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All-solid-stated pH sensors based on metal/ metal oxide were widely used in mixed heterogeneous environment, such as soil or soilless cultivation. In this study, an all-solid-stated pH sensor prepared by magnetron sputtering was presented, of which the working electrode was antimony, and reference electrode was Ag/AgCl electrode, and heat treated process was conducted to improving the performance of all-solid-stated planar pH sensor. The electrodes heat treated at the temperature of 100°C, 200°C, 300°C, and 400°C were tested through surface morphology analysis, energy spectrum analysis and electrochemical experiments. The results showed that the heat-treated temperature had a remarkable effect on the performance of the pH sensor. Specifically, the pH sensor heat-treated at 200°C had excellent performance, with the sensitivity 74.0 mV/pH, the response time less than 3 s, the standard deviation less than 2 mV in 700 s period. The developed sensor can be applied in pH detection in soilless culture and is promising to popularize in industrial production. [ABSTRACT FROM AUTHOR]

A new hydrogen (H2) sensor based on a sputtered aluminum-doped zinc oxide (AZO) layer decorated with evaporated palladium (Pd) nanoparticles (NPs) was manufactured and studied herein. The use of Pd NPs can efficiently improve the hydrogen gas detecting performance owing to the increased effective surface area, enhanced catalytic reactivity, and spillover effect of noble Pd metal. Energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), high-resolution scanning microscopy (HRSEM), and transmission electron microscopy (TEM) were employed to investigate the related material properties. Experimentally, good hydrogen gas detection performance, such as a higher sensing response of $1.86\times 10 ^{4}$ under 1% H2/air gas accompanied by a response (recovery) time of 25 s (52 s) and an extremely low detecting content of 50 ppb H2/air at 250°C were acquired from the studied Pd NP/AZO device. The proposed sensor also shows long-term stability related to hydrogen gas. [ABSTRACT FROM AUTHOR]

An optically tunable perfect light absorber as a refractive index (RI) metamaterial (MM) nanobiosensor (NBS) is designed for sensing chemicals, monitoring the concentration of water-soluble glucose, and detecting viruses. This plasmon induced tunable metasurface works based on multiband super-absorption in the infrared frequency regime. It consists of a metal mirror that facilitates the MM to work as an absorber where the metal pattern at the top layer creates an enhanced evanescent wave that facilitates the metasurface to work as a RI optical sensor. The modelling and numerical analysis are carried out using Finite Difference Time Domain (FDTD) method-based software, CST microwave studio where a genetic algorithm (GA) is used to optimize the geometric parameters. We demonstrate multiband super-absorption spectra having maximum absorption of more than 99%. Furthermore, we show how the multiband super-absorber nanostructure can be used as a RI NBS, where the resonance frequency shifts with the RI of the surrounding medium. The achieved opto-chemical sensitivity is approximately 65 nm/RIU RIU, the bio-optical sensitivity to detect viruses is approximately 76 nm/RIU; and the optical sensitivity of the water-soluble glucose concentration is about 300 nm/RIU; all sensitivities are comparable in comparison with the reported values in the literature. [ABSTRACT FROM AUTHOR]

Excess heat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time constants.  The Mo/Au bilayer transition edge sensor (TES) bolometric detectors initially fabricated for the high resolution mid-infrared spectrometer (HIRMES) exhibited two response thermalization scales, one of which is a few times longer than estimates based upon the properties of the bulk materials employed in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional to the pixel area, which ranges between ∼0.3 and 2.6 mm2.  Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant.  Additional information about the nature of this excess heat capacity is gleaned from glancing incidence X-ray diffraction, which reveals the presence of molybdenum silicides near the silicon surface which is a consequence of the bi-layer deposition.  Quantitative analysis of the concentration of excess molybdenum, estimated with secondary ion mass spectroscopy, is commensurate to the additional heat capacity needed to explain the anomalous time response of the detectors. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots based on lead sulfide (PbS) are very attractive materials for the realization of novel image sensors. They offer low cost synthesis, compatibility with a variety of substrates and processing on large area. The tunable band gap enables selective light detection from the visible wavelengths up to the short-wave-infrared (SWIR). This work describes the roadmap towards the integration of quantum dot photodiodes (QDPD) on top of a Si based CMOS read-out circuit. Photodiodes using an n-p junction architecture are fabricated on Si substrates, showing a dark current of 30 nA/cm2 at −1 V reverse bias, EQE above 20% and specific detectivity above 1012 cm Hz1/2 W−1 at the wavelength of 940 nm. Efficiency is improved by reducing absorption in the top contact through optical design. Furthermore, photolithographic patterning of the thin-film stack is introduced for the first time, showing the feasibility of pixel pitches down to $40~\mu \text{m}$ , opening the way towards high resolution monolithic infrared imagers and the incorporation of infrared and visible sensitive pixels side by side. [ABSTRACT FROM AUTHOR]

