Adjustable Temperature Coefficient Research Articles

Flexible self-assembly carbon nanotube/polyimide thermal film endowed adjustable temperature coefficient of resistance

The development of multi-role flexible thermal films embedded with single-walled carbon nanotubes (SWCNTs) exhibiting an adjustable temperature coefficient of resistance (TCR) is presented. The composite film is prepared by an alternating electric field to assembling CNTs on Ni conductive layer and polyimide. Modified vacuum thermal treatment is then conducted to adjust the TCR behavior of films, thereby gaining the positive, negative and near-zero TCR ranging from −1.5% °C−1 to nearly 1.0% °C−1 at different annealing conditions, respectively. The changes of morphologies, tube crystallinity and chemical elements in films are investigated. The enhanced intertube couplings in bundles of CNTs, formations of chemical bonds and recrystallization in heat-treated films, resulting in the change of charge transport, play a dominant role in the evolution of the TCR behavior. Heat-treated films also exhibit linear temperature dependence and high stability while operating at wide ambient temperature, leading to broad prospects in flexible electronic thermal applications.

Semiconducting Carbon Nanotubes Embedded in a Metallic Film for a Thermistor Device with an Adjustable Temperature Coefficient and Reduced Noise Source Activities

AbstractSemiconducting single‐walled carbon nanotube‐Au (sSWCNT‐Au) hybrid films are prepared to build a thermistor device with an adjustable temperature coefficient and show that the embedded sSWCNTs reduce the resistivity and noise source activities in the nanoscale regions of the film. The temperature coefficient of the hybrid films can be adjusted from negative to positive values simply by increasing the deposited Au thickness. Moreover, scanning noise microscopy is utilized to map the nanoscale variation of the resistivity and noise source density on the sSWCNT‐Au hybrid films. Interestingly, the map shows that the regions with both sSWCNT and Au exhibit three times lower resistivity and 18 times smaller noise source activities than pristine Au regions, indicating that sSWCNTs embedded in metallic films can significantly reduce the resistivity and electrical noise source activities in the film.

温度系数连续可调的带隙基准源电路设计

温度系数连续可调的带隙基准源电路设计

Adjustment of temperature coefficient of electrical resistivity in Cu66Zr34 metallic glass through surface oxidation induced phase decomposition

Amorphous Cu66Zr34 alloy decomposes into Cu, ZrO2, and residual amorphous phase after oxidation, mainly due to differences between the oxygen affinity to Cu and Zr. A four-layer structure formed near the surface consisting of two oxidized layers, a transition region, and the matrix. The crystalline phases exhibited a gradient distribution along the thickness. The oxidized ribbons showed an adjustable temperature coefficient of electrical resistivity as a function of thickness. Near constant electrical resistivity (TCR≈0) could be obtained with a thickness of 20μm. Such transformation can be utilized for producing precision wires or thin-film chip resistors through oxidation.

Developments of Cr-Si and Ni-Cr Single-Layer Thin-Film Resistors and a Bi-Layer Thin-Film Resistor with Adjustable Temperature Coefficient of Resistor

At first, Cr-Si (28 wt% Cr, 72 wt% Si) and Ni-Cr (80 wt% Ni, 20 wt% Cr) thin-film materials were deposited by using sputtering method at the same parameters, and their physical and electrical properties were investigated. The resistances of Cr-Si and Ni-Cr thin-film resistors decreased with the increase of deposition time (thickness) and their resistivity had no apparent variations as the deposition time increased. The temperature coefficient of resistance (TCR) of single-layer Cr-Si thin-film resistors was negative and the TCR value of single-layer Ni-Cr thin-film resistors was positive. For that, we used Cr-Si thin films as upper (or lower) layer and Ni-Cr thin films as lower (upper) layer to investigate a bi-layer thin-film structure. The deposition time of Ni-Cr thin films was fixed at 10 min and the deposition time of Cr-Si thin films was changed from 10 min to 60 min. We had found that as Cr-Si thin films were used as upper or lower layers they had similar deposition rates. We had also found that the thickness and stack method of Cr-Si thin films had large effects on the resistance and TCR values of the bi-layer thin-film resistors.

NiC: a highly sensitive functional layer based on a nickel/graphene thin film for pressure and force sensors.

A functional layer based on nickel and graphene called NiC was developed with the goal of a high strain sensitivity in combination with an adjustable temperature coefficient of resistance (TCR). A gauge factor up to 30 and TCR values of approximately 0±25 ppm/K can be achieved by variation of the film composition. Based on the increased sensitivity the important pressure range of below 2.5 bar is opened up for steel membrane pressure sensors without the need of a sophisticated technical effort. First pressure and force sensors with NiC functional layers were realized in order to demonstrate the high performance of this new material. The enlarged sensitivity of the film leads to a complex re-development of the microsystems “pressure and force sensors” in order to take the advantage of the high linearity, low hysteresis, high overload protection and stability. Due to the high sensitivity, it is possible to produce sensors with significantly increased stability values in the overload region. Using the same output voltage range as usual with NiCr thin film elements, the overload capability of the sensors with the new functional layer is about twenty times the characteristic value of NiCr sensors. On the other hand, the low pressure range is opened up since the membrane needs to be deformed only one tenth of its usual value. Because of this low stress the load cycle stability increases accordingly. Additionally base body materials like 1.4435 (316L), which are not very suitable for the production of pressure sensor membranes, can be used for example for hydrogen applications.

