Organic Dielectric Films Research Articles

Flexible Oxide Thin-Film Transistors Fabricated at Room Temperature By Introducing Polymer Dielectric and Microwave Annealing

Amorphous oxide semiconductors (AOSs) have attracted considerable attention as an active layer material for thin-film transistors (TFTs), due to their many advantages such as high field effect mobility and large area uniformity compared to amorphous Si counterparts. In particular, amorphous indium gallium zinc oxide (a-IGZO) have widely studied for high performance TFTs which require high mobility, high on/off ratio, low leakage current and room temperature fabrication. Even if, a-IGZO TFTs can be deposited at room temperature, additional thermal treatment is still required in order to obtain satisfactory electrical characteristic and stability.Organic materials can be used for dielectrics of flexible TFTs because of their flexible mechanical properties. Generally, organic dielectric films are fabricated by solution process like spin-coating. Spin coating process can be easy and cheap method, however, the quality of films is not as good as the one with vacuum process because of the residual impurities and thermal damage to the substrate during post-coating bake. Poly(chloro para-xylylene) (Parylene C) can be fabricated via pyrolysis-CVD process at room temperature, which lead to unique characteristics of pinhole-free nature. Also, electrical properties of parylene C films are quite enough to utilize as dielectric layer of TFTs. Moreover, parylene C can act as passivation layer due to their remarkable chemical resistance.In this work, microwave annealing and parylene C are adopted to IGZO TFTs to reduce overall process temperature. Microwave can selectively heat target material by conversion of electromagnetic energy to thermal energy inside of the target material. Finally, flexible IGZO TFTs were realized on PET substrate owing to low process temperature of microwave annealing and parylene C deposition.Transfer and output characteristics were measured in order to investigate the possibility of parylene C as an insulator on oxide TFTs. The device exhibit typical output characteristics with a clear pinch-off, current saturation and no current crowding. When the applied gate voltage bias was 20 V, the saturation drain current was around 230 μA at drain voltage of 20 V. From transfer curve, fully room temperature fabricated IGZO TFTs exhibit mobility, Vth, S.S and hysteresis of 12.9 cm2/Vs, 0.796 V, 0.651 V/dec and 0.62 V. Flexible IGZO TFTs were fabricated using PET substrate which shows low glass transition temperature. The device was well operated which indicate microwave annealing and parylene C deposition process is suitable for low glass transition temperature substrate. The electrical stability of the IGZO TFTs with parylene C gate dielectric under bending stress was evaluated. After bending 15,000 times, switching characteristics was still remained. Mobility and S.S were hardly deteriorated, however, Vth shows small negative shift of near -1 V. In this work, IGZO TFTs were fabricated at room temperature by introducing microwave annealing and room temperature deposited gate dielectric, parylene C. By combining microwave annealing and room temperature fabricated parylene C, the process temperature was decreased enough to utilize flexible substrate with low glass transition temperature. Fabricated flexible IGZO TFTs was shown to withstand harsh 15,000 bending test. Figure 1

Organic Dielectric Films for Flexible Transistors as Gas Sensors

Cross-linked polymer films with poly(melamine-co-formaldehyde) methylated (PMF) were investigated in order to integrate flexible organic transistor-based sensors. By blending poly(methyl methacrylate) (PMMA) with PMF, solutions showed reduced viscosity for wet processing. Thin-films from poly (4-vinylphenol) (PVP) blends with PMF featured lower RMS roughness (0.37 nm) and higher dielectric constant (k ~ 3.7 – 5.7). The presence of enhanced cross-linking at higher PMF concentrations was confirmed for both polymers from chemical resistance essays and structural characterization.

