A CMOS-Thyristor Based Temperature Sensor with +0.37 °C/-0.32 °C Inaccuracy

This paper describes a voltage controlled oscillator (VCO) based temperature sensor. The VCOs are composed of complementary metal-oxide-semiconductor (CMOS) thyristor with the advantage of low power consumption. The period of the VCO is temperature dependent and is function of the transistors' threshold voltage and bias current. To obtain linear temperature characteristics, this paper constructed the period ratio between two different-type VCOs. The period ratio is independent of the temperature characteristics from current source, which makes the bias current generator simplified. The temperature sensor was designed in 130 nm CMOS process and it occupies an active area of 0.06 mm². Based on the post-layout simulation results, after a first-order fit, the sensor achieves an inaccuracy of +0.37/-0.32 °C from 0 °C to 80 °C, while the average power consumption of the sensor at room temperature is 156 nW.

Self-Imaging Effect in Liquid-Filled Hollow-Core Capillary Waveguide for Sensing Applications

A high sensitivity fiber-optic sensor based on self-imaging effect in a hollow-core capillary waveguide (HCCW) is presented for sensing applications. The sensor is composed of a section of HCCW fusion spliced between single mode fibers (SMFs). The self-imaging effect in the HCCW is investigated with different fiber lengths and arc-fusion parameters. By infiltrating the hollow core with index matching liquids, the peak wavelength of the proposed device shifts towards longer wavelengths. The temperature and refractive index (RI) responses of the sensor are studied systematically. When temperature is increased from 25 °C to 75 °C, the temperature sensitivity of the device can be improved significantly with the infiltrated structure, and reaches −0.49 nm/°C, compared with that of the un-filled device, which is 9.8 pm/°C. For the RI response, the liquid-filled structure achieves sensitivity of 12,005 nm/RIU in the range between 1.448 and 1.450, slightly higher than the 11,920 nm/RIU achieved by the un-filled one. The proposed sensor exhibits the advantages of simple structure, high sensitivity and low cost, which may find potential applications in physical and chemical sensing.

Comparison of Measurements with Finite-Element Analysis of Silicon-Diaphragm-Based Fiber-Optic Fabry-Perot Temperature Sensors

Silicon-diaphragm-based fiber-optic Fabry–Perot sensors with different intracavity pressures were fabricated by anodic bonding and microelectromechanical techniques. The thermal stress and thermal expansion of the Fabry–Perot (FP) sensor caused by high-temperature bonding and temperature change were simulated by finite-element analysis. The calculated thermal stress is largest in the center and edge regions of the resonance cavity, reaching from 2 to 6 MPa. The reflection spectra and temperature sensitivity of the sensors were simulated by using a two-dimensional wave-optic model in Comsol. Theoretical calculations were also made for the FP cavity without considering silicon-diaphragm deformation and thermal stress. Four sensors with intracavity pressures of 0.01, 0.03, 0.04, and 0.05 MPa were tested at low temperatures, showing a high degree of consistency with the simulation results rather than theoretical calculation, especially for high intracavity pressure. This method is expected to aid the analysis of thermal stress generated during the bonding process and to facilitate better design and control of the temperature sensitivity of the sensor.

Heat Source Forecast of Ball Screw Drive System Under Actual Working Conditions Based on On-Line Measurement of Temperature Sensors

In view of the time-varying complexity of the heat source for the ball screw feed system, this paper proposes an adaptive inverse problem-solving method to estimate the time-varying heat source and temperature field of the feed system under working conditions. The feed system includes multiple heat sources, and the rapid change of the moving heat source increases the difficulty of its identification. This paper attempts to develop a numerical calculation method for identifying the heat source by combining the experiment with the optimization algorithm. Firstly, based on the theory of heat transfer, a new dynamic thermal network model was proposed. The temperature data signal and the position signal of the moving nut captured by the sensors are used as input to optimize the solution of the time-varying heat source. Then, based on the data obtained from the experiment, finite element software parametric programming was used to optimize the estimate of the heat source, and the results of the two heat source prediction methods are compared and verified. The other measured temperature points obtained by the experiment were used to compare and verify the inverse method of this numerical calculation, which illustrates the reliability and advantages of the dynamic thermal network combined with the genetic algorithm for the inverse method. The method based on the on-line monitoring of temperature sensors proposed in this paper has a strong application value for heat source and temperature field estimation of complex mechanical structures.

Analysis and Simulation of Forcing the Limits of Thermal Sensing for Microbolometers in CMOS-MEMS Technology

Room-temperature highly sensitive microbolometers are becoming very attractive in infrared (IR) sensing with the increase in demand for the internet of things (IOT), night vision, and medical imaging. Different techniques, such as building extremely small-scale devices (nanotubes, etc.) or using 2D materials, showed promising results in terms of high sensitivity with the cost of challenges in fabrication and low-noise readout circuit. Here, we propose a new and simple technique on the application of joule heating on a clamped–clamped beam without adding any complexity. It provides much better uniformity in temperature distribution in comparison to conventional joule heating, and this results in higher thermal stresses on fixed ends. This consequently brings around 60.5× improvement in the overall temperature sensitivity according to both theory and COMSOL (multiphysics solver). The sensitivity increased with the increase in the stiffness constant, and it was calculated as 134 N/m for a device with a 60.5× improvement. A considerable amount of decrease in the operation temperature (36× below 383 K and 47× below 428 K) was achieved via a new technique. That’s why the proposed solution can be used either to build highly reliable long-term devices or to increase the thermal sensitivity.

Ultra-High Refractive Index Sensing Structure Based on a Metal-Insulator-Metal Waveguide-Coupled T-Shape Cavity with Metal Nanorod Defects

An ultra-high plasmonic refractive index sensing structure composed of a metal-insulator-metal (MIM) waveguide coupled to a T-shape cavity and several metal nanorod defects is proposed and investigated by using finite element method. The designed plasmonic MIM waveguide can constitute a cavity resonance zone and the metal nanorod defects can effectively trap the light in the T-shape cavity. The results reveal that both the size of defects in wider rectangular cavity and the length of narrower rectangular cavity are primary factors increasing the sensitivity performance. The sensitivity can achieve as high as 8280 nm/RIU (RIU denotes the refractive index unit), which is the highest sensitivity reported in plasmonic MIM waveguide-based sensors to our knowledge. In addition, the proposed structure can also serve as a temperature sensor with temperature sensitivity as high as 3.30 nm/°C. The designed structure with simplicity and ease of fabrication can be applied in sensitivity nanometer scale refractive index sensor and may potentially be used in optical on-chip nanosensor.

