Temperature Coefficient Of Resistance Values Research Articles

Green synthesis of ITO nanoparticles using Carica papaya seed extract: impact of annealing temperature on microstructural and electrical properties of ITO thin films for sensor applications

ABSTRACT This paper reports the synthesis of indium tin oxide (ITO) nanoparticles and the effect of annealing temperature on the microstructural and electrical properties of ITO thin films. The synthesized ITO (90:10) nanoparticles are deposited at 29°C using E beam evaporation to form ITO thin films and annealed at 200, 400 and 500°C. The microstructural properties are investigated using XRD and AFM , and electrical properties such as temperature coefficient of resistance (TCR) and gauge factor are investigated using four-probe and four-point beam bending method, respectively. The investigations results reveal an increase in grain size, carrier concentration and gauge factor with an increase in the annealing temperature. The absolute value of TCR is constant at high temperatures for the film annealed at 500°C. The ITO thin film annealed at 500°C shows improved morphological and electrical properties and can be used for the development of sensors operating at high temperature.

Tuning of zinc oxide temperature sensing and optical absorption properties by tin heavy-doping

This paper presents the feasibility of tin (Sn) heavily doped zinc oxide (ZnO) thin film as an active layer for a microbolometer and the effect of this Sn heavily doping on the structural, optical and electrothermal properties of Sn-doped ZnO (SnxZn1-xO) thin films. The SnxZn1-xO thin films were deposited on substrates using an RF/DC co-sputtering method at room temperature with different Sn dopant concentrations %, x (x = 0.22, 0.26 and 0.32). It was found that the optical and electro-thermal properties were strongly affected by Sn doping. The result revealed an increase in the visible and infrared radiation absorption and electrical conductivity with increasing Sn doping whereas the temperature coefficient of resistance (TCR) decreases. A maximum TCR value of 1.9%/K with a sheet resistance (Rs) of 233 kΩ/□ was observed with 0.22 Sn doping concentration. The result proved that the Sn doping could help to decrease the TCR temperature dependence and the sheet-resistance of ZnO thin film as well as increasing its IR radiation absorption that makes it a strong candidate for the active layer of microbolometer.

A-site Na-doping to enhance room-temperature TCR of La1-xNaxMnO3 polycrystalline ceramics

During the exploration on the temperature coefficient of resistance (TCR) of A-site cation-doped perovskites, divalent cation-doped material systems have received increasing attention; however, the TCR performance of monovalent cation-doped perovskites has been less studied. In order to investigate the effect of monovalent Na cation doping on the TCR of La1-xNaxMnO3 (LNMO, x = 0.1, 0.2, 0.3, 0.4, and 0.5) and obtain LNMO materials possessing high TCR values at room temperature, the LNMO perovskite ceramics were synthesized by the Pechini sol–gel method. The effect of sodium cation doping on their structural and electrical properties was investigated by various characterization methods. An increase in Na content affected the grain size and Mn4+ ion concentration in the LNMO ceramics. Furthermore, increasing quantity of Na significantly increased the TCR from 5.89 % K−1 at x = 0.1 to 8.56 % K−1 at x = 0.4. For a Na-doping level x = 0.4, the peak TCR temperature (Tk) at room temperature reached 299.42 K. Among the feasible reasons that could improve the above electrical parameters are the weakened grain boundary scattering, the increase in A-site vacancy, the enhanced double-exchange effects, and the generation of Jahn–Teller distortions. According to the results of this study, the obtained LNMO ceramics seem to be promising for the application in uncooled infrared bolometer technology.

