Reproducible Negative Differential Resistance Research Articles

Sprayed FeWO4 thin film-based memristive device with negative differential resistance effect for non-volatile memory and synaptic learning applications

Resistive switching (RS) memories have attracted great attention as promising solutions to next-generation non-volatile memories and computing technologies because of their simple device configuration, high on/off ratio, low power consumption, fast switching, long retention, and significant cyclic stability. In this work, uniform and adherent iron tungstate (FeWO4) thin films were synthesized by the spray pyrolysis method with various precursor solution volumes, and these were tested as a switching layer for the fabrication of Ag/FWO/FTO memristive devices. The detailed structural investigation was done through various analytical and physio-chemical characterizations viz. X-ray diffraction (XRD) and its Rietveld refinement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The results reveal the pure and single-phase FeWO4 compound thin film formation. Surface morphological study shows the spherical particle formation having a diameter in the range of 20 to 40 nm. The RS characteristics of the Ag/FWO/FTO memristive device demonstrate non-volatile memory characteristics with significant endurance and retention properties. Interestingly, the memory devices show stable and reproducible negative differential resistance (NDR) effects. The in-depth statistical analysis suggests the good operational uniformity of the device. Moreover, the switching voltages of the Ag/FWO/FTO memristive device were modeled using the time series analysis technique by utilizing Holt’s Winter Exponential Smoothing (HWES) approach. Additionally, the device mimics bio-synaptic properties such as potentiation/depression, excitatory post-synaptic current (EPSC), and spike-timing-dependent plasticity (STDP) learning rules. For the present device, the space-charge-limited current (SCLC) and trap-controlled-SCLC effects dominated during positive and negative bias I–V characteristics, respectively. The RS mechanism dominated in the low resistance state (LRS), and the high resistance state (HRS) was explained based on the formation and rupture of conductive filament composed of Ag ions and oxygen vacancies. This work demonstrates the RS in the metal tungstate-based memristive devices and demonstrates a low-cost approach for fabricating memristive devices.

Room temperature asymmetric negative differential resistance characteristics of AlGaN/GaN resonant tunneling diodes grown by metal-organic chemical vapor deposition

A large area AlGaN/GaN resonant tunneling diode (RTD) grown by metal–organic chemical vapor deposition (MOCVD) is manufactured. The device adopts air-bridge structure suitable for the terahertz (THz) band, and a commercially available high-frequency GaN technology is applied in the process of device fabrication. Negative differential resistance (NDR) characteristics of the device are observed under the bipolar bias voltage at room temperature, which exhibits clear anti-symmetry in the peak-to-valley current ratio (PVCR), peak voltage and peak current density. The work systematically investigates how the built-in electric field introduced by polarization effects modulates the resonant tunneling transport utilizing TCAD tool Silvaco-ATLAS, and analyzes the enhancement of the resonant tunneling under negative bias voltage of the RTD with low-aluminum content AlGaN as barriers. The AlGaN/GaN RTD with conventional double-barrier single (DBS) quantum well (QW) structure shows reproducible NDR characteristics under the bipolar bias voltage at room temperature, which facilitates the design and extensive study of complicated device structures.

DNA-Immobilized CoFe2O4 Magnetic Nanoparticles: A Nature-Friendly Material Manifesting Negative Differential Resistance and Hysteresis Effects

Negative differential resistance (NDR) and hysteresis effects have been successfully achieved by synthesizing DNA-immobilized CoFe2O4 magnetic nanoparticles using wet chemical co-precipitation method. These multiple effects in a single compound particle can open the door for several next generation applications from high frequency communication device development to memory storage device. Here, for both positive and negative bias condition during electrical characterization, reproducible NDR peaks have been found. For the sample with maximum DNA conjugation with CoFe2O4 magnetic nanoparticles consistent hysteresis effects have also been found. Both of these features i.e., NDR and hysteresis can be attributed to conformational changes in crystal structure due to addition of DNA and polaron transform phenomena at the molecular level, respectively. By achieving these two features in one material, multifunctional devices can be developed for molecular electronic applications.

Tuning of electron tunneling: a case study using BODIPY molecular layers.

Redox active π-conjugated organic molecules have shown the potential to be used as electronic components such as diode and memory elements. Here, we demonstrate that using simple surface chemistry, rectification characteristics can be tuned to reproducible negative differential resistance (NDR) with a very high peak-to-valley ratio (PVR) up to 1000 in 2,6-diethyl-4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indecene (BODIPY) grafted on Si. The change in properties is related to oxidation and reduction of BODIPY, which results in the change in resonant to non-resonant tunneling of electrons under bias. This has been explained by the ab initio molecular-orbital theoretical calculations.

Negative differential resistance effect in resistive switching devices based on h-LuFeO3/CoFe2O4 heterojunctions.

