Increase In Tunneling Current Research Articles

Sliding Memristor in Parallel-Stacked Hexagonal Boron Nitride.

Sliding ferroelectricity in 2D materials, arising from interlayer sliding-induced interlayer hybridization and charge redistribution at the van der Waals interface, offers a means to manipulate spontaneous polarization at the atomic scale through various methods such as stacking order, interfacial contact, and electric field. However, the practical application of extending 2D sliding ferroelectricity remains challenging due to the contentious mechanisms and the complex device structures required for ferroelectric switching. Here, a sliding memristor based on a graphene/parallel-stacked hexagonal boron nitride/graphene tunneling device, featuring a stable memristive hysteresis induced by interfacial polarizations and barrier height modulations, is presented. As the tunneling current density increases, the memristive window broadens, achieving an on/off ratio of ≈103 and 2 order decrease of the trigger current density, attributed to the interlayer migration of positively charged boron ions and the formation of conductive filaments, as supported by the theoretical calculations. The findings open a path for exploring the sliding memristor via a tunneling device and bridge the gap between sliding ferroelectricity and memory applications.

Mesoporous Semiconductive Bi2Se3 Films.

Bi2Se3 is a semiconductive material possessing a bandgap of 0.3 eV, and its unique band structure has paved the way for diverse applications. Herein, we demonstrate a robust platform for synthesizing mesoporous Bi2Se3 films with uniform pore sizes via electrodeposition. Block copolymer micelles act as soft templates in the electrolyte to create a 3D porous nanoarchitecture. By controlling the length of the block copolymer, the pore size is adjusted to 9 and 17 nm precisely. The nonporous Bi2Se3 film exhibits a tunneling current in a vertical direction of 52.0 nA, but upon introducing porosity (9 nm pores), the tunneling current increases significantly to 684.6 nA, suggesting that the conductivity of Bi2Se3 films is dependent on the pore structure and surface area. The abundant porous architecture exposes a larger surface area of Bi2Se3 to the surrounding air within the same volume, thereby augmenting its metallic properties.

Photodetection Characteristics of Gold Coated AFM Tips and n-Silicon Substrate nano-Schottky Interfaces

Silicon (Si)-based photodetectors are appealing candidates due to their low cost and compatibility with the complementary metal oxide semiconductor (CMOS) technology. The nanoscale devices based on Si can contribute efficiently in the field of photodetectors. In this report, we investigate the photodetection capability of nano-Schottky junctions using gold (Au) coated conductive atomic force microscope (C-AFM) tips, and highly cleaned n-Si substrate interface. The Au nanotip/n-Si interface forms the proposed structure of a nano Schottky diode based photodetector. The electrical characteristics measured at the nanoscale junction with different Au nanotip radii show that the tunneling current increases with decreasing the tip radius. Moreover, the tunneling process and photodetection effects are discussed in terms of barrier width/height decrease at the tip-semiconductor interface due to the applied electric field as well as the generation of plasmon-induced hot-electron at the nanoparticle (i.e. C-AFM tip)/n-Si interface. Furthermore, the photodetection sensitivity is investigated and it is found to be higher for C-AFM tips with smaller radii. Moreover, this research will open a new path for the miniaturization of photodetectors with high sensitivity based on nano-Schottky interfaces.

Modeling of Electron Transmittance and Tunneling Current through a Trapezoidal Potential Barrier by Considering the Spin Polarization Effect

A modeling of the transmittance and tunneling current through a trapezoidal potential barrier was developed by taking into account the spin polarization of the electrons. The transmittance was calculated by using an Airy wavefunction approach and employing a zinc-blende material for the barrier in the heterostructure, which depends on the spin states indicated as ‘up’ and ‘down’. The obtained transmittance was then used to calculate the tunneling current by using the Gauss-Laguerre quadrature method. It was shown that the transmittance is not symmetric with the incident angle of the electron. It was also shown that the tunneling current increases with increasing the bias voltage and tends to be constant in a high voltage regime.