Impact of K doping on room-temperature temperature coefficient of resistivity of La0.7(Ag0.3-xKx)MnO3 (0.160 ≤ x ≤ 0.180) polycrystalline ceramics

Herein, La0.7(Ag0.3-xKx)MnO3 (LAKMO, x = 0.160, 0.165, 0.170, 0.175 and 0.180) polycrystalline ceramics are prepared by the sol-gel method and the influence of K content on the structure of LAKMO ceramics is investigated using X-ray powder diffraction (XRD), field-emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) and Raman spectroscopy, demonstrating that variations in K content cause significant structural changes. For instance, K doping led to the distortion of MnO6 octahedron and grain growth. Moreover, the energy dispersive spectrometer (EDS), elemental mapping and X-ray photoemission spectroscopy (XPS) confirmed the uniform distribution of constituent elements on the surface. The increase in K-doping ratio resulted in the distortion of MnO6 octahedron, weakening grain boundaries scattering and enhancing the double exchange effect. Consequently, the electrical transport properties of LAKMO ceramics were improved with the increase of K doping, especially the decrease in resistivity and increase in temperature coefficient of resistivity (TCR) values. At x = 0.175, the peak TCR value was found to be 11.15% K−1 at room temperature (Tk = 292.22 K). These results indicated that the K-doped LAKMO ceramics are promising candidates for uncooled infrared bolometers.

High-performance electrical properties of La-based perovskite ceramics for the functional phase of thick film resistors

In order to explore an economical functional phase alternative material for thick film resistors, the crystal structure, microstructure, and electrical properties of (1-x)La0.5Sr0.5Co0.96Ni0.04O3-δ + xLaCo0.4Ni0.58Zn0.02O3 (x = 0.0–1.0) composite ceramics were studied through solid-state reaction experiments. The composite ceramics were characterized by x–ray diffraction, scanning electron microscopy, energy dispersive x–ray spectroscopy, X-ray photoelectron spectroscopy, and DC four–probe method. Results suggested that the main phases of La0.5Sr0.5Co0.96Ni0.04O3-δ and LaCo0.4Ni0.58Zn0.02O3 were formed, along with a small part of impurity phases. The addition of LaCo0.4Ni0.58Zn0.02O3 to La0.5Sr0.5Co0.96Ni0.04O3-δ decreased the electrical conductivity and changed the temperature coefficient of resistance from positive to negative. Zero temperature coefficient of resistance could be achieved around 0.6 < x < 0.8 and relatively low absolute temperature coefficient of resistance values could be obtained for the samples of 0.4 ≤ x ≤ 0.8. The ceramic of 0.6La0.5Sr0.5Co0.96Ni0.04O3-δ + 0.4LaCo0.4Ni0.58Zn0.02O3 showed the optimal performances of conductivity = 1923 S/cm, temperature coefficient of resistance = 379.54 ppm/°C, and relative density = 95.05%.

Optimising porous silicon electrical properties for thermal sensing applications

Present day sensing elements used in thermo-resistive type uncooled detectors or bolometers either suffer from material incompatibility issues or have relatively poor performance in the long wave infrared region (LWIR). This work explores the potential of meso-porous silicon films as the base material for the sensing element in these bolometer applications. The performance of these highly sensitive bolometers depends on the electrical properties, specifically the electrical resistivity and temperature coefficient of resistance (TCR), of the sensing element. In this work, we explore the electrical properties of meso-porous silicon films and optimize these properties through fabrication conditions and surface treatment. We further compare the TCR values of single and multi-layer porous silicon films for use in multilayers to fabricate highly selective distributed Bragg reflectors (DBR) in LWIR detector applications. The experimental results show that a low value of resistance along with high value of TCR can be obtained by altering porosity and surface passivation in single and multi-layer porous silicon films. We measured the TCR within a three-layer porous silicon film (DBR stack) to be 6%/K, which is significantly higher than the TCR from contemporary sensing element materials. Our studies indicate that the use of meso-porous silicon films for the sensing element in bolometers can potentially overcome the performance and the material compatibility issues associated with existing technologies such as amorphous silicon and vanadium oxide in LWIR.

