Conductive Microparticles Research Articles

Stretchable Anisotropic Conductive Film with Position‐Registered Conductive Microparticles Used for Strain‐Insensitive Ionic Interfacing in Stretchable Ionic Sensors

AbstractNumerous approaches are explored to achieve precise position registry of microparticles (MPs) with minimal defects; however, MP assembly in a periodic pattern or an arbitrary manner has been a challenging issue over the past several decades. Utilizing the position‐registered conductive MPs, polymer composites of the MPs are used as anisotropic conductive film (ACF) and soft interfacing. One of the remaining challenges is maintaining the MP positions while producing or utilizing the ACF. This study proposes a simple strategy to produce a stretchable ACF (S‐ACF) by mechanical rubbing, without disturbing the MP positions during the production and use. A practical means of precise MP positioning on a ultraviolet (UV)‐patternable soft template is investigated first. This study investigates, through both experiment and finite element method calculation, the relationship between local adhesion of the template and mechanical rubbing variables (pressure, rubbing velocity, and MP size). Based on this exploration, a fast and simple method to fabricate large‐area S‐ACF is presented. This study demonstrates that the S‐ACF can be used for electronic interfacing in stretchable devices and for ionic interfacing to remove the effect of external mechanical force in ionic sensors.

Pixel detector hybridisation and integration with anisotropic conductive adhesives

A reliable and cost-effective interconnect technology is required for the development of hybrid pixel detectors. The interconnect technology needs to be adapted for the pitch and die sizes of the respective applications. This contribution presents recent results of a newly developed in-house single-die interconnection process based on Anisotropic Conductive Adhesives (ACA). The ACA interconnect technology replaces solder bumps with conductive micro-particles embedded in an epoxy layer applied as either film or paste. The electro-mechanical connection between the sensor and ASIC is achieved via thermocompression of the ACA using a flip-chip device bonder. The ACA technology can also be used for ASIC-PCB/FPC integration, replacing wire bonding or large-pitch solder bumping techniques. A specific pixel-pad topology is required to enable the connection via micro-particles and create cavities into which excess epoxy can flow. This pixel-pad topology is achieved with an in-house Electroless Nickel Immersion Gold (ENIG) process. The ENIG and ACA processes are qualified with a variety of different ASICs, sensors, and dedicated interconnect test structures, with pad diameters ranging from 12 μm to 140 μm and pitches between 20 μm and 1.3 mm. The produced assemblies are characterized electrically, with radioactive-source exposures, and in tests with high-momentum particle beams. This contribution introduces the developed interconnect and plating processes and showcases different hybrid assemblies produced and tested with the above-mentioned methods. A focus is placed on recent optimization of the plating and interconnect processes, resulting in an improved plating uniformity and interconnect yield.

Enhanced proton conductivity and power density of HT-PEMFCs using tin pyrophosphate microparticles-dispersed polybenzimidazole composite electrolyte membranes

Proton conductivity and acid retention property of PBI-based polymer electrolyte membrane is critical factor for high-temperature PEMFCs with high performance. The present study was undertaken in order to demonstrate the effect of SnP2O7 microparticles incorporation for the PBI-based membrane to the fuel cell performance. Besides, the correlation between dispersion property of additives and fuel cell performance was investigated, by taking the larger particle sizes of Sn-originated material into account. Highly dispersed SnP2O7 microparticles derived by the wet mechanochemical treatment has resulted in the novel PBI-based composite membrane with high-proton conductivity (4.17 mS cm−1 at 160 °C, anhydrous) and superior acid retention property. Consequently, the highest peak power density of 373 mW cm−2 at 160 °C under anhydrous conditions was achieved for the composite membrane with wet-mechanical milled SnP2O7, while the membrane without mechanochemical treatment showed lowest peak power density (168 mW cm−2) even inferior to the pure PBI membrane. Investigations into the PBI-based composite electrolyte membrane incorporated with highly dispersed SnP2O7 protonic conductive microparticles have yielded a performance enhancement of high-temperature PEMFCs.