Boron-assisted growth of silica nanowire arrays and silica microflowers for bendable capacitor application

Aligned silica nanowire arrays and silica microflowers were fabricated using boron as the catalyst and under the flow N2 gas. The obtained product had no catalyst contamination. And silica nanowires had long lengths of a few hundreds. The growth of nanowire arrays and microflowers was explained using mechanism. Parallel-plate capacitors using silica nanowire mat as the dielectric were fabricated. The silica nanowire capacitor shows a specific capacitance of 0.24nF/cm2 at the frequency of 100Hz. The capacitor is not monotone changing with the frequency. The measurement of mechanical properties shows that the tunneling current increases along with an increase in bending angle of the capacitor.

MIS(p) Saturation Tunneling Current Controlled by Neighboring MIS Inversion Level Via Coupling Effect

In previous work, current coupling phenomena have been studied. It was reported that, when oxide is thick enough, the saturation current of the inner circle matches well with that of outer concentric ring among two neighboring metal-insulator-semiconductor(p) (MIS) tunnel diodes (TD) [1]. Besides, based on the lateral diffusion (LD) current as well as Schottky barrier height lowering, more source of aggregating electrons under surrounding floating gate makes saturation tunnel current greater [2]. In this work, three different metal patterns of MIS tunnel diodes are used to pore over current coupling phenomena, which mainly come from the LD of minority carrier. Figure 1 and figure 2 show schematic diagrams of the top views and cross sections of the fabricated devices. I-V curves of drain current versus drain voltage with and without floating aluminum rings are shown in figure 3; red curves are those under an irradiance of 4mW/cm2. For three I-V curves in black, with more aluminum rings, the saturation currents are greater due to more aggregating electron source [2]. For another three in red, the similar phenomenon reappears: light-induced e-h pairs are supplements to aggregating electrons below the floating ring and they enhance the LD current as well as the lowering of Schottky barrier height, leading to the increase of saturation tunneling current. Thus, saturation photocurrent is increased compared to that with less or even no rings. Figure 4(a) and 4(b) show current in dark and under irradiance respectively versus total perimeter (TP) extracted from figure 3 when VD is 1V. It is clear that current values are proportional to TP; thus, we assume the saturation ID increasing with longer perimeter is exactly due to extra neighboring aluminum gate ring, which accounts for the major impact of LD current. Figure 5 shows I-V characteristics of devices with electrode pattern shown in figure 1(a). The drain current versus drain voltage, the gate1 current versus gate1 voltage, and the gate2 current versus gate2 voltage are separately exhibited. Three hollow circle curves stand for those under irradiance. Despite the variance of perimeter and area among drain, gate1, and gate2, the saturation dark or light current of those three shows no difference. However, in previous work [3], [4], it was indicated, the saturation current increases with greater perimeter for single MIS(p) TD due to edge fringing field. Accordingly, we consider again the LD current of minority carrier a dominating role in such phenomenon. Since the LD current works for drain current in figure 4, where drain current is elevated by neighboring gate1 and gate2, then it works for gate1 and gate2 currents as well. In view of central drain, applied 1V and thin SiO2 make electrons beneath drain fewer than those beneath gate1 and gate2; therefore, the LD currents are established. Also, in view of gate1, applied 1V and thin SiO2 make electrons beneath gate1 fewer than those beneath drain and gate2. The same phenomenon happens in view of gate2; thus, the mutual coupling effect makes three saturation current values all equal. Photocurrents (three hollow curves) have the same value in saturation region because light-induced e-h pairs supply the minority carrier and it enhances the mutual coupling effect; therefore, photocurrents share the same value just like the dark currents. Under an irradiance of 4mW/cm2, light still plays a role of the supplement to minority carrier. Thus, saturation current of central drain increases with more floating surrounding gate rings no matter whether there is applied light on devices or not. And saturation current increases exactly with TP, which implies the LD as one of potential coupling effects. It is worth attention that the distance between drain and gate1 is only 5um but the coupling effect is clearly observed. What if the distance is minimized to commercially-used nanometer scale and it is believed the coupling effect would be even strengthened impacting ready-made devices. Last but not least, for neighboring MIS(p) structures, the mutual coupling effect makes their saturation currents equal to each other in spite of their different structure perimeter. Therefore it deserves our further exploration in nowadays trend of gate length shrinkage due to the miniature distance among devices. This work was supported by the Ministry of Science and Technology of Taiwan, ROC, under Contract No. MOST 105-2221-E-002-180-MY3 and NTU-ERP-105R89081. [1]C. S. Liao and J. G. Hwu, ECS Trans., 75, 77 (2016). [2]M. H. Yang and J. G. Hwu, IEDMS., 29, PD-3 (2016). [3]T. Y. Chen and J. G. Hwu, ECS Trans., 58, 79 (2013). [4]H. W. Lu and J. G. Hwu, ECS Trans., 58, 339 (2013). Figure 1

