Trench MOS Barrier Schottky Research Articles

Enhancement of positive bevel β-Ga2O3 trench MOS barrier Schottky diode by post-etching treatment

Enhancement of positive bevel β-Ga2O3 trench MOS barrier Schottky diode by post-etching treatment

An improved 4H-SiC trench MOS barrier Schottky diode with current spreading layer and low resistance layer

This paper investigates an improved trench MOS barrier Schottky (TMBS) structure with extra double epitaxial layers (DE-TMBS) based on the conventional TMBS (C-TMBS) featuring a high-doped N-type current spreading layer (CSL) and a high-doped low resistance layer (LRL). Compared to the C-TMBS, the CSL in the improved structure is grown on the N-type drift region, and the LRL is extended on the CSL. According to the numerical simulations and analytical models, the specific on-resistance (Ron,sp) of DE-TMBS can be significantly reduced compared to the conventional one. This is primarily due to the high doping concentration in CSL, which effectively lowers both the JFET resistance and spreading resistance. Additionally, the increased doping concentration in LRL reduces the channel resistance and JFET resistance. Moreover, the doping concentration and thickness of CSL and LRL are optimized to maximize the figure of merit (FOM), that Ron,sp is reduced by 40.9 % and the FOM (BV2/Ron,sp) is improved by 67.9 % compared to the C-TMBS structure.

Post-trench restoration for vertical GaN power devices

The impact of the post-trench restoration on the electrical characteristics of vertical GaN power devices is systematically investigated in this work. Following the achievement of microtrench-free GaN trench structure with modified dry etching conditions, the post-trench tetramethylammonium hydroxide (TMAH)-based wet etching and UV/Ozone-based oxidation process are employed to further refine the trench profile. It is shown that the c-plane trench bottom is restored to the level of unetched surface, as evidenced by the improved Schottky interface. Additionally, the post-trench treatment exhibits the anisotropic characteristics with the preferred rounded corner profile on m-plane sidewall compared to a-plane sidewall. The simulations and experimental results demonstrate that the trench MOS barrier Schottky (TMBS) rectifier based on m-plane sidewall could suppress the electric field crowding at the trench corner and, hence, reduce the reverse leakage current by 1–2 orders of magnitude. Furthermore, the MOSCAP test structures were fabricated on the trenches. The extracted interface trap density (Dit) confirms the effective restoration of trench bottom. However, the sidewall surface exhibits the relatively large Dit, which emphasizes the necessity of optimizing the sidewall, particularly for devices incorporating sidewall channel. The demonstrated post-trench restoration technique improves the surface quality and trench structure for the significantly enhanced electrical performances, which is essential for the development of vertical GaN power devices.

Simulation study of a fast speed trench Schottky rectifier with an isolated gate

A novel trench Schottky rectifier with an isolated gate (IG-TSR) is proposed and investigated by simulation. It features an isolation of a trench MOS poly-gate from an anode metal in a conventional trench MOS barrier Schottky (TMBS) rectifier. In the proposed fabrication process, the isolation can be created by modifying the layout pattern without any additional process step or manufacturing cost. Because of the isolation of the trench MOS poly-gate from the anode metal, the capacitance between the cathode and the anode (Cds) of the proposed IG-TSR decreases significantly, which results in a fast switching performance. According to the simulation results, IG-TSR holds a 17.4% reduction in reverse recovery time (Trr) and a 22.1% reduction in reverse recovery peak current (Irm) compared with TMBS, and other related forward and reverse performances are basically unchanged. Therefore, the proposed IG-TSR is a competitive device for high frequency and high efficiency applications in power systems.

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.

Simulation study for GaN-based hybrid trench MOS barrier Schottky diode with an embedded p-type NiO termination: increased forward current density and enhanced breakdown voltage

In this work, a hybrid trench MOS barrier Schottky diode (TMBS) structure is proposed to improve both the forward current density and the breakdown voltage by using TCAD simulation tools. The hybrid structure means that the conventional TMBS rectifier is combined with a p-NiO/n-GaN diode. According to our study, when the device is in the forward-biased condition, the embedded p-type NiO layer forms a PN junction. This can modulate the lateral energy bands by removing the conduction band barriers for electrons. Thus, the improved current spreading effect and the better conductivity modulation can be obtained, leading to the increased current density. Meanwhile, the embedded p-type NiO layer can also help to reduce the electric field at the Schottky contact interface and the edge of anode contact/p-NiO layer interface. Thus, the breakdown voltage can be improved remarkably. Moreover, a detailed optimization strategy for the hybrid TMBS is also analyzed by varying the p-NiO layer thickness (T NiO) and the lengths of the anode electrode that is covered on the p-NiO layer (L A).