Flexible Lead‐Free Perovskite Oxide Multilayer Film Capacitor Based on (Na0.8K0.2)0.5Bi0.5TiO3/Ba0.5Sr0.5(Ti0.97Mn0.03)O3for High‐Performance Dielectric Energy Storage

AbstractFlexible thin film dielectric capacitors with high energy storage density and a fast charging–discharging rate have attracted increasing attention as the development of microelectronics progresses toward flexibility and miniaturization. In this work, an all‐inorganic thin film dielectric capacitor with a multilayer structure based on (Na0.8K0.2)0.5Bi0.5TiO3and Ba0.5Sr0.5(Ti0.97Mn0.03)O3is designed and synthesized on a mica substrate. By optimizing the periodic number (N), concomitantly enhanced breakdown strength and large polarization difference are achieved in the film withN= 6, which contributes to the large energy density (Wrec) of 91 J cm−3, high efficiency (η) of 68%, and fast discharging rate of 47.6 µs. The obtained energy density is the highest value up to now in flexible dielectric capacitors, including lead‐free and lead‐based inorganic films as well as organic dielectric films. Moreover, no obvious deterioration of the energy storage performance is observed in the wide ranges of working temperature (−50–200 °C), operating frequency (500 Hz to 30 kHz), and fatigue cycles (1–108). Besides, theWrecand η are ultra‐stable under various bending radii (R= 12–2 mm) and even after 104bending cycles atR= 4 mm, demonstrating an outstanding mechanical bending endurance. This excellent performance will allow the capacitor thrive in flexible microenergy storage systems.

All Polymer Dielectric Films for Achieving High Energy Density Film Capacitors by Blending Poly(Vinylidene Fluoride-Trifluoroethylene-Chlorofluoroethylene) with Aromatic Polythiourea

Construct dielectric films with high energy density and efficiency are the key factor to fabricate high-performance dielectric film capacitors. In this paper, an all organic composite film was constructed based on high dielectric polymer and linear dielectric polymer. After the optimized polycondensation reaction of a linear dielectric polymer aromatic polythiourea (ArPTU), the proper molecular weight ArPTU was obtained, which was introduced into poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer for a composite dielectrics. The results indicate that the addition of ArPTU molecules reduces the dielectric loss and improves the breakdown field strength of the PVDF-TrFE-CFE effectively. For the PVDF-TrFE-CFE/ArPTU (90/10) composite film, the maximum energy density about 22.06 J/cm3 at 407.57 MV/m was achieved, and high discharge efficiency about 72% was presented. This composite material can be casted on flexible substrate easily, and PVDF-TrFE-CFE/ArPTU organic composite films having high energy density, high breakdown field strength, low dielectric loss, and higher discharge efficiency are obtained. This is an unreported exploration about high energy density organic dielectric films based on PVDF-TrFE-CFE matrix and linear polymer dielectrics, and the findings of this research can provide a simple and scalable method for producing flexible high energy density materials for energy storage devices.

(Invited) Electro/Electroless Grafting of Organic Dielectric Film on Silicon Surface and Its Application on through Silicon Via

