IEE Proceedings - Circuits, Devices and Systems
Volume 152, Issue 4, August 2005
Volumes & issues:
Volume 152, Issue 4
August 2005
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- Author(s): M. Cahay and S. Bandyopadhyay
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 293 –296
- DOI: 10.1049/ip-cds:20059068
- Type: Article
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293
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- Author(s): J. Nitta and M. Steiner
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 297 –300
- DOI: 10.1049/ip-cds:20050020
- Type: Article
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p.
297
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Magnetisation reversal processes of microstructured NiFe rings are studied by fringing-field-induced local Hall effect (LHE) and numerical model calculations. This semiconductor-based technique yields a high sensitivity of magnetic stray fields and allows the authors to detect magnetisation hysteresis loops of single NiFe rings. For narrow rings, sharp transitions from so called ‘onion’ to the ‘vortex’ state are detected. Only onion and global vortex states are possible magnetisation configurations in narrow rings. In rings with smaller inner diameter, the transitions are more complex. The minor loop analysis of rings shows that onion and global vortex states are stable and independent of the magnetic history, but the local vortex state depends on the way the magnetic field has been swept beforehand. The switching fields can be controlled by the inner diameter in good agreement with the computational results. - Author(s): H. Xi ; K.Z. Gao ; Y. Shi
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 301 –306
- DOI: 10.1049/ip-cds:20045159
- Type: Article
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p.
301
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In the paper, the authors first review the structural and functional characteristics of magnetic nanodevices where magnetisation rotations and microwave oscillations are induced by DC electrical currents due to the spin-transfer torque effect. A comparison is made between devices with different structures. Micromagnetic simulations based on the modified Landau–Lifshitz–Gilbert equation are carried out in detail on one of the structures. The study shows that the spin-polarised direct current drives the inhomogeneous magnetisation configuration to rotate in the constrained square magnet structure. Magnetisation configurations and dynamics depend on the input current density and the structure dimension. - Author(s): C. Reig ; D. Ramírez ; H.H. Li ; P.P. Freitas
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 307 –311
- DOI: 10.1049/ip-cds:20050005
- Type: Article
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307
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While magnetoresistive spin valve (SV) layered structures have been widely used in both analogue and digital applications, more recent specular nano-oxide-layer spin valves (NOL-SV) have been used in read head and related digital applications. In the paper, the authors report on the design, fabrication and fundamental characterisation of NOL-SV-based magnetoresistive sensing elements for low-current monitoring purposes. The sensitivity of NOL-SV devices is improved in two ways. On the one hand, NOL-SV structures display higher magnetoresistance levels when compared with standard SVs. On the other hand, the current paths are patterned into the chip during the microelectronics fabrication process, therefore decreasing the gap space between the current paths and the sensing magnetoresistors. The authors describe in detail the fabrication process and characterise the first fabricated prototypes. Currents of the order of 1 mA have proved to be measured. Moreover, the temperature drift and the frequency response of the elements have been measured. - Author(s): S.J. Pearton ; D.P. Norton ; R. Frazier ; S.Y. Han ; C.R. Abernathy ; J.M. Zavada
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 312 –322
- DOI: 10.1049/ip-cds:20045129
- Type: Article
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p.
312
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Spin-dependent phenomena in semiconductors may lead to devices with new or enhanced functionality, such as polarised solid-state light sources (spin light-emitting diodes), novel microprocessors and sensitive biological and chemical sensors. The realisation of robust semiconductor spin-device technology requires the ability to control the injection, transport and detection of polarised carriers, and to manipulate their density by a field gating. The absence of Si-based or room-temperature dilute magnetic semiconductors has subdued the initial excitement over semiconductor spintronics, but recent reports demonstrate that progress is far from dormant. The authors give examples of a number of different spin-device concepts for polarised light emission, spin field-effect transistors) and nanowire sensors. It is important to re-examine some of the earlier concepts for spintronics devices, such as the spin field-effect transistor, to account for the presence of the strong magnetic field which has deleterious effects. In some of these cases, the spin device appears to have no advantage relative to the conventional charge-control electronic analogue. There have been demonstrations of device-type operation in structures based on GaMnAs and InMnAs at low temperatures. The most promising materials for room-temperature polarised light emission are thought to be GaN and ZnO, but results to date on realising such devices have been disappointing. The short spin-relaxation time observed in GaN/InGaN heterostructures probably results from the Rashba effect. Possible solutions involve either cubic phase nitrides or the use of additional stressor layers to create a larger spin-splitting, to get polarised light emission from these structures, or to look at alternative semiconductors and fresh device approaches. - Author(s): A.M. Bratkovsky and V.V. Osipov
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 323 –333
- DOI: 10.1049/ip-cds:20050017
- Type: Article
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p.
