Showing papers on "Temperature coefficient published in 2017"
TL;DR: In this article, a single Bi2(Li0.5Ta1.5)O7 + xBi2O3 (x = 0, 0.01 and 0.02) ceramics were prepared using a solid state reaction method.
Abstract: Bi2(Li0.5Ta1.5)O7 + xBi2O3 (x = 0, 0.01 and 0.02) ceramics were prepared using a solid state reaction method. All compositions were crystallized in a single Bi2(Li0.5Ta1.5)O7 phase without secondary peaks in X-ray diffraction patterns. Bi2(Li0.5Ta1.5)O7 ceramics were densified at 1025 °C with a permittivity (er) of ∼ 65.1, Qf ∼ 15 500 GHz (Q ∼ microwave quality factor; f ∼ resonant frequency; 16 780 GHz when annealed in O2) and the temperature coefficient of resonant frequency (TCF) was ∼ −17.5 ppm °C−1. The sintering temperature was lowered to ∼920 °C by the addition of 2 mol% excess Bi2O3 (er ∼ 64.1, a Qf ∼ 11 200 GHz/11 650 GHz when annealed in O2 and at a TCF of ∼ −19 ppm °C−1) with compositions chemically compatible with Ag electrodes. Bi2(Li0.5Ta1.5)O7 + xBi2O3 are ideal for application as dielectric resonators in 5G mobile base station technology for which ceramics with 60 < er < 70, high Qf and close to zero TCF are commercially unavailable. They may additionally prove to be useful as high er and high Qf materials in low temperature co-fired ceramic (LTCC) technology.
250 citations
TL;DR: This work presents an uncooled, mid-infrared photodetector, where the pyroelectric response of a LiNbO3 crystal is transduced with high gain into resistivity modulation for graphene, leading to TCRs up to 900% K−1 and the ability to resolve temperature variations down to 15 μK.
Abstract: There is a growing number of applications demanding highly sensitive photodetectors in the mid-infrared. Thermal photodetectors, such as bolometers, have emerged as the technology of choice, because they do not need cooling. The performance of a bolometer is linked to its temperature coefficient of resistance (TCR, ∼2–4% K−1 for state-of-the-art materials). Graphene is ideally suited for optoelectronic applications, with a variety of reported photodetectors ranging from visible to THz frequencies. For the mid-infrared, graphene-based detectors with TCRs ∼4–11% K−1 have been demonstrated. Here we present an uncooled, mid-infrared photodetector, where the pyroelectric response of a LiNbO3 crystal is transduced with high gain (up to 200) into resistivity modulation for graphene. This is achieved by fabricating a floating metallic structure that concentrates the pyroelectric charge on the top-gate capacitor of the graphene channel, leading to TCRs up to 900% K−1, and the ability to resolve temperature variations down to 15 μK. There is emerging interest in photodetectors in the mid-infrared driven by increasing need to monitor the environment for security and healthcare purposes. Sassiet al. show a thermal photodetector, based on the coupling between graphene and a pyroelectric crystal, which shows high temperature sensitivity.
156 citations
TL;DR: Li2MgGeO4 as mentioned in this paper was obtained with a relative permittivity of 6.5 and a temperature coefficient of resonant frequency of 0.1, Q'×'f'='28,500' GHz, and τ f ='74.7' when sintered at 1220'
Abstract: Two low-permittivity dielectric materials Li2AGeO4 (A = Zn, Mg) were prepared via the solid-state reaction method. X-ray diffraction analysis and Rietveld refinement indicated that both ceramics crystallize in an orthorhombic olivine structure with a space group Pmn21. Dense ceramics with high relative density and homogeneous microstructure were obtained. Li2ZnGeO4 densified at 1200 °C possessed a relative permittivity er = 6.5, a quality factor Q × f = 35,400 GHz, and a temperature coefficient of resonant frequency. Li2MgGeO4 exhibited er = 6.1, Q × f = 28,500 GHz, and τf = –74.7 ppm/°C when sintered at 1220 °C. Additionally, the large negative τf values of Li2AGeO4 (A = Zn, Mg) ceramics were successfully adjusted compensated by forming composite ceramics with CaTiO3 and near-zero τf values of +2.9 ppm/°C and +5.8 ppm/°C were achieved in 0.92Li2ZnGeO4-0.08CaTiO3 and 0.90Li2MgGeO4-0.10CaTiO3, respectively.
