Reverse Conduction Research Articles

Vertical GaN Power MOSFET with Integrated Fin-Shaped Diode for Reverse Conduction

A vertical GaN power MOSFET featuring an integrated fin-shaped non-junction diode (FDMOS) is proposed to improve reverse conduction and switching characteristics. Its static and dynamic characteristics are studied and analyzed by Sentaurus TCAD simulation. Compared with the conventional MOSFET (Con. MOS) with a body diode as a freewheeling diode (FWD), the FDMOS uses the integrated fin-shaped diode to reverse conduction, and thus, a low reverse turn-on voltage VON of 0.66 V is achieved, with a decreasing of 77.9%. Moreover, the Qrr of the FDMOS is reduced to 1.36 μC from 1.64 μC of the Con. MOS, without the minority carrier injection. The gate charge (QGD) of the FDMOS is significantly reduced because the fin structure reduces the gate area and transforms some part of CGD to CGS, and thus, a low switching loss is realized. The QGD, the turn-on loss (Eon) and the turn-off loss (Eoff) of the FDMOS are decreased by 56.8%, 33.8% and 53.8%, respectively, compared with those of the Con. MOS. In addition, the FDMOS is beneficial to reduce the parasitic inductance and the total chip area compared with the conventional method of using an externally connected Schottky diode as an FWD.

Characterization and optimization of active negative voltage driving circuit for CoolGaN HEMTs in a phase-leg configuration

The high switching speed of GaN HEMT will cause serious crosstalk in the phase-leg configuration. The negative turn-off driving voltage is usually recommended to avoid the parasitic shoot-through. However, the adoption of negative turn-off voltage will increase the reverse conduction loss during the dead time, which brings impact on the efficiency of GaN-based converter, and the selection of negative turn-off voltage is also limited by the maximum negative voltage capability of gate–source. Taking CoolGaN HEMT drive circuit as the research object, the crosstalk suppression method is analyzed in detail. Then, an active negative voltage driving circuit is proposed. The novel driving circuit realizes the negative-voltage and zero-voltage combined shutdown mode, which can not only meet the requirements of crosstalk suppression, but also minimize the reverse conduction loss of GaN device. The influence of crucial parameters in active negative voltage driving circuit on the reliability and power loss of bridge-arm circuit is explored, and the optimization design method of each parameter is obtained, so as to provide theoretical and design guidance for high efficiency driving circuit with high reliability.

Third quadrant overvoltage ruggedness of p-gate GaN HEMTs

Overvoltage ruggedness is an essential reliability requirement for non-avalanche AlGaN/GaN power devices against inductive transient spikes in the OFF-state breakdown events. In this work, we first report the 3rd-quadrant (i.e. source-to-drain reverse operation) overvoltage ruggedness of the p-gate GaN high-electron-mobility transistors (HEMTs) by performing static current–voltage (I–V) sweeps and dynamic unclamped inductive switching (UIS) experiments. Both experimental results reveal an inferior breakdown performance of the device under 3rd-quadrant blocking conditions, including a low static voltage of 57 V and a dynamic breakdown voltage (BV) of 155 V. In particular, this transient voltage is evidently degraded from 155 V to 114 V (i.e. a 26% reduction) by increasing the load current, which is significantly different from the stable BV (1.4 kV) achieved in the 1st-quadrant dynamic breakdown. Such unusual degradation behavior can be explained by the trapping-related carrier transport mechanism, which is supported by temperature-dependent breakdown characteristics. Further numerical simulations, de-capsulation failure analyses and repeated UIS experiments are carried out to study the failure mechanism and gain insight into the overvoltage capability of the device. These results suggest that the rational design of the p-gate GaN HEMTs with the desired 3rd-quadrant overvoltage ruggedness requires careful consideration, especially in reverse conduction events.

