Negative Differential Resistance Effect Research Articles

Coexistence mechanisms of negative differential resistance and resistive switching effects in a WOx-based memristor

Metal oxide memristors are highly desirable for bionic synaptic applications.

Regulation and mechanism of graphene electrode bending on negative differential resistance of 2-phenylpyridine molecular devices

Combining non-equilibrium Green’s function with density functional theory, we study the electronic transport properties of the molecular devices comprised of 2-phenylpyridine and zigzag graphene nanoribbon (ZGNR) electrodes. The <i>I-V</i> characteristics and transmission coefficients under external voltage biases are analyzed, and the results show that the negative differential resistance (NDR) is effectively adjusted by the bending of ZGNR electrode, which reduces the peak voltage (<i>V</i><sub>p</sub>) and increases the peak-valley ratio (PVR) of the device. When the electrode bending angle is 15°, the PVR of device M2 is a maximum value of 12.84 and <i>V</i><sub>p</sub> is 0.1 V, which is low enough for practical applications. The transmission spectra, the density of states and the real-space scattering state distribution at <i>E</i><sub>f </sub> of device under zero bias explain that the weaker coupling between the molecules and the electrodes is caused by the bending of the ZGNR electrode, which might be responsible for the adjustability of NDR. The analysis shows that the bending of the electrode changes the electronic structure between the 2-phenylpyridine molecule and the ZGNR electrode, and then changes the wave functions overlap between them, the coupling between the molecule and the electrodes gets weaker. An external bias can induce the level to shift. The transmission coefficient for the weaker coupling between the molecules. The electrodes can fluctuate wildly from level to level, and large NDR effect under very low bias is obtained with the variation of external bias. Therefore, for highly symmetric molecular devices, the electronic transport properties can be effectively adjusted by changing the coupling between the central molecule and the electrodes. Our investigations indicate that the 2-phenylpyridine molecular device with ZGNR electrodes may have potential applications in the field of low-power dissipation molecules device.

High anisotropic magnetoresistance, perfect spin-filtering effect, and negative differential resistance effect of Cr-doped anatase phase TiO2

Anisotropy-based half-metallic materials are highly efficient in spintronic devices and have important applications in spintronics. Anatase phase TiO2 has attracted much attention because of its anisotropy, but its non-magnetism limits its applications in spintronics. We investigate the electronic structure of 3d transition metal-doped anatase phase TiO2 by first principles method to achieve spin injection of anatase. The calculation results exhibit that the Sc, Cr, Mn, Fe, and Ni-doped systems are half-metallic ferromagnets while other doped systems behave as magnetic metals except the V-doped system is a magnetic semiconductor. The calculated formation energy under O-rich condition are negative shows that all half-metals are thermodynamically stable, and we construct devices along the y-direction of the half-metal and find that the device based on the Cr-doped system has the best electronic transfer capacity under zero bias. Then we use the Cr-doped system as the electrode and the pure anatase unit cell as the central scattering region to construct devices in different directions. We find that the magnitude of the current along different transport directions varied greatly, and the calculated anisotropic magnetoresistance was as high as 300%. Furthermore, whether spin configurations (PC) or antiparallel configurations (APC), there is a 100% spin-filtering efficiency of the device, and we find a significant negative differential resistance effect of the device in PC. These results suggest that Cr-doped anatase phase TiO2 can be used in spintronics.

A Theoretical Study on Adjustment of Negative Differential Resistance Effect in Monolayer GeS via Substitutional Doping

Density functional theory and nonequilibrium Green's function theory are used to systematically explore the electronic structures and transport characteristics of doped monolayer GeS with group V (N, P, As) atoms. The calculated band structures demonstrate that the doping of N, P, and As atoms results in the transformation of monolayer GeS from semiconducting to metallic properties. Further, an obvious negative differential resistance (NDR) behavior is obtained by altering the dopant atom and the doping concentration. In particular, for N‐doped monolayer GeS, the NDR behavior appears in the millivolt region as the doping concentration decreases, and the current peak‐to‐valley ratio (PVR) is up to 107 (order of magnitude 7). These findings have significant implications for future design of low‐power novel nanoelectronic devices based on monolayer GeS.

Crystalline Unipolymer Monolayer with High Modulus and Conductivity.

