Home About us Contact
|
Home About us Contact | ||
|
|
||
Semiconductor/dielectric Interface (dielectric + interface)
Selected AbstractsModeling Polymer Dielectric/Pentacene Interfaces: On the Role of Electrostatic Energy Disorder on Charge Carrier MobilityADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Nicolas G. Martinelli Abstract Force-field and quantum-chemical calculations are combined to model the packing of pentacene molecules at the atomic level on two polymer dielectric layers (poly(methyl methacrylate) (PMMA) versus polystyrene (PS)) widely used in field-effect transistors and to assess the impact of electrostatic interactions at the interface on the charge mobility values in the pentacene layers. The results show unambiguously that the electrostatic interactions introduce a significant energetic disorder in the pentacene layer in contact with the polymer chains; a drop in the hole mobility by a factor of 5 is predicted with PS chains while a factor of 60 is obtained for PMMA due to the presence of polar carbonyl groups. [source] Transparent and Photo-stable ZnO Thin-film Transistors to Drive an Active Matrix Organic-Light- Emitting-Diode Display PanelADVANCED MATERIALS, Issue 6 2009Sang-Hee K. Park Transparent ZnO thin-film transistors (TFTs) with a defect-controlled channel and channel/dielectric interface maintain good photo-stability during device operation. The figure shows a cross-sectional view of a top-gate ZnO-based transparent TFT/storage capacitor cell structure, connected to front-panel organic-light-emitting-diode pixels to operate in bottom emission mode. [source] Monitoring the Channel Formation in Organic Field-Effect Transistors via Photoinduced Charge TransferADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Thokchom Birendra Singh Abstract Conducting channel formation in organic field-effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C60 as a semiconductor and divinyltetramethyldisiloxane-bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc-phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C60. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated. [source] Intragranular Voids and dc Degradation in (CaO+MgO) Codoped BaTiO3 Multilayer Ceramic CapacitorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Hwan-Wen Lee The microstructure of multilayer ceramic capacitors (MLCC) based on BaTiO3 and nickel electrode, have been analyzed using the scanning and the transmission electron microscopy. In order to investigate how MgO improves MLCC against dc degradation, both CaO doped and (CaO+MgO) codoped chips, pristine as well as highly accelerated life-tested, are studied. BaTiO3 grains are characterized by both the types I and II core shell structure, which is typical of MLCC exhibiting the X7R dielectric behavior. Intragranular voids are found in BaTiO3 grains in the vicinity of the electrode,dielectric interface. Void-containing grains are more frequently observed and voids are more abundant in (CaO+MgO) codoped chips than in CaO doped ones. Higher concentration of oxygen vacanciesis induced extrinsically from both MgO codoping and Ni diffusion into BaTiO3 grains along the electrode,dielectric interface during sintering. Such oxygen vacancies have reacted with both cation vacanciesandby an inverse Schottky defect reaction and condensed to form voids. This reaction requiring cation and oxygen vacancies in the stoichiometric BaTiO3 composition of 1:1:3 has significantly decreased the randomly distributed mobile oxygen vacancies, and contributes to improve against dc degradation. [source] Electrode,Ceramic Inter-Diffusion of Ba(Ti,Zr)O3 -Based Y5V MLCCs with Ni ElectrodesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Lei Chen The Ba(Ti,Zr)O3 -based multilayer ceramic capacitors (MLCCs) with Ni electrodes, which meet the Electronic Industry Association Y5V standard (from ,30° to 85°C, at a temperature capacitance coefficient between ,82% and 22%), have been studied in view of the electrode-ceramic inter-diffusion by several microstructual techniques (scanning electron microscopy/transmission electron microscopy/high-resolution transmission electron microscopy (HRTEM)) with an energy-dispersive X-ray spectrometer (EDS). The EDS analysis shows that the elements' inter-diffusion took place along the metal,dielectric interface and the migration of Ni toward the dielectric layers dominated this process. The incorporation of Ni did not transform the crystal structure but introduced lattice distortions, which were characterized by HRTEM, X-ray diffraction, and EDS. The degree of Ni diffusion in the sample with the thinner dielectric layer was more severe. It was concluded from the results that the Ni diffusion is related to the formation of oxygen vacancies after the annealing process, which should be a noticeable factor in the degradation behavior and reliability of base metal electrode MLCCs. The factors influencing the inter-diffusion are also discussed. [source] Method of moments modelling of cylindrical microwave integrated circuits interconnectionsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 2 2004M. S. Al Salameh Abstract In this paper, a numerical technique suitable for characterizing a wide variety of interconnection configurations printed on cylindrical surfaces, is presented. The interconnection lines may have either finite or infinitesimal cross-sections. To model cylindrical interfaces, suitable