Negative Differential Resistance Effect Research Articles

Resistive switching transparent SnO2 thin film sensitive to light and humidity

Designing and manufacturing memristor devices with simple and less complicated methods is highly promising for their future development. Here, an Ag/SnO2/FTO(F-SnO2) structure is used through the deposition of the SnO2 layer attained by its sol via the air-brush method on an FTO substrate. This structure was investigated in terms of the memristive characteristics. The negative differential resistance (NDR) effect was observed in environment humidity conditions. In this structure, valance change memory and electrometalization change memory mechanisms cause the current peak in the NDR region by forming an OH− conductive filament. In addition, the photoconductivity effect was found under light illumination and this structure shows the positive photoconductance effect by increasing the conductivity. Memristivity was examined for up to 100 cycles and significant stability was observed as a valuable advantage for neuromorphic computing. Our study conveys a growth mechanism of an optical memristor that is sensitive to light and humidity suitable for sensing applications.

Coherent ultrafast photoemission from a single quantized state of a one-dimensional emitter.

Femtosecond laser-driven photoemission source provides an unprecedented femtosecond-resolved electron probe not only for atomic-scale ultrafast characterization but also for free-electron radiation sources. However, for conventional metallic electron source, intense lasers may induce a considerable broadening of emitting energy level, which results in large energy spread (>600 milli-electron volts) and thus limits the spatiotemporal resolution of electron probe. Here, we demonstrate the coherent ultrafast photoemission from a single quantized energy level of a carbon nanotube. Its one-dimensional body can provide a sharp quantized electronic excited state, while its zero-dimensional tip can provide a quantized energy level act as a narrow photoemission channel. Coherent resonant tunneling electron emission is evidenced by a negative differential resistance effect and a field-driven Stark splitting effect. The estimated energy spread is ~57 milli-electron volts, which suggests that the proposed carbon nanotube electron source may promote electron probe simultaneously with subangstrom spatial resolution and femtosecond temporal resolution.

Type I organic quantum wells made of two organic semiconductors

Construction of organic quantum wells (OQWs) has been a challenge due to the difficulty in fabricating high-quality organic films in large area. Here, type I OQWs are successfully fabricated by using two OSCs with different bandgaps, and they exhibit both negative differential resistance (NDR) effect and absorption blueshift. Moreover, the OQW photoswitches show much higher photoresponsivity than the corresponding organic heterojunction ones. All the above results prove the successful construction of OQWs in a physical sense.

Multi-level optical memory with logical operation modulated by surface barrier in a single CH3NH3PbI3 perovskite micro/nanowire device

CH3NH3PbI3 is a potential candidate for optical information storage because of its excellent photoelectric response and hysteresis effect. However, the interface mechanism of the CH3NH3PbI3-based memory is still controversial, and the precise control of the resistive switching effect requires an effective method. Here, single CH3NH3PbI3 micro/nanowire devices with symmetric Ag electrodes were constructed. The role of the reversible redox reaction on the Ag electrode to modulate the interfacial barrier has been proposed, and the hysteresis behavior of the device can be precisely controlled by adjusting the illumination intensity and bias polarity. For example, when strong light and high voltage are applied at the same time, the device exhibits a symmetrical negative differential resistance effect; after being subjected to strong light and high voltage, the device exhibits a bipolar resistive switching effect, and the polarity of the large voltage determines the I-V curve wrapping way. On this basis, the device obtains multi-level optical storage and logic operation functions. This work provides a new way to understand the synergistic memory effect of light and bias on halide perovskite, which is expected to be further applied in the integrated field of optical nonvolatile memory and logical.