Development of novel single-die hybridisation processes for small-pitch pixel detectors

Hybrid pixel detectors require a reliable and cost-effective interconnect technology adapted to the pitch and die sizes of the respective applications. During the ASIC and sensor R&D phase, especially for small-scale applications, such interconnect technologies need to be suitable for the assembly of single dies, typically available from Multi-Project-Wafer submissions. Within the CERN EP R&D programme and the AIDAinnova collaboration, innovative hybridisation concepts targeting vertex-detector applications at future colliders are under development. Recent results of two novel interconnect methods for pixel pitches of 25 µm and 55 µm are presented in this contribution — an industrial fine-pitch SnAg solder bump-bonding process adapted to single-die processing using support wafers, as well as a newly developed in-house single-die interconnection process based on Anisotropic Conductive Film (ACF). The fine-pitch bump-bonding process is qualified with hybrid assemblies from a recent bonding campaign at Frauenhofer IZM. Individual CLICpix2 ASICs with 25 µm pixel pitch were bump-bonded to active-edge silicon sensors with thicknesses ranging from 50 µm to 130 µm. The device characterisation was conducted in the laboratory as well as during a beam test campaign at the CERN SPS beam-line, demonstrating an interconnect yield of about 99.7%. The ACF interconnect technology replaces the solder bumps by conductive micro-particles embedded in an epoxy film. The electro-mechanical connection between the sensor and ASIC is achieved via thermocompression of the ACF using a flip-chip device bonder. The required pixel pad topology is achieved with an in-house Electroless Nickel Immersion Gold (ENIG) plating process. This newly developed ACF hybridisation process is first qualified with the Timepix3 ASICs and sensors with 55 µm pixel pitch. The technology can be also used for ASIC-PCB/FPC integration, replacing wire bonding or large-pitch solder bumping techniques. This contribution introduces the two interconnect processes and presents preliminary hybridisation results with CLICpix2 and Timepix3 sensors and ASICs.

Honeybee-inspired electrostatic microparticle manipulation system based on triboelectric nanogenerator

Electrostatic manipulation of particles or droplets has raised huge interests across many fields including biomedical analysis, microchemistry and microfabrication/patterning, because of its merits of simple configuration and easy operation. However, traditionally applied bulky high voltage sources for electrostatic manipulation not only have potential safety risk to the operator and the devices, but also limit the portability. Here, we proposed an electrostatic microparticle manipulation system (EMMS) based on a triboelectric nanogenerator (TENG). Inspired from the pollen collection principle of honeybees, the EMMS featured a simple pin-to-plate electrodes system, which was electrostatically powered by the high voltage of the TENG. Different manipulation modes, including contact manipulation and noncontact manipulation were systematically studied. With a sliding displacement of 5 cm, the TENG delivered an output voltage of ± 3.2 kV, which could manipulate dielectric microparticles with weights of 1.7 mg, 0.9 mg and 13.3 mg at contact manipulation mode, noncontact manipulation (vertical lift) and noncontact manipulation (parallel move) mode, respectively. Manipulation mechanisms for both dielectric and conductive microparticles under different configurations of the pin-to-plate electrodes system were investigated. Finally, potential applications including micropatterning, dust remove and drug release/microchemistry were demonstrated to show the great prospects of the proposed TENG-based EMMS.

Dispenser Printing with Electrically Conductive Microparticles

Electrically conductive textiles for wearable smart devices are in increasing demand [1]. The advantages of flexible fabric structures are combined with electronic functions, such as sensing or actuating, energy harvesting or illuminating, for the design of a multitude of smart textiles. Those functions are often created by applying conductive layers or patterns onto the textile surface with two-phase systems based on conductive filler particles in polymeric binders. However, those systems alter the textile-typical properties regarding haptic, drape, flexibility or weight, depending on the type of conductive particle used, i.e., metal-or carbon-based ones. Generally, electrical conductivity increases with the increase of conductive filler concentration. The relation between the various factors determining the electrical behavior as well as the percolation threshold for some dispersions and in particular the size and shape of the filler particles were previously assessed for planar coatings [2]. In this research work electrically, conductive patterns were printed with dispenser printing technology using such two-phase dispersions based on polyurethane and polyacrylate binders and various metal microparticle flakes. With this application method linear resistance of approx. 25 to 100 Ohm per 100 cm depending on the textile structure could be realized, which was not even significantly reduced by household washing at 40°C or abrasion by Martindale.

Multivariate Correlation Analysis of the Electroconductive Textiles Obtained Using Functionalization by Radio-Frequency Oxygen Plasma Treatments.

