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Tunnel Junction (tunnel + junction)
Kinds of Tunnel Junction Selected AbstractsSwitching thresholds in MTJ using SPICE model , Effects of spin and Ampere torquesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008M. Malathi Abstract Spin torque due to spin polarized tunneling current can be used to switch the free layer in a magnetic tunnel junction (MTJ). This current also gives rise to an Ampere torque, which influences the switching threshold of the MTJ. We modified the Landau,Lifschitz,Gilbert equation (LLGE) to include an Ampere torque term and solved for the magnetization dynamics under the single domain approximation using a linear solver in SPICE. We also extend the model to a square array of MTJs to study the effect of nearest neighbour interactions in addition to effects like demagnetization and magnetostatic interactions with the pinned layer. The interlayer exchange field between the free and pinned layers of a MTJ and the spin torque are competing factors that decide the threshold current density for switching the MTJ. We used a two current model to study the effects of barrier height and barrier thickness on spin torque and exchange energy. We observe that both the spin torque and exchange energy decrease with an increase in barrier height (for ferromagnetic coupling) and barrier thickness. We find that the inclusion of Ampere torque causes a reduction in the switching current. Varying the thickness of MgO and Al2O3 barriers allows us to minimize the switching threshold voltage. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Long-wavelength (, , 1.3 µm) InGaAlAs,InP vertical-cavity surface-emitting lasers for applications in optical communication and sensingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006Markus-Christian Amann Abstract In this paper we present an overview of the properties and applications of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) based on the InGaAlAs,InP material system. With respect to significant temperature sensitivity of active material gain as well as insufficient thermal conductivity of InP-based epitaxial compound layers, the effective thermal heat management appears as a major issue for application suitable device performance. In this context, the incorporation of a buried tunnel junction (BTJ) in connection with improved heat sinking resembles a breakthrough for long-wavelength VCSELs. With the utilization of n-type spreading layers and consequently ultralow series resistances, BTJ-VCSELs exhibit sharply reduced excess heat generation. Furthermore, the BTJ-approach enables self-aligned optical and current confinement. A hybrid dielectric stack with Au-coating yields an improved thermal heatsinking. The current status of BTJ-VCSELs encompasses a number of superior performance values. At 1.55 µm wavelength, this includes room temperature single- and multimode continuous wave (cw) output powers of more than 3 mW and 10 mW, respectively, laser operation for heat sink temperatures well exceeding 100 °C, and optical data transmission rates up to 10 Gbit/s. The versatility of compound layer composition enables arbitrary emission wavelengths within a broad range of 1.3 and 2 µm. With respect to sensing applications, BTJ-VCSELs appear as ideal components for optical detection of infrared active gases. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of insulating barrier thickness on the magnetoresistance properties of a magnetic tunnel junction with Zr-alloyed Al oxide barrierPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004Chul-Min Choi Abstract We have investigated the magnetoresistive properties and thermal and electrical stability of a magnetic tunnel junction (MTJ) with a high-quality, ultra-thin Zr-alloyed Al oxide (ZrAl oxide) barrier of below 1.0 nm. We obtained the highest bias voltage and breakdown voltage of 711 mV and 1.75 V for a 1.6-nm-thick barrier. The resistance drops from 1850 , to 72 , as the ZrAl thickness decreases from 1.6 to 0.6 nm, respectively. A significant TMR (Tunneling Magneto-resistance) value of 17% and a junction resistance of 98 , were obtained for a MTJ with a ZrAl oxide barrier thickness of 0.8 nm. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thickness dependence of magnetic coupling strength and thermal stability in a spin-dependent tunnel junctionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004C. H. Nam Abstract The change of magnetic coupling strength between two ferromagnetic layers, separated by an insulating barrier, was investigated as a function of the barrier thickness (TB) and thermal annealing temperatures. The magnetic junctions consist of Ta/CoFe/AlOx/NiFe/Ta layers with three different nominal thickness of TB = 1.3, 1.6, and 2.0 nm. Isothermal magnetization at room temperature revealed that, while the junction with a lower TB showed a higher magnetic coupling strength, thermal annealing at T = 225 °C increased (and diminished) the coupling strength of the junctions with TB = 1.3 and 1.6 nm (and 2.0 nm), respectively. This observation was utilized to understand consistently the magneto-resistance behavior and specific junction resistance of the junctions as a function of thermal annealing temperature. This study demonstrated that the physical properties of a magnetic tunnel junction, such as magneto-resistance ratio, specific junction resistance and their thermal stability, were substantially influenced by the