Thin-film Sensors Research Articles

Innovative coaxial high-temperature thin-film sensor with core–shell structure surpassing traditional multilayer films

Innovative coaxial high-temperature thin-film sensor with core–shell structure surpassing traditional multilayer films

CdS thin film sensor for NO2 and H2S detection at room temperature

CdS thin film sensor for NO2 and H2S detection at room temperature

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.

Multi-point thermometry tool and in-situ measurement of temperature fields

In-situ real-time measurement of instantaneous milling temperature distribution is a key issue to realize efficient machining. For the foregoing reasons, the milling model of Inconel 718 was established, and the cloud diagram of tool temperature distribution during milling was obtained. A multi-point temperature measurement tool for milling temperature with an integrated thin-film temperature sensor was designed. The real-time temperature distribution of the tool during milling was obtained from 27 sets of milling tests. The impact of each milling parameter on the milling temperature was analyzed by ANOVA.

Recent progress in piezoelectric thin films as self-powered devices: material and application

Piezoelectric materials have become a key component in sensors and actuators in many industrial fields, such as energy harvesting devices, self-powered structures, biomedical devices, nondestructive testing, owing to the novel properties including high piezoelectric coefficient and electromechanical coupling factors. Piezoelectric thin films integrated on silicon substrates are widely investigated for their high performance and low manufacturing costs to meet the requirement of sensor networks in internet of things (IoT). The aim of this work is to clarify the application and design structure of various piezoelectric thin films types, synthesis methods, and device processes. Based on latest literature, the process of fabricating thin film sensors is outlined, followed by a concise overview of techniques used in microelectromechanical systems (MEMS) processing that can integrate more complex functions to obtain relevant information in surrounding environment. Additionally, by addressing piezoelectric thin films sensors as a cutting-edge technology with the ability to produce self-powered electronic devices, this work delivers incisive conclusions on all aspects of piezoelectric sensor related features. A greater understanding of piezoelectricity is necessary regarding the future development and industry challenges.

3D-Printed Fluorescent Hydrogel Consisting of Conjugated Polymer and Biomacromolecule for Fast and Sensitive Detection of Cr(VI) in Vegetables.

Portable fluorescent film sensors offer a solution to the contamination issue in homogeneous sensor detection systems. However, their special structure leads to low sensitivity and a long response time, resulting in a significant scientific challenge limiting their development and application. In this work, we propose a dual design strategy to prepare highly sensitive film sensors for rapidly detecting Cr2O72-. Specifically, P(Fmoc-Osu)-SA hydrogel films were developed by integrating the biological macromolecule sodium alginate (SA) with the conjugated polymer poly(N-(9-Fluorenylmethoxycarbonyloxy)succinimide) (P(Fmoc-Osu)), using both mold and inkjet 3D printing methods. The "molecular wire effect" of the sensing unit P(Fmoc-Osu) and the water channel within the film substrate are responsible for the improved sensitivity and the reduced response time of this thin film sensor. P(Fmoc-Osu)-SA hydrogel films prepared by these two methods can rapidly detect Cr2O72- with limits of detection of 1.18 and 0.078 nM, respectively. Considering that 3D-printed hydrogel films can be tailored to different shapes according to detection needs, the P(Fmoc-Osu)-SA hydrogel films produced from this method were effectively applied in vegetable samples. This study provides an innovative and effective strategy for the development of biocompatible hydrogel sensors that offer the potential for determining trace amounts of Cr2O72- in agriculture.

Low-noise inverse magnetoelectric magnetic field sensor

In the development of any type of magnetic field sensor based on magnetic films, special consideration must be given to the magnetic layer component. The presented work investigates the use of scalable flux closing magnetostrictive multilayers for inverse magnetoelectric sensors. In such a type of magnetic field sensor, highly sensitive AC and DC field detection relies on strong excitation of the incorporated magnetic layers by piezoelectrically driven cantilever oscillation at mechanical resonances. The provoked periodic flux change is influenced by the magnetic field to be measured and is picked up by a coil, which generates the measured output. The multilayered inverse magnetoelectric sensor is investigated with regard to linearity, noise behavior, and detection limit of DC and AC signals. A significant advancement for inverse magnetoelectric thin film sensors is demonstrated in this study. Using exchange bias stabilized magnetic multilayers with flux closure structures, detection limits are improved by an order of magnitude to less than 8 pT/Hz1/2 at 10 Hz and 18 pT/Hz1/2 at DC.