Systematic Design and Parametric Analysis of GaN Vertical Trench MOS Barrier Schottky Diode With p-GaN Shielding Rings

We report GaN vertical trench MOS barrier Schottky (TMBS) diodes with embedded p-GaN shielding rings (SRs) and systematically investigate the impact of different structural parameters of the p-GaN SRs on the breakdown performance of the GaN-based vertical TMBS diodes by numerical simulation. The charge coupling effect by the embedded p-n junction at the bottom of the trench homogenize the electric field at the trench corner and alleviate the electric field crowding effect at the Schottky contact region, which can effectively avoid the premature breakdown and improve the reverse blocking capability of the TMBS diodes. The p-GaN SRs can also broaden the overlapped depletion region and shift the pinch-off point into the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> -GaN drift region, thus facilitating the 2-D depletion in the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> -GaN drift layer and boosting the breakdown performance of the conventional TMBS diodes. We found that the doping concentration, thickness, and the width of the p-GaN SRs are closely associated with the electric field distribution and the reverse breakdown characteristics of the GaN-based vertical TMBS diodes. The vertical TMBS diodes with optimal p-GaN SR parameters featured a dramatic improvement in the breakdown voltage from 907 to 1281 V, without an obvious degradation in the ON performance. The proposed TMBS diodes with a p-GaN SR structure can pave the way toward a high-performance GaN vertical power device for high-power and high-efficiency power switch applications.

A low loss single-channel SiC trench MOSFET with integrated trench MOS barrier Schottky diode

A single-channel SiC trench MOSFET (SC-TMOS) with integrated trench MOS barrier Schottky diode (TMBS) is proposed and investigated in this paper. The electric field at the Schottky interface is reduced to 0.37 MV cm−1 by the trench MOS and P+ shield under the gate, which completely suppresses the leakage current through the TMBS. The on-state voltage drop (V R_ON) of the SC-TMOS in reverse conduction state is reduced to 1.59 V (@J SD = 400 A cm−2) compared to 2.93 V of the PN body diode of a conventional trench MOSFET (C-TMOS) and 1.61 V of a three-level protection trench MOSFET (TP-TMOS). Meanwhile, higher BFOM (Baliga’s figure of merit: BV2/R on,sp) is obtained, which is 11.8% and 40% improved compared with those of the C-TMOS and TP-TMOS, respectively. Besides, the reverse recovery charge of the SC-TMOS is reduced by 41.7% and 66.4% compared with those of the C-TMOS with or without external junction barrier Schottky diode (JBS), and is comparable with that of the TP-TMOS. Moreover, with optimized design, C GS and C GD decrease dramatically. As a result, the total inductive switching loss of the proposed SC-TMOS is reduced by 19.5%, 43.2% and 28.8% compared with those of the C-TMOS with or without external JBS and TP-TMOS, respectively.

A 600V split-gate VDMOS with integrated trench MOS barrier Schottky

ABSTRACT In this paper, a novel 600 V split-gate VDMOS with the integrated trench MOS barrier Schottky (TMBS) is proposed to reduce the specific gate-drain charge (Q gd,sp) and specific reverse recovery charge (QRR). For the proposed device, the TMBS is distributed in the JFET region, and it offers a majority of the freewheeling current (IF) during the reverse-recovery period resulted in a great reduction in QRR. The TMBS also works as the vertical field plates (VFPs) in the blocking mode; therefore, the breakdown voltage (BV) is not degraded when the anti-JFET implantation is introduced to decreased the specific on-resistance (R on,sp). Compared with the conventional VDMOS (C-VDMOS), the simulation shows that QRR and Q gd,sp of the proposed structure are reduced by 68.8% and 78.4%, respectively, when the work function of Schottky contact is 4.85 eV. Moreover, R on,sp is also decreased by 25.1%.

Influence of Geometrical Dimensions on Negative Differential Resistance in Silicon Based Trench MOS Barrier Schottky Diode

In this paper, ISE-TCAD, a device simulation software, is used to carry out simulation experiments on silicon-based trench MOS Schottky (TMBS) diodes with different trench dimensions under the condition of forward biases and obtain a series of experiment data associated with the negative resistance. Simulation results show that TMBS diodes under forward biases produce the negative resistance effect. The negative resistance effect intensifies linearly with the increase of mesa width and mitigates wavily with the increase of trench depth. The coupling effect of trench oxidization layer on electric field attenuates the change in device field strength, leading to the fact that TMBS devices present a weaker negative resistance effect than trench barrier Schottky (TBS) diodes which have the same parameters, but are free of oxidization layer. The study result provides a feasible basis for the effective application of TMBS negative resistance features to the design and production of corresponding semiconductor devices and circuits.

