Maximum Temperature Coefficient Of Resistance Research Articles

MoS2high temperature sensitive element with a single Si3N4protective layer.

Temperature sensors find extensive applications in industrial production, defense, and military sectors. However, conventional temperature sensors are limited to operating temperatures below 200°C and are unsuitable for detecting extremely high temperatures. In this paper, a method for thermal protection of molybdenum disulfide (MoS2) films is proposed and a MoS2 high temperature sensor is prepared. By depositing a monolayer of Si3N4 onto MoS2, not only is the issue of high-temperature oxidation effectively addressed, but also the contamination by impurities that could potentially compromise the performance of MoS2 is prevented. Moreover, the width of the Schottky barrier of metal/MoS2 is reduced by using PECVD deposition of 400 nm Si3N4 to form an ohmic contact, which improves the electrical performance of the device by three orders of magnitude. The sensor exhibits a positive temperature coefficient measurement range of 25 to 550°C, with a maximum temperature coefficient of resistance (TCR) of 0.32%·°C-1. The thermal protection method proposed in this paper provides a new idea for the fabrication of high-temperature sensors, which is expected to be applied in the high-temperature field.&#xD.

The impact of Ru and Gd dopants on the dielectric and conductive properties of NiO nanoparticles: A comparative study

This comparative study investigates the difference between the transition metal (Ru) and rare earth element (Gd) as dopants in NiO nanoparticles, to unveil their suitability in various applications. Pure, Ru- and Gd-doped NiO nanoparticles have been synthesized by the chemical co-precipitation method, in the presence of polyvinylpyrrolidone, as a capping agent. The EDX pattern revealed the purity, the un-stoichiometric nature of the synthesized nanoparticles, and the influence of the Ru- and Gd-dopants in generating advantageous structural imperfections, including oxygen and nickel vacancies. The dielectric and conductivity measurements have provided valuable insights into the electrical behavior of Ru- and Gd-doped NiO nanoparticles. The influence of the Ru- and Gd-dopants on the Debye model, universal dielectric model, and relaxation mechanism was implemented. The dielectric constant was affected by the dopants, where the Ru-dopants reduced it by a factor of 0.24, however, the Gd-dopants boosted it by a factor of 4. Moreover, the opposing influence of the Ru- and Gd-dopants on the nickel vacancies has tuned the ac conductivity of the NiO lattice, where it was reduced by 75 % with Ru-dopants due to the suppressed nickel vacancies and enhanced by 70 % with the Gd-dopants due to the augmented nickel vacancies. The dc conductivity was examined at ranging temperatures to explore the conduction mechanism and the effect of the dopants. The multi-functional ability of the pure, Ru- and Gd-doped NiO nanoparticles was tested by studying the complex power and temperature coefficient of resistance (TCR), from which the dominating capacitive and resistive nature is identified for the samples. Besides, NiO nanoparticles have attained a maximum TCR value of −10.41 %, rendering it a superior material for bolometric devices, even better than the used conventional materials. The studied dielectric and conductive properties unveiled the potential applicability of the samples in microelectronics, storage capacitor applications, and bolometric devices.

Changing the Ca2+ ion ratio to modulate the temperature coefficient of resistivity (TCR) of La1-xCaxMnO3 films prepared by the sol-gel spin coating method

Perovskite manganese oxides are highly desirable for infrared acquisition owing to their characteristics of ferromagnetic metal-paramagnetic insulators. In this work, the sol-gel spin-coating technique was employed to prepare La1-xCaxMnO3 (LCMO) films with varying Ca2+ content (x = 0.1, 0.2, 0.3, 0.4, 0.5) on the (l00) LaAlO3 (LAO) substrates. In comparison to previous studies, the pre-sintering temperature, final sintering temperature, and final sintering period were modified. The crystal structure, surface topography, elemental valence states, and electrical transport performance of the LCMO films were characterized and analyzed as well. The results demonstrated that the diffraction peaks of the above films were aligned with those of the LAO single-crystal substrate. The change in Ca2+ content caused an increase in the Mn–O bond length, the amount of Mn4+, and the Mn–O–Mn angle in LCMO films, promoting the double exchange effect. These modifications had a considerable impact on the resistivity of LCMO films, increasing their TCR value. The maximum TCR of 22.92% K−1 was reached at x = 0.3 and peak TCR temperature (Tk) of 241.93 K. Therefore, the film has great application potential for infrared bolometers.