The negative differential resistance (NDR) effect enables multilevel storage and gradual resistance modulation in resistive switching (RS) devices to be achieved. However, the poor reproducibility of NDR is the obstacle that restricts their application because the appearance of the NDR effect in RS devices is usually accidental or unstable at room temperature. In this report, we demonstrate a polarization and interfacial defect modulated NDR effect in h-LuFeO3/CoFe2O4 heterojunction-based RS devices; especially, the NDR is reproducible after hundreds of cycles at room temperature. This research provides an effective way for realizing the reproducible NDR effect in ferroelectric RS devices, and it may promote the development and application of RS devices with the NDR effect.

Repeatable Room Temperature Negative Differential Resistance in AlN/GaN Resonant Tunneling Diodes Grown on Sapphire

AbstractResonant tunneling diodes (RTDs) are candidates for high power terahertz oscillators, and form the basis for understanding the quantum confinement and vertical transport in quantum structures such as quantum cascade lasers and quantum cascade detectors. In this work, repeatable negative differential resistance (NDR) is achieved in AlN/GaN RTDs grown on sapphire substrate by plasma‐assisted molecular‐beam epitaxy. Two reproducible NDR regions sequentially following two preresonance replicas are demonstrated at room temperature. A current region exhibiting negative correlation with temperature and oscillation‐like features is first identified under reverse bias, which is interpreted as a combined contribution of weak resonant tunneling channels through different bound states in the well. The revealed peak‐to‐valley current ratio ranges from 1.1 to 1.8, and peak current density ranges from 5 to 164 kA cm−2. Using an analytic model, resonant tunneling transports in both bias directions are quantitatively characterized and show good agreements with experiment results, demonstrating the capability of accurate quantum transport control using III‐nitride grown on sapphire substrate. The findings will promote the implementation of low cost III‐nitride monolithic microwave circuits and resonant tunneling structures based on sapphire, SiC, and even silicon substrates.

Electron transport of oligothiophene derivative molecular device at varied temperature and light illumination

The charge transport of thiol-functionalized thiophene molecular wire incorporated with an α-hydroxyphenyl pyridine group was investigated by a soft stamp-printing approach. Current–voltage characteristics were measured from 95 up to 299K under both dark and light conditions. The molecular junction exhibits asymmetric conducting characteristics and reversible optoelectronic switching; the on/off ratio at 95K is of 3 orders of magnitude. The experimental data was analyzed using the Simmons and Fowler–Nordheim tunneling models. The effective barrier height of device is greatly affected by substrate temperature, light illumination and bias polarity. The degree of electronic coupling between the top electrode and molecule has a great impact on the junction charge transport. Reproducible negative differential resistance was also observed at low temperature in dark. The first-principle calculations show that the conduction mainly takes place through the lowest unoccupied molecular orbital of the molecular wire, and the negative differential resistance may result from effect of resonant tunneling.

Cooperative dynamics in charge-ordered state ofα-(BEDT-TTF)2I3

Electric-field-dependent pulse measurements are reported in the charge-ordered state of alpha-(BEDT-TTF)2I3. At low electric fields up to about 50 V/cm only negligible deviations from Ohmic behavior can be identified with no threshold field. At larger electric fields and up to about 100 V/cm a reproducible negative differential resistance is observed with a significant change in shape of the measured resistivity in time. These changes critically depend whether constant voltage or constant current is applied to the single crystal. At high enough electric fields the resistance displays a dramatic drop down to metallic values and relaxes subsequently in a single-exponential manner to its low-field steady-state value. We argue that such an electric-field induced negative differential resistance and switching to transient states are fingerprints of cooperative domain-wall dynamics inherent to two-dimensional bond-charge density wave with ferroelectric-like nature.

Resistive switching effects in single metallic tunneling junction with nanometer-scale gap

We fabricated a single tunneling junction with a nanometer-scale gap between Pt electrodes. We found that the gap distance became smaller after a current sweep, which was presumably caused by the migration of the Pt atoms at the anode. The junction showed a reproducible negative differential resistance characteristic after reduction in the gap. The junction also showed resistive switching characteristics with a resistance ratio of over 100 by applying voltage of different waveforms. The tunneling area and gap distance for on/off-state were quantitatively estimated by fitting the measured characteristics to the simple model as 100 nm2 and 0.8/1.2 nm, respectively.

Current-voltage characteristics of zinc-blende (cubic) Al0.3Ga0.7N/GaN double barrier resonant tunneling diodes

Measurements of the current-voltage characteristics of zinc-blende (cubic) Al0.3Ga0.7N/GaN, double barrier resonant tunneling diodes are presented. Clear and reproducible negative differential resistance effects are observed, with room temperature peak-to-valley ratios up to 4 and peak currents up to about 1000 A cm−2.

Negative differential resistance effects in spun films of substituted phthalocyanine derivatives

Spun films of novel substituted lead phthalocyanine derivatives between aluminum and indium tin oxide electrodes exhibit large, reproducible negative differential resistance (NDR) in their current–voltage characteristics and can be electrically switched between a high conductance on state and a low conductance off state. Space charge limited conduction mechanism was identified from temperature dependent measurements to be responsible for charge transport. The NDR effect may be due to the charge storage in the structure near the electrodes.

