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Micromagnetic simulations are used to investigate different strategies for tunnel magnetoresistance detection of the Neel skyrmion core direction and Bloch skyrmion chirality. When a Neel skyrmion passes beneath a perpendicularly magnetized dot separated by a tunnel barrier, a peak or dip in the tunnel magnetoresistance as a function of time reveals the core direction. When a Bloch skyrmion travels below a synthetic antiferromagnet, magnetized in-plane with an axis perpendicular to that of the track, the tunnel magnetoresistance as a function of time shows a peak followed by a dip, or vice versa, depending on the chirality. The results are compared with existing detection methods based on the Hall resistance.

The thermoelectric power generated in magnetic tunnel junctions (MTJs) is determined as a function of the tunnel barrier thickness for a matched electric circuit. This study suggests that lower resistance area product and higher tunnel magnetoresistance will maximize the thermoelectric power output of the MTJ structures. Further, the thermoelectric behavior of a series of two MTJs, a MTJ thermocouple, is investigated as a function of its magnetic configurations. In an alternating magnetic configurations the thermovoltages cancel each other, while the magnetic contribution remains. A large array of MTJ thermocouples could amplify the magnetic thermovoltage signal significantly.

Magnetic tunnel junctions (MTJs) have attracted tremendous interests recently because of their potential application in magnetoresistive random access high-density memory and magnetic sensor. However, the performance of them is far from satisfying due to the various problems exist in tunnel barrier materials. Here, we propose to use two-dimensional (2D) Bi 2 O 2 Se material, which is advantageous in reducing the MTJ size, as the tunnel barrier, and demonstrate that it is able to generate very large tunnel magnetoresistance (TMR) when integrated with CoFe electrodes. The underlying mechanism is elaborated by analyzing the band structures, electron transmission and interface properties. These results provide important guidance for designing high-density and high-performance MTJs.

This work proposes a new GaAs 0.51 Sb 0.49 /In 0.53 Ga 0.47 As heterojunction tunnel field effect transistor (HTFET) with a 6-nm In 0.7 Ga 0.3 As layer (pocket) between the source and channel. Compared with InGaAs homojunction TFETs, the proposed HTFET has a steeper subthreshold swing at a higher drain current, owing to its lower source-to-channel tunnel barrier height. It has a maximum on-state current of 11.98 μA/μm at room temperature, which is more than ten times the on-state current obtained from an InGaAs homojunction TFET.

The influence of the magnetization configuration on the Kondo effect in a magnetic tunnel junction is investigated. In the parallel configuration, an additional resistance contribution ( R ⁎ ) below 40 K exhibits a logarithmic temperature dependence, indicating the presence of the Kondo effect. However, in the anti-parallel configuration, the Kondo-effect-associated spin-flip scattering has a nontrivial contribution to the tunneling current, which compensates the reduction of the current directly caused by Kondo scattering, making R ⁎ disappear. These results indicate that suppression and restoration of the Kondo effect can be experimentally achieved by altering the magnetization configuration, enhancing our understanding of the role of the Kondo effect in spin-dependent transport.

In this paper, nonlinear and low-power resistive switching characteristics of Si3N4-based RRAM embedding SiO2 tunnel barrier (TB) with full compatibility to conventional Si CMOS processing have been extensively studied to solve crosstalk issue in a cross-point structure. It is found that the nonlinear characteristics of a simple metal-insulator-insulator-silicon (MIIS) structure are mainly attributed to two different tunneling mechanisms in the SiO2 layer. Furthermore, we offer an optimized solution by modulating compliance current (ICC), read voltage (VREAD), and TB thickness for higher selectivity. Low current operation tuned by ICC, VREAD, and TB thickness is essential to achieve higher selectivity for low-power and high-density cross-point array applications.

A detailed study of a technique to realize a PNPN tunnel field effect transistor (TFET) with a controllable tunnel barrier width on the drain side is reported in this paper. By using the charge plasma concept on a doped N + /P − starting structure, we have demonstrated the possibility of realizing the PNPN TFET without the need for any additional chemically doped junctions. We have showed that using electrostatic doping on the drain side of TFETs provides a new design parameter, the gate–drain electrode gap. This gate–drain electrode gap can be used to control the ambipolar current in TFETs by controlling the tunneling barrier width at the channel–drain junction.

