Solid Dielectric Layer Research Articles

Growth of submicron domain structures in electric field at elevated temperatures in lithium niobate with surface dielectric layer

The formation of submicron stripe domain structures was studied during two-stage switching with a change in the dimensionality of domain growth in congruent lithium niobate with a dielectric layer on the polar surface at elevated temperature. At the first stage, a two-dimensional hexagonal microdomain lattice representing a structure of isolated domains was created using the photoresist mask. After that, the polar surface was covered by solid dielectric layer. Thus, switching at the second stage was carried out under inefficient screening of depolarization field leading to growth of the stripe domains only. Self-organized formation of domain stars and snowflakes was demonstrated.

Simple Fabrication of Highly Sensitive Tactile Sensing Array Inlaid an Enhanced Porous Dielectric Layer for Robotic Manipulation

Highly sensitive flexible tactile sensors with synergistic normal and shear force perception are urgently required for possible grasping, lifting, and other in-hand manipulations of robotic hands. Here, a capacitive 3-D force tactile sensing array inlaid an enhanced porous dielectric layer was presented. The micropores were formed through vacuum-assisted infiltration of polydimethylsiloxane (PDMS) solution applying perfluorotributylamine (C12F27N) as sacrificial solvent, meanwhile, using sugar particles mixed up with PDMS-C12F27N emulsion to create extra macropores. The surface of the sensing array consisted of numbers of pen-cap-like bumps for reliable traction of objects. When normal or shear forces were applied on the surface, the contacted bumps were compressed or declined. The deflections of bumps resulted in possible capacitance variations, which were corresponded to the applied normal and shear forces. Compared with capacitive sensors inlaid an unpatterned solid dielectric layer, the developed sensing array experimentally displayed a high elasticity, a large sensing pressure range (over 250 kPa for normal pressure and over 60 kPa for shear pressures), a high sensitivity (1.63%/kPa and 1.61%/kPa for normal and shear pressure, respectively), a good repeatability, and a good structural stability and durability. Finger attached tests validated the proposed tactile sensing array having great potential for all kinds of robotics and prosthetic hand applications.

Lubrication effects on droplet manipulation by electrowetting-on-dielectric (EWOD)

Electrowetting has the potential to realize stand-alone point-of-care devices. Here, we report droplet-migration characteristics on oil-infused electrowetting-on-dielectric substrates. We prepare sparse micropillars to retain the oil layer in order to exploit the layer as a lubricating film. A physical model of the droplet velocity is developed, and the effects of the lubrication, the oil viscosity, the droplet volume, and the thickness of solid and liquid dielectric layers are discussed. It is found that the droplet velocity is scaled as U≈E2, which differs from a relationship of U≈E3, which is predicted from the dominant drag force for droplets sliding down on liquid-infused surfaces by gravity. Furthermore, our device achieves droplet velocity (19 μl) of ∼1 mm s−1 at the applied voltage of 15 V. The velocity is approximately tenfold as high as the same condition (applied voltage and oil viscosity) on porous-structure-based liquid-infused surfaces. The achieved high velocity is explained by a lubrication-flow effect.

Improved Sensitivity and Stability for SnO Ion-Sensitive Field-Effect Transistor-Based pH Sensor by Electrical Double Layer Gate and AlO Sensitive Film

Hydrogen ion sensor (pH sensor) with high sensitivity and good stability has great potential in modern life, medicine, industry, and other fields. As a core of the pH sensor, an ion-sensitive field-effect transistor (ISFET) based on SnO2 is paired with a high selectivity Al2O3 inorganic insulating film, which enhances its pH sensitivity. In the presence of a voltage applied to the extended gate, the gate and channel act as capacitance plates, and the sensor is equivalent to an electrical double layer (EDL). The hydrogen ions in solution alter the solution capacitance, which changes the capacitance of the solid dielectric layer, regulating the source–drain current. As a result of this work, the sensitivity of the ISFET-based pH sensor with extended gate increased <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.8\times $ </tex-math></inline-formula> to 25.33 nA/pH <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{V}$ </tex-math></inline-formula> when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{{\mathrm {GS}}}$ </tex-math></inline-formula> is 300 mV, compared to a SnO2-based sensor without the extended gate. Also, the stability of the sensor has been greatly improved, as well as the response time of 0.2 s. Our research provides an effective strategy for high-performance ISFET-based pH sensor, and the concept of using the pH-ISFET with an extended gate for direct quantification of pH values in solutions provides a dependable method for industrial applications.

Controlled armoring of metal surfaces with metallodielectric patchy particles.

