Polymer Film Thickness Research Articles

Study of certain regularities of polymeric dielectric film’s destruction under the influence of electric field at partial discharges limitation

The paper is devoted to the electrical aging, destruction and breakdown of polymer dielectric films. The necessity of partial discharges’ limitation is explained because they are the main reason of film aging from electroerossion. It is shown that the necessary condition for the breakdown of a polymer film of micron thickness under the electric field influence is the formation of a cavity with a reduced density in a homogeneous polymer material, thus a pre-breakdown phenomena develops in this cavity. Possible ways of such a cavities’ formation under the influence of strong electric field are discussed. A technically simple and reliable method for partial discharges limiting is described. It implies diminution of polymeric volume, subjected to electric field influence, and limitation of surface discharges due to film samples’ immersion in dielectric liquid. The aim of study – is the hypothesis of destructive events in film polymer dielectric reversibility’s verification. The results of an experiment, testing the hypothesis of the reversibility of changes, occurring in polymer films under the influence of an electric field under the conditions of partial discharges limitation, are considered. It is established that the action of a constant electric field on film samples, at conditions when the influence of partial discharges have been minimized, reduces the longevity of polymer in the case of the subsequent action of the field with the same polarity, but their longevity increases by the electric field’s of opposite polarity action. Possible mechanisms of conditions’ formation for the polymeric dielectrics breakdown under the action of an electric field (at conditions of partial discharges suppression) are discussed. Certain ways of increasing the efficiency and reliability of electrical devices that have polymer films as a dielectric are proposed. The further researches area is outlined.

A graphene resonator as an ultrasound detector for generalized Love waves in a polymer film with two level states

We have investigated surface shear waves at 22 MHz in a 0.5 micron thick polymer film on a SiO2/Si substrate at low temperatures using suspended and non-suspended graphene as detectors. By tracking ultrasound modes detected by oscillations of a trilayer graphene membrane both in vacuum and in helium superfluid, we assign the resonances to surface shear modes, generalized Love waves, in the resist/silicon-substrate system loaded with gold. The propagation velocity of these shear modes displays a logarithmic temperature dependence below 1 K, which is characteristic for modification of the elastic properties of a disordered solid owing to a large density of two level state systems. For the dissipation of the shear mode, we find a striking logarithmic temperature dependence, which indicates a basic relation between the speed of the surface wave propagation and the mode dissipation.

Flexible PET Substrate for High-Definition Printing of Polymer Thick-Film Conductive Pastes

Abstract A major obstacle in screen printing conductive low-temperature curing polymer thick-film (PTF) pastes onto common flexible PET substrate materials is the substantial spread of the pastes beyond the designed line width after printing. Industry observation and controlled testing have shown this spread can be as much as 80% over the circuit design's intended line width. This phenomenon prevents designers from increasing circuit density and/or reducing circuit real estate without incorporating other more involved and higher cost patterning methods. In many cases, flexible circuit fabricators, desiring more accurate high-definition circuit elements, may have to subcontract parts out of house to incorporate alternate patterning methods. This subcontracting, in turn, leads to a loss of control of both cost and lead time. This article will provide results of numerous in-house and field testings, comparing printed line width control, edge definition, and improved conductivity of printed polymer Ag conductors on different flexible PET substrates.

Unusual Thermal Conductivity of Carbon Nanosheets with Self-Emerged Graphitic Carbon Dots.