We introduce a simulation technique suitable to model the tunneling leakage current in the metal(polySi)/CaF 2 /Si(111) MIS structures using TCAD simulators Minimos-NT and ViennaSHE. The simulations are performed using the real physical parameters of the CaF 2 /Si tunnel barrier. The results obtained for the case of near-equilibrium carrier transport are in a good agreement with experimental data and also with the simulation results yielded by our reference physical model. The obtained non-equilibrium hot-electron tunnel leakages in the hypothetical transistors with CaF 2 as a gate dielectric are comparable to those in the structures with silicon dioxide. Being an important step forward for the device application of calcium fluorite, this work opens the possibility of simulating the characteristics of different silicon-based systems with crystalline insulators.

The tunnel barrier thicknesses of Nb/Al–AlO x /Nb tunnel junctions were measured using transmission electron microscopy (TEM) and X-ray Reflection (XRR). By investigating the barrier thickness dependence of current density J c , the barrier height for Nb/Al–AlO x /Nb junctions was calculated. Nb/Al–AlO x /Nb junctions with different J c were fabricated by controlling the O 2 exposure in Al oxidation. The junctions show good tunneling properties with subgap leakage factor V m larger than 30 mV in the range of J c from tens of A/cm 2 to several kA/cm 2 . TEM images showed clear interface and indicated the AlO x thicknesses ranging from 0.8 nm to 1.9 nm, and the average barrier height was estimated to be 0.17 eV for Nb/Al–AlO x /Nb tunnel junctions.

The relaxation of Fe/MgO/Fe tunnel junctions grown epitaxially on (001) MgO substrates has been measured by in-situ grazing incidence in-plane X-ray diffraction during the thermal annealing cycle. We find that the Fe layers are fully relaxed and that there are no irreversible changes during annealing. The MgO tunnel barrier is initially strained towards the Fe but on annealing, relaxes and expands towards the bulk MgO value. The strain dispersion is reduced in the MgO by about 40% above 480 K post-annealing. There is no significant change in the “twist” mosaic. Our results indicate that the final annealing stage of device fabrication, crucial to attainment of high TMR, induces substantial strain relaxation at the MgO barrier/lower Fe electrode interface.

Various metal oxides are probed as extrinsic thin tunnel barriers in Semiconductor Insulator Semiconductor solar cells. Namely Al2O3, ZrO2, Y2O3, and La2O3 thin films are in between n-type ZnO:Al (AZO) and p-type Si substrates by means of Atomic Layer Deposition. Low reverse dark current–density as low as 3×10−7 A/cm2, a fill factor up to 71.3%, and open-circuit voltage as high as 527 mV are obtained, achieving conversion efficiency of 8% for the rare earth oxide La2O3. ZrO2 and notably Al2O3 show drawbacks in performance suggesting an adverse reactivity with AZO as also indicated by X-ray Photoelectron Spectroscopy., Highlights • New approach to form the tunnel barrier in SIS solar cells by metal oxides in combination with AZO. • Comparative XPS analysis of the chemical stability of La2O3, Y2O3, ZrO2, and Al2O3 during the ALD of AZO. • For La2O3, an effective conversion efficiency of 8% is achieved for cells with 1.4 cm2 active area.

We investigated electroforming-free bipolar resistive switching behavior in Pt/Ti/Al 2 O 3 /Al tunnel junctions where the Al 2 O 3 tunnel barrier was naturally formed on Al in air. Various compliance current values for the junction’s set switching successfully lead to various resistance values in its low resistance state, suggesting the possibility for multi-level-operation. A mechanism for the bipolar switching is qualitatively discussed in terms of the modulation of the tunnel barrier by the reactive Ti layer on top of the barrier.

The electrical characteristics of nonvolatile memory, which consists of an asymmetrical ZrO2/SiO2 (ZO) modified tunnel barrier, a high-k HfO2 trapping layer and an Al2O3 blocking layer, were investigated for the application of a tunnel barrier engineered nonvolatile memory at low process temperatures. The efficiency of the ZO modified tunnel barrier on the charge trap flash (CTF) memory cell was compared to a conventional single SiO2 tunnel barrier. The ZO tunnel barrier revealed field sensitivity larger than the single SiO2 tunnel barrier. The programming and erasing speeds as well as the retention and endurance characteristics of CTF memory were largely enhanced. Moreover, the forming gas annealing process in 2% diluted H2/N2 ambient improved the charging trapping property and tunneling sensitivity of the ZO modified tunnel barrier.