118 citations
TL;DR: In this paper, a series of (1 − x)BiVO4-xLaNbO4 (0.0 ≤ x ≤ 1.0) ceramics were prepared via a solid state reaction method.
Abstract: A series of (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) ceramics were prepared via a solid state reaction method. A scheelite-structured solid solution was formed for x ≤ 0.5 but for x > 0.5, tetragonal scheelite, monoclinic LaNbO4-type and La1/3NbO3 phases co-existed. As x increased from 0 to 0.1, the room temperature crystal structure gradually changed from monoclinic to tetragonal scheelite, associated with a decrease in the ferroelastic phase transition temperature from 255 °C (BiVO4) to room temperature or even below. High sintering temperatures were also found to accelerate this phase transition for compositions with x ≤ 0.08. Temperature independent high quality factor Qf >10000 GHz in a wide temperature range 25–140 °C and high microwave permittivity er ∼76.3 ± 0.5 was obtained for the x = 0.06 ceramic sintered at 800 °C. However, small changes in composition resulted in a change in the sign and magnitude of the temperature coefficient of resonant frequency (TCF) due to the proximity of the ferroelastic transition to room temperature. If TCF can be controlled and tuned through zero, then (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) is a strong candidate for microwave device applications.
108 citations
TL;DR: In this article, a newly discovered donor/acceptor co-doped rutile-TiO2 with an extremely high permittivity (e′) and low loss tangent (tanδ) has stimulated much research in capacitors and high energy-density storage devices.
104 citations
TL;DR: In this paper, the authors examined dynamic temperature-sensitive electrical parameters (TSEPs) for SiC MOSFETs and showed that the switching rate of the output current coupled with the gate current plateau (I GP) during turn-ON could be an effective TSEP under specific operating conditions.
Abstract: This paper examines dynamic temperature-sensitive electrical parameters (TSEPs) for SiC MOSFETs. It is shown that the switching rate of the output current ( dI DS /dt ) coupled with the gate current plateau (I GP) during turn-ON could be an effective TSEP under specific operating conditions. Both parameters increase with the junction temperature of the device as a result of the negative temperature coefficient of the threshold voltage. The temperature dependency of dI DS /dt has been shown to increase with the device current rating (due to larger input capacitance) and external gate resistance ( $R_{G}^{\rm EXT}$ ). However, as dI DS /dt is increased by using a small $R_{G}^{\rm EXT}$ , parasitic inductance suppresses the temperature sensitivity of the drain and gate current transients by reducing the “effective gate voltage” on the device. Since the temperature sensitivity of dI DS /dt is at the highest with maximum $R_{G}^{\rm EXT}$ , there is a penalty from higher switching losses when this method is used in real time for junction temperature sensing. This paper investigates and models the temperature dependency of the gate and drain current transients as potential TSEPs for SiC power MOSFETs.
91 citations
TL;DR: In this article, the authors showed that ScNTO ceramics that were 10% (Sc3++Nb5+) co-doped with acceptor and donor Nb5+ ions exhibited very low dielectric loss tangent (tanδ) and high Dielectric permittivity (∆) with a low temperature coefficient (Δ∆(T)/∆′RT).
87 citations
TL;DR: In this paper, the Mg2-xCuxSiO4 (x = 0.40) microwave dielectric ceramics were prepared using solid-state reaction method.
Abstract: In this work, the Mg2-xCuxSiO4(x = 0–0.40) microwave dielectric ceramics were prepared using solid-state reaction method. Compared with the Mg2SiO4 sample, the Cu-substituted Mg samples could be sintered at a lower temperature. The Mg2−xCuxSiO4 ceramics exhibit the composite phases of Mg2SiO4 and a small quantity of MgSiO3. The Cu2+ ion presented a solid solution with the Mg2SiO4 phase and preferentially occupy Mg(1) site. The distortion of MgO6 octahedron was modified by Cu2+ ions, resulting in a positive change in the temperature coefficient of resonance frequency (τf) values. Excellent microwave dielectric properties of er = 6.35, high Qf of ∼ 188,500 GHz and near zero τf = −2.0 ppm/°C were achieved at x = 0.08 under sintering at 1250 °C for 4 h. Thus, the fabricated ceramics were considered as possible candidates for millimeter-wave device applications.
