Positive Temperature Coefficient Of Resistivity Research Articles

Electrically tunable metal–semiconductor behavior in 2H-MoTe2

In this study, we report tunable metallic and semiconducting behavior in molybdenum di-telluride (2H-MoTe2) by manipulating the Joule heating process through electrical control of the channel current. At low voltages, 2H-MoTe2 exhibits semiconducting behavior. As the current surpasses a critical threshold at higher voltages, the material transitions to a metallic-like state, confirmed by a positive temperature coefficient of resistance. Temperature- and voltage-dependent Raman studies confirm that this semiconducting to metal-like transition occurs without any accompanying structural phase transformation. This metallic behavior is likely due to enhanced phonon scattering caused by the increase in lattice temperature. In the metallic state, exposure to H2 gas results in a negative response, with increased resistance due to additional phonon scattering. Conversely, laser exposure at this state produces no noticeable photoresponse because the already high lattice temperature limits the impact of further heating. These effects were suppressed when 2H-MoTe2 was placed on a hexagonal boron nitride/multilayer graphene heat sink. This dynamic modulation of conductivity in 2H-MoTe2 through electrical stimuli highlights its potential for nanoelectronic device applications.

Fabrication of Free-Standing Porous BaTiO Thick Films by Indirect Selective Laser Sintering

The fabrication of free-standing porous thick films of ferroelectric BaTiO3, using a laser-assisted technique, is presented as a novel alternative to conventional methods. This approach adapts Indirect Selective Laser Sintering (ISLS) to create green films in a single laser pass, avoiding the complexities of traditional processes. Using commercial BaTiO3 powder and polyamide 12 as raw materials, laser processing parameters such as scanning laser speed and power were optimized to produce green BaTiO3 thick films with different thicknesses. After laser processing, the films were conventionally sintered and characterized for phase composition, microstructure, porosity, and electrical properties. X-ray diffraction and Raman spectroscopy confirmed the tetragonal BaTiO3 phase, while mercury intrusion porosimetry revealed a bimodal pore distribution. Impedance spectroscopy demonstrated a positive temperature coefficient of resistivity (PTCR) effect, with a peak resistivity near the Curie temperature. The PTCR behavior is hypothesized to arise from better oxygen adsorption due to the porosity and oxygen vacancies generated during sintering by carbon residues from polyamide degradation. The results demonstrate that ISLS is a versatile technique for producing high-quality, free-standing porous ceramic thick films with potential for a wide range of applications.

High-temperature thin-film strain sensors with low temperature coefficient of resistance and high sensitivity via direct ink writing

High-temperature thin-film strain sensors are advanced technological devices for monitoring stress and strain in extreme environments, but the coupling of temperature and strain at high temperature is a challenge for their use. Here, this issue is addressed by creating a composite ink that combines Pb2Ru2O6 and TiB2 using polysilazane (PSZ) as a binder. After direct writing and annealing the PSZ/Pb2Ru2O6/TiB2 film at 800 °C in air, the resulting thin film exhibits a low temperature coefficient of resistance (TCR) of only 281 ppm/°C over a wide temperature range from 100 °C to 700 °C, while also demonstrating high sensitivity with a gauge factor approaching 19.8. This exceptional performance is attributed to the intrinsic properties of Pb2Ru2O6, which has positive TCR at high temperature, and TiB2, which has negative TCR at high temperature. Combining these materials reduces the overall TCR of the film. Tests showed that the PSZ/Pb2Ru2O6/TiB2 film maintains stable strain responses and significant signal output even under varying temperature. These findings provide valuable insights for developing high-temperature strain sensors with low TCR and high sensitivity, highlighting their potential for applications in high-temperature strain measurements.

Indium tin oxide as a dual region resistance temperature detector

Resistance temperature detectors (RTD’s) have seen an increase in popularity due to their measurement accuracy and reliability compared to thermocouples. Most RTD’s are made from refractory noble metals such as platinum due to their resistance to oxidation at temperatures greater than 800 °C and near linear output over large temperature ranges. Conductive oxides have been investigated in high temperature RTD applications due to their stability in oxidizing environments, inherently large temperature coefficients of resistance (TCR) and high melting points. In this study, thin film RTDs comprised of indium tin oxide (ITO) sputter deposited in an argon rich atmosphere were fabricated and tested. ITO RTD’s exhibited a positive TCR between 20 °C and 500 °C and a negative TCR between 700 °C and 1000 °C, thus making it suitable for temperature measurement in two different temperature regions.