The effect of annealing process on the performance of strain nickel–chromium thin film sensor

In order to reduce the resistance value of the sputtering thin film resistor grid and improve the adhesion of the film, a thin film sensor with the NiCr film as a sensitive layer on a 304 stainless steel substrate is annealed in the N2 environment. During the experiment, it is found that the different annealing temperatures (300 °C, 350 °C, 400 °C, 450 °C, and 500 °C) can effectively reduce the resistance value of the thin film resistor grid; the decrease is the largest at 450 °C, and the resistance value change is 1.77 kΩ. The small resistance value enables the thin film sensor to detect smaller strain and has higher measurement accuracy. The thin film has the strongest adhesion on the substrate at 350 °C and 30 min, which is about 37.5% higher than that of the sputtering state. The increase in adhesion makes the thin film less likely to crack and fall off prematurely, which can expand the measuring force range. In addition, the atomic force microscopy results demonstrate that the thin film annealed at a higher annealing temperature has higher surface roughness, which may be caused by the phenomenon of original grain clusters after annealing. In addition, the temperature coefficient of resistance value and strain sensitivity coefficient (kn) increase with the increase in the annealing temperature, with kn increasing only slightly.

The sintering and electrical properties of Zn-substituted LaCo0·4Ni0·6O3 ceramics based upon experiments and calculations

To explore a low–cost functional phase alternative material for thick film resistors, the thermal behavior, sintering and electrical properties of LaCo0·4Ni0.6-yZnyO3 (y = 0.00–0.08, LCNZ) ceramics were investigated through experiments and density functional theory calculations. Results of simultaneous thermal analysis, thermomechanical analysis, scanning electron microscopy, and DC four–probe method indicated that substitution of Ni-ion by Zn–ion could lower the phase formation and densification temperatures of LCNZ, as well as increase the resistivity and decrease the temperature coefficient of resistance (TCR). The resistivity of 0.94 mΩ cm (y = 0.00) and 1.03 mΩ cm (y = 0.02), as well as TCR value of −312.79 ppm/°C (for y = 0.00) and −872.82 ppm/°C (for y = 0.02) could be achieved as the LCNZ ceramics sintered at 1200 °C. The variations of octahedral bond population, electron density around oxygens, and partial density of states near the Fermi level firmly supported the results of experiments.

Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La0.9-xSrxK0.1MnO3 ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr2+ ions, substituting La3+ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K−1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.

Electrical and structural properties of conductive nitride films grown by plasma enhanced atomic layer deposition with significant ion bombardment effect

Conductive metal nitrides are widely used in the microelectronics industry as interconnects, thin film resistors, electrodes, and diffusion barriers. These films are commonly prepared by sputtering and chemical vapor deposition, which are suitable for planar geometries. However, conformal deposition onto 3D and complex structures requires the use of atomic layer deposition (ALD). In this work, we compare the electrical and structural properties of various metallic nitrides (namely, TiNx, ZrNx, HfNx, and TaNx) prepared by ALD from metalorganic precursor and H2/Ar plasma. Despite similar bulk resistivity values of these films, we find significant differences in their measured resistivity for the thin film (by ALD). TiNx and ZrNx show metallic behavior with a positive temperature coefficient of resistance (TCR), whereas HfNx and TaNx show semiconducting behavior with negative TCR values. Microstructure and film chemistry of deposited films are investigated by x-ray photoelectron spectroscopy and transmission electron microscopy, and the correlation between the electrical and structural parameters of the deposited films is discussed. It is shown that a high concentration of carbon contamination is related to smaller grain size and higher electrical resistivity. TiNx exhibits the lowest carbon contamination, largest degree of crystallinity and lowest resistivity (∼60 μΩ cm) highlighting its potential as ALD-grown metal. Other nitrides and their combinations can be used to tailor specific resistivity and TCR values for thin film resistor applications in 3D and complex geometries such as deep trenches. Overall, this study provides useful guidelines toward the development of ALD nitrides for use in the microelectronics industry.