This paper presents a study concerning the preliminary treatments in radiofrequency (RF)oxygen (O2) plasma used to obtain a hydrophilic effect on raw cotton fabrics followed by electroconductive thin film deposition to obtain electroconductive textile surfaces. In addition, this study presents a multivariate correlation analysis of experimental parameters. The treatment using RF plasma O2 aimed to increase the hydrophilic character of the raw fabric and adherence of paste-based polymeric on polyvinyl alcohol (PVA) matrix and nickel (Ni), silver (Ag) or copper (Cu) microparticles. The purpose of the research was to develop electroconductive textiles for flexible electrodes, smart materials using a clean technology such as radiofrequency (RF) plasma O2 to obtain a hydrophilic surface with zero wastewater and reduced chemicals and carbon footprint. To achieve the foreseen results, we used advanced functionalization technologies such as RF plasma O2, followed by scraping a thin film of conductive paste-based Ni, Ag or Cu microparticles, and multivariate correlation methods to observe the dependence between parameters involved (dependent and independent variables). Overall, the fabrics treated in plasma with O2 using a kHz or MHz generator and power 100–200 W present an excellent hydrophilic character obtained in 3 min. After RF O2 plasma functionalization, a thin film based on polymeric matrix PVA and Ni microparticles have been deposited on the fabric surface to obtain electroconductive materials.

Stretchable anisotropic conductive film (S-ACF) for electrical interfacing in high-resolution stretchable circuits.

In stretchable electronics, high-resolution stretchable interfacing at a mild temperature is considered as a great challenge and has not been achieved yet. This study presents a stretchable anisotropic conductive film (S-ACF) that can electrically connect high-resolution stretchable circuit lines to other electrodes whether they are rigid, flexible, or stretchable. The key concepts of this study are (i) high-resolution (~50 μm) but low-contact resistance (0.2 ohm in 0.25 mm2) interfacing by periodically embedding conductive microparticles in thermoplastic film, (ii) low-temperature interfacing through the formation of chemical bonds between the S-ACF and the substrates, (iii) economical interfacing by selectively patterning the S-ACF, and (iv) direct interfacing of chips by using the adhesion of the thermoplastic matrix. We integrate light-emitting diodes on the patterned S-ACF and demonstrate stable light operation at large biaxial areal stretching (εxy = 70%).

Space and Frequency Dependence of Nanocapacitor Array Sensors Response to Microparticles in Electrolyte

We present new experimental evidence and extensive numerical simulations of a few distinct fingerprints generated by dielectric and conductive microparticles in electrolyte environment on the capacitance spectra of nanoelectrode array sensors. Finite element simulations in good agreement with measurements allow us to identify unambiguously the physical origin of these features, and to illustrate their dependence on the system's geometrical and physical properties. In particular, we show that conductive particles induce a response with complex space and frequency dependencies, caused by the formation of an AC electrical double layer at the particle surface, and its interaction with the working and counter electrodes in the array. Furthermore, we highlight features that could lead to false-negative detection events in sensing applications. The theoretical predictions are confirmed by experiments on a state of the art CMOS pixelated nanocapacitor biosensor platform.

2D Colloidal Array of Glucose‐Conjugative Conductive Microparticles for a Pressure‐Mediated Chemiresistive Sensor Platform

AbstractA platform is introduced for pressure‐mediated chemiresistive glucose sensing based on a 2D array of glucose‐conjugating silver nanowire (AgNW)‐deposited conductive microparticles (AgCMPs). Glucose‐conjugating AgCMPs, as transducers of the sensors, are fabricated by decorating the surface of monodisperse polyurethane elastomeric MPs with AgNWs by layer‐by‐layer deposition. Then, the AgNWs are covalently bonded to 4‐mercaptophenylboronic acid (4‐MPBA) to endow them with chemiresistive glucose sensing property against the applied pressure. The 4‐MPBA‐functionalized AgCMPs are positioned with high accuracy on a hole‐patterned stencil film placed between electrodes. Using this sensor system, it is shown that the current induced by the application of constant pressure to the sensor film at a given supply voltage varies linearly with the glucose concentration before and after critical glucose bridging concentration. Notably, the AgCMP‐based chemiresistive sensors could detect glucose over a wide concentration range from 0.56 × 10−6 m to 56 × 10−3 m with remarkable sensitivity and selectivity.