87 citations
TL;DR: The proposed compensation circuit for enhancing the voltage accuracy of the bandgap reference combines an addition circuit, subtraction circuit, and current mirror to achieve an adjusted piecewise linear temperature current over an entire temperature range.
Abstract: This paper presents a precision bandgap reference with an innovative adjusted-temperature-curvature compensation circuit that obtains a good temperature coefficient (TC) over a wide temperature range. The proposed compensation circuit for enhancing the voltage accuracy of the bandgap reference combines an addition circuit, subtraction circuit, and current mirror to achieve an adjusted piecewise linear temperature current over an entire temperature range. The proposed bandgap reference was designed and fabricated using a standard Taiwan Semiconductor Manufacturing Company (TSMC) $0.18~\mu \text{m}$ 1P6M CMOS technology. Measurements on eight samples indicated that the proposed bandgap reference achieved a TC that varies from 1.67 to 10.55 ppm/° from −40 °C to 140 °C with a supply voltage of 1.8 V. The measured 547 mV reference voltage achieved a precision line regulation that is less than 0.08%/V for supply voltages between 1.3 and 1.8 V. The proposed circuit dissipated $28~\mu \text{A}$ with a supply voltage of 1.8 V, and an active area of 0.0094 mm2. The circuit was designed to operate on a low supply voltage down to 1.3 V.
70 citations
TL;DR: In this paper, Schottky diodes were formed on bulk or epitaxial β-Ga2O3 using Ni/Au or Pt-Au and the electrical characteristics measured as a function of temperature in the range 25-200°C.
Abstract: Schottky diodes were formed on bulk or epitaxial β-Ga2O3 using Ni/Au or Pt/Au and the electrical characteristics measured as a function of temperature in the range 25–200°C. The barrier heights were 1.07 eV (Ni/Au) and 1.04 eV (Pt/Au) at 25°C. The barrier heights increased with temperature, while the on-state resistances (RON) decreased over the same range. The temperature coefficient of reverse breakdown voltage (VB), β, was −4 mV/K for Ni/Au and −0.1 mV/K for Pt/Au. The figure-of-merit (VB2/RON) was above 3 MW.cm−2 at 25°C for Ni/Au diodes and was still ~1 MW.cm−2 at 200°C. The reverse recovery times were also measured as a function of temperature and were of the order of 21–28 ns over the range 25–150°C for both epi and bulk diodes. The results show the already high quality of bulk and epitaxial β-Ga2O3 and the potential of this material for high temperature power electronics.
69 citations
TL;DR: In this paper, the dielectric properties of Li 2 Mg 3− x Ca x TiO 6 (x=0-0.18) were studied using a conventional solid-state route to find temperature stable and high Q microwave ceramics.
TL;DR: In this article, the thermal stability of the Nd-Ce-Y-Fe-B sintered magnet was improved via the binary main phase (BMP) approach.
TL;DR: The ultralong conducting lightweight multiwall carbon nanotube (MWCNT)-Cu composite wires with MWCNTs uniformly distributed in a continuous Cu matrix throughout are promising lightweight alternatives to Cu wiring for weight-reducing applications.
