Logic-gate devices based on printed polymer semiconducting nanostripes

The applications of organic semiconductors in complex circuitry such as printed CMOS-like logic circuits demand miniaturization of the active structures to the submicrometric and nanoscale level while enhancing or at least preserving the charge transport properties upon processing. Here, we addressed this issue by using a wet lithographic technique, which exploits and enhances the molecular order in polymers by spatial confinement, to fabricate ambipolar organic field effect transistors and inverter circuits based on nanostructured single component ambipolar polymeric semiconductor. In our devices, the current flows through a precisely defined array of nanostripes made of a highly ordered diketopyrrolopyrrole-benzothiadiazole copolymer with high charge carrier mobility (1.45 cm2 V-1 s-1 for electrons and 0.70 cm2 V-1 s-1 for holes). Finally, we demonstrated the functionality of the ambipolar nanostripe transistors by assembling them into an inverter circuit that exhibits a gain (105) comparable to inverters based on single crystal semiconductors.

High mobility top-gate and dual-gate polymer thin-film transistors based on diketopyrrolopyrrole-naphthalene copolymer

In this letter, the performance characteristics of top-gate and dual-gate thin-film transistors (TFTs) with active semiconductor layers consisting of diketopyrrolopyrrole-naphthalene copolymer are described. Optimized top-gate TFTs possess mobilities of up to 1 cm 2 /V s with low contact resistance and reduced hysteresis in air. Dual-gate devices possess higher drive currents as well as improved subthreshold and above threshold characteristics compared to single-gate devices. We also describe the reasons that dual-gate devices result in improved performance. The good stability of this polymer combined with their promising electrical properties make this material a very promising semiconductor for printable electronics.

Charge-carrier velocity distributions in high-mobility polymer dual-gate thin-film transistors

We report charge-carrier velocity distributions in high-mobility polymer thin-film transistors (PTFTs) employing a dual-gate configuration. Our time-domain measurements of dual-gate PTFTs indicate higher effective mobility as well as fewer low-velocity carriers than in single-gate operation. Such nonquasi-static (NQS) measurements support and clarify the previously reported results of improved device performance in dual-gate devices by various groups. We believe that this letter demonstrates the utility of NQS measurements in studying charge-carrier transport in dual-gate thin-film transistors.

Solution-processed dual-gate polymer field-effect transistors for display applications

We describe the advantages of dual-gate thin-film transistors (TFTs) for display applications. We show that in TFTs with active semiconductor layers composed of diketopyrrolopyrrole-naphthalene copolymer, the on-current is increased, the off-current is reduced, and the sub-threshold swing is improved compared to single-gate devices. Charge transport measurements in steady-state and under non-quasi-static conditions reveal the reasons for this improved performance. We show that in dual-gate devices, a much smaller fraction of charge carriers move in slow trap states. We also compare the activation energies for charge transport in the top-gate and bottom-gate configurations.

Improved performance in diketopyrrolopyrrole-based transistors with bilayer gate dielectrics

There has been significant progress in the past 2 decades in the field of organic and polymer thin-film transistors. In this paper, we report a combination of stable materials, device architecture, and process conditions that resulted in a patterned gate, small channel length (<5 μm) device that possesses a scaled field-induced conductivity in air that is higher than any organic/polymer transistor reported thus far. The operating voltage is below 10 V; the on-off ratio is high; and the active materials are solution-processable. The semiconducting polymer is a new donor-acceptor polymer with furan-substituted diketopyrrolopyrrole and thienyl-vinylene-thienyl building blocks in the conjugated backbone. One of the major striking features of our work is that the patterned-gate device architecture is suitable for practical applications. We also propose a figure of merit to meaningfully compare polymer/organic transistor performance that takes into account mobility and operating voltage. With this figure of merit, we compare leading organic and polymer transistors that have been hitherto reported. The material and device architecture have shown very high mobility and low operating voltage for such short channel length (below 5 μm) organic/polymer transistors.

The influence of atmospheric conditions on the leakage current of ceramic insulators on the Colombian Caribbean coast

The contamination of electrical insulators is one of the major contributors to the risk of operation outages in electrical substations, especially in coastal zones with high salinity levels and atmospheric pollution. By using the measurement of leakage-currents, which is one of the main indicators of contamination in insulators, this work seeks to the determine the correlation with climatic variables, such as ambient temperature, relative humidity, solar irradiance, atmospheric pressure, and wind speed and direction. The results obtained provide an input to the behaviour of the leakage current under atmospheric conditions that are particular to the Caribbean coast of Colombia. Spearman’s rank correlation coefficients and principal component analysis are utilised to determine the significant relationships among the different variables under consideration. The necessary information for the study was obtained via historical databases of both atmospheric variables and the leakage current measured in over a period of one year in a 220-kV potential transformer insulator. We identified the influencing factors of temperature, humidity, radiation, wind speed and direction on the magnitude of the leakage current as the most relevant.

