Organic thin-film transistors for organic light-emitting flat-paneldisplay backplanes

The performance of organic thin-film transistors (OTFTs) has improved significantly in the last several years and it now appears likely that they will find application in low-cost large-area electronic applications. Active-matrix displays are of special interest and integration of OTFTs with organic light-emitting devices (OLEDs) in all-organic displays is particularly attractive. The device requirements for active-matrix OLED displays are very similar to those of active-matrix liquid crystal displays (AMLCDs) and can be satisfied with OTFTs fabricated using stacked pentacene active layers. Such devices have demonstrated field-effect mobility near 1.5 cm²/V·s, on/off current ratio near 10⁸, near-zero threshold voltage, and subthreshold slope less than 1.6 V/decade. These characteristics are similar to those obtained with hydrogenated amorphous silicon (a-Si:H) devices and such devices would allow the use of polymeric substrates with advantages in weight, ruggedness, and cost compared to glass substrates currently used with a-Si:H devices in AMLCDs     

Flexible OLED displays using plastic substrates

Organic light-emitting diodes (OLEDs) displays using plastic substrate have many attractive features. They are ultrathin and light, in addition, it will be realized the flexible display to utilize the flexibility of the substrate. The key issue in achieving such displays is how to protect OLEDs from moisture and oxygen. We developed a barrier film on a plastic substrate and a passivation film on the OLED device itself. As a result, the device showed good emission characteristics after storage, and its characteristics were almost the same as those of a device fabricated on a glass substrate. We also developed a 3-in full-color flexible OLED display.     

The bright future of organic LEDs

Electro-luminescence is light emission from a solid through which an electric current is passed. Electro-luminescence from organic compounds was discovered in the early '60s, but the subject did not receive much attention until the discovery and development of conductive polymers. Compared to other electro-luminescent technologies (such as inorganic compound semiconductors, porous silicon and liquid crystals), polymer/organic light-emitting diodes (PLEDs/OLEDs) are very attractive. The reasons are their very low operating voltage, high brightness and their tunability to produce the three fundamental colors (red, blue and green). Furthermore, they are lightweight and can be grown on flexible substrates. They are fairly easy and inexpensive to fabricate. Today, PLEDs/OLEDs are suitable for applications such as automotive displays. In the future, they will probably conquer a large portion of the micro display market. Their higher efficiency and lower weight will make them quite competitive with LCD displays, the currently favorite technology. The article concludes that the future of organic light-emitting diodes seems very bright indeed.     

一种新型中空纤维膜的油气渗透特性

油气渗透是变压器油中溶解气体在线监测的技术关键。由于高分子膜的油气渗透装置结构简单、分离效果良好,所以具有很好的应用前景。笔者结合高分子膜的渗透机理,采用高分子膜材料,研制了一种中空纤维膜(毛细管),试验室搭建了由油气渗透装置等组成的油气渗透试验平台,在不同油温下对中空纤维膜进行油气渗透试验,对中空纤维膜的渗透性能以及渗透率随温度的变化规律进行研究,分析了膜厚对渗透性能的影响。理论及试验结果为进一步完善变压器油中溶解气体在线监测系统提供了技术支撑。     

Realization of polymeric optical integrated devices utilizing organic light-emitting diodes and photodetectors fabricated on a polymeric waveguide

Direct fabrication of organic light-emitting diodes (OLEDs) and organic photodetectors (OPDs) on polymeric substrates, i.e., polymeric waveguide substrates to form flexile optical integrated devices is demonstrated. The OELD and OPD were fabricated by organic molecular beam deposition (OMBD) technique on a polymeric or a glass substrate, for comparison. The device fabricated on a polymeric substrate shows similar device characteristics to that on a glass substrate. Optical signals of faster than 100 MHz have been created by applying pulsed voltage directly to the OLED utilizing diamine derivative, or rubrene or porphine doped in 8-hydoxyquinolinum aluminum derivatives, as an emissive layer. Electrical signals are successively converted to optical signals for optical transmission of moving picture signals with OLED fabricated on a polymeric waveguide. OPDs utilizing phthalocyanines derivatives with superlattice structure provide increased pulse response with input optical signals, and the OPD with the cutoff frequency of more than 5 MHz has been realized.     

