Showing papers on "Temperature coefficient published in 1981"

Acoustic bulk wave composite resonators

Abstract: This letter reports on a new and unique form of acoustic bulk wave resonator composed of a thin film of ZnO sputtered onto a thin Si membrane supporting structure. The piezoelectric ZnO is used to excite a longitudinal bulk wave which reflects from the free surface of the film and membrane. The structure thus forms an acoustical cavity which exhibits parallel and series electrical resonance responses at the ZnO film electrodes for both even and odd order modes. Fundamental resonant frequencies near 500 MHz have been achieved with parallel resonant Q’s over 9000. The temperature coefficient of resonant frequency was found to be −31 ppm for a Si to ZnO thickness ratio of six.

Electrical properties of carbon black filled crosslinked polyethylene

Abstract: The electrical resistivity of peroxide and radiation crosslinked polyethylene/carbon black compounds was studied as a function of black concentration and, temperature in heating/cooling cycles. Different carbon blacks in compounds with polyethylene responded differently, regarding electrical resistivity, to the effect of crosslinking. In one case (fine black) the resistivity and PTC (positive temperature coefficient) effect did not significantly change, whereas in another case (coarse black) the effect of crosslinking-was to significantly increase the resistivity and reduce the PTC effect. The main advantages of crosslinking were to give compounds having good electrical reproducibility and to practically eliminate the NTC (negative temperature coefficient) effect in compounds containing fine, coarse, or mixtures of carbon blacks. Crosslinked compounds containing mixtures of carbon blacks have shown good conductivity, electrical reproducibility, and switching properties.

ZnO/SiO2-diaphragm composite resonator on a silicon wafer

Abstract: We report on a thickness-extensional-mode piezoelectric resonator consisting of a ZnO/SiO2 diaphragm supported by a silicon wafer. It is found that the temperature coefficient of frequency can be reduced to zero by adjusting the ZnO/SiO2 thickness ratio. A temperature coefficient of frequency as low as 10 ppm/°C was experimentally obtained.

PolySwitch PTC Devices-A New Low-Resistance Conductive Polymer-Based PTC Device for Overcurrent Protection

Abstract: Positive temperature coefficient (PTC) resistors for use as overcurrent protectors are now available with normal conduction mode resistances of about 0.04 \Omega . This resistance is significantly lower than devices made from heretofore available barium titanate ceramics. PolySwitchTM overcurrent protectors are made from conductive polymer compositions, which are newly developed materials. Fabrication of a PolySwitch device includes the creation of the base conductive polymer composite, melt forming it to device shape, attachment of leads, and packaging. The final product looks like a disc capacitor but acts like a solid-state circuit breaker or resettable fuse. The source of the PTC effect in these compositions is volume expansion upon heating and the subsequent disruption of connecting carbon black chains. Resistance characteristics of these compositions are reproducible and consistent from device to device; the concepts of a minimum and maximum base resistance and a resistance recovery curve are discussed. Polymer volume compaction processes are responsible for the recovery behavior. The physics of PolySwitch device behavior is explained by Joule heating. The characteristics important to the designer are ultimate trip current as a function of ambient temperature, a property of thermal and electrical equilibrium; and the trip-time characteristic, a property of the nonequilibrium dynamic response. Knowledge of both these charactistics allows the designer to quickly choose a PolySwitch device for his particular job.

Gas detecting sensor

Abstract: A gas detecting sensor for precisely detecting the partial pressure of oxygen gas in the exhaust gases without being affected by the change of the temperature of the environment thereof, is disclosed. The sensor is provided with a ceramic base member, a film-shaped gas sensing element having a characteristic in response to the partial pressure of oxygen gas which is held by the base member so as to be exposed to the exhaust gases, a film shaped temperature sensing element having temperature coefficient of resistance substantially equal to that of the gas sensing element, which is held by the base member so as to be isolated from the exhaust gases, and an electric current wherein the gas and the temperature sensing elements are connected to each other in series to form an electric junction therebetween, from which output voltage is taken. In the preferred embodiment, the temperature sensing element is embedded within the base member and a heating member is further provided for maintaining both elements within a temperature range in which temperature coefficient of resistance of both elements are substantially equal to each other.