A-site K-doping to enhance room-temperature TCR of polycrystalline La0.8Sr0.2-xKxMnO3 ceramics

Herein, polycrystalline La0.8Sr0.2-xKxMnO3 (LSKMO, 0 ≤ x ≤ 0.2) ceramics with varying K concentration are successfully synthesized via a facile sol-gel method. The electrical transport properties and microstructural of the prepared samples are characterized and analyzed in detail. The different characterization results show that K+ ion substituted La3+ and Sr2+ ions significantly influenced the double exchange (DE) mechanism and Jahn-Teller (JT) effects. The electrical resistivity studies suggest that as the K doping content rose, the resistivity increased and peak resistance temperature decreased. Electrical transport properties of samples are analyzed via the combination of DE mechanism, JT effects, variable-range hopping and small-polaron hopping model. The temperature coefficient of resistance (TCR) measurement demonstrates the enhanced temperature sensitivity for the K-doped polycrystalline ceramics samples as compared to the pure La0.8Sr0.2MnO3 samples. The optimized x content for the polycrystalline LSKMO ceramics is determined to be x = 0.08. At this x value, the peak TCR of the resistivity measured 9.11% K−1 at 292.44 K. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site K doping and demonstrate the potential of polycrystalline La0.8Sr0.12K0.08MnO3 ceramic in room-temperature infrared bolometers.

Development of a Dental Implantable Temperature Sensor for Real-Time Diagnosis of Infectious Disease.

Implantable sensors capable of real-time measurements are powerful tools to diagnose disease and maintain health by providing continuous or regular biometric monitoring. In this paper, we present a dental implantable temperature sensor that can send early warning signals in real time before the implant fails. Using a microfabrication process on a flexible polyimide film, we successfully fabricated a multi-channel temperature sensor that can be wrapped around a dental implant abutment wing. In addition, the feasibility, durability, and implantability of the sensor were investigated. First, high linearity and repeatability between electrical resistance and temperature confirmed the feasibility of the sensor with a temperature coefficient of resistance (TCR) value of 3.33 × 10–3/°C between 20 and 100 °C. Second, constant TCR values and robust optical images without damage validated sufficient thermal, chemical, and mechanical durability in the sensor’s performance and structures. Lastly, the elastic response of the sensor’s flexible substrate film to thermal and humidity variations, simulating in the oral environment, suggested its successful long-term implantability. Based on these findings, we have successfully developed a polymer-based flexible temperature sensor for dental implant systems.

A-site mixed-valence co-doping to optimize room-temperature TCR of polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics

Herein, polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics (A-site = La, K, Ca and Sr, 0.00 ≤ x ≤ 0.16) are successfully synthesized via the sol-gel process and the influence of Sr content on microstructural and electrical transport properties is investigated in detail. The results reveal that the replacement of Ca-ions by Sr-ions resulted in a decreased resistivity and enhanced temperature coefficient of resistance (TCR) peak temperature (Tk). The influence of A-site mixed-valence co-doping, where A-site is occupied by monovalent alkali-metal, divalent alkaline-earth element and trivalent rare-earth element, on electrical transport properties can be explained by using different conduction mechanisms in different temperature regions. At optimal doping content of 0.12, peak TCR of the resistivity was found to be 12.04% K−1 at 290.38 K, which is the best reported TCR for A-site mixed-valence co-doped perovskite manganese oxides. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site mixed-valence co-doping and demonstrate the potential of polycrystalline La0.8K0.04Ca0.04Sr0.12MnO3 ceramic in uncooling infrared bolometers.