This article describes a simple though extremely effective sensor for acetone monitoring in the breath. The sensor is capable of monitoring the presence of acetone at parts per million (ppm) concentrations, thus being suitable for a diabetes diagnosis. It has a dimension of $3 {\,\,\mathrm {mm}} \times 6 {\,\,\mathrm {mm}}$ and a cost of less than one dollar. The small dimensions allow one to greatly limit the power required to increase its temperature, and its high selectivity with respect to other gases present in the breath reduces the risk of false-positive responses. The sensor is based on a thin alumina substrate on which platinum strips are deposited on both faces. A thin Nb2O5 layer with a nanometric thickness provides the required sensitivity and selectivity. Sensor prototypes have been characterized by field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) and proved an inherent linear response up to a few ppm of acetone. [ABSTRACT FROM AUTHOR]

We investigate thin film thermocouples (TFTC) as thermal gradient sensors at the micro-scale and using thermocouples perpendicular to each other with separation distances of 20-100 μm. Pairs of x-direction and y-direction thermocouples sense the thermal gradient while another calibrates the Seebeck coefficient to be S = 22.27 ± 0.01 μV/K. The smallest detectable temperature difference is 10mK, and the sensitivity is 0.5/ μm. The minimal Johnson-noise limited performance for thermocouple devices with typical integrated-circuit dimensions is 1.4 nV/√Hz. Our design further reduces the number of leads L needed to measure N thermocouples to L = N and allows direct measurement of thermal gradient instead of interpolation. Our design implements a local metal layer A at the gradiometer distinct from an extended metal layer B. This design is robust against any erroneous Seebeck contribution caused by minor film thickness variations in the extended leads. This device can be applied for embedded thermal management systems that require high resolution and rapid-response thermal management, such as stacked three-dimensional (3D) integrated circuits. [ABSTRACT FROM AUTHOR]

This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/ $\sqrt{\text{Hz}}$ at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm $^2$. NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions. [ABSTRACT FROM AUTHOR]

Torque measurements are used in a number of controls applications, but indirect coupling, size, and the quality of commercially available sensor materials can limit their utility. Here, a compact magnetostrictive torque sensor is made by electrodeposition of Fe1–xGax (0.1

A simple and fast method for the determination of vanadium in water samples was established using adsorptive stripping voltammetry. The proposed method includes the formation of a complex by reacting vanadium with cupferron and its adsorption on the in situ plated lead film electrode used as a working electrode. The optimum analytical conditions include supporting electrolyte containing 0.3-mol L−1 acetate buffer pH = 5.6, ${3} \times {10}^{-4}$ mol L−1 Pb(II) and ${7} \times {10}^{-{4}}$ mol L−1 cupferron. A linear response of V(V) in the concentration range of ${1} \times {10}^{-9}$ to ${7} \times {10}^{-8}$ mol L−1 (r = 0.998) was obtained with the detection limit of ${3.2} \times {10}^{-10}$ mol L−1 using accumulation time of 30 s. Selectivity of the method was determined by investigating the influence of a number of foreign ions. The interferences of surfactants were precisely studied and successfully minimized by preliminary mixing with resin. The accuracy of the method was tested by analyzing certified reference material (SPS-WW1 waste water) and river water. [ABSTRACT FROM AUTHOR]

A kirigami-based strategy was investigated for strain transduction, using serpentine gold traces embedded in thin-film Parylene C. Multiple kirigami slit designs were evaluated via COMSOL simulation and mechanical force testing; sensors having tightly packed slits stretched up to 17.5 mm (350% strain) before mechanical failure and 9 mm (180% strain) before electrical failure. Strain transduction was achieved by monitoring DC resistance changes during stretching. DC resistance linearly increased with strain, with sensitivities up to 0.16 $\Omega$ /mm (gauge factor = 0.007) and minimal hysteresis. High-frequency trace impedance and inter-trace capacitance were also investigated during strain cycling. Capacitance increased with strain and high-frequency impedance show a nonlinear strain relationship. The biocompatible construction and extremely low profiles (20 $\mu \text{m}$ thick) of these sensors are attractive for minimally invasivein vivostrain sensing applications. [2018-0130] [ABSTRACT FROM AUTHOR]

A novel H2 sensor based on an InGaZnO thin-film transistor (IGZO TFT) with Pd source/drain electrodes as sensing medium is fabricated. Without the need of heating, rapid and concentration-dependent response (in the form of drain-current increase) of the sensor is observed under various cycles of H2 exposure/evacuation with H2 concentration ranging from 200 to 15 000 ppm. The drain-current increase is due to a decrease in barrier height at the interface between the Pd source and IGZO channel induced by the formation of a hydrogen dipole layer at the interface. By comparing this sensor with its counterpart based on pentacene OTFT having an opposite response, it can be claimed that the same hydrogen dipole layer has opposite effect on the two TFTs: it creates an electric field that can assist the flow of electrons from the source electrode to the IGZO channel, but oppose the flow of holes from the source electrode to the pentacene channel. As a result, the IGZO TFT can work in an OFF-to- ON mode during sensing, and so the standby power of sensing circuit could be reduced. Although the OTFT sensor shows higher sensitivity and faster response due to the higher flexibility of the pentacene layer, the proposed sensor has a better stability at high temperature due to the larger bandgap of IGZO and so is suitable for hydrogen-sensing applications in a wider range of operating temperature. [ABSTRACT FROM AUTHOR]