Non-equilibrium electronic properties of ultra-thin SiC NWs influenced by the tensile strain

The effect of the tensile strain on non-equilibrium electronic properties are studied for the ultra-thin SiC NWs (NWs) with different diameters. Results show that the equilibrium conductance fluctuates with the strain, and the maximum decreases with the increase of the size. Essentially, strong conductance originates from large electron transmission and delocalized electronic states. For I–V characteristics, the tensile strain affects significantly the growth rate and intensity of the current. Under any biases, the strongest current appears in late strain (0.7136) for the single-atom chain, while in the starting strains (e.g. 0.1584, 0.2504) for thicker NWs. The tensile strain would weaken the current of thicker NWs. The mechanical stretching contributes to valuable negative differential resistance (NDR) effect, which appears in middle and late stretching stages such as 5408, 0.7136 and 0.8472 for these three SiC NWs, respectively. Furthermore, NDR effect occurs at more strains and presents multistage features as the diameter of NW increases. The conductance waves with voltage. Such fluctuation deepens and show a more concentrated range with the increased size of NWs. The conductance at closer strains changes with the bias in a relatively close range. From structural evolution, when the NWs are fully extended under tensile strain without structural damage, the necking or the formation of single atom chains, the corresponding conductance and current are stronger, deriving from delocalized electronic states. This work provides an approach to get access to valuable NDR effect and strong backing in promising applications of nano piezoelectric electronics for ultra-thin SiC NWs.

Electronic transport across planar gold clusters of eight and nine atoms

The transport properties of gold clusters with eight and nine atoms between gold electrodes are investigated by using non-equilibrium Green’s function method combined with density functional theory. Negative differential resistance effect is found both in Au8 and Au9. From a new respect, the mechanism for the negative differential resistance effect is explored through calculating the number of electrons of the atoms in the clusters at different bias voltages. When Au9 takes vertical orientation, it is found that the voltage can change the coupling strength of the sandwiched system. When the value of the voltage is small, the current increases with decreasing of the cluster-electrode separation. But when the voltage increases to a certain value, the current decreases with decreasing of the cluster-electrode separation. When Au9 takes parallel orientation, different from other electronic transport systems, it is found that the transport behaviors for Au9 are not sensitive to the cluster-electrode separation, showing that this configuration has a better transport stability over the changes in distance, which may provide some new clues for developing future electron device.

Carrier transport and Negative differential resistance of electrically bipolar devices based on poly(3,4-ethylene-dioxythiophene): Poly (styrene sulfonate) film

A poly (3,4-ethylene-dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) film sandwiched between copper electrodes was used to create an electrically bipolar device using a conventional casting technique. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray spectroscopy (EDX) were used to investigate the structure, morphological behaviour, and homogeneous distribution of PEDOT conducting grains in the insulator matrix PSS. The device exhibits normal hysteretic electrical behaviour and a negative differential resistance (NDR) effect in the swept current-voltage (I–V) curves. By varying the PEDOT:PSS films' positive charge voltage and charging rate, the NDR effect may be tuned. A maximum current ratio of 103 can exist between the High Conducting State (HCS) and the Low-Conducting State (LCS). Complex impedance measurements of the Cu/PEDOT:PSS/Cu device were carried out at applied ac-voltage amplitude, Vac, range from 0.1 V to 2 V and over the frequency range from 100 Hz to 10 MHz at room temperature. Different models based on ac and dc experimental data are used to characterize and confirmed the carrier transport processes in the HC, LC-States and NDR.

A first-principles study on the electronic transport properties of symmetric B/N co-doped armchair graphene nanoribbons with H/O co-saturation

Tuning the transport properties of graphene-based devices to achieve better performance is a fascinating but tough challenge. To overcome this challenge, we created one-dimensional nanostructures that resemble chains by symmetrically doping B and N atoms at different positions in armchair graphene nanoribbons (AGNRs) of different widths saturated by H/O atoms. Their transport properties, including band structure, the spatial distribution of eigenstates, the projected density of states (PDOS), and current-voltage (I-V) curve, have been investigated depending on the non-equilibrium Green's function (NEGF) and Density functional theory (DFT) methods. Based on the calculations, the seven-atom-wide armchair graphene nanoribbons (7-AGNRs) have a distinctive negative differential resistance (NDR) effect with a maximum peak-to-valley ratio (PVR) of 3.34 × 106. We speculate that the NDR effect depends on the strength of the coupling between the band structures of the electrodes within the transmission window, and that the degree of overlap between the Pz orbitals of the doped atoms and their delocalized big π orbitals is also relevant. Compared to the existing diodes with fully hydrogenated or fluorinated edges, diodes with H/O co-saturated edges have lower start-up voltages and higher currents in the doped case, as well as rectification ratio of up to 4.48 × 106 in the range of [1.1 V, 1.4 V]. Our results have great promise for applications in digital and storage devices as well as in novel oscillators and nanoelectronics.