Bias-tunable temperature coefficient of resistance in Ge transistors

Ge-based bolometers are widely used for near-infrared detection for a broad range of applications such as thermography or chemical analysis. Notably, for the thermometers used in bolometers, integration, scaling, and sensitivity as well as functionality are of utmost importance. In this regard, Ge exhibits a favorable temperature sensitivity due to the relatively low bandgap and a high intrinsic charge carrier concentration. In this work, we demonstrate a nanoscale thermometer for bolometric applications on the base of Ge-on-insulator nanosheets with monolithic Al source/drain contacts envisioned for future wafer-scale integration. Importantly, electrostatic gating of the nanosheets allows the operation as a Schottky barrier field-effect transistor, providing tunability of the energy landscape and the involved charge carrier injection in interaction with the metal-semiconductor junctions. In this approach, the top-gate electrode and drain contact are connected, thus resembling a two-terminal device with bias-tunable temperature coefficient of resistance (TCR) values between 0%/K and −3.8%/K in the temperature range of T = 125–150 K. Moreover, in this configuration, even at room temperature, a maximum TCR value of −1.6%/K is achieved. The bias-tunable TCR exhibited in these devices may enable advanced concepts for room temperature bolometric applications and allow co-integration with nanoelectronics.

High temperature coefficient of resistivity (TCR) of Nd0.67Sr0.33MnO3 films by optimizing sintering temperature

In this study, Nd0.67Sr0.33MnO3 (NSMO) films are deposited on La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates using sol–gel spin coating method and sintered at different temperatures (Ts = 1250, 1300, 1350, 1400 and 1450 °C). Consolidated analysis of their crystal structure, surface morphology and valence states enables one to conclude that increased Ts facilitates grain growth and enhances crystallinity of films. Moreover, enhancing Ts from 1250 to 1350 °C leads to a decrease in Mn-O bond length (d(Mn-O)) and an increase in Mn-O-Mn bond angle (θ(Mn-O-Mn)). In the XPS analysis, the Mn4+ and O2– content kept increasing with the rise of Ts. When Mn4+ concentration ≤ 33%, the double exchange (DE) interactions was undoubtedly facilitated, which was beneficial for the electrical properties of the NSMO films. These changes eventually result in large temperature coefficient of resistivity (TCR). According to these results, Nd0.67Sr0.33MnO3 film, with a maximum TCR value of 21.85% K−1 at Ts = 1350 °C, are promising materials for the manufacturing of sensitivity switches and infrared bolometers.

DC conductivity mechanism in La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites

La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites with varying concentrations of ZnO have been synthesized using the solution combustion method. A bimodal particle size distribution has been formed in all the samples. The crystallite size increases in the composites as compared to LSMO. The study on electrical resistivity reveals that LSMO exhibits a metal-to-insulator transition at 359 K, while the inclusion of ZnO suppresses the metallic behavior in the composites and increases the resistivity. Transport behavior of the samples in metallic and semiconducting regions has been explained with a known polynomial equation and a two-channel conduction model obeying the small polaron hopping mechanism, respectively. A very low activation energy in the range of 10–12 meV is observed due to smaller-sized particles. The presence of ZnO drives the hopping mechanism from adiabatic in LSMO to become non-adiabatic in the composites and enhances the maximum temperature coefficient of resistance. 80% LSMO-20% ZnO (by weight ratio) composite shows a maximum TCR of −29.81%/K at 248 K, which makes it a potential candidate for several applications in sensing devices. The Curie temperature of the material decreases with the increase in ZnO content in the sample. The results of this study also confirm the existence of correlation between the electrical and magnetic properties of LSMO.

Co-optimization of Ag and K doping to regulate room-temperature coefficient of resistivity of La0.7Ag0.3-xKxMnO3 films

In this study, La0.7Ag0.3-xKxMnO3 (LAKMO, x = 0.15, 0.16, 0.17, 0.18, and 0.19) films with excellent electrical properties and low surface roughness were prepared on SrTiO3 (001) substrates using the spin-coating method. The crystal structures and ion valence states of the LAKMO films were modified by adjusting the doping amounts of Ag and K. The Jahn–Teller effect and electron–lattice coupling were enhanced with the MnO6 octahedron undergoes distortion. Moreover, the double-exchange interaction was improved with an increase in the number of Mn4+/Mn3+ ion pairs. Under the influence of these factors, the electrical transport properties especially the temperature coefficient of resistivity (TCR) of the LAKMO films can be refined modulated or optimized via A-site Ag and K co-doping. When x = 0.17, the maximum TCR of LAKMO reached 11.23 % K−1 at 293.23 K. Thus, La0.7Ag0.13K0.17MnO3 film with a large TCR exhibited excellent thermal properties at room temperature and was considered material for application to uncooled infrared bolometers.