Comparison of the gate drive parameter space for driving power MOSFETs using conventional and cascode configurations

Conventional voltage driven gate drive circuits utilise a resistor to control the switching speed of power MOS-FETs. The gate resistance is adjusted to provide controlled rate of change of load current and voltage. The cascode gate drive configuration has been proposed as an alternative to the conventional resistor-fed gate drive circuit. While cascode drive is broadly understood in the literature the switching characteristics of this topology are not well documented. This paper explores, through both simulation and experimentation, the gate drive parameter space of the cascode gate drive configuration and provides a comparison to the switching characteristics of conventional gate drive.

Characterisation of the cascode gate drive of power MOSFETs in clamped inductive switching applications

This thesis proposes a novel gate drive circuit to improve the switching performance of MOSFET power switches in power electronic converters. The proposed topology exploits the cascode configuration, allowing the minimisation of switching losses in the presence of practical circuit constraints, which enables efficiency and power density improvements. Switching characteristics of the new topology are investigated and key mechanisms that control the switching process are identified. Unique analysis tools and techniques are also developed to demonstrate the application of the cascode gate drive circuit for switching performance optimisation.

Lock the gate: Fracking, investor-state dispute settlement, and the Trans-Pacific Partnership

There has been much debate about the relationship between international trade, the environment, biodiversity protection, and climate change.The Obama Administration has pushed such issues into sharp relief, with its advocacy for sweeping international trade agreements, such as the Trans-Pacific Partnership and the Trans-Atlantic Trade and Investment Partnership. There has been much public concern about the impact of the mega-trade deals upon the protection of the environment. In particular, there has been a debate about whether the Trans-Pacific Partnership will promote dirty fracking. Will the Trans-Pacific Partnership transform the Pacific Rim into a Gasland?There has been a particular focus upon investor-state dispute settlement being used by unconventional mining companies. Investor-state dispute settlement is a mechanism which enables foreign investors to seek compensation from national governments at international arbitration tribunals. In her prescient 2009 book, The Expropriation of Environmental Governance, Kyla Tienhaara foresaw the rise of investor-state dispute resolution of environmental matters. She observed:'Over the last decade there has been an explosive increase of cases investment arbitration. This is significant in terms of not only the number of disputes that have arisen and the number of states that have been involved, but also the novel types of dispute that have emerged. Rather than solely involving straightforward incidences of nationalization or breach of contract, modern disputes often revolve around public policy measures and implicate sensitive issues such as access to drinking water, development on sacred indigenous sites and the protection of biodiversity.'In her study, Kyla Tienhaara observed that investment agreements, foreign investment contracts and investment arbitration had significant implications for the protection for the protection of the environment. She concluded that arbitrators have made it clear that they can, and will, award compensation to investors that claim to have been harmed by environmental regulation. She also found that some of the cases suggest that the mere threat of arbitration is sufficient to chill environmental policy development. Tienhaara was equally concerned by the possibility that a government may use the threat of arbitration as an excuse or cover for its failure to improve environmental regulation. In her view, it is evident that arbitrators have expropriated certain fundamental aspects of environmental governance from states. Tienhaara held: As a result, environmental regulation has become riskier, more expensive, and less democratic, especially in developing countries. This article provides a comparative analysis of the battles over fracking, investment, trade, and the environment in a number of key jurisdictions including the United States, Canada, Australia, and New Zealand. Part 1 focuses upon the United States. Part 2 examines the dispute between the Lone Pine Resources Inc. and the Government of Canada over a fracking moratorium in Quebec. Part 3 charts the rise of the Lock the Gate Alliance in Australia, and its demands for a moratorium in respect of coal seam gas and unconventional mining. Part 4 focuses upon parallel developments in New Zealand. This article concludes that Pacific Rim countries should withdraw from investor-state dispute settlement procedures, because of the threat posed to environmental regulation in respect of air, land, and water.

Assessment of the risk of failure of high voltage substations due to environmental conditions and pollution on insulators

Pollution on electrical insulators is one of the greatest causes of failure of substations subjected to high levels of salinity and environmental pollution. Considering leakage current as the main indicator of pollution on insulators, this paper focus on establishing the effect of the environmental conditions on the risk of failure due to pollution on insulators and determining the significant change in the magnitude of the pollution on the insulators during dry and humid periods. Hierarchical segmentation analysis was used to establish the effect of environmental conditions on the risk of failure due to pollution on insulators. The Kruskal-Wallis test was utilized to determine the significant changes in the magnitude of the pollution due to climate periods. An important result was the discovery that leakage current was more common on insulators during dry periods than humid ones. There was also a higher risk of failure due to pollution during dry periods. During the humid period, various temperatures and wind directions produced a small change in the risk of failure. As a technical result, operators of electrical substations can now identify the cause of an increase in risk of failure due to pollution in the area. The research provides a contribution towards the behaviour of the leakage current under conditions similar to those of the Colombian Caribbean coast and how they affect the risk of failure of the substation due to pollution.