Ternary Holey Carbon Nanohorn/Potassium Chloride/Polyvinylpyrrolidone Nanohybrid as Sensing Film for Resistive Humidity Sensor

The study presents findings on the relative humidity (R.H.) sensing capabilities of a resistive sensor. This sensor utilizes sensing layers composed of a ternary nanohybrid, consisting of holey carbon nanohorn (CNHox), potassium chloride (KCl), and polyvinylpyrrolidone (PVP), with mass ratios of 7/1/2, 6.5/1.5/2, and 6/2/2 (w/w/w). The sensing structure comprises a silicon substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensing film is deposited on the sensing structure via the drop-casting method. The sensing layers’ morphology and composition are investigated through Scanning Electron Microscopy (SEM) and RAMAN spectroscopy. The resistance of thin-film sensors based on ternary hybrids increased with exposure to a range of relative humidity (R.H.) levels, from 0% to 100%. The newly designed devices demonstrated a comparable response at room temperature to that of commercial capacitive R.H. sensors, boasting excellent linearity, swift response times, and heightened sensitivity. Notably, the studied sensors outperform others employing CNHox-based sensing layers in terms of sensitivity, as observed through manufacturing and testing processes. It elucidates the sensing mechanisms of each constituent within the ternary hybrid nanocomposites, delving into their chemical and physical properties, electronic characteristics, and affinity for water molecules. Various alternative sensing mechanisms are considered and discussed, including the reduction in holes within CNHox upon interaction with water molecules, proton conduction, and PVP swelling.

Discriminative analysis of volatile organic compounds using machine-learning assisted Au loaded ZnO and TiO2-based thin film sensors

Noble metal-based particulate catalysts have traditionally been loaded or decorated onto the semiconductor metal oxide (SMO) surfaces to enhance the performance of gas sensors. Fabricating SMO-based sensors for selective detection of particular gases with high sensitivity remains a challenge. This study aims to enhance the efficacy of pure SMO and their heterostructure with gold (Au) decoration, along with an attempt to address the cross-sensitivity towards other gases through machine learning-assisted discriminative analysis. The sensitivity of sputtered ZnO thin films towards different VOCs such as acetone, ethanol, methanol, and toluene was improved by loading particulate Au. The highest sensitivity of 25 and low response time of ∼6 s and ∼4 s were achieved towards 10 ppm of ethanol and toluene, respectively. Further, Au-loaded ZnTiO3-TiO2 (ZTO) layered heterostructure was also adopted to achieve selectivity towards toluene. ZTO thin film sensor was highly sensitive towards 10 ppm of toluene, with a sensitivity of 49 and a response time of ∼6 s. Loading Au on ZnO thin film increases sensitivity towards multiple VOCs, whereas Au on ZTO heterostructure improves the selectivity towards toluene. To overcome the problem arising due to the cross-sensitivity, the idea of operating multiple sensors with different Au loading is proposed. The discriminative property of different sensors as an array, towards VOCs was analysed in detail using machine learning algorithms such as principal component analysis (PCA), linear discriminant analysis (LDA), logistic regression (LR), and artificial neural networks (ANN). The multilayer perceptron model implemented to discriminate multiple VOCs worked at a discrimination accuracy of 100 %.

Relative humidity measurements of a thin-film humidity sensor in condensing conditions in the temperature range from −40 °C to 5 °C

In condensing conditions, metastable states such as supersaturation of water vapour and supercooling of liquid water are commonly observed in the free atmosphere. This study investigates the response of a polymeric thin-film humidity sensor under condensing conditions at various temperatures (−40 °C, −20 °C, −5 °C, and 5 °C) and different relative humidity (RH) levels. To ensure precise control of RH, a saturator-based humidity generator operating in a two-temperature mode is utilized. The condensing conditions are achieved in two ways: by increasing water vapour pressure (WVP) at a fixed temperature and by decreasing the temperature while maintaining a constant WVP. In general, when measuring RH under condensing conditions, the sensor indicates a temporary supersaturation state with an RH peak exceeding 100% before the onset of condensation. Subsequently, the RH value exhibits a delayed decrease when exposed to a non-condensing RH level. The experiments with a constant WVP demonstrate a lower likelihood of ice condensation compared to those with a constant temperature. This study demonstrates the measurement capability and behaviour of thin-film humidity sensors above 100% RH in the supersaturation states that are commonly observed in the free atmosphere at meteorologically-relevant temperatures.

X-ray Induced Electric Currents in Anodized Ta2O5: Towards a Large-Area Thin-Film Sensor.

