Tunneling Resistance Research Articles

Giant tunnelling electroresistance through 2D sliding ferroelectric materials.

Very recently, ferroelectric polarization in staggered bilayer hexagonal boron nitride (BBN) and its novel sliding inversion mechanism were reported experimentally (Science2021, 372, 1458; 2021, 372, 1462), which paved a new way to realizing van der Waals (vdW) ferroelectric devices with new functionalities. Here, we develop vdW sliding ferroelectric tunnel junctions (FTJs) using the sliding ferroelectric BBN unit as an ultrathin barrier and explore their transport properties with different ferroelectric states and metal contacts via first principles. It is found that the electrode/BBN contact electric field quenches the ferroelectricity in the staggered BBN, resulting in a very small tunnelling electroresistance (TER). Inserting high-mobility 2D materials between Au and BN can restore the BBN ferroelectricity, reaching a giant TER of ∼10 000% in sliding FTJs. We finally investigate the metal-contact and thickness effect on the tunnelling property of sliding FTJs. The giant TER and multiple non-volatile resistance states in vdW sliding FTJs show promising applications in voltage-controlled nano-memories with ultrahigh storage density.

MXene/TMD Nanohybrid for the Development of Smart Electronic Textiles Based on Physical Electromechanical Sensors

AbstractWearable technologies are becoming gradually prevalent as a personal health system, facilitating unceasing real‐time monitoring of human health on a regular basis and outside the clinical environments. In this perspective, an urgent requirement for extensively sensitive and wearable sensors has increased to examine health during life activities. The fabrication of Ti3C2Tx/SnSe2 nanohybrid E‐textile based multifunctional physical sensors (pressure, strain) on the cotton substrate to monitor an individual's health during daily activities is demonstrated here. The fabricated nanohybrid E‐textile based physical sensors display an extraordinary sensitivity of 14.959 kPa–1 in the applied pressure range of 1.477–3.456 kPa and a gauge factor of 14.108 for 5–25% of applied strain. In addition, these physical sensors show exceptional stability of ≈2500 cycles for a pressure sensor and ≈3000 cycles for a strain sensor which signifies the sturdiness of the sensor. Detailed underlying physics and transduction mechanism are explained by Schottky barrier and tunneling resistance mechanism. Further, an android/iOS/web‐based app is developed to validate wireless integration of the fabricated multifunctional physical sensors for demonstration toward smart shoe and crepe bandage applications.

Tunable Quantum Tunneling through a Graphene/Bi2Se3 Heterointerface for the Hybrid Photodetection Mechanism.

Graphene-based van der Waals heterostructures are promising building blocks for broadband photodetection because of the gapless nature of graphene. However, their performance is mostly limited by the inevitable trade-off between low dark current and photocurrent generation. Here, we demonstrate a hybrid photodetection mode based on the photogating effect coupled with the photovoltaic effect via tunable quantum tunneling through the unique graphene/Bi2Se3 heterointerface. The tunneling junction formed between the semimetallic graphene and the topologically insulating Bi2Se3 exhibits asymmetric rectifying and hysteretic current–voltage characteristics, which significantly suppresses the dark current and enhances the photocurrent. The photocurrent-to-dark current ratio increases by about a factor of 10 with the electrical tuning of tunneling resistance for efficient light detection covering the major photonic spectral band from the visible to the mid-infrared ranges. Our findings provide a novel concept of using tunable quantum tunneling for highly sensitive broadband photodetection in mixed-dimensional van der Waals heterostructures.

