Trench Junction Research Articles

Design Space of GaN Vertical Trench Junction Barrier Schottky Diodes: Comprehensive Study and Analytical Modeling

We report gallium nitride (GaN) vertical trench junction barrier Schottky (TJBS) diodes and systematically analyzed the effects of the key design parameters on the reverse and forward characteristics of the devices. By taking advantage of the shielding effects from both the trenches and pn junctions in the TJBS structure, the high electric field at the Schottky contact region can be effectively suppressed. We found that the doping concentration, thickness, and spacing of p-GaN, as well as the depth and angle of the trench sidewalls are closely associated with the electric field distribution and the reverse characteristics of the TJBS diodes. With an optimal set of design parameters, the local electric field crowding at either the corner of the trench or the edge of the p-GaN can also be alleviated, resulting in a boosted breakdown voltage of up to 1250 V in the TJBS diodes. In addition, an analytical model was developed to explore the physical mechanism behind the forward conduction behaviors. We believe that the results can provide a systematical design strategy for the development of low-loss, high-voltage, and high-power GaN power diodes towards an efficient power system.

A SiC sidewall enhanced trench JBS diode with improved forward performance

A new high-performance sidewall enhanced trench junction barrier Schottky (SET-JBS) diode is proposed in this article. In the proposed SET-JBS diode, in addition to the Schottky contact on the top anode, the sidewall of the trenches also introduces Schottky contacts, which not only increases the Schottky contact area, but also weakens the junction field-effect transistor effect of the device, resulting in a high forward current density and a low specific on-resistance (R on,sp) with a small increase in reverse leakage current (J L). Simulation results show that the R on,sp of the proposed SET-JBS diode is reduced by 21.6%–46.7% with less than an order of magnitude increase in leakage current compared with that of the conventional trench JBS (T-JBS) diode when the trench distance is from 2.1 μm to 1.2 μm at the 2 μm trench depth. And the SET-JBS diode also performs better than the trench MOS barrier Schottky (TMBS) diode when comprehensively considered the R on,sp and J L. And the figure of merit and the trade-off relationship between the R on,sp and the breakdown voltage of the proposed SET-JBS both are better than those of the conventional T-JBS diode and TMBS diode. The forward I–V analytical model of the SET-JBS is also proposed, which is in good agreement with the simulation results. All the simulation results indicate that the proposed SET-JBS diode has promising potential in power electronics applications.

Deep crustal structure in the Taiwan–Ryukyu arc–trench system junction area: New constraints from gravity modelling

AbstractThe Taiwan–Ryukyu arc–trench junction area is a seismic active region and has high potential to generate large earthquakes. However, the detailed deep structures are not fully revealed because of data resolution problems. The Taiwan Integrated Geodynamic Research (TAIGER) project collected two wide‐angle and multichannel seismic profiles across the Taiwan mountain belt (T5) and the western end of the Ryukyu arc–trench system (T6). In this study, we perform 2‐D gravity modelling for T5 and T6 by taking advantage of well‐constrained P‐wave velocity models, which helps to reduce the nonunique problem. To better fit the observed gravity anomaly, a block with relatively high‐density must exist beneath eastern Taiwan. This high‐density material could be serpentinised mantle, which may be resulted from the dehydration of the subducting Eurasian plate. Also, our result indicates that the subducting Gagua Ridge has a deep crustal root and extends northward to the Ryukyu forearc area.

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.

Mechanisms and Characteristics of Large-Area High-Current-Density 4H-SiC Trench Junction Barrier Schottky Diodes

Mechanisms and characteristics of optimized main junction for 4H-SiC trench junction barrier Schottky (TMJBS) diodes were investigated by theories and experiments. From these simulation and experimental values, we can conclude that TMJBS device has better reverse performance, such as the best reverse blocking capability and lowest reverse surface leakage current than the conventional JBS and TJBS device while maintaining good forward characteristics. Furthermore, The large area TMJBS Diodes with high current density show the better reverse characteristics than the small area one at an acceptable forward characteristics. The TMJBS structure can significantly reduce the influence of the Schottky interface and is more suitable for manufacturing high current density and large area devices.