Negative thermal expansion, magnetic and electronic transport properties in antiperovskite compounds Mn3Ga1-xAgxN (0 ≤ x ≤ 1.0)

The negative thermal expansion (NTE), magnetic and electronic transport properties of Mn3Ga1-xAgxN (0 ≤ x ≤ 1.0) with antiperovskite structure were systematically investigated. Our results indicate that the introduction of Ag in Mn3Ga1-xAgxN can effectively tune the coefficient of NTE from –232.57 × 10−6/K (x = 0, △T = 22 K) to −19.76 × 10−6/K (x = 1.0, △T = 15 K). Correspondingly, the ΔStotal associated with the different amplitude of the lattice contraction at the phase transition gradually decreases from 23.9 J/(kg·K) to 10.9 J/(kg·K) with increasing Ag content. The substitution of Ag in Mn3Ga1-xAgxN also affects significantly the magnetic properties and results in the magnetic evolution from antiferromagnetic (AFM) to ferrimagnetic (FIM) with increasing Ag content. Thus the magnetic transition from ferromagnetic to paramagnetic was observed at high doping level (for x = 0.8 and 1.0). Above transition temperature, the temperature coefficient of resistivity (TCR) can be tuned by Ag substitution and the lowest TCR value is 148.1 ppm/K when x = 0.8. The possible mechanism for the observed tunable TCR is discussed. The obtained results are helpful for understanding the chemical doping effects on the physical properties and the strong correlation effects in Mn-based antiperovskite compounds.

Characteristics of Current Transfer in PVA Films with Dispersed Multiwall Carbon Nanotubes on Silicon Substrates

Planar nanocomposite structures comprising poly(vinyl alcohol) films with dispersed multiwall carbon nanotubes (MWCNTs) deposited on silicon substrates and provided with aluminum contacts possess rectification properties and have asymmetric nonlinear current–voltage characteristics. Forward-biased nanocomposite structures exhibit a positive temperature coefficient of resistance (TCR) in a temperature interval of 270–350 K, whereas analogous PVA film structures without MWNTs have negative TCR values. Under reverse bias, the structures with MWNTs exhibit TCR with a sign changing from negative to positive. The observed behavior is explained in terms of the tunneling current transfer mechanism.

(Pr0.75La0.25)0.7Sr0.3MnO3:Agx (0 ≤ x ≤ 0.25) polycrystalline ceramics with room-temperature TCR improvement for uncooled infrared bolometers

In this work, perovskite manganite (Pr0.75La0.25)0.7Sr0.3MnO3:Agx (PLSMO:Agx, x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) ceramics were successfully prepared by sol-gel route and solid-state reaction. The surface morphologies, peak temperature variation behaviors of temperature coefficient of resistivity (TCR), microstructural and electrical transport properties of all the specimens were analyzed by various testing methods like XRD, SEM, EDS, R-T and XPS. XRD Rietveld refinement data demonstrated that Mn–O bond length, Mn–O–Mn bond angles and the unit cell volume increased along with the rise in x. Consequently, the bandwidth describing the overlap between the O2p and Mn3d orbitals reduced, and this change further affected the electrical transport properties. Scanning electron microscopy (SEM) images indicated that silver was helpful in increasing the grain size. The metal-insulator transition temperature increased due to the enhancement in double exchange (DE) interaction. X-ray photoelectron spectroscopy (XPS) fitting data (percentage of Mn4+ and O2−) along with XRD Rietveld refinement data confirmed the enhancement in DE interaction. The most remarkable thing was that the reduction in resistivity occurred gradually, which resulted in a significant improvement in the TCR. The TCR value achieved 11.35% K−1 with the peak temperature being 300.69 K (room-temperature ~ 300 K) at x = 0.15. Obviously, obtaining a large room-temperature TCR value (≥10% K−1) in praseodymium perovskite oxides was encouraging since such results have not been explored previously. Overall, the proposed PLSMO:Ag0.15 ceramic with large room-temperature TCR value look prospective candidates for future advanced uncooled infrared bolometers.