The effect of barriers on electrical tree propagation in composite insulation materials

The propagation of electrical trees is of a particular interest for the power engineering industry as it is one of the major causes for breakdown in high voltage equipments. Composites, materials with barriers and a surrounding polymer matrix are used to extend time to breakdown of the insulations. Since the material, structure or processing of the barriers are various and can determine time to breakdown significantly, the major influences of barriers on the propagation of electrical trees is described in this paper in experiments and numerical simulations. Although it was the motivation, to determine tree growth in the composite structure of mica-epoxy winding insulations, the results can also be used for other composite materials. The trees grew in needle-plane samples and their growth characteristic was optically analysed. The results show that tree propagation can be slowed down when introducing a barrier between the needle and the plane electrode and may cause significantly increased time to breakdown values. The increase depends on the barrier materials used, their thickness, the dielectric strength of the interface to the surrounding epoxy resin and the width of the barrier. When choosing multiple barriers, their arrangement influences time to breakdown significantly. Overlapped barriers show much higher time to breakdown values than impinged ones. From the results, it can be concluded that the selection of the barrier materials, their processing and their arrangement play a major role towards time to breakdown of composite insulation materials.     

Organic polymer thin-film transistor photosensors

We present our study of the effects of monochromatic illumination on the electrical performance of organic polymer thin-film transistors (OP-TFTs) and the use of these devices as photosensors. In the case of monochromatic illumination that is strongly absorbed by the polymer, the drain current of a device biased in the OFF-state is significantly increased and the threshold voltage is reduced. Light that is not strongly absorbed by the polymer has little effect on the electrical performance of the OP-TFTs. We explain these effects in terms of the photogeneration of excitons in the polymer channel region of the device. The density of excitons generated in the polymer depends on the energy of the incident photons, as well as on the irradiance level of the incident illumination. The photogenerated excitons subsequently dissociate into electrons and holes. The electrons can be trapped by positively charged states, thereby reducing the threshold voltage, while the photogenerated holes contribute to the excess photocurrent measured at the drain. To demonstrate the possible use of OP-TFTs as photosensors, we also present the responsivity, photosensitivity (signal-to-noise ratio), external quantum efficiency, noise-equivalent power, and specific detectivity of these devices. The dependence of these parameters on the incident photon energy and irradiance level is described.     

Assessing the relevance of barriers to energy efficiency implementation in the building and transport sectors in eight European countries

The paper maps and evaluates the main economic, institutional, and behavioural barriers to the implementation of energy efficiency in final uses. Barriers prevent the achievement of targets of energy efficiency policies and measures. Assessing the relevance of barriers can lead to their consideration in goal-setting by policy-makers either by reducing ambition or by incorporating solutions to mitigate barriers, We consider three main categories of barriers: economic, institutional, and behavioural ones, in buildings and transport sectors. In order to assess the relevance of each specific barrier in these categories, a survey to experts in eight Countries (Bulgaria, Germany, Greece, Estonia, United Kingdom, Italy, Belgium and Serbia) has been performed. The relevance of barriers is assessed by two levels of analysis: 1. their impact on policies and measures, and 2. their impact on the diffusion of key clean technologies and interventions in the two sectors. In the building sector, we find that the most relevant barriers relate to economic and behavioural categories. In the transport sector, we find that the most relevant barriers relate to institutional and economic categories. Economic barriers are also the most relevant in limiting the diffusion of technologies and interventions in both sectors. Results highlight the relevance of identifying and assessing barriers in order to improve policy design.     

照明用白光有机电致发光器件的研究进展和发展趋势

有机电致发光器件（Organic Light－Emitting Devices,OLDS）因具有制备工艺简单、材料多样化、柔韧可弯曲、光源面发射、成本低廉和安全环保等诸多优点在显示和照明光源领域展现出诱人的应用前景。在介绍白光OLEDS的相关技术原理后,从OLED材料的角度出发,分别对照明用白光OLEDS中的低工作电压技术、磷光OLED技术和多光子发光技术的原理和最新研究进展进行综述,并对其未来的发展趋势做出展望。     

A new F(ast)-CMS NEGF algorithm for efficient 3D simulations of switching characteristics enhancement in constricted tunnel barrier silicon nanowire MuGFETs

In this paper, we present 3D quantum simulations based on Non-Equilibrium Green’s Function (NEGF) formalism using the Comsol Multiphysics^? software and on the implementation of a new Fast Coupled Mode-Space (FCMS) approach. The FCMS algorithm allows one to simulate transport in nanostructures presenting discontinuities, as the normal Coupled Mode-Space (CMS) algorithm does, but with the speed of a Fast Uncoupled-Mode Space (FUMS) algorithm (a faster algorithm that cannot handle discontinuities). We then use this new algorithm to explore the effect of local constrictions on the performance of nanowire MultiGate Field-Effect Transistors (MuGFETs). We show that cross-section variations in a nanowire result in the formation of energy barriers that can be used to improve the on/off current ratio and switching characteristics of transistors: (1) A small constriction resulting in a barrier of the order of a 0.1 eV can be used as an effective means to improve the subthreshold slope and minimize the on/off current ratio degradation resulting from SD tunneling in ultra scaled transistor, and (2) We also report a new variable barrier transistor (VBT) device concept that is able to achieve sub-kT/q subthreshold slope without using impact ionization or band-to-band tunneling. Intra-band tunneling through constriction barriers is used instead. The device is, therefore, fully symmetrical and can operate at very low supply voltages. A subthreshold slope as low as 56.5 mV/decade is reported at T=300 K. The VBT reported here breaks the 60 mV/dec barrier over more than five decades of subthreshold current, which is the widest current range reported so far.     