The synthesis of crystalline polymer with a well-defined orientated state and a two-dimensional crystalline size beyond a micrometer will be essential to achieve the highest physical feature of polymer material but remain challenging. Herein, we show the synthesis of the crystalline unipolymer monolayer with an unusual ultrahigh modulus that is higher than the ITO substrate and high conductance by simultaneous electrosynthesis and manipulation. We find that the polymer monolayer has fully extended in the vertical and unidirectional orientation, which is proposed to approach their theoretically highest density, modulus, and conductivity among all aggregation formations of the current polymer. The modulus and current density can reach 40 and 1000 times higher than their amorphous counterpart. It is also found that these monolayers exhibit the bias- and length-dependent multiple charge states and asymmetrically negative differential resistance (NDR) effect, indicating that this unique molecular tailoring and ordering design is promising for multilevel resistive memory devices. Our work demonstrates the creation of a crystalline polymer monolayer for approaching the physical limit of polymer electronic materials and also provides an opportunity to challenge the synthetically iterative limit of an isolated ultra-long polymer.

Crystalline Unipolymer Monolayer with High Modulus and Conductivity

AbstractThe synthesis of crystalline polymer with a well‐defined orientated state and a two‐dimensional crystalline size beyond a micrometer will be essential to achieve the highest physical feature of polymer material but remain challenging. Herein, we show the synthesis of the crystalline unipolymer monolayer with an unusual ultrahigh modulus that is higher than the ITO substrate and high conductance by simultaneous electrosynthesis and manipulation. We find that the polymer monolayer has fully extended in the vertical and unidirectional orientation, which is proposed to approach their theoretically highest density, modulus, and conductivity among all aggregation formations of the current polymer. The modulus and current density can reach 40 and 1000 times higher than their amorphous counterpart. It is also found that these monolayers exhibit the bias‐ and length‐dependent multiple charge states and asymmetrically negative differential resistance (NDR) effect, indicating that this unique molecular tailoring and ordering design is promising for multilevel resistive memory devices. Our work demonstrates the creation of a crystalline polymer monolayer for approaching the physical limit of polymer electronic materials and also provides an opportunity to challenge the synthetically iterative limit of an isolated ultra‐long polymer.

Transport properties of As-F-based molecular magnetic tunnel junctions

By combining the density functional theory with non-equilibrium Green's function method, we theoretically design and investigate the spin-dependent transport properties of two molecular magnetic tunnel junctions (MMTJs) with the AsFNRs embedded in zigzag graphene nanoribbons in parallel and antiparallel spin configurations. The findings reveal that the MMTJs have distinct transport characteristics depending upon the orientations of the AsFNRs. Changing the spin configurations leads to two different net spin currents, and the maximal order of the tunneling magnetoresistance magnitude can reach 107%. In addition, a negative differential resistance (NDR) effect is found in our MMTJs. Our findings provide suitable candidates of MMTJs for the future spintronic devices.

Tunable electronic properties and negative differential resistance effect of the intrinsic type-III ZrS[formula omitted]/WTe[formula omitted] van der Waals heterostructure

Van der Waals heterostructure (vdWH) has attracted considerable interest because of its ability to combine the excellent properties of stacked materials to suit different application requirements. The limited presence of type-III vdWH is a serious barrier for the development of two-dimensional materials in the field of tunneling field effect transistors. Herein, we propose a novel ZrS2/WTe2 vdWH with type-III band alignment and investigate its structural, electronic and quantum transport properties using first-principles calculations. The physical mechanism of type-III band alignment is analyzed. The electronic structures of this vdWH can be adjusted to enhance the band-to-band tunneling effect or achieve an interesting transition from type-III to type-II band alignment via external vertical electric field and different strains. Finally, we study the quantum transport properties and confirm again the type-III band alignment. The I–V curve shows apparent negative differential resistance (NDR) behaviors under low bias voltages, which provides substantial evidence supporting the applicability of this vdWH to low power devices. Our study not only expands the field of type-III band alignment heterostructures in 2D materials, but also provides a remarkable candidate material with tunable electronic properties and the favorable NDR effect for experimental designs and practical applications of novel multi-functional nanoelectronic devices.

Multifunctional 2D g-C4N3/MoS2 vdW Heterostructure-Based Nanodevices: Spin Filtering and Gas Sensing Properties.

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C4N3/MoS2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C4N3/MoS2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