Superconducting titanium thin films are good candidates for transition edge sensors. In this paper, we deposit titanium thin films on cooled silicon-on-insulator substrates by using electron-beam evaporation. The deposition rate dependence of the film stress, resistivity, and superconducting transition temperature are presented and analyzed. The relationship between film electrical properties and thickness is discussed. For investigating the heating influence on thin Ti films, a depth profile of oxygen diffusion in the films is also analyzed by X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

This letter develops a thin film electrocardiography (ECG) sensor patch using poly (dimethylsiloxane) as the base material, which can be fabricated with low cost and large area compatible coating processes. This design enables easy integration with the readout circuit board to form a compact ECG patch system for wearable uses. The ultra-thin and soft PDMS film make it conform well to the curvilinear skin surface for low electrode-to-skin impedance and strong adhesion. By using dispensed silver paste on the copper tape film, reliable and highly conductive connection is built between the skin surface electrode and the readout circuit. A two-electrode configuration ECG patch system was made and worn on a volunteer for a whole day. The test results show that the measured signal quality with this ECG sensor patch will not be affected after normal activities. [ABSTRACT FROM PUBLISHER]

Vanadium pentoxide xerogel films deposited onto gold microelectrodes were micropatterned by thermally induced conversion into crystalline \alpha -V2O5, using optical lithography written at the focus of a confocal Raman microscope. The laser scribing process improved the electric contact and promoted the n -doping of the film with V^\mathrm IV ions. In this way, a field effect transistor like device was constructed and successfully applied as humidity sensor, where the combined lithographic design and the application of a negative back gate field ( V \mathrm {G} = -10.0 V) boosted the source–drain current by a hundred times, leading to a large gain in sensitivity. [ABSTRACT FROM PUBLISHER]

We report on investigation of the mechanical properties of paper electronics (printed and made out of paper). One key objective of such paper electronics is to achieve ultraflexibility. Therefore, it is important to understand electrical functionality and reliability of paper electronics under various physical (mechanical) deformations. Here, we show the general mechanical properties of the cellulose paper used and its electrical behavior under applied strain, tackling the main effects that need to be identified when building paper-based systems, from product performance and stability perspective. An overview of the stress–strain behavior of silver ink on paper is discussed, and then, we tackle a more specific analysis of the performance variations of paper sensors made with recyclable household materials when exposed to various mechanical conditions of tensile and compressive bending. This paper is important for developing stable wearable sensors for incorporation into Internet of Everything applications. [ABSTRACT FROM PUBLISHER]

Aerosol effects evaluation on Earth’s radiation budget demands knowledge of its concentration, spatial, and temporal distribution. Therefore, long-term measurements of aerosol properties in different regions of Earth are very important. In this paper, indium nitride (InN)- and indium oxynitride (InNO)-based photodiodes calibration was realized. A pyranometer was used in this paper. Calibrated InN and InNO Schottky photodiodes will be used for aerosol detection. According to the calibration tests, it was found that the most suitable sensors for the continuation of an aerosol statistical study in the atmosphere are those made with the InNO deposited with oxygen 10% and 20%; their correlation coefficient values are almost one. Besides, their measures do not reach the saturation point. In future, we intend to use these devices in a quantitative study of aerosols present in the center of a large city, to get a sense of human interference in the atmosphere composition and its consequences. [ABSTRACT FROM PUBLISHER]

As a natural biopolymer, chitosan has a very unique protonic conductivity that is highly sensitive to water vapor. However, there has been no report on pure chitosan-based resistive humidity sensors, probably due to the difficulty of direct-current measurement of protonic current in chitosan. Here, a simple and cost-effective chitosan-based protonic conductive humidity sensor is presented. The sensor exhibits a large conductance response of four orders of magnitude when relative humidity is increased from 10% up to 90%. The effects of adsorbed water on proton density and dielectric constant change of chitosan could be responsible for the giant humidity response. More importantly, the sensor shows high stability, repeatability, recoverability, and selectivity to water vapor over ethanol, acetone, and toluene vapors. [ABSTRACT FROM PUBLISHER]

This paper deals with the development of an accurate and precise humidity sensor, which is based on the extension of Thompson and Lampard theorem and a sol–gel-based thermally and chemically stable metal oxide thin film. In light of the extension of the theorem, most appropriate conductors are shaped around the material and the resulting sensor has cross conductance, which is the function of thickness only. It is fabricated and tested for different ranges of humidity. It is found that the fabricated sensor has outstanding static and dynamic characteristics. [ABSTRACT FROM PUBLISHER]

In this paper, we are proposing a novel rapid sol–gel thin-film porous metal–oxide-based surface acoustic wave (SAW) humidity sensor. For the SAW sensor, the center frequency of 433.92 MHz has been selected, and the device has been configured in a high-frequency oscillator circuit to explore the frequency response in the presence of water vapor. The sensitive thin film of sol–gel $\gamma $ -Al2O3 coated with a drop dry method offers very high surface-to-volume ratio with the distribution of micropores making the sensor highly sensitive for moisture detection. Pore morphologies of the film have been studied by field emission scanning electron microscope and atomic force microscopy. The \gamma $ phase of alumina of the film has been characterized with X-ray diffraction. The sensor has been tested from 3% relative humidity (RH) to 85% RH. The proposed sensor has very fast ( T_{r}= 1 s) response time and excellent yield ratio in comparison with the conventional commercial capacitive aluminum oxide sensor. The sensitivity (3%–20% RH) and the hysteresis (3%–85% RH) are found to be 120-Hz/% RH and 0.3%, respectively. The sensor can be useful for different applications, including moisture dispersion inside electronic gadgets, dryers, ovens, textile production, semiconductor device processing, food processing, medicine, and sealed packages. [ABSTRACT FROM PUBLISHER]