Ferroelectricity of pure HfOx in metal-ferroelectric-insulator-semiconductor stacks and its memory application

Ferroelectricity in hafnium oxide (HfOx) and its various applications have been rigorously investigated in recent years. In particular, most studies have focused on a non-centrosymmetric ferroelectric phase that is developed via the injection of external ions into HfOx. However, the drawbacks of doped HfOx, such as serious dopant variation and thermal instability, have hindered its commercialization in low-power logic and memory applications. In this study, we demonstrated the ferroelectricity of pure HfOx without additional ion doping in metal-ferroelectric-insulator-semiconductor (MFIS) stacks. We experimentally confirmed that variation-resistant and thermally stable ferroelectric pure HfOx could be achieved with remarkable polarization by controlling the oxygen vacancies inside pure HfOx and the thermal quenching process for orthorhombic phase transition. Furthermore, to verify the feasibility of the ferroelectric pure HfOx in memory devices, the modulation of tunneling resistance was measured using MFIS ferroelectric tunnel junction (FTJ) devices, revealing that the tunneling current was adjustable over a 2-order current range via the polarization of the pure HfOx, implying that multiple current states could be obtained for multilevel memory operations.

A water‐soluble micropatterned MoS2 quantum dots/polyvinyl alcohol film as a transient contact (pressure) and non‐contact (humidity) as touch and proximity sensor

AbstractWater‐soluble electronics have become increasingly popular due to their potential applications in various fields such as biodegradable and wearable‐stretchable electronics. Flexible polymers such as polydimethylsiloxane are hydrophobic. Hence, water‐soluble polymers like polyvinyl alcohol (PVA) have been extensively utilized as substrates for water‐soluble electronics. However, the patterning of the PVA has never been achieved to enhance the sensing capabilities for such devices. Herein we report for the first time the micro‐pyramid patterning of PVA film embedded with MoS2 quantum dots (QDs) for improved pressure‐sensing capabilities. The fabricated sensor displayed superior sensitivity of 1.44 kPa−1 compared to the sensitivity of 0.51 kPa−1 unpatterned PVA films. This enhanced performance can be attributed to the easier transport of the charge carriers from QD‐PVA‐QD film and the decrement in the tunneling resistance between adjacent MoS2 QDs due to localized stress on the micropattern. Further, the fabricated sensor was tested for real‐time application as a touch sensor in both contact (pressure) and noncontact mode (humidity), which finds potential application in security and personal healthcare, and so forth. The fabricated film is subjected to ~1200 stimulus cycles to manifest good reproducibility of sensor responses. Moreover, the device dissolves in water within ~300 s exhibiting magnificent transient behavior.

Direct-write nanocomposite sensor array for ultrasonic imaging of composites

To improve the ultrasonic imaging of composites, an all-printed nanocomposite sensor array (APNSA) is developed using a direct-write approach. Individual sensing elements of APNSA are inkjet printed by directly writing graphene/poly (amic acid) (PAA)-based nanocomposite ink on Kapton film substrates, with an ultra-thin thickness of ∼1 μm only. APNSA is morphologically tuned at a nano scale to be sensitive to acousto-ultrasonic waves of a broad band regime. Each sensing element features a homogenous and consolidated nanostructure, with which transient change of tunneling resistance between adjacent graphene nanoplatelets in the polyimide (PI) matrix can be triggered when the element is loaded with acousto-ultrasonic waves. The triggered quantum tunneling effect endows APNSA with capability to perceive dynamic strains in a broadband regime with high fidelity and accuracy. Compared with a conventional ultrasonic phased array which is of a low degree of compatibility with composites, APNSA can be fully integrated with the inspected composites. In conjunction with the use of the additively manufactured APNSA, ultrasonic imaging of composites can be implemented, spotlighting a nature of full integration of APNSA with composites for in situ structural health monitoring and anomaly detection, yet without degrading the original integrity of the composites.

Memory properties of electromigrated Au nanogaps to realize reservoir computing

The reservoir computing (RC) scheme, which employs the inherent computational capabilities of dynamical systems, is a key technology to implement artificial intelligence systems physically. Ensuring the nonlinear expansion of input data through the dynamics of physical systems is a necessary aspect of RC. Previously, we developed artificial synapses of Au nanogaps by using the “activation” technique, which allowed the implementation of synaptic functions such as short-term plasticity, long-term plasticity, and spike-timing-dependent plasticity. The activation technique is an electromigration-based method to control the tunnel resistance of nanogaps. In this study, the memory property of the Au nanogap, using activation for RC, was evaluated via short-term memory (STM) and parity check (PC) tasks. More specifically, memory capacity was introduced to evaluate the performance of the Au nanogap, defined as the sum of squares of the correlation between the outputs of RC and the teacher for delay D = 1 to 6. By utilizing the simple dynamics of short-term plasticity, the memory capacities of the STM and PC tasks were found to be 1.07 and 0.90, respectively, when 10 virtual nodes were used. This demonstrates that the dynamic process of the activation technique enables the Au nanogap-based reservoir to process information directly in the temporal domain. The experimental results can facilitate the development of compact devices to realize physical RC.