Redox-Mediated Negative Differential Resistance Behavior from Metalloproteins Connected through Carbon Nanotube Nanogap Electrodes

A reproducible negative differential resistance (NDR) behavior with symmetric peaks was observed from the planar-type metalloproteins (ferritins) devices utilizing metallic single walled carbon nan...

Negative Differential Resistance and Memory Effect in Diodes Based on 1,4-Dibenzyl C60 and Zinc Phthalocyanine Doped Polystyrene Hybrid Material

Negative differential resistance (NDR) and memory effect were observed in diodes based on 1,4-dibenzyl C60 (DBC) and zinc phthalocyanine doped polystyrene hybrid material. Certain negative starting sweeping voltages led to a reproducible NDR, making the hybrid material a promising candidate in memory devices. It was found that the introduction of DBC enhanced the ON/OFF current ratio and significantly improved the memory stability. The ON/OFF current ratio was up to 2 orders of magnitude. The write-read-erase-reread cycles were more than 106, and the retention time reached 10,000 s without current degradation.

Negative differential resistance effect in organic devices based on an anthracene derivative

The authors observed a negative differential resistance (NDR) in organic devices consisting of 9,10-bis-(9,9-diphenyl-9H-fluoren-2-yl)-anthracene (DPFA) sandwiched between Ag and indium tin oxide electrodes. The large NDR shown in current-voltage characteristics is reproducible, resulting in that the organic devices can be electrically switched between a high conductance state (on state) and a low conductance state (off state). It can be found that the currents at both on to off states are space-charge limited and attributed to the electron traps at the Ag/DPFA interface. The large and reproducible NDR makes the devices of tremendous potential in low power memory and logic circuits.

Room-temperature negative differential resistance in polymer tunnel diodes using a thin oxide layer and demonstration of threshold logic

Conjugated polymers, with π molecular orbitals delocalized along the polymer chain, are useful organic semiconductors that provide the possibility of molecular electronics for low-power organic-based memory and logic. Quantum functional devices based upon carrier tunneling processes open vistas into very efficient and low-power consumption circuitry that would be ideal for these applications. We demonstrate here strong room temperature negative differential resistance (NDR) for poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer tunnel diodes (PTD) using a thin TiO2 tunneling layer (∼2–8nm) sandwiched between the MEH-PPV and the indium tin oxide anode. A key advantage is the pronounced NDR using a thick polymer layer with a large active area, circumnavigating the need for molecularly-sized junctions. Current-voltage measurements show large and reproducible NDR with a PVCR as high as 53 at room temperature. We also demonstrate basic logic circuit operation using a pair of these PTDs connected in series to form a monostable-bistable transition logic element (MOBILE) latch.

Clustering Effects on Discontinuous Gold Film NanoCells

Reproducible negative differential resistance (NDR)-like switching behavior is observed in NanoCells. This behavior is attributed to the formation of filaments and clusters between the discontinuous gold films. Control experiments are performed by self-assembly of insulating molecules between the gold islands and conducting molecules on these islands. Additional control experiments are performed by removing the filaments and clusters between islands using a piranha bath. The results are consistent with theoretical predictions and extend the domain of molecular electronics based in organic molecules to include nanosized clusters as active units. This facilitates a scenario where synthetically accessible organic molecules, with defined characteristics, can be adjusted by metallic nanoclusters as an in situ fine-tuning element, able to compensate for the lack of addressing in the nanosize regime.

Negative differential resistance in a bilayer molecular junction

Negative differential resistance (NDR) is reported for a bilayer molecular junction. The system is comprised of a Hg–alkanethiol//arenethiol–Au bilayer molecular junction formed by bringing into contact a tetradecanethiol self-assembled monolayer (SAM)-coated drop of Hg with the surface of an oligo(phenylene-ethynylene) SAM on Au. Persistent, reproducible NDR is observed in the current–voltage characteristics with peak-to-valley ratios as high as 4.5 at room temperature. These results open a promising line of investigation of structure/function relationship and mechanisms in molecular NDR components.

High Inverse Voltage Germanium Rectifiers

Rectifying current-voltage characteristics going up to several hundred volts inverse have been observed in metal-germanium point contact rectifiers. A reproducible negative differential resistance region occurs in the inverse characteristic. Certain impurities are desirable in producing high voltage material. Surface treatment, e.g., by etching, is very important. The metal used as a whisker has little effect. Increasing the force of contact increases greatly the current of low voltages but has less effect on the high voltage curve. Pronounced improvement of rectification can be effected by treatment of the contact with large currents. Variation with temperature is very marked, especially for crystals of large inverse resistance; the variation of the inverse peak with temperature indicates that contact heating is responsible for the negative resistance. Time lags in the inverse negative resistance region of the order of 10−5 second occur. When contact is made between two Ge crystals, typical inverse characteristics are observed in both directions. Photoelectric effects are observed and indicate that the barrier thickness is greater the higher the inverse peak voltage.