With the rapid development of electronic industry, the packaging technology requires higher density and integration, which is a great challenge for semiconductor manufacturing. In order to continue the acknowledged “Moore's law”, the three-dimensional through silicon via (TSV) packaging of stacked chips has become the focus of attention, providing fresh ideas for the industry. The preparation of insulators is one of the key technologies for TSV. However it is difficult for conventional methods to prepare SiO2 insulators with high coverage in TSV with small size and high aspect ratio. In addition, higher performance of TSV proposes a big challenge for SiO2. Organic polymers can replace SiO2 used as an insulator for TSV, because their lower dielectric constant can greatly improve the properties of TSV. Electrografting is a novel technology for polymer film preparation, which has the advantages of being simple, low cost and does not required special equipment.. In recent years, the modification of the Si surface with the electrochemical reduction of diazonium salts has become attractive because it can be performed in aqueous media, which is more acceptable for industrial applications. In the best understood reaction, a diazonium salt with an electrolyte such as tetrabutylammonium cations is reduced by an externally applied potential, typically at around −1 V versus the saturated calomel electrode. In our study, the electrografting technology is used to graft polymer film onto a Si surface, and its mechanism and the effects of pulsed voltage and composition of the solution are investigated. In the process of electrografting, 4-nitrobenzene diazonium (NBD) tetrafluoroborate is reduced by electrons provided by an electric source, forming nitrophenyl radicals. These radicals covalently bond to the Si surface to form a polynitrophenyl (PNP) primer layer, and initiate the polymerization of vinyl monomers. The radical-terminated polyvinyl chains formed in the solution and nitrophenyl radicals are then added to the aromatic rings of the primer layer to form the expected polyvinyl film. Consequently the grafted film is composed of PNP and the polymer of monomers. Furthermore, we propose an easier chemical grafting method based on the finding that diazonium salt can be spontaneously reduced at the Si surface when HF is present in the aqueous solution even without an externally applied potential., and study the influence factors of structure, morphology and component of the polymer film. This process is conducted in acidic aqueous media containing HF. From the mechanistic point of view, Si atoms at the Si surface are oxidized by HF, providing electrons for the reduction of NBD cations at the open circuit potential. The mechanism of the grafting of the polymer of monomers is the same as that of an electrografting process. The polymer films prepared by either the electrografting or chemical grafting methods have good adhesion, dielectric properties and thermal properties. Then the polymer film is applied in TSV. As far as we know, insufficient film thickness and low coverage are still serious problems for plasma-enhanced chemical vapor deposition methods. However, both electrografting and chemical grafting overcome these problems. In addition, the narrow diameter and high aspect ratio (≥1:10) are not limitations for grafting methods. Poly(methyl methacrylate) film has a coverage of 76%, while poly(acrylic acid) film has a coverage as high as 100%.

Flexible, Low-Power Thin-Film Transistors Made of Vapor-Phase Synthesized High-k, Ultrathin Polymer Gate Dielectrics.

A series of high-k, ultrathin copolymer gate dielectrics were synthesized from 2-cyanoethyl acrylate (CEA) and di(ethylene glycol) divinyl ether (DEGDVE) monomers by a free radical polymerization via a one-step, vapor-phase, initiated chemical vapor deposition (iCVD) method. The chemical composition of the copolymers was systematically optimized by tuning the input ratio of the vaporized CEA and DEGDVE monomers to achieve a high dielectric constant (k) as well as excellent dielectric strength. Interestingly, DEGDVE was nonhomopolymerizable but it was able to form a copolymer with other kinds of monomers. Utilizing this interesting property of the DEGDVE cross-linker, the dielectric constant of the copolymer film could be maximized with minimum incorporation of the cross-linker moiety. To our knowledge, this is the first report on the synthesis of a cyanide-containing polymer in the vapor phase, where a high-purity polymer film with a maximized dielectric constant was achieved. The dielectric film with the optimized composition showed a dielectric constant greater than 6 and extremely low leakage current densities (<3 × 10-8 A/cm2 in the range of ±2 MV/cm), with a thickness of only 20 nm, which is an outstanding thickness for down-scalable cyanide polymer dielectrics. With this high-k dielectric layer, organic thin-film transistors (OTFTs) and oxide TFTs were fabricated, which showed hysteresis-free transfer characteristics with an operating voltage of less than 3 V. Furthermore, the flexible OTFTs retained their low gate leakage current and ideal TFT characteristics even under 2% applied tensile strain, which makes them some of the most flexible OTFTs reported to date. We believe that these ultrathin, high-k organic dielectric films with excellent mechanical flexibility will play a crucial role in future soft electronics.

Scanning probe microscopy based electrical characterization of thin dielectric and organic semiconductor films

Scanning probe microscopy (SPM) techniques offer various characterization methods for thin organic films. However, the majority of the electrical SPM measurements is currently performed in contact mode operation and may lead to severe damage at the surface of soft organic materials. This work shows the electrical characterization of organic insulator and semiconductor films by use of two SPM techniques operating with reduced lateral forces between SPM tip and sample. The first one is intermittent-contact scanning-capacitance-microscopy (IC-SCM) which is used for the detection of the local surface capacitance. The second one is torsional resonance tunneling-atomic-force-microscopy (TR-TUNA) which shows the local conductivity respectively relative film thickness of the sample. It is found that the tunneling current distribution across 50nm thick organic insulating films is very homogeneous and that inhomogeneities in P3HT and Pentacene films can be pinpointed even if no topographical variations are observable.