Gas sensors have been demonstrated based on the conductivity changes in ultrathin films. These sensors operate in a regime where three different physical phenomena determine the total resistivity of the film; quantum mechanical coupling between metallic islands, bulk material conductivity of the islands, and network resistivity. We present a lumped parameter model that simulates thin-film growth and calculates the total film resistance during the growth process accounting for these three phenomena. The model contains four free parameters and yields a good agreement with experimental data presented for palladium, titanium, and gold. The primary benefit of this model is that it shows the relative contribution of each source of conductivity during the growth process providing insight into the operation of ultrathin films as gas sensors. We then model an ultrathin-film palladium-based hydrogen sensor and show that the sensing mechanism is primarily due to variations in quantum tunneling. [ABSTRACT FROM AUTHOR]

The use of healthcare sensors in portable and wearable devices has drawn increasing attention in the last few months. More particularly, the integration of ultraviolet (UV) light sensors to monitor UV sunlight radiation in next generation smartphones has been widely discussed recently. Here, we propose 4H-SiC Schottky photodiodes with three different geometries suitably designed to operate in photovoltaic condition for UV light monitoring. The electrical and optical characteristics of these devices are investigated as a function of the bias and temperature applied to the detectors. [ABSTRACT FROM PUBLISHER]

A high overload pressure sensor is prepared by surface micromachined technology, and its full scale pressure is 2.5 MPa. The structure of the proposed sensor is based on a seal cavity made by sacrificial layer, a deposition of polysilicon nanofilm acts as piezoresistors on the diaphragm. The stress distribution of the diaphragm of the sensor is simulated by the large displacement static analysis and the nonlinear contact analysis. Due to polysilicon high tensile strength and appropriate cavity height, the sensor full scale output voltage and overload capacity is greatly improved. The measured results indicate that the overpressure of the sensor sample is seven times higher than its full-scale pressure, and its full scale output voltage is 362 mV with a supply voltage of 5 V. [ABSTRACT FROM PUBLISHER]

In this paper, we report the development of an oxygen sensor using a simple device made from a film of ZnO crystals dispersed over a paper surface. Due to the high porosity of this kind of device made from paper and ZnO, a large photoconductive effect is observed as result of the fast absorption and desorption of oxygen from the ZnO surface. To detect oxygen, we propose to use ultraviolet (UV) illumination over the photoconductive surface of the sensor, the applied UV light produces oxygen desorption causing current variations through the sensor that are proportional to the oxygen presence nearby the sensor surface. The sensor developed in this paper is attractive because it is remarkably easy to fabricate, employs only very low-cost materials for its construction, and shows a better sensitivity at low concentration of oxygen at partial vacuum environments. [ABSTRACT FROM PUBLISHER]

The optical and conductometric responses of sol-gel-based ZnO thin films with embedded 5% mol. Au or Pt nanoparticles (NPs) have been compared at different operating temperatures, to assess the effect of noble metal additions on to H2, CO and NO2 gases sensors response. The scanning electron microscopy and X-ray diffraction techniques have been utilized for morphological characterization of the crystal structures of the films after annealing at 400°C for 30 min and the effect of Au and Pt NPs additions on crystallite growth is discussed. Au NPs additions is effective to enhance the optical response to H2 and CO at 390 nm and in the 500-700-nm wavelength range at 300- °C temperature. No optical response to NO2 gas, even at low concentrations has been measured in the optical mode. The catalytic action of Pt NPs additions powerfully improves both the optical to H2 and CO at 390 nm, and the conductometric gas responses. Detection limits as low as 20-ppb NO2 and 50-ppm H2, in line with the best performances reported to the best of our knowledge in literature for ZnO-based sensors, have been measured in the conduction mode. Response times have been also compared, highlighting the positive effects played by Pt additions. [ABSTRACT FROM PUBLISHER]

In this paper, the TiO2/Ag/TiO2 (TAT) multilayer thin films were deposited on a corning glass substrate at room temperature using radio frequency magnetron sputtering technique. The TAT multilayer was characterized by field-emission scanning microscope, atomic force microscopy, X-ray diffraction, and ultraviolet (UV)-visible spectroscopy. The TAT multilayer can be optimized to obtain a transmittance more than 80%. With a 360-nm illumination and 5 V applied bias, it was found that the fabricated UV photodetectors (PDs) with TAT structure showed much higher photoresponse (10 A/W) than traditional TiO2 metal-semiconductor-metal PDs (0.08 A/W). This indicated that the TAT multilayer structures have potential to be employed in the PD devices of high performance. [ABSTRACT FROM PUBLISHER]

