Forward Blocking Research Articles

Design and Experimental Study of 4H-SiC Trenched Junction Barrier Schottky Diodes

This paper presents the design, fabrication, and experimental analysis of 1200 V 4H-SiC trenched junction barrier Schottky (TJBS) diodes. Design considerations and device performances of the TJBS devices are compared with those of the conventional planar JBS diodes via numerical simulation, analytical modeling, and experiments. It was found that, for conventional planar JBS diodes, due to its limited P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> implantation depth, there is a tight tradeoff between forward ON-resistance and blocking voltage. This does not only put stringent requirement on obtaining a narrow photolithography line width ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\sim 1.5\) </tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> m), but also makes the device design window narrow. The TJBS diodes can substantially alleviate such tradeoff and obtain a larger design window that enables good reverse blocking and forward conduction capabilities at the same time. As a result, this structure demands less restriction on line width control (2.2–3.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> m) of the fabrication process and hence can improve the device yield.

PSPICE Simulation of IGCT and its Inverter Circuit

In order to observe the state of Integrated Gate Commutated Thyristor(IGCT) in inverter circuit and analyze the reason of its breakdown, a single 2T-3R subcircuit model of IGCT is used in Personal Simulation Program with IC Emphasis(PSPICE) environment to simulate an IGCT inverter unit of a 6kV/2MVA frequency converter. Simulation results show that when the stray inductance in inverter circuit is large, high forward blocking peak voltage will cause the breakdown of IGCT. This problem is solved by installing an absorption capacitor.

(Invited) Nanocrystalline Diamond for Near Junction Heat Spreading in GaN Power HEMTs

As a wide-bandgap semiconductor, gallium nitride (GaN) is an attractive material for next-generation power devices, but capabilities have been limited by self-heating effects. Attempts to mitigate thermal impairment have been limited due to the difficulties involved with placing high thermal conductivity materials close to heat sources in the device. Heat spreading schemes have involved growth of AlGaN/GaN on single crystal or CVD diamond, or capping of fully-processed HEMTs using nanocrystalline diamond (NCD). All approaches have suffered from reduced HEMT performance or limited substrate size. Recently, we have successfully demonstrated a “gate after diamond” approach, which enables scalable, large-area diamond integration and improves the thermal budget of the process by depositing NCD before the thermally sensitive Schottky metal gate, shown in the cross-section schematic and FIB image in Figure 1 [1,2]. The diamond-capped device appeared to demonstrate improved DC I-V characteristics in most key performance areas, notably improved on-resistance, saturation current, and transconductance, and reduced off-state current and gate leakage, as summarized in Table I. In addition, diamond-capped devices demonstrated improved forward blocking characteristics, manifested by the reduced off-state leakage current and a nearly 200V improvement in breakdown voltage in forward blocking mode. RF devices have produced comparable f T, f MAX, and output power relative to a reference device. Furthermore, channel temperature measurements by Raman thermography, shown in Figure 2, indicate a 20% reduction in channel temperature. Thermal mapping has also indicated a change in the temperature profile through the source-drain region by pulling the hot spot away from the gate edge and broadening the temperature distribution. These results produce a good agreement when compared to a finite-element model. A significant drawback to this approach is that the passivation layer, however thin, acts as a thermal insulator between the hottest part of the device and the heat spreading layer. This process has recently been improved to enable the deposition of diamond directly on the GaN surface, which produced an enhanced heat spreading effect as well as reduced current collapse. In this process, the most critical step is the reliable formation of the gate opening without damaging the now unprotected GaN surface in the diamond etch, which involves a high power plasma etch in O2-based chemistry. To mitigate this effect and produce a reliable gate opening, we have developed a sacrificial gate after diamond process, where the gate “recess” is formed as a SiNXpillar before diamond growth, followed by either a realignment of the gate recess or selective diamond growth outside of the gate region. This approach is expected to improve the yield and scalability of the diamond directly on GaN process. This presentation will review progress in simulation, process integration, channel temperature mapping, and electrical characterization of diamond-capped devices.1. M.J. Tadjer, T.J. Anderson, K.D. Hobart, T.I. Feygelson, J.D. Caldwell, C.R. Eddy, Jr. F.J. Kub, J.E. Butler, B.B. Pate, J. Melngailis. IEEE Electron Dev. Lett. 33, 23-25 (2012)2. T.J. Anderson, A.D. Koehler, M.J. Tadjer, K.D. Hobart, T.I. Feygelson, J.K. Hite, B.B. Pate, C.R. Eddy, Jr, F.J. Kub. 2013 CS Mantech Technical DigestFigure 1. Schematic and FIB cross-section of AlGaN/GaN HEMT with NCD heat spreading filmTable I. Table of DC parameters for reference and diamond-capped HEMTsFigure 2. Raman thermography estimation of channel temperature with and without NCD heat spreading films

Associative repetition priming as a measure of human contingency learning: Evidence of forward and backward blocking.