2D Percolation Design with Conductive Microparticles for Low‐Strain Detection in a Stretchable Sensor

AbstractAlthough a variety of stretchable strain sensors based on electrical percolation have been reported, stretchable sensors detecting low strains have been rarely demonstrated. This is because large stretchability of a strain sensor conflicts with high strain resolution at low strains. Here, the electrical percolation into 2D is confined and a strain sensor that is highly sensitive at low strains and simultaneously highly stretchable is presented. The 2D confinement of the electrical percolation is accomplished by a close‐packed monolayer assembly of conductive microparticles (MPs) on an elastomer substrate. The current profiles of the MP monolayer at low strains are in situ visualized using conductive atomic force microscopy. When the lattice of the MP monolayer is aligned vertically to the strain direction, the resistance is highly sensitive to low‐strain deformations (ε = 0 – 0.05), but the sensor has reasonable stretchability (ε = 0.3). The simultaneous achievement of the high sensitivity at low strains and the reasonable stretchability is explained by the relationship between the strain‐dependent current profile and the relative position changes of the MPs. A high‐precision pulse sensor clearly showing the representative peaks is demonstrated.

Cut-and-Paste Transferrable Pressure Sensing Cartridge Films

Flexible tactile sensors have been intensively studied for healthcare and electronic skin devices. Currently, a sensing material, electrode, and substrate are manufactured as one set by depositing the sensing material on the electrode. For this reason, when another electrode or substrate is used in the sensor or when different sensor characteristics are required, a new sensing material must be developed and the fabrication conditions should be changed. This study proposes a novel method of manufacturing a pressure sensing material like a cartridge film. The cartridge film is made by filling the holes of a stencil film (one MP in each hole) with conductive microparticles (MPs). Using the cartridge film, the sensing material can be cut-and-pasted on electrodes and transferred to other electrodes for reuse. This study analyzes the electrical responses of the sensors made of the cartridge film on the basis of the Hertzian contact theory, and also correlates the sensing performance of the sensors with the cond...

E‐Skin: E‐Skin Tactile Sensor Matrix Pixelated by Position‐Registered Conductive Microparticles Creating Pressure‐Sensitive Selectors (Adv. Funct. Mater. 31/2018)

E‐Skin: E‐Skin Tactile Sensor Matrix Pixelated by Position‐Registered Conductive Microparticles Creating Pressure‐Sensitive Selectors (Adv. Funct. Mater. 31/2018)

E‐Skin Tactile Sensor Matrix Pixelated by Position‐Registered Conductive Microparticles Creating Pressure‐Sensitive Selectors

AbstractElectronic skin (E‐skin) imitates human skin by converting external stimuli into electrical signals. E‐skin requires high flexibility and a high level of device integration. Unlike conventional E‐skin creation methods, a highly sensitive pressure sensor matrix (100 pixels cm−2) made of position‐registered elastic conductive microparticles (MPs) is created. The MPs form a Schottky junction with the bottom electrode and the current through the junction is sensitive to external pressure, forming a simple one‐selector two‐terminal device array. The Schottky junction eliminates the electrical cross talks between the sensor pixels consisting of 64 MPs in each. The flexible pressure sensor matrix is used as an artificial fingertip for Braille reading and as an electronic scale based on detailed force distribution. This work opens up the possibility that assembled MPs, which have been a long‐standing research topic in academia, can be used to make practical electronic devices.

Preparation and morphology characterization of core-shell water-dispersible polystyrene/poly(3,4-ethylenedioxythiophene) microparticles

Ultrafine electrically conductive microparticles have been prepared by in situ oxidative polymerization of 3,4-ethylenedioxythiophene in the presence of sulfonated polystyrene latex beads either in water or in an aqueous solution of poly(4-styrenesulfonic) or 4-toluenesulfonic acid. The particles consist of polystyrene core and continuous poly(3,4-ethylenedioxythiophene) shell which incorporate different counter-ions derived from the oxidant or the sulfonic acid. The presence of poly(4-styrenesulfonic acid) in the polymerization medium enhances the electrical conductivity of the resulting particles by up to two orders of magnitude. The particles prepared in the presence of poly(4-styrenesulfonic acid) exhibit smooth surface morphology and high colloidal stability, while these prepared in the presence of 4-toluenesulfonic acid or in the absence of sulfonic acid show rough sponge-like morphology and do not form stable dispersions.

