Poly Vinylidene Fluoride-trifluoroethylene Research Articles

Neurite extension of primary neurons on electrospun piezoelectric scaffolds

Neural tissue engineering may be a promising option for neural repair treatment, for which a well-designed scaffold is essential. Smart materials that can stimulate neurite extension and outgrowth have been investigated as potential scaffolding materials. A piezoelectric polymer polyvinylidene fluoride–trifluoroethylene (PVDF–TrFE) was used to fabricate electrospun aligned and random scaffolds having nano- or micron-sized fiber dimensions. The advantage of using a piezoelectric polymer is its intrinsic electrical properties. The piezoelectric characteristics of PVDF–TrFE scaffolds were shown to be enhanced by annealing. Dorsal root ganglion (DRG) neurons attached to all fibrous scaffolds. Neurites extended radially on random scaffolds, whereas aligned scaffolds directed neurite outgrowth for all fiber dimensions. Neurite extension was greatest on aligned, annealed PVDF–TrFE having micron-sized fiber dimensions in comparison with annealed and as-spun random PVDF–TrFE scaffolds. DRG on micron-sized aligned, as-spun and annealed PVDF–TrFE also had the lowest aspect ratio amongst all scaffolds, including non-piezoelectric PVDF and collagen-coated substrates. Findings from this study demonstrate the potential use of a piezoelectric fibrous scaffold for neural repair applications.

Intaglio Nanotemplates Based on Atomic Force Microscopy for Ferroelectric Nanodots

We demonstrate the nanointaglio process to form a nanotemplate and a series of nanoscale grooves using atomic force microscopy. Nanopores with a diameter of 20 nm were hoed on the surface of a SrTiO3 thin film epitaxially grown on a Nb-doped SrTiO3 substrate using a diamond tip. For the demonstration of the nanointaglio process, a nanotrench was formed as an intaglio with a length of approximately 150 nm and a width of approximately 20 nm. The nanointaglio process enables the fabrication of a nanotemplate with a highest packed hexagonal array, with a density of approximately 9.3 × 1014/m2. A ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene) (PVDF–TrFE) nanodot with a diameter of about 20 nm was formed by filling a nanopore with a PVDF–TrFE solution, whose ferroelectric properties were confirmed using piezoelectric force microscopy.

High-Resolution Studies of Domain Switching Behavior in Nanostructured Ferroelectric Polymers

We have demonstrated an effective electrical control of polarization in the individual crystalline nanomesas of the ferroelectric polymer, poly(vinylidene fluoride)-trifluoroethylene (PVDF-TrFE) and its relation to the polymer structure. The mechanism of polarization reversal has been investigated via sub-10 nm real space imaging of domain pattern evolution under an applied electric field. The domain switching behavior revealed in PVDF-TrFE nanomesas is drastically different from that observed in inorganic solid-state crystalline ferroelectrics. The nanoscale features of the switching process include remote domain nucleation and spatially nonuniform wall velocity. Local switching spectroscopy and domain dynamics studies relate the observed switching features to a random-bond type disorder associated with defects in conformation and molecular packing.

Fabrication and properties of solution processed all polymer thin‐film ferroelectric device

AbstractA ferroelectric device, making use of a flexible plastic, polyethylenterephtalate (PET), as a substrate was fabricated by all solution processes. PET was globally coated by a conducting polymer, poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) acid (PEDOT/PSSH), which is used as bottom electrode. The ferroelectric copolymer, poly(vinylidenefluoride–trifluoroethylene) (PVDF–TrFE), thin film was deposited by spin‐coating process from solution. The top electrode, polyaniline, was coated by solution process as well. The ferroelectric properties were measured on this all solution processed all polymer ferroelectric thin‐film devices. A square and symmetric hysteresis loop was observed with high‐polarization level at 15‐V drive voltage on a all polymer device with 700 Å (PVDF–TrFE) film. The relatively inexpensive conducting polyaniline electrode is functional well and therefore is a good candidate as electrode material for ferroelectric polymer thin‐film device. The remnant polarization Pr was 8.5 μC/cm2 before the fatigue. The ferroelectric degradation starts after 1 × 103 times of switching and decreases to 4.9 μC/cm2 after 1 × 105 times of switching. The pulse polarization test shows switching take places as fast as a few micro seconds to reach 90% of the saturated polarization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Photonic Heterostructures with Properties of Ferroelectrics and Light Polarizers