Research on the Negative Resistance Characteristics of Silicon-based Trench MOS Barrier Schottky Diodes

The negative resistance characteristics of Trench MOS Barrier Schottky (TMBS) diodes were studied by simulation and theoretical calculation. A reasonable simulation model was established according to the experimental results of Schottky Barrier Diodes (SBD), which were utilized to simulate the TMBS diodes. A theoretical calculation model of TMBS diodes under forward bias was constructed based on existing SBD theoretical analysis to systematically understand the simulation results. Both simulation and theoretical calculation demonstrate that the negative resistance characteristics of TMBS diodes under forward bias are caused by the accumulation of minority carriers at the epitaxial region and the accumulation of majority carriers at the epitaxial region and oxide layer.

An Improved 4H-SiC Trench MOS Barrier Schottky Diode With Lower On-Resistance

An improved 4H-SiC trench MOS barrier Schottky (TMBS) structure that can significantly reduce the specific on-resistance ( $R_{on,sp}$ ) is proposed in this paper. Compared with the conventional TMBS structure, an N-type region is added around the P+ shielding region and along the trench sidewall in the proposed structure, and the doping concentration is higher than that of the drift region. The JFET resistance, and spread resistance can both be reduced significantly during the forward bias to produce a much lower $R_{on,sp}$ , which have been verified through the numeric simulations and modeling analysis. The critical parameters (N-type region width and its doping concentration) of the proposed structure are mainly optimized by the ATLAS simulation tool. As a result, the breakdown voltage and leakage current of the improved structure remain basically unchanged compared with the conventional TMBS. However, the $R_{on,sp}$ and FoM ( BV 2/ $R_{on,sp}$ ) can be effectively improved by 41.9% and 70.9%, respectively.

Features of current-voltage characteristic of nonequilibrium trench MOS barrier Schottky diode

The trench MOS barrier Schottky diodes (TMBS diode) under the influence of the voltage drop of the additional electric field (AEF) appearing in the near-contact region of the semiconductor are in a nonequilibrium state and their closed external circuit flows currents in the absence of an external voltage. When an external voltage is applied to the TMBS diode, the current transmission is described by the thermionic emission theory with a specific feature. Both forward and reverse I-V characteristics of the TMBS diode consist of two parts. In the initial first part of the forward I-V characteristic there are no forward currents, but reverse saturation currents flow, in its subsequent second part the currents increase exponentially with the voltage. In the initial first part of the reverse I-V characteristic, the currents increase in an abrupt way and in the subsequent second part the saturation currents flow under the action of the image force. The mathematical expressions for forward and reverse I-V characteristic of the TMBS diode and also narrow or nanostructure Schottky diode are proposed, which are in good agreement with the results of experimental and calculated I-V characteristics.

Physics-Based Breakdown Voltage Optimization of Trench MOS Barrier Schottky Rectifiers

A comprehensive study of the breakdown voltage optimization of trench MOS barrier Schottky (TMBS) rectifiers is performed by means of drift-diffusion simulations. First, the principles of operation are explained in terms of the charge-sharing effect between the Schottky and trench MOS components of the unit cell, and correlated with the profiles of the electric field along the drift region ${E}_{\textsf {Sch}}$ and the MOS capacitor ${E}_{\textsf {TMOS}}$ . Then, the systematic variation of relevant design parameters is used to determine breakdown voltage and leakage current trends, which are analyzed in terms of the electric field. Our results show that ${E}_{\textsf {Sch}}$ is the dominating component in structures with thick oxides, shallow trenches, or high-doping concentrations, whereas ${E}_{\textsf {TMOS}}$ is the limiting factor for devices with thin oxides, deep trenches, or low doping. Finally, optimum $\textit {BV}$ is found when the peak value of ${E}_{\textsf {Sch}}$ and ${E}_{\textsf {TMOS}}$ is approximately the same, and this condition can be reached in a wide range of trench depths for devices with long drift regions and high doping, but in a very narrow window for thin epi-layers or low-doping concentration.