An Integrated Driver With Bang-Bang Dead-Time Control and Charge Sharing Bootstrap Circuit for GaN Synchronous Buck Converter

This article proposes a high-frequency integrated gate driver for gallium nitride (GaN) synchronous buck converter. The proposed adaptive bang-bang dead-time control minimizes dead-time at any load condition. Thus, it mitigates the excessive power loss caused by GaN device reverse conduction in high-frequency applications. The proposed charge sharing bootstrap circuit ensures sufficient gate overdrive voltage with reduced chip area. Fabricated in a TSMC 0.25- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m BCD process, the driver integrated circuit enabled GaN-based buck converter to operate at 10 MHz switching frequency with minimal dead-time to as low as 0.4 ns under light load and heavy load conditions. Compared with fixed dead-time control, the proposed work improves around 5% efficiency under heavy load condition. The fully integrated bootstrap circuit with 100 and 60 pF (HV) capacitor obtained the lower than 0.6 V driving voltage drop with only 45% capacitance and around half of the voltage drop compared with a conventional bootstrap circuit. Besides, the proposed driver successfully tackled the parasitic ringing and dead-time overcharging issues in the GaN converter.

Tunable Thermal Switch via Order-Order Transition in Liquid Crystalline Block Copolymer.

Organic material-based thermal switch is drawing much attention as one of the key thermal management devices in organic electronic devices. This study aims at tuning the switching temperature (TS) of thermal conductivity by using liquid crystalline block copolymers (BCs) with different order-order transition temperature (Ttr) related to the types of mesogens in the side chain. The BC films with low Ttr of 363 K and high Ttr of 395 K exhibit reversible thermal conductivity switching behaviors at TS of ∼360 K and ∼390 K, respectively. The BC films also exhibit thermal conductivity variation originating from the anisotropy of the internal structures: poly(ethylene oxide) domains and liquid crystals. These results demonstrate that the switching behavior is attributed to an order-order transition between BC films with vertically arranged cylinder domains and the ones with ordered sphere domains. This highlights that BCs become a promising thermal conductivity switching material with tailored TS.

Nonvolatile Control of Metal-Insulator Transition in VO2 by Ferroelectric Gating.

Controlling phase transitions in correlated materials yields emergent functional properties, providing new aspects to future electronics and a fundamental understanding of condensed matter systems. With vanadium dioxide (VO2 ), a representative correlated material, an approach to control a metal-insulator transition (MIT) behavior is developed by employing a heteroepitaxial structure with a ferroelectric BiFeO3 (BFO) layer to modulate the interaction of correlated electrons. Owing to the defect-alleviated interfaces, the enhanced coupling between the correlated electrons and ferroelectric polarization is successfully demonstrated by showing a nonvolatile control of MIT of VO2 at room temperature. The ferroelectrically-tunable MIT can be realized through the Mott transistor (VO2 /BFO/SrRuO3 ) with a remanent polarization of 80 µC cm-2 , leading to a nonvolatile MIT behavior through the reversible electrical conductance with a large on/off ratio (≈102 ), long retention time (≈104 s), and high endurance (≈103 cycles). Furthermore, the structural phase transition of VO2 is corroborated by ferroelectric polarization through in situ Raman mapping analysis. This study provides novel design principles for heteroepitaxial correlated materials and innovative insight to modulate multifunctional properties.

Conductance Switching in Liquid Crystal-Inspired Self-Assembled Monolayer Junctions.

We present the prototype of a ferroelectric tunnel junction (FTJ), which is based on a self-assembled monolayer (SAM) of small, functional molecules. These molecules have a structure similar to those of liquid crystals, and they are embedded between two solid-state electrodes. The SAM, which is deposited through a short sequence of simple fabrication steps, is extremely thin (3.4 ± 0.5 nm) and highly uniform. The functionality of the FTJ is ingrained in the chemical structure of the SAM components: a conformationally flexible dipole that can be reversibly reoriented in an electrical field. Thus, the SAM acts as an electrically switchable tunnel barrier. Fabricated stacks of Al/Al2O3/SAM/Pb/Ag with such a polar SAM show pronounced hysteretic, reversible conductance switching at voltages in the range of ±2-3 V, with a conductance ratio of the low and the high resistive states of up to 100. The switching mechanism is analyzed using a combination of quantum chemical, molecular dynamics, and tunneling resistance calculation methods. In contrast to more common, inorganic material-based FTJs, our approach using SAMs of small organic molecules allows for a high degree of functional complexity and diversity to be integrated by synthetic standard methods, while keeping the actual device fabrication process robust and simple. We expect that this technology can be further developed toward a level that would then allow its application in the field of information storage and processing, in particular for in-memory and neuromorphic computing architectures.