Conduction and Electric Field Effect in Ultra-Thin Tungsten Films

Ultra-thin tungsten films were prepared using hotwire assisted atomic layer deposition. The film thickness ranged from 2.5 to 10 nm, as determined by spectroscopic ellipsometry and verified by scanning electron microscopy. The films were implemented in conventional Van der Pauw and circular transmission line method (CTLM) test structures, to explore the effect of film thickness on the sheet and contact resistance, temperature coefficient of resistance (TCR), and external electric field applied. All films exhibited linear current-voltage characteristics. The sheet resistance was shown to considerably vary across the wafer, due to the film thickness non-uniformity. The TCR values changed from positive to negative with decreasing the film thickness. A field-induced modulation of the sheet resistance up to $\sim 4.6\cdot 10^{-4}\,\,\text{V}^{-1}$ was obtained for a 2.5 nm thick film, larger than that generally observed for metals.

Fabrication, Characterization and Implementation of Thermo Resistive TiCu(N,O) Thin Films in a Polymer Injection Mold

This paper presents the development of metallic thermoresistive thin film, providing an innovative solution to dynamically control the temperature during the injection molding process of polymeric parts. The general idea was to tailor the signal response of the nitrogen- and oxygen-doped titanium-copper thin film (TiCu(N,O))-based transducers, in order to optimize their use in temperature sensor devices. The results reveal that the nitrogen or oxygen doping level has an evident effect on the thermoresistive response of TiCu(N,O) films. The temperature coefficient of resistance values reached 2.29 × 10−2 °C−1, which was almost six times higher than the traditional platinum-based sensors. In order to demonstrate the sensing capabilities of thin films, a proof-of-concept experiment was carried out, integrating the developed TiCu(N,O) films with the best response in an injection steel mold, connected to a data acquisition system. These novel sensor inserts proved to be sensitive to the temperature evolution during the injection process, directly in contact with the polymer melt in the mold, demonstrating their possible use in real operation devices where temperature profiles are a major parameter, such as the injection molding process of polymeric parts.

Effect of high temperature annealing on resistivity and temperature coefficient of resistance of sputtered platinum thin films of SiO2/Pt/SiOx interfaces

The influence of high temperature annealing up to 800∘C on electrical resistivity and temperature coefficient of resistance of magnetron sputtered platinum films were investigated experimentally and theoretically. Highly adherent platinum films were manufactured on silicon oxide interfaces without using additional adhesion layers like titanium or tantalum. Such platinum films can be extremely useful for the fabrication of microelectromechanical sensors. X-ray diffraction studies exhibit grain sizes in the range of 39 nm for the as-deposited case to 162 nm after annealing at 800 ∘C. Thereby film resistivity values decrease from 16.8 ± 0.4 µΩ cm to 12.7 ± 0.2 µΩ cm and temperature coefficient of resistance values increase from 2180 ppm/K to 2810 ppm/K. A good accordance to the model of Mayadas and Shatzkes for resistivity as well as Tellier and Tosser for temperature coefficient of resistance could be found. The reflection coefficient for electrons at grain boundaries is extracted for both models.

High sensitive flexible hot-film sensor for measurement of unsteady boundary layer flow

The detailed flow characteristics in the boundary layer are critical for physical understanding of complex flow and aerodynamic performance optimization of aircraft. In this study, high sensitive micro-electro-mechanical system flexible hot-film sensor was developed for measurement of unsteady boundary layer flow. The effects of annealing temperature and time on the temperature coefficient of resistance (TCR) were studied, the highest TCR value of 5100 ppm °C−1 was obtained after 6 h of vacuum thermal annealing treatment at 400 °C. The flow transition and separation characteristics developed on two-dimensional NACA 0012 airfoil at various Reynolds numbers and angles of attack were investigated by using flexible hot-film sensors with validation by surface pressure distribution and aerodynamic force coefficient. The accurate locations of onset, 50% intermittent and end of transition were detected successfully. The behavior of spatial progression to the leading edge of transition point was found as the Reynolds number and angle of attack increases. The hot-film sensor measurements also demonstrated the static stall of the airfoil was caused by the leading edge separation bubble.