An Optimized 4H-SiC Trench MOS Barrier Schottky (TMBS) Rectifier

This paper proposes an optimal 4H-silicon carbide trench MOS barrier Schottky (TMBS) Rectifier. The optimal structure of this rectifier is achieved by adding an N− wrapping region at the P+ shielding of the conventional TMBS structure, which significantly reduces the depletion region formed by the P+ shielding region. As a result, the proposed structure provides a lower ON-resistance comparing with the conventional P+ shielding structure. Moreover, we study the electric characteristics of the proposed structure via numerical simulation. Such a structure improves the specific ON-resistance and figure of merit of the conventional P+ shielding TMBS by 32.2% and 48.4%, respectively, and offers a high breakdown voltage, i.e., up to 1908 V.

Vertical GaN trench MOS barrier Schottky rectifier maintaining low leakage current at 200 °C with blocking voltage of 750 V

In this paper, we report on a vertical GaN trench MOS barrier Schottky (TMBS) rectifier for attaining low leakage current at high temperature and high reverse voltage. At 200 °C, a high blocking voltage of 750 V was achieved at a leakage current of 1 mA/cm2. To the best of our knowledge, this blocking voltage is the highest ever reported for GaN Schottky rectifiers operating at such a high temperature. Furthermore, the fabricated TMBS rectifier operated at large forward currents up to 10 A. These results verify that the developed vertical GaN TMBS rectifiers have great potential as high-power and high-temperature devices.

Fabrication and Characterization of Graphene-on-Silicon Schottky Diode for Advanced Power Electronic Design

In this study, graphene-on-silicon process technology was developed to fabricate a power rectifier Schottky diode for efficiency improvement in high operating temperature. Trench-MOS-Barrier-Schottky (TMBS) diode structure was used to enhance the device performance. The main objective of this research was to study the effect of reduced graphene oxide (RGO) deposited on silicon surface for Schottky barrier formation and heat transfer in Schottky junction. The study showed RGO deposited on silicon as a heat spreader could help to reduce the effect of heat generated in the Schottky junction that leads to a leakage current reduction and efficiency improvement in the device. With comparison to the conventional metal silicide (titanium silicide and cobalt silicide), the leakage reduced by two-orders of magnitude when tested under high operating temperature (>100°C). TMBS rectifier diode that uses graphene-based heat spreader could produce highly reliable product able to withstand high temperature operating condition.

Additional electric field in real trench MOS barrier Schottky diode

In real trench MOS barrier Schottky diode (TMBS diode) additional electric field (AEF) the whole is formed in the near contact region of the semiconductor and its propagation space is limited with the barrier metal and the metallic electrodes of MOS structures. Effective potential barrier height TMBS diode is formed via resulting electric field of superposition AEF and electric field of space charge region (SCR) semiconductor. The dependence of the resulting electric field intensity of the distance towards the inside the semiconductor is nonlinear and characterized by a peak at a certain distance from the interface. The thickness of the SCR in TMBS diode becomes equal to the trench depth. Force and energy parameters of the AEF, and thus resulting electric field in the SCR region, become dependent on the geometric design parameters TMBS diode. The forward I-V characteristic TMBS diode is described by the thermionic emission theory as in conventional flat Scottky diode, and in the reverse bias, current is virtually absent at initial voltage, appears abruptly at a certain critical voltage.

High-voltage 4H-SiC trench MOS barrier Schottky rectifier with low forward voltage drop using enhanced sidewall layer

In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL–TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL–TMBS rectifier compared with the performance of a conventional TMBS rectifier.

Comparison of the Planar-JBS against the Trench-MOS Rectifier-Design Based on 4H-SiC for 3.3 kV Applications

We compare the static electronic performance of the state-of-the-art Junction-Barrier-Schottky (JBS) rectifier (manufactured by ion-implantation) against the Trench-MOS Barrier Schottky (TMBS) rectifier (manufactured by trench-etching and subsequent oxidation). In our 2D numerical simulations, we have chosen identical specifications for the epitaxial drift-layer (3.3 kV application voltage, e.g. traction) and back-side device-design, while investigating the impact of the top-cell active area design on both rectifier IV-characteristics. To enable a meaningful comparison, we designed the depth d of the shields for the electric field E equally deep (p+ peak-plateau dJBS equals trench-depth dt), such that the peak E-field (close to avalanche breakdown) inside the drift-layer of the device is located at a comparable depth near the anode-side of the rectifier (see Fig. 2). By studying systematically the ratio between shield-to Schottky contact-length (w/s ratio), we found that the unipolar conduction state of the TMBS design is basically unaffected by enlarging the Schottky-contact length s, which is enterly different for the JBS-case.