전산유체해석을 이용한 체험 풍동 유동장 분석

Increase in fatalities and injuries incurred by strong wind has recently observed in particular during typhoons which are responsible for about half of natural disasters in Korea. There are tens of disaster experience facilities in Korea for the purpose of disaster-safety education, which in general include experience wind tunnels. In order to satisfy required performance of the facility, it is essential to design the efficient wind tunnels which are usually allowed only for limited spatial capacity. This study presents the results of computational analysis of flow field inside the experience wind tunnel and spatial resistance parameter as a performance index of the facility. The analysis was carried out by using computational fluid dynamics (CFD) and, the velocity and pressure fields were analyzed. The results show that existing wind tunnel with U-shape wind pathway on the horizontal plane generated high nonuniformity in flow field as well as high spatial resistance. This study suggested a new configuration of the facility by placing the wind pathway on the vertical plane, which greatly increased the uniformity of the flow inside and reduce the spatial resistance.

Conductance-strain behavior in silver-nanowire composites: network properties of a tunable strain sensor

Highly flexible and conductive nano-composite materials are promising candidates for stretchable and flexible electronics. We report on the strain–resistance relation of a silver-nanowire photopolymer composite during repetitive stretching. Resistance measurements reveal a gradual change of the hysteretic resistance curves towards a linear and non-hysteretic behavior. Furthermore, a decrease in resistance and an increase in electrical sensitivity to strain over the first five stretching cycles can be observed. Sensitivity gauge factors between 10 and 500 at 23% strain were found depending on the nanowire concentration and stretching cycle. We model the electrical behavior of the investigated silver nanowire composites upon repetitive stretching considering the strain induced changes in the local force distribution within the polymer matrix and the tunnel resistance between the nanowires by using a Monte Carlo method.

Impact of Fringing Field on Shell Radius and Spacer Dielectric on Device Performance of InAs-GaSb Core-Shell Nanowire nTFET

A comprehensive investigation with the help of 3D device simulation, we demonstrate the impact of fringing field on shell radius of InAs-GaSb core–shell nanowire n-channel tunnel field effect transistor (TFET) in this paper. Increase in shell radius intensifies the magnitude of fringing electric field towards shell region. This results in generation of depletion zone in the shell near the gate edge affects the device performance metrics such as on current and threshold voltage. It is demonstrated that by appropriate gate engineering the influence of fringing electric field can be circumvent. High-k spacer dielectric at the gate underlap shows improvement in device performance metrics such as on current with sub subthreshold swing. An investigation of the effect of drain voltage on the device characteristics exhibits the privation of tunneling resistance limited region. Furthermore, the output characteristics for such an architecture bear a resemblance to long channel MOSFET (metal oxide semiconductor field effect transistor).

