Resistance-temperature Characteristics Research Articles

Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride

The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.

MP-37 MEMS技術を用いた微小熱分析法の研究 : 高温度域への拡張(ポスターセッション)

The cantilever type MEMS calorimeter enables thermal analysis and mass measurement for micro- to nano-gram level samples. In this study, to extend the MEMS-based thermal analysis to high temperature range, a heat-resistant MEMS calorimeter has been developed. The new calorimeter equips a resistance temperature detector, a heater for temperature scan and a strain gauge for detecting the mechanical oscillation of the cantilever, and those resistance devices are made of platinum thin film. A thermal response test of the calorimeter showed fast temperature scanning ability of over 10^4K/s. From the experiment of high temperature scan, it was confirmed that the annealing of the calorimeter is necessary to get the reproducible high temperature resistance characteristics. Moreover, a high temperature DTA for tiny aluminum sample showed clear endothermic and exothermic peaks which correspond to melting and solidification of micro-gram level aluminum. The heat-resistant MEMS calorimeter performed an extension of the analytical temperature range up to 800℃.

Electrical properties of lead-free thick film NTC thermistors based on perovskite-type BaCo IIxCo III2 xBi 1 − 3 xO 3

Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCo II x Co III 2 x Bi 1 − 3 x O 3 ( x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO 3 thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity ( ρ 23), thermistor constant ( B 25/85) and activation energy are in the range of 1.995–2.975 Ω cm, 1140–1234 K and 0.102–0.111 eV, respectively.

수열합성법으로 제조된 Co3O4분말을 사용한후막 가스센서의 CO 감지 특성

CO sensing thick film gas sensors using <TEX>$Co_3O_4$</TEX> powders prepared by hydrothermal reaction method, were fabricated, and their structural, electrical and CO gas sensing properties were investigated. The specific surface area of the <TEX>$Co_3O_4$</TEX> powders obtained from BET analysis was about 79.0 <TEX>$m^2/g$</TEX>. XRD and SEM results show that the thick films heat-treated at <TEX>$500^{\circ}C$</TEX> for 30 min after screen printing had the preferred orientation of (311) direction and the crystalline size was calculated to 221 <TEX>$\AA$</TEX>. The maximum activation energy obtained from the temperature-resistance characteristics was 3.11 eV in the temperature range of <TEX>$290^{\circ}C$</TEX> to <TEX>$310^{\circ}C$</TEX>. The sensitivity to 1,000 ppm CO was about 150 %. The specific surface area, crystalline size, and maximum activation energy were increased significantly and the sensitivity for CO gas was improved largely.

Thickness dependency of sol-gel derived ZnO thin films on gas sensing behaviors

ZnO thin films were fabricated by a sol-gel method using Zn(CH 3COO) 2·2H 2O as starting material in order to prepare an acetone gas sensor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. The sol-gel solution is coated on alumina substrates with various thicknesses by spin coating technique and heat treated to grow crystalline ZnO thin films. The effect of thickness on physical and electrical properties of as deposited ZnO thin films has been studied. The as deposited ZnO thin films were characterized by X-ray diffraction spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The root mean square surface roughness factors increase with thickness of the films and found 3.9, 6.6, 9.0, and 11.28 nm for 80-, 220-, 450- and 620-nm-thin films respectively. The activation energies of the films are calculated from the resistance temperature characteristics. The sensitivities of the ZnO films towards the acetone gas were determined at an operating temperature of 200 °C. The sensitivity towards acetone vapor is strongly depending on surface morphology of the ZnO thin films.

Microstructure and Thermoelectric Properties of Al-Doped ZnO Sintered Body

ZnO is heat-resistant and inexpensive, and the raw material of which is abundant, it is considered to be a good candidate thermoelectric material. Usually, a low-resistance n-type ZnO sintered body is obtained by doping 0.5-5 mol% Al2O3 followed by burning at a high temperature of approximately 1673K. However, this high-temperature burning has drawbacks, such as high power consumption and an increase in thermal conductivity with grain growth. Under these circumstances, we attempted to address these disadvantages. When ZnO was burned with Al as a dopant in an electric furnace at a temperature as low as approximately 1473K, ZnO with relatively good thermoelectric properties was obtained. In addition, the Al-doped sample showed lower electric resistance (332 K: 6.85×10-4Ωcm) than the Al2O3-doped sample, as determined on the basis of the resistance temperature characteristics of these samples. The causes of this low resistance may be as follows: 1) the metal-Al-mediated sample was densified by burning at a low temperature of approximately 1473K and 2) the Al distribution to the entire region of the ZnO bulk, resulting in the spread of Al solid-solution regions in the ZnO. We also found that the thermal conductivity decreased (973 K: 3.66 Wm-1K-1) in the Al-doped sample.