Improved resistive switching performance and mechanism analysis of MoO3 nanorods based memristors

Low dimensional nanomaterials have distinctive physical, chemical, and electrical characteristics, which have led to their widespread use in the preparation of sensors, optoelectronic devices, and nonvolatile memory devices in recent years. MoO3 nanomaterials are transition metal oxides with high work functions and broadband gaps, which have potential applications in electronic, electrochromic, and battery devices. In this work, Ag/MoO3/Ti memristive device was prepared by annealing MoO3 nanospheres, which can improve resistive switching (RS) behavior. In other words, one-dimensional (1D) MoO3 nanorods with uniform size and dense connections was obtained by annealing MoO3 nanospheres at 300 ℃. The RS behavior of the Ag/MoO3/Ti memristor presents obvious nonvolatile memory characteristics with larger resistance window at room temperature. In particular, the device shows N-type negative differential resistance (NDR) effect at relatively high positive voltage region. Based on the obtained data, the RS behavior conduction mechanism of the Ag/MoO3/Ti device was discussed by establishing physical models of Ohmic conduction and Schottky emission. This work establishes the foundation for further understanding the working mechanisms of memristors and exploring potential applications of low dimensional material based memristors.

TiW/SiOX:Al/TiW memristor with negative differential resistance effect for neuromorphic computing

Memristors, acting as artificial synapses, are proposed to be a promising candidate for neuromorphic computing applications. In this work, the CMOS process-compatible TiW/SiOX:Al/TiW memristor with negative differential resistance (NDR) effect is explored for this application. Nonpolar switching with a 340 on/off ratio, data retention beyond 106 s, and endurance of 106 cycles are realized. The device shows excellent analog behavior with nonlinearities of 1.69 and 0.65 of long-term potentiation and depression, respectively, under identical pulse stimuli. The synaptic features such as long-term potentiation (LTP), long-term depression (LTD), spike-timing-dependent plasticity (STDP), and paired-pulse facilitation (PPF) are mimicked. Moreover, on the basis of the symmetry and linearity of the conductance of TiW/SiOX:Al/TiW memristor, the neural network simulation for supervised learning presents successful pattern recognition, with an accuracy of 93.11% achieved after 20 iterations. It is proposed that the nonpolar NDR switching originates from the discontinuous Al metal nanoparticles that form deeply localized states in the energy band and result in the trap/de-trap of electronic carriers. Overall, this memristor with the NDR effect presents a unique way to simulate artificial synapse behavior for neuromorphic computing.

Optimization of Subthreshold Swing and Hysteresis in Hf0.5Zr0.5O2-Based MoS2 Negative Capacitance Field-Effect Transistors by Modulating Capacitance Matching.

Negative capacitance field effect transistors made of Hf0.5Zr0.5O2 (HZO) are one of the most promising candidates for low-power-density devices because of the extremely steep subthreshold swing and high open-state currents resulting from the addition of ferroelectric materials in the gate dielectric layer. In this paper, HZO thin films were prepared by magnetron sputtering combined with rapid thermal annealing. Their ferroelectric properties were adjusted by changing the annealing temperature and the thickness of HZO. Two-dimensional MoS2 back-gate negative capacitance field-effect transistors (NCFETs) based on HZO were prepared as well. Different annealing temperatures, thicknesses of HZO thin films, and Al2O3 thicknesses were studied to achieve optimal capacitance matching, aiming to reduce both the subthreshold swing of the transistor and the hysteresis of the NCFET. The NCFET exhibits a minimum subthreshold swing as low as 27.9 mV/decade, negligible hysteresis (∼20 mV), and the ION/IOFF of up to 1.58 × 107. Moreover, a negative drain-induced barrier lowering effect and a negative differential resistance effect have been observed. This steep-slope transistor is compatible with standard CMOS manufacturing processes and attractive for 2D logic and sensor applications as well as future energy-efficient nanoelectronic devices with scaled power supplies.