Electron Tunneling Current in an n-p-n Bipolar Transistor Based on Armchair Graphene Nanoribbon by Using Airy-Wavefunction Approach

We have developed a model of the tunneling current in n-p-n bipolar transistor based on armchair graphene nanoribbon (AGNR). Airy-wavefunction approach is employed to obtain electron transmittance, and the obtained transmittance is then used to obtain the tunneling current. The tunneling current is calculated for various variables such as base-emitter voltage, base-current voltage, and AGNR width. It is found that the tunneling current increases with increasing the base-emitter voltage or the base-collector voltage. This result is due to the lowered barrier height of the base region caused by the increase in the base-emitter voltage or the base-collector voltage. In addition, the tunneling current density increases with the width for narrow AGNR and, on the other hand, it decreases for wide AGNR. This finding might be due to the contributions of the band gap energy and the electron effective mass of AGNR which are inversely proportional to the AGNR width.

Simulation of Dirac Electron Tunneling Current in Armchair Graphene Nanoribbon Tunnel Field-Effect Transistors Using a Transfer Matrix Method

We simulate quantum mechanical tunneling current in armchair graphene nanoribbon tunnel field-effect transistors (AGNR-TFETs). The relativistic Dirac equation is used to determine electron wave functions in the AGNRs, while the potential profile is solved by the Poisson equation. We use a transfer matrix method (TMM) to calculate the electron transmittance and the Dirac electron tunneling current in the AGNR-TFETs. The results show that the Dirac electron tunneling current increases with increasing the drain and gate voltages. Moreover, the AGNR width and the thickness of insulator affect the characteristics of the Dirac electron tunneling currents.

Simulation of Dirac Tunneling Current of an Armchair Graphene Nanoribbon-Based P-N Junction Using a Transfer Matrix Method

We have studied tunneling current in a p-n junction based on armchair graphene nanoribbon (AGNR) by using the relativistic Dirac equation and a transfer matrix method (TMM). The electron wave function was derived by solving the relativistic Dirac equation. The TMM, which is a numerical approach, was used to calculate electron transmittance and the tunneling current. The results showed that the tunneling current increases with the bias voltage. On the other hand, the tunneling current increases with the decreases in the electron incidence angle and temperature. Moreover, the increases in the AGNR width and electric field in the p-n junction result in the increase in the tunneling current.

A Theoretical Model of Band-to-Band Tunneling Current in an Armchair Graphene Nanoribbon Tunnel Field-Effect Transistor

Tunneling current in an armchair graphene nanoribbon (AGNR) tunnel field-effect transistor (TFET) was modeled. A linear equation was employed in describing a potential distribution within the AGNR due to its simplicity. A parabolic dispersion and an electron effective mass obtained by approximating kx 0 to the parabolic dispersion were applied to AGNR. In order to obtain electron transmittance, electron wavefunctions in AGNR were based on Airy functions. The obtained transmittance was then applied to calculate the tunneling current by employing the Landauer formula. The calculated results showed that the tunneling current increases with the AGNR width. It was also shown that the tunneling current increases as temperature decreases. In addition, the gate voltage influences the saturation condition of tunneling current in AGNR TFETs.

