Electrical Measurement Techniques Research Articles

Label-free GaN HEMT-based biosensing platform for interferon-γ detection

Intracranial injury such as traumatic brain injury is caused by sudden injury to the brain from external mechanical force causing health loss and disability worldwide. The work reports the design and development of a GaN HEMT-based biosensor and system for the detection of IFN-γ for non-invasive detection of TBI. The developed platform can detect and differentiate IFN-γ with a peak sensitivity of 109.08 μA/pg/ml, high specificity, and good reproducibility. The platform offers good linearity with an LOD and LOQ of 6.82 fg/ml and 20.68 fg/ml respectively. The antibody-antigen binding has been confirmed with electrical and FTIR measurement techniques. A comparative analysis of system-level detection with on-chip measurement for validating the proposed readout interface shows a good match and thus confirms the system's suitability for the detection of IFN-γ in clinically relevant concentration ranges. The system level and on-chip measurement show a similar sensitivity of 21.59 μA/pg/ml and 19.05 μA/pg/ml respectively. The proposed platform offers a highly stable biofunctionalization protocol with high specificity and selectivity. Thus, the platform has a good potential for point-of-care system development suitable for on-field and clinical applications.

Investigation of Nondestructive and Noncontact Electrical Characterization of GaN Thin Film on ScAlMgO4 Substrate Using Terahertz Time‐Domain Spectroscopic Ellipsometry with Characteristic Impedance Analytical Model

Semiconductor evaluation methods frequently require sample processing and carry the risk of defects and property changes. Therefore, nondestructive and noncontact electrical property measurement techniques are necessary. Terahertz time‐domain spectroscopic ellipsometry (THz‐TDSE) can simultaneously estimate the electrical properties and film thickness of a sample. However, whether this method can simultaneously determine electrical properties and film thickness for semiconductor thin films of 1 μm or less remains unclear. This study uses THz‐TDSE to evaluate the electrical properties and film thickness of a GaN thin film (≈0.8 μm thick) on a ScAlMgO4 substrate. Using the conventional analysis based on Fresnel's formula (FR model), which is used in the field of optics, uniquely determining the electrical properties and film thickness is not possible owing to multiple optimal solutions. Therefore, a model combining the characteristic impedance model used in the radio‐wave region with the FR model is employed in the analysis. The obtained values of electrical properties of the GaN thin film evaluated using THz‐TDSE are consistent with those using Hall effect measurement. Moreover, the film thickness is consistent with that measured from the cross‐sectional transmission electron microscopy observation.

RF spectra induced by different polarized microwave

Electric field measurement techniques based on Rydberg atoms have proven to have unique advantages in high sensitivity and have drawn wide attention in microwave electric field metrology and communication. The Rydberg states employed for microwave sensing are usually excited by two- or three-step laser irradiation. It leads to the Rydberg atoms being populated by some specific magnetic quantum number states determined by the laser polarization configurations, whose further coupling to another Rydberg state is also constrained by the microwave polarization. Based on a three-laser optical excitation, we demonstrate this effect on the microwave spectra of the 85Rb transitions 41F7/2 → 42D5/2 and 41F7/2 → 41G7/2 at various combining polarization configurations. It shows a strong polarization dependence on the microwave spectrum and then affects the sensitivity of Rydberg atom-based microwave field sensing. Advisable polarization schemes for higher sensitivity are suggested by the two types of transitions.

Non-Destructive Evaluation of Thermal Aging in EPDM Rubber Using Electromagnetic Techniques.