External Boosting of Free Carriers and Phonon Energy in MoS2/Reduced Graphene Oxide Nanosheet-Based Composite Films: Implications for Thermal Management

We present here the fabrication of a MoS2/reduced graphene oxide nanosheet-based composite thin film with optimized stoichiometry to boost free carriers and phononic activity for heat transport, all these in a bid to develop an efficient solid-state thermometer. The possibility is envisaged from theoretical analysis followed by subsequent validation with experimental results on two fundamental material parameters, such as temperature coefficient of resistance (TCR) and thermal hysteresis loss (Hth), which fundamentally govern the heat transport and control the thermal sensor characteristics, such as response magnitude, response- and recovery-time, sensitivity, and resolution. In the static mode, the measured sensing data in the high temperature range (298–373 K) are as follows: TCR of −0.71% K–1, response- and recovery time of ∼73 and ∼75 s, respectively, with ∼0.36% hysteresis loss. In the low-temperature range (298–123 K), the maximum TCR observed is ∼−7.23% K–1 with ∼0.40% hysteresis loss, whereas in the instant mode, TCR increases manifold in the low-temperature range (298–77 K) up to ∼34.19% K–1. Besides, the sensor exhibits a fast response of ∼2 s and recovery time of ∼19 s with negligible hysteresis loss of ∼1.49%; showing the material’s possible application as a superior solid-state thermometer in the low as well as high temperature ranges.

Enhancing the temperature coefficient of resistance of Pt thin film resistance-temperature-detector by short-time annealing

In this work, we report the influence of annealing time on the electrical properties of Pt thin film resistance-temperature-detectors (RTD) with Ti adhesion layers. It is found that the temperature coefficient of resistance (TCR) of the Pt thin film RTD strongly depends on the air annealing time. Increasing the annealing durations from 1, 3, 10 to 60 min at 900 °C, the TCR tends to rise up firstly, and then drops down. A maximum TCR of 3.2 × 10−3/°C at 25 °C is achieved in the RTD annealed for 3 min, which is larger than most of other reported values. It is believed that the annealing time of 3 min may be sufficient to enlarge the grain size and to reduce the lattice defects, giving rise to the maximum TCR by decreasing the resistance at 25 °C. On the contrary, prolonging the annealing duration causes the interdiffusion and oxidation Ti significantly, which has been clearly evidenced by the depth analyses of X-ray photoelectron spectroscopy. Such interdiffusion and oxidation of Ti reduces the TCR by increasing the resistance.

Superior La0.67K0.33-xSrxMnO3 films with room-temperature TCR prepared by spin coating method

La0.67K0.33-xSrxMnO3 thin films were grown on LaAlO3 (010) substrates via sol–gel and spin coating methods. The replacement of K ions with Sr ions affected the eg electron bandwidth and concentration of Mn3+/Mn4+ pairs as well as effectively modulated the magnetic/orbital order and lattice structure. Consequently, the ferromagnetic metal to paramagnetic insulation transition was affected, which further optimized the resistivity, temperature coefficient of resistivity (TCR), peak TCR temperature (TK), and peak resistivity temperature (TP). At temperatures below 230 K, temperature-independent scattering and electron-electron scattering were practically not observed in the films. Overall, electrical properties of films improved with an increase in the Sr doping content. The superior La0.67K0.27Sr0.06MnO3 film exhibited a maximum TCR of 11.88% K−1 (298.3 K), which is approximately 31% higher than that of bulk ceramic with the same composition. The as-developed films exhibit significant potential for application in uncooled infrared bolometers.

Optimization of gold germanium (Au0.17Ge0.83) thin films for high sensitivity resistance thermometry

Gold–germanium (AuxGe1−x) solid solutions have been demonstrated as highly sensitive thin film thermometers for cryogenic applications. However, little is known regarding the performance of the films for thicknesses less than 100 nm. In response, we report on the resistivity and temperature coefficient of resistance (TCR) for sputtered films with thicknesses ranging from 10 to 100 nm and annealed at temperatures from 22 to 200 °C. The analysis is focused upon composition x=0.17, which demonstrates a strong temperature sensitivity over a broad range. The thinnest films are found to provide an enhancement in TCR, which approaches 20% K−1 at 10 K. Furthermore, reduced anneal temperatures are required to crystallize the Ge matrix and achieve a maximum TCR for films of reduced thickness. These features favor the application of ultra-thin films as high-sensitivity, on-device thermometers in micro- and nanolectromechanical systems.