100 dpi 4-a-Si:H TFTs active-matrix organic polymer light-emitting display

In this paper, we report on 100 dpi four hydrogenated amorphous silicon thin-film transistors (4-a-Si:H TFTs) active-matrix organic polymer light-emitting display (AM-PLED). For this display, we have established the operational limitation of our 4-a-Si:H TFTs pixel electrode circuit by performing a load line analysis. Combining this result with the extracted pixel organic polymer light-emitting device (PLED) characteristics, we have found that the change of the AM-PLED pixel operating point, especially of a driving TFT, limits the operational range of AM-PLED pixel. The predicted results are compared with the measured data of 100 dpi monochromatic red light-emitting 4-a-Si:H TFTs AM-PLED. For our AM-PLED, we obtained luminance up to /spl sim/20 cd/m/sup 2/ and Commission Internationale de l'Eclairage color coordinates of (0.67, 0.33), which are calculated from the measured AM-PLED electroluminescence spectrum.     

Reliability and degradation of small molecule-based organiclight-emitting devices (OLEDs)

Studies of degradation mechanisms in small molecule-based organic light-emitting devices (OLEDs) are reviewed. A special emphasis is given to OLEDs based on tris (8-hydroxyquinoline) aluminum (AlQ₃), an emitter and electron transport material used in the majority of OLEDs emitting from the green to the red part of the spectrum. Different strategies used for increasing device stability are addressed and the models proposed to explain experimental observations related to OLED operational stability are discussed. Although none of the presently proposed models can explain all experimental observations, the largest body of experimental evidence appears to be consistent with a model based on the instability of cationic AlQ₃ species, produced by the injection of holes into the AlQ₃ electron transport and emitter layer. Other models may be of importance in explaining degradation behavior on different time scales. Models based on redistribution of space charge appear to be responsible for reversible short-term degradation, while a model based on indium migration may be important for degradation on very long time scales     

Band structure effect on the electron current oscillation in ultra-scaled GaSb Schottky MOSFET: tight-binding approach

This paper explores band structure effect on the quantum transport of a low-dimensional GaSb Schottky MOSFET (SBFET) for the implementation of III–V transistor with a low series resistance. Precise treatment of the full band structure is employed applying sp ³ d ⁵ s ^? tight-binding (TB) formalism. A remarkable distinction between the thickness dependent effective masses extracted from the TB and the bulk values imply that the quantum confinement modifies the device performance. Strong transverse confinement leads to the effective Schottky barrier height increment. Owing to the adequate enhanced Schottky barriers at low drain voltages, a double barrier gate modulated potential well is formed along the channel. The double barrier profile creates a longitudinal quantum confinement and induces drain current oscillation at low temperatures. Significant factors that may affect the current oscillation are thoroughly investigated. Current oscillation is gradually smoothed out as the gate length shrinks down in ultra scaled structure. The results in this paper are paving a way to clarify the feasibility of this device in nanoscale regime.     

Effect of surface treatment on polypropylene film-oil interactions

The results are being presented of an investigation to explore the possibility of using surface modification of biaxially oriented polypropylene (BOPP) film in the control of some polymer-oil interactions. The deposition of thin-film polymer structures by means plasma polymerization of styrene in r.f. glow discharges have been used as a method of polymer surface treatment. The change of some characteristics of polypropylene after treatment and effect of use of plasma polymer coating on polymer-oil interaction as well as on resulting dielectric properties of polymer-oil system have been investigated     

Role of policy in the development of business models for battery storage deployment: The California case study

California has been one of the early adopters of battery storage technologies within the United States. The state has used multiple policy initiatives such as deployment targets, financial incentives, and market mechanisms to facilitate such a market development. This motivates us to try to understand the various business models in the state and the minimum set of barriers that must be overcome for its successful deployment (and thereby the development of the market). In our study, the former is achieved by assessing the various projects in the state, and the latter by creating a barrier-solution framework and verifying it by identifying the role of various policies/drivers in supporting various business models within California. We find that there are predominantly three business models in California: Front-of-the-meter, Behind-the-meter, and Aggregated Behind-the-meter business models. We also find that at least one barrier from barrier categories associated with market demand and project economics along with all the barriers related to interconnection and market participation must be addressed for successful deployment of battery storage. Additionally, we recommend policymakers seeking to develop a battery storage market to start with developing Behind-the-meter market as it requires the least amount of intervention and then move to develop Front-of-the-meter market, and finally to the aggregated Behind-the-meter market.     

