A Novel 4H-SiC SGT MOSFET with Improved P+ Shielding Region and Integrated Schottky Barrier Diode.

A silicon carbide (SiC) SGT MOSFET featuring a ""-shaped P+ shielding region (PSR), named SPDT-MOS, is proposed in this article. The improved PSR is introduced as a replacement for the source trench to enhance the forward performance of the device. Its improvement consists of two parts. One is to optimize the electric field distribution of the device, and the other is to expand the current conduction path. Based on the improved PSR and grounded split gate (SG), the device remarkably improves the conduction characteristics, gate oxide reliability, and frequency response. Moreover, the integrated sidewall Schottky barrier diode (SBD) prevents the inherent body diode from being activated and improves the reverse recovery characteristics. As a result, the gate-drain capacitance, gate charge, and reverse recovery charge (Qrr) of the SPDT-MOS are 81.2%, 41.2%, and 90.71% lower than those of the DTMOS, respectively. Compared to the double shielding (DS-MOS), the SPDT-MOS exhibits a 20% reduction in on-resistance and an 8.1% increase in breakdown voltage.

A Novel Deep-Trench Super-Junction SiC MOSFET with Improved Specific On-Resistance.

In this paper, a novel 4H-SiC deep-trench super-junction MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) with a split-gate is proposed and theoretically verified by Sentaurus TCAD simulations. A deep trench filled with P-poly-Si combined with the P-SiC region leads to a charge balance effect. Instead of a full-SiC P region in conventional super-junction MOSFET, this new structure reduces the P region in a super-junction MOSFET, thus helping to lower the specific on-resistance. As a result, the figure of merit (FoM, BV2/Ron,sp) of the proposed new structure is 642% and 39.65% higher than the C-MOS and the SJ-MOS, respectively.

Vertical GaN MOSFET Power Devices.

Gallium nitride (GaN) possesses remarkable characteristics such as a wide bandgap, high critical electric field, robust antiradiation properties, and a high saturation velocity for high-power devices. These attributes position GaN as a pivotal material for the development of power devices. Among the various GaN-based devices, vertical GaN MOSFETs stand out for their numerous advantages over their silicon MOSFET counterparts. These advantages encompass high-power device applications. This review provides a concise overview of their significance and explores their distinctive architectures. Additionally, it delves into the advantages of vertical GaN MOSFETs and highlights their recent advancements. In conclusion, the review addresses methods to enhance the breakdown voltage of vertical GaN devices. This comprehensive perspective underscores the pivotal role of vertical GaN MOSFETs in the realm of power electronics and their continual progress.

An Analytical Model of Dynamic Power Losses in eGaN HEMT Power Devices.

In this work, we present an analytical model of dynamic power losses for enhancement-mode AlGaN/GaN high-electron-mobility transistor power devices (eGaN HEMTs). To build this new model, the dynamic on-resistance (Rdson) is first accurately extracted via our extraction circuit based on a double-diode isolation (DDI) method using a high operating frequency of up to 1 MHz and a large drain voltage of up to 600 V; thus, the unique problem of an increase in the dynamic Rdson is presented. Then, the impact of the current operation mode on the on/off transition time is evaluated via a dual-pulse-current-mode test (DPCT), including a discontinuous conduction mode (DCM) and a continuous conduction mode (CCM); thus, the transition time is revised for different current modes. Afterward, the discrepancy between the drain current and the real channel current is qualitative investigated using an external shunt capacitance (ESC) method; thus, the losses due to device parasitic capacitance are also taken into account. After these improvements, the dynamic model will be more compatible for eGaN HEMTs. Finally, the dynamic power losses calculated via this model are found to be in good agreement with the experimental results. Based on this model, we propose a superior solution with a quasi-resonant mode (QRM) to achieve lossless switching and accelerated switching speeds.

In Situ H-Radical Surface Treatment on Aluminum Gallium Nitride for High-Performance Aluminum Gallium Nitride/Gallium Nitride MIS-HEMTs Fabrication.