Reversible Grafting of α‐Naphthylmethyl Radicals to Epitaxial Graphene

The Kolbe electrochemical oxidation strategy has been utilized to achieve an efficient quasireversible electrochemical grafting of the alpha-naphthylmethyl functional group to graphene. The method facilitates reversible bandgap engineering in graphene and preparation of electrochemically erasable organic dielectric films. The picture shows Raman D-band maps of both systems.

Experimental cartographies of mechanical deformations induced by a dc electrical field in organic insulator films

Experimental cartographies of mechanical deformations induced by a dc electrical field in organic insulator films

Measurement of full-field deformation induced by a dc electrical field in organic insulator films

Digital image correlation method (DIC) using the correlation coefficient curve-fitting for full-field surface deformation measurements of organic insulator films is investigated in this work. First the validation of the technique was undertaken. The computer-generated speckle images and the measurement of coefficient of thermal expansion (CTE) of aluminium are used to evaluate the measurement accuracy of the technique. In a second part the technique is applied to measure the mechanical deformation induced by electrical field application to organic insulators. For that Poly(ethylene naphthalene 2,6-dicarboxylate) (PEN) thin films were subjected to DC voltage stress and DIC provides the full-field induced deformations of the test films. The obtained results show that the DIC is a practical and robust tool for better comprehension of mechanical behaviour of the organic insulator films under electrical stress.

Plasma‐Polymerized Multistacked Organic Bipolar Films: A New Approach to Flexible High‐κ Dielectrics

Organic-based flexible dielectric films with high permittivity (e) are desirable for future applications of organic thin-film transistors, such as smartcards and radio frequency identification (RFID) tags, that concurrently desire flexible or conformable substrates. Advances in the development of all-polymer field-effect transistors (PFETs) have been particularly significant for their potential in a flexible form. Major improvements have been reported for both the semiconductor and the dielectric components of PFETs. For example, with respect to semiconductor considerations, noteworthy gains have been achieved in increasing carrier mobility and in identifying lower-cost production technology, however, PFET operational voltages tend to be too high for the intended portable applications. But the voltages could be significantly lowered if a suitable dielectric with a high dielectric constant (k), compatible with the PFET process and in a flexible form factor with thicknesses that is controllably thin, was identified. This Communication focuses on the organic dielectric film component of PFETs, required for all-polymer PFETs by tailoring high-k polymer films. The much-needed advances in this area pose difficult challenges in terms of materials science considerations. One such problem centers on the fact that organic films are inherently low-k; having k values significantly less than those of ceramic (inorganic) materials. Additionally, leakage currents through the film also pose potential problems given the generally porous nature of organic based polymeric films. On the other hand, organic films offer far more favorable

Electrodeposition of Water-Repellent Organic Dielectric Film as an Anti-Sticking Coating on Microelectromechanical System Devices

In this paper, we propose a technique of preventing both wet-release-related and in-use sticking of actuators in microelectromechanical system (MEMS) devices. The technique involves the electrodeposition of a water-repellent organic dielectric film that renders the microstructure surface inactive towards the water used for rinsing. The source material is a core/shell emulsion, which consists of sulfonium cations with epoxy groups containing water-repellent silicone polymers. Applying this technique to the encapsulation of a microstructure confirms its effectiveness in preventing both release-related sticking and in-use sticking of a MEMS structure.