Investigation of the Positive Temperature Coefficient Resistivity of Nb-Doped Ba0.55Sr0.45TiO3 Ceramics

The demands of low-Curie-temperature (~−10 °C) positive temperature coefficient (PTC) thermistors are increasing in advanced precision integrated circuits and other industries. In this paper, the Nb-doped Ba0.55Sr0.45TiO3(BST)-based PTC resistivity materials are reported. The effects of the sintering process, especially the cooling rate on the PTC properties of the material, are investigated. The results indicate that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 composition of the prepared PTC ceramics demonstrates promising PTC characteristics. These include a Curie temperature as low as −13 °C, a high temperature coefficient of 0.296 at −3.4 °C, a large enough resistivity change of 3.1 over a narrow phase transition temperature range of approximately 38 °C, and moderate resistivity below the Curie temperature. Such properties suggest that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 ceramics are likely suitable for use in thermal management systems designed for low-temperature control.

Effect of Deposition Pressure and Temperature on Tungsten Thin-Film Heater for Phase-Change Switch Applications.

Tungsten (W) film is increasingly utilized in various microheater applications due to its numerous advantages. These advantages include a high melting point, positive constant temperature coefficient of resistance (TCR), good mechanical stability, and compatibility with semiconductor processes. In this paper, deposition parameters for enhancing the properties of W film were investigated, and an optimized microheater was fabricated. It was found that the deposition temperature and pressure can modify the TCR to be negative or positive and the crystalline phase of W films to be alpha phases or mixed with beta phases. A W film deposited under 650 °C with a pressure of 1 pa has a positive TCR and pure alpha phase crystalline structure. We applied this optimized W film as a microheater in an RF phase-change switch (RFPCS), and the maximum voltage of the optimized W microheater increased by at least 48% in this work. By optimizing the microheater, the phase-change switch can be successfully actuated in both on and off states, demonstrated by the Raman results of the phase-change material. A voltage pulse of 20 V/200 ns was enough to turn the switch off with MΩ, and 11 V/3 μs could turn the switch on with 138 Ω. The optimized microheater and device can cycle 500 times without failure. The insertion loss and isolation of the device at 20 GHz was 1.0 dB and 22 dB.

Investigation of electrical properties and PTCR effect in double-donor doping BaTiO3 lead-free ceramics

Abstract Utilizing the conventional approach, the positive temperature coefficient of resistivity (PTCR) performance of lead-free ceramics based on (1 − x%)(Ba1−y Y y )(Ti1.011−z Nb0.001Mn z )O3 − x%(Bi0.5Na0.5)TiO3 (BBNTx) was examined. The BBNTx ceramics were prepared using the double donor dopant under firing at 1,350°C for 120 min in the air. The findings exhibited that when the Y3+ concentration elevates, the room-temperature resistivity of 99%(Ba1−y Y y )(Ti1.011−z Nb0.001Mn z )O3 – 1%(Bi0.5Na0.5)TiO3 (BBNT1) samples initially falls and subsequently elevates. Moreover, the critical content of the samples is 0.15 mol%. Furthermore, the samples’ resistance jumping ratio can be effectively improved by adding Mn2+. The manganese dioxide level of 0.05 mol% yields the greatest resistance-jumping ratio. Besides, the impact of (Bi0.5Na0.5)TiO3 (BNT) concentration on ceramics’ Curie temperature was examined in the work. Therefore, good free-lead PTCR thermistors were successfully prepared by doping 3% BNT, with a resistance jump of 4.1 magnitude.

