Large Resistance Change Research Articles

A piezoresistive dielectric elastomer switch consisting of inkjet-printed carbon black

The piezoresistive effect is a key physical property utilized in soft and stretchable electronics, functioning as intrinsic electromechanical sensors. However, most conventional piezoresistive sensors can only passively measure and quantify external stimuli. To address these limitations, this work integrates an inkjet-printed piezoresistive pattern and a dielectric elastomer actuator (DEA) into a single monolithic dielectric elastomer film, creating a dielectric elastomer switch (DES). This DES can realize dramatic resistance changes along with DEA actuation, leveraging DEA-driven piezoresistivity for active and effective circuit control and signal processing. Theoretically, the DES operates by exhibiting resistance change through the periodic compression induced by DEA actuation. Experimentally, the piezoresistive pattern and the DEA electrodes were fabricated on an acrylic dielectric elastomer (VHB) using inkjet-printed piezoresistive carbon black (CB) and manually brushed conductive grease, respectively. The optimized DES demonstrated approximately 3.77 (±0.11) orders of magnitude in resistance change at a DEA frequency of 0.1 Hz. Compared to previously reported methods (smearing and stamping), inkjet-printed CB patterns showed significant improvements. These included negligible Joule heating impact, precise digital fabrication control, larger resistance change (up to 3.77 orders of magnitude), faster response speeds to DEA actuation (∼0.25 s for 3 orders of magnitude in resistance change), and greater durability (operating at 0.5 Hz for 112 min). Scanning electron microscopy (SEM) characterization revealed that these improvements were attributed to a more uniform distribution of conductive “CB islands” and appropriate non-conductive gap size among them. For demonstrating the applications of DES, it was employed for LED control, DEA-based soft gripper control, and as a multiplexer for signal processing.

Iterative Decomposition Algorithm for Electrical Impedance Tomography to Image Large Resistivity Changes

Iterative Decomposition Algorithm for Electrical Impedance Tomography to Image Large Resistivity Changes

Ultrathin WO3 Nanosheets/Pd with Strong Metal-Support Interactions for Highly Sensitive and Selective Detection of Mustard-Gas Simulants.

Exposure to mustard gas can cause damage or death to human beings, depending on the concentration and duration. Thus, developing high-performance mustard-gas sensors is highly needed for early warning. Herein, ultrathin WO3 nanosheet-supported Pd nanoparticles hybrids (WO3 NSs/Pd) are prepared as chemiresistive sulfur mustard simulant (e.g., 2-chloroethyl ethyl sulfide, 2-CEES) gas sensors. As a result, the optimal WO3 NSs/Pd-2 (2 wt % of Pd)-based sensor exhibits a high response of 8.5 and a rapid response/recovery time of 9/92 s toward 700 ppb 2-CEES at 260 °C. The detection limit could be as low as 15 ppb with a response of 1.4. Moreover, WO3 NSs/Pd-2 shows good repeatability, 30-day operating stability, and good selectivity. In WO3 NSs/Pd-2, ultrathin WO3 NSs are rich in oxygen vacancies, offer more sites to adsorb oxygen species, and make their size close to or even within the thickness of the so-called electron depletion layer, thus inducing a large resistance change (response). Moreover, strong metal-support interactions (SMSIs) between WO3 NSs and Pd nanoparticles enhance the catalytic redox reaction performance, thereby achieving a superior sensing performance toward 2-CEES. These findings in this work provide a new approach to optimize the sensing performance of a chemiresistive sensor by constructing SMSIs in ultrathin metal oxides.