Bipolar nonlinear photo-controlled thyristor with variable-resistance effect

With the advancement of artificial intelligence technology, volatile memristors emulating neurons have gained widespread attention in the field of neuromorphic computing. This paper proposes a volatile bipolar nonlinear photo-controlled thyristor (PCT) compatible with CMOS technology, providing a reference for the structural design of silicon-based neurons. Technology computer aided design (TCAD) simulation is used to analyze the variable-resistance mechanism and photoelectric effect of the device. The PCT fabricated based on the 0.18 μm Bipolar-CMOS-DMOS (BCD) process has two electrode ports. When a fixed amplitude bipolar periodic excitation signal is applied to the anode of the device, the output current and voltage of PCT show nonlinear changes at the same time due to the negative differential resistance effect, satisfying the fundamental requirements of an oscillatory neuron. By further coupling the photoelectric effect, the device can achieve continuous switching from high-resistance state to low-resistance state under light source driving conditions. Finally, the transient data of PCT is extracted and the hysteresis loop is fitted, which verifies the accuracy of the device theory and model simulation.Index Terms—CMOS technology, variable-resistance effect, photoelectric effect, TCAD simulation.

Composition and sequence-controlled conductance of crystalline unimolecular monolayers.

Understanding how the charge travels through sequence-controlled molecules has been a formidable challenge because of simultaneous requirements in well-controlled synthesis and well-manipulated orientation. Here, we report electrically driven simultaneous synthesis and crystallization as a general strategy to study the conductance of composition and sequence-controlled unioligomer and unipolymer monolayers. The structural disorder of molecules and conductance variations on random positions can be extremely minimized, by uniform synthesis of monolayers unidirectionally sandwiched between electrodes, as an important prerequisite for the reproducible measurement on the micrometer scale. These monolayers show tunable current density and on/off ratios in four orders of magnitude with controlled multistate and massive negative differential resistance (NDR) effects. The conductance of monolayer mainly depends on the metal species in homo-metal monolayers, while the sequence becomes a matter in hetero-metal monolayers. Our work demonstrates a promising way to release an ultra-rich variety of electrical parameters and optimize the functions and performances of multilevel resistive devices.

Multifunctional spin transport behaviors of biphenyl-molecule-based nanodevices

For the development of low-power spin-multifunctional devices, we have explored the spin-dependent transport properties of nanodevices based on zigzag graphene nanoribbons bridged respectively by oblique, horizontal, and vertical connecting biphenyl molecules. Utilizing the first-principles calculations associated with the non-equilibrium Green's function methods, we found the superb transport results demonstrate that almost 100% spin polarization exists for the obliquely connected and horizontally connected biphenyl molecules devices in the parallel state (P). All of the designed devices exhibit excellent dual spin filtering efficiency and rectification effect in the antiparallel state (AP) with the rectification ratios up to 103, 104, and 105 for obliquely, horizontally, and vertically connected model devices, respectively. Simultaneously, a pronounced negative differential resistance effect can be observed in these devices independent of the spin state. Moreover, the thermal spin transport properties of the obliquely connected model device reveal an apparent Seebeck effect. Then, the length effect on the spin-resolved transport properties for the obliquely connected device have been conducted. Results reveal that the current values are highly tunable by changing the length of obliquely connected biphenyl molecules in the P state. Meanwhile, the doual spin filtering effect still remains, but its rectification effect gradually disappears with the increasing length of center scattering region in AP state. This study provides new insights into the design of multifunctional spin carbon-based and low power consumption devices.

