Coplanar Electrodes Research Articles

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).

Self-heating controlled current–voltage and noise characteristics in graphene

Pulsed current–voltage characteristics have been measured for epitaxial SiC graphene under controlled lattice temperature conditions. The monolayer and AB stacked bilayer graphene is dry transferred on SiO2. The measured characteristics of two-terminal samples with coplanar electrodes demonstrate non-ohmic behaviour up to intermediate-high fields. At high currents thermal effects come into play and soft damage of the samples takes place. Bilayer graphene samples withstand 20 kV cm−1 electric field when few nanosecond voltages pulses are applied. The results are treated in terms of hole drift velocity estimated from the data on current under the assumption of uniform electric field and constant hole density. The highest velocity of ∼3.5–5 × 106 cm s−1 (∼1.5 × 107 cm s−1) is estimated for the bilayer (monolayer) graphene. The velocity results are interpreted with hot phonons. High frequency noise is measured at 10 GHz for the monolayer graphene and the associated shot noise is resolved.

Dendritic structures by glass electrolysis: Studies and SERS capability

We have grown silver dendrites by electrolysis of silver-to-sodium ion-exchanged silicate glass slides. The DC voltage of 150 and 300 V was applied to thin film coplanar electrodes deposited on the slide surface. Exposing the silver structures with weak etchant resulted in some increase in optical absorption and in the essential enhancement of Raman scattering, by the factor of ~106-107. The solid state nature of the glass-dendrite system provided stability of the formed structures, and the prepared SERS substrates did not require special conditions for storage, but a short etching before use.

Breakdown Behavior of GaAs PCSS with a Backside-Light-Triggered Coplanar Electrode Structure

The competitive relationship between the surface flashover of the coplanar electrodes and the body current channel was investigated. Breakdown behavior of GaAs photo-conductive semiconductor switch (PCSS) with a backside-light-receiving coplanar electrode structure was studied in this paper. GaAs PCSS was triggered by the laser pulse with an extrinsic absorption wavelength of 1064 nm. Special insulating construction was designed for GaAs PCSS, while the surface of the electrodes was encapsulated with transparent insulating adhesive. Our first set of experiments was at a bias voltage of 8 kV, and the surface flashover breakdown of GaAs PCSS was observed with 10 Hz triggering laser pulse. In the second experiment, at a bias voltage of 6 kV, the body current channel breakdown appeared on the backside of the GaAs PCSS. Compared with these results, the existence of a competitive relationship between the surface flashover breakdown and the body current channel breakdown of the GaAs PCSS was confirmed. When the bias voltage is set within a certain range (just reaching avalanche mode), GaAs PCSS with a backside-light-receiving coplanar electrode structure will undergo the body current channel breakdown. This finding is also consistent with the simulation results.

Coplanar electrode directly modulated lasers with different cavity length

AbstractA ridge‐waveguide (RW) directly modulated laser (DML) with a coplanar electrode structure is proposed and measured in this paper. Since utilizing the coplanar electrode can significantly reduce parasitic capacitance, the frequency responses of DMLs exhibit a quite low roll‐off. Shortening the cavity length L is attractive to enhance the high‐speed performance of DMLs, but it will increase the mirror loss and the chip resistance at the same time. We analyzed the static and dynamic characteristics of 200‐μm, 250‐μm, and 300‐μm lasers experimentally and theoretically to investigate the impact of L on the coplanar‐electrode DML. Shortening the cavity length can improve the relaxation oscillation frequency fr effectively. The 200‐μm DML achieves a bandwidth of 15.3 GHz. The fr is the most important limiting factor for the laser to obtain a wide bandwidth. Decreasing L and increasing the differential gain are promising for the further improvement of fr. However, shortening L causes a more severe thermal effect and the deterioration of the linearity. This trade‐off must be considered in the future study.