Enhancing magnetoresistive features of iron-substituted La0·8Sr0·2MnO3 ceramic manganites

The influence of iron content on the structural, microstructural, magnetic, and electrical-transport features of the ceramic perovskite manganites of the form La0·8Sr0·2Mn1-xFexO3 (x=0.0, 0.05, 0.1, and 0.2) was investigated. A single phase of rhombohedral-distorted structure with an R 3‾ c space group was confirmed for all synthesized ceramic samples. The microstructures of the manganite ceramics were improved by iron substitution. The magnetic and electrical-transport studies show that samples with x=0.0, 0.05, and 0.1 display phase transitions from ferromagnetic to paramagnetic state and metallic to insulating one with increasing temperature. The phase transition temperatures, i.e., Curie temperature, TC, and the resistance transition temperature TMI, are found to be lowered with the increase in the Fe concentration. The temperature coefficient of resistance (TCR) value for the x=0.0 sample is obtained ∼2.16% K−1 and slightly decreased to ∼1.55% K−1 with a 5% Fe substituted sample. As x rise to 0.1, we obtain the maximum TCR value of ∼8.23% K−1. At the same time, the maximum magnetoresistance is obtained as 48.1% at 233 K for the x=0.1 sample. One of the most important findings in this paper is that Fe substitution is very useful for improving magneto-electrical features of the La0·8Sr0·2MnO3 ceramics. Moreover, to better understand the temperature dependence of the electrical resistivity data, the experimental findings were fitted to the equations of several models.

Germanium nanowire microbolometer

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in the μm range, limiting miniaturization for future highly integrated ‘More than Moore’ concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of −0.07 K−1 at T = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Large temperature coefficient of resistivity and magnetoresistance for polycrystalline La0.68Nd0.04Ca0.28MnO3 at low magnetic field

To obtain comprehensive materials with both high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at low magnetic fields, the polycrystalline La0.72−xNdxCa0.28MnO3(x = 0.02, 0.04, 0.06, and 0.08) were synthesized using the sol–gel method, which is a significant practical application in magnetic sensors and bolometers. We observe an enhancement of TCR and MR by substituting La3+ with Nd3+. The excellent TCR (19.21%·K−1) and MR (73.10%) are observed in La0.68Nd0.04Ca0.28MnO3 at the 1 T magnetic field. Meanwhile, the maximum TCR reaches 22.68%·K−1 without a magnetic field. This substitution increased the total magnetic moment and a slight increase in average grain size. The Mn3+ and Nd3+ spin within the disordered region realign along the field direction with a magnetic field. Therefore, Nd-doped La0.72Ca0.28MnO3 ceramic materials can effectively improve the material properties.

Large temperature coefficient of resistivity (TCR) of La1-xCaxMnO3 films prepared by spin-coating method

La1-xAxMnO3 (A = alkaline-earth or alkali metal) perovskites with large temperature coefficient of resistivity (TCR) offer immense opportunity for the application in high-performance infrared bolometer. However, numerous studies have revealed that the manganite films with large TCR values are not easily obtained by various fabrication technologies. Herein, a facile sol-gel spin-coating technique was used to prepare La1-xCaxMnO3 (LCMO, 0.280 ≤ x ≤ 0.375) films. All the samples were highly oriented along the out-of-plane direction of La0.3Sr0.7Al0.65Ta0.35O3 (001) substrates. With the rise in Ca doping amount, the resistivity of the films first decreased, and then, increased. This change can be attributed to the competition between the carrier concentration and lattice distortion. The LCMO films displayed large TCR and low-field magnetoresistance (MR) values, which exceeded those of previously reported thin films. The maximum TCR and low-field MR values were observed at x = 0.330, reaching 30.13% K−1 (266.43 K) and 68.6% (270.08 K), respectively. The La0.67Ca0.33MnO3 film with large TCR and MR values presents potential for the applications in high-sensitivity infrared bolometers and magnetic sensors.

