High Temperature Coefficient Of Resistance Research Articles

Semiconductor Nanoparticle Anchored Single-Walled Carbon Nanotubes for a Bolometer.

The bolometer is developed using single-walled carbon nanotubes (SWCNT) anchored with semiconductor nanoparticles of cadmium sulfide, stannous disulfide, and zinc oxide (ZnO). The bolometric responses were recorded at varying temperatures from 10 K to room temperature. The anchored SWCNTs provided a higher temperature coefficient of resistance (TCR) than pristine SWCNTs. The largest TCR is recorded from SWCNTs/ZnO (-0.11%/K) at room temperature, which is 200% higher than pristine SWCNTs. The largest photoresponsivities of SWCNTs/ZnO under near-infrared (NIR) and wide wavelength source (200-1200 nm) illuminations are 5.06 and 37.51 mV/W, respectively. The extraordinary performance of SWCNTs/ZnO stands out at ∼17 × 104% under IR illumination. The study presents a significant advancement in the development of high-performance SWCNT bolometric materials by anchoring with semiconductor nanoparticles.

Study on Mn3O4 - La1-xCaxMnO3 composite ceramics with high temperature coefficient of resistance in large temperature range

Study on Mn3O4 - La1-xCaxMnO3 composite ceramics with high temperature coefficient of resistance in large temperature range

Optimization of electrical transport and magnetoresistance of La0.72Ca0.28-xPbxMnO3 ceramics by Pb2+ doping

Here, La0.72Ca0.28-xPbxMnO3 (LCPMO, 0 ≤ x ≤ 0.06) polycrystalline ceramics are prepared by the sol-gel method and the influence of Pb2+ doping on microstructure, chemical composition, and electrical transport properties of LCPMO ceramics is systematically investigated. The study was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and four-probe method. The four-probe test shows that all samples have MIT (metal-insulator transition) behavior, and the peak resistance gradually decreases with the increase of Pb2+ doping amount. With the increase of Pb2+ doping amount, the temperature coefficient of resistance (TCR) and magnetoresistance (MR) first increased and then decreased, the TCR increased from 24.6 % to 36.5 %·K−1, and the MR value increased from 47 % to 71.5 %, and both corresponded to high temperature direction. Referring to previous studies, higher TCR and MR values near room temperature are what researchers have been pursuing for a long time. it can be seen that the LCPMO ceramics prepared in this article can have good application prospects in infrared detection and magnetic storage.

Effects of annealing on the microstructure and performance of thin-film Pt resistance temperature sensors: experiments and finite element simulations

Platinum resistance temperature sensors have a wide range of applications in various fields, where a high temperature coefficient of resistance (TCR) is a crucial requirement. In this study, thin-film Pt resistance temperature (TPRT) sensors were fabricated on an Al2O3 substrate using a micro-electro-mechanical system (MEMS) based surface micromachining process, and Pt resistance wafers were annealed at a temperature range from 500°C to 800°C using rapid thermal process (RTP). Experimental and simulation results show that TPRT sensors fabricated on the substrate with a rough surface exhibit lower thermal stress. Meanwhile, more pores appear in the Pt thin film, reducing TCR. However, high temperature annealing significantly influences the microstructure of the Pt film and brings about an obvious increase in TCR despite, introducing thermal stress at the interface. Considering the impact of the heat treatment process, the fabricated TPRT sensors demonstrate excellent performance with a TCR of 3512 ppm/°C.

Development of new materials for electrothermal metals using data driven and machine learning.