Three-phase electric power driven electroluminescent devices

Current power supply networks across the world are mostly based on three-phase electrical systems as an efficient and economical way for generation, transmission and distribution of electricity. Now, many electrically driven devices are relying on direct current or single-phase alternating current power supply that complicates utilization of three-phase power supply by requiring additional elements and costly switching mechanisms in the circuits. For example, light-emitting devices, which are now widely used for displays, solid-state lighting etc. typically operate with direct current power sources, although single-phase alternating current driven light-emitting devices have also gained significant attention in the recent years. Yet, light-emitting devices directly driven by a three-phase electric power has never been reported before. Benefiting from our precious work on coplanar electrodes structured light-emitting devices, in this article we demonstrate proof of a concept that light-emitting components can be driven by three-phase electric power without utilizing intricate back-end circuits and can compose state detection sensors and pixel units in a single device inspiring from three primary colors. Here we report a three-phase electric power driven electroluminescent devices fabricated featuring of flexibility and multi-functions. The design consists of three coplanar electrodes with dielectric layer(s) and light emission layer(s) coated on a top of input electrodes. It does not require transparent electrodes for electrical input and the light emission occurs when the top light-emitting layers are connected through a polar bridge. We demonstrate some applications of our three-phase electric power driven electroluminescent devices to realize pixel units, interactive rewritable displays and optical-output sensors. Furthermore, we also demonstrate the applicability of three-phase electrical power source to drive organic light-emitting devices with red, green and blue-emitting pixels and have shown high luminance (up to 6601 cd/m2) and current efficiency (up to 16.2 cd/A) from fabricated three-phase organic light-emitting devices. This novel geometry and driving method for electroluminescent devices is scalable and can be utilized even in a wider range of other types of light-emitting devices and special units.

An enzyme-free capacitive glucose sensor based on dual-network glucose-responsive hydrogel and coplanar electrode.

Glucose sensors are vital devices for blood glucose detection in the diabetes care. Different from traditional electrochemical devices based on glucose oxidase, the glucose sensor based on the glucose-responsive hydrogel is more robust owing to its enzyme-free principle. However, integrating the high sensitivity, fast response, wide measuring range and low-cost fabrication into a hydrogel sensor is still challenging. In this study, we present a physical capacitive sensor, which consists of interdigital carbon electrodes (ICEs) fabricated by a direct laser writing technology and glucose-responsive hydrogel (DexG-Con A hydrogel) built by UV curing in situ. The dielectric property of DexG-Con A hydrogel changes accordingly with the change in environmental glucose concentration. Experimental results demonstrate that in a glucose concentration range of 0-30 mM, the proposed hydrogel sensor is capable of measuring the glucose level in a repeatable and reversible manner, showing a short responsive time of less than 2 min and a high sensitivity of 8.81 pF mM-1 at a glucose range of 0-6 mM. Owing to its simple fabrication process, low-cost and high performance, the proposed glucose sensor shows great potential on batch production for continuous glucose monitoring application.

Light confinement in liquid crystals for optofluidic integrated microsystems -INVITED

In this paper technology to make optical waveguides and microfluidic channels integrated on the same substrate will be reported to envisage novel micro-optofluidic chips. PolyDiMethylSiloxane (PDMS) is used to make microchannels to be filled with biological solutions. Liquid crystals (LC) are used to confine light to produce optical interaction with biological fluidic specimen. Optical waveguides base on PDMS channels filled with LC, named LC:PDMS waveguides, including both straight and bending channels are reported to design photonic devices. Electro-optic effect of LC allows to make tuneable optical waveguides to reconfigure the entire optofluidic microsystem which can include gold nanoparticles for photo-thermal therapies. Coplanar gold electrodes can switch LC molecules with applied voltage of about 2 V. Such electrode configuration can be used to make optical switches and wavelengths demultiplexers. A zero-gap directional coupler based on LC:PDMS waveguides has been designed to switch light from one waveguide to another with an extinction ratio of 16 dB by applying a voltage of just 1.62 V. A multimode interference demultiplexer has been also designed to demultiplex wavelengths at 980 nm and 1550 nm in two output waveguides with an extinction ratio better than 11 dB by applying about 7 V.