Fabrication and Characterization of Wrapped Metal Yarns-based Fabric Temperature Sensors

Textile temperature sensors are highly in demanded keep a real-time and accurate track of human body temperature for identification of healthy conditions or clinical diagnosis. Among various materials for textile temperature sensors, temperature-sensitive metal fibers have highest precision. However, those metal fibers are mechanically too weak, and break constantly during the weaving process. To enhance the mechanical strength of the metal fibers, this paper proposes to make wrapped metal fibers using wrapping technology, and characterize the effect of wrapped metal yarns on both mechanical properties and sensing behaviors. The wrapped yarns were woven into fabrics, forming the fabric temperature sensors. Results show that strength and maximum strain of the wrapped yarns are 2.69 and 1.82 times of pure Pt fibers. The response time of fabric temperature sensors using wrapped yarns was observed as 0.78 s and 1.1 s longer compared to that using Pt fibers when front and back sides contacted heat source, respectively. It is recommended that the wrapping method should be implemented for the protection of Pt fibers in fabric temperature sensors.

Temperature Sensor Based on Side-Polished Fiber SPR Device Coated with Polymer

A highly sensitive temperature sensor based on surface plasmon resonance (SPR) of a side-polished single mode fiber is demonstrated. The sensor consists of a gold film coated side-polished fiber covered by a layer of UV-curable adhesive. Before introducing the UV-curable adhesive, the gold-coated fiber exhibits refractive index (RI) sensitivity of 1691.6 nm/RIU to 8800 nm/RIU in the range of 1.32 to 1.43. The resonant wavelength of the SPR sensor shifts to 650 nm when the adhesive is coated on the gold film, and is fixed at about 725 nm when the adhesive is cured. Due to the high thermo-optic and thermal expansion coefficient of the adhesive, the sensor structure achieves a temperature sensitivity of −0.978 nm/°C between 25 °C and 100 °C. The proposed optical fiber SPR sensor is simple, highly sensitive and cost effective, which may find potential applications for temperature measurements in the biomedical and environmental industries.

Source Separation Using Sensor's Frequency Response: Theory and Practice on Carbon Nanotubes Sensors

Nowadays, there is an increased demand in integrated sensors for electronic devices. Multi-functional sensors provide the same amount of data using fewer sensors. Carbon nanotubes are non-selectively sensitive to temperature, gas and strain. Thus, carbon nanotubes are perfect candidates to design multi-functional sensors. In our study, we are interested in a dual humidity-temperature sensor. Here, we present a novel method to differentiate at least two sources using the sensor's frequency responses based on multiwall carbon nanotubes sensors. The experimental results demonstrate that there are temperature- or moisture-invariant frequencies of the impedance magnitude, and their values depend on the sensor's geometry. The proposed measurement model shows that source-invariant frequencies of the phase can be also determined. In addition, the source separation method is generalized to other materials or sources enabling multi-functional sensors for environment monitoring.

Methylammonium Lead Iodide Incorporated Poly(vinylidene fluoride) Nanofibers for Flexible Piezoelectric-Pyroelectric Nanogenerator

This work introduces a piezoelectric-pyroelectric nanogenerator (P-PNG) based on methylammonium lead iodide (CH₃NH₃PbI₃) incorporated electrospun poly(vinylidene fluoride) (PVDF) nanofibers that are able to harvest mechanical and thermal energies. During the application of a periodic compressive contact force at a frequency of 4 Hz, an output voltage of ∼220 mV is generated. The P-PNG has a piezoelectric coefficient (d₃₃) of ∼19.7 pC/N coupled with a high durability (60 000 cycles) and quick response time (∼1 ms). The maximum generated output power density (∼0.8 mW/m²) is sufficient to charge up a variety of capacitors, with the potential to replace an external power supply to drive portable devices. In addition, upon exposure to cyclic heating and cooling at a temperature of 38 K, a pyroelectric output current of 18.2 pA and a voltage of 41.78 mV were achieved. The fast response time of 1.14 s, reset time of 1.25 s, and pyroelectric coefficient of ∼44 pC/m² K demonstrate a self-powered temperature sensing capability of the P-PNG. These characteristics make the P-PNG suitable for flexible piezoelectric-pyroelectric energy harvesting for self-powered electronic devices.

A Brief Review of the Shape Memory Phenomena in Polymers and Their Typical Sensor Applications

In this brief review, an introduction of the underlying mechanisms for the shape memory effect (SME) and various shape memory phenomena in polymers is presented first. After that, a summary of typical applications in sensors based on either heating or wetting activated shape recovery using largely commercial engineering polymers, which are programmed by means of in-plane pre-deformation (load applied in the length/width direction) or out-of-plane pre-deformation (load applied in the thickness direction), is presented. As demonstrated by a number of examples, many low-cost engineering polymers are well suited to, for instance, anti-counterfeit and over-heating/wetting monitoring applications via visual sensation and/or tactual sensation, and many existing technologies and products (e.g., holography, 3D printing, nano-imprinting, electro-spinning, lenticular lens, Fresnel lens, QR/bar code, Moiré pattern, FRID, structural coloring, etc.) can be integrated with the shape memory feature.

Carbon Nanotubes and Carbon Nanotube Structures Used for Temperature Measurement

Accurate measurement of temperatures with low power consumption with the highest sensitivity and smallest possible elements is still a challenge. The thermal, electrical, and mechanical properties of carbon nanotubes (CNTs) have suggested that their use as a very sensitive sensing element will allow the creation of different sensors, far superior to other devices of similar size. In this paper, we present a short review of different constructive designs of CNTs based resistive sensors used for temperature measurement, available in literature, assembled using different processes, such as self-assembly, drop-casting from a solution, thin films obtained by gluing, printing, spraying, or filtration over a special membrane. As particular cases, temperature sensors obtained from CNT-polymer nanocomposite structures, CNTs filled with uniformly dispersed Fe₃O₄ nanoparticles or with gallium, and carbon nanotube wires (CNWs) hybrids are presented. Using these preparation procedures, mixtures of CNTs with different dimensions and chirality, as well as with a variable level of impurities and structural defects, can be produced. The sensors’ performance charts are presented, highlighting a number of aspects regarding the applicability of CNT structures for temperature measurement ranging from cryogenic temperatures to high temperatures, the limitations they have, their characteristics and advantages, as well as the special situations that may arise given the particular structure of these new types of materials, together with basic relationships and parameters for CNTs characterization. Further research will be required to develop the techniques of manipulating and depositing individual CNTs on supports and electrodes for the development of temperature sensors.