After adopting a combined approach of data-driven methods and machine learning, the prediction of material performance and the optimization of composition design can significantly reduce the development time of materials at a lower cost. In this research, we employed four machine learning algorithms, including linear regression, ridge regression, support vector regression, and backpropagation neural networks, to develop predictive models for the electrical performance data of titanium alloys. Our focus was on two key objectives: resistivity and the temperature coefficient of resistance (TCR). Subsequently, leveraging the results of feature selection, we conducted an analysis to discern the impact of alloying elements on these two electrical properties.The prediction results indicate that for the resistivity data prediction task, the radial basis function kernel-based support vector machine model performs the best, with a correlation coefficient above 0.995 and a percentage error within 2%, demonstrating high predictive capability. For the TCR data prediction task, the best-performing model is a backpropagation neural network with two hidden layers, also with a correlation coefficient above 0.995 and a percentage error within 3%, demonstrating good generalization ability. The feature selection results using random forest and Xgboost indicate that Al and Zr have a significant positive effect on resistivity, while Al, Zr, and V have a significant negative effect on TCR. The conclusion of the composition optimization design suggests that to achieve both high resistivity and TCR, it is recommended to set the Al content in the range of 1.5% to 2% and the Zr content in the range of 2.5% to 3%.

Flexible and freestanding temperature sensors based on laser carbonization of carbon nanofibers

A new single-step, low-cost method for producing a wearable, flexible temperature sensor has been developed using laser writing technology. The process involves carbonizing and patterning polymeric nanofibers to create a standalone laser-carbonized nanofibers (LCNFs) substrate. A large-area polyacrylonitrile nanofibers mat is first prepared using electrospinning and then carbonized with a high-power CO2 laser beam. The resulting LCNFs are highly conductive and retain their fibrous structure. The near-complete disappearance of polyacrylonitrile peaks in the FTIR measurements and the high-intensity characteristic peaks of carbon materials obtained in the Raman scattering measurements of the LCNFs confirm their complete carbonization. SEM microscopy showed that the fibrous structure of the LCNFs remained intact after the laser carbonization process with no significant damage. Additionally, TEM microscopy revealed that the LCNFs are made up of axially ordered graphene sheets, which form their unique fibrous structure. LCNFs' temperature sensor exhibits >87% higher temperature coefficient of resistance (TCR) than laser-induced graphene (LIG) temperature sensor on a polyamide substrate when tested under the same experimental conditions. The LCNFs sensor also boasts excellent resistance stability, mechanical stability, and flexibility. To fit various wearable applications and enhance the temperature-sensing capabilities, three different sensor patterns of LCNFs were created: square, serpentine, and heater. Among these patterns, the heater design exhibited superior TCR and temperature response. However, it also had a higher thermal mass compared to the other patterns.

Aligned and unaligned single-walled carbon nanotube bilayer films for uncooled infrared sensors

Semiconducting single-walled carbon nanotube (SWCNT) film fabrication using the dip-coating method has successfully produced a unique film with two layers of different morphologies, an upper layer of aligned SWCNT film and a lower layer of non-aligned SWCNT network film. In the upper layer, SWCNTs form SWCNT bundles of several SWCNT thicknesses, and the bundles form thin aligned SWCNT films of 2–7 nm in thickness with parallel and equally spaced bundles of SWCNTs. When a bolometer device with this bilayer film was fabricated on electrodes, the upper aligned SWCNT film was the main conductive path with a low resistivity of about 0.2 Ωcm around room temperature. The alignment film also achieved a high temperature coefficient of resistance (TCR) of more than −5%/K due to its thin thickness, which is hardly affected by the slight metallic SWCNT presence. These excellent properties of a high TCR and low resistance are advantageous for the development of innovative sensor elements.

Tuning strain-stress and electron-lattice effects to enhance electrical transport properties of La0.7Ca0.25K0.05MnO3 films via optimizing sintering temperatures

Facile-prepared films with a high-temperature coefficient of resistivity (TCR) are crucial for application in high-sensitivity bolometers. In this study, La0.7Ca0.25K0.05MnO3 (LCKMO) films were grown on (001)-oriented La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates using the spin-coating method. Various sintering temperatures (900 °C ≤ Ts ≤ 1050 °C) were utilized in the film preparation, causing the lattice mismatch between films and substrate degraded. The effect of Ts on the strain state of films was investigated through X-ray diffraction (XRD) analysis. The distortion of MnO6 octahedra and the Mn–O bond were assessed using Raman and FTIR spectra, respectively. The structural perfection and elemental valence of films were adjusted via optimizing Ts. Meanwhile, the strain state and defect structure were effectively improved with Ts increasing. These results indicate that the LCKMO films with high crystalline quality can be achieved by optimizing the sintering process. The TCR of LCKMO films was modified. When Ts at 1000 °C, the LCKMO films exhibit the remarkable TCR of 16.29% K-1 at 269.54 K, indicating the substantial potential of LCKMO films in infrared bolometers.