Analysis of augmented droplet transport during electrowetting over triangular coplanar electrode array

The improvements in the dynamic performance of droplet movement over a newly designed and fabricated triangular coplanar electrode system utilizing the principle of electrowetting on dielectric (EWOD) is extensively probed and compared with results available in the literature. The process is further explored by developing a model, taking into account the pertinent driving and retarding forces, the role of the effective contact line length and an in-situ evaluation of the contact line friction coefficient. Furthermore, the efficiency of the fabricated digital microfluidic platform is quantified and compared in terms of driving force and velocities.

Numerical study and Taguchi optimization of fluid mixing by a microheater-modulated alternating current electrothermal flow in a Y-shape microchannel

This paper presents the numerical analysis and Taguchi optimization of fluid mixing by alternating current electrothermal flow (ACET) in a Y-shape microchannel. In the numerical study, ACET is simulated through the interaction of a non-uniform electric field provided through co-planar electrodes and the temperature gradients produced by a micro-heater. To achieve the efficient ACET mixing of fluids, a parametric study of various factors affecting the structure and strength of ACET is first performed and then, a detailed physical interpretation of the results is presented. The factors include the applied electric potential, the location, size, and heating intensity of a micro-heater, the inlet velocity ratio of fluids mixed, and the cross-sectional aspect ratio of a Y-shape microchannel. Optimum condition of the factors is determined using the Taguchi method to maximize the fluid mixing by ACET. Results show that the ACET-based mixing is affected, in order of importance, by the inlet velocity ratio of fluids, the applied electric potential, the cross-sectional aspect ratio of a Y-shape microchannel, and the location, heating intensity, and size of a micro-heater. Under the optimum condition of the factors, a high mixing efficiency of 90.4 % is achieved in the microchannel. The ACET mixing at the optimum condition is experimentally verified by fabricating micro-mixers and confirming the concentration change of fluids introduced into the mixers. These results provide valuable engineering insights into the design and development of not only ACET-based microfluidic devices including a micro-mixer but also lab-on-a-chip systems for bioassay where the devices are integrated.

Experimental Study of Argon and Helium Dielectric Barrier Discharge with Coplanar Electrodes at Intermediate Pressure for Reducing Radar Cross Section

Experimental Study of Argon and Helium Dielectric Barrier Discharge with Coplanar Electrodes at Intermediate Pressure for Reducing Radar Cross Section

Coplanar Electrode Polymer Modulators Incorporating Fluorinated Polyimide Backbone Electro-Optic Polymer

High-speed coherent optical communication has been expanding to handle the ever-increasing data traffic, and the large modulation bandwidth of electro-optic (EO) polymer modulators has been especially appreciated. However, to be useful in optical communication, the EO polymer device should address several issues, such as thermal stability, photo-oxidation, and bias drift. In this work, as a part of the experiments to address these challenges, an EO polymer with a fluorinated polyimide backbone is utilized to create EO polymer modulators with improved thermal stability. A coplanar electrode structure is introduced to enhance the poling efficiency and reduce the bias drift.

In-Plane Amorphous Oxide Ionotronic Devices and Circuits with Photochemically Enabled Favorable Interfaces.