Modifying self-sensing cement-based composites through multiscale composition

This paper aims to develop self-sensing cement-based composites with high sensitivity through building a multiphasic and multiscale conductive network formed by hybrid super-fine stainless steel wires (SSWs) and carbon nanotubes (CNTs)/nano-TiO2 particles (NTs). Experimental results show that 0.15 vol% SSWs are already in the percolation threshold zone, and incorporating CNTs/NTs has a synergistic effect of decreasing the electrical resistivity and increasing the strain sensitivity of cement-based composites under cyclic/monotonic compressive loading. The hybrid modification effect is closely related to the dosage and conductivity of nano-fillers. The sensing mechanisms mainly include the change of capacitance, tunneling resistance between fillers and intrinsic resistivity of fillers. For cement-based composites with 0.3 vol% SSWs, the electrical resistivity and self-sensing properties are primarily dominated by the SSW network, and are barely affected by the addition of CNTs. However, the strain sensitivity corresponding to the maximum absolute value of fractional change in electrical resistivity under monotonic loading is increased by 62.8% and reaches up to 140 as NTs are added, resulting from the semiconductor and nano-core properties of NTs to form a barrier between overlapping SSW conductive networks. It can therefore be concluded that tailoring different conductive networks by incorporating hybrid multiscale and multicharacteristic fillers is an effective method of developing self-sensing cement-based composites with high sensitivity.

Ant Colony Optimization Inversion Using the L1 Norm in Advanced Tunnel Detection

During the construction of the tunnel, there may be water-bearing anomalous structures such as fault fracture zone. In order to ensure the safety of the tunnel, it is necessary to carry out advanced tunnel detection. The traditional linear inversion method is highly dependent on the initial model in the tunnel resistivity inversion, which makes the inversion results falling into the local optimal optimum rather than the global one. Therefore, an inversion method for tunnel resistivity advanced detection based on ant colony algorithm is proposed in this paper. In order to improve the accuracy of tunnel advanced detection of deep anomalous bodies, an ant colony optimization (ACO) inversion is used by integrating depth weighting into the inversion function. At the same time, in view of the high efficiency and low cost of one-dimension inversion and the advantages of L1 norm in boundary characterization, a one-dimensional ant colony algorithm is adopted in this paper. In order to evaluate the performance of the algorithm, two sets of numerical simulations were carried out. Finally, the application of the actual tunnel water-bearing anomalous structure was carried out in a real example to evaluate the application effect, and it was verified by excavation exposure.

Computational Study of Graphene–Polypyrrole Composite Electrical Conductivity

In this study, the electrical properties of graphene–polypyrrole (graphene-PPy) nanocomposites were thoroughly investigated. A numerical model, based on the Simmons and McCullough equations, in conjunction with the Monte Carlo simulation approach, was developed and used to analyze the effects of the thickness of the PPy, aspect ratio diameter of graphene nanorods, and graphene intrinsic conductivity on the transport of electrons in graphene–PPy–graphene regions. The tunneling resistance is a critical factor determining the transport of electrons in composite devices. The junction capacitance of the composite was predicted. A composite with a large insulation thickness led to a poor electrochemical electrode. The dependence of the electrical conductivity of the composite on the volume fraction of the filler was studied. The results of the developed model are consistent with the percolation theory and measurement results reported in literature. The formulations presented in this study can be used for optimization, prediction, and design of polymer composite electrical properties.

Design strategy and simulation of single-gate SET for novel SETMOS hybridization

This paper presents a design methodology for a single-gate single-electron transistor (SG-SET) for room temperature operation of SET and hybrid SETMOS circuits. Initially, the SET electrostatics is analytically modeled using a free-energy equation. Tunneling probability is determined by modifying the Mahapatra–Ionescu–Banerjee model. The SET is designed systematically so as to achieve process and supply voltage compatibility with 22-nm CMOS technology. A Si–Al–Si SG-SET with 3-nm ultra-thin $$\hbox {SiO}_2$$ tunnel barriers is proposed and simulated with drift-diffusion, Philips unified mobility, and Schenk direct tunneling models. A 1D Schrodinger equation was solved in the critical region that covered two tunnel barriers and a conductive island. The current-voltage characteristic of the SG-SET is plotted to observe a Coulomb blockade of ± 0.8 V at room temperature. The tunnel resistance and total island capacitance of the proposed SET for circuit simulations are extracted as 20 M $$\varOmega$$ and 0.193 aF, and they are in very close agreement with the analytical values. The tunnel resistance extracted from TCAD simulations is used in the MIB model for validation of SET functionality. Further, we propose the use of this SET in hybrid SETMOS logic implementation at room temperature with ultra-low power consumption.