The thermal conductivity (κ) of two-dimensional conducting and transparent carbon nanosheets (CNSs) prepared by a catalyst- and transfer-free process is calculated for the first time by the optothermal Raman technique. A systematic structural analysis of CNSs reveals that the thickness of polymer films affects the interaction between molecules and a Si wafer significantly, thus helping to determine the ratio of sp2 and sp3 bonding configurations of carbon (C) atoms in the CNS. Notably, the holding time of carbonization can realize a hierarchical structure with graphitic carbon dots emerging from the CNS through the rearrangement of carbon atoms, leading to the excellent κ value of 540 W/(m·K) at 310 K. It is demonstrated that an appropriate increase in carbonization time can be an effective approach for improving the ratio of sp2- to sp3-bonded C atoms in the CNS. The thermal conductivity of the CNS with the highest ratio of sp2- to sp3-bonded C atoms exhibits superior behavior and is comparable to that of reduced graphene oxide and supported graphene, respectively. Finally, when the CNS with the highest κ value of 540 W/(m·K) was applied to a heater as the heat-dissipating material, the heater showed the temperature decrease by 14 °C compared to the case without the CNS. The catalyst- and transfer-free approach for the synthesis of CNSs is highly desirable for use as heat sink materials or substrates with heat dissipation functions for extensively integrated electronic devices.

Ultra high frequency acoustic wave propagation in fully polymer based surface acoustic wave device

Surface acoustic wave (SAW) device, which integrates the generation, propagation and detection of acoustic waves into the same device, has been known to be an essential functional unit for sensors and electromechanical systems. However, high substrate cost and process complexity of traditional inorganic SAW devices have triggered extensive research efforts to seek for alternative low cost solution, especially for disposable application. Poly(vinylidenefluoride)[P(VDF)] and its co-polymer, despite being promising materials for acoustic transducer with inexpensive processing technique, have rarely been used in SAW device due to exhibiting extremely low operating frequency (few tens of MHz) compared to the traditional SAW device (few hundreds of MHz to GHz) based on inorganic piezoelectric material. Here we demonstrate SAW device, which is entirely based on Poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)], as piezoelectric material, offering transduction and propagation of acoustic waves with a frequency around 450 MHz. The drawbacks of the previous attempts by the others are addressed and rectified systematically to obtain high operating frequency comparable to the traditional SAW. The influence of periodicity of interdigitated transducer and thickness of polymer film on device performance is thoroughly investigated. Temperature dependent variation of resonance frequency, which can be exploited as temperature sensor in integrated systems, is also demonstrated.

Efficient Thick-Film Polymer Solar Cells with Enhanced Fill Factors via Increased Fullerene Loading.

Developing effective methods to make efficient bulk-heterojunction polymer solar cells at roll-to-roll relevant active layer thickness is of significant importance. We investigate the effect of fullerene content in polymer:fullerene blends on the fill factor (FF) and on the performance of thick-film solar cells for four different donor polymers PTB7-Th, PDPP-TPT, BDT-FBT-2T, and poly[5,5′-bis(2-butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT). At a few hundreds of nanometers thickness, increased FFs are observed in all cases and improved overall device performances are obtained except for PDCBT upon increasing fullerene content in blend films. This fullerene content effect was studied in more detail by electrical and morphological characterization. The results suggest enhanced electron mobility and suppressed bimolecular recombination upon increasing fullerene content in thick polymer:fullerene blend films, which are the result of larger fullerene aggregates and improved interconnectivity of the fullerene phases that provide continuous percolating pathways for electron transport in thick films. These findings are important because an effective and straightforward method that enables fabricating efficient thick-film polymer solar cells is desirable for large-scale manufacturing via roll-to-roll processing and for multijunction devices.

Applicability of Different Bio-based Polymers for Wiring Boards

The paper gives a review of experiments for the application of biodegradable, sustainable polymers as a wiring board material. In the paper two different biobased materials and the standard PCB materials FR4 and FR2 were compared. The investigations refer to mechanical, electrical performance, surface quality the flammability and applicability for Polymer Thick Film Technology (PTFT) of the biobased material. The biobased materials are polylactic acid (PLA) mixed with different contents of cellulose acetate (CA) or flame retardant zinc pyrophosphate (ZnPP) and polyurethane (PU) with CA. The results show that the addition of CA to the polymers leads to a change of different properties for PLA and to a significant change in mechanical properties for PU. The use of ZnPP in PLA shows major improvements regarding the flammability of the polymer. The properties of the samples are in the same order of magnitude as the properties of FR2.