Theoretical study on negative differential resistance in transition metal dichalcogenide planar heterostructures

Two types of WS2/MoX2/WS2 (X = S, Se) planar heterostructures driven by bias are theoretically proposed and studied, showing the pronounced negative differential resistance (NDR) effect. It is demonstrated that the maximum peak-to-valley ratio (mPVR) and current peak strongly depend on the temperature, and the enhanced mPVR can be realized by tuning the device length. In particular, type B (X = Se) has a more remarkable NDR effect than type A (X = S). Our work provides promising possibilities for designing and manufacturing future low-power electronic devices based on monolayer transition metal dichalcogenide planar heterostructures under low bias regime.

Evolution between Volatile and Nonvolatile Resistive Switching Behaviors in Ag/TiOx/CeOy/F-Doped SnO2 Nanostructure-Based Memristor Devices for Information Processing Applications

It is well known that higher requirements have been put forward for the computing efficiency and storage speed of the data processing of memory devices in the post Moore era. In particular, if a memory device with multiple physical characteristics can be developed, it will play an important role in realizing multifunctional applications of electronic systems. Here, a nanoscale memristor device with a Ag/TiOx/CeOy/F-doped SnO2 structure was prepared, which shows many interesting physical phenomena with the changing of the applied voltage. In the low-voltage region (<1.5 V), the device presents a volatile property, while it presents a nonvolatile behavior when a higher voltage (>2 V) was applied. Interestingly, the non-zero-crossing current–voltage (I–V) hysteresis behavior caused by the internal electromotive force appears in the voltage region of 0.5–1 V. Furthermore, as the applied voltage increases, the device gradually displays ideal memristor behavior and exhibits the standard resistance switching characteristic accompanied by the negative differential resistance effect in the region of 3.5–4.0 V. Therefore, this nanoscale device with multiple physical properties opens up a promising way for understanding the emerging physical phenomena, and it will be expected to become a potential candidate for the next generation of multifunctional electronic devices.

High temperature UV photodetectors based on the negative differential resistance effect of WO3/diamond PN junctions

A positive-negative (PN) junction tunneling diode ultraviolet (UV) photodetector of p-boron-doped diamond (BDD)/n-WO3 nanorods (NRs) with broad-band and good thermal stability was fabricated using heavily boron-doped degenerate semiconductor diamond (BDD) as a substrate. The operating temperature of the p-BDD/n-WO3 photodetector was increased to 300 °C through the negative differential resistance effect, benefiting from the excellent properties of diamond such as an increase in the concentration of boron atoms, a wideband gap (∼5.5 eV), and high thermal conductivity. In particular, the devices exhibited a negative differential resistance phenomenon in the range of 30–240 °C, accompanied by a rapid increase in photocurrent values and the phenomenon disappeared as the temperature rises to 300 °C. Moreover, a quick response speed (tr1 = 1.2 s), a high photocurrent (0.11 A at 5 V), a good rectification ratio (1.81), and a photo to dark current ratio (0.15) can be demonstrated in the p-BDD/n-WO3 NRs photodetector at 300 °C, indicating its excellent thermal stability. This work provides an effective way method for realizing UV photodetectors based on the negative differential resistance effect and reclaims the potential application of p-BDD/n-WO3 in high temperature semiconductor optoelectronic devices.

Negative differential resistance effect and current rectification in WS2 nanotubes: A density functional theory study

Electronic properties of (n,0) zigzag tungsten disulfide WS2 nanotubes and transport properties of (7,0) zigzag nanotube heterojunction are investigated by utilizing non-equilibrium Green's function formalism (NEGF). The results reveal that inclusion of the spin-orbit (SO) coupling significantly reduces the value of the band gap about 15.52\\%. Additionally, strong negative differential resistances take place in voltage regions between −0.2 and −0.4 V as well as between −0.5 and −0.6 V. Moreover, temperature dependent transport properties are elaborately investigated in this work. The results show that, as the temperature increases to 600 K the stronger negative differential resistance occurs in both positive and negative bias voltages. Finally, a reasonably large degree of rectification ratio can be established. Our analysis can provide a comprehensive perspective on the NDR effect and current rectification in WS2 nanotubes and can be used as a beneficial guide for future designing of novel logical and nanoelectronic and spintronic devices.