Here, we demonstrate a side-gated in-plane structure of solution-processed amorphous oxide semiconductor ionotronic devices and logic circuits enabled by ion gel gate dielectrics with a monolithically integrated nanoscale passivation architecture. The large capacitance of the electric double layer (EDL) in the ion gel allows a device structure to be a side gate geometry, forming an in-plane structured amorphous In-Ga-Zn-O (a-IGZO) ionotronic transistor, which can be translated into a simplified logic gate configuration with a low operation voltage. Particularly, the monolithic passivation of the coplanar electrodes offers advantages over conventional inhomogeneous passivation, mitigating unintentional parasitic leakage current through the ion gel dielectric layer. More importantly, the monolithically integrated passivation over electrodes was readily obtained with a complementary metal-oxide semiconductor-compatible photochemical process by employing a controlled ultraviolet light manipulation under ozone ambient, which introduced not only much enhanced electrical characteristics but also a scalable device architecture. We investigated various electrical behaviors of the side-gated a-IGZO ionotronic transistor based on EDL, which is called an electric double layer transistor (EDLT), and logic circuits enabled by photochemically realized monolithic aluminum oxide (AlOX) passivation comparing to the native or polymerized passivation layer, which reveals that the photoassisted AlOX secures high-performance a-IGZO EDLTs with a low off current (<5.23 × 10-8 A), high on/off ratio (>1.87 × 105), and exceptional high carrier mobility (>14.5 cm2 V-1 s-1). Owing to the significantly improved electrical characteristics, an inverter circuit was successfully achieved with broad operation voltages from an ultralow VDD of 1 mV to 1.5 V, showing a fully logical voltage transfer characteristic with a gain of more than 4 V V-1.

PSA detection using label free graphene FET with coplanar electrodes based microfluidic point of care diagnostic device

Affordable point-of-care (PoC) diagnostic devices enable detection of prostate specific antigen (PSA) in resource limited settings. Despite the advancements in PoC systems, most of the reported methods for PSA detection have unsatisfactory detection limits and are based on labelled assays, requiring multiple reagent flow steps which increases both expenses and inconvenience. Circumventing these constraints, we report here the development and validation of a label free, affordable dielectrophoresis (DEP) based graphene field effect transistor (FET) sensor implemented using coplanar electrodes and integrated uniquely with a compact disc based microfluidic platform along with electronics readout for the estimation of PSA at the point of care. Design of coplanar gate electrode which has not been explored earlier is not a straightforward approach. In fact, it has been observed that there is a non-monotonic dependence of the capture of PSA molecules in the channel region of the FET with varying widths and spacings of the gate electrode. The graphene FET based PoC device with optimized coplanar gate electrode is the only label free analytical system for PSA detection requiring simple operation and achieving a detection limit of 1 pg/ml in serum with a wide dynamic range upto 4 ng/ml and appreciable selectivity against potential interferents like bovine serum albumin (BSA) and human immunoglobulin G (IgG). Further, it has been validated satisfactorily with commercially available existing systems using human serum samples. Moreover, the proposed sensing system lowers the detection limit by three orders of magnitude compared to a recent study on label free PoC device on other cancer biomarkers.

Metal–Semiconductor–Metal Thin‐Film X‐Ray Detector Based on Halide Perovskites

Halide perovskite materials as emerging optoelectronic materials are very appealing for the X‐ray detection due to their superior charge transport, high‐absorption cross section for X‐rays and solution processability. Herein, thin‐film X‐ray detectors are demonstrated using methylammonium lead iodide perovskite (MAPbI3) thin films. Controlled nucleation of halide perovskites is realized using patterned Au dots as nucleation promoters, resulting in uniform thin films with large grains. A metal–semiconductor–metal (MSM) device architecture with coplanar electrodes is used, and the thin‐film detectors with an active layer thickness of 700 nm exhibit a sensitivity of 2.48 × 10−2 μC Gyair−1 cm−2 under a bias of 10 V. The device is relatively stable in air without encapsulation, showing no degradation after 15 min continuous biasing at 5 V. Such solution‐based perovskite detector can enable X‐ray detecting and imaging with low‐cost, high efficiency, and high sensitivity.