Using airbrushes to pattern reagents for microarrays and paper-fluidic devices

We report using an airbrush to pattern a number of reagents, including small molecules, proteins, DNA, and conductive microparticles, onto a variety of mechanical substrates such as paper and glass. Airbrushing is more economical and easier to perform than many other patterning methods available (for example, inkjet printing). In this work, we investigated the controllable parameters that affect patterned line width and studied their mechanisms of action, and we provide examples of possible patterns. This airbrushing approach allowed us to pattern lines and dot arrays from hundreds of μm to tens of mm with length scales comparable to those of other patterning methods. Two applications, enzymatic assays and DNA hybridization, were chosen to demonstrate the compatibility of the method with biomolecules. This airbrushing method holds promise in making paper-based platforms less expensive and more accessible.

Ethanol-to-methane activity of Geobacter-deprived anaerobic granules enhanced by conductive microparticles

Abstract Direct interspecies electron transfer (DIET) has been typically proposed as mechanism of electron transfer among methanogenic populations in granules during anaerobic digestion where Geobacter species play a key role. Using anaerobic granules where Geobacteraceae members were not prevalent − representing only 0.3% of total bacteria −, tests incubated with two co-substrates showed that the rate of methanogenesis from formate and hydrogen diminished in the presence of a non-methanogenic co-substrate such as ethanol. This could indicate that biological DIET occurs and competes with hydrogen and formate during methanogenesis. Moreover, the addition of conductive microparticles, such as stainless steel and granular activated carbon, was found to increase methanogenic activity in disintegrated granules by 190 ± 18% and 175 ± 22% respectively as compared to disintegrated granules devoid of microparticles. The addition of non-conductive microparticles such as porcelain however decreased methanogenic activity by 65 ± 3% of the disrupted granules without microparticle activity. These results indicate that syntrophic bacteria from anaerobic sludge excluding Geobacter species can also carry out conductive mineral mediated DIET.

Elastic instabilities of a ferroelastomer beam for soft reconfigurable electronics

We examine the flexural deformation and snap-through instability of a pre-buckled ferroelastomer beam. The beam is composed of ferromagnetic and electrically conductive microparticles suspended in a polydimethylsiloxane (PDMS) matrix. Bending and snap-through are controlled remotely with an external magnetic field. The observed magneto-flexural coupling is in reasonable agreement with predictions from an analytic model based on elastic rod theory and variational techniques. Moreover, such coupling results in stable and unstable bending modes that can be exploited for a soft-matter, field-controlled, reconfigurable electrical relay. These two flexural modes correspond to (i) low-power binary (stable) switching and (ii) a more rapid >10Hz response that is achieved by momentarily driving the beam to a slightly deformed configuration. This combination of stable and unstable switching states provides a new approach for harnessing elastic instabilities and a means to create a low power, yet rapidly responsive switch for soft electronic systems.

The dust nature of micro field emitters in accelerators

Field emission currents emitted by micro-emitters are a limiting factor for the operational gradients of accelerating radio frequency (rf) cavities. Within the rf field emission theory the existence of needle like micro field emitters with very high length relative to the radius and corresponding high enhancement factor (β) is assumed. In this article the hypothesis that micro field emitters consists of long chains of conductive micro-particles is considered. Five different forces acting onto the particles in a high rf field are considered and the respective equations are derived. Some experimental observations and their explanation within this hypothesis are discussed.

Voltammetric determination of homovanillic acid and vanillylmandelic acid on a disposable electrochemical measuring cell system with integrated carbon composite film electrodes

An array of carbon composite electrodes embedded in a 96-well microtitration plate was applied to differential pulse voltammetry determination of standards of tumor biomarkers 2-(4-hydroxy-3-methoxy-phenyl) acetic acid (homovanillic acid, HVA) and (RS)-hydroxy(4-hydroxy-3-methoxy-phenyl) acetic acid (vanillylmandelic acid, VMA). For the preparation of composite electrodes, graphitic conductive microparticles and nonconductive polystyrene binder were used. For the measurement, a buffer of pH 2 was selected as the optimum medium for both analytes. In this medium, concentration dependences of stand-alone standards were measured; calculated quantification limits were 0.3 µmol dm−3 for HVA and 0.8 µmol dm−3 for VMA. Sorption of analytes on employed working electrode was examined in order to verify, whether the current is influenced by the time period between cell filling and measurement. The sorption was not observed and the current was stable even after 10 min. Developed method was verified by the determination of a mixture of standards of both analytes. Mixtures of analytes of various proportions were measured and the obtained calibration curves showed good agreement with standard values. Furthermore, the results showed that the behavior of the mixture of analytes is not different from the behavior of the actual standards, so that it is possible to calculate the concentration of both analytes side by side.