Novel Method for NTC Thermistor Production by Aerosol Co-Deposition and Combined Sintering

A novel three-stage process to produce NTCR sensors is presented. In this process, an uncalcined powder mixture of NiO and Mn₂O₃ was deposited onto an alumina substrate via aerosol co-deposition (AcD). Then, an electrode structure was screen-printed onto the surface and the composite film was sintered in a multifunctional temperature treatment. Thereby, the sintering of the electrode, the formation of the NiMn₂O₄ spinel and the removal of film strains took place simultaneously. This enabled a significant reduction in energy demand and workload. The manufactured sensors, both as first prototypes, as well as miniaturized chip components, were characterized by a single-phase cubic NiMn₂O₄ spinel structure, mechanical stability and electrical properties that were similar to those of classical NiMn₂O₄ bulk ceramics or tempered aerosol deposited (AD) NiMn₂O₄ films. Particularly noteworthy was the high reproducibility and low variation of the NTCR parameters, such as the specific resistivity at 25 °C ρ₂₅, the electrical resistance at 25 °C R₂₅ and the thermistor constant B. The NTCR parameters were as aging-stable as for NiMn₂O₄ bulk ceramics or tempered NiMn₂O₄ AD-films and could even be further improved by thermal post-treatment.

A Miniature Fabry Perot Sensor for Twist/Rotation, Strain and Temperature Measurements Based on a Four-Core Fiber

In this article, a novel miniature Fabry-Perot twist/rotation sensor using a four core fiber and quadruple interferometer setup is presented and demonstrated. Detailed sensor modeling, analytical evaluation and test measurement assessment were conducted in this contribution. The sensor structure comprises a single lead-in multicore fiber, which has four eccentrically positioned cores, a special asymmetrical microstructure, and an inline semi-reflective mirror, all packed in a glass capillary housing. A four core fiber positioned in front of a special asymmetrical microstructure and the inline semi reflective mirror defines four Fabry-Perot interferometers. Rotation of the sensors' asymmetrical microstructure around the axis of the in-line four core fibers´ modulates the path lengths of all four interferometers simultaneously. Proper processing of path length changes of all four interferometers allows for unambiguous and temperature independent determination of the sensor's rotation angle.

Evaluation on Context Recognition Using Temperature Sensors in the Nostrils

We can benefit from various services with context recognition using wearable sensors. In this study, we focus on the contexts acquired from sensor data in the nostrils. Nostrils can provide various contexts on breathing, nasal congestion, and higher level contexts including psychological and health states. In this paper, we propose a context recognition method using the information in the nostril. We develop a system to acquire the temperature in the nostrils using small temperature sensors connected to glasses. As a result of the evaluations, the proposed system can detect breathing correctly, workload at an accuracy of 96.4%, six behaviors at an accuracy of 54%, and eight behaviors in daily life at an accuracy of 86%. Moreover, the proposed system can detect nasal congestion, therefore, it can log nasal cycles that are considered to have a relationship with the autonomic nerves and/or biological states.

Li4SrCa(SiO4)2:Eu2+: A Potential Temperature Sensor with Unique Optical Thermometric Properties

Investigations on luminescence properties of lanthanide-activated phosphors are not only essential to understanding the fundamental structure-property relationship but also important to advancing the development and application of relevant research techniques. We report herein a promising optical thermometric material Eu²⁺-doped Li₄SrCa(SiO₄)₂ utilizing the different sensitivities of Eu_Sr²⁺ and Eu_Ca²⁺ emission intensities to temperature. A unique evolution of Eu²⁺ luminescence in the as-prepared sample is identified under the simultaneous action of UV illumination and thermal treatment. The maximum relative sensitivities are 2.87% K^-1 (at 440 K) and 1.51% K^-1 (at 460 K) for the as-prepared and illuminated samples, respectively. These temperature sensing features reflect a great potential of Eu²⁺-doped Li₄SrCa(SiO₄)₂ for applications in the optical thermometry field.

Thermal-Feature System Identification for a Machine Tool Spindle

The internal temperature is an important index for the prevention and maintenance of a spindle. However, the temperature inside the spindle is undetectable directly because there is no space to embed a temperature sensor, and drilling holes will reduce its mechanical stiffness. Therefore, it is worthwhile understanding the thermal-feature of a spindle. This article presents a methodology to identify the thermal-feature model of an externally driven spindle. The methodology contains self-made hardware of the temperature sensing and wireless transmission module (TSWTM) and software for the system identification (SID); the TSWTM acquires the temperature training data, while the SID identifies the parameters of the thermal-feature model of the spindle. Then the resulting thermal-feature model is written into the firmware of the TSWTM to give it the capability of accurately calculating the internal temperature of the spindle from its surface temperature during the operation, or predicting its temperature at various speeds. The thermal-feature of the externally driven spindle is modeled by a linearly time-invariant state-space model whose parameters are identified by the SID, which integrates the command "n4sid" provided by the System ID Toolbox of MATLAB and the k-fold cross-validation that is common in machine learning. The present SID can effectively strike a balance between the bias and variance of the model, such that both under-fitting and over-fitting can be avoided. The resulting thermal-feature model can not only predict the temperature of the spindle rotating at various speeds but can also calculate the internal temperature of the spindle from its surface temperature. Its validation accuracy is higher than 98.5%. This article illustrates the feasibility of accurately calculating the internal temperature (undetectable directly) of the spindle from its surface temperature (detectable directly).

Towards an Ultra-Sensitive Temperature Sensor for Uncooled Infrared Sensing in CMOS⁻MEMS Technology

Microbolometers and photon detectors are two main technologies to address the needs in Infrared Sensing applications. While the microbolometers in both complementary metal-oxide semiconductor (CMOS) and Micro-Electro-Mechanical Systems (MEMS) technology offer many advantages over photon detectors, they still suffer from nonlinearity and relatively low temperature sensitivity. This paper not only offers a reliable solution to solve the nonlinearity problem but also demonstrate a noticeable potential to build ultra-sensitive CMOS–MEMS temperature sensor for infrared (IR) sensing applications. The possibility of a 31× improvement in the total absolute frequency shift with respect to ambient temperature change is verified via both COMSOL (multiphysics solver) and theory. Nonlinearity problem is resolved by an operating temperature sensor around the beam bending point. The effect of both pull-in force and dimensional change is analyzed in depth, and a drastic increase in performance is achieved when the applied pull-in force between adjacent beams is kept as small as possible. The optimum structure is derived with a length of 57 µm and a thickness of 1 µm while avoiding critical temperature and, consequently, device failure. Moreover, a good match between theory and COMSOL is demonstrated, and this can be used as a guidance to build state-of-the-art designs.