Fundamental absorption edge of evaporated amorphous WO3 films

Abstract: The fundamental absorption edge of evaporated WO3 films is investigated. The optical gap of the virgin film is estimated to be 3.41 eV at room temperature and it decreases with increase of annealing temperature up to 200°C. Annealing at 300°C leads to change in the spectral shape, which is caused by crystallization. For the films annealed at 200°C, temperature coefficient of the optical gap is estimated to be −2×10−4 eV/K and the slope of Urbach's tail is found to be independent of measuring temperature up to 200°C. With electrolytic coloration, shift of the optical gap toward higher energy is observed. Magnitude of this shift is estimated to be 0.05 eV at the color center concentration of 7.5×1021 cm−3 when H+ electrolyte is used. If Li+ electrolyte is used, the magnitude of this shift is about three times larger than in the case of H+ electrolyte. This fact is interpreted by a small change in the host matrix structure owing to the injection of proton or Li+ during coloration.

Surface acoustic wave and piezoelectric properties of (Pb, Ln) (Ti, Mn)O3 ceramics (Ln = rare earths)

Abstract: The surface acoustic wave (SAW) and piezoelectric properties of PbTi03 ceramics modified by the partial substitution of rare earths for Pb, particularly (Pb, Ln) (Ti, Mn)03 (Ln = La, Ce, Pr, Nd, Sm, or Gd) ceramics, are examined. The effects of the rare earths introduced on these properties are noted. Properties, such as velocities and electromechanical coupling factors, for bulk wave and SAW vary monotonically with the ionic sizes of the rare earths. On the other hand, the temperature coefficient of SAW delay time takes a minimum value when the Ln is Nd. It is shown that the variation of the temperature coefficient with rare earths corresponds well with those of the temperature coefficients of elastic constants CE33 and CE44.

Pressure measurement at high temperatures in the diamond anvil cell

Abstract: The frequency shift of the R1 ruby fluorescence peak has been measured in the diamond anvil cell along the ice/water melting curve in the temperature interval 25–200 °C and pressure interval 0–40 kbars. The temperature and pressure coefficients of the frequency shift were found to be independent in this region. Using a least‐squares‐fitting program to find the fluorescence peak positions, we could reproducibly measure pressures to ±0.2 kbar at 25 °C and to ±0.5 kbar at 300 °C. The temperature coefficient of the frequency shift of R1 in the interval 25–300 °C was determined to be −0.149 cm−1/°K. Large systematic errors in the pressure determination were found to arise when nonuniformity of temperature in the diamond anvil cell caused uncertainty in the ruby temperature.

Negative temperature coefficient thermistors

Abstract: Inexpensive Mn or Mg ferrites may be used as negative temperature coefficient thermistors. Fabrication of devices with the desired high temperature coefficients is facilitated by a processing method which forms a thin layer of oxidized and high resistivity material on a low resistivity layer of ferrite material.

Universal temperature control circuits

Abstract: Various electronic circuits are disclosed for controlling the temperature of an object by means of a resistive heating element. Some of the circuits include a digital display for displaying the actual temperature A plurality of different temperature sensors may be used, such, for example, as a resistive sensor, a thermocouple or a thermistor. The sensor may either have a positive or a negative temperature coefficient. Since most of the sensors are not strictly linear, different means are disclosed for compensating for their nonlinearity. Some of the control circuits feature a proportional control to which may be added an anticipatory control. Less sophisticated and more inexpensive circuits simply provide an on-off control.

Controlled temperature coefficient thin-film circuit element

Abstract: To form a temperature sensor, for example suitable in an automotive vehicle, to determine ambient temperatures, or to provide a temperature compensated thin-film circuit, for example for incorporation with an oscillator circuit, two stable thin-film layers are applied to a non-conductive substrate, the layers being capable of being etched. The overall temperature coefficient of resistance can be matched to a predetermined value by selective interconnection of at least two thin-film resistance elements formed by the thin films, of which one thin film resistance element for example comprises a nickel layer over a tantalum base, with a predetermined temperature coefficient of resistance, the other resistance element merely being the tantalum layer with essentially zero temperature coefficient of resistance, the overall temperature coefficient of resistance of the combination being determined by adjustment of the relative resistance values after measurement of the temperature coefficient of resistance of the nickel-tantalum layer to determine its actual temperature coefficient so that, in spite of tolerances in the manufacture of the thin films, interchangeable elements of highly accurate overall resistance and temperature coefficient of resistance values can be obtained.