Using multilayer structures to enhance the electrical properties of porous silicon for thermal sensing

Porous silicon holds great promise as an optically and electrically tuneable material platform for high performance thermo-resistive sensing. Fulfilling this promise requires the ability to independently control the two critical parameters which determine the sensitivity (specifically the minimum temperature difference resolution) of thermal detectors: the temperature coefficient of resistance (TCR) and 1/f noise of the sensing material. In single porosity films these two properties are monolithically dependent, with both TCR and 1/f noise constant increasing with porosity. Here we show that use of multilayer films allows manipulation of properties of the overall structure to simultaneously achieve high TCR and low 1/f noise. Characterization of electrical properties of various porosity combinations revealed that using a two-layer heterostructure on Si substrate with low porosity (48 %) as the top layer and a high porosity (80 %) as the lower layer, both high TCR (∼ 4.4 %/K) and low 1/f noise constant (4 × 10−13) could be simultaneously achieved. This transforms the ability to exploit porous silicon for future high sensitivity based thermal detectors.

A self-healable and highly flame retardant TiO2@MXene/P, N-containing polyimine nanocomposite for dual-mode fire sensing

Scalable early fire warning sensors that integrate passive flame-retardant strategies and active fire alarm sensing are highly requirable in diverse areas. However, the single-mode fire response and performance degradation or even malfunction under mechanical damages remain key challenges for current early fire warning sensors. Herein, a self-healable and flame retardant TiO2@MXene/P, N-containing polyimine nanocomposite (TMPNP) is designed as repeatable dual-mode fire warning sensors. On the one hand, the TMPNP exhibits a high temperature coefficient of resistance of −2.21 %/℃, which endows nanocomposite with an extraordinarily sensitive non-contacting fire warning performance; on the other hand, the TMPNP demonstrates outstanding fire contact warning features of responsive time being less than 1 s and repeatable alarming response, as well as excellent flame-retardant functionality of LOI reaching up to 32.0 %. Moreover, the TMPNP can be effectively recovered after 30 cutting-and-healing cycles with a healing efficiency of 89.3 % via dynamic imine bonds. Particularly, its flame retardancy and fire warning properties in contact/non-contact mode are well maintained after self-healing. These merits support the scalable assembly TMPNP onto cotton textile to develop a wireless household fire early warning sensor linked to the Internet of Things, contributing to construct fire-safety smart buildings. This work provides a scalable strategy for preparing healable sensitive fire warning sensors, opening up a new opportunity for the practical application of eliminating indoor fire hazards.

Fabrication and characterization of suspended La0.7Sr0.3MnO3 nanofibers for high-sensitive and fast-responsive infrared bolometer

La1−x Sr x MnO3 manganite oxides have shown great potential for infrared (IR) sensing. In this study, La0.7Sr0.3MnO3 (LSMO) nanofibers, synthesized by a simple electrospinning process, are suspended between gold interdigitated electrode (IDE). These electrodes, which acts as a supporting platform for the dangling nanofiber, are microelectromechanical systems based that can be fabricated quickly and economically with fewer fabrication steps. Due to the large surface-area-to-volume ratio, these fibers have outstanding thermo-electrical properties, which puts them in the leagues of materials suitable for IR sensing. Performance-wise these hanging nanofibers belong to a class of promising thermal sensors due to negligible thermal loss. The optoelectrical characterization shows its temperature coefficient of resistance (TCR) is −1.48%K−1, and its electrical resistance follows an inverse square law for distance from the IR source. The fabricated LSMO nanofibers based microbolometer has a significantly low thermal time constant with average thermal response and recovery time of 63 ms and 77 ms, respectively. Furthermore, they show encouraging bolometric properties with thermal conductance, thermal capacitance, voltage responsivity, and thermal noise limited detectivity of 3.6 × 10−3WK−1, 0.2268 × 10−3JK−1 , 1.96 × 105VW−1, and 3.7 × 108cm Hz1/2W−1 respectively. The high voltage responsivity and TCR, commensurate with the ultralow response and recovery time confirm that the fabricated Microbolometer can find industrial applications as thermal sensors.