Comparative Experimental Study of a High-Temperature Raman-Based Distributed Optical Fiber Sensor with Different Special Fibers

An experimental study of a high temperature distributed optical fiber sensor based on Raman Optical-Time-Domain-Reflectometry (ROTDR) (up to 450 °C) and optical fibers with different coatings (polyimide/carbon, copper, aluminum and gold) is presented. Analysis of the distributed temperature sensor (DTS) measurements determined the most appropriate optical fiber to be used in high temperature industrial environment over long periods of time. To demonstrate the feasibility of this DTS for an industrial application, an optical cable was designed with the appropriate optical fiber and it was hermetically sealed to provide the required mechanical resistance and isolate the fiber from environmental degradations. This cable was used to measure temperature up to 360 °C of an industrial furnace during 7 days.

Humidity Sensing Behavior of Endohedral Li-Doped and Undoped SWCNT/SDBS Composite Films

We have investigated single-walled carbon nanotube (SWCNT) networks wrapped with the cationic surfactant sodium dodecyl-benzenesulfonate (SBDS) as promising candidates for water detection. This is the first time that the humidity behavior of endohedral Li-doped (Li@) and undoped SWCNTs/SDBS has been shown. We identified a strong and almost monotonic decrease in resistance as humidity increased from 11 to 97%. Sensitivities varied between −3 and 65% in the entire humidity range. Electrical characterization, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) analysis revealed that a combination of the electron donor behavior of the water molecules with Poole-Frenkel conduction accounted for the resistive humidity response in the Li@SWCNT/SDBS and undoped SWCNT/SDBS networks. We found that Li@SWCNTs boosted the semiconducting character in mixtures of metallic/semiconducting SWCNT beams. Moreover, electrical characterization of the sensor suggested that endohedral Li doping produced SWCNT beams with high concentration of semiconducting tubes. We also investigated how frequency influenced film humidity sensing behavior and how this behavior of SWCNT/SDBS films depended on temperature from 20 to 80 °C. The present results will certainly aid design and optimization of SWCNT films with different dopants for humidity or gas sensing in general.

Wireless Real-Time Temperature Monitoring of Blood Packages: Silver Nanowire-Embedded Flexible Temperature Sensors

Real-time temperature monitoring of individual blood packages capable of wireless data transmission to ensure the safety of blood samples and minimize wastes has become a critical issue in recent years. In this work, we propose flexible temperature sensors using silver nanowires (NWs) and a flexible colorless polyimide (CPI) film integrated with a wireless data transmission circuit. The unique design of the temperature sensors was achieved by patterning Ag NWs using a three-dimensional printed mold and embedding the patterned Ag NWs in the CPI film (p-Ag NWs/CPI), which resulted in a flexible temperature sensor with electrical, mechanical, and temperature stability for applications in blood temperature monitoring. Indeed, a reliable resistance change of the p-Ag NWs/CPI was observed in the temperature range of -20 to 20 °C with a robust bending stability of up to 5000 cycles at 5 mm bending radius. Real-time and wireless temperature monitoring using the p-Ag NWs/CPI was demonstrated with the packages of rat blood. The result revealed that the stable and consistent temperature monitoring of individual blood packages could be achieved in a blood box, which was mainly attributed to the conformal attachment of the p-Ag NWs/CPI to different packages in a blood container.

Plant Temperature Sensors

Temperature is one of the most important environmental signals for plants. High and low temperatures have a variety of effects that affect plant growth and development profoundly. Further, temperature is an indication of seasonal change. Plants must survive under severe conditions in winter and prepare to resume growth and reach their reproductive stage in the following spring. Recent studies have focused on plant mechanisms responsible for sensing temperature and the molecular systems underlying plant reactions in response to this signal. In this review, we describe how plants sense ambient temperature to adapt to ambient-temperature changes.

Application of Additive Layer Manufacturing Technique on the Development of High Sensitive Fiber Bragg Grating Temperature Sensors

This paper presents the development of temperature sensors based on fiber Bragg gratings (FBGs) embedded in 3D-printed structures made of different materials, namely polylatic acid (PLA) and thermoplastic polyurethane (TPU). A numerical analysis of the material behavior and its interaction with the FBG sensor was performed through the finite element method. A simple, fast and prone to automation process is presented for the FBG embedment in both PLA and TPU structures. The temperature tests were made using both PLA- and TPU-embedded FBGs as well as an unembedded FBG as reference. Results show an outstanding temperature sensitivity of 139 pm/°C for the FBG-embedded PLA structure, which is one of the highest temperature sensitivities reported for FBG-based temperature sensors in silica fibers. The sensor also shows almost negligible hysteresis (highest hysteresis below 0.5%). In addition, both PLA- and TPU-embedded structures present high linearity and response time below 2 s. The results presented in this work not only demonstrate the feasibility of developing fully embedded temperature sensors with high resolution and in compliance with soft robot application requirements, but also show that the FBG embedment in such structures is capable of enhancing the sensor performance.

Enhanced Accuracy of CMOS Smart Temperature Sensors by Nonlinear Curvature Correction

In this paper, we demonstrate an improvement in the accuracy of a low-cost smart temperature sensor, by measurement of the nonlinear curvature correction at multiple temperature references. The sensors were positioned inside a climate chamber and connected outside to a micro-controller via a network cable. The chamber temperature was increased systematically over a wide range from -20 °C to 55 °C. A set of calibration curves was produced from the best fitting second-order polynomial curves for the offset in temperature between the sensor and reference. An improvement in accuracy of ±0.15 °C is with respect to the mentioned temperature range, compared to the significantly higher value reported of ±0.5 °C by the manufacturer for similar conditions. In summary, we demonstrate a significant improvement in the calibration of a low-cost, smart sensor frequently used in research and academic projects over a useful range of temperatures.