Soft, bioresorbable coolers for reversible conduction block of peripheral nerves.

Implantable devices capable of targeted and reversible blocking of peripheral nerve activity may provide alternatives to opioids for treating pain. Local cooling represents an attractive means for on-demand elimination of pain signals, but traditional technologies are limited by rigid, bulky form factors; imprecise cooling; and requirements for extraction surgeries. Here, we introduce soft, bioresorbable, microfluidic devices that enable delivery of focused, minimally invasive cooling power at arbitrary depths in living tissues with real-time temperature feedback control. Construction with water-soluble, biocompatible materials leads to dissolution and bioresorption as a mechanism to eliminate unnecessary device load and risk to the patient without additional surgeries. Multiweek in vivo trials demonstrate the ability to rapidly and precisely cool peripheral nerves to provide local, on-demand analgesia in rat models for neuropathic pain.

High performance SiC trench-type MOSFET with an integrated MOS-channel diode

A novel SiC double-trench metal-oxide-semiconductor field effect transistor (MOSFET) with integrated MOS-channel diode is proposed and investigated by Sentaurus TCAD simulation. The new SiC MOSFET has a trench gate and a stepped-trench source, and features an integrated MOS-channel diode on the top sidewall of the source trench (MT MOS). In the reverse conduction state, the MOS-channel diode turns on firstly to prevent the internal parasitic body diode being activated, and thus reduces the turn-on voltage V F and suppresses the bipolar degradation phenomena. The V F of 1.70 V (@I ds = –100 A/cm2) for the SiC MT MOS is 38.2% lower than that of SiC double-trench MOSFET (DT MOS). Meanwhile, the reverse recovery charge Q rr of the MT MOS is 58.7% lower than that of the DT MOS at I load = 700 A/cm2, and thus the reverse recovery loss is reduced. Furthermore, owing to the modulation effect induced by the double trenches, the MT MOS preserves the same superior forward conduction and blocking performance as those of DT MOS, with 22.9% and 18.2% improvement on breakdown voltage and R ON,sp compared to the trench gate MOSFET with planar integrated SBD (ST MOS).

Rectifying Performance Induced by B/P, B/As, and B/Sb Co-doped Armchair Graphene Nanoribbons P-N Junction: A DFT Investigation

In this work, we investigated the effect of B, P, As and Sb on the electronic and transport properties of 7-armchair graphene nanoribbons (7-AGNRs) nanoscale p-n junctions, where 7 was the width of nanoribbons. The first-principles study has been employed in the present analysis to reveal that selected dopants significantly reduced the band gap of pristine 7-AGNRs. The current-voltage (I-V) curves of doped devices showed a robust inverse rectification direction, i.e., positive cut-off and reverse conduction, and the rectifying ratio (RR), which can reach up to 107. This was because the asymmetric electron accumulation phenomenon after doping led to the carriers in the device appearing an unbalanced effect under the action of the potential barrier, thereby resulting in a large reverse rectification effect. Simultaneously, these molecular devices possessed a reverse-bias current that increased almost linearly, a very low threshold voltage, and a negligible low forward leakage current that was not over 6.5μA. An obvious negative differential resistance (NDR) effect was also occurred in B/P co-doped molecular device with a peak-to-valley ratio of 2.3 × 105. In addition, under the same doping position, by varying the width of AGNRs, the results showed that the rectification effect varied with the width of the nanoribbons.