Electrical Transport Properties and Hopping Mechanism of ZrCuSiAs Type Compound GdFeAsO

Abstract Iron-based ceramic GdFeAsO has been prepared using the solid-state reaction method. This material exhibits unique properties, showing superconductivity at extremely low temperatures and behaving as a semiconductor at high temperatures. Raman spectroscopy revealed various Raman active modes in the sample. UV-visible spectroscopy was employed to study the optical properties of the material in the wavelength range of 200-800 nm. Using Tauc's plot, the optical band energy values of the sample were estimated to be approximately 2.78 eV. The electrical characterizations have been performed through an impedance analyzer. Additionally, the sample displayed negative temperature coefficient of resistance behavior and positive temperature coefficient resistance. The thermistor parameters are evaluated using the bulk resistance at various temperatures. This opens up potential uses for thermistors in devices like fuses and temperature sensors. The ac conductivity spectrum of the sample followed both Jonscher's universal power law and the Arrhenius equation. The activation energy was calculated for different temperature regions. The correlated barrier hopping model is used to analyze the electrical conduction mechanism in the sample. This study provides insights into the unique electrical and optical properties of the GdFeAsO ceramic and sheds light on its potential applications in various fields.

Inkjet-printed sub-zero temperature sensor for real-time monitoring of cold environments

Real-time monitoring of low temperatures (usually below 0 °C) or cold environments is a specific requirement that finds its high demand in the aerospace, pharmaceutical, food, and beverage industries to maintain the temperature at high altitudes or in refrigerators and cold storage. In general, this purpose is achieved by using a sub-zero temperature sensor coupled with a control system. However, the market available such temperature sensors are very expensive, and bulky, thus not being suitable for portable operation, and also they suffer from poor accuracy. Therefore, the development of high-performance, low-cost, lightweight, and portable sub-zero temperature sensors is highly desired. In our recent work, we developed such sensors and integrated them with auxiliary electronics to demonstrate their wireless operation for the continuous and real-time monitoring of cold environments. So, in order to obtain low-cost sensors a cost-effective inkjet printing technology was employed for the fabrication of devices. A lightweight polydimethylsiloxane (PDMS) was used as the substrate and an electrically conducting graphene nanocomposite was used as the temperature-sensing material. To obtain a functional graphene nanocomposite film with a thickness of 530 nm and a conductivity of ~189 S m−1, the printed graphene nanocomposite was photonically sintered using a xenon flash lamp. This step was crucial for obtaining a sensor on the soft PDMS platform. The graphene nanocomposite film exhibited a positive temperature coefficient resistance value of approximately 0.119 %/°C, and its resistance values varied almost linearly (with an Adjusted R2 value (model accuracy) of 0.99) with temperature within the operating range of −30 °C to 80 °C. The sensor was properly encapsulated for protection without significantly affecting its performance. The sensors demonstrated sufficient flexibility, with a bending radius of 20 mm, and sustained 500 continuous bending cycles. Finally, the real-time operation of the sensors was demonstrated by wirelessly transmitting and monitoring the temperature over a smartphone platform.

New insights into the positive temperature coefficient of resistance model of BaTiO3‐based ceramics

AbstractThe speculation concerning the presence of interfacial states in the BaTiO3‐based positive temperature coefficient of resistance (PTCR) model originating from the formation of the grain boundary barrier in semiconductor is argued to be unsuitable. This communication provides new insights into the formation of the grain boundary barrier without the grain boundary phase of the BaTiO3‐based PTCR model. New insights into the temperature and voltage dependences of the resistance or resistivity with and without grain boundary phase of the BaTiO3‐based PTCR model are proposed. Concerning the absence of the grain boundary phase, two new plausible models are proposed: the net dipolar polarization field due to the applied voltage and effective permittivity owing to the net dipole charges accumulated near the grain boundary. As for the presence of the grain boundary phase, a new thinking concerning the field emission tunneling with the conduction band conduction mechanism for the occurrence of low resistance at low applied voltage is posited.

3D Printing Assisted‐Fabrication of Low‐Temperature Strain Sensors with Large Working Range and Outstanding Stability