323
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The authors describe recent theoretical and experimental advances in achieving large accumulated spin polarisation in semiconductors and suggest new classes of low-power ultrafast devices. Tunnelling of electrons between nonmagnetic semiconductors (S) and ferromagnets (FM) through a Schottky barrier modified by a δ-doped layer at the interface is described. It is shown that, in such reverse (forward) biased FM-S junctions, electrons with a certain spin projection can be efficiently injected in (extracted from) S, while electrons with the opposite spin can efficiently accumulate in S near the interface. This occurs due to spin filtering of electrons in the tunnelling process, and the authors found conditions for most efficient accumulation of spin polarisation. Extraction of spin can proceed in degenerate semiconductors at low temperatures. Novel spin-valve ultrafast devices with small dissipated power are described: a magnetic sensor, a spin transistor, an amplifier, a frequency multiplier, a square-law detector and a source of polarised radiation. - Author(s): Z.G. Yu ; M.A. Berding ; S. Krishnamurthy
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 334 –339
- DOI: 10.1049/ip-cds:20050043
- Type: Article
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p.
334
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The authors present a theory to describe spin transport across a polymer sandwiched between magnetic contacts and propose organic spin devices based on this theory. It is found that even a weak magnetic field can significantly modify spin transport in polymers through spin precession. This sensitivity can be exploited to design ultrasensitive magnetometers and low-power magnetic-field-effect transistors. It is shown that, at room temperature, the organic magnetometers are capable of detecting sub-nanotesla magnetic fields, and the I–V characteristics of the magnetic-field-effect transistors can be strongly modified by magnetic fields of a few gauss with response times of a few nanoseconds. - Author(s): C.L. Dennis ; C.V. Tiusan ; J.F. Gregg ; G.J. Ensell ; S.M. Thompson
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 340 –354
- DOI: 10.1049/ip-cds:20050008
- Type: Article
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p.
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The realisation that everyday electronics has ignored the spin of the carrier in favour of its charge is the foundation of the field of spintronics. Starting with simple two-terminal devices based on giant magnetoresistance and tunnel magnetoresistance, the technology has advanced to consider three-terminal devices that aim to combine spin sensitivity with a high current gain and a large current output. These devices require both efficient spin injection and semiconductor fabrication. In the paper, a discussion is presented of the design, operation and characteristics of the only spin transistor that has yielded a current gain greater than one in combination with reasonable output currents. - Author(s): S. Sugahara and S. Sugahara
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 355 –365
- DOI: 10.1049/ip-cds:20045196
- Type: Article
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p.
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The paper describes a new class of spin transistors referred to as spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs). The fundamental and feasible device structures and the theoretically predicted device performance are presented. The spin MOSFETs not only can exhibit significant magnetotransport effects such as large magnetocurrent, but also can satisfy important requirements for integrated-circuit applications such as high transconductance, low power-delay product, and low off-current. In particular, the additional spin-related degree of freedom in controlling output currents makes the spin MOSFETs attractive building blocks for a nonvolatile memory cell and reconfigurable logic gates on spin-electronic integrated circuits. - Author(s): S. Saikin ; Y.V. Pershin ; V. Privman
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 366 –376
- DOI: 10.1049/ip-cds:20045225
- Type: Article
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p.
366
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The authors summarise semiclassical modelling methods, including drift-diffusion, kinetic transport equation and Monte Carlo simulation approaches, utilised in studies of spin dynamics and transport in semiconductor structures. As a review of the work by the authors' group, several examples of applications of these modelling techniques are presented. - Author(s): D.V. Melnikov ; J. Kim ; L.-X. Zhang ; J.-P. Leburton
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 377 –384
- DOI: 10.1049/ip-cds:20050021
- Type: Article
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p.