Enhanced TCR and MR by grain boundary modification and phase competition in La0.67Ca0.33MnO3: Aux (x=0, 0.05, 0.1, 0.15) composite ceramics

La0.67Ca0.33MnO3 (LCMO) ceramics exhibit high temperature coefficient of resistance (TCR) and colossal magnetoresistance effect (CMR). Increasing their TCR and MR values can enhance potential applications in uncooled infrared detectors and magnetic storage devices. However, presence of inherent grain boundaries and defects within these ceramics significantly limits their performance. Therefore, this work proposed modifying grain boundaries of LCMO ceramic using low-resistivity and stable Au to enhance its electrical transport and improve magnetoresistance performance through competition between antiferromagnetic Au and ferromagnetic La0.67Ca0.33MnO3. A series of La0.67Ca0.33MnO3: Aux (x = 0, 0.05, 0.10, 0.15) composite ceramics was prepared by sol-gel and solid-state methods. Introduction of Au increased TCR from 40.1 %·K−1 to 55.2 %·K−1 and MR from 60.4 % to 74.2 %, when x = 0.10. This study demonstrates that proposed strategy involving multiphase interactions can significantly improve electrical transport and magnetic properties of functional materials, with promising applications in areas such as thermoelectric and magnetoelectric conversion.

High temperature coefficient of resistivity (TCR) of Nd0.67Sr0.33MnO3 films by optimizing sintering temperature

In this study, Nd0.67Sr0.33MnO3 (NSMO) films are deposited on La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates using sol–gel spin coating method and sintered at different temperatures (Ts = 1250, 1300, 1350, 1400 and 1450 °C). Consolidated analysis of their crystal structure, surface morphology and valence states enables one to conclude that increased Ts facilitates grain growth and enhances crystallinity of films. Moreover, enhancing Ts from 1250 to 1350 °C leads to a decrease in Mn-O bond length (d(Mn-O)) and an increase in Mn-O-Mn bond angle (θ(Mn-O-Mn)). In the XPS analysis, the Mn4+ and O2– content kept increasing with the rise of Ts. When Mn4+ concentration ≤ 33%, the double exchange (DE) interactions was undoubtedly facilitated, which was beneficial for the electrical properties of the NSMO films. These changes eventually result in large temperature coefficient of resistivity (TCR). According to these results, Nd0.67Sr0.33MnO3 film, with a maximum TCR value of 21.85% K−1 at Ts = 1350 °C, are promising materials for the manufacturing of sensitivity switches and infrared bolometers.

Role of Ar dilution of SiH4/PH3 gas mixture on PECVD based film growth process, hydrogen bonding configuration, and optical properties of n-type a-Si:H thin films

Amorphous silicon is considered as one of the most promising materials for solar cell applications due to its enhanced optical absorption, high temperature coefficient of resistance, controllable forbidden-band gap, and to reduce the costs of solar panels. In this study, we took notice of the film growth, hydrogen bonding configuration, and optical properties of the phosphorus doped a-Si:H films by varying the dilution of silane using argon gas. Argon gas is a chemically non-reactive gas, but it affects the percentage of silicon atoms during processing. A change in growth process and microstructure factor with varying Ar gas flow is observed, which causes changes in the optical properties of P-doped a-Si:H films. The proportion of SiH bonding rises with increasing argon flow rate, as seen by the infrared-absorption spectra. According to optical tests of the films, the refractive index of the films rises with the Ar flow rate, whereas the band gap Eg decreases. Dilution of SiH4 results in a good-quality film with increased optical conductivity. We established experimental proof of a correlation between band gap and refractive index and compared it with previously reported theoretical models. An investigation into the band gap's dependency on Urbach energy revealed its linearity.