insulating barrier structure as well as the interface quality between the layers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A theoretical study of an amorphous aluminium oxide layer used as a tunnel barrier in a magnetic tunnel junctionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007E. S. Noh Abstract An amorphous aluminium oxide layer is assumed to be a condensed gas phase composed of (AlOx)N molecules. The total energy and the electron affinity of (AlOx)N molecules is calculated by using a DFT program. The effective tunnel barrier height in the MTJ is presumed from a difference between the work function of the ferromagnetic metal and the electron affinity of (AlOx)N molecules. By using a quantum-mechanical free electron model the TMR and the R×A product are calculated as a function of the thickness of an amorphous aluminium oxide layer in the F/I/F tunnel junction. It is inferred that the tunnel barrier width determined by subtracting 6 Å from the thickness of an amorphous aluminium oxide layer is more suitable to explain an experimental report qualitatively than the tunnel barrier width equivalent to the thickness of an amorphous aluminium oxide layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructure and exchange coupling parameters of MTJ with CoFeB bottom electrodePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006J. Kanak Abstract In this study, we report the relationship between interface roughness, texture and the exchange bias and the interlayer-Néel coupling fields of the spin-valve magnetic tunnel junction (SV-MTJ). SV-MTJs with the structure: Si(100)/SiO2/buffer/IrMn/CoFeB/AlOx/NiFe/Ta were deposited on two buffers: Cu and Ta/Cu/Ta/Cu, and next the samples were annealed in vacuum and in a magnetic field. XRD analysis reveals that the texture degree of MTJ with Cu buffer is significantly lower than that of the sample with Ta/Cu/Ta/Cu buffer. The enhancement of IrMn and CoFeB texture leads to a higher amplitude of roughness and an increase of exchange bias and Néel coupling fields. The comparison of junctions with CoFe and CoFeB bottom electrodes shows that addition of 5% B in a CoFe layer makes the surface of the pinned layer smoother. This leads to a lower Néel coupling field, which is desirable for application of MTJ in MRAM technology. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dependence of transport properties in tunnel junction on boron dopingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010M. J. Shi Abstract Boron-doped hydrogenated silicon films with different gaseous doping ratio (B2H6/SiH4) were fabricated as recombination p layers in tunnel junctions. The measurements of I-V characteristics of the junctions and transparency spectra of p layer indicated that the best gaseous doping ratio of the recombination layer is 0.04, which is correlated to the degradation of short range order (SRO) in the inserted p thin film. The junction with such recombination layer has small resistance, near ohmic contact. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photon-assisted tunneling in GaN nanowire white light emitting diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009P.-C. Yeh Abstract We reported intensive greenish white light electroluminescence, accompanied with 364 nm bandedge emission from GaN nanowires/p-GaN light emitting diode operated in the high-field forward bias regime. Strong bandedge emission, dominant over visible luminescence from bandgap state transitions, was also observed in the reverse bias regime. These observations were ascribed to a formation of n+ -p tunnel junction in the high-field regime and emission mechanism due to photon-assisted tunneling process. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Broadband spectrally dynamic solid state illumination sourcePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006David B. Nicol Abstract Solid state lighting has done well recently in niche markets such as signage and displays, however, no available SSL technologies incorporate all the necessary attributes for general illumination. Development of a novel solid state general illumination source is discussed here. Two LEDs emitting at two distinct wavelengths can be monolithically grown and used to excite two or more phosphors with varied excitation spectra. The combined phosphorescence spectrum can then be controlled by adjusting the relative intensities of the two LED emissions. Preliminary phosphor analysis shows such a scheme to be viable for use in a spectrally dynamic broadband general illumination source. A tunnel junction is envisioned as a means of current spreading in a buried layer for three terminal operation. However, tunnel junction properties in GaN based materials are not well understood, and require further optimization to be practical devices. Preliminary results on GaN tunnel junctions are presented here as well. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tunneling in quantum confined GaAs ultrashallow sidewall tunnel junctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006Takeo Ohno Abstract Temperature dependence of current-voltage (I - V ) characteristics of quantum-confined GaAs ultra-shallow sidewall p+n+ tunnel junctions has been investigated. The sidewall tunnel junctions with junction depths ranging from 5 nm to 50 nm were achieved by the combination of intermittent injection of TEG/AsH3 in an ultra high vacuum and a wet etching process of the GaAs growth layer. From the I - V results, abrupt negative differential resistances (NDR) were observed, which relate to direct/indirect tunneling and sub-band formation. The change in the number instances of NDR and their voltage positions also depended on the junction depth. Mechanisms of tunneling in the present sidewall tunnel junction will be discussed from the point of the sub-band formation in conduction bands. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Current,Voltage Characteristics of a Homologous Series of Polycyclic Aromatic HydrocarbonsCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2007Thilo Böhme Dr. Abstract A novel alkyl-substituted polycyclic aromatic hydrocarbon (PAH) with D2h symmetry and 78 carbon atoms in the aromatic core (C78) was synthesized, thereby completing a homologous series of soluble PAH compounds with increasing size of the aromatic , system (42, 60, and 78 carbon atoms). The optical band gaps were determined by UV/Vis and fluorescence spectroscopy in solution. Scanning tunneling microscopy (STM) and spectroscopy (STS) revealed diode-like current versus voltage (I,V) characteristics through individual aromatic cores in monolayers at the interface between the solution and the basal plane of graphite. The asymmetry of the current,voltage (I,V) characteristics increases with the increasing size of the aromatic core, and the concomitantly decreasing HOMO,LUMO gap. This is attributed to resonant tunneling through the HOMO of the adsorbed molecule, and an asymmetric position of the molecular species in the tunnel junction. Consistently, submolecularly resolved STM images at negative substrate bias are in good agreement with the calculated pattern for the electron densities of the HOMOs. The analysis provides the basis for tailoring rectification with a single molecule in an STM junction. [source] Crossing an Interface: Ferroelectric Control of Tunnel Currents in Magnetic Complex Oxide HeterostructuresADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Michael Hambe Abstract Experimental results on entirely complex oxide ferromagnetic/ferroelectric/ferromagnetic tunnel junctions are presented in which the tunneling magnetoresistance is modified by applying low electric field pulses to the junctions. The experiments indicate that ionic displacements associated with the polarization reversal in the ferroelectric barrier affect the complex band structure at ferromagnetic,ferroelectric interfaces. The results are discussed in the framework of the theoretically predicted magnetoelectric interface effect and may lead to novel multistate memory devices. [source] Low frequency noise in Co/Al2O3,Si,/Py magnetic tunnel junctionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008R. Guerrero Abstract Low frequency noise and dynamic tunneling resistance have been studied in Co(80 Å)/Al2O3(12 Å)/Py(100 Å) magnetic tunnel junctions (MTJs) with and without asymmetric Si doping of the insulating barrier (Si , 1.8 Å). Variation of the dynamic resistance and tunneling resistance with Si doping and applied bias in these MTJs indicate a transition from the Si-doped regime to Si cluster formation above a , -layer thickness of about 1.2 Å, close to 1 monolayer coverage. The measurements show anomalously strong enhancements of the low frequency noise for Si thickness above 1.2 Å, mainly due to the appearance of random telegraph noise. A simple model, which considers suppression of Coulomb blockade in the array of Si dots, opening two-step tunnel channels, qualitatively explains the variation of both conductivity and noise with Si content. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhanced reliability of magnetic tunnel junctions with thermal annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004Kwang-Seok Kim Abstract Time-dependent dielectric breakdown (TDDB) of magnetic tunnel junctions (MTJs) under a constant voltage stress, tunneling magnetoresistance (TMR), and barrier properties, e.g. effective barrier height and thickness, were investigated as a function of thermal annealing temperatures. A Weibull failure distribution function was plotted in terms of time to breakdown (TBD) of MTJs. The TBD when 63 fraction of as-fabricated MTJs cumulatively failed increased significantly after thermal annealing at 210 °C while the TMR also increased from 8.85% to 14.22% before and after thermal annealing at 210 °C, respectively. We believe that the enhanced reliability of the MTJs is due to healing effect of bulk defects in the barrier during the annealing process, likely leading to the reduction of defect trap density. The reduction of bulk defects in the barrier was also confirmed by the lowered 1/f noise power spectral density from voltage fluctuation measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of annealing and ion implantation on interlayer exchange coupling in Fe/Cr multilayersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003T. Nowak Abstract Antiferromagnetic interlayer coupling in layered structures exhibiting giant magnetoresistance (GMR) is frequently destroyed by pinholes in the nonmagnetic layers. Therefore pinholes play a key role in limiting performance of GMR structures or magnetic tunnel junctions. We report temperature measurements of magnetization reversal in annealed and ion beam mixed [Fe-3.0 nm/Cr-1.1 nm] multilayers. Analysis of the experimental data shows that both annealing and ion mixing lead to similar subtle changes in the layered structure related to creating