Recently, low‐temperature wearable strain sensors, referring to those working at sub‐zero temperatures, are attracting increasing attentions. However, the fabrication of low‐temperature strain sensors with large working ranges, high sensitivity, and good stability remains a major challenge. In this study, a novel low‐temperature wearable strain sensor is fabricated by depositing the silver nanoplates (Ag NPs)/carbon nanotubes (CNTs) composite onto a cured silicone (DS) substrate that is constructed by using a 3D printing technology. The synergistic effect of the Ag NPs with positive temperature coefficient of resistance (TCR) and the CNTs with negative TCR enable the Ag NPs/CNTs/DS strain sensor's TCR value (−1.16 × 10−5 K−1) to approach zero. The Ag NPs/CNTs/DS strain sensor demonstrates a high gauge factor over a large working range (0–100%) and fast response and recovery rates. Simultaneously, the Ag NPs/CNTs/DS strain sensor displays outstanding reproducibility and long‐term stability at −40 °C as well as excellent temperature cycling resistance under cyclic temperature of −40 to 60 °C. The Ag NPs/CNTs/DS strain sensor is further validated by incorporating into a wireless sensing system for remotely monitoring various human activities at −40 °C. This work provides wearable strain sensors for monitoring human‐machine interaction under low‐temperature condition.

Temperature‐Independent Conductive Ceramic for High‐Temperature Strain‐Sensing Applications

Temperature‐independent properties are critical for high‐temperature thin‐film strain gauges (TFSGs). In this study, by controlling the electron scattering and tunneling effects in the TiB2/SiCN composites, the environmental interference of temperature fluctuations is successfully eliminated, and a temperature‐independent TFSG is fabricated. The effects of pyrolysis temperature and TiB2 content on the microstructural evolution and electrical properties of the ceramic films are studied. The temperature insensitivity is mainly attributed to the balance between the intrasheet resistance with a positive temperature coefficient of resistance (TCR) and the intersheet resistance with a negative TCR. This composite shows nearly constant resistance values over an ultrawide temperature range of 300–700 °C, with less than 0.05% deviation of the normalized resistance and TCR values as low as 1.6 ppm °C−1. In addition, the TiB2/SiCN films exhibited stable piezoresistive responses, with a gauge factor of 4.28, and the temperature‐independent strain response in the high‐temperature range is verified.

Correlation between positive temperature coefficient of resistance, double Schottky barrier, and anionic substituents in BiFeO3

Various types of conduction (leakage current) mechanisms in metal oxides deteriorate the system's electrical response. The existence of impurity phases, the formation of oxygen vacancies, and high porosity are the main source of free charge carriers in the system. Acceptor states are created due to the formation of oxygen vacancies in the system. In BiFeO3, acceptor states are formed within the grains and at the grain boundaries. The formation of double Schottky barriers at the grain boundaries is interpreted to be associated with the formation of such acceptor states formed at the grain boundary. These acceptor states are the consequence of oxygen stoichiometry which is also responsible for the appearance of a positive temperature coefficient of resistance (PTCR). The effect of substituting isovalent and aliovalent dopants in BFO has been comprehensively analyzed in the present study. These substitutions are responsible for forming a double Schottky barrier at the grain boundary. Barrier potential and barrier width are calculated and plotted as a function of the substituent (di, tri, or tetravalent) to highlight the role of the substituent's valence in the formation of a double Schottky barrier at the grain boundary and the appearance of the PTCR effect in the resistivity profile. The present study reveals that the occupation of the acceptor states at the grain boundaries affects the inter-grain conductivity.

Self-Powered Bipolar Photodetector Based on a Ce-BaTiO3 PTCR Semiconductor for Logic Gates.

Ferroelectric materials bring new opportunities for self-powdered photodetectors, taking advantage of their anomalous bulk photovoltaic effect. However, ferroelectric-based photodetectors suffer from relatively poor responsivity and detectivity due to obstacles of low electrical conductivity and low photoelectric conversion ability. The present work proposes a strategy based on heterovalent ion Ce-doping into BaTiO3 (Ce-BTO) that gives rise to a good room temperature conductivity combined with a significant PTCR (positive temperature coefficient of resistivity) effect. By utilizing a Ce-BTO PTCR semiconductor, a high-performance self-powered photodetector ITO/Ce-BTO/Ag is fabricated, demonstrating a polarity-switchable photoresponse with the change of wavelength due to the competition between hot electrons induced by the Ag plasmonic effect and electron-hole pairs separated by a Schottky barrier. Moreover, benefiting from the reduced bandgap and the introduced impurity states, good responsivity (9.85 × 10-5 A/W) and detectivity (1.25 × 1010 Jones) as well as fast response/recovery time (83/47 ms) is achieved under 450 nm illumination. Finally, four representative logic gates ("OR", "AND", "NOR", and "NAND") are demonstrated with one photodetector via the bipolar photoresponse. This work opens an avenue to promote the application of PTCR semiconductors in optoelectronics, offering a conceivable means toward high-performance self-powered photodetectors.