We investigated the characteristics of radiation-induced current in nano-porous pellet and thin-film anodized tantalum exposed to kVp X-ray beams. We aim at developing a large area (≫cm2) thin-film radiation sensor for medical, national security and space applications. Large area (few cm2) micro-thin Ta foils were anodized and coated with a counter electrode made of conductive polymer. In addition, several types of commercial electrolytic porous tantalum capacitors were assembled and prepared for irradiation with kVp X-rays. We measured dark current (leakage) as well as transient radiation-induced currents as a function of external voltage bias. Large transient currents (up to 50 nA) under X-ray irradiation (dose rate of about 3 cGy/s) were measured in Ta2O5 capacitors. Small nano-porous Ta and large-area flat Ta foil capacitors show similar current-voltage characteristic curve after accounting for different X-ray attenuation in capacitor geometry. The signal is larger for thicker capacitor oxide. A non-negligible signal for null external voltage bias is observed, which is explained by fast electron production in Ta foils. Anodized tantalum is a promising material for use in large-area, self-powered radiation sensors for X-ray detection and for energy harvesting.

E-nose analysis of milk to detect the inclusion of hydroponic barley forage in the buffalo diet

This study explores the use of an electronic nose (E-nose), equipped with ten metal oxide semiconductor thin-film sensors, to detect raw milk samples from buffaloes fed hydroponic barley forage as a substitute for maize silage. 108 samples were collected on three different days, from three groups of twelve Italian Mediterranean buffaloes each. The control group (C) was fed a diet based on maize silage, which in the other groups was replaced by hydroponic forage at 50 % (LH group) and 100 % (HH group). The data pattern from the E-nose sensor responses data was analysed using linear discriminant analysis (LDA) and principal component analysis (PCA) as pattern recognition methods, to investigate the discrimination capability of the sensor array. Confusion matrix, obtained from LDA, correctly classified C, LH and HH milk at 90 %. Solid-phase microextraction with gas chromatography–mass spectrometry revealed that C samples had the highest total level of volatile organic compounds, particularly ketones, volatile fatty acids and esters, while HH had the lowest quantity of volatile fatty acids and higher amounts of p-cresol, 1-octen-3-ol and dimethyl sulfone. This has resulted in a greater response intensity of most E-nose sensors for C, such as W1S, W2S, W3S and W6S, which react to high concentrations of broad-range and aliphatic compounds. E-nose proves effective in rapidly identifying hydroponic forage in buffalo diets.

Experimental study on local scour protection and contact pressure of the facing water surface at the pier based on the guide pillar

The safety of pier foundations is an important issue in bridge construction, where local bridge scour is a major cause of bridge damage worldwide, exacerbated by ice sheets. This paper offers a live bed scour experimental investigation that assesses the impacts of the new anti-scour device guide pillar of different sizes on geometric properties of scour, downflow velocity distribution, and turbulence intensity around the pier under different flow velocities and roughnesses, and to select the optimum installation position and size of the guide pillar. The results demonstrate that the guide pillar has a considerable effect on the scour hole and downflow around the pier, and the maximum reduction rate of scour depth is 59.3% in the optimal installation position (2d). By arranging distributed thin-film pressure sensors on the pier and measuring the pressure distribution on the facing water surface of the pier and the position of the center of gravity, this paper analyzes the distribution characteristics of the water flow force on the pier and the impact resistance of the guide pillar to the pier scour. The study found that the guide pillar reduces the water flow force by 61.3% without considering the effect of hydrostatic pressure.

Modular slot-die coater for in situ grazing-incidence x-ray scattering experiments on thin films.

Multimodal in situ experiments during slot-die coating of thin films pioneer the way to kinetic studies on thin-film formation. They establish a powerful tool to understand and optimize the formation and properties of thin-film devices, e.g., solar cells, sensors, or LED films. Thin-film research benefits from time-resolved grazing-incidence wide- and small-angle x-ray scattering (GIWAXS/GISAXS) with a sub-second resolution to reveal the evolution of crystal structure, texture, and morphology during the deposition process. Simultaneously investigating optical properties by in situ photoluminescence measurements complements in-depth kinetic studies focusing on a comprehensive understanding of the triangular interdependency of processing, structure, and function for a roll-to-roll compatible, scalable thin-film deposition process. Here, we introduce a modular slot-die coater specially designed for in situ GIWAXS/GISAXS measurements and applicable to various ink systems. With a design for quick assembly, the slot-die coater permits the reproducible and comparable fabrication of thin films in the lab and at the synchrotron using the very same hardware components, as demonstrated in this work by experiments performed at Deutsches Elektronen-Synchrotron (DESY). Simultaneous to GIWAXS/GISAXS, photoluminescence measurements probe optoelectronic properties in situ during thin-film formation. An environmental chamber allows to control the atmosphere inside the coater. Modular construction and lightweight design make the coater mobile, easy to transport, quickly extendable, and adaptable to new beamline environments.