pinholes, changes in their density and average volume. [source] High-performance nanoparticle-enhanced tunnel junctions for photonic devicesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010Adam M. Crook Abstract We describe GaAs-based tunnel junctions that are compatible with photonic devices, including long-wavelength vertical-cavity surface-emitting lasers and multi-junction solar cells. Tunneling was enhanced with semimetallic ErAs nanoparticles, particularly when grown at reduced substrate temperatures. Additionally, we present the first direct measurement of the quality of III-V layers grown above ErAs nanoparticles. Photoluminescence measurements indicate that III-V material quality does not degrade when grown above ErAs nanoparticles, despite the mismatch in crystal structures. These findings validate these tunnel junctions as attractive candidates for GaAs-based photonic devices (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dependence of transport properties in tunnel junction on boron dopingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010M. J. Shi Abstract Boron-doped hydrogenated silicon films with different gaseous doping ratio (B2H6/SiH4) were fabricated as recombination p layers in tunnel junctions. The measurements of I-V characteristics of the junctions and transparency spectra of p layer indicated that the best gaseous doping ratio of the recombination layer is 0.04, which is correlated to the degradation of short range order (SRO) in the inserted p thin film. The junction with such recombination layer has small resistance, near ohmic contact. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Broadband spectrally dynamic solid state illumination sourcePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006David B. Nicol Abstract Solid state lighting has done well recently in niche markets such as signage and displays, however, no available SSL technologies incorporate all the necessary attributes for general illumination. Development of a novel solid state general illumination source is discussed here. Two LEDs emitting at two distinct wavelengths can be monolithically grown and used to excite two or more phosphors with varied excitation spectra. The combined phosphorescence spectrum can then be controlled by adjusting the relative intensities of the two LED emissions. Preliminary phosphor analysis shows such a scheme to be viable for use in a spectrally dynamic broadband general illumination source. A tunnel junction is envisioned as a means of current spreading in a buried layer for three terminal operation. However, tunnel junction properties in GaN based materials are not well understood, and require further optimization to be practical devices. Preliminary results on GaN tunnel junctions are presented here as well. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tunneling in quantum confined GaAs ultrashallow sidewall tunnel junctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006Takeo Ohno Abstract Temperature dependence of current-voltage (I - V ) characteristics of quantum-confined GaAs ultra-shallow sidewall p+n+ tunnel junctions has been investigated. The sidewall tunnel junctions with junction depths ranging from 5 nm to 50 nm were achieved by the combination of intermittent injection of TEG/AsH3 in an ultra high vacuum and a wet etching process of the GaAs growth layer. From the I - V results, abrupt negative differential resistances (NDR) were observed, which relate to direct/indirect tunneling and sub-band formation. The change in the number instances of NDR and their voltage positions also depended on the junction depth. Mechanisms of tunneling in the present sidewall tunnel junction will be discussed from the point of the sub-band formation in conduction bands. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The role of phonons in establishing a non-equilibrium quasiparticle state in small gap multiple tunnelling superconducting tunnel junctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004A. G. Kozorezov Abstract We derive expressions for phonon escape times from a thin superconducting film. The escape time is determined by the rate of scattering conversion for phonons propagating beyond the critical cone for total internal reflection. The conversion is due to different scattering processes for the groups of Cooper pair breaking and sub-gap phonons. For pair breaking phonons the most efficient conversion mechanism is through the interaction with the condensate. For sub-gap phonons the conversion rate is much slower and for plane parallel films is due to elastic scattering at surface or interface roughness resulting in significantly slower escape times. We discuss implications of slow escape time for sub-gap phonons for the properties of the recently observed new non-equilibrium state in small gap multiple tunnelling superconducting tunnel junctions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ground-State Equilibrium Thermodynamics and Switching Kinetics of Bistable [2]Rotaxanes Switched in Solution, Polymer Gels, and Molecular Electronic DevicesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2006Jang Wook Choi Abstract We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a ,-electron-deficient cyclobis(paraquat- p -phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90,%) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a ,-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs. [source] | |||||||||||||