High Dielectric Capacitors Research Articles

Negative permittivity at kHz regulated by length-diameter ratio of short carbon fibers in phenolic resin composites

Negative dielectric materials show bright application prospects in the electromagnetic protection, energy storage and radio transmission fields. However, high negative permittivity and expensive manufacturing costs limit their applications in above fields. Here, phenolic resin composites containing short carbon fibers (SCF) with different length-diameter ratios were prepared by mechanical mixing and dry pressing. The effects of length-diameter ratio and mass fraction of SCF on conductivity, permittivity and impedance were investigated. The AC conduction mechanism changed from jump conduction to metal-like conduction due to the increased carrier concentration resulting from improved connectivity of the 3D conductive network. In addition, a weak negative permittivity was obtained in SCF429-10/PF composite. At SCF of 20 wt%, when the length-diameter ratio increased from 114 to 429, the negative permittivity mechanism changed from Lorentz & Drude to Drude model, indicating that the plasma oscillation of delocalized electrons was the main cause of negative permittivity. The relationship between reactance and permittivity were discussed by impedance and equivalent circuit analysis. This work provided a new strategy for obtaining weak negative permittivity, which exhibited potential applications in the fields of electromagnetic protection, high dielectric capacitors, and perfect absorption.

Effect of TiO2 as Filler in NaCl: Possible Applications in Ionic Storage Systems

High dielectric capacitors are increasingly used for energy storage in sustainable nanotechnologies. Here, we observed large enhancement of dielectric constant by 3 order at frequency 1kHz with moderate loss when TiO2 is added as a filler in NaCl bulk matrix. The TiO2 nanoparticles are synthesized via sol gel process and is subsequently added in varying weight percentage x in the ionic matrix of NaCl, which is represented as TiO2(x)NaCl. The parameters like dielectric constant, dissipation Loss and ac conductivity are measured with varying fraction of TiO2 in frequency range less than 25 KHz. The steady increase of dielectric constant with increasing filler content at low frequency indicates percolation type behavior which accounts for the first dielectric peak at x= 50. The dielectric loss is found to be around 1 for x< 45 whereas it tends to increases with higher filler fraction. Moreover, the frequency dependent polarization in this composite system also accounts for hopping type behavior of mobile charge carriers contributed by TiO2 as confirmed from ac conductivity measurement. Further, the samples are characterized by X-ray diffraction and Field emission scanning electron microscopy in order to study the structure and morphology of the samples. Overall, TiO2 incorporation strongly improves the dielectric behavior of the ionic matrix at low frequency, making it suitable for super dielectric material (SDM).

Intrinsically ionic conductive cellulose nanopapers applied as all solid dielectrics for low voltage organic transistors

Biodegradability, low-voltage operation, and flexibility are important trends for the future organic electronics. High-capacitance dielectrics are essential for low-voltage organic field-effect transistors. Here we report the application of environmental-friendly cellulose nanopapers as high-capacitance dielectrics with intrinsic ionic conductivity. Different with the previously reported liquid/electrolyte-gated dielectrics, cellulose nanopapers can be applied as all-solid dielectrics without any liquid or gel. Organic field-effect transistors fabricated with cellulose nanopaper dielectrics exhibit good transistor performances under operation voltage below 2 V, and no discernible drain current change is observed when the device is under bending with radius down to 1 mm. Interesting properties of the cellulose nanopapers, such as ionic conductivity, ultra-smooth surface (~0.59 nm), high transparency (above 80%) and flexibility make them excellent candidates as high-capacitance dielectrics for flexible, transparent and low-voltage electronics.