Electrodeposition of Co-Mo Alloys and Its Applications in Electrochemical Sensing of Phosphate

Quantification of phosphate ions in water ecosystems is crucial for maintaining a healthy aquatic environment and optimizing aquaculture parameters. While cobalt (Co) thin film modified electrodes are widely used as phosphate sensors, their selectivity and stability often require improvements for on-site measurement. The present work addresses this challenge by introducing a novel phosphate sensing platform utilizing Cobalt-Molybdenum (Co-Mo) alloy film deposited on copper substrate. The developed Co-Mo thin film sensor exhibited a good thermal stability (up to 60 °C) and significantly improved the detection ranges (10−6 M to 10−2 M). The influence of electrolyte pH and temperature toward potentiometric sensing of phosphate were investigated and the conditions were optimized to improve the sensor sensitivity. The sensor showed a sensitivity of −56 mV.dec−1 with a good correlation coefficient (0.988). The detection limit was determined to be 0.987 μM and the relative standard deviation (RSD) was 1.3% (n = 3). The Co-Mo thin film sensor exhibited negligible interference even in the presence of 10-fold excess concentrations of common interfering analytes, demonstrating its robust performance in real-world environment. To validate the field practicality, the sensor’s performance was successfully tested in real shrimp culture water samples, demonstrating its compatibility with complex environmental matrices.

Structural design and performance optimization of Co/Bi0.5Sb1.5Te3 artificially tilted multilayer thermoelectric devices

Due to the complex principle of transverse thermoelectric conversion and the specific preparation technique, there are few studies on the three-dimensional structure of artificially tilted multilayer thermoelectric devices (ATMTDs), which also lags the development of ATMTDs for applications. It is necessary to optimize the three-dimensional structure of ATMTDs to satisfy the requirements of practical applications in thermal sensors, power generation, refrigeration, and so on. In this paper, Co/Bi0.5Sb1.5Te3 ATMTDs are selected as the research object. A COMSOL Multiphysics simulation analysis and experimental validation are used to establish the relationship between the structure and its thermal sensing, power generation, and cooling performance. Results indicate that increasing the length significantly improves the thermal response voltage. Increasing the length and width enhances output power while increasing the height of the ATMTD improves the thermoelectric conversion efficiency. The effective cooling temperature improves when the heat transfer area decreases or the height increases. Based on these findings, flexible thin-film thermal sensors, high-efficiency waste heat power generation tubular devices, and high-efficiency refrigeration pyramidal devices are designed. The results will lead to effective optimization and promote the multi-field application of ATMTDs.

Study on the overall performance of ZrO2 nanoparticle reinforced Co and CoP composite coating prepared by electrodeposition

Co coating and CoP alloy coating reinforced by ZrO2 nanoparticles are prepared on the surface of the brass substrate by DC electrodeposition to improve the magnetic property and corrosion resistance. The Co/ZrO2 and CoP/ZrO2 composite coating electrodeposited on the surface of brass can be used in the field of thin-film magnetic heads, thin-film sensors and electronic circuits. By comparing the performance of different cobalt-based alloy coatings, the influence of ZrO2 nanoparticles on the electrodeposition and performance of Co coating and CoP alloy coating is studied. It is found that cobalt electrodeposition is a typical irreversible process with diffusion control. The CoP alloy coating comprises about 81% Co and 19% P. However, the electrodeposited CoP/ZrO2 composite coating possesses about 86% Co, 3% P, and 11% Zr. The incorporation of a 15 g/L ZrO2 nanoparticle with the size of 50 nm is beneficial to improve the cobalt content and decrease the amount of phosphorus in the CoP/ZrO2 composite coating. The hardness of CoP alloy coating is about 350 HV. However, the surface hardness of Co/ZrO2 and CoP/ZrO2 composite coating is about 400 HV and 470 HV, respectively. All the cobalt-based coatings show cellular surface morphology. The ZrO2 nanoparticles incorporated in the cobalt coating can enter into the cobalt lattice or disperse at the grain boundary to refine the grain size and limit the displacement of magnetic domain to improve the corrosion resistance and coercivity extremely. It is found out that the electrodeposited CoP/ZrO2 composite coating has the best corrosion resistance with only 9.7 μA/cm2 corrosion current density and the largest coercivity of 665.1 Oe. The optimal corrosion resistance and good magnetic performance of prepared CoP/ZrO2 is a promising material in the field of microelectromechanical systems as micro pumps, magnetic read heads, micro motors, and so on.