Surface acoustic wave properties of (Pb,Ln)(Ti, Mn, In)O3 ceramics (Ln = La and Nd)

Abstract: The surface acoustic wave properties of PbTiO3 ceramics are improved. The ceramic systems investigated are (Pb,Ln)(Ti,Mn,In)O3(Ln = La,Nd). The temperature coefficients of delay time are lowered to 46×10−6/ °C, when Ln is La. A zero temperature coefficient of delay can be achieved when Ln is Nd. The Nd and In substitution also cause the electromechanical coupling factor to increase and the dielectric constant to decrease.

Chromium-silicon-nitrogen resistor material

Abstract: Improved thin film resistors and electrical devices and circuits with thin film resistors are fabricated utilizing a chromium, silicon, and nitrogen compound formed preferably by rf reactive sputtering of chromium and silicon in a nitrogen bearing atmosphere. An annealing step is used to produce time-stable resistance values and in combination with variations in the partial pressure of nitrogen during sputter deposition to control the temperature coefficient of resistivity to have positive, negative or zero values.

Semiconductor strain gauge

Abstract: A semiconductor strain gauge is arranged as a bridge having four piezoresistive elements which each include a low impurity concentration diffused portion and a heavily-doped diffused portion. The resistance values of the two low impurity concentration diffused portions opposite each other in the bridge are greater than the resistance values of the other two lower impurity concentration portions. The resistances of the heavily-doped diffused portion are selected so that the resistance of the piezoresistive elements are equal. However, by virtue of the fact that the resistance temperature coefficient of the low impurity portions are greater than the resistance temperature coefficients of the high impurity portions, the overall resistance temperature coefficients of the bridge arms will be different. This permits the zero-point voltage of the bridge to always increase with an increase in temperature.

Double layer structure at the mercury/methanol solution interface

Abstract: Differential capacity against electrode potential data are presented for the mercury/methanol interface for a variety of salts at 25 °C and for NaClO4 solutions as a function of temperature. Ionic specific adsorption from solutions of KF, NaClO4, and LiBF4 was shown to be absent on the basis of the usual criteria. The dielectric properties of the inner layer are discussed on the basis of the three-state model for solvent structure from which it is deduced that the majority of solvent molecules are adsorbed at mercury with their dipole vectors parallel to the interface. The deep minimum in inner layer differential capacity, which occurs at the same electrode charge density independent of the nature of the salt (−0.05 C m−2), corresponds to conditions for which the surface concentrations of the minority components, dipoles oriented with the field or against it, are equal. The experimental temperature coefficient of the inner layer capacity is a maximum at this charge density in agreement with the prediction...

Thermal printing head

Abstract: An electrical heating resistor of the type deposited on a substrate plate constituting the basis element of a thermal printing head. In order to concentrate the heat given off in the free surface of said heating resistor towards the paper to print, the invention provides for the deposition on the substrate of at least one layer having a relatively constant resistivity and then at least one surface layer with a non-linear resistivity and a negative temperature coefficient. Starting from a high value when cold, the resistance of the surface layer drops abruptly as soon as it reaches the triggering temperature, thus switching the heat resistor by command of a control circuit.

Temperature compensated reference circuit

Abstract: A compensated current reference circuit (10) includes bipolar transistors (32, 48) which have corresponding base-to-emitter resistors (36, 52). A bipolar transistor (70) and associated circuitry produces a variable amplitude tail current which has a predetermined temperature coefficient and regulates the current flow through the bipolar transistors (32, 48). The combination of tail current for the transistor (48) and the impedance size of its corresponding resistor (52) are adjusted to produce a reference current through a transistor (44) which has a relatively large negative temperature coefficient. The bipolar transistor (32) and its associated base-to-emitter resistor (36) together with the tail current through transistor (38) are adjusted such that a current through transistor (22) is produced which has a relatively small negative temperature coefficient. The difference of these currents is produced through a transistor (18) to produce a reference current having a relatively small controlled temperature coefficient. The control voltage at node (96) is provided to a transistor (81) to produce a stable reference current therethrough. The selection of appropriate values for tail currents and the base-to-emitter resistor impedances for the bipolar transistors (32, 48) can produce any of a wide range of values of temperature compensated currents. The reference currents are also mirrored to a node (100) and summed to produce an output current having a desired temperature coefficient which is in turn passed through a resistor (116) to produce a temperature compensated voltage at a node (94).

