112 research outputs found
Flexible and Transparent All-Graphene Circuits for Quaternary Digital Modulations
In modern communication system, modulation is a key function that embeds the
baseband signal (information) into a carrier wave so that it can be
successfully broadcasted through a medium such as air or cables. A flexible
signal modulation scheme is hence essential to wide range of applications based
on flexible electronics. Here we report a fully bendable all-graphene modulator
circuit with the capability to encode a carrier signal with quaternary digital
information for the first time. By exploiting the ambipolarity and the
nonlinearity in a graphene transistor, we demonstrated two types of quaternary
modulation schemes: 4-ary amplitude-shift keying (4-ASK) and quadrature
phase-shift keying (QPSK). Remarkably, 4-ASK and QPSK can be realized with just
1 and 2 all-graphene transistors, respectively, representing a drastic
reduction in circuit complexity when compared with conventional digital
modulators. In addition, the circuit is not only flexible but also highly
transparent (~95% transmittance) owing to their all-graphene design with every
component (channel, interconnects, load resistor, and source/drain/gate
electrodes) fabricated from graphene films. Taken together, these results
represent a significant step toward achieving a high speed communication system
that can be monolithically integrated on a flexible and transparent platform.Comment: 29 pages, 8 figures, 1 tabl
Stencil Nano Lithography Based on a Nanoscale Polymer Shadow Mask: Towards Organic Nanoelectronics
A stencil lithography technique has been developed to fabricate organic-material-based electronic devices with sub-micron resolution. Suspended polymethylmethacrylate ( PMMA) membranes were used as shadow masks for defining organic channels and top electrodes. Arrays of pentacene field effect transistors (FETs) with various channel lengths from 50 mu m down to 500 nm were successfully produced from the same batch using this technique. Electrical transport measurements showed that the electrical contacts of all devices were stable and the normalized contact resistances were much lower than previously studied organic FETs. Scaling effects, originating from the bulk space charge current, were investigated by analyzing the channel-length-dependent mobility and hysteresis behaviors. This novel lithography method provides a reliable means for studying the fundamental transport properties of organic materials at the nanoscale as well as enabling potential applications requiring the fabrication of integrated organic nanoelectronic devices.open1155sciescopu
Extraordinarily Weak Temperature Dependence of the Drain Current in Small‐Molecule Schottky‐Contact‐Controlled Transistors through Active‐Layer and Contact Interplay
Abstract Low saturation voltages and extremely high intrinsic gain can be achieved in contact‐controlled thin‐film transistors (TFTs) with staggered device architecture, enabled by the energy barrier introduced at the source contact. The resulting device, the source‐gated transistor (SGT), is limited in its usefulness by the high temperature dependence of the drain current induced by the source energy barrier. Here, the interaction between the thermal characteristics of the source contact and the semiconductor to show drastically reduced temperature dependence for SGTs based on organic semiconductors (OSGTs) is exploited. This extraordinarily weak temperature dependence of the drain current is observed regardless of the height of the source energy barrier (27.8% in OSGTs with Ti contacts compared to 22.1% when using Au contacts, over a 34 K range). The reduction in mobility of the semiconductor offsets an increase in thermionic‐field emission of charge carriers at the source. This is a first for SGTs and provides a route to removing one of the last hurdles to their wider adoption. The OSGTs with Ti contacts also demonstrate: drain‐current saturation at very low drain‐source voltages (saturation factor of 0.22); noteworthy stability after 70 days; and minimal drain‐current variation with channel length or illumination
Reliability of new SiC BJT power modules for fully electric vehicles
Wide-bandgap semiconductors such as silicon carbide (SiC) or gallium nitride (GaN) have the potential to considerably enhance the energy efficiency and to reduce the weight of power electronic systems in electric vehicles due to their improved electrical and thermal properties in comparison to silicon based solutions. In this paper, a novel SiC based power module will be introduced, which is going to be integrated into a currently developed drive-train system for electric commercial vehicles. Increased requirements with respect to robustness and lifetime are typical for this application field. Therefore, reliability aspects such as lifetime-limiting factors, reliability assessment strategies as well as possible derived optimization measures will be the main focus of the described work
Modeling of SiC power modules with double sided cooling
Silicon Carbide (SiC) based transistor devices have demonstrated higher efficiency switching operation compared to silicon-based, state-of-the-art solutions due to the superior electrical and thermal properties of the SiC material. The improved current density and thermal conductivity allows SiC-based power modules to be smaller than their silicon counterparts for comparable current densities. The active chip area can be reduced further by effectively cooling the devices. In this work, a new power module including SiC bipolar junction transistors (BJT) and diodes and integrated double sided cooling will be introduced. The target application of these modules is a new drive-train system for commercial electric vehicles
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