Conformal Coating of Organic Dielectric Film on Gold Electrodes in Microelectromechanical System Devices by Electrodeposition

This paper describes a technology to prevent sticking between actuator and control electrode during microelectromechanical system device operation. The technology involves the electrodeposition of organic dielectric film on the gold electrode. The focus is on solving the problems found on gold surfaces that have passed through many fabrication-process steps, which are an incubation period and two types of anomalous growth (selectivity loss and skirt growth). Two pre-treatments and one post-treatment solve each problems, respectively. The incubation period is eliminated by dipping in hydrochloric acid as a pre-treatment, which dissolves gold oxides formed during the oxygen plasma exposure used for surface cleaning or sacrificial layer ashing. The anomalous growth is suppressed by adding a hydrofluoric acid dip as a pre-treatment to improve the selectivity and by annealing the films below the glass-transition temperature as a post-treatment to suppress large film reflow. The fabricated cantilever structure with the electrode coated using this technology exhibits a conformal coating with excellent isolation between the cantilever and the electrode.

Electrodeposition of Organic Dielectric Film and Its Application to Vibrational Microelectromechanical System Devices

In this paper, we describe the application of electrodeposition to microelectromechanical system (MEMS) devices made of gold. After the release ashing of an organic sacrificial layer by oxygen plasma exposure, the thickness of the organic dielectric film electrodeposited on gold surfaces was found to be nonuniform. A surface analysis by X-ray photoelectron spectroscopy revealed that the causes of the nonuniformity were the differences in chemical states and amounts of gold oxide that arose from oxygen plasma exposure at different places. A uniform coating was obtained by removing the gold oxide by hydrochloric acid dipping before electrodeposition on gold comb-shaped electrodes in a vibrational MEMS device. This uniform coating prevents electrical shorts and in-use sticking between the gold vibrator and electrode in the device, ensuring high durability.

High-resolution synchrotron X-ray reflectivity study of the density of plasma-treated ultra low- k films

The density changes of porous SiLK (p-SiLK) organic dielectric films were studied by X-ray reflectivity technique. Blanket films on Si were studied under different plasma etch conditions, that are conventionally used in the etch processes of interconnects. X-ray reflectivity measurements were performed using a high-resolution Huber diffractometer and monochromatic 8.048 keV photons at the Singapore Synchrotron Light Source (SSLS). The results show that un-treated (as-grown) films are of good quality in terms of surface and interface roughness. All of the plasma-treated films keep their density (within 1–3% error), whereas the surface roughness increases and layer thickness decreases accordingly. The surface roughness is severely increased by oxidation for oxygen plasma-treated samples.

Three-dimensional interconnect with excellent moisture resistance for low-cost MMICs

The moisture resistance of three-dimensional (3-D) interconnects using organic insulator films and Au metals has been investigated to ascertain the feasibility of housing monolithic-microwave integrated circuits with these interconnects in inexpensive nonhermetic packages. By comparing polyimide and benzocyclobutene (BCB) for organic insulator films, it was found that although polyimide has higher moisture absorption than BCB, it has a greater moisture resistance. This suggests that moisture absorption is not the dominant factor in moisture resistance and that BCB has higher water permeability than polyimide. As an adhesion layer between Au metal and insulator film, W and WN have better moisture resistance than WSi and WSiN; adhesion layer compositions containing Si oxidize easily. Further, the metal patterning method has an effect on moisture resistance in terms of leakage current. Reactive ion etching (RIE) with SF/sub 6/ gas is necessary in order to completely remove the metal atom residue left after ion milling with Ar gas. An interconnect using polyimide insulator film, W or WN adhesion metal, and metal patterned by ion milling and RIE, did not fail in terms of contact resistance and leakage current under stress of 85/spl deg/C and 85% relative humidity with a bias for 1000 h.