Thickness-dependent a1/a2 domain evolution in ferroelectric PbTiO3 films

Ferroelectric a1/a2 domain structure has great potentials in high dielectric capacitors and tunable microwave devices. Understanding its structure is crucial to better control the domain configurations for future applications. In this paper, PbTiO3 thin films with variant thicknesses are deposited on (110)-oriented GdScO3 substrates by Pulsed Laser Deposition (PLD) and investigated by using conventional transmission electron microscopy (TEM) and Cs-corrected Scanning TEM. Contrast analysis and electron diffractions reveal that PbTiO3 films are domain oriented consisting of a1/a2 and a/c domain structure. The a1/a2 domains are found to distribute periodically and its width increases with increasing film thickness following square root rule. Cs-corrected STEM imaging demonstrates that the domain walls of a1/a2 domain structure have the rotation characteristic of 90° ferroelastic domain wall. The interchange of a1/a2 domains induces the formation of vertex domains composed of two 90° and one 180° domain walls. Strains are mainly concentrated on the domain walls. The formation of this complex domain configuration is discussed in terms of the effect of the misfit strain, film thickness and cooling rate. These results provide novel information about a1/a2 domain structures and are expected to shed some light on modulating a1/a2 ferroelectric domain patterns in the design of ferroelectric-based devices.

Influence of calcination temperature on sol–gel synthesized single-phase bismuth titanate for high dielectric capacitor applications

Abstract An inexpensive sol–gel combustion method using citric acid as fuel has been used to synthesize bismuth titanate, Bi4Ti3O12 nanopowders. Thermogravimetric analysis proved that a calcination temperature of 900 °C is sufficient for the preparation of single-phase bismuth titanate. X-ray diffraction and Fourier transform infrared spectroscopy are used to examine the influence of calcination temperature on the structural growth of the Bi4Ti3O12 nanopowder. The average crystallite size estimated by using the Scherrer method and the Williamson–Hall method was found to increase with calcination temperature. Photoluminescence behavior as a function of calcination temperature was observed at two different excitation wavelengths of 300 nm and 420 nm. The morphology of the particles analyzed using images obtained from field emission scanning electron microscopy displayed irregular, random sized, and spherical-shaped structures. The stoichiometry and purity of the nanopowder are confirmed by energy-dispersive spectroscopy. The broadband dielectric results established the highest dielectric constant (∊r = 450) for a frequency of 100 Hz achieved with a potential capacitance of 138 pF m−2. This establishes Bi4Ti3O12 as a promising dielectric material for achieving high energy density capacitors for the next-generation passive devices.

Three dimensional printing of high dielectric capacitor using projection based stereolithography method

We report that efficient high dielectric polymer/ceramic composite materials can be optically printed into three-dimensional (3D) capacitor by the projection based stereolithography (SLA) method. Surface decoration of Ag on Pb(Zr,Ti)O3(PZT@Ag) particles were used as filler to enhance the dielectric permittivity. Polymer nanocomposites were fabricated by incorporating PZT@Ag particles into the photocurable polymer solutions, followed by exposure to the digitally controlled optical masks to generate 3D structures. The dielectric permittivity of Flex/PZT@Ag composite reaches as high as 120 at 100Hz with 18vol% filler, which is about 30 times higher than that of pure Flex. Furthermore, the dielectric loss is as low as 0.028 at 100Hz. The results are in good agreement with the effective medium theory (EMT) model. The calculated specific capacitance of our 3D printed capacitor is about 63Fg−1 at the current density of 0.5Ag−1. Cyclic voltammetry (CV) curves indicate 3D printed capacitors possess low resistance and ideal capacitive properties. These results not only provide a tool to fabricate capacitor with complex shapes but lay the groundwork for creating highly efficient polymer-based composites via 3D printing method for electronic applications.

Polymer/metal oxide hybrid dielectrics for low voltage field-effect transistors with solution-processed, high-mobility semiconductors

Transistors for future flexible organic light-emitting diode (OLED) display backplanes should operate at low voltages and be able to sustain high currents over long times without degradation. Hence, high capacitance dielectrics with low surface trap densities are required that are compatible with solution-processable high-mobility semiconductors. Here, we combine poly(methyl methacrylate) (PMMA) and atomic layer deposition hafnium oxide (HfOx) into a bilayer hybrid dielectric for field-effect transistors with a donor-acceptor polymer (DPPT-TT) or single-walled carbon nanotubes (SWNTs) as the semiconductor and demonstrate substantially improved device performances for both. The ultra-thin PMMA layer ensures a low density of trap states at the semiconductor-dielectric interface while the metal oxide layer provides high capacitance, low gate leakage and superior barrier properties. Transistors with these thin (≤70 nm), high capacitance (100–300 nF/cm2) hybrid dielectrics enable low operating voltages (&amp;lt;5 V), balanced charge carrier mobilities and low threshold voltages. Moreover, the hybrid layers substantially improve the bias stress stability of the transistors compared to those with pure PMMA and HfOx dielectrics.