NbC thin films via reactive DC sputtering in a CH4/Ar atmosphere

We have demonstrated the growth of NbC-Amorphous C films that manifest a well-known nanocomposite structure (Klages and Memming, 1990; Nedfors et al., 2011; Sala et al., 2021). The films were deposited using reactive DC sputtering in a CH4/Ar atmosphere using an insulating substrate near room temperature. A metallic Nb sputtering target was sputtered in an argon/CH4 atmosphere with a pressure range of 5.9 to 8.5 mTorr as the CH4 flow was also varied. Crystalline NbC films were deposited at room temperature at the lowest CH4 flow rate. The films exhibited ohmic electrical response at room temperature. The DC electrical resistivity scaled almost 4 orders of magnitude from 4.39 × 10−4 Ω-cm to 1.08 × 10−1 Ω-cm through changes in CH4 flow rates and the resultant C content of the films. The large variation in resistivity cannot be attributed to the changes in sample composition, e.g. volumetric mixing. It is postulated from XRD and TEM results that the large change in resistivity is due to the decreasing NbC crystallite size with increasing CH4. This leads to additional three-dimensional nanoscale intragranular interfaces and results in increased resistivity. X-ray reflectivity measurements were conducted, and the modelled film density was found to match the expected density for the film compositions as measured using X-ray photoelectron spectroscopy. Elastic recoil detection analysis (ERDA) was used to quantify H content of the films. The H content increased from 5.5 to 22 atomic percent with corresponding increase in CH4 flow. Transmission electron microscopy utilizing precession electron diffraction (PED) was conducted and showed a strong dependence of crystallinity on CH4 flow. A multilayer layer sample with varying CH4 flowrates was examined with TEM and showed that films were amorphous in nature for flow rates above 10 SCCM CH4; in agreement with XRD results.

Modulation of insulator metal transition of VO₂ films grown on Al2O3 (001) and TiO2 (001) substrates by the crystallization of capping Ge2Sb2Te5 layer

We demonstrate modulation of insulator metal transition (IMT) of VO2 films grown on single crystalline substrates through the effect of in-plane compression with crystallization of capping chalcogenide layer on the targeted VO2 films. Chalcogenide germanium–antimony–telluride (Ge2Sb2Te5: GST), which shows large volume reduction of 6.8% with its phase change from amorphous to crystal, was deposited on VO2 films grown on Al2O3 (001) and TiO2 (001) substrates, where V–V atoms along the cR-axis in the tetragonal VO2 phase align parallel and perpendicular to the substrate surfaces, respectively. As a result, counter shifts in temperature-dependence of resistance characteristics, to lower and higher directions, were observed for VO2 films on Al2O3 (001) and TiO2 (001), consistent with the lattice modulation of VO2 films by the in-plane compression introduced by GST crystallization. The obtained results open a way to realize large resistance change of IMT under constant temperature by controlling GST phases.

Practical Considerations for Laser-Induced Graphene Pressure Sensors Used in Marine Applications.

Small, low-power, and inexpensive marine depth sensors are of interest for a myriad of applications from maritime security to environmental monitoring. Recently, laser-induced graphene (LIG) piezoresistive pressure sensors have been proposed given their rapid fabrication and large dynamic range. In this work, the practicality of LIG integration into fieldable deep ocean (1 km) depth sensors in bulk is explored. Initially, a design of experiments (DOEs) approach evaluated laser engraver fabrication parameters such as line length, line width, laser speed, and laser power on resultant resistances of LIG traces. Next, uniaxial compression and thermal testing at relevant ocean pressures up to 10.3 MPa and temperatures between 0 and 25 °C evaluated the piezoresistive response of replicate sensors and determined the individual characterization of each, which is necessary. Additionally, bare LIG sensors showed larger resistance changes with temperature (ΔR ≈ 30 kΩ) than pressure (ΔR ≈ 1-15 kΩ), indicating that conformal coatings are required to both thermally insulate and electrically isolate traces from surrounding seawater. Sensors encapsulated with two dip-coated layers of 5 wt% polydimethylsiloxane (PDMS) silicone and submerged in water baths from 0 to 25 °C showed significant thermal dampening (ΔR ≈ 0.3 kΩ), indicating a path forward for the continued development of LIG/PDMS composite structures. This work presents both the promises and limitations of LIG piezoresistive depth sensors and recommends further research to validate this platform for global deployment.