SiC nano-particles on tunnel layer with variable oxide thickness composed of SiO2 and Si3N4 layers were fabricated and their electrical properties were evaluated. The flat-band voltage shifts due to the memory effect of multilayered SiC nano-particles in the non-volatile memory (NVM) device with SiO2/Si3N4/SiO2, Si3N4/SiO2/Si3N4 and SiO2 tunnel layer were observed about 1.5, 1.4 and 0.2 V after the voltage sweep from −6 to 3 V under applied program/erase voltages at ±13 V for 10 ms, respectively. The program/erase speeds of ONO and NON tunnel layered devices were faster than that of the SiO2 tunnel layer device. The memory window of the NVM devices with ONO tunnel layers after applied program/erase bias at ±10 V for 500 ms was maintained about 1.6 V after 105 s. These results indicate that the ONO and NON tunnel barriers can provide a thin effective tunneling thickness for the fast P/E speeds and comparatively thick physical thickness for the long charge retention characteristic.

In this work, we investigated the physical properties of (ZrO 2 ) x (SiO 2 ) 1− x such as band-gap, band-offset, structural stability, and the tunneling characteristics of (ZrO 2 ) x (SiO 2 ) 1− x /SiO 2 tunnel barrier with total EOT of 4.5 nm for the application to charge trap memory devices. It was observed that the band-gap and band-offset of (ZrO 2 ) x (SiO 2 ) 1− x can be controlled by changing the composition for (ZrO 2 ) x (SiO 2 ) 1− x films. However, the sensitivity of band-gap and band-offset of (ZrO 2 ) x (SiO 2 ) 1− x films on ZrO 2 content was minimal for the cycle ratio of ZrO 2 :SiO 2 above 1:1. The Zr-silicate film with the ZrO 2 :SiO 2 cycle ratio of 1:7 maintained amorphous even after annealing at 1050 °C. However, and Zr-silicate film with the ZrO 2 :SiO 2 cycle ratio of 1:1 and 3:1 were crystallized after annealing at 950 °C and 850 °C, respectively. The band-engineered tunnel barrier of (ZrO 2 ) x (SiO 2 ) 1− x /SiO 2 bi-layer showed enhanced tunnel efficiency at high gate bias, while showed smaller tunnel current at low gate bias than a single SiO 2 tunnel barrier of the similar EOT.

The local topographic and conducting properties of ultra-thin MgO films with polycrystalline Ru and amorphous CoFeB as lower electrodes were investigated. The local conductance and topography of the ultra-thin MgO films (from 0.5 to 1.0 nm) were simultaneously measured with a modified conducting atomic force microscope (CAFM). The imaging force was carefully chosen in order to avoid structural damages in the insulating layers. The promising results include the decrease of the density of hotspots with large conductance with the thickness of MgO and show that an insulating barrier is obtained at 1 nm thickness. (C) 2009 Elsevier B.V. All rights reserved.

We investigated the electrical characteristics of MgO tunnel barriers while we add F during oxidation process of nm-thick Mg layer. Specifically we measured d I /d V and d 2 I /d V 2 data of MgO tunnel barriers as we add F. When comparing the data of magnesium oxyfluoride tunnel barriers to those of aluminum oxyfluoride data, we have found that effect of F-inclusion in MgO is different from that in AlO x ; F-inclusion in MgO barrier makes the barrier more symmetric while F-inclusion in AlO x barrier makes the barrier more asymmetric. However, the d 2 I /d V 2 data of MgO did not change much even after F-inclusion, suggesting a very small amount of F-doping can make significant change in oxidation process of nm-thick Mg layer. We believe this result from the fact the oxidation process of nm-thick Mg layer is reaction-limited while the oxidation process of Al layer is diffusion-limited.

La 0.8 Bi 0.2 MnO 3 /MgO/Co trilayer devices fabricated on well-polished perovskite-type La 0.8 Bi 0.2 MnO 3 (LBMO) substrates by vacuum evaporation with an electron gun were used to investigate the relation between their magnetoresistance and the thickness of the MgO tunnel barrier. Experiments showed that the devices have a transition temperature at around 240 K, below which they are ferromagnetic and above which they are semiconductor-like. The magnetoresistance was 33% of its maximum value when the barrier was 2.0 nm thick and the spin-polarization ratio of LBMO was about 0.42.