SnO2:(Cu,In) films with high transmittance in ultraviolet region

By reactive evaporation method, the SnO2:(Cu,In) transparent conductive films are prepared on glass, Corning7059 glass and quartz glass substrates separately. The element contents are analyzed, the distributions of all elements in the films are given, and the transmittances of samples are also measured. The results show that the UV transmittance of individual sample is high, and the transmittance of the film depends on annealing process. The resistance-temperature characteristics are measured and explained. The relationship between optical band gap and absorption coefficient is discussed. The simple method in which the transmittance curve is used to determine the optical band gap is given. The relation between mobility of the extended state and mobility edge with Fermi level is discussed. The results show that the preparation of copper and indium co-doped tin oxide transparent conductive films has achieved the purpose of reducing the cost, and some particular samples have wide band gap.

Differential Platinum Thin Film Hydrogen Gas Sensor Fabricated by MEMS Techniques

In this paper, thermo-resistive platinum (Pt) thin film sensor, which was produced using Micro Electro Mechanical Systems (MEMS) fabrication techniques, is proposed. The sensor design incorporated resistor elements that would facilitate the temperature-resistance characteristics and mechanisms of Pt based thin film thermo-resistors. Especially, this paper reports the characteristics of a new differential Pt thin film hydrogen gas sensor. The fabricated hydrogen sensor detected the concentration of hydrogen gas in the air from 2% to 10%. It was possible to achieve the correct the heat transfer with this new differential Pt thin film hydrogen gas sensor. The characteristics of sensor's output are higher than conventional ones that we developed.

Wet chemical route to transparent BiFeO 3 films on SiO 2 substrates

BiFeO 3 nanoparticles were prepared by a wet chemical synthesis method. Transparent films were deposited on glass and quartz substrates by dip and spin coating processes from the synthesized sol. We obtained thicker films (~ 2 µm) by dip coating process and thinner films (~ 200 nm) by spin coating process. Transmission electron microscopy images confirmed that the particles are nanocrystalline in size. From the optical transmittance spectra the band gap of the BiFeO 3 nanoparticles was determined in the range of ~ 3.03–2.88 eV (~ 410–430 nm). Electrical resistivity, polarization, zero-field-cooled and field-cooled magnetizations versus temperature characteristics were also studied for these films.

Nylon 6 induced morphological developments and electrical conductivity improvements of polypropylene/carbon black composites

AbstractIn this study, a polar conductive filler [carbon black (CB)], a nonpolar polymer [polypropylene (PP)], and a polar polymer [nylon 6 (PA6)] were chosen to fabricate electrically conductive polymer composites by melt blending and compression molding. The morphological developments of these composites were studied. Scanning electron microscopy results showed that in a CB‐filled PP/PA6 (CPA) composite, CB particles were selectively dispersed in PA6 phases and could make the dispersed particles exist as microfiber particles, which could greatly improve the electrical conductivity. The PA6 and CB contents both could affect the morphologies of these composites. The results of electrical resistivity measurements of these composites proved the formation of conductive networks. The resistivity–temperature behaviors of these composites were also studied. For CB‐filled PP (CP) composites, there were apparent positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects and an unrepeatable resistivity–temperature characteristic. However, for CPA composites, there were no PTC or NTC effects from room temperature to 180°C, and the resistivity–temperature behavior showed a repeatable characteristic; this proved that CB particles were selectively dispersed in the PA6 phase from another point of view. All experimental results indicated that the addition of PA6 to a CP composite could lead to an expected morphological structure and improve the electrical conductivity of the CP composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

