Coplanar Interdigitated Electrodes Research Articles

Expansion of the Analytical Modeling of Capacitance for 1-N-1 Multilayered CID Structures with Monotonically Increasing/Decreasing Permittivity.

Capacitive sensors that utilize the Coplanar Interdigitated (CID) electrode structure are widely employed in various technical and analytical domains, such as healthcare, infectious disease management, pharmaceuticals, metrology, and environmental monitoring. The present exigency for lab-on-a-chip contrivances and the requisite for the miniaturization of sensors have led to the widespread adoption of CID sensors featuring multiple dielectric layers (DLs), either in the form of substrates or superstrates. Previously, we derived an analytical model for the capacitance of CID capacitive sensors with four distinct 1-N-1 patterns (namely, 1-1-1, 1-3-1, 1-5-1, and 1-11-1) using partial capacitance (PC) and conformal mapping (CM) techniques. The aforementioned model has been employed in various applications wherein the permittivity of successive layers exhibits a monotonic decrease as one moves away from the electrode plane, resulting in highly satisfactory outcomes. Nevertheless, the PC technique is inadequate for structures with multiple layers where the permittivity exhibits a monotonic increase as the distance from the electrodes increases. Given these circumstances, it is necessary to adapt the initial PC method to incorporate these novel configurations. In this work, we have discussed a new approach, splitting the concept of PC into partial parallel capacitance (PPC) and partial serial capacitance (PSC), where new CM transformations are proposed for the latter case. Thus, the present study proposes a novel methodology to expand upon our prior analytical framework, which aims to incorporate scenarios where the permittivity experiences a reduction across successive layers. The outcomes are juxtaposed with the finite element simulation and analytical findings.

Plasmonic Near-Infrared Photoconductor Based on Hot Hole Collection in the Metal-Semiconductor-Metal Junction.

Harvesting energetic carriers from plasmonic resonance has been a hot topic in the field of photodetection in the last decade. By interfacing a plasmonic metal with a semiconductor, the photoelectric conversion mechanism, based on hot carrier emission, is capable of overcoming the band gap limitation imposed by the band-to-band transition of the semiconductor. To date, most of the existing studies focus on plasmonic structural engineering in a single metal-semiconductor (MS) junction system and their responsivities are still quite low in comparison to conventional semiconductor, material-based photodetection platforms. Herein, we propose a new architecture of metal-semiconductor-metal (MSM) junctions on a silicon platform to achieve efficient hot hole collection at infrared wavelengths with a photoconductance gain mechanism. The coplanar interdigitated MSM electrode’s configuration forms a back-to-back Schottky diode and acts simultaneously as the plasmonic absorber/emitter, relying on the hot-spots enriched on the random Au/Si nanoholes structure. The hot hole-mediated photoelectric response was extended far beyond the cut-off wavelength of the silicon. The proposed MSM device with an interdigitated electrode design yields a very high photoconductive gain, leading to a photocurrent responsivity up to several A/W, which is found to be at least 1000 times higher than that of the existing hot carrier based photodetection strategies.

ε‐Ga2O3 Thin Film Avalanche Low‐Energy X‐Ray Detectors for Highly Sensitive Detection and Fast‐Response Applications

AbstractLow‐energy X‐ray detectors are widely used in diverse areas, including medical diagnosis, space exploration, environmental monitoring, industrial inspection, and scientific research. Developing large area, highly sensitive, and fast low‐energy X‐ray detectors is challenging owing to material and device operation mechanism limitation. Herein, an epitaxial ε‐Ga2O3 thin film over a large area (2 in.) is prepared by metal–organic chemical vapor deposition and applied in the efficient low‐energy X‐ray detectors. The detectors are highly sensitive to detecting low‐energy X‐rays owing to the high mass attenuation coefficients achieved in the low‐energy X‐ray range (1–30 keV). The avalanche multiplication mechanism in back‐to‐back Au–Ga2O3 Schottky diodes is explored to realize high carrier multiplication and photocurrent gain. The charge collection efficiency is improved by reducing the spacing gap of the fingers within the coplanar interdigitated Au electrodes in the film, thus achieving a high detection sensitivity of up to 1.9 × 104 μCGyair−1 cm−2 for 30 keV X‐ray. Furthermore, the ε‐Ga2O3 thin films demonstrate high crystallization quality with low trap density and high breakdown voltage with a low noise current that enable their usage in applications requiring fast response time (e.g., 37 ms) and low detectable dose rate (e.g., 42.3 μGyair s−1).