Associative theories have been widely used to explain human contingency learning. Standard experimental procedures in the field have requested verbal judgments as a measure of the cue-outcome relationships learned. According to these theories, knowledge retrieval is based on spreading activation processes. However, verbal judgments may allow or even promote the engagement of high-order processes that may hinder the interpretation of verbal judgments as the output of automatic retrieval processes like those posited. However, previous studies on human associative memory have shown that priming tests, under the right conditions, can minimize the engagement of high-order processes and serve as a measure of low-level automatic retrieval processes. Thus, a new human contingency learning task that incorporates a recognition priming test was developed and tested here. The results showed that, as predicted by associative theories, repetition priming was found after training. In addition, the results showed that relevant learning phenomena such as forward and backward blocking could also be detected using this test. Finally, training based on instructions did not modulate the priming effect. The relevance of these findings for theories of human contingency learning and priming is discussed.

Trapezoid mesa와 Half Sidewall Technique을 이용한 4H-SiC Trench MOS Barrier Schottky(TMBS) Rectifier

In this study, an 4H-SiC Trench MOS Barrier Schottky (TMBS) rectifier which utilizes the trapezoid mesa structure and the upper half of the trench sidewall is proposed to improve the forward voltage drop and reverse blocking voltage concurrently. The proposed 4H-SiC TMBS rectifier reduces the forward voltage drop by 12% compared to the conventional 4H-SiC TMBS rectifier with the tilted sidewall and improves the reverse blocking voltage by 11% with adjusting the length of the upper sidewall. The Silvaco T-CAD was used to analyze the electrical characteristics.

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

In this paper, the influence of a drain field plate (FP) on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate—drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD = 10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.

Analysis and Optimization of a Thyristor Structure Using Backside Schottky Contacts Suited for the High Temperature

In high current, high voltage, high temperature power applications, commercially available conventional silicon thyristors are not suited because they present high leakage current. In this context, this paper presents a high-symmetrical (voltage) thyristor structure that presents a lower leakage current and higher breakover voltage as compared with the conventional thyristor at. It is shown through 2-D physical simulations that the replacement of the P-emitter of a standard symmetrical thyristor by a judicious association of P diffusions and Schottky contacts at the anode side contributes to the reduction of the leakage current in the forward blocking state at high temperature. A fine tune of the anode side configuration will improve the forward OFF-state behavior with only a negligible ON-state voltage drop degradation. Moreover, the comparison with the conventional anode short thyristor shows that the insertion of Schottky contacts leads to the same improvements in terms of OFF-state forward breakover voltage and leakage current and also presents a high reverse blocking voltage.

Collision-Aware Routing and Spectrum Assignment in GMPLS-Enabled Flexible-Bandwidth Optical Network

In a flexible-bandwidth optical network (FBON) with a generalized multiprotocol label switching control plane, the resource reservation protocol with traffic engineering extensions (RSVP-TE) is employed to establish end-to-end bandwidth variable lightpaths. The resource reservation can be blocked due to spectrum contention of different concurrent RSVP instances (called backward blocking), and it is the predominant blocking contribution when traffic load is low and arrival highly dynamic. Also, due to its flexible traffic granularity in FBON, the backward collision would happen more frequently and the collision scenario would be more complicated than that in wavelength-routed networking; thus the need for a collision evaluation and avoiding method. So, a collision-avoiding routing with maximum available spectrum allocation (SA) options and an SA scheme to search the spectrum segment with minimum collision possibility are proposed for backward blocking reduction, as well as an extension to the RSVP-TE. Simulation results show that the proposed algorithm could achieve better blocking performance through significantly reducing the backward reservation collision but with acceptable forward blocking deterioration. At the same time, with the proposed algorithm, different granularity traffic could be served more fairly in FBON.

Evidence that a transient but cognitively demanding process underlies forward blocking

Blocking is a learning phenomenon in which prior experience inhibits learning about novel cues. Though the phenomenon itself has been well documented, the details of blocking-related processes still remain contentious. Two experiments investigated whether participants were engaged in demanding cognitive processing during different portions of a standard blocking paradigm. Participants in Experiment 1 engaged in a simple secondary task while completing a standard blocking procedure. Results showed that performance on the secondary task was briefly diminished early in the second phase of the blocking paradigm, when the novel cue is first paired with the pretrained cue. Participants in Experiment 2 performed a difficult cognitive load task during either the early or the late portions of the second phase of blocking. The blocking effect was eliminated when learners were under load early in the second phase, but not when learners were under load late in the second phase. These results suggest that blocking relies on a cognitively demanding process with a distinct time course. Computational simulations illustrate how a model that includes top-down (i.e., cognitively demanding) attentional modulation can reproduce the observed behaviour. This suggests that purely associative processes are not sufficient to explain the observed behaviour. Implications for current accounts of blocking are discussed.