The incorporation and controlled release of dopamine from a sulfonated β–cyclodextrin–doped conducting polymer

Pyrrole was electropolymerised in the presence of sulfonated β–cyclodextrin to give a conducting polypyrrole film doped with the anionic cyclodextrin, PPy–sβ–CD. On reduction of the polymer film at −0.80 V vs SCE, high concentrations of dopamine (DA) were incorporated and the DA was subsequently released at a potential of 0.10 V vs SCE. Much higher levels of DA were incorporated and released at PPy–sβ–CD compared to polypyrrole films doped with smaller anions and doped with the larger para–toluene sulfonic acid. In addition to releasing higher concentrations of DA, the DA was less prone to oxidation and degradation in the presence of the sulfonated β–cyclodextrin. This was attributed to the formation of an inclusion complex between the protonated DA molecule and the anionic CD. The higher release rates were explained in terms of the immobile nature of the large CD and the high charge density with approximately 9 sulfonated groups attached to the rim of the CD cavity, which facilitated the uptake of high levels of DA. Approximately 6.0 μmol cm−2 of DA was released at 0.10 V vs SCE over 60 min on reducing the PPy–sβ–CD film for 30 min at −0.80 V vs SCE. Higher levels of 9.6 μmol cm−2 were obtained on increasing the reduction period to 60 min, while levels of 14.0 μmol cm−2 were achieved with thicker polymer films.

PLASMA PARAMETERS, DENSITIES OF ACTIVE SPECIES AND ETCHING KINETICS IN C4F8+Ar GAS MIXTURE

In this work, we performed the combined (experimental and model-based) study of gas-phase plasma characteristics and etching kinetics for both Si and SiO2 in the C4F8 + Ar gas mixture. The experiments were carried out at constant total gas pressure (p = 6 mTorr), input power (W = 900 W) and bias power (Wdc = 200 W) while the C4F8/Ar mixing ratio was varied in the range of 0–75% Ar. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained by both Langmuir probe diagnostics and 0-dimensional plasma modeling. The etching mechanisms were investigated through the analysis of relationships between the measured etching rates and the model-predicted fluxes of active species (F atoms, polymerizing CFx radicals and positive ions). It was found that, under the given set of experimental conditions, the Si and SiO2 etching process 1) appears in the steady-state etching regime; 2) exhibits the features of the ion-assisted chemical reactions in the neutral-flux-limited mode; and 3) is influenced by the fluorocarbon polymer film thickness. It was shown that the influence of input process parameters on the effective probability of chemical reaction between Si, SiO2 and fluorine atoms may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

Photo-Seebeck Effects in Doped P3HT Composites

ABSTRACTAs the global energy and environmental preservation needs continue to grow, the demand for renewable and clean energy conversion materials and devices continues to rise as well. Thermoelectric (TE) materials and devices can convert waste heat into electricity and therefore it can be a potential renewable and clean energy source. Organic and polymeric materials typically exhibit low electrical conductivities, high Seebeck coefficients, and orders of magnitude lower thermal conductivities as compared to their inorganic counterparts. However, the electrical conductivities of organic/polymeric materials are tunable via doping or molecular engineering. In this study, a series of carefully doped P3HT composites are systematically evaluated for heat as well as light modulated devices. Along with a high absorption coefficient, when the polymer film thickness is less than the penetration depth of the incoming photons, the photo effects are significant and could be very useful for light modulations of thermoelectric functions. With further systematic studies and a better understanding of the mechanisms behind the photo-Seebeck effect, the development of potential high-efficiency multi-function materials and devices appears feasible.

Accurate determination of the layer thickness of a multilayer polymer film by non-invasive multivariate confocal Raman microscopy.