Microsupercapacitor with a 500 nm gap between MXene/CNT electrodes

Abstract Decreasing the size of portable, wearable, and integrated electronics requires subsequent reduction in the accompanying energy storage devices. To further decrease the size of supercapacitors without compromising device performance, adequate materials are required as well as appropriate device design. Traditionally, carbon nanomaterials have been utilized within high-performance electrochemical energy storage applications, however carbides, specifically two-dimensional (2D) transition metal carbides and or nitrides (MXenes) have shown promise. Herein, a focused-ion-beam (FIB) process is used for patterning of titanium carbide (Ti3C2) carbon nanotube (CNT) electrodes into a finely controlled coplanar interdigitated configuration. The symmetric micro supercapacitors produced have a narrow, 500 nm gap between the electrode fingers and exhibit high areal capacitance of ~317 mF cm−2 at a scan rate of 50 mV s−1 and still retain >30% of their capacitance (~104 mF cm−2) at 100 V s−1. In addition, electron beam lithography and photolithography are utilized to create almost-invisible devices with ultra-small footprints (0.04 mm2 device areas) that can be used for securing electronic components. This study provides a simple and reliable method for fabrication of on-chip symmetric MSCs with coplanar interdigitated electrodes.

Binder-assisted electrostatic spray deposition of LiCoO2 and graphite films on coplanar interdigitated electrodes for flexible/wearable lithium-ion batteries

Flexible battery technologies have lately attracted much attention in the field of wearable electronics. A coplanar interdigitated electrode design encompasses the merits of bending tolerance and increased kinetics owing to shortened diffusion length for applications in these batteries. However, the fabrication of a coplanar patterned electrode remains a challenge because the conventional slurry casting method is unsuitable. In this study, we present a new process to prepare an interdigitated coplanar electrode using binder-assisted electrostatic spray deposition (ESD) without vacuum or high-cost techniques. Using the binder-assisted ESD method, it is possible to deposit powder of any type or size. Moreover, this approach is versatile and universal for application to the design of any coplanar cell configuration and is achieved using a binder-assisted dispersion method based on a commercially available active material. A full-cell flexible battery is fabricated with a coplanar interdigitated electrode using a LiCoO2 cathode and graphite anode. The low cost, simplicity, efficacy, and flexibility of this method are very promising attributes in the design and fabrication of flexible/wearable batteries.

Design, Modeling and Simulation of a Capacitive Size-Discriminating Particulate Matter Sensor for Personal Air Quality Monitoring

We applied the well-established thermophoretic effect to air quality monitoring. We developed a novel method for particulate matter distribution analysis in an in-flow capacitive detection device. The proposed Multiphysics model combines fluid dynamics of particulate matter influenced by thermophoresis with electric field variations in the active volume space of a charged coplanar interdigitated electrodes. The model allows to anticipate the effect of thermophoresis in separating particles of PM10 and PM2.5 size ranges into different streams from a single particle-entrained flow and provides an estimated value of sensitivity for capacitive PM detection. The model is described through the Finite Element Method from the main equations to the simulation run using COMSOL Multiphysics and validated by comparing the results with literature. We obtained high sensor sensitivity of up to 0.48 zF/particle as far as $18~\mu \text{m}$ from coplanar electrode surface using the Computational Fluid Dynamics and Heat Transfer, Electrostatics and Particle tracing modules. We compare results of the simulations for different particle positions, electrode width and inter-electrode spacing, then we use the results to identify optimal design parameters for a novel architecture of a PM detection system with high sensitivity down to PM2.5 single particles and embedded particle size discrimination by using $10~\mu \text{m}$ electrode width and $1\mu \text{m}$ inter-electrode spacing.

Effect of annealing temperature on the performance of photoconductive ultraviolet detectors based on ZnO thin films

ZnO films prepared by sol–gel method and the ultraviolet detectors based on this material have been investigated in this paper. X-ray diffraction (XRD) patterns showed ZnO films present hexagonal wurtzite structure with a preferential orientation of (002) plane, and the crystallite size of films gradually increased from 44.3 to 54.8 nm as the annealing temperature increased from 400 to 600 °C. Ultraviolet–visible (UV–Vis) spectra indicated that the optical band gap decreases gradually with the increase of annealing temperature, and the minimum band gap is 3.06 eV at 600 °C. Photoluminescence (PL) spectra revealed that increasing annealing temperature can significantly reduce the defects and improve the crystallinity. Finally, gold (Au) coplanar interdigital electrodes were deposited on ZnO film surface and used to fabricate the ultraviolet photodetectors. The response performance of the devices improved as the annealing temperature of ZnO films increased, and the fastest response speed with a rise time of 4.172 s and a fall time of 11.012 s was obtained.