Thermal Treatment of Aerosol Deposited NiMn₂O₄ NTC Thermistors for Improved Aging Stability

This paper examines the influence of a short-term thermal treatment of aerosol deposited negative temperature coefficient (NTC) thermistor films on the NTCR characteristics and their long-term stability with different electrode materials. An aerosol deposition of a spinel-based NiMn₂O₄ powder on alumina substrates with screen-printed AgPd and Au interdigital electrode structures was performed. The manufactured components of the typical size of 1206 were tempered in a moderate temperature range of 200 °C to 800 °C and aged for 1000 h at 125 °C in air. Based on R-T measurements in a high-precision silicone oil thermostat bath and high temperature XRD analyses, the influence of the thermal treatment was analyzed and discussed. A 60-min tempering at 400 °C proved to be optimal, as both the NTCR parameters and their ageing stability could be significantly improved. The findings are explained.

Sensors Based on Metal Nanoclusters Stabilized on Designed Proteins

Among all new nanomaterials, metal nanoclusters (NCs) have attracted special attention due to their interesting optical properties, among others. Metal NCs have been recently studied and used as sensors for different analytes. However, there is a need to explore the potential of these new sensors in a systematic manner and to develop new systems to broaden the possibilities that sensing offers to the industry. In this work, we show the potential use of repeat protein scaffolds as versatile templates for the synthesis and stabilization of various metal NCs, specifically Au, Ag, and CuNCs. The resulting protein-metal NCs hybrids are evaluated as sensors for different stimuli such as temperature, ions, or reactive oxygen species (ROS). Among the three protein-metal NCs, all performed nicely as temperature sensors, AuNCs responded to metal ions, and AgNCs were able to detect ROS.

Applications of Photonic Crystal Nanobeam Cavities for Sensing

In recent years, there has been growing interest in optical sensors based on microcavities due to their advantages of size reduction and enhanced sensing capability. In this paper, we aim to give a comprehensive review of the field of photonic crystal nanobeam cavity-based sensors. The sensing principles and development of applications, such as refractive index sensing, nanoparticle sensing, optomechanical sensing, and temperature sensing, are summarized and highlighted. From the studies reported, it is demonstrated that photonic crystal nanobeam cavities, which provide excellent light confinement capability, ultra-small size, flexible on-chip design, and easy integration, offer promising platforms for a range of sensing applications.

Virtual FBGs Using Saturable Absorbers for Sensing with Fiber Lasers

The spectral narrowing of Fiber Bragg Gratings (FBGs) introduced by unpumped Er-doped fiber (EDF) was analyzed for fiber lasers (FL). Owing to spatial hole burning (SHB), the spectral response of a virtual FBG can be employed for narrowing the band pass filter employed to determine the lasing wavelength of laser cavities. A common FL was mounted to analyze the spectral stability of the method, and a FL sensor for strain and temperature measurements was experimentally characterized to determine the stability of the narrowing effect achieved by the unpumped EDF, which acts as a virtual FBG. The results exhibited remarkably good narrowing effects of the spectral response of uniform FBGs.

Iono-Elastomer-Based Wearable Strain Sensor with Real-Time Thermomechanical Dual Response

An ultrastretchable iono-elastomer with resistance sensitive to both elongation strain and temperature has been developed by hierarchical self-assembly of an end functionalized triblock copolymer in a protic ionic liquid (ethylammonium nitrate) followed by cross-linking. Small-angle X-ray scattering experiments in situ with uniaxial elongation reveal a nanoscale microstructural transition of the hierarchically self-assembled cross-linked micelles that is responsible for the material's remarkable mechanical and ionic conductivity responses. The results show that the intermicelle distance extends along the deformation direction while the micelles organize into a long-range ordered face-centered-cubic structure during the uniaxial elongation. Besides good cyclability and resistance to selected physical damage, the iono-elastomer simultaneously achieves an unprecedented combination of high stretchability (340%), highly linear resistance vs elongation strain ( R² = 0.998), and large temperature gauge factor (Δ R/ R = 3.24%/°C@30 °C). Human subject testing demonstrates that the iono-elastomer-based wearable thermomechanical sensor is able to effectively and accurately register both body motion and skin temperature simultaneously.

Ultrafast Energy Dissipation via Coupling with Internal and External Phonons in Two-Dimensional MoS2

Atomically thin two-dimensional materials have emerged as a promising system for optoelectronic applications; however, the low quantum yield, mainly caused by nonradiative energy dissipation, has greatly limited practical applications. To reveal the details for nonradiative energy channels, femtosecond pump-probe spectroscopy with a detection wavelength ranging from visible to near-infrared to mid-infrared is performed on few-layer MoS₂. With this method, the many-body effects, occupation effects, and phonon dynamics are clearly identified. In particular, thermalization of the MoS₂ lattice via electron-phonon scattering is responsible for a redshift of the exciton resonance energy observed within tens to hundreds of picoseconds after photoexcitation, which provides a direct real-time sensor for measuring the change in lattice temperature. We find that the excess energy from the cooling of hot carriers and the formation of bound carriers is efficiently transferred to the internal phonon system within 2 ps, while that from Shockley-Read-Hall recombination (∼9 ps) is mainly dissipated from the MoS₂ surfaces to external phonons.

Bragg-Grating-Based Photonic Strain and Temperature Sensor Foils Realized Using Imprinting and Operating at Very Near Infrared Wavelengths

Thin and flexible sensor foils are very suitable for unobtrusive integration with mechanical structures and allow monitoring for example strain and temperature while minimally interfering with the operation of those structures. Electrical strain gages have long been used for this purpose, but optical strain sensors based on Bragg gratings are gaining importance because of their improved accuracy, insusceptibility to electromagnetic interference, and multiplexing capability, thereby drastically reducing the amount of interconnection cables required. This paper reports on thin polymer sensor foils that can be used as photonic strain gage or temperature sensors, using several Bragg grating sensors multiplexed in a single polymer waveguide. Compared to commercially available optical fibers with Bragg grating sensors, our planar approach allows fabricating multiple, closely spaced sensors in well-defined directions in the same plane realizing photonic strain gage rosettes. While most of the reported Bragg grating sensors operate around a wavelength of 1550 nm, the sensors in the current paper operate around a wavelength of 850 nm, where the material losses are the lowest. This was accomplished by imprinting gratings with pitches 280 nm, 285 nm, and 290 nm at the core-cladding interface of an imprinted single mode waveguide with cross-sectional dimensions 3 × 3 µm². We show that it is possible to realize high-quality imprinted single mode waveguides, with gratings, having only a very thin residual layer which is important to limit bend losses or cross-talk with neighboring waveguides. The strain and temperature sensitivity of the Bragg grating sensors was found to be 0.85 pm/µε and −150 pm/°C, respectively. These values correspond well with those of previously reported sensors based on the same materials but operating around 1550 nm, taking into account that sensitivity scales with the wavelength.

