56 research outputs found
Dual Gate Graphene FETs with fT of 50 GHz
A dual-gate graphene field-effect transistors is presented, which shows
improved RF performance by reducing the access resistance using electrostatic
doping. With a carrier mobility of 2700 cm2/Vs, a cutoff frequency of 50 GHz is
demonstrated in a 350-nm gate length device. This fT value is the highest
frequency reported to date for any graphene transistor, and it also exceeds
that of Si MOSFETs at the same gate length, illustrating the potential of
graphene for RF applications
Operation of Graphene Transistors at GHz Frequencies
Top-gated graphene transistors operating at high frequencies (GHz) have been
fabricated and their characteristics analyzed. The measured intrinsic current
gain shows an ideal 1/f frequency dependence, indicating an FET-like behavior
for graphene transistors. The cutoff frequency fT is found to be proportional
to the dc transconductance gm of the device. The peak fT increases with a
reduced gate length, and fT as high as 26 GHz is measured for a graphene
transistor with a gate length of 150 nm. The work represents a significant step
towards the realization of graphene-based electronics for high-frequency
applications
Self-Aligned Ballistic Molecular Transistors and Electrically Parallel Nanotube Arrays
Carbon nanotube field-effect transistors with structures and properties near
the scaling limit with short (down to 50 nm) channels, self aligned geometries,
palladium electrodes with low contact resistance and high-k dielectric gate
insulators are realized. Electrical transport in these miniature transistors is
near ballistic up to high biases at both room and low temperatures. Atomic
layer deposited (ALD) high-k films interact with nanotube sidewalls via van der
Waals interactions without causing weak localization at 4 K. New fundamental
understanding of ballistic transport, optical phonon scattering and potential
interfacial scattering mechanisms in nanotubes are obtained.Comment: Nano Letters, in pres
Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission
We utilize bias-dependent internal photoemission spectroscopy to determine the metal/dielectric/silicon energy barrier profiles for Au/HfO2/Si and Au/Al2O3/Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0 V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03+/-0.1 eV. Measurements on HfO2 give a conduction band offset value of 2.7+/-0.2 eV (at 1.0 V) and Al2O3 gives an offset of 3.3+/-0.1 (at 1.0 V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au/HfO2 barrier height was found to be 3.6+/-0.1 eV while the Au/Al2O3 barrier is 3.5+/-0.1 eV
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Atomic Layer Deposition to Fine-Tune the Surface Properties and Diameters of Fabricated Nanopores
Atomic layer deposition of alumina enhanced the molecule sensing characteristics of fabricated nanopores by fine-tuning their surface properties, reducing 1/f noise, neutralizing surface charge to favor capture of DNA and other negative polyelectrolytes, and controlling the diameter and aspect ratio of the pores with near single Ã…ngstrom precision. The control over the chemical and physical nature of the pore surface provided by atomic layer deposition produced a higher yield of functional nanopore detectors.Molecular and Cellular BiologyPhysicsChemistry and Chemical BiologyEngineering and Applied Science
Electronic transport and device prospects of monolayer molybdenum disulphide grown by chemical vapour deposition
Layered transition metal dichalcogenides display a wide range of attractive
physical and chemical properties and are potentially important for various
device applications. Here we report the electronic transport and device
properties of monolayer molybdenum disulphide (MoS2) grown by chemical vapour
deposition (CVD). We show that these devices have the potential to suppress
short channel effects and have high critical breakdown electric field. However,
our study reveals that the electronic properties of these devices are at
present, severely limited by the presence of a significant amount of band tail
trapping states. Through capacitance and ac conductance measurements, we
systematically quantify the density-of-states and response time of these
states. Due to the large amount of trapped charges, the measured effective
mobility also leads to a large underestimation of the true band mobility and
the potential of the material. Continual engineering efforts on improving the
sample quality are needed for its potential applications.Comment: 23 pages, 5 figure
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