Capacitive humidity sensing properties of CdS/ZnO sesame-seed-candy structure grown on silicon nanoporous pillar array

Utilizing silicon nanoporous pillar array (Si-NPA) as substrate, a kind of CdS/ZnO sesame-seed-candy structure was prepared by successively growing ZnO nanorods and CdS nanograins via chemical vapor deposition and successive ion layer adsorption reaction method, respectively. The capacitive humidity sensing properties of CdS/ZnO/Si-NPA were studied by constructing coplanar interdigital electrodes. With the relative humidity (RH) increasing from 11% to 95%, a capacitance response over 201,530% was achieved, which indicates that CdS/ZnO/Si-NPA is highly sensitive to humidity. The response and the recovery times were determined to be ∼110 s and 32 s, respectively, with a maximum hysteresis being ∼2.67% at 75% RH. The high humidity sensitivity of CdS/ZnO/Si-NPA is attributed to the enlarged specific surface area induced by its unique nanostructure, while the short response/recovery times and the small hysteresis were due to the channel network brought by Si-NPA. These results indicate that CdS/ZnO/Si-NPA might be an ideal material system for fabricating high-performance humidity sensors.

Combined AC electroosmosis and dielectrophoresis for controlled rotation of microparticles.

Electrorotation is widely used for characterization of biological cells and materials using a rotating electric field. Generally, multiphase AC electric fields and quadrupolar electrode configuration are needed to create a rotating electric field for electrorotation. In this study, we demonstrate a simple method to rotate dielectrophoretically trapped microparticles using a stationary AC electric field. Coplanar interdigitated electrodes are used to create a linearly polarized nonuniform AC electric field. This nonuniform electric field is employed for dielectrophoretic trapping of microparticles as well as for generating electroosmotic flow in the vicinity of the electrodes resulting in rotation of microparticles in a microfluidic device. The rotation of barium titanate microparticles is observed in 2-propanol and methanol solvent at a frequency below 1 kHz. A particle rotation rate as high as 240 revolutions per minute is observed. It is demonstrated that precise manipulation (both rotation rate and equilibrium position) of the particles is possible by controlling the frequency of the applied electric field. At low frequency range, the equilibrium positions of the microparticles are observed between the electrode edge and electrode center. This method of particle manipulation is different from electrorotation as it uses induced AC electroosmosis instead of electric torque as in the case of electrorotation. Moreover, it has been shown that a microparticle can be rotated along its own axis without any translational motion.

Capacitive humidity sensitivity of SnO2:Sn thin film grown on silicon nanoporous pillar array

A SnO2:Sn composite thin film was grown on silicon nanoporous pillar array (Si-NPA) by a vapor–liquid–solid growth method. The main phase of the film is rutile SnO2, with the amount of Sn can be changed through controlling the oxidation time. A capacitive humidity sensor was fabricated through sputtering coplanar interdigital silver electrodes onto SnO2:Sn/Si-NPA and its room-temperature humidity-sensing properties were studied at 25°C. The SnO2:Sn/Si-NPA sensor prepared with an oxidation time of 30min shows superior humidity-sensing properties. A humidity response over 265% was obtained in the relative humidity (RH) range of 11–95% at 1kHz. The response and recovery times were determined to be ∼20s and the maximum hysteresis was ∼2% at 75% RH. The sensor shows high measurement reproducibility, long-term stability and good selectivity. These results indicated that SnO2:Sn/Si-NPA might be a promising candidate for fabricating practical humidity sensor.