Plastic films of multiple layers are widely used in packaging. While a detailed spatially resolving analysis is highly relevant, the currently used approaches are either tedious or lack spatial resolution. An advanced method of confocal Raman microscopy was therefore developed in this work, using a water immersion objective combined with multivariate data analysis and ray tracing models for analysing a commercial-grade five-layer plastic film. The water immersion objective and ray tracing models are able to reduce the refraction induced artefacts in depth profiling and ensure a correct and accurate interpretation of each layer thickness. The multivariate data analysis can distinguish each layer without prior knowledge of the sample and unique markers of each composition. Finally, the resulting thicknesses of the film layers could be successfully compared to complementary experimental results. In conclusion, each layer thickness of a multilayer polymer film and its chemical composition could be measured accurately and non-invasively without sample preparation.

Evaluation of the optical properties for thick films of epoxy-diamond paste blend prepared by the casting method

Abstract Diamond paste is used in many various fields due to its distinctive and unique optical properties. In this study, the diamond paste content at different concentrations (0.15, 0.35, 0.55 and 0.75 wt. %) with epoxy resins was used to fabricate the polymer blend. Thick films were prepared of polymer blend by casting method; deposit them on thin plastic substrates. The effects of polymeric blends were studied carefully investigated on the optical properties of the blends through a variation in the concentration of additions of diamond paste. The thick films study results revealed that additive of diamond paste led to a structure improvement of the polymer blend and then improve optical properties. The optical properties of the blends were characterized by a clear effect of the additions on the absorption coefficient of the polymer blends. The optimal value for diamond paste content concentration that maximize the absorption coefficient were x = 0.55 where the absorption coefficient was at this content (4.2 × 106 cm-1). Also, it has been observed direct transport allowed occurred in thick polymer films and the permissible direct energy gap was 3.1ev - 3.7ev, respectively.

Highlighting spin selectivity properties of chiral electrode surfaces from redox potential modulation of an achiral probe under an applied magnetic field.

Impressive spin-related effects are observed in cyclic voltammetry (CV) experiments performed under an applied magnetic field on a non-ferromagnetic electrode modified with a thin electroactive oligothiophene film, either "inherently chiral" or featuring chiral pendants with stereogenic centres. When flipping the magnet's north/south orientation, the CV peaks of two achiral, chemically reversible Fe(iii)/Fe(ii) redox couples in aqueous or organic solution undergo impressive potential shifts (up to nearly 0.5 V depending on protocol conditions), specularly by changing the film's (R)- or (S)-configuration. The magnitude of the potential shift decreases upon increasing both the polymer film thickness and the distance between the permanent magnet and the electrode surface. Such unprecedented spin-related redox potential modulation, obtained in the absence of a magnetic electrode acting as a spin injector, provides striking evidence (as well as an attractive evaluation criterion) of the spin selectivity properties of chiral thin films.

Studies on the Thermal Variations of Resistance of PVC-Graphite Thick Film Resistors

Abstract The percentage variations of resistance of polymer thick film resistors i.e. PVC-graphite thick film resistors has been studied. Four different compositions of PVC-graphite are used in the preparation of polymer thick film resistors. Among the four different PVC-graphite compositions 90% graphite: 10% PVC thick film resistors shows the least variation with temperature changes. This can be attributed to the high composition of graphite content. The variation will be lowered down with an increase in the loading fraction of graphite in polymer thick film resistors. The percentage variations of resistance of polymer thick film resistors, after stored 70°C for 1000hours, or after 25 cycle thermal shock tests as well as the variations after the short term over load tests have also been measured and studied. The variations are still smaller in 90%graphite: 10% PVC polymer thick film resistors. A possible explanation on this smaller variation in 90% graphite: 10 % PVC polymer thick film resistors is also presented.