Electronic, Optoelectronic, and Thermoelectric Single‐Molecule Devices with Different Molecular Unit‐Length

AbstractMolecular devices have given impetus to the development of new electronic components. The transport process of organic molecules has a significant impact on device performance. Diketopyrrolopyrrole (DPPn, n = 1,2,3,4.) and derivative molecules have been widely explored due to their long‐range and efficient transport properties. In this paper, the electronic, optoelectronic, and thermoelectric properties of single diketopyrrolopyrrole molecular devices with different molecular units are investigated. By adjusting the bias voltage, the single molecular devices show a negative differential resistance effect, for which the reasons are given. Molecular orbital energy levels are regulated by gate voltages to enable conversion of conductivity. The transformation of molecular device functions in time‐varying alternating current transport is discussed in detail. Bias voltage regulation is performed for the molecular device optical response to produce better photocurrent, and finally the thermoelectric current of the device is also analyzed. This results reveal that single molecular electronic, optoelectronic, and thermoelectric properties are highly correlated with molecular unit‐length, which provides guidance for the development of molecular devices with different unit lengths.

Superconformal Film Growth: From Smoothing Surfaces to Interconnect Technology.

ConspectusElectronics manufacturing involves Cu electrodeposition to form 3D circuitry of arbitrary complexity. This ranges from nanometer-wide interconnects between individual transistors to increasingly large multilevel intermediate and global scale on-chip wiring. At larger scale, similar technology is used to form micrometer-sized high aspect ratio through-silicon vias (TSV) that facilitate chip stacking and multilevel printed circuit board (PCB) metallization. Common to all of these applications is void-free Cu filling of lithographically defined trenches and vias. While line-of-sight physical vapor deposition processes cannot accomplish this feat, the combination of surfactants and electrochemical or chemical vapor deposition enables preferential metal deposition within recessed surface features known as superfilling. The same superconformal film growth processes account for the long-reported but poorly understood smoothing and brightening action provided by certain electroplating additives. Prototypical surfactant additives for superconformal Cu deposition from acid-based CuSO4 electrolytes include a combination of halide, polyether suppressor, sulfonate-terminated disulfide, and/or thiol accelerator and possibly a N-bearing cationic leveler. Many competitive and coadsorption dynamics underlie functional operation of the additives. Upon immersion, Cu surfaces are rapidly covered by a saturated halide layer that makes the interface more hydrophobic, thereby supporting the formation of a polyether suppressor layer. Also, halide serves as a cosurfactant supporting the adsorption of amphiphilic molecular disulfide species on the surface while inhibiting copper sulfide formation and incorporation into the growing deposit. Furthermore, the dangling hydrophilic sulfonate end group of the accelerator enables activated metal deposition by hindering polyether suppressor assembly. A common thread in superconformal feature filling is additive-derived positive feedback of the metal deposition reaction within recessed or re-entrant regions. For submicrometer features or optically rough surfaces, area reduction that accompanies the motion of concave surface segments results in the most strongly bound adsorbates' enrichment, which for the suppressor-accelerator systems is the sulfonate-terminated disulfide accelerator species. The superfilling and smoothing process is quantitatively captured by the curvature-enhanced adsorbate coverage mechanism. For larger features, such as TSV, whose depths approach the thickness of the hydrodynamic boundary layer, significant compositional and electrical gradients couple with the metal deposition process to give a negative differential resistance and related nonlinear effects on morphological evolution. For certain suppressor-only electrolytes, remarkable bottom-up feature filling occurs where metal deposition disrupts inhibiting adsorbates at the bottom of the TSV or overruns the ability of the suppressor to form due to kinetic or transport limitations. Because the electrical response to changes in interface chemistry is more rapid than mass transport processes, deposition on planar substrates proceeds by bifurcation into passive and active zones, generating Turing patterns. On patterned substrates, active zone development is biased toward the most recessed regions. The distinction between packaging and on-chip metallization will be blurred as the dimensions of the former merge with those of early day on-chip 3D metallization.