In this work, we demonstrated a low current collapse normally on Al2O3/AlGaN/GaN MIS-HEMT with in situ H-radical surface treatment on AlGaN. The in situ atomic pretreatment was performed in a specially designed chamber prior to the thermal ALD-Al2O3 deposition, which improved the Al2O3/AlGaN interface with Dit of ~2 × 1012 cm-2 eV-1, and thus effectively reduced the current collapse and the dynamic Ron degradation. The devices showed good electrical performance with low Vth hysteresis and peak trans-conductance of 107 mS/mm. Additionally, when the devices operated under 25 °C pulse-mode stress measurement with VDS,Q = 40 V (period of 1 ms, pulse width of 1 µs), the dynamic Ron increase of ~14.1% was achieved.

GaN/Si Heterojunction VDMOS with High Breakdown Voltage and Low Specific On-Resistance.

A novel VDMOS with the GaN/Si heterojunction (GaN/Si VDMOS) is proposed in this letter to optimize the breakdown voltage (BV) and the specific on-resistance (Ron,sp) by Breakdown Point Transfer (BPT), which transfers the breakdown point from the high-electric-field region to the low-electric-field region and improves the BV compared with conventional Si VDMOS. The results of the TCAD simulation show that the optimized BV of the proposed GaN/Si VDMOS increases from 374 V to 2029 V compared with the conventional Si VDMOS with the same drift region length of 20 µm, and the Ron,sp of 17.2 mΩ·cm2 is lower than 36.5 mΩ·cm2 for the conventional Si VDMOS. Due to the introduction of the GaN/Si heterojunction, the breakdown point is transferred by BPT from the higher-electric-field region with the largest radius of curvature to the low-electric-field region. The interfacial state effects of the GaN/Si are analyzed to guide the fabrication of the GaN/Si heterojunction MOSFETs.

Improvement of Dynamic On-Resistance in GaN-Based Devices with a High-Quality In Situ SiN Passivation Layer.

In this paper, we compared the characteristics of normally-on/off AlGaN/GaN MISHEMTs passivated by an in situ/ex situ SiN layer. The devices passivated by the in situ SiN layer revealed enhanced DC characteristics, such as the drain current of 595 mA/mm (normally-on) and 175 mA/mm (normally-off) with the high on/off current ratio of ~107, respectively, compared with those of the devices passivated by the ex situ SiN layer. The MISHEMTs passivated by the in situ SiN layer also exhibited a much lower increase of dynamic on-resistance (RON) of 4.1% for the normally-on device and 12.8% for the normally-off device, respectively. Furthermore, the breakdown characteristics are greatly improved by employing the in situ SiN passivation layer, suggesting that the in situ SiN passivation layer can remarkably not only suppress the surface-trapping effects, but also decrease the off-state leakage current in the GaN-based power devices.

Buffer Traps Effect on GaN-on-Si High-Electron-Mobility Transistor at Different Substrate Voltages.

Substrate voltage (VSUB) effects on GaN-on-Si high electron mobility transistors (HEMTs) power application performance with superlattice transition layer structure was investigated. The 2DEG conductivity and buffer stack charge redistribution can be affected by neutral/ionized donor and acceptor traps. As the donor/acceptor traps are excessively ionized or de-ionized by applying VSUB, the depletion region between the unintentionally doped (UID)/Carbon-doped (C-doped) GaN layer may exhibit a behavior similar to the p-n junction. An applied negative VSUB increases the concentration of both the ionized donor and acceptor traps, which increases the breakdown voltage (BV) by alleviating the non-uniform distribution of the vertical electric field. On the other hand, an applied positive VSUB causes the energy band bending flattener to refill the ionized traps and slightly improves the dynamic Ron degradation. Moreover, the amount of electrons injected into the buffer stack layer from the front side (2DEG channel/Ohmic contact) and the back side (AlN nucleation layer/superlattice transition layer) are asymmetric. Therefore, different VSUB can affect the conductivity of 2DEG through the field effect, buffer trapping effect, and charge redistribution, which can change the electrical performance of the device.

A New Cell Topology for 4H-SiC Planar Power MOSFETs for High-Frequency Switching.

A new cell topology named the dodecagonal (a polygon with twelve sides, short for Dod) cell is proposed to optimize the gate-to-drain capacitance (Cgd) and reduce the specific ON-resistance (Ron,sp) of 4H-SiC planar power MOSFETs. The Dod and the octagonal (Oct) cells are used in the layout design of the 650 V SiC MOSFETs in this work. The experimental results confirm that the Dod-cell MOSFET achieves a 2.2× lower Ron,sp, 2.1× smaller high-frequency figure of merit (HF-FOM), higher turn on/off dv/dt, and 29% less switching loss than the fabricated Oct-cell MOSFET. The results demonstrate that the Dod cell is an attractive candidate for high-frequency power applications.