Silicon-based Multi-nanowire Biosensor with High-k Dielectric and Stacked Oxide Sensing Membrane for Cardiac Troponin I Detection

In order to diagnose acute myocardial infraction (AMI) quickly by detection of cTnI, silicon nanowire (Si-NW) transistor is chosen to be the bio-sensor. We demonstrate Si-NW biosensors coated with different dielectric materials to detect cTnI. Based on the experimental results of 14nm SiO2 and 28nm SiO2, it is found that high capacitance dielectrics contribute better sensitivity than that of low capacitance dielectrics. In addition, high-k material dielectrics stacked with ultrathin SiO2 sensing membrane structures are used for Al2O3 and HfO2 because SiO2 has better compatibility with 3-Aminopropyltriethoxysilane (APTES). The results show that high-k stacked structure improve the sensitivity. Based on this work, the proposed Si-NW biosensor structure is experimentally demonstrates a good potential for future applications in cTnI detections.

π-Conjugated Zwitterions as Paradigm of Donor–Acceptor Building Blocks in Organic-Based Materials

The very peculiar characteristics of zwitterions, as well as a clearand unambiguous definition, have been overlooked in past literature. However, these compounds are particularly important in view of the impact they have had in the recent past and will likely continue to have in the future as components of performing functional organic and hybrid materials. In this Account, we primarily aim to define critically important organic concepts of zwitterions regarding both their design and nomenclature. We will particularly focus on a specific kind of zwitterions we define as π-conjugated zwitterions. These types of zwitterions are systems pertaining to the class ofdonor-acceptor (push-pull) molecules. In the ground state, they are preferentially represented in terms of an electron donor moiety bearing a negative net charge, and electron acceptor one bearing a positive net charge connected by a conjugated bridge. As such, they are possibly the most effective example of push-pull structure, possessing relevant features for applications like nonlinear optics, photovoltaics, imaging, and high capacitance dielectrics. In addition, the interaction between these dipolar compounds and the environment is highly specific and can be exploited in the construction of well-organized nanostructures, both in solution and in the solid state. According to the Gold Book of IUPAC for nomenclature, the distinction between zwitterions and the charged molecule called a betaine is subtle. The betaine is a particular class of zwitterion possessing an onium atom not bearing a hydrogen. The two terms are often considered equivalent, thus generating confusion while retrieving literature. In this Account, we define and describe π-conjugated zwitterions systems that are dipolar in the ground state, admitting resonance limiting structures that are neutral and chargeless. For the purpose of this Account and to the benefit of researchers striving to retrieve materials-related zwitterion literature data, we suggest to use the term π-zwitterions instead of the commonly used plain term "zwitterions". We show that this definition enables the clear identification of a class of compounds having unique properties distinct from "dipolar conjugated compounds." We describe the most common donor and acceptor groups in π-zwitterions. In particular, we focus our attention on the special case of the nitrile functionality, which tends to be contiguous to a negative charge. We also address special emphasis to benzenoid components that are substituted by heteroaromatic units in π-zwitterions, because the HOMO-LUMO energetic consequences are specifically involved in these cases. We make reference to the paradigmatic case of π-zwitterions second order nonlinear optical properties. Here, the value of the first hyperpolarizability β versus the alternation in bond length turns out to be a measure of the balance of the chargeless and the dipolar contribution to the description of the zwitterion ground state. We also report literature data, collected both from our group and others, concerning π-zwitterions containing heteroaromatic and/or nitrile groups, those based on the most performing acceptors so far described, and merocyanines. With particular reference to merocyanines, we show how π-zwitterions can play a fundamental role in the fast growing field of organic photovoltaics. Finally, we present π-zwitterions made up of heteroaromatic groups that open new scenarios in heteroaromatic chemistry.