MoS2/Si tunnel diodes based on comprehensive transfer technique

Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor (TFET) is considered as one of the most promising low-power devices that can simultaneously obtain low off-state current (I OFF), high on-state current (I ON) and steep subthreshold swing (SS). As a key element for the 2D/3D TFET, the intensive exploration of the tunnel diode based on the 2D/3D heterostructure is in urgent need. The transfer technique composed of the exfoliation and the release process is currently the most common approach to fabricating the 2D/3D heterostructures. However, the well-established transfer technique of the 2D materials is still unavailable. Only a small part of the irregular films can usually be obtained by mechanical exfoliation, while the choice of the chemical exfoliation may lead to the contamination of the 2D material films by the ions in the chemical etchants. Moreover, the deformation of the 2D material in the transfer process due to its soft nature also leads to the nonuniformity of the transferred film, which is one of the main reasons for the presence of the wrinkles and the stacks in the transferred film. Thus, the large-scale fabrication of the high-quality 2D/3D tunnel diodes is limited. In this article, a comprehensive transfer technique that can mend up the shortages mentioned above with the aid of the water and the thermal release tape (TRT) is proposed. Based on the method we proposed, the MoS2/Si tunnel diode is experimentally demonstrated and the transferred monolayer MoS2 film with the relatively high crystal quality is confirmed by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman characterizations. Besides, the prominent negative differential resistance (NDR) effect is observed at room temperature, which verifies the relatively high quality of the MoS2/Si heterojunction. The bilayer MoS2/Si tunnel diode is also experimentally fabricated by repeating the transfer process we proposed, followed by the specific analysis of the electrical characteristics. This study shows the advantages of the transfer technique we proposed and indicates the great application foreground of the fabricated 2D/3D heterostructure for ultralow-power tunneling devices.

Negative differential resistance in novel nanoscale devices

Negative differential resistance (NDR) is a physical effect, which is widespread in quantum electronics from tunneling diodes up to memristors. Although NDR has been discovered many decades ago, there are still hundreds of papers published in the last years dealing with this effect. Since many quantum devices are nowadays fabricated at atomic scale, the NDR effect opens new applications. This manuscript is an overview of various physical phenomena, which produce NDR effects in nanoscale devices. These phenomena include quantum tunneling, the ballistic electronic transport in nanostructures and insulator–metal transitions, which are common in nanoscale devices for high-frequency applications or for new computing architectures, such as reversible computation, quantum computation and neuromorphic computing.

Understanding the Origin of Tensile Response in a Graphene Textile Strain Sensor with Negative Differential Resistance.

The flexible strain sensors based on the textile substrate have natural flexibility, high sensitivity, and wide-range tensile response. However, the textile's complex and anisotropic substructure leads to a negative differential resistance (NDR) response, lacking a deeper understanding of the mechanism. Therefore, we examined a graphene textile strain sensor with a conspicuous NDR tensile response, providing a requisite research platform for mechanism investigation. The pioneering measurement of single fiber bundles confirmed the existence of the NDR effect on the subgeometry scale. Based on the in situ characterization of tensile morphology and measurement, we conducted quantitative behavior analyses to reveal the origin of tensile electrical responses in the full range comprehensively. The results showed that the dominant factor in generating the NDR effect is the relative displacement of fibers within the textile bundles. Based on the neural spiking-like tensile response, we further demonstrated the application potential of the textile strain sensor in threshold detection and near-sensor signal processing. The proposed NDR behavior model would provide a reference for the design and application of wearable intelligent textiles.

A physics-oriented memristor model with the coexistence of NDR effect and RS memory behavior for bio-inspired computing

Bio-inspired computing promises fundamentally different ways to advances in artificial intelligence with extreme energy efficiency. Memristive technologies due to the non-volatility, high density, low-power, and synaptic bionic properties can help in realizing bio-inspired architecture and its hardware implementation. This paper proposes a novel physics-oriented memristor model with coexistence of negative differential resistance (NDR) effect and resistive switching (RS) memory behavior for bio-inspired computing. Firstly, an Ag/TiOx/FTO memristor is fabricated using sol-gel and magnetron sputtering method, and its performance test demonstrates that the coexistence of NDR effect and RS memory behavior can be modulated by the moisture. Then, a physical-oriented memristor model is constructed, which provides the possibility to explore the dynamics of the coexistence of NDR effect and RS memory behavior in simulation. Furthermore, a memristor-based affective computing circuit emulating the process of human affective associative learning is designed. The experiment demonstrates that the coexistence of NDR effect and RS memory behavior can change the memory time without additional circuit and cost, which is expected to realize the automatic conversion from short-term memory to long-term memory in bio-inspired computing.