The optical and electro-optical properties of a new type of photonic heterostructure composed of alternating ferroelectric molecular layers and optically anisotropic layers of another material are considered. A numerical simulation of the real prototype of this heterostructure, which can be prepared by the Langmuir—Blodgett method from layers of a ferroelectric copolymer (polyvinylidene fluoride trifluoroethylene) and an azo dye with photoinduced optical anisotropy, has been performed. It is shown that this heterostructure has pronounced polarization optical properties and yields a significant change in the polarization state of light at the photonic band edges in the ranges of the maximum density of photon states. The latter property can be used to obtain an enhanced electro-optic effect at small spectral shifts of the photonic band (the latter can be provided by the piezoelectric effect in ferroelectric layers).

FABRICATION AND ELECTRICAL PROPERTIES OF Au/PVDF-TrFE/LaZrOx/Si(100) STRUCTURE

Metal-ferroelectric-insulator-semiconductor structure capacitors with a polyvinylidene fluoride trifluoroethylene (75/25) (PVDF-TrFE) ferroelectric and a lanthanum zirconium oxide ( LaZrO x) insulator layers were fabricated on a p-type Si(100) substrate in this work. The thin films were prepared using the spin-coating method. The LaZrO x thin films were crystallized at 750°C for 30 min in an O 2 ambient. Negligible hysteresis was observed from the C–V (capacitance-voltage) characteristic of the LaZrO x/ Si structure. The equivalent oxide thickness (EOT) was about 8.2 nm. Then the PVDF-TrFE film was spin-coated on the LaZrO x/ Si structure. To crystallize the PVDF-TrFE, the structure was annealed at 165°C for 30 min. The memory window width in the C–V curve of the Au/PVDF - TrFE/LaZrO x/ Si structure was about 4 V for a voltage sweep of ±5 V, and the leakage current density was about 10-8 A/cm 2 at 35 kV/cm for a 100-nm-thick film.

Demonstration of second-harmonic IVUS feasibility with focused broadband miniature transducers

Focused broadband miniature polyvinylidene fluoride-trifluoroethylene (PVDF TrFE) ultrasonic transducers were investigated for intravascular (IVUS) second-harmonic imaging. Modeling and experimental studies demonstrated that focused transducers, unlike conventional flat transducers, build up second harmonic peak pressures faster and stronger, leading to an increased SNR of second harmonic content within the coronary geometry. Experimental results demonstrated that focused second harmonic pressures could be controlled to occur at specific depths by controlling the f-number of the transducer. The experimental results were in good agreement with the modeled results. Experiments were conducted using three imaging modalities: fundamental 20 MHz (F20), second harmonic 40 MHz (H40), and fundamental 40 MHz (F40). The lateral resolutions for a 1-mm transducer (f-number 3.2) at F20, F40, and H40 were experimentally measured to be 162, 123, and 124 microm, respectively, which agreed well with the theoretical calculations with <<8% error. Lateral resolution was further characterized in the three modes, using a micromachined phantom consisting of fixed bars and spaces with widths ranging from 20 to 160 microm. H40 exhibited better lateral resolution, clearly displaying 40- and 60-microm bars with about 4 dB and 7 dB greater signal strength compared with F20. Ex vivo human aorta images were obtained in the second-harmonic imaging mode to show the feasibility of high resolution second-harmonic IVUS using focused transducers.