Electrothermal study of carbon loaded ethylene‐vinylacetate copolymer

Abstract: Temperature dependence of resistance of carbon black loaded ethylene-vinylacetate (EVA) copolymer was studied from −100 to 250°C in a modified differential scanning calorimeter (DSC) apparatus. Both room temperature resistivity and positive temperature coefficient of resistance (PTC) effects can be correlated with carbon black parameters (structure, surface area, porosity). Room temperature resistivity and the degree of increase of resistivity, (ratio of maximum to minimum) progressively decrease with carbon black structure if occlusion of polymer by carbon black is considered in calculating the volume fraction. An integrated surface areastructure-porosity equivalence of the carbon black is derived by introducing factors proportional to the volume and porosity of the black used. Any black parameter that increases conductivity (loading, surface area, structure, porosity) decreases the PTC effect. A cable compounder can therefore minimize the undesirable impact of PTC by suitable choice of black-parameters. The necessary considerations for other uses, where PTC effect is used for microswitches, heaters, etc., will be just the opposite. The modified DSC method provides a quick scanning tool for determining the suitability of semicrystalline polymer recipes, either for cable or for any other material using the PTC effect.

Electrical Characteristics of Polymer Thick Film Resistors, Part I: Experiemental Results

Abstract: The electrical characteristics of some polymer thick film (PTF) resistors have been studied. There are four different kinds of carbon blacks and two different kinds of polymer resin, i.e., epoxy resin and polyimide resin, selected in the preparations of the PTF resistors. In this paper, the electrical characteristics, which include the sheet resistivity, current noise indices (CNI), temperature coefficient of resistance (TCR) and the percentage variations of resistance ( \Delta R/R, %), are discussed. It will be shown that there exists a correlation between the "structure" of the carbon blacks and the electrical characteristics of the PTF resistors. The effects of the blended carbon blacks on the electrical characteristics of the PTF resistors are also discussed.

Thermal conductivity of gaseous fluorocarbon refrigerants R 12, R 13, R 22, and R 23, under pressure

Abstract: The thermal conductivity of four gaseous fluorocarbon refrigerants has been measured by a vertical coaxial cylinder apparatus on a relative basis. The fluorocarbon refrigerants used and the ranges of temperature and pressure covered are as follows: R 12 (Dichlorodifluoromethane CCl2F2): 298.15–393.15 K, 0.1–4.28 MPa R 13 (Chlorotrifluoromethane CClF3): 283.15–373.15 K, 0.1–6.96 MPa R 22 (Chlorodifluoromethane CHClF2): 298.15–393.15 K, 0.1–5.76 MPa R 23 (Trifluoromethane CHF3): 283.15–373.15 K, 0.1–6.96 MPa The apparatus was calibrated using Ar, N2, and CO2 as the standard gases. The uncertainty of the experimental data is estimated to be within 2%, except in the critical region. The behavior of the thermal conductivity for these fluorocarbons is quite similar; thermal conductivity increases with increasing pressure. The temperature coefficient of thermal conductivity at constant pressure, (∂λ/∂T) p , is positive at low pressures and becomes negative at high pressures. Therefore, the thermal conductivity isotherms of each refrigerant intersect each other in a specific range of pressure. A steep enhancement of thermal conductivity is observed near the critical point. The experimental results are statistically analyzed and the thermal conductivities are expressed as functions of temperature and pressure and of temperature and density.

Surface acoustic wave element

Abstract: PURPOSE: To ensure the stable characteristics to the temperature change by forming a silicon dioxide film and then an aluminum nitride film having an oriented voltage axis on an elastic material substrate made mainly of a silicon single crystal having a positive temperature coefficient for delay time to a surface acoustic wave. CONSTITUTION: A substrate 1 is made of a silicon single crystal which is cut at a crystal face 111 and a face equivalent to a crystal face 110 or 100. A silicon dioxide film 2 is formed on the substrate 1, and furthermore an aluminum nitride film 3 is formed on the film 2 so that the voltage axis is set vertically to the substrate 1. Then a comb-shaped surface acoustic wave generating electrode 4 and detecting electrode 5 are formed on the surface of the film 3. When the length of a surface acoustic wave is set at λ, the value of 2πH/λ is set at ≤3.0 with the substrate 1 containing a face equivalent to the face 111 and at ≤6.0 with the substrate 1 of a face equivalent to the face 110 or 100 respectively. Thus, the stable characteristics to the temperature change as well as a high speed of a surface acoustic wave is ensured. COPYRIGHT: (C)1984,JPO&Japio