202 research outputs found
Temperature-dependent contact resistances in high-quality polymer field-effect transistors
Contact resistances between organic semiconductors and metals can dominate
the transport properties of electronic devices incorporating such materials. We
report measurements of the parasitic contact resistance and the true channel
resistance in bottom contact poly(3-hexylthiophene) (P3HT) field-effect
transistors with channel lengths from 400 nm up to 40 m, from room
temperature down to 77 K. For fixed gate voltage, the ratio of contact to
channel resistance decreases with decreasing temperature. We compare this
result with a recent model for metal-organic semiconductor contacts. Mobilities
corrected for this contact resistance can approach 1 cm/Vs at room
temperature and high gate voltages.Comment: 10 pages, 4 figures, accepted to Appl. Phys. Let
Nonlinear charge injection in organic field-effect transistors
Transport properties of a series of poly(3-hexylthiophene) organic field
effect transistors with Cr, Cu and Au source/drain electrodes were examined
over a broad temperature range. The current-voltage characteristics of the
injecting contacts are extracted from the dependence of conductance on channel
length. With reasonable parameters, a model of hopping injection into a
disordered density of localized states, with emphasis on the primary injection
event, agrees well with the field and the temperature dependence of the data
over a broad range of temperatures and gate voltages.Comment: 7 pages, 7 figures, sub. to J. Appl. Phy
Doping dependent charge injection and band alignment in organic field-effect transistors
We have studied metal/organic semiconductor charge injection in
poly(3-hexylthiophene) (P3HT) field-effect transistors with Pt and Au
electrodes as a function of annealing in vacuum. At low impurity dopant
densities, Au/P3HT contact resistances increase and become nonohmic. In
contrast, Pt/P3HT contacts remain ohmic even at far lower doping. Ultraviolet
photoemission spectroscopy (UPS) reveals that metal/P3HT band alignment shifts
dramatically as samples are dedoped, leading to an increased injection barrier
for holes, with a greater shift for Au/P3HT. These results demonstrate that
doping can drastically alter band alignment and the charge injection process at
metal/organic interfaces.Comment: 5 pages, 4 figure
Gated nonlinear transport in organic polymer field effect transistors
We measure hole transport in poly(3-hexylthiophene) field effect transistors
with channel lengths from 3 m down to 200 nm, from room temperature down
to 10 K. Near room temperature effective mobilities inferred from linear regime
transconductance are strongly dependent on temperature, gate voltage, and
source-drain voltage. As is reduced below 200 K and at high source-drain
bias, we find transport becomes highly nonlinear and is very strongly modulated
by the gate. We consider whether this nonlinear transport is contact limited or
a bulk process by examining the length dependence of linear conduction to
extract contact and channel contributions to the source-drain resistance. The
results indicate that these devices are bulk-limited at room temperature, and
remain so as the temperature is lowered. The nonlinear conduction is consistent
with a model of Poole-Frenkel-like hopping mechanism in the space-charge
limited current regime. Further analysis within this model reveals consistency
with a strongly energy dependent density of (localized) valence band states,
and a crossover from thermally activated to nonthermal hopping below 30 K.Comment: 22 pages, 7 figures, accepted to J. Appl. Phy
Extracting contact effects in organic field-effect transistors
Contact resistances between organic semiconductors and metal electrodes have
been shown to play a dominant role in electronic charge injection properties of
organic field-effect transistors. These effects are more prevalent in short
channel length devices and therefore should not be ignored when examining
intrinsic properties such as the mobility and its dependence on temperature or
gate voltage. Here we outline a general procedure to extract contact
current-voltage characteristics and the true channel mobility from the
transport characteristics in bottom contact poly(3-hexylthiophene) field-effect
transistors, for both Ohmic and nonlinear charge injection, over a broad range
of temperatures and gate voltages. Distinguishing between contact and channel
contributions in bottom contact OFETs is an important step toward improved
understanding and modeling of these devices.Comment: 7 pages, 8 figures. To appear in July 2005 Proc. of the IEEE, Special
Issue on Flexible Electronic
Interfacial charge transfer in nanoscale polymer transistors
Interfacial charge transfer plays an essential role in establishing the
relative alignment of the metal Fermi level and the energy bands of organic
semiconductors. While the details remain elusive in many systems, this charge
transfer has been inferred in a number of photoemission experiments. We present
electronic transport measurements in very short channel ( nm)
transistors made from poly(3-hexylthiophene) (P3HT). As channel length is
reduced, the evolution of the contact resistance and the zero-gate-voltage
conductance are consistent with such charge transfer. Short channel conduction