Reconfigurable Sensor Analog Front-End Using Low-Noise Chopper-Stabilized Delta-Sigma Capacitance-to-Digital Converter

This paper proposes a reconfigurable sensor analog front-end using low-noise chopper-stabilized delta-sigma capacitance-to-digital converter (CDC) for capacitive microsensors. The proposed reconfigurable sensor analog front-end can drive both capacitive microsensors and voltage signals by direct conversion without a front-end amplifier. The reconfigurable scheme of the front-end can be implemented in various multi-mode applications, where it is equipped with a fully integrated temperature sensor. A chopper stabilization technique is implemented here to achieve a low-noise characteristic by reducing unexpected low-frequency noises such as offsets and flicker noise. The prototype chip of the proposed sensor analog front-end is fabricated by a standard 0.18-μm 1-poly-6-metal (1P6M) complementary metal-oxide-semiconductor (CMOS) process. It occupies a total active area of 5.37 mm² and achieves an effective resolution of 16.3-bit. The total power consumption is 0.843 mW with a 1.8 V power supply.

Reader Architectures for Wireless Surface Acoustic Wave Sensors

Wireless surface acoustic wave (SAW) sensors have some unique features that make them promising for industrial metrology. Their decisive advantage lies in their purely passive operation and the wireless readout capability allowing the installation also at particularly inaccessible locations. Furthermore, they are small, low-cost and rugged components on highly stable substrate materials and thus particularly suited for harsh environments. Nevertheless, a sensor itself does not carry out any measurement but always requires a suitable excitation and interrogation circuit: a reader. A variety of different architectures have been presented and investigated up to now. This review paper gives a comprehensive survey of the present state of reader architectures such as time domain sampling (TDS), frequency domain sampling (FDS) and hybrid concepts for both SAW resonators and reflective SAW delay line sensors. Furthermore, critical performance parameters such as measurement accuracy, dynamic range, update rate, and hardware costs of the state of the art in science and industry are presented, compared and discussed.

A Low Power Energy-Efficient Precision CMOS Temperature Sensor †

This paper presents a low power, energy-efficient precision CMOS temperature sensor. The front-end circuit is based on bipolar junction transistors, and employs a pre-bias circuit and bipolar core. To reduce measurement errors arising from current ratio mismatch, a new dynamic element-matching mode is proposed, which dynamically matches all current sources in the front-end circuit. The first-order fitting and third-order fitting are used to calibrate the output results. On the basis of simulation results, the sensor achieves 3σ-inaccuracies of +0.18/−0.13 °C from −55 °C to +125 °C. Measurement results demonstrate sensor 3σ-inaccuracies of ±0.2 °C from 0 °C to +100 °C. The circuit is implemented in 0.18 μm CMOS, and consumes 6.1 μA with a 1.8 V supply voltage.

Study of CMOS-SOI Integrated Temperature Sensing Circuits for On-Chip Temperature Monitoring

This paper investigates the concepts, performance and limitations of temperature sensing circuits realized in complementary metal-oxide-semiconductor (CMOS) silicon on insulator (SOI) technology. It is shown that the MOSFET threshold voltage (V_t) can be used to accurately measure the chip local temperature by using a V_t extractor circuit. Furthermore, the circuit’s performance is compared to standard circuits used to generate an accurate output current or voltage proportional to the absolute temperature, i.e., proportional-to-absolute temperature (PTAT), in terms of linearity, sensitivity, power consumption, speed, accuracy and calibration needs. It is shown that the V_t extractor circuit is a better solution to determine the temperature of low power, analog and mixed-signal designs due to its accuracy, low power consumption and no need for calibration. The circuit has been designed using 1 µm partially depleted (PD) CMOS-SOI technology, and demonstrates a measurement inaccuracy of ±1.5 K across 300 K–500 K temperature range while consuming only 30 µW during operation.

Design of a Low-Power, Small-Area AEC-Q100-Compliant SENT Transmitter in Signal Conditioning IC for Automotive Pressure and Temperature Complex Sensors in 180 Nm CMOS Technology

In this paper, a low-power and small-area Single Edge Nibble Transmission (SENT) transmitter design is proposed for automotive pressure and temperature complex sensor applications. To reduce the cost and size of the hardware, the pressure and temperature information is processed with a single integrated circuit (IC) and transmitted at the same time to the electronic control unit (ECU) through SENT. Due to its digital nature, it is immune to noise, has reduced sensitivity to electromagnetic interference (EMI), and generates low EMI. It requires only one PAD for its connectivity with ECU, and thus reduces the pin requirements, simplifies the connectivity, and minimizes the printed circuit board (PCB) complexity. The design is fully synthesizable, and independent of technology. The finite state machine-based approach is employed for area efficient implementation, and to translate the proposed architecture into hardware. The IC is fabricated in 1P6M 180 nm CMOS process with an area of (116 μm × 116 μm) and 4.314 K gates. The current consumption is 50 μA from a 1.8 V supply with a total 90 μW power. For compliance with AEC-Q100 for automotive reliability, a reverse and over voltage protection circuit is also implemented with human body model (HBM) electro-static discharge (ESD) of +6 kV, reverse voltage of -16 V to 0 V, over voltage of 8.2 V to 16 V, and fabricated area of 330 μm × 680 μm. The extensive testing, measurement, and simulation results prove that the design is fully compliant with SAE J2716 standard.

A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things

Flexible electronics, which can be distributed on any surface we need, are highly demanded in the development of Internet of Things (IoT), robot technology and electronic skins. Temperature is a fundamental physical parameter, and it is an important indicator in many applications. Therefore, a flexible temperature sensor is required. Here, we report a simple method to fabricate three lightweight, low-cost and flexible temperature sensors, whose sensitive materials are reduced graphene oxide (r-GO), single-walled carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). By comparing linearity, sensitive and repeatability, we found that the r-GO temperature sensor had the most balanced performance. Furthermore, the r-GO temperature sensor showed good mechanical properties and it could be bent in different angles with negligible resistance change. In addition, the performance of the r-GO temperature sensor remained stable under different kinds of pressure and was unaffected by surrounding environments, like humidity or other gases, because of the insulating layer on its sensitive layer. The easy-fabricated process and economy, together with the remarkable performance of the r-GO temperature sensor, suggest that it is suitable for use as a robot skin or used in the environment of IoT.