Pyroresistive Properties of Composites Based on HDPE and Carbon Fillers.

Electrothermal processes were studied in pyroresistive composites based on high-density polyethylene (HDPE) containing 8 vol.% carbon black (CB), 8 vol.% carbon fibers (CF), and their mixture 4 vol.% CB + 4 vol.% CF. It is shown that the kinetic heating curves of composites are well described by an exponential dependence with a certain heating rate constant k for each type of composite. After a short heating time, the equilibrium temperature Te is reached in the sample. When the applied voltage exceeds a certain value, the Te value decreases due to the presence of the positive temperature coefficient of resistance (PTC) effect. Due to the PTC effect, the composites exhibit a self-regulating effect relative to the Te. Relations between the applied voltage, electric power, and equilibrium temperature are found, the Te value depends on the applied voltage according to the quadratic law whereas there is a linear relationship between the Te and electric power. A possible application of such pyroresistive composites is resistance welding of plastics using a heating element (HE) made of a pyroresistive material. The use of HDPE-CB composite to create HE for resistance welding is demonstrated and the welded joint of HDPE parts obtained using HE is shown.

Electrical characteristics of Mg doped GeO2 NWs based device

In this article, the growth of a undoped GeO2 and Mg doped GeO2 nanowires (NWs) by electron beam evaporation method and analysis of its electrical properties has been reported. Au/GeO2 and Au/Mg-GeO2NWs based devices on Si substrate was fabricated. The optical band gap (Eg) for both the undoped GeO2 and Mg doped GeO2NWswas estimated to be 3.78 eV and 3.37 eV from UV–Vis spectrum. The temperature dependence current(I)–voltage(V) characteristics of undoped GeO2 based device shows a gradual increase of conductivity with the increase of temperature. Where, Mg doped GeO2NWs based device demonstrates a decreasing nature of conductivity with the increase of temperature. This anomalous characteristic has been explained by the positive temperature coefficient of resistance (PTCR) effect. The temperature dependent ideality factor of Mg doped GeO2NWsand undoped GeO2 NWs devices were studied. The increase in barrier height on increasing of temperature also been observed for the Mg doped GeO2NWs based device. Owing to the PTCR effect, the calculated series resistance of Mg doped GeO2NWs based device also shows an anomalous increasing behavior with the increasing of temperature where as undoped GeO2 based device shows a normal behavior of decreasing of series resistance with increase of temperature.

Electrical transport behaviors of Ni layer on carbon fiber

Recently, carbon materials have been employed for the core of metal wires, contributing to their weight reduction. Low weight is a required characteristic for cables used in air, water, and ground transportations, in order to maximize fuel efficiency. Nowadays, the hybridization of C with metal for the creation of C-based metal wires is achieved through different approaches. A thin metal layer of Ni is usually applied through electroless plating on the surface of C fibers (CFs; diameter = 7 μm). Transport studies conducted on a single strand of Ni-coated CFs (Ni-CF) have indicated that, depending on the grain size, phonon-supported hopping or phonon-driven electron scattering transport can dominate. At a given P concentration (∼11 at.wt.%) and when the average grain size is < 100 nm, phonon-driven electron scattering transport dominates: as the temperature increases, the resistance increases as well, resulting in a positive temperature coefficient of resistance (TCR) (∼1.5 × 10 −3 /K at 300 K). This is a conduction behavior typically observed in metals. However, when the average grain size is > 100 nm, impurity-related variable range hopping (VRH) transport dominated, leading to a negative TCR (∼1.0 × 10 −4 /K at 300 K); in this case, the resistance decreases with increasing temperature, as in a semiconductor. Our results imply that, by controlling the plating condition and surface morphology of CF, it is possible to modulate metal properties (i.e., the metal-insulator transition (MIT)). • A Ni layer was deposited on the outside of carbon fibers (CFs) by electroless electrochemistry. • The temperature-dependent resistance of the Ni-CFs was measured in a closed-cycle refrigerator (CCR). • Transport studies conducted on a single strand of Ni-coated CFs have indicated that, depending on the grain size, phonon-supported hopping or phonon-driven electron scattering transport can dominate.