This study investigates the use of eddy-current technology and impedance spectroscopy in sensing the change in rubber properties after it is exposed to accelerated thermal aging. The thermal aging process, by application of temperature and pressure over time, of ethylene propylene diene monomer (EPDM) rubbers containing both carbon black (CB) and graphene are investigated. Both eddy-current sensing and electrical impedance measurement techniques were used for electromagnetic analysis. Both methods measure the in- and out-of-phase responses as a function of excitation frequency at room temperature. The measurements were performed before and after the aging process. The electrical percolation threshold was detected in the rubber samples by varying the CB content from 0 to 40 wt%. In the rubber sample containing 30 wt% CB, 0-5 wt% of the CB was replaced with graphene flakes. The substitution of graphene for CB in the EPDM rubber formulation provided an enhanced eddy-current and electrical impedance response. The findings demonstrate the feasibility of employing electromagnetic analysis techniques to investigate the extent of aging.

Chemical Sensors using Single-Molecule Electrical Measurements.

Driven by the digitization and informatization of contemporary society, electrical sensors are developing toward minimal structure, intelligent function, and high detection resolution. Single-molecule electrical measurement techniques have been proven to be capable of label-free molecular recognition and detection, which opens a new strategy for the design of efficient single-molecule detection sensors. In this review, we outline the main advances and potentials of single-molecule electronics for qualitative identification and recognition assays at the single-molecule level. Strategies for single-molecule electro-sensing and its main applications are reviewed, mainly in the detection of ions, small molecules, oligomers, genetic materials, and proteins. This review summarizes the remaining challenges in the current development of single-molecule electrical sensing and presents some potential perspectives for this field.

Linear dynamic range of a Rydberg-atom microwave superheterodyne receiver

In recent years, electric field measurement techniques based on Rydberg atoms have shown unique advantages in high sensitivity and wideband applications and miniaturization. The Rydberg atom receiver senses the electromagnetic signal using the quantum coherence effect, which overcomes the inherent defects of traditional electronic receivers in terms of thermal noise, insertion loss of microwave devices, and the use of wavelength-dependent antennas, thus providing the Rydberg atomic receivers the potential to become the next generation of microwave receivers. For some particular application scenarios such as radar and communication, superheterodyne reception is a critical technical approach, and the linear dynamic range is an essential factor in evaluating the performance of the superheterodyne receivers. It is challenging to promote the Rydberg atomic receiver without figuring out the influence of system parameters on the linear dynamic range. This paper starts with the response mechanism of the Rydberg atomic superheterodyne receiver, and a theoretical model is established to simulate the atom-microwave responses. Then the harmonics' generation mechanism is discussed, and the atomic linear dynamic range under different probe light Rabi frequencies is studied further. Furthermore, a method to evaluate the antiblocking performance of the system is proposed. This work is expected to provide theoretical guidance for the design and performance optimization of the Rydberg atomic superheterodyne receiver.

Microflow cytometer chip with multiple electro-rotation units for measuring electrical properties of single yeast cells

At present, many single-cell electrical parameter measurement techniques have exhibit broad application prospects, but there are still some limitations such as complex single-cell operation and time-consuming measurement. This paper proposed a microflow cytometer chip with multiple electro-rotation units for measuring the electrical properties of single cells. The microdevice leverages three serial electro-rotation units to rapidly obtain rotation speeds under different signal frequencies. According to the rotation results, the electrical parameters (membrane permittivity and cytoplasmic conductivity) are estimated by using Maxwell's mixture equation fitting and neural network fitting methods respectively. We demonstrated the measurement advantages of combining microflow and electro-rotation techniques. Experimental results show that the cytometer measurement method greatly improves the throughput of single-cell characterization with a guaranteed error of less than 0.8%. The microdevice provides a microfluidic platform capable of characterizing the electrical properties of cells and the possibility of combining with neural networks.