A patchy colloidal particle possesses distinctive regions with different physical or chemical properties on its surface and thus exhibits anisotropic interactions with another particle or object. By utilizing the large van der Waals attraction between metal surfaces and the electric double layer repulsion originating from surface charge, we succeeded in controlling the adsorption behavior of metallodielectric particles (MDPs), which were composed of dielectric spheres each with a thin gold patch modified with dissociable groups, to gold surfaces. When MDPs were dispersed on a dielectric substrate with a thick gold pattern in aqueous solution, the particles selectively adsorbed onto the gold surface of the substrate at a moderate salt concentration. Furthermore, when MDPs were mixed with large particles coated with a thick gold film, MDPs adsorbed on the gold surface at a moderate salt concentration and formed a monolayer. In the monolayer, gold patches of MDPs bonded to the gold surface and the dielectric surface of MDPs faced outward. In other words, this monolayer was a solid dielectric layer formed on the metal surface of a large particle. Such selectivity, i.e., that a gold patch of an MDP bonded to a gold surface but the patches did not bond to each other, was realized by controlling the thickness and surface charge of gold patches.

Simple implantable wireless sensor platform to measure pressure and force

Smart implants have the potential to enable personalized care regimens for patients. However, the integration of smart implants into daily clinical practice is limited by the size and cost of available sensing technology. Passive resonant sensors are an attractive alternative to traditional sensing technologies because they obviate the need for on-sensor signal conditioning or telemetry and are substantially simpler, smaller, less expensive, and more robust than other sensing methods. We have developed a novel simple, passive sensing platform that is adaptable to a variety of applications. Sensors consist of only two disconnected parallel Archimedean spiral coils and an intervening solid dielectric layer. When exposed to force or pressure, the resonant frequency of the circuit shifts which can be measured wirelessly. We fabricated prototype pressure sensors and force sensors and compared their performance to a lumped parameter model which predicts sensor behavior. The sensors exhibited a linear response (R2 > 0.91) to dynamic changes in pressure or force with excellent sensitivity. Experimental data were within 13.3% and 6.2% of the values predicted by the model for force and pressure respectively. Results demonstrate that the sensors can be adapted to measure various measurands through a span of sensitivities and ranges by appropriate selection of the intervening layer.

Effect of substrate topography, material wettability and dielectric thickness on reversible electrowetting

Recent experiments by Kavousanakis et al., Langmuir, 2018 [1], showed that reversible electrowetting on superhydrophobic surfaces can be achieved by using a thick solid dielectric layer (e.g. tens of micrometers). It has also been shown, through equilibrium (static) computations, that when the dielectric layer is thick enough the electrostatic pressure is smoothly distributed along the droplet surface, thus the irreversible Cassie to Wenzel wetting transitions can be prevented. In the present work we perform more realistic, dynamic simulations of the electrostatically-induced spreading on superhydrophobic surfaces. To this end, we employ an efficient numerical scheme which enables us to fully take into account the topography of the solid substrate. We investigate in detail the role of the various characteristics of the substrate (i.e. the dielectric thickness, geometry and material wettability) and present relevant flow maps for the resulting wetting states. Through our dynamic simulations, we identify the conditions under which it is possible to achieve reversible electrowetting. We have found that not only the collapse (Cassie-Baxter to Wenzel) transitions but also the contact angle hysteresis of the substrate significantly affects the reversibility.

Electrostatic Energy Harvester Using Magnetically Actuated Liquid Dielectric Layers

We propose a fully liquid-based energy harvester that uses ferrofluid droplets as a movable dielectric material. The proposed device consists of top and bottom plates with conducting electrodes coated with a thin solid dielectric layer, a conducting liquid, and oil-based ferrofluid droplets as movable dielectric layers. The rotational motion of the ferrofluid droplets is actuated by a magnetic field that causes a capacitance variation that is used to generate electric power. An average output power of $19.3~\mu \text{W}$ is generated when eight ferrofluid droplets are used at a rotational speed of 180 r/min. [2014-0387]

A critical review of partial-discharge models

Partial-discharge (PD) measurements in compliance with the standard IEC 60270 are based on the main quantity apparent charge. This term is deduced from a simple PD model comprising a capacitive network. However, from a physical point of view, a PD defect cannot be represented by a capacitance, as argued by Pedersen and his coworkers. As an alternative, Pedersen proposed a field theoretical approach that is based on a dipole model. This more sophisticated concept has been ignored in the past, whereas the capacitive PD model is accepted also nowadays. Apparently, the reason for that is that the charge transfer can easily be calculated for the capacitive equivalent circuit, which is not the case if the field theoretical approach based on the dipole concept is adopted. As will be reported in this article, the analysis can substantially be simplified if instead of gaseous discharges in spherical, elliptical, or cylindrical cavities, as commonly regarded in the relevant literature, the establishment of a dipole moment in a uniform field between solid dielectric layers is considered.