An AlGaN/GaN HEMT with enhanced breakdown and a near-zero breakdown voltage temperature coefficient

An AlGaN/GaN high-electron mobility transistor (HEMT) with a novel source-connected air-bridge field plate (AFP) is experimentally verified. The device features a metal field plate that jumps from the source over the gate region and lands between the gate and drain. When compared to a similar size HEMT device with a conventional field plate (CFP) structure, the AFP not only minimizes the parasitic gate to source capacitance, but also exhibits higher OFF-state breakdown voltage and one order of magnitude lower drain leakage current. In a device with a gate to drain distance of 6 μm and a gate length of 0.8 μm, three times higher forward blocking voltage of 375 V was obtained at VGS = −5 V. In contrast, a similar sized HEMT with a CFP can only achieve a breakdown voltage no higher than 125 V using this process, regardless of device dimensions. Moreover, a temperature coefficient of 0 V/K for the breakdown voltage is observed. However, devices without a field plate (no FP) and with an optimized conventional field plate (CFP) exhibit breakdown voltage temperature coefficients of −0.113 V/K and −0.065 V/K, respectively.

Fabrication of a P-Channel SiC-IGBT with High Channel Mobility

We fabricated and characterized an ultrahigh voltage (&gt;10kV) p-channel silicon carbide insulated gate bipolar transistor (SiC-IGBT) with high channel mobility. Higher field-effect channel mobility of 13.5 cm2/Vs was achieved by the combination of adopting an n-type base layer with a retrograde doping profile and additional wet re-oxidation annealing (wet-ROA) at 1100°C in the gate oxidation process. The on-state characteristics of the p-channel SiC-IGBT at 200°C showed the low differential specific on-resistance of 24 mΩcm2 at VG = -20 V. The forward blocking voltage of the p-channel SiC-IGBT at 25°C was 10.2 kV a the leakage current density of 1.0 μA/cm2.

Mechanistic Basis of Partial Agonism at 5-HT3A Receptors

Partial agonists are unable to elicit full maximal responses. The characterization of a genuine partial agonist is complex because other mechanisms, such as channel block, may also limit maximum open probability. Taking advantage of the high conductance form of the 5-HT3A receptor, we evaluated at the single-channel level its activation by 2-Me-5HT and tryptamine, which have been classically considered as partial agonists of 5-HT3 receptors. For all ligands, activation appears as openings in quick succession grouped in clusters showing high open probability (Popen>0.9), and open time distributions show three components. The slowest open component is 6.5- and 3.5-fold briefer for 2-Me-5HT and tryptamine, respectively, than for 5-HT. The duration of this component decreases as a function of agonist concentration due to open-channel block. For 2-Me-5HT, the forward blocking rate is 10-fold faster than for tryptamine and 5-HT. Single-channel kinetic analysis shows that 2-Me-5HT is actually a full agonist, its maximum response being limited by channel block. In contrast, tryptamine is a genuine partial agonist and its low efficacy is mainly due to a slow transition from the fully-liganded closed state to a pre-open state. After reaching the latter state, activation proceeds similarly as in the presence of 5-HT. Molecular docking shows that interactions at the binding site are similar for 2-Me-5HT and 5-HT. In contrast, the potential to form the cation-Pi interaction with W183 seems to be reduced for tryptamine. The mechanism by which ligands produce non maximal responses has implications for the design of partial agonists for therapeutic use.

Supplemental Material for Associative Repetition Priming as a Measure of Human Contingency Learning: Evidence of Forward and Backward Blocking

Supplemental Material for Associative Repetition Priming as a Measure of Human Contingency Learning: Evidence of Forward and Backward Blocking

A Comparative Study of Gate Structures for 9.4-kV 4H-SiC Normally On Vertical JFETs

This paper reports the development of 9.4-kV 4H-SiC normally on lateral-channel vertical JFETs. The developed JFETs utilize a buried layer to create a lateral conduction channel, shielding the source from the effects of drain bias. The lowest measured $R_{\rm on, sp}$ was 127 $\hbox{m}\Omega\cdot\hbox{cm}^{2}$ . Measurements indicate that the channel resistivity can be further reduced by channel optimization. The fabricated JFETs exhibit pentode-like $I_{D}$ – $V_{\rm DS}$ characteristics with a high forward direct-current blocking gain of over 500. This paper provides a comparative study of gate structures in order to achieve the lowest on -state switching losses and to provide stable forward blocking characteristics for a normally on JFET.