Evaluation of Activated Carbon and Platinum Black as High-Capacitance Materials for Platinum Electrodes

The application of direct current (DC) produces a rapid and reversible nerve conduction block. However, prolonged injection of charge through a smooth platinum electrode has been found to cause damage to nervous tissue. This damage can be mitigated by incorporating high-capacitance materials (HCM) (e.g., activated carbon or platinum black) into electrode designs. HCMs increase the storage charge capacity (i.e., “Q value”) of capacitive devices. However, consecutive use of these HCM electrodes degrades their surface. This paper evaluates activated carbon and platinum black (PtB) electrode designs in vitro to determine the design parameters which improve surface stability of the HCMs. Electrode designs with activated carbon and PtB concentrations were stressed using soak, bend and vibration testing to simulate destructive in vivo environments. A Q value decrease represented the decreased stability of the electrode–HCM interface. Soak test results supported the long-term Q value stabilization (mean = 44.3 days) of HCM electrodes, and both HCMs displayed unique Q value changes in response to soaking. HCM material choices, Carbon Ink volume, and application of Nafion™ affected an electrode’s ability to resist Q value degradation. These results will contribute to future developments of HCM electrodes designed for extended DC application for in vivo nerve conduction block.

ID:16031 Noninvasive Thermal Nerve Block of Occipital Nerves in Patients With Occipital Neuralgia

Occipital neuralgia is a painful condition where the occipital nerves are injured or inflamed. There is no cure; thermal- and cryo-ablative techniques are often used to block axonal conduction through nerve destruction. Zhang et al. (1) demonstrated a thermal nerve block protocol that enables reversible nerve conduction block at a safe 15°C room temperature by first warming the nerve to 45°C. (1) This reversible nerve block has therapeutic potential for conditions modulated by peripheral nerves. We present promising results from 14 subjects who have intractable pain from occipital neuralgia.

Tissue Adhesive, Conductive, and Injectable Cellulose Hydrogel Ink for On-Skin Direct Writing of Electronics.

Flexible and soft bioelectronics used on skin tissue have attracted attention for the monitoring of human health. In addition to typical metal-based rigid electronics, soft polymeric materials, particularly conductive hydrogels, have been actively developed to fabricate biocompatible electrical circuits with a mechanical modulus similar to biological tissues. Although such conductive hydrogels can be wearable or implantable in vivo without any tissue damage, there are still challenges to directly writing complex circuits on the skin due to its low tissue adhesion and heterogeneous mechanical properties. Herein, we report cellulose-based conductive hydrogel inks exhibiting strong tissue adhesion and injectability for further on-skin direct printing. The hydrogels consisting of carboxymethyl cellulose, tannic acid, and metal ions (e.g., HAuCl4) were crosslinked via multiple hydrogen bonds between the cellulose backbone and tannic acid and metal-phenol coordinate network. Owing to this reversible non-covalent crosslinking, the hydrogels showed self-healing properties and reversible conductivity under cyclic strain from 0 to 400%, as well as printability on the skin tissue. In particular, the on-skin electronic circuit printed using the hydrogel ink maintained a continuous electrical flow under skin deformation, such as bending and twisting, and at high relative humidity of 90%. These printable and conductive hydrogels are promising for implementing structurally complicated bioelectronics and wearable textiles.

Nodopathies in the Early Diagnosis of Axonal Forms of Guillain-Barré Syndrome.

