4,249 research outputs found
Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
In this article, we study the properties of metal contacts to single-layer
molybdenum disulfide (MoS2) crystals, revealing the nature of switching
mechanism in MoS2 transistors. On investigating transistor behavior as contact
length changes, we find that the contact resistivity for metal/MoS2 junctions
is defined by contact area instead of contact width. The minimum gate dependent
transfer length is ~0.63 {\mu}m in the on-state for metal (Ti) contacted
single-layer MoS2. These results reveal that MoS2 transistors are Schottky
barrier transistors, where the on/off states are switched by the tuning the
Schottky barriers at contacts. The effective barrier heights for source and
drain barriers are primarily controlled by gate and drain biases, respectively.
We discuss the drain induced barrier narrowing effect for short channel
devices, which may reduce the influence of large contact resistance for MoS2
Schottky barrier transistors at the channel length scaling limit.Comment: ACS Nano, ASAP (2013
Introduction to Graphene Electronics -- A New Era of Digital Transistors and Devices
The speed of silicon-based transistors has reached an impasse in the recent
decade, primarily due to scaling techniques and the short-channel effect.
Conversely, graphene (a revolutionary new material possessing an atomic
thickness) has been shown to exhibit a promising value for electrical
conductivity. Graphene would thus appear to alleviate some of the drawbacks
associated with silicon-based transistors. It is for this reason why such a
material is considered one of the most prominent candidates to replace silicon
within nano-scale transistors. The major crux here, is that graphene is
intrinsically gapless, and yet, transistors require a band-gap pertaining to a
well-defined ON/OFF logical state. Therefore, exactly as to how one would
create this band-gap in graphene allotropes is an intensive area of growing
research. Existing methods include nano-ribbons, bilayer and multi-layer
structures, carbon nanotubes, as well as the usage of the graphene substrates.
Graphene transistors can generally be classified according to two working
principles. The first is that a single graphene layer, nanoribbon or carbon
nanotube can act as a transistor channel, with current being transported along
the horizontal axis. The second mechanism is regarded as tunneling, whether
this be band-to-band on a single graphene layer, or vertically between adjacent
graphene layers. The high-frequency graphene amplifier is another talking point
in recent research, since it does not require a clear ON/OFF state, as with
logical electronics. This paper reviews both the physical properties and
manufacturing methodologies of graphene, as well as graphene-based electronic
devices, transistors, and high-frequency amplifiers from past to present
studies. Finally, we provide possible perspectives with regards to future
developments.Comment: This is an updated version of our review article, due to be published
in Contemporary Physics (Sept 2013). Included are updated references, along
with a few minor corrections. (45 pages, 19 figures
All CVD Boron Nitride Encapsulated Graphene FETs with CMOS Compatible Metal Edge Contacts
We report on the fabrication and characterization of field effect transistors
(FETs) based on chemical vapor deposited (CVD) graphene encapsulated between
few layer CVD boron nitride (BN) sheets with complementary metal oxide
semiconductor (CMOS) compatible nickel edge contacts. Non-contact Tera-hertz
time domain spectroscopy (THz-TDS) of large-area BN/graphene/BN (BN/G/BN)
stacks reveals average sheet conductivity >1 mS/sq and average mobility of 2500
cm/Vs. Improved output conductance is observed in direct current (DC)
measurements under ambient conditions, indicating potential for radio-frequency
(RF) applications. Moreover, we report a maximum voltage gain of 6 dB from a
low frequency signal amplifier circuit. RF characterization of the GFETs yields
an f x L product of 2.64 GHzm and an f x L
product of 5.88 GHzm. This study presents for the first time THz-TDS usage
in combination with other characterization methods for device performance
assessment on BN/G/BN stacks. The results serve as a step towards scalable, all
CVD 2D material-based FETs for CMOS compatible future nanoelectronic circuit
architectures.Comment: 6 page
Application of Graphene within Optoelectronic Devices and Transistors
Scientists are always yearning for new and exciting ways to unlock graphene's
true potential. However, recent reports suggest this two-dimensional material
may harbor some unique properties, making it a viable candidate for use in
optoelectronic and semiconducting devices. Whereas on one hand, graphene is
highly transparent due to its atomic thickness, the material does exhibit a
strong interaction with photons. This has clear advantages over existing
materials used in photonic devices such as Indium-based compounds. Moreover,
the material can be used to 'trap' light and alter the incident wavelength,
forming the basis of the plasmonic devices. We also highlight upon graphene's
nonlinear optical response to an applied electric field, and the phenomenon of
saturable absorption. Within the context of logical devices, graphene has no
discernible band-gap. Therefore, generating one will be of utmost importance.
Amongst many others, some existing methods to open this band-gap include
chemical doping, deformation of the honeycomb structure, or the use of carbon
nanotubes (CNTs). We shall also discuss various designs of transistors,
including those which incorporate CNTs, and others which exploit the idea of
quantum tunneling. A key advantage of the CNT transistor is that ballistic
transport occurs throughout the CNT channel, with short channel effects being
minimized. We shall also discuss recent developments of the graphene tunneling
transistor, with emphasis being placed upon its operational mechanism. Finally,
we provide perspective for incorporating graphene within high frequency
devices, which do not require a pre-defined band-gap.Comment: Due to be published in "Current Topics in Applied Spectroscopy and
the Science of Nanomaterials" - Springer (Fall 2014). (17 pages, 19 figures
High On/Off Ratio Graphene Nanoconstriction Field Effect Transistor
We report a method to pattern monolayer graphene nanoconstriction field
effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET
fabrication is enabled by the use of feedback controlled electromigration (FCE)
to form a constriction in a gold etch mask that is first patterned using
conventional lithographic techniques. The use of FCE allows the etch mask to be
patterned on size scales below the limit of conventional nanolithography. We
observe the opening of a confinement-induced energy gap as the NCFET width is
reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off
ratios we obtain with this procedure can be larger than 1000 at room
temperature for the narrowest devices; this is the first report of such large
room temperature on/off ratios for patterned graphene FETs.Comment: 18 pages, 6 figures, to appear in Smal
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