Resonant electric probe to axionic dark matter

The oscillating light axion field is known as wave dark matter. We propose an LC (inductor-capacitor)-resonance enhanced detection of the narrow band electric signals induced by the axion dark matter using a solenoid magnet facility. We provide full 3D electromagnetic simulation results for the signal electric field. The electric signal is enhanced by the high $Q$-factor of a resonant LC circuit and then amplified and detected by the state-of-the-art cryogenic electrical transport measurement technique. The cryogenic amplifier noise is the dominant noise source in the proposed detection system. We estimate that the detection system can have a promising sensitivity to axion dark matter with mass below ${10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{eV}$. The projected sensitivities improve with the size of the magnetic field, and the electric signal measurement can be potentially sensitive to the quantum chromodynamics (QCD) axion with ${g}_{a\ensuremath{\gamma}}\ensuremath{\sim}{10}^{\ensuremath{-}16}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ around ${m}_{a}\ensuremath{\sim}{10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{eV}$, with a multimeter scale magnetized region. This limit is around five orders of magnitude below the current constraint from the cosmic rays.

Measurement technique of magnetic anisotropy field on patterned magnetic structures

We propose an electric measurement technique for the magnetic anisotropy field of ferromagnetic thin films and their tiny patterned structures, particularly, in the case of in-plane magnetic anisotropy. This technique measures the anomalous Hall resistance by sweeping the angle or strength of the external magnetic field. The magnetic anisotropy field can be determined explicitly from the linear dependence of the Hall resistance on the angle and strength of the external magnetic field. The present technique can be applied to both ferromagnetic thin films and their patterned magnetic structures with small volumes, overcoming the signal resolution limit of conventional techniques.

Quantitative study of tumor angiogenesis in three-dimensional matrigel barrier using electric impedance measurement technique

Tumor angiogenesis refers to the development of new blood vessels in tumors and is a vital indicator of cancer metastasis which is the major cause of cancer-related deaths. Study of tumor angiogenesis is critical for the development of potential therapeutic strategies of suppressing cancer metastasis. In the current work, a microfluidic device has been developed and was composed of 2 reservoirs connecting with a Matrigel-filled microchannel. The microchannel was mimicked as a biological barrier and embedded with measurement microelectrodes. New blood vessels were successfully induced to extend along the microchannel. Meanwhile, real-time impedance measurement was conducted to quantitatively monitor the tumor angiogenesis process. The results revealed the extension speed of new blood vessels was proportional to chemical induction level, i.e., VEGF165 concentration. Moreover, tumor angiogenesis was shown to be induced by the VEGF released from cancer cells and significantly correlated to the number of cancer cells. In addition, anti-VEGF suppressor was quantitatively evaluated to study the suppression efficacy of tumor angiogenesis. The current microfluidic device provides a promising tool to study tumor angiogenesis in 3D biological barrier. The impedance technique offers reliable and quantitative evidences for evaluating drug efficacy. Development of tumor angiogenesis analytical platform can potentially lead to develop novel therapeutic strategies of suppressing cancer metastasis.

Measurement of the low-frequency charge noise of bacteria

Bacteria meticulously regulate their intracellular ion concentrations and create ionic concentration gradients across the bacterial membrane. These ionic concentration gradients provide free energy for many cellular processes and are maintained by transmembrane transport. Given the physical dimensions of a bacterium and the stochasticity in transmembrane transport, intracellular ion concentrations and hence the charge state of a bacterium are bound to fluctuate. Here we investigate the charge noise of hundreds of nonmotile bacteria by combining electrical measurement techniques from condensed matter physics with microfluidics. In our experiments, bacteria in a microchannel generate charge density fluctuations in the embedding electrolyte due to random influx and efflux of ions. Detected as electrical resistance noise, these charge density fluctuations display a power spectral density proportional to 1/f^{2} for frequencies 0.05Hz≤f≤1Hz. Fits to a simple noise model suggest that the steady-state charge of a bacterium fluctuates by ±1.30×10^{6}e(e≈1.60×10^{-19}C), indicating that bacterial ion homeostasis is highly dynamic and dominated by strong charge noise. The rms charge noise can then be used to estimate the fluctuations in the membrane potential; however, the estimates are unreliable due to our limited understanding of the intracellular concentration gradients.