space-domain integral equations are formulated to represent the potential on conductors and electric field at dielectric interfaces. The solution of the integral equations is then obtained numerically by applying the method of moments (MOM). The objective of this approach is to determine the capacitance matrix of cylindrical interconnection systems with different configurations. From the capacitance matrix, other quantities such as characteristic impedance, coupling coefficient and effective permittivity can be determined. The numerical technique described in this paper is implemented as a general computer program. Various circular cylindrical as well as elliptical cylindrical structures have been solved including microstrip lines and coplanar waveguide lines. The results obtained compare very well with other published data. Copyright © 2004 John Wiley & Sons, Ltd. [source] Time-resolved two-photon photoemission at metal,dielectric interfacesISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005Wolfram Berthold We review the influence of rare-gas layers on image-potential states at metal surfaces. Experiments on Xe, Kr, and Ar on Cu(100) and on Xe/Ru(0001) that use the technique of time-resolved two-photon photoemission are discussed. The energetic position of the electron affinity, the geometry of the adsorbate layer, and dielectric screening are the factors that influence the dynamical and energetic properties of the states. Theories on various levels are compared, including 1- and 3-dimensional models and the GW approximation of many-body theory. We also present new results on buried interface states that exist in the band gaps of both the Cu(100) substrate and a thick adsorbed Ar layer. [source] The Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Ajay Virkar Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two-dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3,cm2,V,1,s,1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport. [source] Threshold Voltage Shifts in Organic Thin-Film Transistors Due to Self-Assembled Monolayers at the Dielectric SurfaceADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Stefan K. Possanner Abstract Recently, it has been shown by several groups that the electrical characteristics of organic thin-film transistors (OTFTs) can be significantly influenced by depositing self-assembled monolayers (SAMs) at the organic semiconductor/dielectric interface. In this work, the effect of such SAMs on the transfer characteristics and especially on the threshold voltage of OTFTs is investigated by means of two-dimensional drift-diffusion simulations. The impact of the SAM is modeled either by a permanent space charge layer that can result from chemical reactions with the active material, or by a dipole layer representing an array of ordered dipolar molecules. It is demonstrated that, in both model cases, the presence of the SAM significantly changes the transfer characteristics. In particular, it gives rise to a modified, effective gate voltage Veff that results in a rigid shift of the threshold voltage, ,Vth, relative to a SAM-free OTFT. The achievable amount of threshold voltage shift, however, strongly depends on the actual role of the SAM. While for the investigated device dimensions, an organic SAM acting as a dipole layer can realistically shift the threshold voltage only by a few volts, the changes in the threshold voltage can be more than an order of magnitude larger when the SAM leads to charges at the interface. Based on the analysis of the different cases, a route to experimentally discriminate between SAM-induced space charges and interface dipoles is proposed. The developed model allows for qualitative description of the behavior of organic transistors containing reactive interfacial layers; when incorporating rechargeable carrier trap states and a carrier density-dependent mobility, even a quantitative agreement between theory and recent experiments can be achieved. [source] Monitoring the Channel Formation in Organic Field-Effect Transistors via Photoinduced Charge TransferADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Thokchom Birendra Singh Abstract Conducting channel formation in organic field-effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C60 as a semiconductor and divinyltetramethyldisiloxane-bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc-phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C60. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated. [source] Charge Transport Physics of Conjugated Polymer Field-Effect TransistorsADVANCED MATERIALS, Issue 34 2010Henning Sirringhaus Abstract Field-effect transistors based on conjugated polymers are being developed for large-area electronic applications on flexible substrates, but they also provide a very useful tool to probe the charge transport physics of these complex materials. In this review we discuss recent progress in polymer semiconductor materials, which have brought the performance and mobility of polymer devices to levels comparable to that of small-molecule organic semiconductors. These new materials have also enabled deeper insight into the charge transport physics of high-mobility polymer semiconductors gained from experiments with high charge carrier concentration and better molecular-scale understanding of the electronic structure at the semiconductor/dielectric interface. [source] | ||||||||||