Study of High-Performance GaN-Based Trench CAVET with Stepped Doping Microstructure.

In this article, an innovative GaN-based trench current-aperture vertical electron transistor (CAVET) with a stepped doping microstructure is proposed and studied using Silvaco-ATLAS. According to the simulation and analyzed characteristics, the best performance renders a remarkable Baliga's figure of merit (FOM) of 4.767 GW·cm2 owing to the modulation of the electric-field distribution. By adjusting the size of the stepped doping microstructure and doping concentration in the GaN drift, the maximum optimized result can achieve a relatively high breakdown voltage (BV) of 2523 V with a very low specific on-resistance (Ron,sp) of 1.34 mΩ·cm2, or the BV can be improved to 3024 V with a specific on-resistance (Ron,sp) of 2.08 mΩ·cm2. Compared with the conventional superjunction GaN-based trench CAVET, the newly demonstrated structure can achieve a 43% reduction in Ron,sp and increase by almost 20% the original BV. These results indicate the superiority of using the stepped doping microstructure in a trench CAVET to improve the BV and decrease Ron,sp, providing a reference for further development of GaN-based CAVETs.

Novel Step Floating Islands VDMOS with Low Specific on-Resistance by TCAD Simulation.

A novel VDMOS with Step Floating Islands VDMOS (S-FLI VDMOS) is proposed for the first time in this letter, in order to optimize the breakdown voltage (BV) and the specific on-resistance (Ron,sp). The innovative terminal technology of Breakdown Point Transfer (BPT) is applied to S-FLI VDMOS, which transfers the breakdown point from the high electric field region to the low electric field region, and the S-FLI VDMOS structure uses multiple layers of charge compensation blocks to generate multiple electric field peaks in the drift region in order to optimize the electric field distribution. In the TCAD simulation, the BV of the proposed S-FLI VDMOS is improved to 326 V, which is higher than that of 281 V for the conventional Si VDMOS with the same drift region length of 15 µm, and the Ron,sp is reduced from 21.54 mΩ·cm2 for the conventional Si VDMOS to 7.77 mΩ·cm2 for the S-FLI VDMOS. Compared with the conventional Si VDMOS, the current density of the effective current conduction path is increased when the forward bias is applied to the proposed device.

High performance and low power consumption resistive random access memory with Ag/Fe2O3/Pt structure.

Due to magnetic field tunability and the abundance of iron in the Earth's crust, iron oxide-based resistive random access memory (RRAM) is considered to be low cost and potential for multi-level storage. However, the relatively high operation voltage (>1 V) and small storage window (<100) limit its application. In this work, the devices with simple Ag/Fe2O3/Pt structure exhibit typical bipolar resistive switching with ultralow set voltage (Vset) of 0.16 V, ultralow reset voltage (Vreset) of -0.04 V, high OFF/ON resistance ratio of 103, excellent cycling endurance more than 104and good retention time longer than 104s. Each major parameter has about an order of magnitude improvement compared to the previous data. The devices demonstrate outstanding stable low power consumption quality. Based on the analysis of the experimental results, a percolation model of silver ion migration was established and confirmed that low operation voltage is attributed to the amorphous oxide layer with large porosity. During electrical testing, the compliance current (Ic) and maximum reset voltage (Vmax) can also affect the device performance. This discovery suggests Fe2O3memristor has significant potential for application and provides a new idea for the realization of high-performance low-power RRAM.

Investigation of 3.3 kV 4H-SiC DC-FSJ MOSFET Structures.

This research proposes a novel 4H-SiC power device structure-different concentration floating superjunction MOSFET (DC-FSJ MOSFET). Through simulation via Synopsys Technology Computer Aided Design (TCAD) software, compared with the structural and static characteristics of the traditional vertical MOSFET, DC-FSJ MOSFET has a higher breakdown voltage (BV) and lower forward specific on-resistance (Ron,sp). The DC-FSJ MOSFET is formed by multiple epitaxial technology to create a floating P-type structure in the epitaxial layer. Then, a current spreading layer (CSL) is added to reduce the Ron,sp. The floating P-type structure depth, epitaxial layer concentration and thickness are optimized in this research. This structure can not only achieve a breakdown voltage over 3300 V, but also reduce Ron,sp. Under the same conditions, the Baliga Figure of Merit (BFOM) of DC-FSJ MOSFET increases by 27% compared with the traditional vertical MOSFET. Ron,sp is 25% less than that of the traditional vertical MOSFET.