Revisiting the role of within-compound associations in cue-interaction phenomena

Although it is thought that within-compound associations are necessary for the occurrence of both backward blocking and unovershadowing, it is not known whether this variable plays a similar role in mediating the two phenomena. Similarly, the roles of within-compound associations in forward blocking and in reduced overshadowing have not been tested independently. The present experiments evaluated how the strength of within-compound associations affects backward blocking, unovershadowing, forward blocking, and reduced overshadowing. Using an allergy task, the strength of within-compound associations was varied by taking advantage of the participants' prior knowledge of common and uncommon food pairings. Backward blocking and unovershadowing effects were present only when highly memorable compound cues were used. Moreover, the magnitudes of both retrospective revaluation effects were affected by the strength of within-compound associations. Forward blocking and reduced overshadowing effects were independent of within-compound associations. These results have important theoretical implications for causal learning research.

Design of an Integrated SiC JFET Power Switch and Flyback Diode

In this paper, we describe the design of a high voltage SiC VJFET monolithically integrated with a JBS diode. The integrated device that was demonstrated up to 834 V in forward blocking doesn’t add any steps to the VJFET fabrication process. While the diode and VJFET share the same surface field termination mechanism, they are partially isolated using implanted field rings. We describe TCAD based optimization of the dimensions of these field rings and outline the design of the JBS diode using a fully analytical 2-D model.

Breakdown-Voltage-Enhancement Technique for RF-Based AlGaN/GaN HEMTs With a Source-Connected Air-Bridge Field Plate

An AlGaN/GaN high-electron-mobility transistor (HEMT) with a novel source-connected air-bridge field plate (AFP) is proposed. The device features a metal field plate (FP) that jumps from the source over the gate region and lands between the gate and drain. The fabrication process is based on a commercially available radio-frequency GaN-on-SiC technology. Device characteristics for this work were optimized via layout changes only. When compared to a similar-sized HEMT device with a conventional FP structure, the AFP not only minimizes the parasitic gate-to-source capacitance but also exhibits a higher off-state breakdown voltage and one order of magnitude lower drain leakage current. In a device with a gate-to-drain distance of 6 μm and a gate length of 0.8 μm, a three-times-higher forward blocking voltage of 375 V was obtained at VGS = -5 V. In contrast, a similar-sized HEMT with a conventional FP can only achieve a breakdown voltage no higher than 125 V using this process, regardless of device dimensions. The specific on-resistance for the device with the proposed AFP is 0.58 mΩ·cm2 at VGS = 0 V, which compares favorably with 0.79 mΩ·cm2 for the best device with a conventional FP.

Experimental study of the anode injection efficiency reduction of 3.3-kV-class NPT-IGBTs due to backside processes

The anode injection efficiency reduction of 3.3-kV-class non-punch-through insulated-gate bipolar transistors (NPT-IGBTs) due to backside processes is experimentally studied through comparing the forward blocking capabilities of the experiments and the theoretical breakdown model in this paper. Wafer lifetimes are measured by a μ-PCD method, and well designed NPT-IGBTs with a final wafer thickness of 500 μm are fabricated. The test results show higher breakdown voltages than the theoretical breakdown model in which anode injection efficiency reduction is not considered. This indicates that anode injection efficiency reduction must be considered in the breakdown model. Furthermore, the parameters related to anode injection efficiency reduction are estimated according to the experimental data.

Wavelength Adaptive Assignment Scheme for Optical Transport Network in Intelligent Highway System

In this paper, a wavelength adaptive assignment scheme called CExF (collision-evaluated adaptive fit) has been proposed for Optical Transport Network in Intelligent Highway to solve the date intensive scheduling. CExF assign a limited and more accurate weight, where the weight denotes the concurrent reservation probability, and the destination can select a wavelength with less collision probability by a new adaptive wavelength assignment according to the weight. Simulations show that CExF performs better in backward blocking, and even in forward blocking under medium traffic loads.

A token-based routing mechanism for GMPLS-controlled WDM networks

This paper analyzes destination initiated reservation for Generalized Multi-Protocol Label Switching (GMPLS) based wavelength division multiplexing (WDM) networks and determines, via simulation, probabilities of both forward blocking and backward blocking. During light traffic load, any degradation in performance is due to backward blocking, whereas during heavy traffic load forward blocking dominates. In order to minimize performance degradation due to blocking, this paper proposes a token based routing scheme that is capable of searching for the availability of more than one route from source to destination, meeting the desired quality of service (QoS). Extensive simulation results show that the proposed technique significantly improves the blocking performance and setup delay.