377
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The electronic properties of devices based on double and triple quantum dots are studied numerically with an emphasis on their application for quantum computation. Simulations were conducted within the self-consistent multiscale approach where electrons in quantum dots are treated within the density-functional theory, while the semi-classical Thomas–Fermi model is used for outside regions. This approach allows fundamental description of quantum dot properties without any a priori assumptions, and at the same time, it provides new computer-aided design (CAD) methodologies suitable for optimisation of device performance. The authors apply this method to obtain stability diagrams for two laterally coupled quantum dots. Preliminary analysis of the singlet–triplet energy separation in a two-electron system is also given. The effect of different designs on the sensitivity of quantum point contacts is then considered. The charging diagram of the novel triple vertically coupled quantum dot structure with up to four electrons is also investigated. - Author(s): M. Wohlgenannt ; Z.V. Vardeny ; J. Shi ; T.L. Francis ; X.M. Jiang ; Ö. Mermer ; G. Veeraraghavan ; D. Wu ; Z.H. Xiong
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 385 –392
- DOI: 10.1049/ip-cds:20045226
- Type: Article
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p.
385
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The authors describe three spin and magnetic field effects in organic semiconductor devices: First, injection, transport and detection of spin-polarised carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40%. Secondly, spin-dependent exciton formation: pairs of electrons and holes show different reaction rates (the reaction products being spin singlet or triplet excitons, respectively) dependent on whether they recombine in spin-parallel or spin-antiparallel orientation. It is believed that this effect ultimately determines the maximum possible electroluminescent efficiency of organic light-emitting diodes (OLEDs). And, finally, a large magnetoresistance (MR) effect in OLEDs in weak magnetic fields that reaches up to 10% at fields of 10 mT at room temperature. Negative MR is usually observed, but positive MR can also be achieved under certain operation conditions. The authors present an extensive experimental characterisation of this effect in both polymer and small molecular OLEDs. The last two effects do not, to the authors' best knowledge, occur in inorganic semiconductor devices and are therefore related to the peculiarities of organic semiconductor physics. The authors discuss their findings, contrasting organic and inorganic semiconductor physics, respectively. - Author(s): L. Lagae ; R. Wirix-Speetjens ; C.-X. Liu ; W. Laureyn ; G. Borghs ; S. Harvey ; P. Galvin ; H.A. Ferreira ; D.L. Graham ; P.P. Freitas ; L.A. Clarke ; M.D. Amaral
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 152, Issue 4, p. 393 –400
- DOI: 10.1049/ip-cds:20050022
- Type: Article
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p.
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The paper reports on the development of a magnetic biosensing platform for genetic analysis. The sensing technique is based on the on-chip manipulation of magnetically labelled biomolecules by the magnetic field gradient force created by current-carrying conductors; on biomolecular reactions such as the binding of complementary DNA material; and on the detection of the fringe field of the magnetic label by a magnetoresistive spin valve sensor. Different experiments will demonstrate the advantages, difficulties, prospects and potential of the combination of magnetic bead manipulation and detection on a single microchip. Early detection of DNA coding for the cystic fibrosis (CF) gene is used as a model system for proof-of-concept of the magnetic DNA biosensor platform.
Editorial: Spintronics
Semiconductor/ferromagnet hybrid devices to probe magnetisation states in microstructured NiFe rings
Spin-current-induced high-frequency magnetisation rotations and microwave oscillations in magnetic nanodevices
Low-current sensing with specular spin valve structures
Spintronics device concepts
Ultrafast low-power spin-injection devices based on modified ferromagnetic-semiconductor junctions
Spin transport in organics and organic spin devices
Silicon spin diffusion transistor: materials, physics and device characteristics
Spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs) for integrated spin electronics
Modelling for semiconductor spintronics
Three-dimensional self-consistent modelling of spin-qubit quantum dot devices
Spin and magnetic field effects in organic semiconductor devices
Magnetic biosensors for genetic screening of cystic fibrosis
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