Performance of Piezoelectrets Made of Non-Porous Polytetrafluoroethylene and Fluoroethylenepropylene Layers

The thermal stability of piezoelectricd33coefficients and charge dynamics in the piezoelectret films with tailored microstructure, made of non-porous polytetrafluoroethylene (PTFE) and fluoroethylenepropylene (FEP) layers, are investigated by the measurements of the isothermal decay of piezoelectricd33coefficients at elevated temperatures and the analysis of thermally stimulated discharge (TSD) current spectra in short circuit, respectively. The results show that the quasi-static piezoelectricd33coefficient up to 300 pC/N is achieved and its Young's modulus is about 0.28 MPa. Thed33values in the present studied films show improved thermal stability compared with the films without regular microstructure. The drift path for the most of detrapped charges in the films is through the solid dielectric layer.

Thermal stability and charge dynamics of piezoelectrets with tailored micro-structure

The laminated fluoroethylenepropylene (FEP) and porous polytetrafluoroethylene (PTFE) films with regular void structure are prepared by using a rigid template with a periodic-structured surface. The porous PTFE film is firstly patterned with the rigid template surface by applying force on the stack of porous PTFE film and the template, then followed by the fusion bonding process to bond the FEP and patterned porous PTFE together. The corona charging technique is used to make the laminated film piezoelectric, i.e., to become piezoelectrets. The Young’s modulus of the laminated FEP/PTFE films is determined by dielectric resonance spectra. The thermal stability of the piezoelectric d33 coefficients are characterized by measuring the decay of d33 at elevated temperatures. The charge dynamics in such FEP/PTFE piezoelectrets is investigated by analying the thermally stimulated discharge current spectra in short circuit. The results show that laminated FEP/PTFE films with very regular void structure can be made by using rigid template and fusion bonding process. The Young's modulus of such films is about 0.53 MPa. The maximum quasi-static piezoelectric d33 coefficient up to 500 pC/N is achieved. The laminated FEP/PTFE films show improved thermal stability. For example, the remnant d33value is around 22% of the initial value for the sample annealed at 150 ℃ for 5000 min. For the samples after annealing treatment, the main drift path of the detrapped charges is through the solid dielectric layer.

Pressure Mapping Using a Double Layer Dielectric System

Results of investigation of a double layer dielectric system applied for distribution determination is discussed in the paper. The system consists of elastic and rigid solid dielectric layers. The trybo-charge is generated on the contact between the rough surface of the elastic and dielectric layers when the system is subjected to an external stress. It was shown that the local effective surface charge density on the rigid dielectric layer depends on the local value. The generated charge produces a proportional voltage across the solid dielectric layer after removing the elastic one (foam). This way, the may be converted into a voltage signal, which is 'memorised by a solid dielectric layer. Finally, the pressure map converted into 'an electric potential map can be visualised by potential distribution determination. The potential distributions obtained in the system for different cases of non-uniform distributions and different elastic layers are presented in the paper.

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Influence of macroscopic dipoles on the charge storage and charge dynamics of polypropylene ferroelectret films

In this work, influence of the formation of macroscopic dipoles with space charges enclosed in a void (electric domain) and their polarization enhancement on the charging current characteristic and the conductivity of cellular polypropylene (PP) film were studied by the corona charging with a grid in combination with the reverse-polarity corona charging compensation method. By measuring the isothermal surface potential decay and analyses of open-circuit and short-circuit thermally stimulated discharging current spectra, the charge stability and charge dynamics of PP ferroelectrets in relation to the formation and density variety of macroscopy dipoles were also discussed. The experimental results indicate that the decrease of charge stability of cellular PP film with high polarization should be attributed to the increase of the conductivity induced by the self-field of macroscopic dipoles. For cellular electret film with weak polarization, macroscopic dipoles formed by space charges should only be trapped at two sharp ends of lens-like void and, therefore, detrapped charges will transport along the side surfaces at both ends of the void. When the sample has high polarization, the trapped charges are distributed in the whole surface layer of the void. Most of the detrapped charges excited by the electret field drift through the solid dielectric layer between adjacent voids, which leads to their decay.