Cellulose‐Based Ionogels for Paper Electronics

A new class of biofriendly ionogels produced by gelation of microcellulose thin films with tailored 1‐ethyl‐3‐methylimidazolium methylphosphonate ionic liquids are demonstrated. The cellulose ionogels show promising properties for application in flexible electronics, such as transparency, flexibility, transferability, and high specific capacitances of 5 to 15 μF cm−2. They can be laminated onto any substrate such as multilayer‐coated paper and act as high capacitance dielectrics for inorganic (spray‐coated ZnO and colloidal ZnO nanorods) and organic (poly[3‐hexylthiophene], P3HT) electrolyte‐gated field‐effect transistors (FETs), that operate at very low voltages (&lt;2 V). Field‐effect mobilities in ionogel‐gated spray‐coated ZnO FETs reach 75 cm2 V−1 s−1 and a typical increase of mobility with decreasing specific capacitance of the ionogel is observed. Solution‐processed, colloidal ZnO nanorods and laminated cellulose ionogels enable the fabrication of the first electrolyte‐gated, flexible circuits on paper, which operate at bending radii down to 1.1 mm.

Ferroelectric-based nanocomposites: fabrication and characteristic properties

Ferroelectric ceramics are widely used in a variety of applications, ranging from high dielectric capacitors, mechanical actuators, micro–transducers to memory devices. Here we present chemical and physical processes to obtain nanocomposites based on ferroelectric perovskites, from metal–oxide to dual–phase oxide materials. The changes in the structural, dielectric and magnetic properties are studied. Interesting observations such as the percolation effect and anomaly in temperature dependence of magnetisation are also mentioned. The results are discussed in view of effects of the spatial distribution of each phase, the stress–induced structural phase transition and the ferroelectric–magnetic coupling. Additionally, recent results on epitaxial growth of PZT film on Si are presented.

Printed, Sub-3V Digital Circuits on Plastic from Aqueous Carbon Nanotube Inks

Printing electronic components on plastic foils with functional liquid inks is an attractive approach for achieving flexible and low-cost circuitry for applications such as bendable displays and large-area sensors. The challenges for printed electronics, however, include characteristically slow switching frequencies and associated high supply voltages, which together impede widespread application. Combining printable high-capacitance dielectrics with printable high-mobility semiconductors could potentially solve these problems. Here we demonstrate fast, flexible digital circuits based on semiconducting carbon nanotube (CNT) networks and high-capacitance ion gel gate dielectrics, which were patterned by jet printing of liquid inks. Ion gel-gated CNT thin-film transistors (TFTs) with 50 microm channel lengths display ambipolar transport with electron and hole mobilities >20 cm(2)/V.s; these devices form the basis of printed inverters, NAND gates, and ring oscillators on both polyimide and SiO(2) substrates. Five-stage ring oscillators achieve frequencies >2 kHz at supply voltages of 2.5 V, corresponding to stage delay times of 50 micros. This performance represents a substantial improvement for printed circuitry fabricated from functional liquid inks.

Transfer Technology of Ferroelectric Films onto the Polymer Substrate for the Application of High Density Capacitor

High dielectric capacitors , that has around 1000 in dielectric constant, can be successfully formed by nanotransfer on non-heat-resisting substrates. PZT film could be released from the Si substrate and bonded onto the polymer one. The releasing characteristics have the relationships with the thickness of Pt layer. The formed PZT has perovskite structure and clear columnar texture.

P-MNS-07 NANOTRANSFER METHOD FOR THE FERROELECTRIC FILMS ONTO THE POLYMER SUBSTRATE(Micro/Nanosystem Science and Technology,Technical Program of Poster Session)

High dielectric capacitor, that has around 1000 in dielectric constant, can be successfully formed by nanotransfer on non-heat-resisting substrates. PZT film could be released from the Si substrate and bonded onto the polymer one. The releasing characteristics have the relationships with the thickness of Pt layer. The formed PZT has perovskite structure and clear columnar texture.