Characterization of polymeric films derived from α- and β-substituted N-vinylpyrroles

Abstract Electrochemical oxidation of N-vinyl-2-(2-thienyl)pyrrole (TP) and N-vinyl-2-(2-furyl)pyrrole (FP) in Bu4NClO4+CH3CN solutions leads to the formation of polymeric films that exhibit voltammetric doping and de-doping waves similar to those of poly(pyrrole) and poly(thiophene). The films generated from the oxidation of TP and FP are stable upon electrochemical cycling for hundreds of scans in acetonitrile media, and in their dry, doped state exhibit conductivities in the ∼10 mS cm−1 range. Organic dielectric films can be formed from the oxidation of N-vinyl-4,5,6,7-tetrahydroindole (THI) in Bu4NClO4+CH3CN solutions. Poly(THI) films prepared by scanning the potential nine times between 0 and +1.4 V vs. SSCE block the rotated-disk voltammetric response of decamethylferrocene and ferrocene by 94 and 48%, respectively. The observation that film permeabilities are dependent on redox probe molecular volume indicates that the films are not riddled with pin-hole defects. In addition, although the surface of the poly(THI) films is relatively hydrophilic, as noted by aqueous contact angle measurements, the permeability of the films toward redox probes dissolved in aqueous electrolyte is substantially lower than that found for probes in acetonitrile media.

Surface-Enhanced Raman Scattering on Uniform Transition-Metal Films: Toward a Versatile Adsorbate Vibrational Strategy for Solid-Nonvacuum Interfaces?

Procedures are outlined for the electrodeposition of ultrathin films of Pt-group transition metals onto gold that provide intense surface-enhanced Raman scattering (SERS) for adsorbates bound to the overlayers yet (unlike earlier reports) are sufficiently "pinhole-free" to avoid significant spectral and chemical interferences from the underlying substrate. Constant-current electrodeposition of Pd, Rh, Pt, and Ir from perchloric acid and/or phosphate electrolytes yields essentially layer-by-layer growth, so that near-ideal pinhole-free electrochemical and spectral characteristics are achieved for film thickness of ∼2 monolayers or more. The desired film uniformity is diagnosed from the voltammetric oxide formation-removal behavior and, especially, from the absence of the characteristic C-O stretching (ν(CO)) SERS band at 2110-2120 cm(-)(1) due to CO binding to Au surface sites. Carbon monoxide is also employed as a surface environment-sensitive adsorbate to probe the electrochemical SERS characteristics as a function of the transition-metal film thickness. The Raman enhancement was observed to decrease by 2-fold every 10-20 Å or so, exhibiting a "spacer distance" dependence that is weaker than (but functionally similar to) recently reported organic insulator films. The practical value of the present films for obtaining rich vibrational spectra for diverse adsorbates on transition metals is pointed out and briefly illustrated for benzonitrile on a Pt film electrode. The more general promise of this overlayer film SERS strategy as a versatile vibrational technique for characterizing other types of chemically important surface materials is also noted.

Diffusion in several materials relevant to Cu interconnection technology

Knowledge of copper diffusion in conducting, dielectric and diffusion barrier thin films relevant to the upcoming Cu interconnection technology is important in order to understand electromigration and prevent degradation of the active devices in Si. Copper diffusion in several thin films considered essential for substitution of Al with Cu interconnects to reduce RC delays is discussed, and the available data are compiled. Fast diffusion of Cu has been observed through inorganic and organic dielectric films, so that the conducting Cu films will require encapsulation. Diffusion of Cu through CVD-W, TiAl 3-0.5%Cu, TiCu and β-Ta diffusion barriers has also been studied in a comparative manner.

Radiation effects on organic insulator films at low temperature

The radiation effects of some organic insulator films have been studied at low temperature. The specimens used were thin films of polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyether etherketone (PEEK), and polypyromellitimide (PPMI, Kapton H). Reactor irradiations were performed at 20 K and tensile properties of the irradiated films were measured at 77 K. In the irradiated PET, the tensile strength remarkably decreased with an increase in the absorbed dose above 2 MGy and the ultimate elongation gradually reduced with increasing dose. On the other hand, no essential changes in mechanical properties were observed for both PPS and PEEK films after irradiation up to 8 MGy at 20 K. As far as the present experiments are concerned, the radiation tolerances of PPS and PEEK films have been proved to be of the same level as that of PPMI film.