LTCC microreactor for urea determination in biological fluids

This article presents design, fabrication and testing of an enzymatic microreactor with integrated heater and a temperature sensor. The microsystem was fabricated using low temperature co-fired ceramics (LTCCs) technology, which has a few advantages over silicon-based fabrication processes. Computational fluid dynamics (CFD) and finite element method (FEM) analysis was used to arrive at an optimum microreactor and heater design. The heater performance was evaluated using thermographic measurements, and the temperature resistance characteristics of the temperature sensor revealed good electrical properties and stability at higher temperatures (up to 140°C). As an enzyme carrier, the glass beads coated with polyacrylonitrile layer and porous glass beads were used. The microreactor was used to measure urea concentration with high output signal (ca. 2.5 pH units) and large scale. The maximal output signal enabled to apply presented microreactor for determination of urea in biological or environmental fluids. The properties of the LTCC-based enzymatic microreactor were comparable with the features of a similar one made in silicon.

Cap effect of (Bi,Pb) 2Sr 2Ca 2Cu 3O y thick films during post-annealing process

We prepared (Bi,Pb) 2Sr 2Ca 2Cu 3O y (BiPb-2223) thick films on MgO substrates by a spin coating method and investigated their superconducting property. The surface of BiPb-2223 thick films was capped with MgO, Ag or BiPb-2223/MgO during sintering process. From the results of X-ray diffraction patterns and resistance–temperature characteristics, we found that the caps of MgO and Ag were useful for obtaining the 30 μm-BiPb-2223 thick films with the T c above 100 K. Although the T c of the thick films with the thickness less than 5 μm decreased, the T c of the BiPb-2223 films with the thickness less than 5 μm was improved by use of the BiPb-2223/MgO cap.

Formation of a nanobarrel structure in CPP-GMR spin-valve films

As a new approach for current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) spin-valve films, we have proposed a new nanostructure to cause mesoscopic phenomena. For this purpose, we have successfully formed a nanobarrel structure composed of Cu granular-like shape surrounded by Al 2O 3 insulator in which Cu nanoconducting channel punches through the Al 2O 3 insulator both at the top and at the bottom. This nanobarrel structure was confirmed by high-resolution transmission electron microscope (HR-TEM) analysis. Both the resistance–voltage characteristics and the resistance–temperature characteristics showed the metallic conductance property, which is in good agreement with the nanostructure identified by HR-TEM analysis. The nanobarrel structure offers features compatible with both nano-ordered electron-confined structure by insulator and low resistance with metallic conductance.

STUDY ON METAL MEMBRANE TEMPERATURE SENSOR AND MICROHEATER FOR PCR CHIP

The development of PCR chip shortens the reaction time of DNA amplification, reduces the bulk of reaction reagents; therefore, it is widely applied to biomedicine and other related fields. Since PCR reaction is completed through three different precise temperature zones periodically, the sensitivity of temperature measurement and the heating property of the metal membrane must be highly regarded. In this paper, three kinds of membranes, Ni , Pt , and Ni – Cr , were fabricated on silicon substrates; their resistance–temperature characteristics and heating properties are discussed. The results show that Ni and Pt films have good linear resistance–temperature relationship; the heating property of Pt film is superior to that of Ni – Cr film. The PCR chip with Pt film microheater can reach 150°C in a short time with 25 V voltage.

Preliminary Results on New Prototypes of Precision Rh-0.5at%Fe Resistance Thermometers of Chinese Production

Given the practical impossibility of obtaining new precision Rh-0.5at%Fe resistance thermometers in recent years, the possible re-starting of the production of such thermometers in Yunnan (China) was explored by Istituto Nazionale di Ricerca Metrologica (INRIM). Ten prototypes of the new production were made available in early 2006. The paper reports the preliminary data from the testing performed to date on these prototypes at National Institute of Metrology (NIM) and Instytut Niskich Temperatur i Badan Strukturalnych (INTiBS). Although a problem with the alloy composition was detected, the reproducibility results on thermal cycling are very encouraging. Resistance-temperature (R-T) characteristics below 30 K, though not identical with those of similar thermometers formerly available from Tinsley and VNIIFTRI, are still suitable for accurate metrology.