Resistive switching localization by selective focused ion beam irradiation

Materials displaying resistive switching have emerged as promising candidates for implementation as components for neuromorphic computing. Under an applied electric field, certain resistive switching materials undergo an insulator-to-metal transition through the formation of a percolating filament, resulting in large resistance changes. The location and shape of these filaments are strongly influenced by hard-to-control parameters, such as grain boundaries or intrinsic defects, making the switching process susceptible to cycle-to-cycle and device-to-device variation. Using focused Ga+ ion beam irradiation, we selectively engineer defects in VO2 and V2O3 thin films as a case study to control filament formation. Using defect pre-patterning, we can control the position and shape of metallic filaments and reduce the switching power significantly. A greater than three orders of magnitude reduction of switching power was observed in V2O3, and a less than one order of magnitude reduction was observed in VO2. These experiments indicate that selective ion irradiation could be applied to a variety of materials exhibiting resistive switching and could serve as a useful tool for designing scalable, energy efficient circuits for neuromorphic computing.

Pressure Mapping With Piezoresistive Sensor on Oxide TFTs Backplane

We report a pixel circuit with a piezoresistive sensor using amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) backplane for large-area pressure mapping. The proposed pixel circuit consists of TFTs, piezoresistive sensor, and a capacitor. The pressure sensor shows a large resistance change between 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> ohm. The RC charging time to the capacitance can be modulated by pressure-dependent resistance within pre-charging period for sensing. The pressure sensor array has a resolution of 0.625 mm, rising and falling times of 40 μs and 10 μs, respectively. The output voltage is between 0.15 V (zero pressure) and 1 V (2 kPa) without an external amplifier. We demonstrate the pressure mapping over 32 x 32 active-matrix pressure sensor array.

Tissue Resistance Decrease during Irreversible Electroporation of Pancreatic Cancer as a Biomarker for the Adaptive Immune Response and Survival

PurposeTo correlate irreversible electroporation (IRE) procedural resistance changes with survival outcomes and the IRE-induced systemic immune response in patients with locally advanced pancreatic cancer (LAPC). Materials and MethodsData on IRE procedural tissue resistance (R) features and survival outcomes were collected from patients with LAPC treated within the context of 2 prospective clinical trials in a single tertiary center. Preprocedural and postprocedural peripheral blood samples were prospectively collected for immune monitoring. The change (ie, decrease) in R during the first 10 test pulses (ΔR10p) and during the total procedure (ΔRtotal) were calculated. Patients were divided in 2 groups on the basis of the median change in R (large ΔR vs small ΔR) and compared for differences in overall survival (OS) and progression-free survival and immune cell subsets. ResultsA total of 54 patients were included; of these, 20 underwent immune monitoring. Linear regression modeling showed that the first 10 test pulses reflected the change in tissue resistance during the total procedure appropriately (P < .001; R2 = 0.91). A large change in tissue resistance significantly correlated with a better OS (P = .026) and longer time to disease progression (P = .045). Furthermore, a large change in tissue resistance was associated with CD8+ T cell activation through significant upregulation of Ki-67+ (P = .02) and PD-1+ (P = .047). Additionally, this subgroup demonstrated significantly increased expression of CD80 on conventional dendritic cells (cDC1; P = .027) and PD-L1 on immunosuppressive myeloid-derived suppressor cells (P = .039). ConclusionsIRE procedural resistance changes may serve as a biomarker for survival and IRE-induced systemic CD8+ T cell and cDC1 activation.

Enhanced ethanol sensors based on MOF-derived ZnO/Co3O4 bimetallic oxides with high selectivity and improved stability

ZnO/Co3O4 ethanol sensors based on metal-organic framework (MOF-74) were prepared by one-step hydrothermal method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and gas-sensitive tests were performed. The gas sensing test results show that MOF-derived ZnO/Co3O4 (ZnO/Co3O4-MOF1:2) has higher sensitivity, better selectivity, and lower operating temperature than ZnO/Co3O4 without MOF template (ZnO/Co3O4–N1:2). The response value of ZnO/Co3O4-MOF1:2–50 ppm ethanol gas can reach 19.75, which is 13 times higher than that of ZnO/Co3O4–N1:2. Moreover, ZnO/Co3O4-MOF1:2 has excellent selectivity, outstanding reproducibility and good stability. The limit of detection concentration is up to 500 ppb. The improved ethanol sensing performance of MOF-74-derived ZnO/Co3O4 is mainly due to the porous structure of MOF-74 with a large number of internal pores, which provides more active sites for the surface adsorption and desorption of gas molecules. In addition, the amount of surface-defective and adsorbed oxygen involved in the sensing reaction is significantly increased, leading to a larger change in resistance during the redox reaction and a higher final response.