Robust and Latch-Up-Immune LVTSCR Device with an Embedded PMOSFET for ESD Protection in a 28-nm CMOS Process.

Low-voltage-triggered silicon-controlled rectifier (LVTSCR) is expected to provide an electrostatic discharge (ESD) protection for a low-voltage integrated circuit. However, it is normally vulnerable to the latch-up effect due to its extremely low holding voltage. In this paper, a novel LVTSCR embedded with an extra p-type MOSFET called EP-LVTSCR has been proposed and verified in a 28-nm CMOS technology. The proposed device possesses a lower trigger voltage of ~ 6.2 V and a significantly higher holding voltage of ~ 5.5 V with only 23% degradation of the failure current under the transmission line pulse test. It is also shown that the EP-LVTSCR operates with a lower turn-on resistance of ~ 1.8 Ω as well as a reliable leakage current of ~ 1.8 nA measured at 3.63 V, making it suitable for ESD protections in 2.5 V/3.3 V CMOS processes. Moreover, the triggering mechanism and conduction characteristics of the proposed device were explored and demonstrated with TCAD simulation.

Fabrication and Characterization of Simple Structure Fluidic-Based Memristor for Immunosensing of NS1 Protein Application.

Non-structural protein 1 (NS1 protein) is becoming a commonplace biomarker for the diagnostic of early detection of dengue. In this study, we sought to use a label-free approach of detecting NS1 protein by harnessing fluidic-based memristor sensor. The sensor was fabricated using sol-gel spin coating technique, by which TiO2 thin film is coated on the surface of Indium tin oxide (ITO) and a glass substrate. The sensor was then functionalized with glycidoxypropyl-trimethoxysilane (GPTS), acting as antibody for NS1. The addition of the target NS1 formed an antibody-antigen complex which altered the physical and electrical properties in sensing region. Sensing of the sensor is incumbent upon the measurement of Off-On resistance ratio. Imaging with Field Emission Scanning Electron Microscope (FESEM) evinced the successful immobilization of the antibody and the subsequent capture of the NS1 protein by the immobilized antibody. The detection limit actualized by the developed sensor was 52 nM and the diameter of 2 mm gives the most optimal measurement. The developed sensor demonstrated an immense potential towards the development of label-free diagnostic of early dengue infection.

150-200 V Split-Gate Trench Power MOSFETs with Multiple Epitaxial Layers.

A rating voltage of 150 and 200 V split-gate trench (SGT) power metal-oxide- semiconductor field-effect transistor (Power MOSFET) with different epitaxial layers was proposed and studied. In order to reduce the specific on-resistance (Ron,sp) of a 150 and 200 V SGT power MOSFET, we used a multiple epitaxies (EPIs) structure to design it and compared other single-EPI and double-EPIs devices based on the same fabrication process. We found that the bottom epitaxial (EPI) layer of a double-EPIs structure can be designed to support the breakdown voltage, and the top one can be adjusted to reduce the Ron,sp. Therefore, the double-EPIs device has more flexibility to achieve a lower Ron,sp than the single-EPI one. When the required voltage is over 100 V, the on-state resistance (Ron) of double-EPIs device is no longer satisfying our expectations. A triple-EPIs structure was designed and studied, to reduce its Ron, without sacrificing the breakdown voltage. We used an Integrated System Engineering-Technology Computer-Aided Design (ISE-TCAD) simulator to investigate and study the 150 V SGT power MOSFETs with different EPI structures, by modulating the thickness and resistivity of each EPI layer. The simulated Ron,sp of a 150 V triple-EPIs device is only 62% and 18.3% of that for the double-EPIs and single-EPI structure, respectively.

High Breakdown Voltage and Low Dynamic ON-Resistance AlGaN/GaN HEMT with Fluorine Ion Implantation in SiNx Passivation Layer.