The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L 2,3 edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.

Fueled by the ever-increasing demand for larger hard disk drive storage capacities, extensive research over the past decade has resulted in the development of AlO x - and TiO x -based magnetic tunnel junctions that exhibit a large magnetoresistive effect at room temperature. As their commercialization in various applications begins, a new type of magnetic tunnel junction with a crystalline MgO tunnel barrier has emerged that shows a much larger room-temperature magnetoresistive effect. We present a brief overview of the development of magnetic tunnel junctions, introducing the underlying physics. We also discuss two important commercial applications: read sensors in hard disk drives and memory elements in magnetoresistive random access memory. An emphasis is placed on the material aspects of magnetic tunnel junctions.

To improve reproducibility of full-epitaxial NbN/MgO/NbN tunnel junctions, we fabricated junctions using an ion-beam sputtered MgO tunnel barrier. The tunnel junctions were fabricated on single-crystal MgO(100) substratesand X-ray analysis showed that all the layers of NbN/MgO/NbN forming the junction had been epitaxially grown. The junctions showed good tunneling characteristics, with large gap voltages and small subgap leakage currents. The junctions were fabricated in the range of R N A products of 25-26,000 Ωμm 2 . By using ion-beam sputtering, the stability of the MgO tunnel barrier's deposition rate could be increased and the controllability of the barrier thickness was improved.

The time a particle spends while tunneling is a subject of long dispute, whose recent history owes much to Rolf Landauer. While I do not have the space to say a great deal about the history of the tunneling time, I am going to try to argue that the tunneling time itself may have a great deal to teach us about history . After an abbreviated description of some of the surprising results of optical experiments on tunneling, this paper outlines a new theoretical approach to the reconstruction of the past in quantum mechanics; for questions of particles known to have been transmitted through a tunnel barrier, this is precisely the type of formalism required. We will see that our results have much in common with earlier approaches due to Landauer and Buttiker, although the interpretations may diverge. Roughly speaking, our view is that the history of a tunneling particle may be described more completely than merely by its wavefunction. We will discuss the measurable consequences of this claim, and (briefly) an atom optics experiment being assembled at Toronto in order to test them. Finally, I will present some recent speculations about a quantifiable sense in which a tunneling particle may be ‘in two places at one time’, which we also hope to be able to test at Toronto.

We fabricate X-ray detectors based upon superconducting Ta/Al/Al x O y /Al hetero tunnel junctions. Device characteristics are significantly influenced by the fact that the gap energies on the two sides of the tunnel barrier are not equal. We present experimental data showing the dependence of signal height and polarity on bias voltage in heterojunctions. The best energy resolution obtained in a single Ta/Al/Al x O y /Al heterojunction is 60 eV at 1.487 keV. We also report the observation of correlated signals from two separate tunnel junctions attached to one common Ta absorber strip.

A quantum-statistical theory of injection of spin-polarized current into a semiconductor in ferromagnet/tunnel barrier/semiconductor system is presented. The presence of Schottky barrier in the semiconductor is taken into account. The case of degenerated and non-degenerated semiconductors are considered. Both the diffusive and ballistic transport regime are investigated. The dependence of current polarization on barrier thickness and temperature is calculated.

We have observed very large tunneling magneto-resistance (TMR) in GaMnAs/AlAs/GaMnAs single-barrier ferromagnetic semiconductor tunnel junctions grown on a (0 0 1) GaAs substrate by low-temperature molecular beam epitaxy. The TMR ratio of 72 % was obtained in a junction with a thin (1.6 nm) AlAs tunnel barrier when the magnetic field was applied along the [1 0 0] axis in the film plane. The TMR ratio was larger when the applied magnetic field direction was along [1 0 0], compared with other directions of [1 1 0] and [−1 1 0]. Also, the TMR ratio was found to decrease with increasing the AlAs barrier thickness.

Simultaneous monitoring of both capacitance and resistance during the exposure of tunnel junctions to water vapour is shown to be a powerful technique for studying the infusion doping process. Results depend critically on the metal used for the top electrode and show capacitance increases on exposure to water vapour. Observed changes in both capacitance and resistance can be explained in terms of current ideas about tunnel junction structure.