Light-Amplified CISS-Based Hybrid QD-DNA Impedimetric Device for DNA Hybridization Detection.

We design and build a novel light-amplified electrochemical impedimetric device based on the CISS effect to detect DNA hybridization using a hybrid quantum dot (QD)-DNA monolayer on a ferromagnetic (FM) Ni/Au thin film for the first time. Using spin as a detection tool, the current research considers the chiral-induced spin selectivity (CISS) phenomenon. After injecting a spin current into the QD-DNA system with opposite polarities (up and down), the impedimetric device revealed a large differential change in the charge-transfer resistance (ΔRct) of ∼100 ohms for both spins. Nearly, a threefold increase in the ΔRct value to ∼270 ohms is observed when light with a wavelength of 532 nm is illuminated on the sample, owing to the amplified CISS effect. The yield of spin polarization as extracted from the Nyquist plot increases by a factor of more than 2 when exposed to light, going from 6% in the dark to 13% in the light. The impact of light on the CISS effect was further corroborated by the observation of the spin-dependent asymmetric quenching of photoluminescence (PL) in the same hybrid system. These observations are absent in the case of a noncomplementary QD-DNA system due to the absence of a helical structure in DNA. Based on this, we develop a spin-based DNA hybridization sensor and achieve a limit of detection of 10 fM. These findings open a practical path for the development of spin-based next-generation impedimetric DNA sensors and point-of-care devices.

Highly conductive fiber with design of dual conductive Ag/CB layers for ultrasensitive and wide‐range strain sensing

AbstractRecently the ever‐increasing demand for wearable electronics has greatly triggered the development of flexible strain sensors. However, it is still challenging to simultaneously achieve high sensitivity, wide working range, and good wearability. Herein, we developed a highly stretchable fiber strain sensor based on wet‐spun porous polyurethane (PU) fiber, and especially a unique conductive network of dual silver (Ag)/carbon black (CB) layers is constructed. Under strain, the rapid crack propagation on the brittle Ag layer brings a large resistance change and thus high sensitivity, while the tunneling‐effect dominated CB layer bridges the separated Ag islands to maintain the integrity of conductive pathways under large strain. By means of the synergistic effect of Ag/CB layers, this composite fiber of Ag/CB@PU presents not only high conductivity of 5139.9 S/m, but also ultrahigh sensitivity with a gauge factor of 2.52 × 106 and a wide working range of up to 200%. Besides that, it is also capable of detecting very tiny strain of 0.1% and working stably for over 8000 cycles. Using mature weaving technology, this fiber strain sensor can be seamlessly integrated into the textile to conformally track different movements of the human body. Together with the facile all‐solution‐based fabrication protocol, this work proposed a new strategy to prepare high‐performance fiber strain sensor, promising the textile‐based wearable applications.

Multifunctional and Washable Carbon Nanotube-Wrapped Textile Yarns for Wearable E-Textiles.

Carbon nanotube (CNT) yarns are promising for wearable electronic applications due to their excellent electromechanical and thermal properties and structural flexibility. A spinning system was customized to produce CNT-wrapped textile yarns for wearable applications. By adjusting the spinning parameters and core yarn, a highly tailored hybrid CNT yarn could be produced for textile processing, e.g., knitting and weaving. The electrical resistance and mechanical properties of the yarn are influenced by the core yarn. The high flexibility of the yarn enabled state-of-the-art three-dimensional (3D) knitting of the CNT-wrapped yarn for the first time. Using the 3D knitted technology, CNT-wrapped textile yarns were seamlessly integrated into a wrist band and the index finger of a glove. The knitted structure exhibited a large resistance change under strain and precisely recorded the signal under the different movements of the finger and wrist. When the knitted fabric was connected to a power source, rapid heating above skin temperature was observed at a low voltage. This work presents a novel hybrid yarn for the first time, which sustained 30 washing cycles without performance degradation. By changing the core yarn, a highly stretchable and multimodal sensing system could be developed for wearable applications.

