Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.

Organic Thin Film Transistors for Large Area Electronics

Allergic rhinitis is a symptomatic disorder of the nose induced after allergen exposure by an IgE-mediated inflammation of the membranes lining the nose. It is a global health problem that causes major illness and disability worldwide. Over 600 million patients from all countries, all ethnic groups and of all ages suffer from allergic rhinitis. It affects social life, sleep, school and work and its economic impact is substantial. Risk factors for allergic rhinitis are well identified. Indoor and outdoor allergens as well as occupational agents cause rhinitis and other allergic diseases. The role of indoor and outdoor pollution is probably very important, but has yet to be fully understood both for the occurrence of the disease and its manifestations.

In 1999, during the Allergic Rhinitis and its Impact on Asthma (ARIA) WHO workshop, the expert panel proposed a new classification for allergic rhinitis which was subdivided into 'intermittent' or 'persistent' disease.

This classification is now validated. The diagnosis of allergic rhinitis is often quite easy, but in some cases it may cause problems and many patients are still under-diagnosed, often because they do not perceive the symptoms of rhinitis as a disease impairing their social life, school and work.

The management of allergic rhinitis is well established and the ARIA expert panel based its recommendations on evidence using an extensive review of the literature available up to December 1999. The statements of evidence for the development of these guidelines followed WHO rules and were based on those of Shekelle et al. A large number of papers have been published since 2000 and are extensively reviewed in the 2008 Update using the same evidence-based system. Recommendations for the management of allergic rhinitis are similar in both the ARIA workshop report and the 2008 Update. In the future, the GRADE approach will be used, but is not yet available.

Another important aspect of the ARIA guidelines was to consider co-morbidities. Both allergic rhinitis and asthma are systemic inflammatory conditions and often co-exist in the same patients. In the 2008 Update, these links have been confirmed.

The ARIA document is not intended to be a standard-of-care document for individual countries. It is provided as a basis for physicians, health care professionals and organizations involved in the treatment of allergic rhinitis and asthma in various countries to facilitate the development of relevant local standard-of-care documents for patients.

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Allergic rhinitis and its impact on asthma (ARIA) 2008 update (in collaboration with the World Health Organization, GA(2)LEN and AllerGen)

Authors Jan L. Brozek, MD, PhD – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada Jean Bousquet, MD, PhD – Service des Maladies Respiratoires, Hopital Arnaud de Villeneuve, Montpellier, France, INSERM, CESP U1018, Respiratory and Environmental Epidemiology Team, France, and WHO Collaborating Center for Rhinitis and Asthma Carlos E. Baena-Cagnani, MD – Faculty of Medicine, Catholic University of Cordoba, Cordoba, Argentina Sergio Bonini, MD – Institute of Neurobiology and Molecular Medicine – CNR, Rome, Italy and Department of Medicine, Second University of Naples, Naples, Italy G. Walter Canonica, MD – Allergy & Respiratory Diseases, DIMI, Department of Internal Medicine, University of Genoa, Genoa, Italy Thomas B. Casale, MD – Division of Allergy and Immunology, Department of Medicine, Creighton University, Omaha, Nebraska, USA Roy Gerth van Wijk, MD, PhD – Section of Allergology, Department of Internal Medicine, Erasmus Medical Centre, Rotterdam, the Netherlands Ken Ohta, MD, PhD – Division of Respiratory Medicine and Allergology, Department of Medicine, Teikyo University School of Medicine, Tokyo, Japan Torsten Zuberbier, MD – Department of Dermatology and Allergy, Charite Universitatsmedizin Berlin, Berlin, Germany Holger J. Schunemann, MD, PhD, MSc – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada

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Allergic Rhinitis and Its Impact on Asthma

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.

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Nanoscale thermal transport

It is shown that clock frequencies in excess of 200 MHz are feasible in a 3- mu m CMOS process. This performance can be obtained by means of clocking strategy, device sizing, and logic style selection. A precharge technique with a true single-phase clock, which increases the clock frequency and reduces the skew problems, is used. Device sizing with the help of an optimizing program improves circuit speed by a factor of 1.5-1.8. The logic depth is minimized to one instead of two or more, and pipeline structures are used wherever possible. Experimental results for several circuits which work at clock frequencies of 200-230 MHz are presented. SPICE simulation shows that some circuits could work up to 400-500 MHz. >

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High-speed CMOS circuit technique

An MOS transistor in silicon with 10−nm silicon dioxide as gate insulator and 10−nm palladium as gate electrode was fabricated. The threshold voltage of this transistor was found to be a function of the partial pressure of hydrogen in the ambient atmosphere. At a device temperature of 150 °C it was possible to detect 40 ppm hydrogen gas in air with response times less than 2 min.

A hydrogen−sensitive MOS field−effect transistor

One of the most important degradation effects observed in MNOS memory transistors is a negative shift of the threshold window. This negative shift is caused by a strong increase of the density of Si‐SiO2 surface traps. This effect has been proposed to be caused by the same effect that is observed in MOS devices subjected to negative‐bias stress (NBS). In this paper, a detailed study of the increase of the number of surface traps in MOS structures after NBS at temperatures (25–125 °C) and fields (400–700 MV/m) comparable to those used in MNOS devices is presented. Two different behaviors are observed. At low fields the surface‐trap density increases as t1/4 and at high fields it increases linearly with the stress time t. The low‐field behavior is temperature and field dependent and the zero‐field activation energy is determined to be 0.3 eV. The high‐field behavior is strongly field dependent but independent of temperature. A physical model is proposed to explain the surface‐trap growth as being diffusion ...

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Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices

We investigated scaling of the atmospheric neutron soft error rate (SER) which affects reliability of CMOS circuits at ground level and airplane flight altitudes. We considered CMOS circuits manufactured in a bulk process with a lightly-doped p-type wafer. One method, based on the empirical model, predicts a linear decrease of SER per bit with decreasing feature size L/sub G/. A different method, based on the MBGR model, predicts even faster decrease of SER per bit than linear. If the increasing number of bits is taken into account, then the SER per chip is not expected to increase faster than linearly with decreasing L/sub G/.

Impact of CMOS technology scaling on the atmospheric neutron soft error rate

An n‐channel MOS transistor with palladium gate was fabricated. The threshold voltage of this transistor was found to depend on the partial pressure of hydrogen in the ambient atmosphere. At a device temperature of 150 °C, 10 ppm hydrogen in air is easily detected, and in nitrogen or argon the sensitivity is considerably larger. A model, based on hydrogen adsorption on the palladium–silicon dioxide interface, is proposed. This model explains the device behavior and is also able to predict the absolute sensitivity for hydrogen in argon.

Christer Svensson

Papers

High-speed CMOS circuit technique

A hydrogen−sensitive MOS field−effect transistor

Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices

Impact of CMOS technology scaling on the atmospheric neutron soft error rate

A hydrogen-sensitive Pd-gate MOS transistor