In this letter, TiO2 thin films were prepared via sol-gel method and metal/semiconductor/metal ultraviolet (UV) detectors with Pt Schottky contact were fabricated. At 5 V bias, the dark current of the device was only 80 pA. Diffusion theory was adopted to analyze the low dark current mechanism, which is consistent with the experimental results. The device shows a remarkably reduced decay time of 41.53 ms. The low dark current and improved time response performance may be attributed to the high effective Schottky barrier between Pt and TiO2 film. High responsivity of 34.5 A/W was achieved at 300 nm UV light and the ratio of photocurrent to dark current is about five orders of magnitude, which is much larger than that of other semiconductor photodetectors. [ABSTRACT FROM PUBLISHER]

A miniature Fabry-Pérot interferometer is proposed and experimentally demonstrated for temperature measurement. The cavity of the interferometer is a small air gap between the end-face of a single-mode fiber and an ultrathin graphene. A well-defined interference spectrum is obtained, and the dip wavelengths are employed to demonstrate the temperature change. Due to the smart intrinsic characteristics of the graphene film, the proposed device can measure the temperature up to 1008°C, and shows an ultrahigh sensitivity of 1.56 and 1.87 nm/°C at the temperature range of 500°C-510°C and 1000°C-1008°C, respectively, making it a good candidate for high-temperature monitoring in the harsh environment. [ABSTRACT FROM PUBLISHER]

In this paper, we report on the development of a highly sensitive, relatively low-temperature ethanol sensor based on sol-gel derived p-TiO2 thin film. The p-type anatase TiO2 thin film was deposited by sol-gel technique on a thermally oxidized <;100> p-Si (resistivity 5 Ω cm) substrate. Anatase TiO2 phase with <;101> nanocrystallinity was confirmed with an average particle size of ~11 nm from X-ray diffraction and field emission scanning electron microscopic study. Ethanol sensor study, in the resistive mode, was carried out at a relatively low operating temperature range (75 °C-175 °C) for sensing low concentrations of ethanol in air (5-100 ppm). Response magnitude of ~146% was observed at 150 °C toward 100-ppm ethanol (in air) with corresponding response time and recovery time of 39 and 15 s, respectively. The sensor showed appreciably high-response magnitude (129%) even at low ethanol concentration (5 ppm) with acceptable response and recovery time (54 and 22 s, respectively) at the same operating temperature (150 °C). At a particular temperature, for all the ethanol concentrations, sensor showed minimal base line resistance drift, thereby offering highly repeatable and stable sensing performance. Ethanol selectivity study against other volatile organic compounds, such as methanol, acetone, and 2-butanone, was also investigated and was found to be quite promising. Ethanol sensing mechanism for such p-type TiO2 has also been discussed in the light of corresponding oxygen vacancy model. [ABSTRACT FROM PUBLISHER]

In this paper, microbolometers with different geometric designs were fabricated using polycrystalline silicon (polysilicon) films from TSMC 0.35 μm (D35 type) and 0.18 μm (T18 type). D35 microbolometers with high-resistance films showed negative temperature coefficient of resistance (TCR) values, whereas T18 microbolometers with low-resistance films showed positive TCR values. Results indicate that conventional designs with large areas of infrared absorbers can be optimized using uniform suspended arms throughout the microbolometer in the two types of devices. Finite element modeling indicates that the heat flux of microbolometers with uniform beams is evenly distributed and thus results in improved TCR values. [ABSTRACT FROM PUBLISHER]

In this paper, poly (dimethyldiallylammonium chloride) (PDDA)/graphene oxide (GO) composite thin films with multilayer are layer-by-layer (LbL) assembled on quartz crystal microbalance (QCM) for humidity detection. The static and dynamic humidity sensing performances are successively studied using impedance analysis and oscillating circuit methods. The experiment results show that PDDA/GO composite thin films coated QCM humidity sensor exhibits large humidity sensing response, low humidity hysteresis, fast response and recovery, and excellent repeatability. In addition, the influence of the number of assembled layers of PDDA/GO on the performances of QCM humidity sensor has also been investigated. Meanwhile, the origin of the obtained excellent humidity sensing performances has been analyzed by considering the water adsorption/desorption mechanism of PDDA/GO composite multilayer thin films. This paper suggests that LbL self-assembly technique is a promising candidate method for fabricating high-performance QCM humidity sensor using PDDA/GO composite multilayer thin films as sensing material. [ABSTRACT FROM PUBLISHER]

A localized surface plasmon resonance sensor based on molecularly imprinted polymer (MIP) coated Au nanoparticle (AuNP) was developed to selectively detect α-pinene vapor. AuNPs were deposited on glass slides via Au ion sputtering method. The MIP was synthesized using methacrylic acid as monomer, ethylene glycol dimethylacrylate as cross-linker, and α-pinene as template. Adsorption characteristics of MIP powder and coating films were evaluated using gas chromatography mass spectrometry. The influence of molar ratio of template (α-pinene) to monomer on the absorption characteristics of MIP film was investigated. The largest affinity absorption amount of polymer film was achieved when the molar ratio of template to monomer was 1:4. Prepolymerized MIP mixture was spin coated on the sputtered AuNPs. The results showed that plasmon resonance peak in spectrum and the refractive index sensitivity depended on the polymer layer thickness. Better sensitivity and selectivity of MIP coated AuNPs sensor were realized at the spin coating speed about 1400 r/min. The real-time responses of α-pinene imprinted polymer coated AuNP sensor to three terpene vapors: α-pinene, limonene, and y-terpinene were verified to be selective, rapid, and reversible. [ABSTRACT FROM PUBLISHER]

