10,581 research outputs found
Modeling a Schottky-barrier carbon nanotube field-effect transistor with ferromagnetic contacts
In this study, a model of a Schottky-barrier carbon nanotube field- effect
transistor (CNT-FET), with ferromagnetic contacts, has been developed. The
emphasis is put on analysis of current-voltage characteristics as well as shot
(and thermal) noise. The method is based on the tight-binding model and the
non- equilibrium Green's function technique. The calculations show that, at
room temperature, the shot noise of the CNT FET is Poissonian in the
sub-threshold region, whereas in elevated gate and drain/source voltage regions
the Fano factor gets strongly reduced. Moreover, transport properties strongly
depend on relative magnetization orientations in the source and drain contacts.
In particular, one observes quite a large tunnel magnetoresistance, whose
absolute value may exceed 50%.Comment: 8 pages, 4 figure
Graphene Field Effect Transistors: Diffusion-Drift Theory
Based on explicit solution of current continuity equation in the graphene
FET's channel the semi-classical diffusion-drift description of the carrier
transport and I-V characteristics model has been developed. Role of
rechargeable defects (interface traps) near or at the interface between
graphene and insulated layers has also described.Comment: 24 pages, 13 figures, a chapter in "Graphene, Theory, Research and
Applications", INTEC
Design of a single-chip pH sensor using a conventional 0.6-μm CMOS process
A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-/spl μm CMOS process is presented. The sensor comprises a circuit for making differential measurements between an ion-sensitive field-effect transistor (ISFET) and a reference FET (REFET). The ISFET has a floating-gate structure and uses the silicon nitride passivation layer as a pH-sensitive insulator. As fabricated, it has a large threshold voltage that is postulated to be caused by a trapped charge on the floating gate. Ultraviolet radiation and bulk-substrate biasing is used to permanently modify the threshold voltage so that the ISFET can be used in a battery-operated circuit. A novel post-processing method using a single layer of photoresist is used to define the sensing areas and to provide robust encapsulation for the chip. The complete circuit, operating from a single 3-V supply, provides an output voltage proportional to pH and can be powered down when not required
High operating temperature in V-based superconducting quantum interference proximity transistors
Here we report the fabrication and characterization of fully superconducting
quantum interference proximity transistors (SQUIPTs) based on the
implementation of vanadium (V) in the superconducting loop. At low temperature,
the devices show high flux-to-voltage (up to 0.52) and
flux-to-current (above 12) transfer functions, with the
best estimated flux sensitivity 2.6
reached under fixed voltage bias, where is the flux quantum. The
interferometers operate up to 2 , with an
improvement of 70 of the maximal operating temperature with respect to
early SQUIPTs design. The main features of the V-based SQUIPT are described
within a simplified theoretical model. Our results open the way to the
realization of SQUIPTs that take advantage of the use of higher-gap
superconductors for ultra-sensitive nanoscale applications that operate at
temperatures well above 1 K.Comment: Published version with Supplementary Informatio
Phase-driven collapse of the Cooper condensate in a nanosized superconductor
Superconductivity can be understood in terms of a phase transition from an
uncorrelated electron gas to a condensate of Cooper pairs in which the relative
phases of the constituent electrons are coherent over macroscopic length
scales. The degree of correlation is quantified by a complex-valued order
parameter, whose amplitude is proportional to the strength of the pairing
potential in the condensate. Supercurrent-carrying states are associated with
non-zero values of the spatial gradient of the phase. The pairing potential and
several physical observables of the Cooper condensate can be manipulated by
means of temperature, current bias, dishomogeneities in the chemical
composition or application of a magnetic field. Here we show evidence of
complete suppression of the energy gap in the local density of quasiparticle
states (DOS) of a superconducting nanowire upon establishing a phase difference
equal to pi over a length scale comparable to the superconducting coherence
length. These observations are consistent with a complete collapse of the
pairing potential in the center of the wire, in accordance with theoretical
modeling based on the quasiclassical theory of superconductivity in diffusive
systems. Our spectroscopic data, fully exploring the phase-biased states of the
condensate, highlight the profound effect that extreme phase gradients exert on
the amplitude of the pairing potential. Moreover, the sharp magnetic response
observed near the onset of the superconducting gap collapse regime can be
exploited to realize ultra-low noise magnetic flux detectors.Comment: 7 pages, 5 color figures plus supporting inf
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