in devices with Pt contacts is greatly enhanced compared to analogous devices
with Au contacts, consistent with charge transfer expectations. Alternating
current scanning tunneling microscopy (ACSTM) provides further evidence that
holes are transferred from Pt into P3HT, while much less charge transfer takes
place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure
Controlling charge injection in organic field-effect transistors using self-assembled monolayers
We have studied charge injection across the metal/organic semiconductor
interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect
transistors, with Au source and drain electrodes modified by self-assembled
monolayers (SAMs) prior to active polymer deposition. By using the SAM to
engineer the effective Au work function, we markedly affect the charge
injection process. We systematically examine the contact resistivity and
intrinsic channel mobility, and show that chemically increasing the injecting
electrode work function significantly improves hole injection relative to
untreated Au electrodes.Comment: 5 pages, 2 figures. Supplementary information available upon reques
Safety and efficacy of parsaclisib in combination with obinutuzumab and bendamustine in patients with relapsed or refractory follicular lymphoma (CITADEL-102): A phase 1 study
Parsaclisib is a potent and highly selective PI3Kδ inhibitor that has shown clinical benefit with monotherapy in a phase 2 study in relapsed or refractory (R/R) follicular lymphoma (FL). CITADEL-102 (NCT03039114), a phase 1, multicenter study, assessed the efficacy of parsaclisib in combination with obinutuzumab and bendamustine in patients with R/R FL. Patients were ≥18 years of age with histologically confirmed and documented CD20-positive FL, and R/R to previous rituximab-containing treatment regimens. Part one (safety run-in) determined the maximum tolerated dose of parsaclisib in combination with standard dosage regimens of obinutuzumab and bendamustine. Part two (dose expansion) was an open-label, single-group design evaluating safety, tolerability (primary endpoint), and efficacy (secondary endpoint) of parsaclisib combination therapy. Twenty-six patients were enrolled in CITADEL-102 and all patients received parsaclisib 20 mg once daily for 8 weeks, followed by 20 mg once weekly thereafter, in combination with obinutuzumab and bendamustine. One patient in safety run-in experienced a dose-limiting toxicity of grade 4 QT interval prolongation that was considered related to parsaclisib. Eight patients (30.8%) discontinued treatment due to treatment-emergent adverse events (TEAEs) of colitis (2 [7.7%]), alanine aminotransferase and aspartate aminotransferase increase (both in one patient [3.8%]), neutropenia, thrombocytopenia, QT prolongation, tonsil cancer, and maculopapular rash (each 1 [3.8%]). The most common reported TEAEs were pyrexia (53.8%), neutropenia (50.0%), and diarrhea (46.2%). Twenty-three patients (88.5%) experienced grade 3 or 4 TEAEs; the most common were neutropenia (34.6%), febrile neutropenia (23.1%), and thrombocytopenia (19.2%). Seventeen patients (65.4%) had a complete response and 3 patients (11.5%) had a partial response, for an objective response rate of 76.9%. Overall, results from CITADEL-102 suggest that the combination of parsaclisib with obinutuzumab and bendamustine did not result in unexpected safety events, with little evidence of synergistic toxicity, and demonstrated preliminary efficacy in patients with R/R FL who progressed following prior rituximab-containing regimens
System Dynamic Modelling of Three Different Wind Turbine Gearbox Designs under Transient Loading Conditions
A survey of performance enhancement of transmission control protocol (TCP) in wireless ad hoc networks
This Article is provided by the Brunel Open Access Publishing Fund - Copyright @ 2011 Springer OpenTransmission control protocol (TCP), which provides reliable end-to-end data delivery, performs well in traditional wired network environments, while in wireless ad hoc networks, it does not perform well. Compared to wired networks, wireless ad hoc networks have some specific characteristics such as node mobility and a shared medium. Owing to these specific characteristics of wireless ad hoc networks, TCP faces particular problems with, for example, route failure, channel contention and high bit error rates. These factors are responsible for the performance degradation of TCP in wireless ad hoc networks. The research community has produced a wide range of proposals to improve the performance of TCP in wireless ad hoc networks. This article presents a survey of these proposals (approaches). A classification of TCP improvement proposals for wireless ad hoc networks is presented, which makes it easy to compare the proposals falling under the same category. Tables which summarize the approaches for quick overview are provided. Possible directions for further improvements in this area are suggested in the conclusions. The aim of the article is to enable the reader to quickly acquire an overview of the state of TCP in wireless ad hoc networks.This study is partly funded by Kohat University of Science & Technology (KUST),
Pakistan, and the Higher Education Commission, Pakistan
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