High room-temperature TCR and MR of La1-xSrxMnO3 thin films for advanced uncooled infrared bolometers and magnetic sensors

Perovskite manganese films had promising applications in the field of photoelectronic materials and devices. However, the utilization of manganese films remained severely challenging due to high fabrication cost and inferior electrical and magnetic properties. Herein, La1-xSrxMnO3 (LSMO) thin films were fabricated on La0.3Sr0.7Al0.65Ta0.35O3 (LSATO) substrates using a facile sol–gel spin-coating technique. All the LSMO films displayed (001)-orientation with orthorhombic structure. The LSMO films exhibited high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) values at room-temperature. The maximum TCR value was 10.4 % K−1 (301.2 K, for x = 0.175). This result can be attributed to high carrier concentration and mobility of optimal × content LSMO films with low film-substrate lattice mismatch (-0.4%), leading to low resistivity, and thus, increased TCR value. The maximum MR value reached 42.85% (290.95 K, for x = 0.150). The LSMO films with high room-temperature TCR and MR values are potential materials for advanced uncooled infrared bolometers and magnetic sensors.

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.

Study on the Stability of the Electrical Connection of High-Temperature Pressure Sensor Based on the Piezoresistive Effect of P-Type SiC.

In this study, a preparation method for the high-temperature pressure sensor based on the piezoresistive effect of p-type SiC is presented. The varistor with a positive trapezoidal shape was designed and etched innovatively to improve the contact stability between the metal and SiC varistor. Additionally, the excellent ohmic contact was formed by annealing at 950 °C between Ni/Al/Ni/Au and p-type SiC with a doping concentration of 1018cm−3. The aging sensor was tested for varistors in the air of 25 °C–600 °C. The resistance value of the varistors initially decreased and then increased with the increase of temperature and reached the minimum at ~450 °C. It could be calculated that the varistors at ~100 °C exhibited the maximum temperature coefficient of resistance (TCR) of ~−0.35%/°C. The above results indicated that the sensor had a stable electrical connection in the air environment of ≤600 °C. Finally, the encapsulated sensor was subjected to pressure/depressure tests at room temperature. The test results revealed that the sensor output sensitivity was approximately 1.09 mV/V/bar, which is better than other SiC pressure sensors. This study has a great significance for the test of mechanical parameters under the extreme environment of 600 °C.

Critical positive temperature coefficient of resistivity of Li/Y co-doped ZnO ceramics modified by Cr-ions

ZnO-based ceramics doped with Li/Y and modified by various contents of Cr-ions, (Zn0.9475Y0.0025Li0.05)1-xCrxO (0 ≤ x ≤ 0.025), were prepared by a wet chemical route followed by a traditional ceramic sintering technology. The effect of Cr-ion content on the electronic conductivity and resistance–temperature characteristics of the prepared ceramics was investigated. All the ceramics have hexagonal wurtzite ZnO structure, and exhibit critical positive temperature coefficient of resistivity (C-PTCR) effect. With various contents of Cr-ions, the maximum temperature coefficient of resistivity (TCR) reaches 61.1%·°C−1 or the resistivity jump log(ρmax/ρmin) is up to 4.74. The critical transition temperature of resistivity can be adjusted in the temperature range of 76–147 °C for different various contents of Cr-ions. The complex impedance analysis shows that the C-PTCR effect of the ZnO ceramics resulted from both grain effect and grain boundary effect. According to the analysis of the dielectric temperature spectra, the ZnO-based ceramics have ferroelectricity at room temperature, and the ferroelectric–paraelectric transition around the critical transition temperature of resistivity during the temperature increases.

Effect of growth and electrical properties of TiOx films on microbolometer design

This paper presents the feasibility of non-stoichiometric TiOx thin films as an active material for bolometer application. The TiOx films have been deposited on glass substrate by DC sputtering with oxygen flow rate of 0.1–0.7 sccm at room temperature and their electrical properties have been studied. The TiOx films were found to be amorphous with dense and smooth surface morphology. The thickness of the films was found to decrease from 150 to 30 nm with an increase in oxygen flow rate. The TiOx film corresponding to 0.7 sccm showed maximum temperature coefficient of resistivity of 0.72%/°C. Performance of TiOx-based bolometer pixel (pitch: 56 μm) is simulated using the electrical characteristics of the deposited films. The TiOx film corresponding to the 0.7 sccm O2 flow rate displayed thermal conductance of 2.95 × 10–7 W/K along with a maximum Figure of Merit of 2.45 × 106 and a time constant of 8.2 ms. The Noise equivalent temperature difference of the bolometer structure is estimated (~ 107 mK).