Two-dimensional tetragonal ZnB: A nodalline semimetal with good transport properties

Nodal-line semimetals have become a research hot-spot due to their novel properties and great potential application in spin electronics. It is more challenging to find 2D nodal-line semimetals that can resist the spin–orbit coupling (SOC) effect. Here, we predict that 2D tetragonal ZnB is a nodal-line semimetal with great transport properties. There are two crossing bands centered on the S point at the Fermi surface without SOC, which are mainly composed of the p xy orbitals of Zn and B atoms and the p z orbitals of the B atom. Therefore, the system presents a nodal line centered on the S point in its Brillouin zone (BZ). And the nodal line is protected by the horizontal mirror symmetry Mz . We further examine the robustness of a nodal line under biaxial strain by applying up to −4% in-plane compressive strain and 5% tensile strain on the ZnB monolayer, respectively. The transmission along the a direction is significantly stronger than that along the b direction in the conductive channel. The current in the a direction is as high as 26.63 μA at 0.8 V, and that in the b direction reaches 8.68 μA at 0.8 V. It is interesting that the transport characteristics of ZnB show the negative differential resistance (NDR) effect after 0.8 V along the a (b) direction. The results provide an ideal platform for research of fundamental physics of 2D nodal-line fermions and nanoscale spintronics, as well as the design of new quantum devices.

Trans-polyacetylene based organic spin valve for a multifunctional spin-based device: A first principle analysis

Carbon-based materials are the promising candidates for the design of multifunctional spintronic devices, owing to their fascinating inherent attributes such as the ballistic transport nature, long spin coherence time, etc. Here, we report the spin-dependent electron transport properties of a trans-polyacetylene channel sandwiched between two semi-infinite hydrogen-passivated zigzag graphene nanoribbon (ZGNR) electrodes within the framework of spin-polarized density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalisms. The proposed device exhibits an excellent spin-dependent transport behavior within the bias window of [-0.5 V, 0.5 V]. In parallel configuration (PC), the device offers an ideal spin filtration efficiency of almost 100% within the bias range of [-0.4 V, 0.4 V], and in antiparallel configuration (APC), it exhibits negative differential resistance (NDR), dual-spin rectification, and dual-spin filtration effects. Also, a high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. To validate the aforementioned effects, the transmission spectra along with the area enclosed by the curve, eigenvalues, eigenstates, and quantum conductance have also been analyzed. In addition, the impact of hybridization and torsion defects on the spin-dependent transport phenomenon through trans-polyacetylene has been investigated. Furthermore, the modelled device is observed to exhibit the spin Seebeck effect in PC under the influence of temperature gradient. The proposed device may stand as a good contender for various spintronic and spin caloritronic applications. • First principle based analysis of a trans-polyacetylene based multifunctional spin-based device. • The device displays a perfect spin filtration efficiency and dual rectification effects. • A high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. • Thermal Spin Seebeck and spin filtering effects are observed in the proposed model. • A potential candidate in the field of spintronic and spin caloritronic applications.

TPV radical-based multifunctional molecular spintronic device: A first-principles study

We design a multifunctional molecular spintronic device consisting of two 1,3,5-triphenylverdazyl (TPV) radicals with carbon nanotube bridge and electrodes , and investigate its spin-polarized transport properties using the first-principles density functional theory and nonequilibrium Green's function method. The results show that the spin-polarized transport properties depend strongly on the external magnetic field modulation and high-efficiency spin-filtering, giant magnetoresistance , spin-rectifying and low-bias voltage negative differential resistance effects can be realized in this designed device. The mechanisms are proposed for these interesting physical effects based on the bias-dependent spin-resolved transmission function, projected density of states and corresponding molecular projected self-consistent Hamiltonian orbitals analysis. These results hold great potential for the development of high-performance multifunctional molecular spintronic devices. High-efficiency spin-filtering, giant magnetoresistance, spin-rectifying and low-bias voltage negative differential resistance effects are realized in a TPV radical-based molecular spintronic device with carbon nanotube bridge and electrode. • Spin-polarized transport properties of a TPV radical-based molecular spintronic device are investigated. • Spin-polarized transport properties depend strongly on the external magnetic field modulation. • High-efficiency spin-filtering, GMR, spin-rectifying and low-bias voltage NDR effects are realized.

Improved analog performance of FDSOI based NCFET with a ferroelectric–paraelectric–dielectric gate stack