Gate Tunneling Current Predicting Model for Scaled NMOSFET Devices

With the scaling of MOS devices, gate tunneling current increases significantly due to thinner gate oxides, and static characteristics of devices and circuit are severely affected by the presence of gate tunneling currents. In this paper, a novel theory gate tunneling current predicting model using integral approach is presented in ultra-thin gate oxide MOS devices that tunneling current changes with gate-oxide thickness. To analyze quantitatively the behaviors of scaled MOS devices in the effects of gate tunneling current and predict the trends, the characteristics of MOS devices are studied in detail using HSPICE simulator. The simulation results in BSIM4 model well agree with the model proposed. The theory and experiment data are contributed to the VLSI circuit design in the future.

Effects of confinement and electron transport on magnetic switching in single Co nanoparticles

This work reports the first study of current-driven magnetization noise in a single, nanometerscale, ferromagnetic (Co) particle, attached to normal metal leads by high-resistance tunneling junctions. As the tunnel current increases at low temperature, the magnetic switching field decreases, its probability distribution widens, while the temperature of the environment remains nearly constant. These observations demonstrate nonequilibrium magnetization noise. A classical model of the noise is provided, where the spin-orbit interaction plays a central role in driving magnetic tunneling transitions.

Tunneling Currents That Increase with Molecular Elongation

We present a model molecular system with an unintuitive transport-extension behavior in which the tunneling current increases with forced molecular elongation. The molecule consists of two complementary aromatic units (1,4-anthracenedione and 1,4-anthracenediol) hinged via two ether chains and attached to gold electrodes through thiol-terminated alkenes. The transport properties of the molecule as it is mechanically elongated in a single-molecule pulling setting are computationally investigated using a combination of equilibrium molecular dynamics simulations of the pulling with gDFTB computations of the transport properties in the Landauer limit. Contrary to the usual exponential decay of tunneling currents with increasing molecular length, the simulations indicate that upon elongation electronic transport along the molecule increases 10-fold. The structural origin of this inverted trend in the transport is elucidated via a local current analysis that reveals the dual role played by H-bonds in both stabilizing π-stacking for selected extensions and introducing additional electronic couplings between the complementary aromatic rings that also enhance tunneling currents across the molecule. The simulations illustrate an inverted electromechanical single-molecule switch that is based on a novel class of transport-extension behavior that can be achieved via mechanical manipulation and highlight the remarkable sensitivity of conductance measurements to the molecular conformation.

Band Engineering of Rutile TiO2 by Cobalt Doping in Ru/Rutile-TiO2/Ru Capacitor aiming 40-nm DRAM and Beyond

A Feasible fabrication process of Ru/rutile-Co-doped TiO2/Ru capacitor for 40-nm DRAM and beyond is developed. As-deposited Ru lower electrode is found out to crystallize Co-doped TiO2 overlayer into rutile having relative permittivity beyond 90 owing to lattice matching. Furthermore, we predicted doping of element having small ionic radius, such as Co, increase Schottky barrier, leading to decrease in leakage current. Temperature dependence of leakage current of RIR-Co-doped-TiO2 capacitor and band structure analysis with X-ray photoelectron spectroscopy shows that leakage current is determined by balancing between thermionic current and tunneling current through Schottky barrier. By doping of Co, the thermionic current decreases, whereas the tunneling current increases. With calculation using theoretical dependence of amount of doped element on leakage current, optimum percentage of Co is estimated as 0.3-0.6 % to achieve a sufficiently low leakage-current. This technology opens possibility to utilize 40-nm DRAM and beyond.

