiral diffused resistor connecting anode and cathode region is presented. Leakage current through the spiral resistor results in optimized voltage distribution between the spiral turns which effectively reduces high electric field at the anode junction curvature. By circuit mode device modeling approach, the influence of several design parameters of importance on the breakdown properties were investigated. A major concern was shown to be the possibility of a premature reach-through between the spiral turns, resulting in increased leakage current and soft breakdown characteristics. A design with nonuniform spiral width and optimized spacing between the spiral turns is proposed, enabling almost ideal breakdown voltages with reduced spiral leakage current and eliminated reach-through between the spiral turns. Low susceptibility to oxide charges is confirmed by irradiation test, showing improvement of breakdown properties after irradiation. Further improvement in operation is obtained by a floating spiral structure due to spiral resistance limiting the increase of the multiplication induced current through the spiral. In comparison with common termination structures the spiral junction termination offers simple design and processing, close to ideal breakdown voltages and high reliability of operation.

Analysis of a junction termination structure for ideal breakdown voltage in p-n junction devices

Electric-field distribution and avalanche breakdown voltage in reverse-biased p-n junction devices having a concave p-n junction termination structure are analyzed by a two-dimensional numerical method. It is shown that there are two peaks in the electric field of the device. One peak, near the p-n junction edge, is smaller than the other peak, found in the one-dimensional region, so that an ideal breakdown voltage can be obtained. This desirable feature comes partly from the excessive spreading of the depletion layer around the p-n junction edge due to the concave junction shape. One of the merits of this junction termination structure is that the allowable range of device parameters for the ideal breakdown voltage is much wider than for any other junction termination structure. Experimental breakdown voltage of a diode with the concave p-n junction structure agrees well with the ideal breakdown voltage calculated in the one-dimensional region of the device.