With the superior analog/RF performance of planar device architectures such as fully depleted silicon-on-insulator (FDSOI) MOSFETs, it becomes important to investigate the impact of a ferroelectric material in the gate stack, resulting in negative capacitance (NC) behavior, on the device performance. In this work, through calibrating the FDSOI MOSFET (as the baseline device architecture) with experimental data, we compare the impact of ferroelectric–dielectric (FE–DE) and ferroelectric–paraelectric–dielectric (FE–PE–DE) gate stacks on the electrostatics of an NCFET device for a practically realisable metal–ferroelectric–insulator–semiconductor (MFIS) structure. A suitable thickness of the ferroelectric (FE) layer in the FE–DE stack and the maximum drain–source voltage () that can be applied (determining the power supply voltage), are identified so as to ensure that constraints such as no negative differential resistance (NDR) effects, threshold voltage (), sub-threshold slope (SS) invariability with drain voltage variations and hysteresis-free behavior in transfer characteristics (–) are all satisfied. From the thickness of the FE layer in the FE–DE stack, the thickness of the FE layer in the FE–PE–DE stack (PE layer thickness is fixed at 1 nm) is determined where with a thicker FE layer, we obtain similar capacitance from the FE–PE–DE gate stack to that obtained from the FE–DE stack, while meeting all the constraints applied to the FE–DE stack based NCFET, enabling determination of the power supply voltage. Through showing good SSs with reduced output conductance (), resulting in improved dc gain () and improved linearity parameters ( and ) along with scaling of power supply, an FE–PE–DE stack shows better analog performance, with lower power consumption, compared to an FE–DE stack, for an FDSOI NCFET, at 14 nm gate length.

Negative Differential Resistance in Oxygen-ion Conductor Yttria-stabilized Zirconia for Extreme Environment Electronics.

Oxygen-ion conductors have traditionally been studied in the context of high temperature (≈ 873 to 1773 K) energy conversion and sensor technologies. However, there is growing interest in exploring ion-based electronics for harsh environments (400 to 573 K) that represents an emerging field. Here, we utilize a blocking electrode to modify the interface properties of oxygen-ion conducting yttria-stabilized zirconia (YSZ) thin film electrochemical cells. The modified YSZ cell exhibits negative differential resistance (NDR) in the current-voltage curves at 543 K in the air. A double-sweep method and analysis of the scan-rate dependence of the j-V characteristics clearly suggest that the NDR behavior is formed by the reduction reaction of adsorbed oxygen or platinum oxide at the YSZ/Pt interface. A stable and switchable YSZ NDR device is realized with a high peak-to-valley current ratio of 5.8 at 543 K. Utilizing the NDR effect, we demonstrate a proof-of-concept switchable ternary inverter by interfacing with a silicon transistor. Oxygen-ion conductors and their interfaces offer new directions to design electronics for extreme environments.

Computational study of transition metal dichalcogenide cold source MOSFETs with sub-60 mV per decade and negative differential resistance effect

To extend the Moore’s law in 5 nm node, a large number of two dimensional (2D) materials and devices have been researched, among which the ‘cold’ metals 2H MS2 (M = Nb, Ta) with unique band structures are expected to achieve the sub-60 mVdec−1 subthreshold swing (SS). We explored the electronic properties and ballistic quantum transport performance of ‘cold’ metals and the corresponding MOSFETs with idealized structures. The studied ‘cold’ metal field-effect transistors (CM-FETs) based on the ‘cold’ metals are capable to fulfill the high-performance (HP) and low-dissipation (LP) goals simultaneously, as required by the International Technology Roadmap for Semiconductors (ITRS). Moreover, gaps of ‘cold’ metals CM-FETs also demonstrate negative differential resistance (NDR) property, allowing us to further extend the use of CM-FETs. Owing to the wide transmission path in the broken gap structure of NbS2/MoS2 heterojunction, the 4110 μAμm−1 peak current, several orders of magnitude higher than the typical tunneling diode, is achieved by NbS2/MoS2 CM-FET. The largest peak-valley ratio (PVR) 1.1×106 is obtained by TaS2/MoS2 CM-FET with VGS = −1 V at room temperature. Our results claim that the superior on-state current, SS, cut-off frequency and NDR effect can be obtained by CM-FETs simultaneously. The study of CM-FETs provides a practicable solution for state-of-the-art logic device in sub 5 nm node for both more Moore roadmap and more than Moore roadmap applications.

A Room-Temperature Ferroelectric Resonant Tunneling Diode.

Resonant tunneling is a quantum-mechanical effect in which electron transport is controlled by the discrete energy levels within a quantum-well (QW) structure. A ferroelectric resonant tunneling diode (RTD) exploits the switchable electric polarization state of the QW barrier to tune the device resistance. Here, the discovery of robust room-temperature ferroelectric-modulated resonant tunneling and negative differential resistance (NDR) behaviors in all-perovskite-oxide BaTiO3 /SrRuO3 /BaTiO3 QW structures is reported. The resonant current amplitude and voltage are tunable by the switchable polarization of the BaTiO3 ferroelectric with the NDR ratio modulated by ≈3 orders of magnitude and an OFF/ON resistance ratio exceeding a factor of 2×104 . The observed NDR effect is explained an energy bandgap between Ru-t2g and Ru-eg orbitals driven by electron-electron correlations, as follows from density functional theory calculations. This study paves the way for ferroelectric-based quantum-tunneling devices in future oxide electronics.