A wireless powered fully integrated SU-8-based implantable LC transponder

In this work, we report a SU-8-based fully integrated miniaturized inductively powered LC transponder for generic implantable wireless sensor applications. It consists of a 1 mm diameter octagonal spiral inductor and a micro fabricated MIM (metal insulator metal) capacitor. Polyvinylidene Fluoride–Trifluoroethylene (PVDF–TrFE) copolymer is applied as a dielectric material for the capacitor fabrication due to its high dielectric constant. The 1 mm diameter, 154 nH spiral inductor is built on top of the capacitor. The capacitor and the inductor are in parallel connection through SU-8 via holes. SU-8 is used as a packaging material due to its biocompatibility, and also it serves as an insulator between the capacitor and the spiral inductor. The operating frequencies of the LC tanks are decided by the sizes of the capacitors (45 × 45, 55 × 55, 95 × 95 and 100 × 100 μm), and measured operating frequency range is from 385 to 485 MHz. The fabricated LC tanks are held to the power transmitting coil coaxially at distances of 2, 5, 7 and 10 mm, and rectified induced voltage at the LC tank is 8.5 V with 29 dBm input power at a 5 mm distance.

Dual-mode operation of flexible piezoelectric polymer diaphragm for intracranial pressure measurement

The dual-mode operation of a polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) piezoelectric polymer diaphragm, in a capacitive or resonant mode, is reported as a flexible intracranial pressure (ICP) sensor. The pressure sensor using a capacitive mode exhibits a higher linearity and less power consumption than resonant mode operated pressure sensor. In contrast, the latter provides better sensitivity and easier adaption for wireless application. The metrological properties of the dual-mode ICP sensor being described are satisfactory in vitro. We propose that the piezoelectric polymer diaphragm has a promising future in intracranial pressure monitoring.

Electrical characterization of LiTaO3:P(VDF–TrFE) composites

Composites of pyroelectric ceramics and polymers are very important as their unique features and properties can be easily tailored for various specific applications. Lithium tantalatum oxide (LiTaO3, LT), the pyroelectric ceramic powder has been incorporated into a polyvinylidene fluoride–trifluoroethylene [P(VDF–TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. The composite films were prepared using ‘solvent casting’ (SC) method to disperse the ceramic powder homogeneously in the P(VDF–TrFE) copolymer matrix with various wt% of LT powder. In order to derive high pyroelectric performance, the samples were poled. Electric properties, such as the dielectric constant, dielectric loss, and pyroelectric coefficient, have been measured as a function of temperature and frequency. In addition, material figures-of-merit, very important factors for assessing many sensor applications have also been calculated. The results show that the fabricated lead free lithium tantalite: P(VDF–TrFE) composite materials have a good potential for pyroelectric infrared sensor applications.

Design and validation of the control circuits for a micro-cantilever tool for a micro-robot

The objective of this paper is to present the design and validation of a cantilever-based contact sensing system for a micro-robot. Key elements of the fabrication process of the sensor and the electrical model extraction used to design the control electronics are described. The architecture used for the sensor corresponds to a micro-cantilever fabricated of piezoelectric–polyvinylidene fluoride–trifluoroethylene stacked in a multilayer structure with the possibility of both actuating and sensing. A lumped electro mechanical equivalent model of the micro-cantilever was used to design the control electronics for the cantilever. A driving signal from, the control system is used to vibrate the cantilever at its first mechanical resonance frequency. The control system contains an analog front-end to measure the sensor output signal and a digital control unit designed to track and keep the resonance frequency of the cantilever. By integrating the cantilever control system is integrated in the application specified integrated circuit used to control of the circuit is simplyfied and very compact. Experimental results show a similar behavior between the electrical model and the fabricated system, and the deviations between the model and the measured structure are analyzed. The results also show that the designed control system is capable to detect the resonance frequency of the system and to actuate despite small deviations in process parameters of different batches of cantilevers. The whole system was designed to be integrated into an autonomous micro-robot, although it can be used in other applications.