Optimized Designing to Improve Electrical Characteristics of 4H–SiC Wide Trench Junction Barrier Schottky Diode

Optimized Designing to Improve Electrical Characteristics of 4H–SiC Wide Trench Junction Barrier Schottky Diode

Seismogenesis of dual subduction beneath Kanto, central Japan controlled by fluid release

Dual subduction represents an unusual case of subduction where one oceanic plate subducts on top of another, creating a highly complex tectonic setting. Because of the complex interaction between the two subducted plates, the origin of seismicity in such region is still not fully understood. Here we investigate the thermal structure of dual subduction beneath Kanto, central Japan formed as a consequence of a unique case of triple trench junction. Using high-resolution three-dimensional thermo-mechanical models tailored for the specific dual subduction settings beneath Kanto, we show that, compared with single-plate subduction systems, subduction of double slabs produces a strong variation of mantle flow, thermal and fluid release pattern that strongly controls the regional seismicity distribution. Here the deepening of seismicity in the Pacific slab located under the Philippine Sea slab is explained by delaying at greater depths (~150 km depth) of the eclogitization front in this region. On the other hand, the shallower seismicity observed in the Philippine Sea slab is related to a young and warm plate subduction and probably to the presence of a hot mantle flow traveling underneath the slab and then moving upward on top of the slab.

Effect of trench structure on reverse characteristics of 4H-SiC junction barrier Schottky diodes

We investigated 4H-SiC trench junction barrier Schottky (JBS) diodes from the viewpoints of the tradeoff between the electric field at the Schottky contact interface (Es) and the forward voltage drop, the effect on reduction of reverse leakage current, and the device yield. By calculating Es, we found that the trench JBS structure can make Es one order of magnitude smaller than that of the planar JBS structure, when the bevel angle (θ) is set between 80 and 90°. Moreover, 600 V/50 A trench JBS diodes were fabricated, and their reverse leakage current at 600 V was made 102 times smaller than that of the planar JBS diode by effectively reducing Es. We also found that this reduction in reverse leakage current decreases the number of low breakdown voltage samples below 600 V and improves the yield.

Simulation of 4H-SiC Trench Junction Barrier Schottky Diodes with High-k Dielectrics

In this paper, a novel 4H-SiC trench JBS (TkJBS) with high-k semi-insulating polycrystalline silicon (SIPOS) is proposed. By adopting a new high-k dielectrics-trench structure, the peak electric field at the corner of P+ region (COP) in Silicon Carbide (SiC) can be weakened significantly, and the device breakdown voltage can be enhanced significantly. SiC TkJBS has a 60.7% higher breakdown voltage (BV) and a 110.6% higher Baliga’s figure of merit (BFOM) than the conventional SiC JBSs, and the surface electric field (Esf) of the SiC TkJBS is 0.73 MV/cm lower than it at breakdown voltages, resulting in a much lower tunneling current (Ir). The reverse recovery characteristics of SiC TkJBS are also slightly better than those of the SiC JBS. It is indicated that SiC TkJBS is a promising candidate for next-generation high power diodes.

On the analogy of the potential barrier of trenched JFET and JBS devices

4H–SiC Trench Junction Barrier Schottky (TJBS) diodes are good candidates for ultra–high voltage applications when low doped epilayers are required. In that case, electric fields of p+–n junctions deeply extend under the Schottky contact which may induce a potential barrier at thermal equilibrium condition, similarly to what happens into the channel of Trench Junction Field Effect Transistors (TJFET). For the first time, the analogy between potential barriers of 4H–SiC TJBS and TJFET devices is in depth investigated by using an original analytical model. For both devices, the model allows an accurate analysis of the potential barrier height into the channel as a function of the channel width, of the p+–region and trench depths, of the doping concentration and of the reverse voltage. Since the model is also capable to calculate the reverse diode current of TJBS until the vanishing of the potential barrier, it is used to explain the intrinsic differences of devices as the non–monotonic reverse behaviour of TJBs with the depth of the trenched mesa. The accuracy of the model is verified by comparisons with numerical simulations. The model makes a further contribution to the understanding of the role of p+–regions on TJBS performance.