Ozone generation in dry air using pulsed discharges with and without a solid dielectric layer

Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide range of industrial applications. Ozonizers usually use dielectric barrier discharges and employ alternating current (ac) with consequent heat generation, which necessitates cooling. In the present study, very short duration pulsed voltage is employed resulting in reduced heating of the gas and discharge reactor. A comparison of ozone generation in dry air using a coaxial concentric electrode system with and without a solid dielectric layer is reported. Two types of dielectric layers were employed, ceramic and polyvinylchloride (pvc). The effects of peak pulsed voltage (12.5 to 62 kV), reactor length (0.1 to 1 m), pulse repetition rate (25 to 400 pulses per second, pps), gas flow rate (1.5 to 3.0 1/min) and variation of the pitch length of the spiral wire forming the central electrode (5 to 10 mm) on the concentration and production yield of ozone (g/kWh) are reported. A comparison is made between the performance of discharge reactors with (ceramic reactor Type IIC and pvc reactor Type IIP) and without (reactor Type I) a dielectric layer, using the same electrode gap separation (15 mm) and reactor lengths (0.157 and 1 m). High production yields of ozone in dry air of /spl sim/125 52 and 60 g/kWh were obtained when using, respectively ceramic, pvc, and no dielectric layer, for a fixed pulse rate of 100 pps, 15 1/min now rate and for a relatively short length of the reactor of 157 mm.

Durability of dielectric protective layers against repetitious thermal stress in phase-change optical recording

We studied the influence of the mechanical strength of dielectric thin films on the durability against the thermal stress cycle during repetitious overwriting in phase-change optical recording. Dielectric thin films such as tantalum oxide (TaOx), silicon nitride (SiNx), and a compound of zinc sulfide and silicon dioxide (ZnS:SiO2), were applied for the protective layers that sandwich a GeSbTe alloy active layer. Thermal stress that led this sandwiched medium to fail must mainly be associated with a deformation due to melting or amorphization of the active layer, and a thermal expansion of the solid dielectric protective layers. The thermal stresses during repetitious overwriting caused microstructural changes in the protective layers: a plastic deformation, and cracking and void formations. The stresses also caused a deformation of a substrate surface below the bottom protective layer. These microscopic defects accumulated, and subsequently resulted in optically detectable macroscopic defects. TaOx and SiNx films having high density, especially of more than 80% of the bulk density, could suppress the plastic deformation during overwriting effectively, whereas nucleated cracking defects were easily enlarged due to their brittleness. Contrary to these brittle films, ZnS:SiO2 could suppress the cracking propagation by its plastic deformation.

Quenching of the luminescence of ZnS:Mn at high excitation levels

Photoluminescence of ZnS:Mn films (-1% by mass) 0.8 Dm thick was excited by nitrogen laser light (~ = 337 nm, i0 nsec pulse length). A sinusoidal voltage of variable amplitude and frequency was used to excite electroluminescence of films sandwiched between two dielectric layers 1.1 ~m thick and metallic and transparent electrodes. In both cases we measured the time-averaged luminance and power absorbed by the phosphor (by the oscillographic method in the case of electroluminescence). We also used powdered samples of ZnS:Cu, Mn with orange luminescence (EI-580 type phosphor) which were distributed in a solid dielectric layer about 50 Dm thick and were likewise excited by a variable voltage.

Photographic investigation of breakdown of composite insulation

The alternating and impulse-voltage breakdown of a composite consisting of a column of air in series with a solid dielectric layer has been investigated. Breakdown is initiated in the solid some 60 ns before voltage collapse, and not by the establishment of a plasma throughout the air column, as supposed by a current hypothesis. This is also true for a liquid/solid composite.

The breakdown of electrical insulation in a plane layer of insulating fluid by electrocapillary instability

A theoretical and experimental study is made of the failure of electrical insulation in a layer of dielectric fluid filling a circular hole in a horizontal solid dielectric sheet. A potential difference is applied between conducting fluids which bound the fluid and solid dielectric layer above and below. It is observed that a critical potential difference is reached at which the fluid dielectric becomes statically unstable under the action of surface tension and normal electrical stresses at its interfaces. When this potential is reached the dielectric fluid insulation fails.The critical potential difference is calculated by both an approximate and an exact theory. The approximate theory ignores the changes in the electrostatic field within the solid dielectric by allowing a charge distribution at the curved surface of the hole. Comparison with the results of an exact theory shows that such an approximation introduces only small errors in the calculated points of transition to instability.It is shown that failure may take the form of a symmetric (sausage) mode of displacement, or an antisymmetric (kink) mode, depending on whether the radius of the hole is greater or less than approximately the depth of the layer respectively. The two forms of failure were indicated in the experiments, and the observed critical voltages are in good agreement with those predicted by the theory.