Magnetic Force Microscopy of in a Polymer Matrix Embedded Single Magnetic Nanoparticles

Embedding superparamagnetic iron oxide nanoparticles (SPIONs) in functional thin films is of high interest for nanocomposites as well as for biomedical applications. However, there is still the need for high‐resolution mapping of the hidden nanoparticles. Magnetic force microscopy (MFM) has proved to be a suitable technique to image SPIONs at ambient conditions and provide information about spatial distribution, size, and magnetic behavior in a single pass. This work reports on high‐resolution mapping of magnetite nanoparticles of various sizes embedded in polymer films of various thicknesses. A quantification of the magnetic signals is used to determine the size of the magnetic core of the embedded nanoparticles.

Experimental Test of the Cooperative Free Volume Rate Model under 1D Confinement: The Interplay of Free Volume, Temperature, and Polymer Film Thickness in Driving Segmental Mobility.

We show that the Cooperative Free Volume (CFV) rate model, successful at modeling pressure-dependent dynamics, can be employed to describe the temperature and thickness dependence of the segmental time of polymers confined in thin films (1D confinement). The CFV model is based on an activation free energy that increases with the number of cooperating segments, which is determined by the system's free volume. Here, we apply the CFV model to new experimental results on the segmental relaxation of 1D confined poly(4-chlorostyrene), P4ClS, and find remarkable agreement over the whole temperature and thickness ranges investigated. This work further validates the robustness of the CFV model, which relates the effects of confinement on dynamics to pressure changes in the bulk, and supports the idea that confinement effects originate from local perturbations in density.

Using the Surface Features of Plant Matter to Create All-Polymer Pseudocapacitors with High Areal Capacitance

Controlling mesoscale organization in thick films of electroactive polymers is crucial for studying and optimizing charge and ion transport in these disordered materials. Conventional approaches focus on directing long-range polymer aggregation and/or crystallization during film formation by using interfaces, flow and/or shear forces. Here, we describe an alternative method that takes advantage of naturally textured biological substrates and vapor-coating to structure thick-conjugated polymer films. Reactive vapor-coating is a technique that enables in situ synthesis of doped conjugated polymers inside a reduced-pressure reactor. Reactive vapor deposition conformally coats the surface of plant matter, such as leaves and flower petals, with conducting polymer films while leaving these living substrates undamaged. Importantly, the intricate surface features of plant matter are faultlessly reproduced in the coating, effectively creating thick, high-surface-area, electrochemically active conducting polymer electrodes on plant matter. A microstructured, 10 μm thick film of p-doped poly(3,4-ethylenedioxythiophene) on a pilea involucrata leaf acts as an all-polymer pseudocapacitor with a higher areal capacitance (142 mF/cm2) than an analogous film on a planar plastic substrate lacking microstructure (50 mF/cm2). Taken together, reactive vapor deposition and microstructured plant matter present a unique combination of processing technique and substrate than can yield a diverse library of controllably microstructured electronic polymer films.

Hydrophobic Antioxidant Polymers for Corrosion Protection of an Aluminum Alloy

We explore synthetic polymeric antioxidants as powerful inhibitors of corrosion of metals. Antioxidant copolymers were designed to have polyphenol, gallol, or catechol moieties along with hydrophobic groups brought by hexyl methacrylamide units. The polymers were deposited on aluminum alloy 2024-T3 as submicrometer thick films of individual polymers or as 10 wt % additives to epoxy-based ∼100 μm thick coatings. Thin antioxidant polymer films provided significant corrosion protection of AA2024. Unlike poly(hexyl methacrylamide), which lacked polyphenol functional units, the antioxidant polymers were compatible with standard epoxy coatings and provided exceptional protection of surfaces in extreme corrosion conditions (0.6 M NaCl solution) for over 100 days. Anticorrosion performance of antioxidant-containing coatings was characterized using scanning electron microscopy, optical microscopy, and electrochemical impedance spectroscopy (EIS) and further evaluated with the equivalent electrical circuit analysis of the EIS data. Importantly, unlike small-molecule analogues, such as tannic acid, antioxidant copolymers were not leachable from epoxy coatings into water or ethanol. Taken together, these results show that antioxidant copolymers are efficient materials for protection of metals against corrosion.