受关节软骨启发的耐疲劳和耐苛刻环境的三维超弹 海绵导体

Spongy conductors generally suffer from mechanical brittleness and irreversible conductive network damage when subjected to extreme compression and harsh environments. The development of elastic conductors combining the unique characteristics of light weight, super-elasticity, and extraordinary fatigue resistance is massively desired but challenging. Herein, a surface-constrained atomized water templating strategy is presented for fabricating a honeycomb-patterned spongy carbon nanotube conductor (h-SCNTC). By mimicking articular cartilage architecture with gradient energy dissipation under deformation, the resultant h-SCNTC exhibits outstanding compressibility with rapid recovery from deformation (i.e., 0% to 90% compressive strain) and extraordinarily high fatigue resistance (i.e., >95% height retention after 5000 cycles). The developed sensor possesses remarkable features, including superelasticity, durability, and large relative resistance changes across a wide strain range (i.e., 0% to 90%), which can be ascribed to the combination of “connect-disconnect” transition of nanogaps between individual carbon nanotubes in the skeleton under a low compressive strain and compressive contact of the conductive skeletons under a high compressive strain. In particular, the conductor can effectively inhibit water erosion, making it ultradurable against harsh environments in extreme humidity and machine washing conditions. The surface-constrained atomized water templating strategy for fabricating spongy superelastic conductors opens a new avenue to explore the potential of wearable sensors and deformation-tolerant electronics.

Electromechanical Performance of Strain Sensors Based on Viscoelastic Conductive Composite Polymer Fibers.

Flexible conductive polymer composite (CPC) fibers that show large changes in resistance with deformation have recently gained much attention as strain-sensing components for future wearable electronics. However, the electrical resistance of these materials decays with time during dynamic cyclic loading, a deformation performed to simulate their real application as strain sensors. Despite the extensive research on CPC fibers, the mechanism leading to this decay in the electromechanical response under repetitive cycles remains unreported. Herein, this behavior is investigated using fiber-based strain sensors wet spun from thermoplastic polyurethane (TPU) consisting of a carbonaceous hybrid conductive filler system of carbon black (CB) and carbon nanotubes (CNTs). We found electrical viscosity to predict the observed electromechanical resistance decay. This implies that cycling these materials enables the relaxation of both the polymer chains and the conductive network. In addition, the resulting piezoresistive fibers are sensitive to deformation in the region of low strain (gauge factor of 6.0 within 3.0% strain), remain conductive under 280.5% deformation, and are stable for more than 2000 cycles. Finally, we demonstrate the potential of TPU/CB-CNT fibers as strain sensors for monitoring human motion.

High-speed hydrogen sensor fabricated using a platinum/titanium oxide nanocontact

Titanium dioxide (TiO2) thin films have been extensively studied for use in solid-state hydrogen (H2) gas sensors. In this work, TiOx/platinum (Pt) nanocontacts which constitute a Schottky-diode sensor were developed using shadow evaporation. Large resistance changes and short reaction times were achieved through measurement of the resistance of the contacts. The sensing was quite depended on the thickness of the TiOx layer. The results indicate that the large sensor response over 105 was achieved just neighboring outermost surfaces of TiOx layer. As this sensor can be fabricated at temperatures less than 400 K, it is expected to be applicable to on-tip sensors.

Printing Polymeric Convex Lenses to Boost the Sensitivity of a Graphene-Based UV Sensor.

Ultraviolet (UV) is widely used in daily life as well as in industrial manufacturing. In this study, a single-step postprocess to improve the sensitivity of a graphene-based UV sensor is studied. We leverage the advantage of electric-field-assisted on-demand printing, which is simply applicable for mounting functional polymers onto various structures. Here, the facile printing process creates optical plano-convex geometry by accelerating and colliding a highly viscous droplet on a micropatterned graphene channel. The printed transparent lens refracts UV rays. The concentrated UV photon energy from a wide field of view enhances the photodesorption of electron-hole pairs between the lens and the graphene sensor channel, which is coupled with a large change in resistance. As a result, the one-step post-treatment has about a 4× higher sensitivity compared to bare sensors without the lenses. We verify the applicability of printing and the boosting mechanism by variation of lens dimensions, a series of UV exposure tests, and optical simulation. Moreover, the method contributes to UV sensing in acute angle or low irradiation. In addition, the catalytic lens provides about a 9× higher recovery rate, where water molecules inside the PEI lens deliver fast reassembly of the electron-hole pairs. The presented method with an ultimately simple fabrication step is expected to be applied to academic research and prototyping, including optoelectronic sensors, energy devices, and advanced manufacturing processes.