We have performed conductance measurements with a gold–molecule–gold junction employing the mechanically controlled break-junction technique. The organic sample molecules form a stable covalent bridge between the electrodes. Two molecules, which differ essentially by their spatial symmetry, showed discrete stable conductance patterns (IVs), which reflect the symmetry/asymmetry of the sample molecules. A third molecule with an additional tunnel barrier in the central axis shows a strongly suppressed conductance. The correlation between these obvious properties of the molecules and the observed IVs unambigously shows that the junction is indeed formed of the sample molecules. Vice versa, these observations demonstrate that IV characteristics can be appropriately designed by a proper choice of molecules.

We have investigated the quasiparticle noise phenomena of Nb/Al/AlOx/Nb Josephson tunnel junctions fabricated with a window geometry. In the subgap region the I–V characteristics display excess currents at voltages corresponding to submultiples of the gap value. These structures can be ascribed to higher-order processes through the tunnel barrier. In the same voltage region, measurements performed by using a low-frequency technique are strongly indicative of shot noise levels higher than the expected ideal values.

At sufficiently low temperatures, 1D arrays of ultrasmall tunnel junctions with low electron scattering rate (for example, semiconductor superlattices) may exhibit a new type of electron transfer. This process can be considered as fast “Bloch” oscillations with frequency fB=ɛ/h (where ɛ is the electron energy change due to tunneling through one tunnel barrier), modulated with lower “SET” frequency fS=I/e (where I is the dc electric current through the array).

We have observed an anomalous resistance increase in a mesoscopic Al loop near the superconducting transition temperature of the line and interpreted it by assuming a normal-current path in parallel with a normal-superconductor-normal quasi-particle tunnel barrier forming at the node area of the dangling voltage probes. The model gives quantitative fits to the dependence of the anomaly on various external parameters.

We have prepared thin film superconducting tunnel junctions YBa2Cu3O7−δ/Pb of Giaever's type and performed a study of their tunneling characteristics. Dynamic conductivity of the junctions exhibits parabolic dependence on voltage with the height of the tunnel barrier above 500 mV. The shape of the second derivative of U-I curves exhibits typical features of Pb and YBCO gaps as well as some other structure above the gap. The maximum gap observed in our YBCO thin films is 2Δ= 31.6 meV which for zero-resistance critical temperature Tce = 68 K gives 2Δ kT ce = 5.4 and for onset temperatur Tco = 93 K is 2Δ kT co = 3.9 . Various possible mechanisms are suggested to explain the results.

A new type of tunnelling phenomenon in forward-biased single-barrier n + (InGa)As/n − (InGa)As/InP/n + (InGa)As/n + InP heterostructures has been observed when a quantizing magnetic field is applied in the plane of the InP barrier. The occurrence of two distinct series of resonances in the voltage- or field-dependence of the current is interpreted in terms of electron tunnelling from a 2DEG in the n − layer into interfacial Landau states in the n + (InGa)As. These states correspond to classical skipping orbits of an electron along the tunnel barrier interface. For devices in which the n + (InGa)As/n + InP interface at the back end of the gate is within − 0.3 μm of the barrier, the interfacial Landau states are observed to evolve into box-quantized states as the magnetic field is reduced to zero.

We report on the fabrication and measurements of sandwich-type tunnel junctions on the HTSC materials of the 1-2-3 type and the 80 K Bi-oxides. For the 1-2-3 materials gaplike structures were obtained with high reproducibility corresponding to a gap near 16 meV and or near 30 meV depending on the fabrication procedure of the tunnel barrier. Both results agree well with tunnel data from other groups. For the 80 K Bi-oxides a similar spread in the gap values is found comparing the results of different groups.

The discreteness of the carrier's energy spectrum in small tunnel junctions is shown to cause the anomalous dependence of noise power on temperature S (ω)∼ T -1 at low temperatures instead of the proportionality predicted by the Nyquist formula. The effect manifest itself in the second order of the expansion in powers of the tunnel barrier transparency.

We have observed a first order transition of a superconducting lead film due to quasiparticle injection through a tunnel barrier for the temperatures below Tλ using a double-tunnel-junction configuration. Comparison with the existing nonequilibrium model is discussed.