We demonstrate an integrated waveguide platform and optomechanical transduction circuit for chip-scale displacement sensing. The waveguide consists of a thin silicon nitride core layer, a thick silicon oxide bottom cladding, and a top air cladding with a large evanescent field at the waveguide surface. Although the structures feature subwavelength (<;λ/4ncore) vertical confinement, they are fabrication tolerant with micrometer-scale lateral features. We demonstrate via simulations and measurements that the waveguides exhibit a low confinement with a maximized evanescent field as well as an effective index only slightly larger than the SiO2 bottom cladding index. Despite the low confinement, the waveguide platform enables complex photonic circuits. As a demonstration of this technology, we fabricate and characterize an unbalanced Mach-Zehnder interferometer for chip-scale displacement sensing. A micrometer-scale fiber taper interacts with the waveguide's evanescent field and induces a phase shift proportional to displacement, thereby acting as an optomechanical transducer. We analyze the responsivity, displacement limit of detection, and strength of optomechanical coupling for high-resolution sensing. An outlook toward other applications is also given. [ABSTRACT FROM PUBLISHER]

Based on the design of a lithium ion battery cell and the resulting thermophysical properties, considerable temperature gradients may form within the cell not only during abusive scenarios. While the temperature gradients during normal operation are mostly negligible for small cells, which are commonly employed in mobile applications, the discrepancy between the temperature inside a battery cell and the cell's surface can be significant for larger scaled cells, which are employed, e.g., in automotive applications. Battery management systems that rely on a monitoring of the cell's surface temperature may consequently lead to an unfavorable operation of the whole battery in terms of aging and safety aspects. Thus, we hereby present an approach of designing, producing, and incorporating an all Kapton-based temperature sensor for an in situ temperature monitoring of lithium ion pouch cells. First prototypes are developed as a proof of concept when using a common potential for a thermocouple matrix that will later allow for a spatially resolved temperature monitoring within a lithium ion pouch cell. The interactions between the sensor and the cell are investigated and further design steps for improvements in functionality are elaborated. [ABSTRACT FROM PUBLISHER]

An adaptive neurofuzzy (ANFIS) evaluation study has been applied on tapered plastic multimode sensors. This study is basically using tapered plastic multimode fiber polymethyl methacrylate (PMMA) optical as a sensor. It is proposed and demonstrated for continuous monitoring of solutions based on different concentration of sodium chloride and glucose in deionized water. The tapered PMMA fiber was fabricated using an etching method involving deionized water and acetone to achieve a waist diameter and length of 0.45 and 10 mm, respectively. In addition, a tapered PMMA probe, which was coated by silver film, was fabricated and demonstrated using calcium hypochlorite (G70) solution. The working mechanism of such a device is based on the observation increment in the transmission of the sensor that is immersed in solutions at higher concentration. As the concentration varies from 0 to 6 ppm, the output voltage of the sensor increases linearly from 3.61 to 4.28 mV with a sensitivity of 0.1154 mV/ppm and a linearity of more than 99.47%. The silver film coating increases the sensitivity of the proposed sensor due to the effective cladding refractive index, which increases with the coating and thus allows more light to be transmitted from the tapered fiber. To estimate the output voltage response of the sensors with and without silver film, this paper constructed a process, which simulates the sensors voltage output in regard to different concentration of calcium hypochlorite with ANFIS method. This intelligent estimator is implemented using MATLAB/SIMULINK and the performances are investigated. The simulation results presented in this paper show the effectiveness of the developed method. [ABSTRACT FROM PUBLISHER]

In this paper, we present a multiparametric microsensor platform for metabolic monitoring in vivo. In contrast to silicon or ceramic-based systems, the flexible, implantable polymer-based sensor strip is manufactured in a cost-effective hybrid of thin-film and laminate technology in a wafer-level process. Flexibility allows easy handling and placement in soft tissue. It comprises a microelectrode array for up to four electrochemical, amperometric micro-(bio)sensors, and an integrated reference electrode. The energy metabolism parameters glucose, lactate, and oxygen as well as the neurotransmitter glutamate were measured. The sensors allow dynamic, highly sensitive, localized, long-term, online measurement of up to four metabolic parameters with a single device. The reliable analytical performance of the sensors, stability of the reference electrode, and the multiparametric measurement are shown. The sensor can be inserted directly into the tissue for in vivo applications. [ABSTRACT FROM PUBLISHER]

The cupric oxide (CuO) thin films are promising materials in gas sensor applications. The CuO exhibits the highest sensitivity for hydrogen sulfide, but it may be also used as a sensor for carbon monoxide or nitrogen dioxide. The sensitivity and long-term stability are the critical issues in such applications. The author presents the investigation results on amorphous films of the CuO and nanocrystalline CuO doped with Au, Pd, and Cr. The films have been deposited in magnetron sputtering technology on low temperature cofired ceramics substrates. The results of gas sensors' response are as well presented and discussed. The long-term stability test has been performed. The films phase composition, microstructure, and surface topography have been assessed by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy methods. [ABSTRACT FROM PUBLISHER]