Group 14 element-based non-centrosymmetric quantum spin hall insulators with large bulk gap

To date, a number of two-dimensional (2D) topological insulators (TIs) have been realized in Group 14 elemental honeycomb lattices, but all are inversionsymmetric. Here, based on first-principles calculations, we predict a new family of 2D inversion-asymmetric TIs with sizeable bulk gaps from 105 meV to 284 meV, in X2–GeSn (X = H, F, Cl, Br, I) monolayers, making them in principle suitable for room-temperature applications. The nontrivial topological characteristics of inverted band orders are identified in pristine X2–GeSn with X = (F, Cl, Br, I), whereas H2–GeSn undergoes a nontrivial band inversion at 8% lattice expansion. Topologically protected edge states are identified in X2–GeSn with X = (F, Cl, Br, I), as well as in strained H2–GeSn. More importantly, the edges of these systems, which exhibit single-Dirac-cone characteristics located exactly in the middle of their bulk band gaps, are ideal for dissipationless transport. Thus, Group 14 elemental honeycomb lattices provide a fascinating playground for the manipulation of quantum states.

Effect of organic gate dielectric material properties on interfacial charging and discharging of pentacene MIM device

The effect of material properties of an environmentally friendly, optically transparent dielectric material, polyterpenol, on the carrier transients within the pentacene-based double-layer MTM device was investigated. Polyterpenol films were RF plasma polymerised under varied process conditions, with resultant films differing in surface chemistry and morphology. Independent of type of polyterpenol, time-resolved EFISHG study of IZO/polyterpenol/pentacene/Au structures showed similar transient behaviour with carriers injected into pentacene from Au electrode only, confirming polyterpenol to be a suitable blocking layer for visualisation of single-species carrier transportation during charging and discharging under different bias conditions. Polyterpenol fabricated under higher input power show better promise due to higher chemical and thermal stability, improved uniformity, and absence of defects.

Fabrication and characterization of polyterpenol as an insulating layer and incorporated organic field effect transistor

A non-synthetic polymer material, polyterpenol, was fabricated using a dry polymerization process namely RF plasma polymerization from an environmentally friendly monomer and its surface, optical and electrical properties investigated. Polyterpenol films were found to be transparent over the visible wavelength range, with a smooth surface with an average roughness of less than 0.4 nm and hardness of 0.4 GPa. The dielectric constant of 3.4 for polyterpenol was higher than that of the conventional polymer materials used in the organic electronic devices. The non-synthetic polymer material was then implemented as a surface modification of the gate insulator in field effect transistor (OFET) and the properties of the device were examined. In comparison to the similar device without the polymer insulating layer, the polyterpenol based OFET device showed significant improvements. The addition of the polyterpenol interlayer in the OFET shifted the threshold voltage significantly; + 20 V to -3 V. The presence of trapped charge was not observed in the polyterpenol interlayer. This assisted in the improvement of effective mobility from 0.012 to 0.021 cm 2/Vs. The switching property of the polyterpenol based OFET was also improved; 107 compared to 104. The results showed that the non-synthetic polyterpenol polymer film is a promising candidate of insulators in electronic devices.

John Frazer

John Frazer, Professor, trained at the Architectural Association, taught first at Cambridge University and then the AA in the 1970s and again in the '90s. He was Head of School of Design Research History and Criticism at the University of Ulster in the 1980s, he also ran a systems and design consultancy with his wife Julia (including projects for Cedric Price and Walter Segal) and was founder and chairman of Autographics software. He is currently Swire Chair Professor and Head of School of Design in Hong Kong.----- This is a very personal perspective on a concept of universal and future significance. It is personal, both is the sense that it is an unashamedly biased view of both the significance of the project, and the nature of that significance and because the author was personally involved as one of the consultants on GENERATOR and subsequently involved Cedric Price in its educational application at the Architectural Association. GENERATOR is still very much alive and was still developing whilst this chapter was being written.

Asia

Reporters sans frontiéres (RSF) has repeatedly declared Asia to be the most demanding continent for journalists and their news organizations to operate in, and in some countries, even simply to survive in. The many reports issued by RSF and other global agencies regularly show Asia to be the region in which the largest number of murders of journalists occur per year, even when Asian–Arabic states and Central Asia are not included in the definition of ‘Asia’. The reports describe numerous physical, legal and economic threats as well as serious political repression and restrictions that journalists face as they attempt to function as watch-dogs, agenda-setters and gate-keepers for their societies. The statistics and examples provided within these reports, however, do not provide the full picture. Most Asian nations also host vibrant media cultures in which journalists play an important role in supporting social and democratic processes and activities. This chapter outlines the political and economic influences on Asian journalism; the impact of new technologies; the debates about philosophies such as 'development journalism', 'peace journalism' and 'Asian values'; and the influence of the so-called 'envelope culture' or practices of gift-giving and bribery that pervade journalism in some countries. To illustrate how these principles affect journalists' practice, the chapter presents a comparison of the starkly contrasting situations in India versus North Korea (Democratic People's Republic of Korea). The chapter also describes issues affecting countries as far afield as China to Kazakhstan, including a short case study of journalism during the so-called Saffron Revolution in Burma in 2007. The chapter concludes with suggestions about how training and aid for the Asian should be contextualized to take into account the specific cultural, economic and political factors that shape and limit the media’s performance, and how journalists might be best placed to negotiate around them. Such training needs to be sensitive to valid variations in perceptions of what kind of governance and journalism best serves development, without serving politically motivated rhetoric.