Regulating self-organizing nanostructures via external mechanism

Self-organizing nanostructures are ubiquitous in both natural and synthetic materials. They are not only appealing scientifically, by revealing the intrinsic atomic and molecular interactions that might be difficult to detect otherwise, but may also hold the key for the development of novel functional structures and devices. For their technological potential to be fully realized, the size, morphology, and distribution of the self-organizing nanostructures must be regulated. In this paper, we investigate the principles under which the self-organizing nanostructures can be regulated via external mechanisms. Using nanomesa and nanowell formation in polyvinylidene fluoride trifluoroethylene copolymer film as an example, we demonstrate that the external mechanism, if appropriately applied, can not only change the structure stability and trigger pattern formation in the otherwise stable films where self-organizing nanostructure is impossible to form, but can also regulate the size, morphology, and distribution of self-organizing nanostructures in a very effective manner. While the analysis is carried out for a particular system, the principles should be applicable for a wide range of self-organizing materials and structures.

Effect of Thickness on Electrical Properties of PVDF-TrFE (51/49) Copolymer

In this study, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) in the composition from 51/49, was deposited on platinum for a metal-ferroelectric-metal structure. From XRD patterns, the 70 nm- and 140 nm-thick PVDF-TrFE films showed the intensity peak of near connected to a ferroelectric phase. Moreover, the thicker film indicated the higher intensity than thinner one. The difference of the remanent polarization (2Pr) at 0 V is decreased gradually from 10.19 to as the thickness decrease from 140 to 70 nm. However, when the thickness decreased to 50 nm, the 2Pr rapidly drop to so the minimum critical thickness might be at least 70 nm for device. Both different thickness films, 70 and 140 nm, indicated that the characteristic of current density-voltage was measured for below 15 V and the thicker film maintained relatively lower current density than thinner one. From these results, we can expect that the electrical properties for the devices particularly ferroelectric thin film transistor using PVDF-TrFE copolymer were able to be on the trade-off relationship between the remanent polarization with the bias voltage and the leakage current.

CHARACTERIZATION OF METAL-FERROELECTRIC-SEMICONDUCTOR STRUCTURE USING FERROELECTRIC POLYMER POLYVINYLIDENE FLUORIDE-TRIFLUOROETHYLENE (PVDF-TrFE) (51/49)

ABSTRACT In this work, we fabricated metal-ferroelectric-semiconductor (MFS) diodes with polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) (51/49) thin films for application to one transistor-type (1T-type) ferroelectric random access memories (FeRAMs). The thin films, with various thicknesses, were prepared on a silicon substrate by using a spin-coating method. The β-phase crystallinity and the grain size of the PVDF-TrFE increased as the film-thickness increased. Typical ferroelectric hysteresis loops were obtained from the capacitance-voltage (C-V) curves. These loops might be considered to be due to the ferroelectric nature of the PVDF-TrFE films. The values of the memory window width for 50-nm-, 150-nm-, and 350-nm-thick PVDF-TrFE films were about 1.4, 2.0, and 3.5 V for a bias sweeping from −5 V to 5 V, respectively. The values of the leakage current density, at a sweeping range of ± 5 V, were about 2.7 × 10−5 A/cm2, 1.1 × 10−5 A/cm2, and 5.6× 10−6 A/cm2 for 50-nm-, 150-nm-, and 350-nm-thick films, respectively. These results are useful and promising for realizing 1T-type FeRAMs operating at a low voltage.

Electro‐active polymer transduction for distributed netted sensing

The Naval Undersea Warfare Center in Newport, RI is developing an electro‐active polymer‐based sensing node for use in a persistent distributed underwater surveillance system. Persistence demands extreme energy conservation measures. The node will resemble a jellyfish in form, complete with tentacles housing a volumetric array of light‐weight piezoelectric polyvinylidene fluoride trifluoroethylene (PVDF‐TrFE) copolymer cylindrical hydrophones designed for an ultra‐low power acoustic receiver. Each cylinder has conductive silver electrodes on the inside and outside surfaces, a length of 2.5 cm, an outside diameter of 11 mm, a 1 mm wall thickness, and a mass less than 2 g. Operating in the hydrostatic mode, the hydrophone sensitivity is typically ‐195 dB//1 V/μPa and is stable with both hydrostatic pressure (50 to 1000 psi) and temperature (‐1 to 35°C). [Work supported by the Office of Naval Research.]