Charge transport in molecular junctions: General physical pictures, electrical measurement techniques, and their challenges

AbstractInvestigations on charge transport (CT) at a molecular scale are essential for both fundamental science and miniaturized electronic devices. A prototypical platform for studying CT through molecules is configured as electrode‐molecule‐electrode (EME). The quantum mechanical nature and microscopic interfacial interaction enrich the journey of the transporting charge through EME junctions, which have inspired many theoretical efforts into this interdisciplinary topic. In parallel, several experimental techniques have been developed to characterize EME CT properties. This mini‐review aims to provide general physical pictures for those new to this field to comprehend molecular‐scale CT. Prevalent experimental techniques termed break‐junctions are briefly reviewed, which are often corroborated with simple physical models to characterize CT through EME junctions. Challenges of these techniques and concerns over the use of simple models are also complied herein to facilitate the understanding of CT through various EME systems.

Silver-coated copper particles as a new raw material for manufacturing electrical contacts

Electrical contacts were prepared from copper, silver, and silver-coated copper (Cu@Ag) powders by cold-press and sintering. Then, they were used in an electrical circuit and evaluated their performance under AC (7 A, 6000 switchings) and DC (10 A, 20 A, 200 switchings) currents. The microstructure, phase structure, thermal stability, and electrical resistance of the contacts were studied using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), and two-point electrical resistance measurement techniques. Results showed that the electrical resistance of copper contacts after 6000 switchings under AC current reaches from the initial value of 0.1 to 0.7 Ω. However, the electrical resistance of the silver and Cu@Ag contacts remained unchanged close to 0.1 Ω under the same conditions. The electrical resistance of copper contacts under 10 A-DC current increased from 0.11 Ω to 18 kΩ after 200 switchings, while the electrical resistance of the air and argon-sintered Cu@Ag contactsafter 200 switchings in the same conditions increased from 0.11 to 0.14 and 0.18 Ω, respectively. Increasing the DC current from 10 to 20 A increased the final electrical resistance of the copper contact from 18 kΩ to 35 kΩ and increased the electrical resistance of the Cu@Ag contact (sintered in air) from 0.18 Ω to 0.93 Ω after 200 switchings. Increasing the DC current from 10 A to 20 A did not affect the electrical resistance of the Cu@Ag contact sintered in argon. The study of microstructure of the contacts showed that surface of the copper contact oxidizes and cavities and micro-cracks appear on it during switchings. The Cu@Ag contacts sintered in argon were more resistant against oxidation than other contacts under switching.

Are Liquid Metals Bulk Conductors?

Stretchable electronics have potential in wide-reaching applications including wearables, personal health monitoring, and soft robotics. Many recent advances in stretchable electronics leverage liquid metals, particularly eutectic gallium-indium (EGaIn). A variety of EGaIn electromechanical behaviors have been reported, ranging from bulk conductor responses to effectively strain-insensitive responses. However, numerous measurement techniques have been used throughout the literature, making it difficult to directly compare the various proposed formulations. Here, the electromechanical responses of EGaIn found in the literature is reviewed and pure EGaIn is investigated using three electrical resistance measurement techniques: four point probe, two point probe, and Wheatstone bridge. The results indicate substantial differences in measured electromechanical behavior between the three methods, which can largely be accounted for by correcting for a fixed offset corresponding to the resistances of various parts of the measurement circuits. Yet, even accounting for several of these sources of experimental error, the average relative change in resistance of EGaIn is found to be lower than that predicted by the commonly used bulk conductor assumption, referred to as Pouillet's law. Building upon recent theories proposed in the literature, possible explanations for the discrepancies are discussed. Finally, suggestions are provided on experimental design to enable reproducible and interpretable research.