Percolation mechanism and effective conductivity of mechanically deformed 3-dimensional composite networks: Computational modeling and experimental verification

In this work, the structural evolution of conductive polymer composites (CPCs) in response to mechanical deformation (uniaxial and biaxial compressive and tensile strains) is theoretically modeled and experimentally verified. The structural responses in mechanically deformed CPCs were simulated by incorporating the corresponding topological changes in representative volume element (RVE) and embedded filler networks. The percolating filler networks were then modeled as an equivalent electrical circuit consisting of tunneling and intrinsic resistances to examine the effect of deformation on the percolation threshold and the effective electrical conductivity. The results revealed that the filler alignment caused by strain changed both the vertical and lateral percolation thresholds, albeit with different trends. With an increase of uniaxial tensile (or equivalently, biaxial compressive) strain, applied on the vertical direction, the vertical percolation threshold initially reached a minimum value before rising, while the lateral percolation threshold monotonically increased. On the other hand, following incremental uniaxial compression (or equivalently, biaxial tension), the lateral percolation threshold reached a minimum value before increasing, while the vertical percolation threshold monotonically increased. The same relationship was observed in CPCs containing 1D fillers with different aspect ratios. The validity of the theoretical models was verified by comparing the predicted electrical conductivity values with the experimentally observed data obtained from polypropylene - multiwalled carbon nanotube nanocomposites.

Enhancement of thermal stability and wettability for epoxy/Cu coated carbon fiber composites

This research study the effect of surface modification and copper (Cu) plating carbon fiber (CF) surface on the thermal stability and wettability of carbon fiber (CF)/epoxy (EP) composites. The TGA result indicates that the thermal-stability of carbon fiber may be enhanced after Cu coating CF. TGA curve showed that the treatment temperature was enhanced thermal stability of Ep/CF, this is due to the oxidation during heating. The Cu plating increased the thermal conductivity, this increase might be due to reduce in contact resistance at the interface due to chemical modification and copper plating and tunneling resistance.
 The increase of surface polarity after coating cause decrease in the value of contact angle. As well as the increase of CuO as a function of the heat temperature cause the rapid contact angle decrease and can strongly enhance the wettability.

Formulation of tunneling resistance between neighboring carbon nanotubes in polymer nanocomposites

We aim to express the tunneling resistance in polymer nanocomposites by carbon nanotube (CNT) concentration, interphase depth, CNT curliness, tunneling distance, interfacial tension, network portion and CNT size. The suggested equation is applied to determine the tunneling resistance in some specimens and to estimate the inspirations of dissimilar parameters on the tunneling resistance. The samples do not show a determinate trend between tunneling resistance and filler concentration. Some factors including tunneling distance, percolation onset, CNT content and CNT curliness directly manage the tunneling resistance. Therefore, short tunneling distance, small percolation onset, low CNT content and low CNT curliness produce the poor tunneling resistance. Nonetheless, the resistance of tunnels inversely depends on the portion of attached CNTs, CNT conductivity, CNT length, interphase depth, CNT radius and interfacial tension (i.e. the high levels of these parameters cause the low tunneling resistance). Among the studied parameters, tunneling distance and percolation threshold are the most important parameters manipulating the tunneling resistance, whereas the concentration and length of CNTs have the least effects. As a result, low tunneling distance and small percolation threshold are vital to reduce the tunneling resistance and obtain the conductive nanocomposites.

Effective use of nano-carbons in controlling the electrical conductivity of epoxy composites

Glass fiber reinforced epoxy composites were fabricated using MWCNT and GNP fillers, individually and in combination. The objective of combining the two conductive fillers was to enhance the electrical conductivity of the composites. The DC and AC conductivity measurements were carried out to assess the influence of individual fillers and their combinations on the electrical conductivity. High DC conductivity of 3.1 × 10−3 S/m and AC conductivity of 1.31 × 10−2 S/m at 8 MHz were observed, at 2 wt% of MWCNT and 3 wt% of GNP and the values were significantly reduced below 3 wt% of GNP. The observed increase in electrical conductivity is attributed to low contact resistance (299.85Ω) of fillers, reduced tunneling resistance (5.35 × 109Ω) and tunneling distance (1.65 nm) of the composites. The DC and AC conductivity, contact resistance, tunneling resistance and tunneling distance showed reduced dependence on temperature. The AC conductivity of the hybrid composites follows power law. The cut-off frequency of composites was 200 kHz at 3 wt% of GNP and 2 KHz with reduction in weight percentage of GNP. In composite with 2 wt% of MWCNT and 3 wt% of GNP, validity of the percolation model is established.