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.

An Experimental Evaluation of SiC Switches in Soft-Switching Converters

Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimensioned with respect to additional losses due to the dynamic conduction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transistors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, therefore, several types of SiC transistors are compared to a state-of-the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied frequency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors.

Demonstration of SiC Vertical Trench JFET Reliability

This paper demonstrates the reliability of SiC vertical trench junction field-effect transistors (VJFET). Measurements are shown which prove that the device’s intrinsic gate-source pn junction is immune to degradation associated with recombination-enhanced dislocation glide. And after subjecting VJFETs to 1,000 hours of high-temperature bias stress, no measured parameter deviated from datasheet specifications. These results reflect the maturity and reliability of SemiSouth’s SiC VJFET technology, as well as tight process control over device parameters that are critical to circuit design and long-term system operation.

A Comparison of 1200 V Normally-OFF & Normally-on Vertical Trench SiC Power JFET Devices

Equivalent sized (4.5 mm2 die area), 1200 V, 4H-SiC, vertical trench Junction Field Effect Transistors (JFETs) were characterized in terms of DC and switching performance. The 100 mΩ Enhancement-Mode (EM) JFET was found to have natural advantages in safe operation being normally-off, whereas the Depletion-Mode (DM) JFET was found to have advantages with ~ twice as high saturation current, less on-resistance (85 mΩ) and no gate current required in the on-state. The JFETs were found to both have radically less (five to ten times) switching energies than corresponding 1200 V Si transistors, with the DM JFET and EM JFET having EON and EOFF of only 115 µJ and 173 µJ, respectively when tested at half-rated voltage (600 V) and 12 A.

A performance comparison of normally-off and normally-on SiC JFETs toward use in high-temperature power modules

The high-temperature static and dynamic characteristics of the new 1200 V, 45 mΩ, 9 mm2 depletion-mode SiC vertical trench junction field-effect transistor (vtJFET) are compared with those of a 1200 V, 50 mΩ, 9 mm2 enhancement-mode SiC vtJFET. It is shown that both devices are fully capable of high-temperature operation and that each type has its own unique advantages. For applications operating in extreme high-temperature environments, the larger saturation current (~2.5x) and lower on-state resistance (~150 mΩ at 250 °C) of the depletion-mode SiC vtJFET provide very attractive performance at temperatures beyond silicon's fundamental limitations. In addition, operating the normally-on vtJFET at VGS less than 2 V reduces the gate drive's current requirements to a negligible level, which is an important design factor for high-temperature power modules that use multiple die in parallel.

Normally-off trench JFET technology in 4H silicon carbide

A double gate normally-off silicon carbide (SiC) trench junction field effect transistors (JFET) design is considered. Innovative migration enhanced embedded epitaxial (ME 3) growth process was developed to replace the implantation process and realize high device performance. Strong anisotropic behavior in electrical characteristics of the pn junction fabricated on (1 1 −2 0) and (1 −1 0 0) trench a-planes was observed, although quality of the pn diodes was found to be independent of trench plane orientations. Fabricated normally-off trench 4H-SiC JFET demonstrates the potential for lower specific on-resistance ( R onS) in the range of 5–10 mΩ cm 2 (1200 V class). A relative high T −2.6 dependence of R onS is observed. A breakdown voltage of 400 V in the avalanche mode was confirmed at zero gate bias conditions for cell design without edge termination. It was demonstrated that the normally-off JFETs are suitable for high temperature applications. Average temperature coefficient of threshold voltage ( V th) was calculated as −1.8 mV/°C, which is close to the MOS based Si power devices.