Optimized electrical transport properties of La0.7Ca0.18Sr0.12MnO3 film by adjusting sintering temperature

Perovskite manganites Lax(Ca1-ySry)1-xMnO3 have conspicuous electrical transport properties used for the application of uncooled bolometers. Thus, considerable attention has paid to the researches on electrical transport properties of Lax(Ca1-ySry)1-xMnO3. Temperature coefficient of resistivity (TCR) and the corresponding peak temperature (Tk) are crucial parameters for uncooled bolometers. Optimal La0.7Ca0.18Sr0.12MnO3 (LCSMO) films with highly oriented growth were prepared on (00l) LaAlO3 substrate at different sintering temperature (Ts) using a facile sol-gel spin coating method. Based on the analysis of microstructure, ionic valence, surface morphology and electrical transport properties, LCSMO films exhibit high crystallinity and large room-temperature TCR at higher Ts. Theoretical Curie temperature and the coupling of the electron lattice weaken gradually with the increase in Ts, which is the dominant factor for the optimization of electrical transport properties. Additionally, the results suggest that the active energy and theoretical Curie temperature play a crucial role in adjusting TCR and Tk. With the increase in Ts, the former increases while the latter decreased, resulting in a high TCR value (12.10%/K) at room temperature (297.38 K). The peak TCR value of LCSMO sintered at 1673 K is about 25% higher than that of the film sintered at 1473 K. The resulting LCSMO films demonstrate great potential for application in uncooled bolometers. Further theoretical basis on the effects of Ts on electrical transport properties was provided.

Low temperature synthesis of VO2 and hysteresis free VOx thin films with high temperature coefficient of resistance for bolometer applications

Vanadium dioxide (VO2) is an insulator to metal phase transition material, which finds many electronic and optical applications due to its reversible switching while VOx-based bolometers are widely used in commercial uncooled infrared detectors due to their high-temperature coefficient of resistance and low resistivity. Atmospheric pressure thermal oxidation (APTO) of Vanadium (V) is a simple process used to synthesize VO2 films without the need for precise control of oxygen partial pressure unlike other synthesis methods. In this work, we report the effect of reducing the V oxidation temperature to 250–450 °C during APTO and synthesize films with different oxidation durations. For an optimized oxidation duration at each oxidation temperature, VO2 films are obtained with more than two orders of resistance switching. This optimum oxidation duration is found to decrease exponentially with increase in oxidation temperature with an activation energy of 1.05 eV. The phase transition temperature of these VO2 films is found to decrease monotonically with decrease in oxidation temperature. We also observe that partially oxidized (oxidation time less than optimized oxidation duration to form VO2) VOx films show broad resistance switching from room temperature up to 70 °C instead of steep switching at the phase transition temperature. The partially oxidized film shows a temperature coefficient of resistance (TCR) as high as ∼10%/K, which is 3–4 times greater than TCR of commercial VOx thin films used in bolometers while showing similar resistivity. The resistivity of these films also exhibits almost zero hysteresis with temperature, an important requirement for bolometer applications. This study will widen the usefulness of the APTO process for fabricating VO2-based devices and high TCR VOx films for bolometer applications. The demonstrated low temperature process will especially be suitable to integrate VO2/VOx on substrates which can sustain only low temperatures such as some of the flexible substrates.

A micro graphene high temperature sensor with a single Si3N4 protective layer

Temperature sensors are widely used in industrial production, national defense and military fields. The traditional temperature sensors normally operate in a limited temperature range no more than 200 °C, which cannot be used for extreme high temperature detections. In this paper, a thermal protection method for the sensing graphene membrane is proposed and a graphene high temperature sensor has been fabricated and investigated. By growing a single silicon nitride (Si3N4) protective layer on top of graphene, our design not only solves the problem that graphene is easily oxidized at high temperature, but also prevents graphene from being polluted by impurities, which would lead to the degradation of graphene performance. We further explore the protective effect of Si3N4 layer with different thicknesses on the performance of the sensor. It has been found that the 400 nm Si3N4 protective layer gives the best protective capability. The sensor exhibits a positive temperature coefficient (PTC) from 50 to 600 °C and a maximal temperature coefficient of resistance (TCR) value of 0.29% °C−1 at 150 °C is achieved. It has been demonstrated that our graphene high temperature sensor with protective layer structure maintains good stability not only at high temperature up to 600 °C, but also over a long-period of time under room temperature. In short, the high temperature sensor possesses a wide temperature measurement range with micro dimensions, a relatively high TCR and a smaller thermal hysteresis. The thermal protection approach proposed in this paper provides a new idea for the fabrication of high temperature pressure sensor, which is expected to be applied in aerospace engines and oil wells, etc.