Effective addition of nanoclay in enhancement of mechanical and electromechanical properties of SWCNT reinforced epoxy: Strain sensing and crack-induced piezoresistivity

Many studies were performed to improve CNT dispersion into epoxy using different mechanical dispersion methods as well as CNT functionalization. In this study, a novel method is introduced to enhance CNT dispersion using 2D nanoclay as a secondary filler. Hence, this study was aimed to investigate the effect of nanoclay platelets on electrical, mechanical, and piezoresistive characteristics of the SWCNTs doped epoxy nanocomposites. Two different types of nanocomposites were prepared for comparison including binary (SWCNT/epoxy) and hybrid (SWCNT-nanoclay/epoxy) states. CNT content of 0.1 wt% was used for the binary and hybrid states while two different nanoclay loadings (0.5 wt% and 1.0 wt%) were employed in the hybrid nanocomposites. Tensile and mode I fracture tests were performed for the mechanical and electromechanical characterization using two probe techniques while electron microscopy and X-ray diffraction were used for microstructural analysis. Results showed severe CNT agglomeration in the binary state whilst a homogenous CNT dispersion was achieved in the ternary states. The binary nanocomposite showed weak performance in terms of electrical, mechanical and piezoresistive properties caused by severe CNT aggregates. On the other hand, addition of nanoclay into CNTs doped epoxy manifested a significant increase in the electrical, mechanical and piezoresistive-sensitivity performance of the hybrid nanocomposites compared to the binary one. The best performance was achieved at 0.5 wt% nanoclay loading where electrical conductivity increased by six orders of magnitude, UTS increased by 37%, KIC and GIC increased by 34% and 64%, respectively, with respect to the binary nanocomposite. Crack-pinning and crack deflection were accounted for the fracture toughness increase in ternary composites. Nonlinear piezoresistivity resulting from the predominate effect of tunneling resistance ruled piezoresistivity in the hybrid nanocomposites. A sensitivity of 2.1 and 2.0 at strain of 0.01 were obtained for 0.5 wt% and 1.0 wt% nanoclay contents, respectively, whereas no sensitivity was achieved for the binary composite.

Frequency-dependent alternating current piezoresistive switching behavior in self-sensing carbon nanofiber composites

Carbon nanofillers have received much attention for piezoresistive-based self-sensing of deformation in polymeric, cementitious, and ceramic composites. To date, direct current (DC) conductivity has been overwhelmingly favored for self-sensing. This is important because alternating current (AC) methods, though much less studied, have advantages over DC methods. Therefore, we herein explore AC conductivity-strain relations for polymeric carbon nanofiber (CNF) composites. It was found that Jonscher’s power law accurately describes AC conductivity as a function of both normal and shear strain. This provides a framework by which macroscale AC piezoresistivity can be characterized. Further, it was observed that the coefficients of this power law are non-linear in strain. During this testing, it was also observed that the CNF/epoxy exhibits a frequency-dependent piezoresistive switching behavior. At low frequencies, the material exhibits positive piezoresistivity. At higher frequencies, however, the material exhibits negative piezoresistivity. A state of zero piezoresistivity also exists between these cases. Computational micro-modeling revealed that this piezoresistive switching behavior is the consequence of inter-CNF AC transport behaving like a parallel resistor-capacitor arrangement and strain affecting the parallel or tunneling resistance. This novel switching behavior opens the door to many exciting possibilities for frequency-selective piezoresistive behavior in next-generation carbon nanofiller-based sensors.