Origin of negative gravity anomaly landward of trench junction

Off Urakawa, Hokkaido district landward of a junction of Chishima trench and Japan trench, there is a large negative gravity anomaly of about 200 mgals. Off Miyazaki, Kyushu district landward of a junction of Ryukyu trench and Nankai trough, there is also large negative gravity anomaly.If the oceanic plate uniformly moves, an excess mass is produced at the trench junction and the excess mass should be observed as a positive gravity anomaly. However, on the contrary, large negative anomaly is actually observed. The idea presented in this paper is that, the excess mass falls in the mantle, and this causes a depression of earth surface (free surface), and lack of mass at the surface produces negative free air gravity anomaly.The problems of surface deformation due to falling ball which is rigid and denser than the surround viscous material, were discussed by Morgan in 1965, 1), 2) and excellent papers were published. The deformations of the surface due to a rigid falling ball are divided into two parts. The one is due to direct attraction of the ball and gravity does not change though the surface sink in. The other is due to a current within the viscous fluid and the surface sink in and gravity changes. The amount of the change in gravity is roughly twice as large as gravity due to descending ball, with opposite sign.The water contained in sediment on the ocean floor is transported to a deeper part of the mantle by a descending plate. The water is released into a mantle of continent at the depth of about 150 km and, lowers melting temperature there and negative buoyancy of the plate changes to buoyancy. Therefore the depth is a limit of negative buoyancy of the plate. According to the idea, the excess mass at trench junction off Urakawa and off Miyazaki were estimated and tried to explain origin of negative gravity anomaly landward of trench junction.(Contributed by Yoshibumi TOMODA, M. J. A., Feb. 12, 2003)

Design and Processing of High-Voltage 4H-SiC Trench Junction Field-Effect Transistor

Design and Processing of High-Voltage 4H-SiC Trench Junction Field-Effect Transistor

Seismic evidence for a mantle plume oceanwards of the Kamchatka-Aleutian trench junction

SUMMARY A non-linear iterative P-wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km, rising across the 600 km discontinuity, and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate. Data from the Geophysical Survey of Russia (1955–1997) were inverted jointly with the catalogues of International Seismological Centre and USGS National Earthquake Information Centre (1964– 1998). The result shows a 300–500 kmwide cylindrical low-velocity anomaly (yx2 per cent) that extends from a depth of greater than 900 km to shallower than 200 km. The anomaly is almost vertical at depths up to y400 km and rises obliquely to the north up to y200 km under the ocean floor near the northern end of Emperor seamounts. Above y300 km depth a subsidiary anomaly extends subhorizontally to the NW in fair agreement with the direction of movement of the Pacific Plate. The overlying seafloor is characterized by anomalously high heat flow, which may be attributed to the thermal effect of the mantle plume.

The multiple inverse method applied to meso-scale faults in mid-Quaternary fore-arc sediments near the triple trench junction off central Japan

The multiple inverse method for fault-slip data is applied to meso-scale faults observed in mid-Quaternary fore-arc sediments near the triple trench junction off the Boso Peninsula, Japan. Data from the Otadai, Umegase and Kokumoto Formations were processed, and three stresses were obtained as significant solutions: vertical, axial compression, and triaxial stresses with the σ 3 axis in WNW–ESE and NNE–SSW directions. The triaxial stresses were determined from the Otadai and Umegase data. However, the WNW–ESE tensile stress is not detected from the youngest, Kokumoto, suggesting that the stress is older than the formation. The area was subject to a WNW–ESE tensile stress ∼1.2–1.0 Ma, but tensile direction changed to a NE–SW trend thereafter. The succession was simultaneous with a tectonic event in the landward slope of the Sagami Trough, suggesting that the subduction of the Philippine Sea plate affected the stresses in the overriding plate. The older tensile stress was probably a manifestation of the gravitational collapse of the Hayama–Mineoka ridge, which was growing parallel to the trough. The inferred stress history is concordant with the variation of plate convergence at the trough.