激光清障技术在电网中的应用现状与发展

电能是现代社会最重要的动力源,而附着于输电线路上的各类障碍,如异物、覆冰、树障等对输电线路与电网的安全稳定运行造成了巨大威胁。传统的清障方法存在各自的缺点,有的存在安全隐患,有的耗能较高,且大多需要停电处理。激光有着能量高,准直性好等优点,可用于远距离无接触地击落异物或融化覆冰,因此激光清障技术近年来受到越来越多的关注。本文总结了国内激光清障技术在电网中的应用与研究成果,阐述了目前使用激光清除覆冰、异物、树障等不同类型障碍的原理以及优缺点;介绍了常用于清障的几种激光器的特点;分析了激光波长、激光功率、光斑直径等常见参数对于清障效率的影响;总结了激光辐照可能对导线以及绝缘子等电力设备的影响。分析了光功率密度与辐照时间的安全阈值问题;展望了未来激光清障技术的几种可能的发展方向。     

Formation of ceramic thin films using electrospray in cone-jet mode

An electrostatic atomization technique has been developed to generate ultrafine spray droplets of ZrO₂ and SiC ceramic suspensions in a range of a few micrometers with a narrow size distribution. The aim of this paper is to deposit uniform thin films (from a few micrometers to a few tens of micrometers) of these ceramic materials on alloy substrates. Compared to some other thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma spray (PS), etc., the thin-film deposition process using electrostatic atomization is not only cheap but also capable of depositing a very thin multilayer with abrupt interfaces. CVD and PVD are expensive techniques. They require either a high vacuum, even an ultrahigh vacuum environment or complex gas handling system. Their deposition rate is also low. PS is normally used to grow thermal barrier coatings which usually have a thickness of a few tens to a few hundreds micrometers. Its application is limited by the quality of the coatings (high porosity, coarse and nonuniform microstructure). Preliminary results in this work have shown that, for low through-put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution, which is crucial to produce uniform thin films. It was found that the size of ceramic particles in ZrO₂ and SiC thin films is less than 10 μm. Microstructures of these thin films show very homogenous morphologies. These results indicate that ceramic thin films with high homogeneity can be deposited using electrostatic atomization. It was also observed that the morphology of the underlayer has some influence on the morphology of the top layer     

Monolayer-Mediated Patterning of Integrated Electroceramics

Integrated electroceramic thin-film devices on semiconducting or insulating substrate materials offer a wide variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electrical, electromechanical, magnetic and optical functions. Thus the ability to pattern such electroceramic thin films is a critical technology for future device realization. Patterned oxide thin-film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment i.e., a subtractive method. We review here an upset technology, a different way of patterning, by an additive approach, which allows for the selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective functionalization is achieved through microcontact printing (-CP) of self-assembled monolayers of the chemical octadecyltrichlorosilane on substrates of current technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron-scale dielectric oxide devices have been fabricated by this method, with lateral resolution as fine as 0.5 m. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)O₃ [PZT], LiNbO₃, and Ta₂O₅. A multilevel example is also given which combines selective MOCVD deposition of metal electrodes and sol-gel patterned PZT for Pt//PZT//Pt//Si(100) ferroelectric memory cells.     

High‐responsivity AlGaN–GaN multi‐quantum well UV photodetector

In this paper, we propose a set of AlGaN–GaN multi‐quantum well (MQW) photodetectors based on p‐i‐n heterostructures with 14 AlGaN–GaN MQW structures in i‐region, where GaN quantum well has 6 nm thickness and Al_xGa_1−xN barrier thickness is 3 nm. In this structure, the peak responsivity of 0.19 A/W at 246 nm is reported. In addition, we investigate effects of various parameters on responsivity, and we show that responsivity of MQW‐based photodetectors strongly depends on proper device design, that is, number of quantum wells, well thickness, barrier thickness, and mole fraction. We also show that increasing number of quantum wells, thickness of wells, and mole fraction as well as decreasing thickness of barriers, increase the responsivity. Using obtained results, we proposed optimal structure. Copyright © 2013 John Wiley & Sons, Ltd.