The effects of Barium Strontium Titanate (BST) on the soft magnetic properties and loss performance of MnZn ferrites

With the increasing power density of the switched mode power supply (SMPS) developed nowadays, higher efficiency is required from the magnetic core, where the MnZn ferrites are often adopted. However, the relatively high operating temperature of the SMPS often results in reduced resistivity of the MnZn, which increases the eddy current loss. To enhance the resistivity of MnZn ferrite at high temperature range (>100 °C), donor-doped barium strontium titanate (BST) with a positive temperature coefficient of resistivity (PTCR) is prepared and dopped in the MnZn ferrite. The influence of BST addition from 0.000 wt% to 0.020 wt% on the MnZn ferrite is investigated over a wide temperature range from 25 °C to 140 °C. The XRD result suggests ionic exchange between the spinel phase and perovskite phase. The SEM result shows a refined and more uniform microstructure of MnZn ferrite brought about by the BST addition. At the maximum of 0.020 wt%, the BST addition shows almost no influence on density and the saturation magnetic induction. However, the initial permeability is slightly reduced by the BST addition, due to the microstructural change. Moreover, the BST concentrating at the grain boundaries improves the DC-resistivity across the temperature range from 25 °C to 140 °C. Due to the addition of BST, the reduction in eddy current loss at 300kHz/100 mT is around 35% at 25 °C, and ∼20% reduction at 140 °C.

Effect of film thickness on the electrical transport in Co2FeAl0.5Si0.5 thin films

The effect of film thickness on the structural- and electrical-properties is investigated in Co2FeAl0.5Si0.5 (CFAS) thin films of thickness, t, in the range 12–75 nm. These films are grown by ultrahigh vacuum dc magnetron sputtering on Si(100) substrates with SiO2 buffer layer (300 nm), at the substrate temperature of 500 ◦C. The GIXRD patterns reveal that B2 structural order decreases with increasing t. The film with t = 75 nm has sizable A2 disorder. Irrespective of t, ρ(T, H = 0) goes through a minimum at Tmin. An elaborate quantitative analysis of the ρ(T, H = 0) data, taken over the temperature range 5 K to 300 K, demonstrates that the electron-diffuson (e–d) and weak localization (WL) effects (responsible for the negative temperature coefficient of resistivity (TCR) for T &amp;lt; Tmin) compete with the electron-magnon (e–m) and electron–phonon (e–p) scattering (positive TCR) contributions to produce a minimum at Tmin. Residual resistivity, ρ5K, and the e–d, wl, e–m and e–p scattering contributions to ρ(T, H = 0), ρe–d, ρwl, ρe–m and ρe–p, all go through a minimum at t = 50 nm. Regardless of t, the thermal renormalization of the spin-wave stiffness makes a significant contribution to ρe–m.

Positive temperature coefficient of resistance of Mg-GeO2 nanowire array film

Here, glancing angle deposition is employed to synthesize the undoped GeO2 and Mg-doped (0.4 and 0.8 at. %) GeO2 nanowires (NWs) on a Si substrate. The microscopic images show the formation of the NW-like morphology of the grown materials. The gradual decrease in the average ratio of length to diameter depicts the worsening of the formation of NWs with the incorporation of Mg into the GeO2 host lattice. This also affects the crystallinity characteristics of the materials, which have been demonstrated from the selected area electron diffraction (SAED) pattern of the materials. The polycrystallinity nature of undoped GeO2 NWs changes to amorphous due to the introduction of Mg, which has been confirmed from both the obtained SAED and x-ray diffraction patterns of the samples. The presence of Mg was confirmed from the obtained broad bands at 473 and 437 cm−1 in the Fourier transmission spectrum of the doped samples. The increasing conductance with the temperature of Au/undoped GeO2 devices can be explained by the thermionic emission process, whereas the Mg-GeO2 device shows an overall decrease in conductance with increasing temperature. We have ascribed the origin of this abnormal conductance as the positive temperature coefficient of resistance, which is one of the first reports, due to the generation of random grain boundaries and enormous electron trapping at the Au/Mg-GeO2 NW junction. Furthermore, the undoped GeO2 NW device shows good temperature-dependent conductivity as well as stability compared to the doped one.