Abstract: We report ultralong conducting lightweight multiwall carbon nanotube (MWCNT)-Cu composite wires with MWCNTs uniformly distributed in a continuous Cu matrix throughout. With a high MWCNT vol% (40–45%), the MWCNT-Cu wire density was 2/3rd that of Cu. Our composite wires show manufacturing potential because we used industrially compatible Cu electrodeposition protocols on commercial CNT wires. Further, we systematically varied Cu spatial distribution on the composite wire surface and bulk and measured the associated electrical performance, including resistivity (ρ), temperature dependence of resistance, and stability to current (measured as current carrying capacity, CCC in vacuum). We find that a continuous Cu matrix with homogeneous MWCNT distribution, i.e., maximum internal Cu filling within MWCNT wires, is critical to high overall electrical performances. Wires with maximum internal Cu filling exhibit (i) low room temperature ρ, 1/100th of the starting MWCNT wires, (ii) suppressed resistance-rise with temperature-increase and temperature coefficient of resistance (TCR) ½ that of Cu, and (iii) vacuum-CCC 28% higher than Cu. Further, the wires showed real-world applicability and were easily soldered into practical circuits. Hence, our MWCNT-Cu wires are promising lightweight alternatives to Cu wiring for weight-reducing applications. The low TCR is specifically advantageous for stable high-temperature operation, e.g., in motor windings.
TL;DR: In this article, the authors employed a segregated and double-percolated composite microstructure to inhibit the polymer volume expansion effect and flake-like graphene as conductive filler to construct a resistant conductive network by its overlapping contact mode, targeted at developing a favorable NTC material.
Abstract: Electrically conductive polymer composites (CPCs) show considerable promise in thermistors owing to their characteristics of positive temperature coefficient (PTC) effect and negative temperature coefficient (NTC) effect of resistance. In contrast to traditional rigid ceramic thermistors, CPCs are lightweight with good processibility, flexibility and variety. However, the development of polymer-based NTC thermistors has been impeded by the polymer volume expansion effect, which usually leads to a PTC effect. Here, we employed a segregated and double-percolated composite microstructure to inhibit the polymer volume expansion effect and flake-like graphene as conductive filler to construct a resistant conductive network by its overlapping contact mode, targeted at developing a favorable NTC material. This strategy was carried out by selectively distributing graphene in a polyamide 6 (PA6) phase between isolated ultrahigh molecular weight polyethylene (UHMWPE) particles. As a result, the graphene/PA6/UHMWPE composites exhibited a relatively linear NTC effect through the whole heating process, a high NTC intensity of 5.1, a wide temperature range of 30–260 °C, good reproducibility as well as high mechanical properties. The underlying mechanism of the NTC effect originates from the morphology evolution from crumpled to stretched morphology, enhanced electron mobility in the crumpled morphology, and the improved conductivity of graphene triggered by increasing the temperature.
TL;DR: The work reveals theoretically that the zero-TCR could be achieved by adjusting competing contributions from thermally assisted tunnelling transport at CNT junctions and thermal expansion of matrices and the potential resistance change ratio could be improved by the glass transition in nanocomposites.
Abstract: Effectively tailoring the temperature coefficient of resistance (TCR) is critical for multifunctional carbon nanotube (CNT) polymer composites with sensing capability. By developing a new multiscale percolation network model, this work reveals theoretically that the zero-TCR could be achieved by adjusting competing contributions from thermally assisted tunnelling transport at CNT junctions and thermal expansion of matrices. On the other hand, the negative temperature coefficient of nanocomposites above glass transition temperature could be greatly enhanced because the transport mechanism at the CNT junctions experienced a transition from tunnelling to hopping. Both tube-tube and/or tube-matrix interactions at conjunction and the structural distortion of nanotubes are considered in the newly proposed model. To validate the model, CNT/polymer nanocomposites with nearly constant resistance values (zero-TCR) below the glass transition temperature and a high TCR (98% resistance change ratio) resulting from the glass transition of the polymer matrix are successfully developed. The study also suggests that the desired parameters to achieve the zero-TCR property and the potential resistance change ratio could be improved by the glass transition in nanocomposites. This could be beneficial for the development of high quality sensing materials.
TL;DR: In this paper, a series of water insoluble ultra-low temperature firing (Na,Ag)2MoO4 microwave dielectrics were prepared via the traditional solid state reaction method.