Fabrication and characterization of smart titanium alloy bolt based on high-frequency piezoelectric thin-film.

We reported here on the fabrication and characterization of a smart titanium alloy bolt based on a high-frequency piezoelectric thin-film sensor. The thin-film sensor was directly deposited on a titanium alloy bolt head with radio frequency magnetron sputtering and characterized by a scanning electron microscope and an atomic force microscope. The ultrasonic characteristics of the smart bolt, which include a pure and broad frequency spectrum peaked at 14.81MHz, high measurement accuracy below 3%, and high repeatability free from some interference from bolt detection position change, were fully characterized. No obvious frequency shift was observed with the increase in axial preload. Based on the mono-wave method [TOF (time of flight) of longitudinal mode wave], TOF change increased linearly with preload force in the range of 0-20kN. With the increase in temperature from 22 to 150°C, the TOF linearly increases while the longitudinal wave velocity linearly decreases. The results indicate the prepared smart titanium alloy bolt is suitable as a smart aviation and automotive fastener.

Study on aluminium oxide doping modification of indium oxide and thermoelectric properties

Traditional thermocouples face challenges in meeting the temperature measurement requirements of crucial aero-engine components, such as low interference, high temperature resistance, quick response, and in-situ measurement. The temperature measurement requirements mentioned above can be satisfied by thin film thermocouples, thanks to advancements in thin-film preparation technology. In this study, the indium oxide (In2O3) was calculated using first principle calculation both before and after doping. It was found that doping Aluminium oxide (Al2O3) can increase the Seebeck coefficient of In2O3. Solid-phase sintering was used to create aluminum oxide-doped In2O3 nanopowders, and thin film thermocouples were fabricated using screen printing. The thermoelectric characteristics of thin film thermocouples were studied to analyze the effects of different annealing procedures and doping concentrations. The optimal annealing process was determined to be at 1300 °C for 1 h, and the ideal doping ratio was found to be Al0.1In2O3.15. The indium oxide film doped with aluminum oxide exhibits a Seebeck coefficient that is 45.9% higher than that of the undoped indium oxide film. The thin film thermocouples underwent tests for impact and vibration resistance, laser pulse response, surface and cross-section morphology, X-ray diffraction, and thermoelectric output. It has been confirmed that doping indium oxide with aluminum oxide can increase a material's Seebeck coefficient. Additionally, a thin-film temperature sensor that has been prepared can be used in challenging conditions to meet the temperature measurement requirements of an aero engine.

Mechanical behavior monitoring of composite hybrid bonded‐riveted joints using high‐stability MXene sensors

AbstractComposite adhesive rivet hybrid connection structure has been more and more recognized and applied in aerospace, automobile, and other industries due to its high strength, corrosion resistance, and good stability. However, due to the particularity of the composite structure and the complex nonlinear coupling factors existing in the bearing process of the adhesive rivet hybrid connection structure, it is difficult to carry out structural health monitoring of the composite adhesive rivet hybrid connection structure. In this paper, a new fabrication technique is proposed to fabricate MXene thin film sensors with excellent performance. The MXene sensor can be tailored to the required size and arrangement to monitor the hybrid connection structure. The multi‐stage loading‐unloading test verifies the feasibility of using the MXene sensor to monitor the hybrid connection structure. The monitoring curves of the MXene sensor for composite adhesive rivet mixed connection structure specimens under low‐speed impact test and vibration fatigue test were obtained, and the sensing mechanism of the MXene sensor was explained. The proposed monitoring method based on the MXene sensor is suitable for the health monitoring of adhesive rivet hybrid connection structures under tensile‐compression, impact, and vibration conditions.Highlights MXene sensors can be integrated into composite hybrid bonded‐riveted joints without defects. MXene sensors combined with flexible circuits can form a high‐stability monitoring array. Monitor the mechanical behavior of bonded and riveted areas by the resistance change rate of MXene sensors. Real‐time monitor the micro damage and acceleration changes under the vibration environments.