Implications of advanced capacitor dielectrics for performance of metallized film capacitor windings

A range of high dielectric capacitor films is under development with the objective of improving the energy density of pulsed discharge capacitors. A substantial change in capacitor film dielectric constant has implications for capacitor design and function. This paper develops formulas for equivalent series resistance (ESR) and equivalent series inductance (ESL) of a cylindrical capacitor winding as a function of material properties and winding design. A numerical approach is used to investigate the frequency-dependent ESR and ESL, after which formulas are developed for winding inductance based on a resistive current distribution in the winding. Analyses are carried out for a cylindrical metallized film winding in which the return conductor is brought either through the center of the core on which the film is wound or coaxially up the outside of the winding, so that both connections are made from the same end of the capacitor with minimal inductance. The implications of moving to high dielectric constant film are investigated on the basis of this analysis.

Printable ion-gel gate dielectrics for low-voltage polymer thin-film transistors on plastic

An important strategy for realizing flexible electronics is to use solution-processable materials that can be directly printed and integrated into high-performance electronic components on plastic. Although examples of functional inks based on metallic, semiconducting and insulating materials have been developed, enhanced printability and performance is still a challenge. Printable high-capacitance dielectrics that serve as gate insulators in organic thin-film transistors are a particular priority. Solid polymer electrolytes (a salt dissolved in a polymer matrix) have been investigated for this purpose, but they suffer from slow polarization response, limiting transistor speed to less than 100 Hz. Here, we demonstrate that an emerging class of polymer electrolytes known as ion gels can serve as printable, high-capacitance gate insulators in organic thin-film transistors. The specific capacitance exceeds that of conventional ceramic or polymeric gate dielectrics, enabling transistor operation at low voltages with kilohertz switching frequencies.

Low temperature metal-organic chemical vapor deposition of Ru thin films as electrode for high dielectric capacitors

Low temperature metal-organic chemical vapor deposition (MOCVD) process of Ru films for use as electrode material was studied using a noble dome type reactor, liquid delivery technique and a new precursor. The films were grown at temperatures ranging from 275°C to 480°C in which film growth was controlled by a surface chemical reaction with a small activation energy of 0.21 eV. The root-mean-squared surface roughness was as low as 23 Å for a film grown at 290°C on a SiO2 surface.

Investigation of the Electrical Properties of Tantalum‐Ruthenium Dioxide as a Diffusion Barrier for High Dielectric Capacitors

The effects of addition on the electrical properties of a diffusion barrier for capacitor bottom electrodes were investigated as a function of the composition ratio of and contact size, at a temperature range of 650–800°C in air. When the Ta film was deposited without addition, it exhibited a higher total resistance and a nonohmic behavior with increasing annealing temperature, originating from the formation of a nonconductive phase by reaction between the Ta film and the external ambient oxygen after annealing. For both the and the contact system, no other phase, such as , Pt‐silicides, and Pt‐Ta compounds, was observed except for the formation of a conductive crystalline phase after annealing, followed by the prevention of surface oxidation of the diffusion barrier itself as well as the retention of the bottom electrode structure up to 800°C. This resulted in a lower total resistance and an ohmic characteristic. Therefore, it can be concluded that ohmic behavior does not depend on contact size for both contact systems and all compositions in this study. © 2000 The Electrochemical Society. All rights reserved.

High temperature platinum etching using Ti mask layer

Platinum is a strong candidate for an electrode material of the high dielectric capacitors in highly integrated dynamic random access memory devices. However, it is extremely difficult to etch the fine patterns of Pt due to an inherently low etch slope. This characteristic comes from the physical sputtering nature of the Pt etching process. This article reveals that the Pt etching profile depends on the change of the Ti mask layer caused by the increase of wafer temperature during etching. The Pt etching slope of 80° in 0.40 μm pitch was attained by heating the wafer substrate up to 220° with plasma-on. From the transmission electron microscopy analysis the Ti mask is considered to be deformed to TiOx layer in oxygen plasma at high wafer temperature, elevated either by high electrode temperature or plasma irradiation.