All Resistive Pressure-Temperature Bimodal Sensing E-Skin for Object Classification.

Electronic skin (E-skin) with multimodal sensing ability demonstrates huge prospects in object classification by intelligent robots. However, realizing the object classification capability of E-skin faces severe challenges in multiple types of output signals. Herein, a hierarchical pressure-temperature bimodal sensing E-skin based on all resistive output signals is developed for accurate object classification, which consists of laser-induced graphene/silicone rubber (LIG/SR) pressure sensing layer and NiO temperature sensing layer. The highly conductive LIG is employed as pressure-sensitive material as well as the interdigital electrode. Benefiting from high conductivity of LIG, pressure perception exhibits an excellent sensitivity of -34.15 kPa-1 . Meanwhile, a high temperature coefficient of resistance of -3.84%°C-1 is obtained in the range of 24-40°C. More importantly, based on only electrical resistance as the output signal, the bimodal sensing E-skin with negligible crosstalk can simultaneously achieve pressure and temperature perception. Furthermore, a smart glove based on this E-skin enables classifying various objects with different shapes, sizes, and surface temperatures, which achieves over 92% accuracy under assistance of deep learning. Consequently, the hierarchical pressure-temperature bimodal sensing E-skin demonstrates potential application in human-machine interfaces, intelligent robots, and smart prosthetics.

Design and Analysis of High-Performance and Small-Size Piezoresistive Pressure Sensors

In this article, a rapid thermal process is proposed to manufacture piezoresistance to improve the performance of piezoresistive devices, and an absolute piezoresistive pressure sensor is prepared by anodic bonding between silicon film and glass with the cavity to reduce the size of the device. The size of the sensor is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.0\times 1.0\times0.513$ </tex-math></inline-formula> mm. At the same time, the arrangement of piezoresistance is optimized by the finite element method. In addition, the deformation of the diaphragm is measured with a profiler, which verified the feasibility of Ti as the absorption of oxygen generated in the anodic bonding process. In the pressure range of 0–200 kPa, the output voltage and nonlinearity of the pressure sensor prepared by the rapid thermal annealing (RTP) process are 91.6 mV and 0.14%FSO, respectively, and the temperature coefficient of resistance (TCR) and the temperature coefficient of sensitivity (TCS) are 571 and −1676 ppm/°C respectively. Compared with the pressure sensor prepared by the common piezoresistive process, the TCR and TCS of the designed sensor are reduced by 73% and 24%, respectively, which has the advantages of high output voltage, low TCR and TCS, and small-size.

Annealing temperature effect on the temperature coefficient of resistance for vanadium oxide (VOx) thin films as bolometer materials

Vanadium oxides (VOx) are representative materials with a high temperature coefficient of resistance (TCR); however, VOx films can have complex phase structures that are dependent on their fabrication method. While past research has focused on the TCR behavior of VOx thin films, this study investigates the TCR of VOx thin films annealed at different temperatures as well as focuses on the relation between the VOx phase, surface morphology, sheet resistance, and TCR. VOx thin films were deposited via radio-frequency magnetron sputtering and annealed at 150 °C–500 °C in 20% O2. Alongside morphological changes, the deposited VOx thin films exhibited phase changes from V2O5 to VO2 with increasing annealing temperature. The VOx thin films annealed at 300 °C and 330 °C showed the lowest and highest average TCR of 1.25%/°C and 3.34%/°C, respectively. Furthermore, a bolometer fabricated using the higher-TCR film showed more than 5-fold infrared responsivity under the same infrared intensity.