In this paper, the fabrication and results of zinc oxide (ZnO) thin-film CO gas sensor are discussed. The thin film of c-axis oriented ZnO is deposited on Si/SiO2 substrate at room temperature using RF magnetron sputtering technique. The deposited ZnO film is annealed at different temperatures starting from 200 °C to 400 °C. The crystalline structural properties are analyzed by X-ray diffraction technique and the preferred orientation of ZnO thin film (along 002 direction) is found at 400 °C. Further, ZnO thin film is characterized by scanning electron microscopy and surface profilometer to analyze the surface properties and thickness. The deposited ZnO film is supported by Au electrodes and Pt microheater to couple the sensing signal with outer circuitry. A measurement system is also developed to measure the gas sensing properties and the results are discussed in detail. [ABSTRACT FROM PUBLISHER]

We demonstrate the capacity of a double layer thin-film system, composed of polyaniline and fluoral-p, to sensitively detect and selectively bind formaldehyde vapor using an interdigitated electrode assembly. The sensor response scales with the concentration of formaldehyde vapor and does not respond significantly to other potentially interfering molecules. This heightened response and selectivity result from imprinting the polyaniline layer with a molecular memory for ammonia. The chemistry of the double layer detection is discussed in terms of the Hantzsch reaction and the p-type semiconducting activity of polyaniline. [ABSTRACT FROM PUBLISHER]

This paper presents a surface-micromachining technology to fabricate silicon carbide (SiC)-based capacitive micromachined ultrasonic transducers (CMUTs). The use of dc-sputtered amorphous SiC as a structural layer allows the fabrication process to limit the temperature to a thermal budget of 200 °C, which is the lowest reported to date, making this technology ideally suited for above-IC integration. The high Young's modulus of the deposited SiC film, along with its very low residual stress, results in high strength and resilient CMUT membranes. The placement of the suspended aluminum electrode directly at the bottom side of the membrane reduces the effective size of the electrostatic transduction gap, resulting in superior electro-mechanical coupling. Fabricated transducers are tested in air with both continuous-wave and pulsed signals, using a pitch-and-catch configuration. The transducer pair, composed of 110-μm-diameter membrane arrays, exhibits a resonant frequency of 1.75 MHz, a 3 dB-bandwidth of 0.15 MHz, and a transmission gain of -38 dB. The CMUT prototypes showcase the versatility of low-temperature dc-sputtered SiC films applied in the field of MEMS. [ABSTRACT FROM AUTHOR]

We present an enhanced in-plane capacitive readout for sensing out-of-plane displacement in a MEMS acoustic sensor. The sensor is fabricated in a multi-user silicon-on-insulator process, using a thicker device layer to reduce misalignment between moving and fixed comb fingers. This misalignment is found to reduce the sensitivity and render the response nonlinear. In addition, incorporation of a branched comb design doubles the readout capacitor surface area for a given sensor size, to further increase the sensitivity. These two modifications restore linearity to the readout and increase its sensitivity to displacement by an order of magnitude. [ABSTRACT FROM AUTHOR]

We report on the design, fabrication, and characterization of a microfabricated 3D magnetic field sensor that is suitable for co-integration with inertial sensors to form single-chip inertial measurement units. In contrast to classical resonant MEMS magnetometers, which are based on Lorentz force measurement, our sensor uses permanent magnetic materials and piezoresistive detection with silicon strain gauges of nanometric section, leading to low power consumption and high sensitivity for small sensor size. Thin multilayers of CoFe and PtMn as ferro- and antiferromagnetic materials are integrated within the MEMS fabrication process. Sensitivities of 1.09 V/T for x- and y- components of the magnetic field and 0.124 V/T for z- component of the magnetic field were measured, respectively. To be sensitive to magnetic fields along all three spatial directions, two permanent magnetization directions on the same die are required. Implementation of the two magnetization directions was validated by a measured correlation of 99.7% between x- and y- sensitivity axes. Power consumption of the 3D sensor is for polarization with a 100 μA dc current. With resolutions of 100 nT/√Hz for x- and y-component of the magnetic field and 350 nT/√Hz for z- component, the sensor is suitable for precise measurement of earth magnetic field. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical analysis of a new zigzag C-axis inclined multi-layer ZnO thin-film bulk acoustic wave resonator (FBAR) as a viscosity sensor to monitor the lubrication performance of engine oil and other liquids. Free vibration and forced vibration for the FBAR loaded with liquids are analyzed. Equations necessary to calculate the sensitivity are derived. The numerical analysis shows that as the number of layers increases, the absolute sensitivity increases as well. The influences on the sensitivity of C-axis inclined angle, Q-factor, and thickness are also investigated. The results provide a foundation for further design of multi-layer FBAR viscosity sensors. [ABSTRACT FROM AUTHOR]

We demonstrated a novel intensity-modulated strain sensor based on a fiber in-line Mach-Zehnder interferometer with a large fringe visibility of up to 17 dB, which was fabricated by splicing a section of thin core fiber between two sections of single mode fibers with one misalignment-spliced joint. Such a strain sensor exhibited an ultrahigh sensitivity of -0.023 dBm/με within a measurement range of 500 με, which is about one order of magnitude higher than that reported in references. Displacement and stress distributions at the misalignment spliced joint were simulated by use of finite element method. In addition, the proposed strain sensor has an advantage of compact size of ~10 mm. [ABSTRACT FROM PUBLISHER]