Surface modification of a-Si0.60C0.40:H films by Al-assisted photochemical etching: humidity sensing application

The paper investigates the formation of thin porous amorphous silicon carbide (PASiC) by Al-assisted photochemical etching using HF/AgNO3 solution under UV illumination at ? = 254 nm. Different etching times varying from 2 to 10 min have been used on thin a-Si0.60C0.40:H films, which are elaborated by co-sputtering DC magnetron using a single crystal Si target and who deposited onto 86 of hot pressed polycrystalline 6H-SiC stripes of 12.5 mm3. Because of the high electrical resistivity of the thin a-Si0.60C0.40:H film higher than 2 MΩ cm, and in order to facilitate the chemical etching, a thin metallic film of high purity aluminum (Al) has been deposited under vacuum, follow-up of a thin palladium deposited under a grid to reduce attacked surface and reinforced solution etching. The etched surface was characterized by scanning electron microscopy, infrared spectroscopy, spectrophotometer UV, and photoluminescence. Results show that the morphology of etched a-Si0.60C0.40:H surface evaluates with etching time and presents a spongy and macroporous layers. Where, the diameter of pore size increases with the increasing etching time. A humidity sensors were fabricated through evaporating coplanar interdigital gold electrodes on PASiC and the humidity sensing properties were tested, it show, that the measured resistance Au-PASiC structure, depends highly on the applied bias voltage. Finally, the sensing performances are attributed to the unique surface structure, morphology of the pore and its size, that provide an effective pathway for vapor transportation and enlarged the sensing area of Au-PASiC.

Extraction of Signal from Noise: Impedance Cytometry Using Multi-electrode Sensing

We demonstrate a novel multielectrode sensing method for extracting signal from noise in a microfluidic impedance cytometer through introducing redundancy in our measurements and coding the signal. We use a pair of coplanar interdigitated electrodes (IDEs), where we can sense the change in impedance between any two neighboring fingers of the IDE pair. In the context of impedance cytometry, the passage of beads or cells over each two neighboring fingers partially occludes the current measured between the IDE pair. Therefore, as each particle enters and leaves the electrode area, we measure a train of pulses. By applying the equivalent matched filter we can exploit this train of pulses to proportionally increase the signal-to-noise ratio in our measurements.

Epitaxial growth and in-plane dielectric properties of orthorhombic HoMnO3 films

Orthorhombic HoMnO3 (HMO) thin films were grown epitaxially on LaAlO3 (001) substrates by using pulsed laser deposition technique. The films showed perfect orthorhombic crystallization and were well-aligned with the substrates. The in-plane dielectric constant and loss of HMO films were measured as functions of temperature (80–300 K) and frequency (120 Hz–100 kHz) by using coplanar interdigital electrodes. Two thermally activated dielectric relaxations were found, and the respective peaks shifted to higher temperatures as the measuring frequency increased. The in-plane dielectric properties of epitaxial orthorhombic HMO films were considered as universal dielectric response behavior, and the dipolar effects and the hopping conductivity induced by the charge carriers were used to explain the results.

Lipid Nanotube Formation Using Space-Regulated Electric Field above Interdigitated Electrodes

Lipid nanotubes have great potential in biology and nanotechnology. Here we demonstrate a method to form lipid nanotubes using space-regulated AC electric fields above coplanar interdigitated electrodes. The AC electric field distribution can be regulated by solution height above the electrodes. The ratio of field component in x axis (Ex) to field component in z axis (Ez) increases dramatically at solution height below 50 μm; therefore, at lower solution height, the force from Ex predominantly drives lipids to form lipid nanotubes along with the electric field direction. The forces exerted on the lipid nanotube during its formation were analyzed in detail, and an equation was obtained to describe the relationship among nanotube length and field frequency, amplitude, and time. We believe that the presented approach opens a way to design and prepare nanoscale materials with unique structural and functional properties using space-regulated electric fields.

AC Complex Impedance Study on the Resistive Humidity Sensors with Ammonium Salt-Containing Polyelectrolyte using a Different Electrode Pattern

We examined the effect of electrode fingers and gaps of coplanar interdigitated electrode (IDE) structures to characterize the ammonium salt-containing polyelectrolyte film of resistance-based humidity sensors. IDEs designed for this purpose were flexible gold electrodes deposited on a polyimide substrate using a printing process because the geometry presents a potential for tunable sensitivity over other electrode designs. The basic design of the sensors consisted of IDEs with a different number of electrode fingers such as 3, 4, and 5 and gap sizes of 310, 360, 410, and <TEX>$460{\mu}m$</TEX>. Details of the AC complex impedance characteristics such as the Nyquist plot, Bode plot, and activation energy based on electrode construction were investigated.