ＰＣＳ法により作製したＺｎＯ‐ＴｉＯ２‐ＣｏＯ‐Ａｌ２Ｏ３系熱電材料の抵抗温度特性

Specimens with a molar ratio of 100ZnO-2TiO2-2CoO-2Al2O3 (hereafter, ZTCA) were heat-treated by pulse current sintering (PCS) at a sintering temperature of 1423 K for 10 min and at applied pressures of 30-80 MPa. The thermoelectric characteristics of the obtained specimens were investigated from the viewpoint of their microstructure. On the basis of the resistivity-temperature characteristics of the specimens that were obtained by sintering ZTCA at 60 and 80 MPa, the resistance of the specimens locally increased at approximately 800 K during heating and the resistance during cooling remained higher than that during heating in the thermal history (hysteresis). The local increase and the hysteresis in the resistance were not observed for the specimen sintered at the low pressure of 30 MPa, which had large crystal grains and was densified, but they were observed for those sintered at the high pressures of 60 and 80 MPa, which had fine particles and were porous. In addition, a following problem has come up, that is, the local increase in the resistance of the ZTCA specimen observed at approximately 800 K may lead to a reduction in the power factor of the thermoelectric characteristics.

Correlation between current–voltage (I–V) characteristic in the electric–thermal equilibrium state and resistivity‐temperature behavior of electro‐conductive silicone rubber

AbstractIn the electric–thermal equilibrium state the current–voltage (I–V) characteristics of conductive silicone rubbers above the percolation threshold are found to be nonlinear. A mathematic model as I = a1U ± (a2U2 + C) has been built for the nonlinear I–V relations. Constant C and quadratic term a2U2 can be considered as deviation from Ohm's law. For the first time, a correlation is found for conductive silicone rubber between the I–V characteristic in the electric–thermal equilibrium state and the resistivity–temperature characteristic. Samples with positive temperature coefficient (PTC) resistivity effect exhibit negative deviation from linearity, with an I–V relation as I = a1U − (a2U2 + C). Samples with negative temperature coefficient (NTC) resistivity effect exhibit positive deviation, with an I–V relation as I = a1U + (a2U2 + C). The higher the loaded voltage, the more pronounced the deviation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Fabrication and Application of MoSi&lt;sub&gt;2&lt;/sub&gt;-Thin-Film Electric Heaters

Thin-film heaters made of molybdenum silicide (MoSi2) were fabricated by RF magnetron sputtering, and the heating characteristics of these heaters in a high vacuum were evaluated. The crystal structure of thin-film was hexagonal contrary to the tetragonal one of the target. MoSi2 thin-film heaters deposited outside an alumina crucible showed almost linear resistance-temperature (R-T ) characteristics. However, resistance decreased due to repeated heatings. The heaters generated almost no contamination in vacuum. The temperature of the crucible reached 1000°C at an electric power of 190 W.

Modeling the resistance-temperature characteristic of a positive temperature coefficient thermistor, using experimentally determined permittivity data

The resistivity-temperature [ρ(T)] and current-voltage [j(V)] characteristics of a (Ba,Ca)TiO3 based donor/acceptor codoped positive temperature coefficient of resistivity thermistor have been analyzed in the context of the double Schottky barrier (DSB) model, using experimentally measured permittivity data. The best fit between the modeled and experimental ρ(T) behavior occurred for a broad acceptor energy fluctuation width (Δ=0.35eV). Modeling the ρ(T) behavior below the Curie temperature required a nonvanishing surface charge, consistent with a residual potential barrier. j(V) characteristics showed satisfactory agreement with the DSB model at low applied voltages per grain boundary (Vgb⩽0.13–0.22eV).

Preparation of Multilayer Barium Titanate PTC Thermistor with Low Room Temperature Resistance

Chip-type PTC thermistors with multilayer stacked structure have been fabricated by bonding sintered ceramic chips with internal electrodes to offer low resistance at room temperature and correspondence to surface mounted technology. The resistance-temperature characteristics of multiplayer stacked PTC thermistors made up of different numbers (N = 1, 3, 5) of layers were experimentally investigated (the typical size of each layer was 10 mm × 7.0 mm × 0.38 mm). The selection and extraction of additives in roll-forming process were also discussed. This resulted in a crack-free multiplayer stacked PTC thermistor.