In this study, we proposed and experimentally demonstrated a high breakdown voltage (BV) and low dynamic ON-resistance (RON, D) AlGaN/GaN high electron mobility transistor (HEMT) by implanting fluorine ions in the thick SiNx passivation layer between the gate and drain electrodes. Instead of the fluorine ion implantation in the thin AlGaN barrier layer, the peak position and vacancy distributions are far from the two-dimensional electron gas (2DEG) channel in the case of fluorine ion implantation in the thick passivation layer, which effectively suppresses the direct current (DC) static and pulsed dynamic characteristic degradation. The fluorine ions in the passivation layer also extend the depletion region and increase the average electric field (E-field) strength between the gate and drain, leading to an enhanced BV. The BV of the proposed HEMT increases to 803 V from 680 V of the conventional AlGaN/GaN HEMT (Conv. HEMT) with the same dimensional parameters. The measured RON, D of the proposed HEMT is only increased by 23% at a high drain quiescent bias of 100 V, while the RON, D of the HEMT with fluorine ion implantation in the thin AlGaN barrier layer is increased by 98%.

Ultra-Low Specific On-resistance Lateral Double-Diffused Metal-Oxide-Semiconductor Transistor with Enhanced Dual-Gate and Partial P-buried Layer.

An ultra-low specific on-resistance (Ron,sp) lateral double-diffused metal-oxide-semiconductor transistor (LDMOS) with enhanced dual-gate and partial P-buried layer is proposed and investigated in this paper. On-resistance analytical model for the proposed LDMOS is built to provide an in-depth insight into the relationship between the drift region resistance and the channel region resistance. N-buried layer is introduced under P-well to provide a low-resistance conduction path and reduce the resistance of the channel region significantly. Enhanced dual-gate structure is formed by N-buried layer while avoiding the vertical punch-through breakdown in off-state. Partial P-buried layer with optimized length is adopted under the N-drift region to extend vertical depletion region and relax the electric field peak in off-state, which enhances breakdown voltage (BV) with low drift region resistance. For the LDMOS with enhanced dual-gate and partial P-buried layer, the result shows that Ron,sp is 8.5 mΩ·mm2 while BV is 43 V.

An Overview of the Ultrawide Bandgap Ga2O3 Semiconductor-Based Schottky Barrier Diode for Power Electronics Application.

Gallium oxide (Ga2O3) is a new semiconductor material which has the advantage of ultrawide bandgap, high breakdown electric field, and large Baliga's figure of merit (BFOM), so it is a promising candidate for the next-generation high-power devices including Schottky barrier diode (SBD). In this paper, the basic physical properties of Ga2O3 semiconductor have been analyzed. And the recent investigations on the Ga2O3-based SBD have been reviewed. Meanwhile, various methods for improving the performances including breakdown voltage and on-resistance have been summarized and compared. Finally, the prospect of Ga2O3-based SBD for power electronics application has been analyzed.

The effect of ephrin-A1 on resistance to Photofrin-mediated photodynamic therapy in esophageal squamous cell carcinoma cells.

Esophageal squamous cell carcinoma (ESCC), the most prevalent cell type of esophageal cancer, remains a dismal disease with poor prognosis. Photodynamic therapy (PDT) is a minimally invasive treatment option for early esophageal cancer. To explore possible factors involved in resistance to PDT in esophageal cancer cells, we selected PDT-resistant subcell lines by repeated treatment of CE48T/VGH (CE48T) ESCC cells with Photofrin-PDT and then analyzed the global gene modulations in the PDT-resistant cells by whole-genome microarray. More than 700 genes reached a fold change greater than 1.5 in each of the PDT-resistant cells compared to parental cells. Among these genes, both tumor necrosis factor (TNF) and EFNA1 genes were significantly upregulated in resistant cell lines. However, they were significantly downregulated in Photofrin-PDT-treated cells compared to untreated cells. The observations made in the microarray analysis were further confirmed by quantitative PCR. We observed that recombinant tumor necrosis factor alpha (TNF-α) activated the gene expression of EFNA1 at both the messenger RNA (mRNA) level and the protein level in CE48T cells. Functional analysis showed that when incubated with oligomeric and monomeric ephrin-A1 simultaneously, ESCC cells became significantly resistant to Photofrin-PDT. Functional analysis further suggested that transmembrane and soluble ephrin-A1 may cooperate to enhance resistance to Photofrin-PDT in ESCC cells.