Low-cost capacitive sensor for detecting palm-wood moisture content in real-time

sIn this study, we analyze a non-invasive and low-cost wood moisture meter by means of a capacitive detection circuit. The process of the design and development of an oil-palm-wood moisture meter is described. As part of the study, two electrode structures, i.e., parallel-plate and coplanar electrodes, are tested. The capacitive detection circuit includes a square-wave-generator circuit, low-pass filter circuit, and signal-conditioning circuit. The frequencies of the square-wave excitation signal are in the range of 200 kHz and are analyzed via a microcontroller to interpret the percentage of oil-palm-wood moisture content. The applicability of the capacitive moisture measurement is investigated under various moisture conditions of the oil palm wood i.e., 5%–20%. The experimental results show that the measurement accuracy of the detection circuit is high, with an acceptable measurement error.

New Schottky-Type Wire-Based Solar Cell with NiSix Nanowire Contacts.

Solar cells built with arrays of semiconductor wires have been studied for several years. They present some potential advantages over their bulk counterparts, such as (much) less use of semiconductor material, as well as improved light absorption properties. Most wire-based solar cells are fabricated with arrays of semiconductor p-n junctions, either radial or axial. Here, using a newly developed random connection process based on nickel silicide nanowires, we have built Schottky-type solar cells on interdigitated base and emitter coplanar electrodes that reach an efficiency of 6.5% when only 64% of the footprint area of the device is covered with p-type Si wire light-absorbers. To the best of our knowledge, this is the best efficiency reported so far for a Schottky-type wire-based solar cell; a simple extrapolation of the surface area suggests that an efficiency of more than 10% can be reached, which is comparable to that of single-junction hydrogenated amorphous Si cells. We also compare the Schottky-type cell with a "control" p-i-n one using the same device layout and the same nickel silicide nanowire random connection process: the efficiency of the p-i-n cell is higher (∼8%) but this is due to a higher VOC, the short-circuit current density (ISC) being very similar in both cases, close to 20 mA/cm2. The maximum temperature reached throughout the fabrication process of the cells (whether Schottky-type or p-i-n) is 550 °C, corresponding to the growth of the crystalline Si wires. Altogether, the results presented here hold promises toward cheap photovoltaics based on the use of randomly organized and randomly connected Si wire arrays.

One Cell, One Drop, One Click: Hybrid Microfluidics for Mammalian Single Cell Isolation

Generating a stable knockout cell line is a complex process that can take several months to complete. In this work, a microfluidic method that is capable of isolating single cells in droplets, selecting successful edited clones, and expansion of these isoclones is introduced. Using a hybrid microfluidics method, droplets in channels can be individually addressed using a co-planar electrode system. In the hybrid microfluidics device, it is shown that single cells can be trapped and subsequently encapsulate them on demand into pL-sized droplets. Furthermore, droplets containing single cells are either released, kept in the traps, or merged with other droplets by the application of an electric potential to the electrodes that is actuated through an in-house user interface. This high precision control is used to successfully sort and recover single isoclones to establish monoclonal cell lines, which is demonstrated with a heterozygous NCI-H1299 lung squamous cell population resulting from loss-of-function eGFP and RAF1 gene knockout transfections.

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.

Plasmonic-enhanced light emission from a waveguide-integrated tunnel junction

Light emission from inelastic electron tunneling has been demonstrated for 40 years. The ultrafast response rate and the ultracompact footprint make it promising for high-speed miniaturized light sources. But the application of the tunnel junction is limited by extremely low external quantum efficiency due to the low proportion of inelastic tunneling electron and wave vector mismatch between surface plasmons and photon emission. Here, we present a plasmonic-enhanced metal-insulator-semiconductor (MIS) junction coupled to a silicon waveguide with a coplanar electrode connected to a nanoantenna. The proposed tunnel junction can be fabricated using existing semiconductor planar processes to achieve controllable barrier thickness and quality for vertical current injection. Finally, an electrically driven light source with a radiation power nearly 8000 times higher than the spontaneous emission power in free space is shown to be achievable with the new structure at an operating wavelength of 1.31 µm. It is 510-fold higher than that of typical planar MIS junctions.