CoFeB/MgO-based magnetic tunnel junctions for film-type strain gauge

We show that a CoFeB/MgO-based magnetic tunnel junction (MTJ) formed directly on a flexible substrate has considerable potential as a high-sensitivity strain gauge. A gauge factor of ∼1000, which represents the highest sensitivity reported, thus far, for a film-type strain gauge and is ∼500 times larger than that of the most prevalent metal-foil strain gauge, is realized in the flexible MTJ with a pseudo-spin valve structure under the condition of external magnetic-field assistance. Additionally, using a flexible MTJ with strain-insensitive exchange-biased pinned and strain-sensitive free layers, we demonstrate that a large resistance change due to the strain application can be achieved under magnetic field-free conditions. According to simulations based on the coherent magnetization rotation model, conditions are suggested for improving the gauge factor, as well as for using the flexible MTJ as a strain gauge in practical applications.

Step-like resistance changes in VO2 thin films grown on hexagonal boron nitride with in situ optically observable metallic domains

Vanadium dioxide (VO2) thin films grown on hexagonal boron nitride (hBN) flakes show three orders of magnitude resistance change due to metal–insulator transition (MIT). The MIT property of VO2 thin films is strongly dependent on the metallic domain size, which should be identified to derive the resistance change owing to the single metallic domain. In this study, we investigated the relationship between the metallic domain size and the device-size-dependent MIT property of VO2 thin films grown on hBN. We observed by temperature-dependent Raman spectroscopy and optical microscopy the emergence of the metallic domains and determined the metallic domain size in VO2 thin films grown on hBN. The metallic domain size of the VO2 thin films grown on hBN was determined to be ∼500 nm on average in length and up to sub-micrometer scale. Electric transport measurements revealed that VO2/hBN microwires exhibit multi-level step-like resistivity changes that change by one to two orders when the length and width are ∼2 μm owing to the confined metallic domains in the micrometer scale. Our results open a way for VO2 devices, showing a steep and large resistance change even in the micrometer scale.

Morphology and size effect of Pd nanocrystals on formaldehyde and hydrogen sensing performance of SnO2 based gas sensor

In order to investigate the morphology and size effect of Pd nanocrystals on gas sensing performance of SnO2, Pd nanocrystals with different sizes (3, 20, 50 nm) and morphologies were synthesized and a series of Pd-SnO2 composites were prepared by decorating Pd nanoparticles (PdNP, ~3 nm), Pd nanocube (PdNC1, ~20 nm), Pd nanocube (PdNC2, ~50 nm), Pd rhombic dodecahedron (PdRD, ~50 nm), Pd octahedron (PdOC, ~50 nm) on the surface of SnO2 nanosheets. The test results showed that all Pd-SnO2 sensors exhibited dual selectivity to H2 at 200 °C and HCHO at 260 °C. In all Pd-SnO2 composites with different sizes of Pd, 2%PdNP-SnO2 sensor exhibited the best sensing performance. In all Pd-SnO2 composites with different shapes of Pd but similar size, PdNC1-SnO2 and PdOC-SnO2 sensors exhibited better sensing performance to HCHO and H2, respectively. Pd-SnO2 composites showed Pd shape and size-dependent sensing performance, and the size effect is more significant than morphology effect. Size effect is ascribed to the smaller size with more active sites and PdO species, and shape effect is attributed to the different adsorption energies of different facets to HCHO, which is proved by DFT calculation. In addition, the improved performance of SnO2 can be ascribed to two aspects: one is the suitable catalytic activity of Pd to HCHO and H2 oxidation; the other is that the transformation of Pd⇋PdO in air and HCHO or H2 leads to a large resistance change of SnO2.