Abstract: In the present work, a novel series of water insoluble ultra-low temperature firing (Na,Ag)2MoO4 microwave dielectrics were prepared via the traditional solid state reaction method A spinel structured solid solution was formed in the full composition range in the (NaxAg2−x)MoO4 (0 ≤ x ≤ 2) As x increased from 0 to 20, cell volume decreased linearly from 932 A to 910 A Sintering behavior were described using a so-called ‘bowing’ effect and densification was achieved below 420 °C for 05 ≤ x ≤ 12 with grain size, 1 to 5 μm Optimum microwave dielectric properties were obtained for (Na12Ag08)MoO4 ceramics sintered at 410 °C with a permittivity ∼81, a microwave quality factor ∼44 800 GHz and the temperature coefficient of the resonant frequency ∼−82 ppm °C−1 at 139 GHz Silver within the solid solution inhibited hydrolyzation of ceramics and also reduced their sintering temperature Compared with the sintering temperatures of traditional microwave dielectric ceramic (Al2O3, >1400 °C) and normal low temperature co-fired ceramics (<960 °C), this system will save lots of energy during processing and accelerate developments of sustainable electronic materials and devices
TL;DR: This paper describes an MOSFET-only voltage reference realized in 65-nm CMOS featuring a temperature coefficient (TC) of 5.6 ppm/°C from -40 °C to 125 °C, a power supply rejection ratio of 87 dB from dc up to 800 kHz, and an impedance-adapting frequency compensation scheme.
Abstract: This paper describes an MOSFET-only voltage reference realized in 65-nm CMOS featuring a temperature coefficient (TC) of 5.6 ppm/°C from -40 °C to 125 °C, a power supply rejection ratio of 87 dB from dc up to 800 kHz (and 75 dB at 1 MHz), a minimum supply voltage of 0.8 V, and a power dissipation of 13 μW. These attributes are achieved by exploiting the zero-TC point of an MOSFET and combining it with a novel curvature-compensation technique, an active attenuator, and an impedance-adapting frequency compensation scheme.
TL;DR: In this article, a sort of W/Cr co-doped Bi4Ti3O12 ceramics with different additional amount of Cr2O3: Bi4 Ti2.95W0.05O12.
TL;DR: In this article, a record of 94.73kJ/m 3 at 773k with a high intrinsic coercivity of 652.72kA/m was made.
TL;DR: In this article, an indium-tin-oxide (ITO) thin film resistance temperature detector (RTD) was fabricated on alumina substrates by RF sputtering.
TL;DR: In this paper, the authors showed that polycrystalline Sr−doped La1-y(Cay-xSrx)MnO3 (LCSMO, y=3/8) ceramics with x = 0, y/25, 2y/25 and y/3 were prepared by sol−gel methods and X-ray diffraction patterns indicated that all the bulk samples were single phase without any impurities.
TL;DR: In this article, a two-step positive temperature coefficient (PTC) effect companied extremely favorable PTC reproducibility, where the first sharp increase and the second increase of resistivity could be attributed to the sequential volume expansion of HDPE and PVDF at their melting point.
Abstract: Distinct “island-bridge” structure was purposely designed by appointing carbon nanofiber (CNF) filled high density polyethylene (HDPE) and polyvinylidene fluoride (PVDF) blend, in which, very dense electrical conductive networks were formed in HDPE dispersion phase (islands) and these islands were then linked by CNF particles partly stretched out from HDPE phase or distributed in PVDF phase (bridges). The HDPE/PVDF/CNF composites with “island-bridge” electrical conductive network showed unique positive temperature coefficient (PTC) effect, namely, a two-step PTC effect companied extremely favorable PTC reproducibility. The first sharp increase and the second increase of resistivity could be attributed to the sequential volume expansion of HDPE and PVDF at their melting point, where the electrical conductive networks were broken twice. In addition, the existence of dense electrical conductive networks in HDPE phase and the additional compression on them by the volume shrinkage of PVDF phase during the cooling process resulted in the favorable PTC reproducibility.
TL;DR: In this paper, the density of liquid Inconel 718 alloy was experimentally measured by electrostatic levitation technique, where the maximum undercooling of 100 K was realized for the commercial sample.
TL;DR: In this paper, the microstructure and microwave dielectric properties of (La1−xSmx)NbO4 (x=0-0.10) ceramics were discussed in detail.