Efficiency improvement of radial basis function meshless method in conjunction with bayesian theorem for electrical tomography of heterogeneous concrete

Electric potential measurement technique (tomography) has been presented as a non-destructive method to evaluate concrete's physical properties and durability. In this study, a radial basis function (RBF) meshless method combined with the Bayesian probabilistic theorem was proposed to solve Poisson's differential equation that simulates electric potential distribution for heterogeneous concrete with inclusion in 2D. Thus, prior information about shape coefficient (c) and electrical conductivity could contribute to problem-solving, leading to an accurate high-speed tomography. Two types of concrete mixes with significant differences in electrical conductivity were used to create heterogeneity in concrete. For this purpose, concrete samples with iron block inclusion in various locations were made. Probabilistic tomography was performed using optimized c and Bayes' method. Since c plays a significant role in RBF, different validation patterns were used to optimize it. Results showed that c is highly dependent on the validation pattern, injecting pair electrode, location of inclusions, and degree of uncertainty of concrete. Deterministic and probabilistic tomography was performed to detect the iron block inclusion. The experimental results showed that using various validation patterns, the proposed hybrid method of meshless and Bayesian theorem can eliminate the substantial physical uncertainty, and tomography can be performed with appropriate accuracy.

Electroforming free enhanced resistive switching in reduced graphene oxide films embedded with silver nanoparticles for nonvolatile memory applications

In this paper, the reduced graphene oxide (rGO)-based resistive random access memory (RRAM), embedded with Ag NPs, for nonvolatile memory applications has been investigated. The device exhibited enhanced I on/I off current ratio at lower switching voltage. The rGO-Ag thin film was deposited by spin-coating technique on an indium tin oxide coated glass substrate. Top contacts of aluminum (Al) were deposited by thermal evaporation technique for electrical measurements. The morphology of thin film has been characterized by scanning electron microscopy, and elemental quantification has been done using energy-dispersive x-ray spectroscopy. The structural and chemical analysis of thin film has been performed using x-ray diffraction (XRD) characterization and x-ray photoelectron spectroscopy, respectively. During applied potential, the device switches between two resistance states; low resistance state (LRS) and high resistance state (HRS). Initially when potential is applied across the device, the deposited thin film (rGO-Ag) was found in LRS which did not require initial forming voltage to activate the device. The requirement of this forming voltage may induce severe mechanical and electrical stress in the device and degrades the device performance. The rGO-Ag-based RRAM devices required (<1 V) to switch from LRS to HRS or vice versa with a large (∼103) on/off current ratio. The electrical stability of the devices has been tested for 4 × 103 s and repeatability for >60 cycles, which did not exhibit too much degradation. In rGO-Ag thin film-based RRAM devices, Ag NPs act as charge trapping sites, which results in enhanced switching characteristics. The trapping and detrapping mechanism of charges by Ag NPs is responsible for the enhanced switching characteristics in these films.

(Invited) Probing Charge-Carrier Transport in Chemically Doped Polymeric Semiconductors

With organic semiconductors demonstrating potential for use in various electronic and optoelectronic applications, some attention has turned to an understanding of charge-carrier doping and transport processes in such material systems. Here we demonstrate a novel electrical transport measurement technique, based on microwave spectroscopy, to probe redox-based chemical p-type doping in conjugated semiconducting polymers. Through a comparison of these measurements with macroscopic charge-transport probes, we illustrate that charge injection from a prototypical dopant like 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) initially results in charge-carriers that are bound to the reduced F4-TCNQ counterion, but that the coulomb attraction can be overcome by doping to high charge-carrier concentrations. In contrast, a series of novel charge-transfer dopants based on dodecaborane clusters appended with various organic moieties results in injected charge-carriers that are spatially separated from the counterion. This behavior results from the unique chemical and electronic structure of these dopants, which localizes the negative counter-charge on the center of the dodecaborane cluster, thereby reducing the coulomb attraction for all measurable charge-carrier concentrations and resulting in enhanced charge-carrier transport. These observations point to chemical control over the charge-injection and transport processes that can yield highly doped organic semiconductors with impressive electrical transport properties, in spite of the limitations that their low dielectric constants would suggest.