Flexible Dome and Bump Shape Piezoelectric Tactile Sensors Using PVDF-TrFE Copolymer

In this paper, a new mold-transfer method to pattern piezoelectric polymer has been developed and applied to fabricate innovative dome and bump shape polyvinylidene-fluoride-trifluoroethylene (PVDF-TrFE) films. The dome and bump shape PVDF-TrFE films have been successfully fabricated and characterized as a sensing component for flexible tactile sensors. The tactile sensors developed using these polymer microstructures show a high sensitivity which can measure as small as 40 mN force for bump shape sensors and 25 mN for dome shape sensors. The newly developed fabrication method provides a flexible way to pattern the piezoelectric polymer with different shapes and dimensions, including bump and dome shape piezoelectric polymer microstructures. In addition, a selective dc poling method for the PVDF-TrFE film has been developed for fabricating precisely located piezoelectric sensors with minimum crosstalk. The bump and dome shape PVDF-TrFE films developed in this paper can have numerous applications for microcatheters or other minimally invasive biomedical devices.

The influence of ferroelectric KTN particles on electric properties of 0–3 ferroelectric composites

A triphasic ferroelectric composite is obtained when ferroelectric potassium tantalate niobate particles [KTN] with a high dielectric constant and electric conductivity are embedded in a traditional 0–3 manganese and niobate modified lead zirconate titanate [PMNZT]/polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] copolymer biphasic-ferroelectric composite. The electric properties are studied for the ferroelectric composite in which the volume fraction of KTN particles is in the range 0%–24% and KTN is a passive phase. The experimental data show that the volume fraction of KTN particles strongly influence the electric properties of ferroelectric composite, and that the triphasic composite doped with KTN has higher ferroelectric, piezoelectric and pyroelectric properties than the biphasic composite with the same PMNZT volume fraction.

Characterization of polymer nanocomposite films using quartz thickness shear mode (TSM) acoustic wave sensor

Quartz thickness shear mode (TSM) resonator is adopted to characterize the viscoelastic properties of polymer nanocomposite thin films deposited on the resonators surface. The input electric admittance of multilayer loaded TSM acoustic wave resonator is first derived using transfer matrix method by taking into account the acoustic wave impedance of the polymeric layer. Nanocomposite thin films of multi-wall carbon nanotubes (MWCNTs) in copolymers of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) are deposited on TSM resonators through spin-on coating processing. The electric impedance spectra of the unloaded and loaded acoustic wave resonators are measured experimentally, and a data fitting approach is applied to extract the properties of the polymer nanocomposites films. It has been found that the thickness of the polymer layer plays a very important role in the extraction of the viscoelastic properties of the films through data fitting. Viscoelastic properties of PVDF-TrFE/CNT nanocomposite thin films with CNT concentrations of 0%, 1% and 2% have been extracted by this method. The results indicate that under the current experimental conditions, for low CNT concentrations the reinforcement of the elastic shear modulus of polymer nanocomposite films is not significant.

Memory window in ferroelectric PVDF copolymer gate integrated MOSFET devices for nondestructive readout memory application

AbstractMetal-Ferroelectric-Oxide-Si (MFEOS) field effect transistor (FET) with ferroelectric polyvinylidene fluoride trifluoroethylene copolymer (PVDF-TrFE) gate for nonvolatile memory application is demonstrated. Memory window ascribed to ferroelectric polarization switching has been quantified by shift of threshold voltage are ~ 4-5V. Non saturating IDS is due to free ionic polarization field. IDS-VDS characteristics of functional FET are realized after AC poling.

Polyvinylidene fluoride–trifluoroethylene as a reservoir for absorbed water

The absorption of water in Langmuir–Blodgett films of ferroelectric copolymers of polyvinylidene fluoride with trifluoroethylene is shown to depend upon the film thickness. This water absorption can have a profound effect on the dielectric properties of the copolymer films.