Adherence Over Time: The Course of Adherence to Customized Diabetic Insoles as Objectively Assessed by a Temperature Sensor

BACKGROUND

Temperature sensors are an objective way to assess adherence to diabetic footwear. Good adherence is essential for the prevention of diabetic foot problems. Little is known about the long-term course of adherence in patients at risk for diabetic foot problems.

METHOD

A temperature sensor was incorporated into the specialized footwear of patients with type 2 diabetes after their first plantar ulceration. Kaplan-Meier curve was used to analyze when patients started to become nonadherent (not wearing the footwear for two straight weeks). Gender effects on adherence were also analyzed.

RESULTS

26 patients with a mean observation time of 133.5 days could be analyzed. Mean wearing time of diabetic footwear was 4.2 ± 3.6 h/day (Mdn = 3.4 h/day; interquartile range = 0.5-7.0 h/day) and on 51% of the days patients did not wear their footwear at all. Kaplan-Meier curve revealed that the mean time of adherence was 27.5 weeks. Men achieved a mean time of adherence of 30.5 weeks, while women only achieved 14 weeks. However, due to the small sample size, this difference was not statistically significant.

CONCLUSIONS

Temperature sensors revealed a low long-term adherence to diabetic footwear. Women seemed to be at a higher risk for earlier nonadherent behavior. Adherence to diabetic footwear should be closely monitored and tailored intervention strategies should be developed.

Stretchable Tattoo-Like Heater with On-Site Temperature Feedback Control

Wearable tissue heaters can play many important roles in the medical field. They may be used for heat therapy, perioperative warming and controlled transdermal drug delivery, among other applications. State-of-the-art heaters are too bulky, rigid, or difficult to control to be able to maintain long-term wearability and safety. Recently, there has been progress in the development of stretchable heaters that may be attached directly to the skin surface, but they often use expensive materials or processes and take significant time to fabricate. Moreover, they lack continuously active, on-site, unobstructive temperature feedback control, which is critical for accommodating the dynamic temperatures required for most medical applications. We have developed, fabricated and tested a cost-effective, large area, ultra-thin and ultra-soft tattoo-like heater that has autonomous proportional-integral-derivative (PID) temperature control. The device comprises a stretchable aluminum heater and a stretchable gold resistance temperature detector (RTD) on a soft medical tape as fabricated using the cost and time effective “cut-and-paste” method. It can be noninvasively laminated onto human skin and can follow skin deformation during flexure without imposing any constraint. We demonstrate the device’s ability to maintain a target temperature typical of medical uses over extended durations of time and to accurately adjust to a new set point in process. The cost of the device is low enough to justify disposable use.

Measurement of Temperature and Relative Humidity with Polymer Optical Fiber Sensors Based on the Induced Stress-Optic Effect

This paper presents a system capable of measuring temperature and relative humidity with polymer optical fiber (POF) sensors. The sensors are based on variations of the Young’s and shear moduli of the POF with variations in temperature and relative humidity. The system comprises two POFs, each with a predefined torsion stress that resulted in a variation in the fiber refractive index due to the stress-optic effect. Because there is a correlation between stress and material properties, the variation in temperature and humidity causes a variation in the fiber’s stress, which leads to variations in the fiber refractive index. Only two photodiodes comprise the sensor interrogation, resulting in a simple and low-cost system capable of measuring humidity in the range of 5–97% and temperature in the range of 21–46 °C. The root mean squared errors (RMSEs) between the proposed sensors and the reference were 1.12 °C and 1.36% for the measurements of temperature and relative humidity, respectively. In addition, fiber etching resulted in a sensor with a 2 s response time for a relative humidity variation of 10%, which is one of the lowest recorded response times for intrinsic POF humidity sensors.

Fabrication of High-Sensitivity Skin-Attachable Temperature Sensors with Bioinspired Microstructured Adhesive

In this study, we demonstrate the fabrication of a highly sensitive flexible temperature sensor with a bioinspired octopus-mimicking adhesive. A resistor-type temperature sensor consisting of a composite of poly(N-isopropylacrylamide) (pNIPAM)-temperature sensitive hydrogel, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and carbon nanotubes exhibits a very high thermal sensitivity of 2.6%·°C^-1 between 25 and 40 °C so that the change in skin temperature of 0.5 °C can be accurately detected. At the same time, the polydimethylsiloxane adhesive layer of octopus-mimicking rim structure coated with pNIPAM is fabricated through the formation of a single mold by utilizing undercut phenomenon in photolithography. The fabricated sensor shows stable and reproducible detection of skin temperature under repeated attachment/detachment cycles onto skin without any skin irritation for a long time. This work suggests a high potential application of our skin-attachable temperature sensor to wearable devices for medical and health-care monitoring.

Mn4+-Doped Magnesium Titanate-A Promising Phosphor for Self-Referenced Optical Temperature Sensing

Phosphors based on magnesium titanate activated with Mn4+ ions are of great interest because, when excited with blue light, they display a strong red-emitting luminescence. They are characterized by a luminescence decay which is strongly temperature dependent in the range from −50 ∘C to 150 ∘C, making these materials very promising for temperature sensing in the biochemical field. In this work, the optical and thermal properties of the luminescence of Mg2TiO4 are investigated for different Mn4+ doping concentrations. The potential of this material for temperature sensing is demonstrated by fabricating a fiber optic temperature microsensor and by comparing its performance against a standard resistance thermometer. The response of the fiber optic sensor is exceptionally fast, with a response time below 1 s in the liquid phase and below 1.1 s in the gas phase.

A Review of Microfiber-Based Temperature Sensors

Optical microfiber-based temperature sensors have been proposed for many applications in a variety of industrial uses, including biomedical, geological, automotive, and defense applications. This increasing demand for these micrometric devices is attributed to their large dynamic range, high sensitivity, fast-response, compactness and robustness. Additionally, they can perform in-situ measurements remotely and in harsh environments. This paper presents an overview of optical microfibers, with a focus on their applications in temperature sensing. This review broadly divides microfiber-based temperature sensors into two categories: resonant and non-resonant microfiber sensors. While the former includes microfiber loop, knot and coil resonators, the latter comprises sensors based on functionally coated/doped microfibers, microfiber couplers, optical gratings and interferometers. In the conclusions, a summary of reported performances is presented.