Introduction:Guillain-Barré syndrome (GBS) has been classified into demyelinating and axonal subtypes or forms, such as acute motor axonal neuropathy (AMAN) and regional pharyngeal-cervical-brachial variant (PCBv).ObjectiveTo study the relationship between motor nerve conduction blocks (CBs) and prognosis in AMAN and PCBv.Patients and MethodsWe retrospectively analyzed six cases of AMAN and PCBv with serial nerve conduction studies (NCS) and electromyography (EMG).ResultsThe serial NCS (1st−2nd and 3rd week) showed, as the most constant data, a decreased amplitude of the compound muscle action potential (CMAP) in 100% of cases. CBs were present in 66.6% of cases. EMG (3rd week) showed signs of severe denervation in 33.3%. All patients were treated from the 1st−2nd week of evolution with intravenous immunoglobulins (IVIGs). Patients with CBs (1st−2nd and 3rd week), showed reversible CBs or reversible conduction failure (RCF) and complete recovery at 1 month. Patients without CBs, with persistent reduced distal CMAP amplitude (dCMAP), showed severe acute denervation due to axonal degeneration (3rd week and 1st−3rd month) and a slow recovery of several months.ConclusionsNot all axonal forms of GBS have a poor prognosis. This study of AMAN and PCBv shows that patients with CBs can have reversible CBs or RCF, and good prognosis. Patients without CBs, with persistent reduction of dCMAP amplitude decrement, have severe acute denervation, and a worse prognosis. AMAN and PCBv have a continuous spectrum ranging from CBs due to dysfunction/disruption of Nodes of Ranvier, called nodopathies, with reversible CBs or RCF and good prognosis, to axonal degeneration with worse prognosis.

An open-label, single-arm trial of cryoneurolysis for improvements in pain, activities of daily living and quality of life in patients with symptomatic ankle osteoarthritis

ObjectiveCryoneurolysis, cold-induced reversible conduction block of peripheral nerves, is an effective treatment for reducing knee osteoarthritis (OA) symptoms and opioid use following knee arthroplasty. There are however, limited data concerning its use for ankle OA. Our aim was to assess clinically significant long-term symptomatic relief of ankle OA with cryoneurolysis. MethodThis single-center, open-label trial included participants aged >18 years with radiographic tibiotalar OA, unilateral ankle pain ≥5/10 on Numerical Rating Scale (NRS), and with no ankle surgery within 6-months of screening. Following ultrasound-guided cryoneurolysis of nerves in the participant's pain distribution (sural, saphenous, superficial and/or deep fibular nerves), outcomes were assessed at clinic visits (6, 12 and 24-weeks) and by telephone interview (3, 9, 18-weeks). The primary endpoint was change in Foot and Ankle Outcome Score (FAOS) (pain subscale) at 12-weeks. Change in quality of life (FAOS-QoL), activities of daily living (FAOS-ADL), NRS-pain, and physical performance measures were also assessed. Longitudinal mixed models were constructed to evaluate changes from baseline at 6, 12- and 24-weeks post-treatment. ResultsForty participants enrolled (50% female, mean ​± ​SD age 63.0 ​± ​12.8 years). At 12-weeks post treatment, FAOS-pain (20.8, p ​< ​0.0001), ADL (18.1, p ​= ​0.0003), QoL (19.9, p ​= ​0.0003) and NRS-pain (−2.6, p ​< ​0.0001) were significantly improved from baseline. No difference in 40-m fast-paced walking test was detected at 12-weeks post-treatment (−1.2sec, p ​= ​0.59). For all outcomes, similar findings were observed at 6- and 24-week visits. ConclusionCryoneurolysis resulted in statistically significant improvements in ankle pain, physical function and QoL for up to 24-weeks in participants with unilateral, symptomatic ankle OA.

Snapback-Free Reverse-Conducting SOI LIGBT with an Integrated Self-Biased MOSFET

A novel snapback-free RC-LIGBT with integrated self-biased N-MOSFET is proposed and investigated by simulation. The device features an integrated self-biased N-MOSFET(ISM) on the anode active region. One side of the ISM is shorted to the P + anode electrode of RC-LIGBT and the other side is connected to the N + anode via a floating ohmic contact. The adaptively turn-on/off of the ISM contributes to improve the static and dynamic performance of the ISM RC-LIGBT. In the forward-state, due to the off-state of the ISM, the snapback could be effectively suppressed without requiring extra device area compared to the SSA (separated shorted anode) and STA (segmented trenches in the anode) LIGBTs. In the reverse conduction, the ISM is turned on and the parasitic NPN in the ISM is punched through, which provides a current path for the reverse current. Meanwhile, during the turn-off and reverse recovery states, the ISM turns on, providing a rapid electron extraction path. Thus, a superior tradeoff between the on-state voltage drop (Von) and turnoff loss (Eoff) as well as an improved reverse recovery characteristic can be obtained. Compared to the STA device, the proposed ISM RC-LIGBT reduces Eoff by 21.5% without snapback. Its reverse recovery charge is reduced by 53.7%/58.6% compared to that of the SSA LIGBT with Lb = 40/60 μm at the same Von. Due to the prominent static and dynamic characteristic, the power loss of ISM RC-LIGBT in a completed switching cycle is reduced.