Disposable capacitive electrical droplet measurement (DisC-EDM) based on a film-chip technique

For droplet-based microfluidics, a simple and easy-to-use method to measure the size and number of droplets in real-time is required to generate droplets with high uniformity, stability, and throughput. This study introduces a disposable capacitive electrical droplet measurement (DisC-EDM) technique that consists of a disposable microchannel superstrate and a reusable sensing substrate, which can be assembled and disassembled by vacuum pressure. Because the disposable microchannel superstrates can be fabricated easily and cost-effectively with an ultrathin polymer film, it can be replaced after a single use to prevent biological contamination and can also be used to detect the droplet size with a high sensitivity. Meanwhile, the sensing substrate can be continuously reused to achieve cost reduction and ease of use. Owing to three interdigitated electrode configurations, the amplitude of the output signal is linearly proportional to the size of the droplets. Consequently, the need for a complex calculation algorithm or expensive equipment to determine the droplet size is eliminated. Furthermore, because the sensing principle of the DisC-EDM is based on a capacitive detection method, its sensitivity remains constant, even for changes in the conductivity and velocity of the droplets. To demonstrate the effectiveness of the DisC-EDM, it was used to evaluate and compare the performance of a pressure-driven pump and a screw-driven syringe pump in droplet generation. As a cost-effective, reliable, and easy-to-use technique, the DisC-EDM can be used to control the size and uniformity of the droplets in a variety of droplet-based applications.

SYNTHESIS AND CHARACTERIZATION STUDY OF HGXCR2-X S4 COMPOSITE THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION TECHNIQUE

The ternary thin films of composite HgxCr2-xS4 (x = 0.6) have been deposited by simple chemical bath deposition (CBD) technique on glass substrate. The thin films have been deposited at optimized conditions pH at 10 0.1, bath temperature 650C, deposition time 120 minutes. The films were uniform and adherent to glass substrates. They were characterized by structural, optical, and electrical measurement techniques. According to their X-ray diffraction patterns HgxCr2-xS4(x = 0.6) films are crystalline with band gap of 2.4 eV. Scanning electron micrographs showed that the substrates were well covered with films no cracks or pinholes were observed. The electrical resistivity of the films is found to be 1.3703 x 103 Ω-cm to 2.1243 x 103 Ω-cm at temperature range 3030k to 4230K. According to thermoelectric power measurements HgxCr2-xS4(x = 0.6) thin films are of n-type nature.

Optically detected spin–orbit torque ferromagnetic resonance in an in-plane magnetized ellipse

Time-resolved scanning Kerr microscopy has been used to perform optically detected, phase-resolved spin–orbit torque ferromagnetic resonance (SOT-FMR) measurements on a microscale CoFeB ellipse at the center of a Pt Hall cross subject to RF and DC current. Time-resolved polar Kerr images revealed localized dynamics with large amplitude at the center and weaker amplitude at the edges. Therefore, field swept SOT-FMR spectra were acquired from the so-called center mode to probe the SOTs active at the center of the ellipse, thus minimizing non-uniform edge contributions. When the magnetic field was applied at 30° from the hard axis of the ellipse and a DC current was applied, a marked asymmetry was observed in the amplitude and linewidth of the FMR peaks as the applied field was reversed. Both absorptive and dispersive parts of the spectra were in good agreement with a macrospin calculation. The damping parameter (α) and the Slonczewski torque parameter were determined to be 0.025 and (6.75 ± 0.75) × 10−7 Oe A−1 cm2, respectively. The hard axis SOT-FMR linewidth was found to be almost independent of the DC current value, suggesting that the SOT has a minimal influence in the hard axis configuration and that thermal effects were insignificant. This study paves the way for spatially resolved measurements of SOT probed using localized modes of microscale devices that go beyond the spatially averaged capability of electrical measurement techniques.