Bias-voltage induced surface reaction of para-nitrobenzoic acid adsorbed on Ag/AlOx/Al tunnel junction

Surface-enhanced Raman scattering (SERS) spectra of para-nitrobenzoic acid (PNBA) adsorbed on the Ag electrodes of Ag/AlOx/Al tunnel junctions fabricated on plain and CaF2-covered glass substrates are measured under bias-voltage applications. The SERS bands caused by the adsorbed PNBA- on the Ag electrode increase in intensity with positive bias-voltage and a new band attributable to the azo-group emerges at voltages greater than +2.2 eV. In contrast, the bands remain nearly unaltered under negative bias-voltage. The intensity profile of the newly emerged band is similar to the junction's Tafel plot, in which the tunnel current increases steeply at the same voltage because of Fowler-Nordheim tunneling. The azoband intensity change with elapsed time at +2.0 eV bias voltage is remarkable for the junction on the CaF2 roughened glass substrate. These results suggest that the PNBA reductive coupling reaction might correlate with surface plasmon polariton (SPP) excitations by the generated hot-electrons.

The conduction band alignment of HfO2caused by oxygen vacancies and its effects on the gate leakage current in MOS structures

Based on the first-principles simulations, the oxygen vacancies in the ultrathin HfO 2 layer as the gate dielectric in a metal-oxide-semiconductor structure is found to result in the conduction band offset alignment around the vacancy. Thus an increase in the gate leakage current tunneling current comes when the oxygen vacancies appear in the HfO 2 layer wherever the oxygen vacancies locate. The relative increase in the tunneling current caused by the oxygen vacancies slightly change with the increasing oxide thickness for a low oxide electric field.

Spin-polarized transport in ferromagnet–marginal Fermi liquid systems

Spin-polarized transport through a marginal Fermi liquid (MFL) which is connected to two noncollinear ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function approach. It is found that the current-voltage characteristics deviate obviously from the ohmic behavior, and the tunnel current increases slightly with temperature, in contrast to those of the system with a Fermi liquid. The tunnel magnetoresistance (TMR) is observed to decay exponentially with increasing bias voltage, and to decrease slowly with increasing temperature. With increasing coupling constant of the MFL, the current is shown to increase linearly, while the TMR is found to decay slowly. The spin-valve effect is observed.

Tunneling Current through Ultrathin Silicon Dioxide Films under Light Exposure

Tunneling current through ultrathin silicon dioxide films with a thickness of approximately 3.1 nm, formed on n-Si (100) by controlling preoxide growth during heating, is examined using Al/oxide/n-Si structures. Electron tunneling current through the oxide from n-Si to Al is decreased and the dielectric breakdown voltage is increased by the preoxide growth control. Electron tunneling current from Al to n-Si is increased by light exposure. The increase in electron tunneling current can be explained by the increase in oxide voltage with an inversion layer formed by photoexcitation.

Scanning tunneling microscopy/spectroscopy observation of intrinsic hydrogenated amorphous silicon surface under light irradiation

Continuous visible light irradiation is used to observe intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). A deposited a-Si:H surface is wet-cleaned in order to terminate the a-Si:H surface with H atoms. A current-sample bias ( I– V) curve shows a rectifying behavior in the dark, and the tunneling current increases dramatically only under the reverse-bias condition with light irradiation. This is attributed to the photoexcited minority carriers that lead to the appearance of a higher voltage across the vacuum than that in the dark. Experiments with both p-type and n-type substrates justify the suggested model. High tunneling current under irradiation enables us to obtain highly resolved STM images. Current imaging tunneling spectroscopy observations show that the detected tunneling current in the reverse direction is increased over the entire surface with irradiation, and the increment of the tunneling current is different at each surface site.

Influence of tip-surface interactions and surface defects on Si(100) surface structures by low-temperature (5 K) scanning tunneling microscopy

The Si(100) surface structures on n-type dcgenerately doped samples (p∼0.005 Ω cm) have been investigated with a scanning tunneling microscope (STM) at very low temperature (∼5 K). We have developed a method to monitor quantitatively the proportion of the various observed surface structures [p(2×2), c(4 X 2) and flickering]. This study has been performed as a function of the tunnel current and the presence (or not) of surface defects in the observed areas. The normal surface areas having a low density of defects (∼1%) have been observed to vary from the p( 2 × 2 ) to the c (4 × 2) structures when the tunnel current increases. This indicates that the STM tip-surface interaction strongly influences the observed structures. Furthermore, sulfate areas completely free of any defects are dominated by flickering structures.