Mathematical Modeling of EMI Spectrum Envelope Based on Switching Transient Behavior

Compared with Si devices, wide bandgap (WBG) devices will cause more serious electromagnetic interference (EMI) problems due to their fast switching speeds. In order to better compare and predict their EMI, this article proposes an improved mathematical modeling method to calculate the EMI spectrum envelope. It is based on an accurate time-domain decomposition of switching transient behavior together with a frequency-domain calculation. Detailed EMI spectrum envelope analytic expressions are derived with full consideration of Miller platform (MP), reverse conduction (RC), and ringing effects, while traditional calculation mainly focused on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">du/dt</i> . The proposed mathematical modeling method has been applied to Si, silicon carbide (SiC), and gallium nitride (GaN) devices, respectively, and verified by comparing calculated and simulated results. In order to further verify this method, double-pulse test circuits of Si, SiC, emode GaN, and cascade GaN are built, and CM and DM EMI are also compared. The result reveals that, compared with Si devices, the MP, RC, and ringing effects of WBG devices have more serious effects on EMI.

Crosstalk Suppression Method for GaN-Based Bridge Configuration Using Negative Voltage Self-Recovery Gate Drive

In order to suppress the crosstalk in gallium nitride (GaN) based bridge configuration, a novel negative voltage self-recovery gate drive (NVSRGD) is proposed in this article. The resistor–capacitor–diode voltage divider is applied to establish the negative gate–source voltage and suppress the impact of positive crosstalk. The antiparallel diode is added to constitute a low-impedance Miller current path from the driver integrated circuit (IC) to the GaN device. It works together with the self-recovery gate–source voltage to suppress the negative crosstalk, which not only prevents the GaN device from the negative overstresses but also reduces the reverse conduction loss during the dead time. The NVSRGD is composed of a few passive components, which are suitable for integrating into the driver IC. The capacitors and resistors of the NVSRGD are designed to determine the negative voltage level and the restore time. Additive separate negative voltage power supplies or active devices are not needed. The double-pulse test based on GS66508B verifies the effectiveness of the proposed method for suppressing the positive and negative crosstalk of GaN devices.

Dead Time Optimization in a GaN-Based Buck Converter

A gallium nitride (GaN) field effect transistor can provide superior performance over a Si- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> due to its low <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance and low junction capacitances. However, a GaN-based converter exhibits higher dead time loss during reverse conduction. Thus, to improve the efficiency, dead time optimization is required. This article proposes simple models for dead time optimization in a GaN-based buck converter under different load conditions. The proposed models are analytical in nature compared to the conventional models available for Si-based converters. A buck converter prototype is designed using a 100 V GaN device (GS61008P from GaN Systems) and the proposed analytical model-based dead time optimization techniques are validated experimentally. The proposed modeling techniques can be extended for other GaN-based dc–dc converters.

Modeling Schottky Diode Rectifiers Considering the Reverse Conduction for RF Wireless Power Transfer

The aim of this work is to model Schottky diodes series rectifier for application in Radio Frequency Energy Harvesting (RFEH). A time-domain approach is proposed, including the reverse conduction of the diodes, which can significantly degrade the Power Conversion Efficiency (PCE) as the diode input power increases. The influences of the load, temperature, matching network and choke inductor have also been considered. The representativeness of the model was validated by means of computer simulations and experimental results.