Investigation properties of Au–porous a-Si0.70C0.30 as humidity sensor

Abstract In this letter, we report the study of a humidity sensor based on porous amorphous silicon carbide (PASiC) as a function of exposure time and relative humidity (RH). Resistive humidity sensors Au–PASiC/Si(p) were fabricated through evaporating coplanar interdigital gold electrodes. The PASiC was formed by anodization of a-Si 0.70 C 0.30 in HF/ethylene glycol (ETG) solution at current density of 50 mA/cm 2 for 30 s. The structural properties of a-Si 0.70 C 0.30 thin films deposited by DC magnetron co-sputtering using single silicon crystal, 6H-SiC targets and the PASiC films were investigated by FT-IR and Raman spectroscopy. Hygroscopicity was studied by measuring the resistance of the PASiC under various RH. The results show that the measured resistance highly depends on the applied bias voltage. Moreover, the response signal against RH is found linear for an applied voltage of 2 V. Finally, the response and recovery times were determined around 13 s and 20 min, respectively.

A novel humidity sensor based on alumina nanowire films

Alumina nanowire (ANW) films were prepared by etching porous anodic aluminium oxide (AAO), and then humidity sensors with coplanar interdigitated electrodes based on ANWs were fabricated. The ANWs not only present tremendous surface area for water molecule adsorption but also provide efficient sites for attracting water molecules at low relative humidity (RH) levels. The sensors based on the particular morphology of ANWs with large open voids show high sensitivity and small hysteresis, and have fast response and recovery time to humidity. The capacitance rises slowly at a lower RH and increases rapidly after 70% RH, which is associated with the humidity mechanism of chemisorption at lower RH and physisorption at higher RH levels. The impendence analysis suggests that the ANWs are the main factor for sensing humidity, and AAO also contributes to humidity sensing. This study demonstrates that ANWs have promising applications in humidity monitoring.

Capacitive humidity sensing properties of SiC nanowires grown on silicon nanoporous pillar array

A large quantity of entangled SiC nanowires (nw-SiC) with an average diameter of ∼15nm were grown on a silicon nanoporous pillar array (Si-NPA) by a catalyst-assisted chemical vapor deposition method. The room-temperature capacitive humidity sensing properties of nw-SiC/Si-NPA were studied by evaporating coplanar interdigital silver electrodes onto its surface. With the relative humidity (RH) changing from 11% to 95%, a capacitance increment over 960% was achieved at the measuring frequency of 100Hz. The response and recovery times were measured to be ∼105 and 85s, respectively, with a maximum humidity hysteresis of 4.5% at 75% RH. The humidity sensor was also proved to be with high measurement reproducibility and long-term stability. Our results indicate that one-dimensional SiC materials might be competitive as a novel sensing material for fabricating humidity sensors with high performances.

Experimental model of a silica/epoxy interface submitted to a hygrothermal aging: a dielectric characterization

In order to investigate the influence of a hygrothermal aging on the organic/mineral interfaces of a silica filled epoxy resin, a macroscopic experimental model of a silica/epoxy interface was designed and realized. It consisted in coplanar interdigitated electrodes deposited on a quartz substrate moulded in epoxy resin. The dielectric properties have been followed at 80°C and 80% relative humidity. These properties have been compared with the evolutions of sheets and mouldings of unfilled epoxy resin submitted to the same conditioning. Measurements evidenced the formation of an interphase at the quartz/resin interface which appeared precisely when the water reached the quartz after its diffusion through the resin. The water bound to the resin during the conditioning of the unfilled samples induced a drop of resistance of nearly 3 decades. In the same time, due to the interphase which has grown at the organic/mineral interface, the resistance between the interdigitated electrodes fell of five decades, i.e. two more decades. This interphase is characterized by a surface resistivity of 80.106 Ω. This data may be used to evaluate prebreakdown phenomena resulting from a hygrothermal aging of silica/epoxy insulations.

Identifying severity of electroporation through quantitative image analysis

Electroporation is the formation of reversible hydrophilic pores in the cell membrane under electric fields. Severity of electroporation is challenging to measure and quantify. An image analysis method is developed, and the initial results with a fabricated microfluidic device are reported. The microfluidic device contains integrated microchannels and coplanar interdigitated electrodes allowing low-voltage operation and low-power consumption. Noninvasive human buccal cell samples were specifically stained, and electroporation was induced. Captured image sequences were analyzed for pixel color ranges to quantify the severity of electroporation. The method can detect even a minor occurrence of electroporation and can perform comparative studies.