Abstract: The (La1−xSmx)NbO4 (x=0-0.10) ceramics were prepared by the conventional solid-state reaction method. The microstructure and the microwave dielectric properties were discussed in detail. The X-ray diffraction patterns of (La1−xSmx)NbO4 (x=0-0.10) showed that only a single monoclinic fergusonite structure of LaNbO4 could be found. The dielectric constant (er) was affected by the dielectric polarizabilities and the B-site bond valence. The variation trend of Q×f0 was in accordance with packing fraction. The temperature coefficient of resonant frequency (τf) had a close relationship with the B-site bond valence, which was determined by the bond strength and bond length. When sintered at 1325°C for 4 hours, the (La1−xSmx)NbO4 ceramics with x=0.08 exhibited enhanced microwave dielectric properties: er=19.37, Q×f0=62203 GHz and τf=2.57 ppm/°C. In addition, we made an overview about the ceramics that possess the same packing fraction and bond valence relationships, the results show that this structure-property relationship has a wide applicability.
TL;DR: In this paper, the electrical resistivity of sputter-deposited Cu/V multilayer films with different individual layer thicknesses varying from 2.5 to 100nm was evaluated in the temperature range of 150-300 k.
TL;DR: In this article, the scalability of RGO-Ag nanocomposite films based temperature sensor on kapton sheet for the flexible technology platform was demonstrated and the sensor developed shows exceptional temperature sensing properties, with a promise for wide range of potential application possibilities.
Abstract: We have demonstrated the scalability of RGO-Ag nanocomposite films based temperature sensor on kapton sheet for the flexible technology platform. The RGO nanosheets are known to have the tendency to form an agglomeration, which was removed by insertion of Ag nanoparticles to the RGO sheets. This resulted in the formation of nanocomposite material having an excellent conductivity suitable for temperature sensor applications. The electro thermal performance of the RGO-Ag nanocomposite sensing film was investigated using the Hot-Cold temperature setup. The sensor developed shows exceptional temperature sensing properties, with a promise for wide range of potential application possibilities. Till today the performance of temperature sensors are limited by the flexibility, lower sensitivity, non linearity viz. Thermistors and Platinum based sensors viz. RTD & Pt 100 while linear are expensive. In contrast, the sensor developed in our present work shows negative temperature coefficient (NTC) of -1.64 x 10(-3) Omega/Omega/K, sensitivity of 0.5553 Omega/K, with a non-linearity of about 1% and hysteresis close to 1%. The measured response time (470 m s) of this sensor is much faster than majority of commercially available temperature sensors with good repeatability and stability. The linearity of the developed sensor lends itself for simpler signal conditioning circuits without requiring linearization front end. (C) 2017 Elsevier B.V. All rights reserved.
TL;DR: Grain boundary diffusion with TbH3 nanoparticles was applied to fabricate Tb-less sintered Nd-Fe-B permanent magnets with high coercivity as discussed by the authors.
TL;DR: In this article, the authors investigated the mechanisms for hot-spot formation and pressure wave development associated with end-gas autoignition during knocking combustion of n -heptane/air mixture.
TL;DR: In this paper, the authors reported the results of impedance and conductivity analysis of BiFeO3-BaTiO3 (BFO-BT) system prepared by solid state reaction route.
TL;DR: In this article, the temperature dependence of barrier height in a Ni/n-GaN Schottky barrier diode fabricated on a GaN homoepitaxial layer was investigated by capacitance, current, and internal photo-emission measurements in the range of 223-573 K.
Abstract: The temperature dependence of barrier height in a Ni/n-GaN Schottky barrier diode fabricated on a GaN homoepitaxial layer was investigated by capacitance–voltage, current–voltage, and internal photoemission measurements in the range of 223–573 K. The barrier height obtained by these methods linearly decreased with increasing temperature. The temperature coefficient was −(1.7–2.3) × 10−4 eV/K, which is about half of the temperature coefficient of the band gap reported previously. This indicates that the decrease in the barrier height may mainly reflect the shrinkage of the band gap (lowering of the conduction band edge) in GaN with increasing temperature.