Multifunctional Sensor Based on Porous Carbon Derived from Metal-Organic Frameworks for Real Time Health Monitoring

Flexible and sensitive sensors that can detect external stimuli such as pressure, temperature, and strain are essential components for applications in health diagnosis and artificial intelligence. Multifunctional sensors with the capabilities of sensing pressure and temperature simultaneously are highly desirable for health monitoring. Here, we have successfully fabricated a flexible and simply structured bimodal sensor based on metal-organic frameworks (MOFs) derived porous carbon (PC) and polydimethylsiloxane (PDMS) composite. Attributed to the porous structure of PC/PDMS composite, the fabricated sensor exhibits high sensitivity (15.63 kPa^-1), fast response time (<65 ms), and high durability (∼2000 cycles) for pressure sensing. Additionally, its application in detecting human motions such as subtle wrist pulses in real time has been demonstrated. Furthermore, the as-prepared device based on the PC/PDMS composite exhibits a good sensitivity (>0.11 °C^-1) and fast response time (∼100 ms), indicating its potential application in sensing temperature. All of these capabilities indicate its great potential in the applications of health monitoring and artificial skin for artificial intelligence system.

Energetically Autonomous, Wearable, and Multifunctional Sensor

Self-powered tactile sensing is the upcoming technological orientation for developing compact, robust, and energy-saving devices in human-machine interfacing and electronic skin. Here, we report an intriguing type of sensing device composed of a Pt crack-based sensor in series with a polymer solar cell as a building block for energetically autonomous, wearable, and tactile sensor. This coplanar device enables human activity and physiological monitoring under indoor light illumination (2 mW/cm²) with acceptable and readible output signals. Additionally, the device can also function as a photodetector and a thermometer owing to the rapid response of the solar cell made from polymers. Consequently, the proposed device is multifuntional, mechanically robust, flexible, stretchable, and eco-friendly, which makes it suitable for long-term medical healthcare and wearable technology as well as environmental indication. Our designed green energy powered device therefore opens up a new route of developing renewable energy based portable and wearable systems.

A Polymer Optical Fiber Temperature Sensor Based on Material Features

This paper presents a polymer optical fiber (POF)-based temperature sensor. The operation principle of the sensor is the variation in the POF mechanical properties with the temperature variation. Such mechanical property variation leads to a variation in the POF output power when a constant stress is applied to the fiber due to the stress-optical effect. The fiber mechanical properties are characterized through a dynamic mechanical analysis, and the output power variation with different temperatures is measured. The stress is applied to the fiber by means of a 180° curvature, and supports are positioned on the fiber to inhibit the variation in its curvature with the temperature variation. Results show that the sensor proposed has a sensitivity of 1.04 × 10⁻³ °C⁻¹, a linearity of 0.994, and a root mean squared error of 1.48 °C, which indicates a relative error of below 2%, which is lower than the ones obtained for intensity-variation-based temperature sensors. Furthermore, the sensor is able to operate at temperatures up to 110 °C, which is higher than the ones obtained for similar POF sensors in the literature.

A Monolithic Multisensor Microchip with Complete On-Chip RF Front-End

In this paper, a new wireless sensor, designed for a 0.35 µm CMOS technology, is presented. The microchip was designed to be placed on an object for the continuous remote monitoring of its temperature and illumination state. The temperature sensor is based on the temperature dependence of the I-V characteristics of bipolar transistors available in CMOS technology, while the illumination sensor is an integrated p-n junction photodiode. An on-chip 2.5 GHz transmitter, coupled to a mm-sized dipole radiating element fabricated on the same microchip and made in the top metal layer of the same die, sends the collected data wirelessly to a radio receiver using an On-Off Keying (OOK) modulation pattern.

Design of a Toolbox of RNA Thermometers

Biomolecular temperature sensors can be used for efficient control of large-volume bioreactors, for spatiotemporal imaging and control of gene expression, and to engineer robustness to temperature in biomolecular circuit design. Although RNA-based sensors, called "thermometers", have been investigated in both natural and synthetic contexts, an important challenge is to design diverse responses to temperature differing in sensitivity and threshold. We address this issue by constructing a library of RNA thermometers based on thermodynamic computations and experimentally measuring their activities in cell-free biomolecular "breadboards". Using free energies of the minimum free energy structures as well as melt profile computations, we estimated that a diverse set of temperature responses were possible. We experimentally found a wide range of responses to temperature in the range 29-37 °C with fold-changes varying over 3-fold around the starting thermometer. The sensitivities of these responses ranged over 10-fold around the starting thermometer. We correlated these measurements with computational expectations, finding that although there was no strong correlation for the individual thermometers, overall trends of diversity, fold-changes, and sensitivities were similar. These results present a toolbox of RNA-based circuit elements with diverse temperature responses.

Design and Implementation of 2.45 GHz Passive SAW Temperature Sensors with BPSK Coded RFID Configuration

A surface acoustic wave based passive temperature sensor capable of multiple access is investigated. Binary Phase Shift Keying (BPSK) codes of eight chips were implemented using a reflective delay line scheme on a Y-Z LiNbO₃ piezoelectric substrate. An accurate simulation based on the combined finite- and boundary element method (FEM/BEM) was performed in order to determine the optimum design parameters. The scaling factor ‘s’ and time delay factor ‘τ’ were extracted using signal processing techniques based on the wavelet transform of the correlation function, and then evaluated at various ambient temperatures. The scaling factor ‘s’ gave a more stable and reliable response to temperature than the time delay factor ‘τ’. Preliminary results show that the sensor response is fast and consistent subject to ambient temperature and it exhibits good linearity of 0.9992 with temperature varying from 0 to 130 °C.

Flexible Polymer Device Based on Parylene-C with Memory and Temperature Sensing Functionalities

Polychloro-para-xylylene (parylene-C) is a flexible and transparent polymer material which has excellent chemical stability and high biocompatibility. Here we demonstrate a polymer device based on single-component parylene-C with memory and temperature sensing functionalities. The device shows stable bipolar resistive switching behavior, remarkable storage window (>10⁴), and low operation voltages, exhibiting great potential for flexible resistive random-access memory (RRAM) applications. The I-V curves and conductive atomic force microscopy (CAFM) results verify the metallic filamentary-type switching mechanism based on the formation and dissolution of a metal bridge related to the redox reaction of the active metal electrode. In addition, due to the metallic properties of the low-resistance state (LRS) in the polymer device, the resistance in the LRS exhibits a nearly linear relationship at the temperature regime between 25 °C and 100 °C. With a temperature coefficient of resistance (TCR) of 2.136 × 10^-3/°C, the device is also promising for the flexible temperature sensor applications.