Solderable Polymer Thick-film Conductors for Low Temperature Substrates

Abstract For decades, polymer thick-film (PTF) systems have provided a low cost, non-fired option for screen-printing simple electronic circuits. The ability to apply these types of pastes on temperature sensitive substrates such as PET, polycarbonate, polyimide, and other polymers has facilitated a variety of applications, for instance membrane touch-switch keypads, buss bars for touch screens, various types of sensors, and flexible circuitry. Polymer thick-film is also one of the primary technology solutions utilized in the rapidly emerging Printed Electronic market, where flexible, durable materials are paramount to the success of these technologies. One of the largest emerging markets for polymer thick-film is wearable electronics, where engineers are designing “smart fabrics” with active circuitry for medical monitoring, performance enhancement in sports, and personal comfort. Polymer thick-film pastes include silver pastes for conductors, carbon pastes for resistive applications, silver-silver chloride fillers for glucose sensors, and dielectric pastes. The major challenge with PTF silver conductors is that they are not conducive to soldering. This hinders the ability to attach components, leads, dies, wires, or other features to the prints. As copper is solderable, one possible solution would be a copper polymer thick-film metallization; however they start oxidizing at the typical paste curing temperatures, 110 – 130°C, rendering them unsuitable for the vast majority of conductive applications. In order to meet these challenges, Heraeus has developed a new line of solderable polymer thick-film conductors based on a high-performance silver-coated copper conductive filler. These metallizations are solderable, resistant to solder leaching, and result in sheet resistivities approaching that of pure silver polymer conductors. The prints do not degrade in performance when cured at temperatures as high as 200°C. The new product line was formulated to accept different types of solders, especially traditional SAC-305, which provides a complete matched solution for designers. The new metallization opens up new applications given its ability to print polymer circuitry on a variety of substrates including aluminum, steel, FR4, Kapton, Mylar, and glass. The technology also allows for the fabrication of more complex circuitry on these types of substrates, giving circuit designers a powerful new tool in their toolbox in applications such as LED lighting, sensors, and heaters. Finally, these materials may provide a lower-cost option for solderable flexible polymer end terminations for components used in vibration sensitive applications, for instance the automotive industry. In our paper, we will present the properties of the new pastes and printed conductors. Performance testing includes surface resistivity, solderability, solder leach resistance, voiding, and adhesion on two substrates: FR4 and Kapton. Furthermore, we show that the solderable PTF conductor will provide a potential cost- savings over the current technology used on FR4 boards, stamped copper films. By replacing the stamped copper with our solderable PTF conductor, manufacturers will have the advantage of replacing a subtractive process for etching their patterns with an additive, environmentally friendly process, not only saving processing time but eliminating a large, dangerous copper waste stream. Finally, we will summarize the applications that the new technology enables.

Flexible PET Substrate for High Definition Printing of Polymer Thick Film Conductive Pastes

Abstract A major obstacle in screen printing conductive low temperature curing polymer thick film (PTF) pastes onto common flexible PET substrate materials is the substantial spread of the pastes beyond the designed line width after printing. Industry observation and controlled testing have shown this spread can be as much as 80% over the circuit design's intended line width. This phenomenon prevents designers from increasing circuit density and/or reducing circuit real estate without incorporating other, more involved and higher cost patterning methods. In many cases, flexible circuit fabricators, desiring more accurate high definition circuit elements, may have to subcontract parts out of house in order to incorporate alternate patterning methods. In-turn this subcontracting leads to a loss of control of both cost and lead time. This paper will provide results of numerous in-house and field testing, comparing printed line width control, edge definition, and improved conductivity of printed polymer Ag conductors on different flexible PET substrates.