Lamb-wave acoustic devices have been proposed as a promising platform for sensing applications. In this paper, the performance of a GaN Lamb wave device as a liquid-based mass sensor is studied with respect to the effect of environmental parameters to the device performance, namely, the liquid flow-rate, device temperature, and presence of a thin gold film deposited on the GaN membrane. [ABSTRACT FROM PUBLISHER]

Nano-structured In2O3 thin film was made using a pulsed laser deposition technique. The surface topography and structural properties of the thin film were characterized by atomic force microscopy and X-ray diffraction, respectively. Complex impedance spectroscopy of In2O3 thin film gas sensor was investigated from 275 °C to 425 °C when exposed into clean air and air containing a trace level of NOx. Significant NOx sensing characteristics of thin film were observed at 325 °C by ac impedance spectroscopic analysis. The resistance and capacitance of indium oxide film increased when exposed into the trace level of NOx. A mechanism for this increase of resistance and capacitance is proposed. [ABSTRACT FROM PUBLISHER]

This paper introduces an improved method for monitoring and controlling the contact condition of terahertz on-wafer probes to enhance the measurement repeatability as well as probe lifetime. This method enables accurate contact force and contact angle measurements without modification to the standard probe station. Both probe contact force and contact angle are crucial for RF measurement repeatability. Repeatable probe contact force can be achieved by properly monitoring and controlling the strain generated at designated positions on the terahertz probe due to probe deformation induced by contacting the test substrate. Contact angle can be measured by asymmetrical strain on symmetrical positions of the probe when the probe is contacting the test substrate with angular misalignment. In this work a WR-1.5 (500 GHz-750 GHz) probe with integrated strain sensor is developed and tested. Mechanical tests show that the integrated sensors have a contact force resolution of 0.2 mN and a contact angle resolution of 0.05^\circ about the center. RF tests show that repeatable measurements can be achieved with 3 mN contact force after adjusting probe contact angle using the integrated sensors, as compared to a previously reported value of 15 mN. [ABSTRACT FROM AUTHOR]

This paper describes the design, fabrication, and performance of a thin film humidity sensor fabricated in standard CMOS process, hence it may be combined with an integrated circuit. The sensor is based on a capacitance between interdigitated electrodes in the top metal layer and water adsorption in the polyimide layer. The design is optimized by analytical and then finite element models which show that, within the constraint of the CMOS structure, the sensitivity can be no greater than one third of the sensitivity of the polyimide alone. Experimental sensors were fabricated in-house before an improved design was fabricated in a commercial foundry. The different behavior of these sensors, despite their similar designs, leads to an investigation into the effects of fabrication process on the sensor linearity. Characterizing the polyimide film by contact angle, AFM and FTIR revealed that the difference in linearity of the response between the two sensors resulted from different etching techniques employed to pattern the film. [ABSTRACT FROM PUBLISHER]

Rutile TiO2 (1 0 1) and cassiterite SnO2 (1 0 1) epitaxial single and double nanolayers, the latter stacked in either sequence, are atomic layer deposited on r-cut \alpha\-Al2O3(0~1~\bar{1}~2) substrates. Thickness of the layers is varied. Epitaxial quality of the films is characterized by X-ray diffraction (XRD), reflection high-energy electron diffraction, and transmission electron microscopy. In gas response measurements, as-grown films and the films coated with electron-beam evaporated Pt nanoclusters are exposed, at 350^\circC, to H2, CO, and CH4 diluted in air. In response to test gas concentrations of 30 parts per million (ppm), the films with a thickness of order of 10 nm exhibit, depending on the makeup and gas, as high as two- to five-fold decrease in the resistance. It is shown that the platinum surface catalyst is effective in accelerating the response and recovery processes. The transition times of the order of a few tens of seconds are observed. The results demonstrate the feasibility of gas sensing with single-crystal-like nanolayer films. Comparison of sensor characteristics of such quasi-2D nanostructures and the literature data relevant to individual nanowires, nanorods, and nanobelts, i.e., typical representatives of the quasi-1D structures, shows that, as to H2, CO, and CH4, both structures are worthy competitors. [ABSTRACT FROM PUBLISHER]

SrTiO3 (STO) thin film has been fabricated on fused-quartz wafer by radio-frequency magnetron sputtering. The Ag interdigited electrodes were then evaporated on STO thin film in order to form the metal-insulator-metal photoconductive detector. Our photodetector exhibits a high photoresponse in the range of 225-340 nm with an ultraviolet-visible rejection ratio (R310 nm/R400 nm) of two orders of magnitude, indicating an intrinsic characteristic of visible-blindness. The maximum photocurrent responsivity is about 105 mA/W measured at 310 nm and the corresponding quantum efficiency is 42.1%. The dark current is only 0.4 nA at 50 V bias. Furthermore, the STO thin film detector presents a transient photovoltaic signal with a rise time of ~330 ps and a fall time of ~480 ps under the excitation of a 355-nm-pulsed laser, suggesting an ultrafast response characteristic of our STO thin film detector. [ABSTRACT FROM PUBLISHER]