Ultra‐Low Fire Glass‐Free Li3FeMo3O12 Microwave Dielectric Ceramics

A new ultra‐low fire glass‐free microwave dielectric material Li3FeMo3O12 was investigated for the first time. Single phase ceramics were obtained by the conventional solid‐state route after sintering at 540°C–600°C. The atomic packing fraction, FWHM of the Ag oxygen‐octahedron stretching Raman mode and Qf values of samples sintered at different temperatures correlated well with each other. The sample with a Lower Raman shift showed a higher dielectric constant. Interestingly, the system also showed a distinct adjustable temperature coefficient of resonant frequency (from −84× 10−6/°C to 25 × 10−6/°C).

Dielectrophoretic alignment of polymer compounds for thermal sensing

In this work polymer compounds with an electrically conducting filler material, being aligned in an inhomogeneous electric field using dielectrophoresis, were investigated. Chemically synthesized semi-conducting tellurium nanorods were used as filler material. Resulting resistances of the aligned polymer compounds can be accurately tailored between 500 kΩ and 10 TΩ. The corresponding temperature behavior of the resistance was examined and showed strong dependence on the degree of alignment and on the matrix polymer used. The adjustable temperature coefficient of resistivity (TCR) has values of (−0.7…−4.1)%/K. Additionally, structuring techniques based on lithography and stamping processes are exemplary described and demonstrated for resistive thermal sensor elements.

Low temperature sintering of Li1.1Nb0.58Ti0.5O3-xBi2O3 dielectric with adjustable temperature coefficient

Ceramics of Li1.1Nb0.58Ti0.5O3-xBi2O3 with low sintering temperature have been prepared by the solid-solution reaction method using B2O3 (2 wt% added) as sintering aid. For all compounds, the sintering temperature achieves 900 °C. Microstructure and dielectric properties of Li1.1Nb0.58Ti0.5O3-2 wt% B2O3-xBi2O3 (LNT-B-xBi) ceramics have been investigated. The X-ray diffraction patterns indicate for higher Bi2O3 content (x = 0.1 mol%) that the material is composed by two phases identified as M-phase and Bi4Ti3O12. The Li1.1Nb0.58Ti0.5O3 + 0.15 mol% Bi2O3 composition sintered at 900 °C with B2O3 addition exhibits attractive dielectric properties (er = 59.68, tan δ = 1.2×10−4 and a temperature coefficient of the relative permittivity near zero) at 1 MHz. It is also shown that the introduction of Bi2O3 can tune the temperature coefficient of the relative permittivity. All dielectric properties lead this system compatible to manufacture sliver based electrodes multilayer dielectric devices.

Middle-permittivity LTCC dielectric compositions with adjustable temperature coefficient

Middle-permittivity low-temperature co-fired ceramics (LTCC) dielectric compositions with adjustable temperature coefficient have been studied based on CaZrO 3–CaTiO 3. To lower the densification temperature from 1450 °C to less than 900 °C, a series of lithium–borosilicate glass system was designed and added to the CaZrO 3–CaTiO 3 system. As the τ f of glass frits and CaZrO 3 are slightly negative (−5 to −200 ppm/°C) and that of CaTiO 3 is significantly positive, zero τ f could be realized by mixing an appropriate amount of CaTiO 3 (10–20 wt.%) with CaZrO 3. Microstructures, physical properties, and microwave dielectric properties were measured as a function of the compositional ratio of CaZrO 3–CaTiO 3. Nearly zero τ f, together with an acceptable microwave quality factor, was obtained at the composition of CaZrO 3/CaTiO 3/frit=70:15:15 wt.%.

Newly developed ternary (Ca, Sr, Ba) zirconate ceramic system for microwave resonators

Abstract In Ca, Sr-rich region with orthorhombic perovskite-type structure, successful results such as high dielectric Q (2000∼3000 at 11GHz), suitable dielectric constant, (29∼32) and widely adjustable temperature coefficient of dielectric constant (−50 to +50 ppm/°C) were obtained. It was also found that substitution of small amounts of Ti for Zr brings some decrease in temperature coefficient with increase in dielectric Q. Using above described ceramics in microwave integrated circuits oscillator with GaAs FET, a compensation for temperature dependence of circuit elements was well achieved within the value which corresponds to the deviation of oscillation frequency within ± 500KHz at 11.66GHz (−20∼+60°C).

Reactive sputtering of NiCr resistors with closely adjustable temperature coefficient of resistance : J. Griessing. Electrocomp. Sci. Technol.4, 133 (1977)

Reactive sputtering of NiCr resistors with closely adjustable temperature coefficient of resistance : J. Griessing. Electrocomp. Sci. Technol.4, 133 (1977)

Reactive Sputtering of NiCr Resistors With Closely Adjustable Temperature Coefficient of Resistance

A process is described to obtain NiCr resistors with adjustable temperature coefficient of resistance (TCR) by reactive sputtering in an Ar-atmosphere with a small amount of oxygen in the range of 2% to 6%. As deposited the films show a TCR < −200 ppm/K. By heat treatment in air at a temperature of 350°C the TCR can be raised to values above −20 ppm/K. The time of heat treatment necessary to obtain a given TCR depends on the oxygen/argon ratio during sputtering. The long term stability is not affected by the choice of this ratio in a wide range.Resistor networks with a solderable conductor pattern of TiPdAu have a TCR of 0±7 ppm/K and a long term resistance drift ≤ 2‰ in the first 1,000 hours at 125°C.

Electronic circuit for temperature compensation of a conductivity meter

The principle of operation and design of a circuit for the temperature compensation of a conductivity meter are reported. The circuit provides for both automatic and manual compensation with an adjustable temperature coefficient whose value may be many times greater than the coefficient of the temperature sensor.