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Device Design (device + design)
Selected AbstractsThe Effect of Polymer Optoelectronic Properties on the Performance of Multilayer Hybrid Polymer/TiO2 Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 4 2005P. Ravirajan Abstract We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2-methoxy-5-(2,-ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymers and a fluorene,bithiophene copolymer are compared. We use photoluminescence quenching, time-of-flight mobility measurements, and optical spectroscopy to characterize the exciton-transport, charge-transport, and light-harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic-device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip-coating step before spin-coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge-transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip-coated and PEDOT:PSS layers produced a short-circuit current density of about 1,mA,cm,2, a fill factor of 0.50, and an open-circuit voltage of 0.86,V under simulated AM,1.5 illumination (100,mW,cm,2, 1,sun). The corresponding power conversion efficiency under 1,sun was ,,0.4,%. [source] The Development of Light-Emitting Dendrimers for Displays,ADVANCED MATERIALS, Issue 13 2007L. Burn Abstract Dendrimers are now an important class of light-emitting material for use in organic light-emitting diodes (OLEDs). Dendrimers are branched macromolecules that consist of a core, one or more dendrons, and surface groups. The different parts of the macromolecule can be selected to give the desired optoelectronic and processing properties. The first light-emitting dendrimers were fluorescent but more recently highly efficient phosphorescent dendrimers have been developed. OLEDs containing light-emitting dendrimers have been reported to have external quantum efficiencies of up to 16,%. The solubility of the dendrimers opens the way for simple processing and a new class of flat-panel displays. In this Review we show how the structure of the light-emitting dendrimers controls key features such as intermolecular interactions and charge transport, which are important for all OLED materials. The advantages of the dendrimer architecture for phosphorescent emitters and the way the structure can be varied to enhance materials performance and device design are illustrated. [source] Could interchangeable use of dry powder inhalers affect patients?INTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 2005D. Price Summary The aim of asthma treatment is optimal disease control. Poor asthma control results in considerable patient morbidity, as well as contributing to the considerable burden placed by the disease on healthcare budgets. There is a need for costs to be carefully scrutinised, with the switching of patients to inhaler devices with lower acquisition costs likely to be increasingly considered. However, before such practice becomes widespread, it is important to establish whether or not this could adversely impact on patients and the level of disease control. For approval to have been given, all marketed inhalers must have satisfied current regulatory requirements for devices. Full preclinical and clinical development programmes are not required when application is made for authorisation to market a new inhaler containing an existing chemical entity, although clinical equivalence testing must be used. Both beneficial and adverse effects should be tested, and the limits of equivalence must be clearly defined, based on therapeutic relevance. It should be noted that equivalence studies are invalid when the end point is not responding (i.e. at the top of the dose,response curve) and when equivalence limits approach or are equal to the magnitude of the drug effect. Approval on the basis of regulations designed to safeguard quality of dry powder inhalers does not mean that devices are interchangeable. When using an inhaler, there are many stages between the patient and the therapeutic effect, involving device design, pharmaceutical performance and patient behaviour. Regulations governing new devices cover only a few of the many factors affecting disease control. Furthermore, clinical trials to assess equivalence may not take into account factors in patient behaviour or variations in patient inhaler technique that may affect use of devices in real-life situations. When assessing the consequences of interchangeable use of dry powder inhalers on healthcare costs, it is important to ensure that the acquisition cost of the devices is not the only cost considered. Other costs that should be considered include the cost of time spent demonstrating to the patient how to use the new device, the cost of additional physician visits to address patient concerns and the management costs if disease control is adversely affected. [source] Reliability of capacitive RF MEMS switches at high and low temperaturesINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2004Yong Zhu Abstract Some applications of RF MEMS switches, such as aircraft condition monitoring and distributed satellite communication, present a unique challenge for device design and reliability. This article examines these switches when operational temperatures in the range ,60°C to 100°C are envisioned. The basic operation of a capacitive MEMS switch is described and two tools for examining device reliability, modeling, and on-chip experimentation, are discussed in the case of capacitive MEMS switches. 1D, 2D, and 3D models are presented with emphasis on 3D coupled-field finite-element analysis, including temperature effects. Results and findings from the 3D simulations are reported. In particular, the advantages of employing corrugated membranes in the design of RF MEMS switches are assessed. Their performance in terms of reliability as a function of temperature is quantified. The effects of corrugation on the geometric parameters are discussed in the context of device-design optimization. In order to assess reliability experimentally, the M-test and the membrane deflection experiment (MDE) are reviewed due to their on-chip characteristic and simplicity. Ways in which these experimental/computational methodologies can be combined for identifying material properties and device performance is also highlighted. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 317,328, 2004. [source] Tailored (Meth)Acrylate Shape-Memory Polymer Networks for Ophthalmic ApplicationsMACROMOLECULAR BIOSCIENCE, Issue 10 2010Li Song Abstract The unique features of shape-memory polymers enables their use in minimally invasive surgical procedures with a compact starting material switching over to a voluminous structure in vivo. In this work, a series of transparent, thermoset (meth)acrylate shape-memory polymer networks with tailored thermomechanics have been synthesized and evaluated. Fundamental trends were established for the effect of the crosslinker content and crosslinker molecular weight on glass transition temperature, rubbery modulus and shape-recovery behavior, and the results are intended to help with future shape-memory device design. The prepared (meth)acrylate networks with high transparency and favorable biocompatibility are presented as a promising shape-memory ophthalmic biomaterial. [source] Current collapse and reliability of III-N heterostructure field effect transistorsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3 2007A. Koudymov Abstract Measurements of GaN HFET lifetime as a function of temperature show that different degradation mechanisms are involved at low temperatures (close to room temperature) and high temperatures (above 150 °C). The degradation at low temperatures is linked to the trap generation and can be explained using the current collapse model. At higher tempe- ratures, other degradation mechanisms become important or even dominant. The current collapse related degradation can be diminished by using improved device design, which will greatly increase the overall lifetime (up to long lifetimes obtained by extrapolating high temperature data to room temperature). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reliability aspects of SiC Schottky diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2009Matthias Holz Abstract In recent years, silicon carbide (SiC) high-voltage power devices have gained an ever-increasing market share. The fast development of new device concepts and technologies, e.g. for SiC Schottky diodes, has led to devices with superior switching behaviour, which renders SiC power devices especially favourable for high-frequency applications. As of today, SiC devices enter various fields like, e.g. server power supplies, solar inverters, and drives. These applications pose quite different requirements not only on the electrical properties, but also on the long-term reliability of the devices. In this paper, we describe in detail how Infineon's SiC Schottky diodes excel the reliability requirements. We point out how material properties, device design and packaging technology affect the overall device reliability and how they can be optimized. In addition, we describe measurement results after stress tests that go far beyond standard stress tests according to JEDEC. E.g., we show that SiC devices can safely be operated at high voltage slopes of 120 V/ns. In addition, we show that the use of high performance die attach further improves the device properties and reliability. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical spin injection into InGaAs quantum dots: single dot devices and time-resolved studiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009M. Hetterich Abstract In the context of a potential future quantum information processing we investigate the concurrent initialization of electronic spin states in InGaAs quantum dots (QDs) via electrical injection from ZnMn(S)Se spin aligners. Single dots can be read out optically through metallic apertures on top of our spin-injection light-emitting diodes (spin-LEDs). A reproducible spin polarization degree close to 100% is observed for a subset of the QD ensemble. However, the average polarization degree is lower and drops with increasing QD emission wavelength. Our measurements suggest that spin relaxation processes outside the QDs, related to the energetic position of the electron quasi-Fermi level, as well as defect-related spin scattering at the III,V/II,VI interface should be responsible for this effect, leading us to an improved device design. Finally, we present first time-resolved electroluminescence measurements of the polarization dynamics using nanosecond-pulsed electrical excitation. The latter should enable us to gain a more detailed understanding of the spin relaxation processes in our devices. They are also the first step towards future time-resolved spin manipulation experiments. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN-based Schottky diodes for hydrogen sensing in transformer oilPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006Peter Sandvik Abstract We report the demonstration of robust, GaN-based hydrogen sensors for use directly in transformer oil. These 1 mm2 Schottky diodes were immersed in a closed loop with Voltesso insulating oil for 21 months of continuous testing. They showed good reproducibility in response to hydrogen gases, while exposed to varying temperatures. We will briefly discuss the transformer monitoring application, the device design and fabrication process, and the sensor performance from 21-months of testing. Transfer functions from oil temperature and dissolved gas concentration have been quantified, and those will be briefly discussed. These new sensors offer a novel alternative to electrochemical cell-based sensors for various applications. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thin-film solar cells: an overviewPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2-3 2004K. L. Chopra Abstract Thin film solar cells (TFSC) are a promising approach for terrestrial and space photovoltaics and offer a wide variety of choices in terms of the device design and fabrication. A variety of substrates (flexible or rigid, metal or insulator) can be used for deposition of different layers (contact, buffer, absorber, reflector, etc.) using different techniques (PVD, CVD, ECD, plasma-based, hybrid, etc.). Such versatility allows tailoring and engineering of the layers in order to improve device performance. For large-area devices required for realistic applications, thin-film device fabrication becomes complex and requires proper control over the entire process sequence. Proper understanding of thin-film deposition processes can help in achieving high-efficiency devices over large areas, as has been demonstrated commercially for different cells. Research and development in new, exotic and simple materials and devices, and innovative, but simple manufacturing processes need to be pursued in a focussed manner. Which cell(s) and which technologies will ultimately succeed commercially continue to be anybody's guess, but it would surely be determined by the simplicity of manufacturability and the cost per reliable watt. Cheap and moderately efficient TFSC are expected to receive a due commercial place under the sun. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||