Fabrication and characterization of NiCr-based films with high resistivity and low temperature coefficient of resistance

As a metal alloy,NiCr films have a relatively high resistivity and low temperature coefficient of resistance (TCR) and are widely used in electronic components and sensors.However,the resistivity of pure NiCr is insufficient for high-resistance and highly stable film resistors.In this study,a quaternary NiCrAlSi target (47:33:10:10,wt.%) was successfully used to prepare resistor films with resistivities ranging from 1000 to 10 000μΩcm and TCR within±100 ppm/K.An oxygen flow was introduced during the sputtering process.The films exhibit hightemperature stability at 450℃.The films were analyzed using Auger electron spectroscopy,x-ray diffraction,time-of-flight secondary-ion mass spectrometry,and x-ray photoelectron spectroscopy.The results show that the difference in the oxide proportion of the films caused the differences in resistivity.The near-zero TCR values were considered to be due to the competition between silicon and other metals.This study provides new insights into the electrical properties of NiCr-based films containing Si,which will drive the manufacturing of resistors with high resistivity and zero TCR.

Assembly-level analysis on temperature coefficient of reactivity in a graphite-moderated fuel salt reactor fueled with low-enriched uranium

To provide a reliable and comprehensive data reference for core geometry design of graphite-moderated and low-enriched uranium fueled molten salt reactors,the influences of geometric parameters on the temperature coefficient of reactivity(TCR)at an assembly level were characterized.A four-factor formula was introduced to explain how different reactivity coefficients behave in terms of the fuel salt volume fraction and assembly size.The results show that the fuel salt temperature coefficient(FSTC)is always negative owing to a more negative fuel salt density coefficient in the over-moderated region or a more negative Doppler coefficient in the under-moderated region.Depending on the fuel salt channel spacing,the graphite moderator temperature coefficient(MTC)can be negative or positive.Furthermore,an assembly with a smaller fuel salt channel spacing is more likely to exhibit a negative MTC.As the fuel salt volume fraction increases,the negative FSTC first weakens and then increases,owing to the fuel salt density effect gradually weakening from negative to positive feedback and then decreasing.Meanwhile,the MTC weakens as the thermal utilization coefficient caused by the graphite temperature effect deteriorates.Thus,the negative TCR first weakens and then strengthens,mainly because of the change in the fuel salt density coefficient.As the assembly size increases,the magnitude of the FSTC decreases monotonously owing to a monotonously weakened fuel salt Doppler coefficient,whereas the MTC changes from gradually weakened negative feedback to gradually enhanced positive feedback.Then,the negative TCR weakens.Therefore,to achieve a proper negative TCR,particularly a negative MTC,an assembly with a smaller fuel salt channel spacing in the under-moderated region is strongly recommended.

Analysis of burnup performance and temperature coefficient for a small modular molten‑salt reactor started with plutonium

In a thorium-based molten salt reactor(TMSR),it is difficult to achieve the pure 232Th–^(233)U fuel cycle without sufficient^(233)U fuel supply.Therefore,the original molten salt reactor was designed to use enriched uranium or plutonium as the starting fuel.By exploiting plutonium as the starting fuel and thorium as the fertile fuel,the high-purity^(233)U produced can be separated from the spent fuel by fluorination volatilization.Therefore,the molten salt reactor started with plutonium can be designed as a^(233)U breeder with the burning plutonium extracted from a pressurized water reactor(PWR).Combining these advantages,the study of the physical properties of plutonium-activated salt reactors is attractive.This study mainly focused on the burnup performance and temperature reactivity coefficient of a small modular molten-salt reactor started with plutonium(SM-MSR-Pu).The neutron spectra,^(233)U production,plutonium incineration,minor actinide(MA)residues,and temperature reactivity coefficients for different fuel salt volume fractions(VF)and hexagon pitch(P)sizes were calculated to analyze the burnup behavior in the SM-SMR-Pu.Based on the comparative analysis results of the burn-up calculation,a lower VF and larger P size are more beneficial for improving the burnup performance.However,from a passive safety perspective,a higher fuel volume fraction and smaller hexagon pitch size are necessary to achieve a deep negative feedback coefficient.Therefore,an excellent burnup performance and a deep negative temperature feedback coefficient are incompatible,and the optimal design range is relatively narrow in the optimized design of an SM-MSR-Pu.In a comprehensive consideration,P=20 cm and VF=20%are considered to be relatively balanced design parameters.Based on the fuel off-line batching scheme,a 250 MWth SM-MSR-Pu can produce approximately 29.83 kg of ^(233)U,incinerate 98.29 kg of plutonium,and accumulate 14.70 kg of MAs per year,and the temperature reactivity coefficient can always be lower than−4.0pcm/K.

Positive temperature coefficient of resistivity effects of semiconducting (Bi(1/2)Na(1/2)) TiO_3-CaTiO_3-BaTiO_3 ceramics sintered in air atmosphere

Y^3＋-doped （Bi 1/2 Na 1/2） TiO 3-CaTiO 3-BaTiO 3 （BNCBT） positive temperature coefficient of resistivity （PTCR） ceramics sintered in air atmosphere were investigated in this study. （Bi 1/2 Na 1/2） TiO 3 （BNT） component can remarkably increase the onset temperature T c of PTCR ceramics with the expense of the resistivity R 25 increase. CaTiO 3 （9–27 mol%） component can decrease the resistivity, and adjust the effects of BNT phase on the T c point. For the sample containing 3 mol% CaTiO 3 , T c raises from 122 ℃ to 153 ℃ when only 0.6 mol% BNT added, while for the ones with higher CaTiO 3 content （9–27 mol%）, T c is only increased by a rate of 8–9℃/1.0 mol% BNT. The effects of BNT and CaTiO 3 components on R25/Rmin （negative temperature coefficient effect） are also discussed.

Preparation and study on performance of submicron nickel powder for multilayer chip positive temperature coefficient resistance

Base metal nickel is often used as the inner electrode in multilayer chip positive temperature coefficient resistance （PTCR）. The fine grain of ceramic powders and base metal nickel are necessary. This paper uses reducing hydrazine to gain submicron nickel powder whose diameter was 200-300 nm through adjusting the consumption of nucleating agent PVP properly. The submicron nickel powder could disperse well and was fit for co--fired of multilayer chip PTCR. It analyes the submicron nickel powder through x-ray Diffraction （XRD） and calculates the diameter of nickel by PDF cards. Using XRD analyses it obtains several conclusions： If the molar ratio of hydrazine hydrate and nickel sulfate is kept to be a constant, when enlarging the molar ratio of NaOH/Ni^2＋, the diameter of nickel powder would become smaller. When the temperature in the experiment raises to 70-80 ℃, nickel powder becomes smaller too. And if the molar ratio of NaOH/Ni2＋ is 4, when molar ratio of （C2H5O）2/Ni^2＋ increases, the diameter of nickel would reduce. Results from viewing the powders by optical microscope should be the fact that the electrode made by submicron nickel powder has a better formation and compactness. Furthermore, the sheet resistance testing shows that the electrode made by submicron nickel is smaller than that made by micron nickel.

Characterization of the BaBiO_3-doped BaTiO_3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with T_c=155℃

BaBiO3-doped BaTiO3 （BB-BT） ceramic, as a candidate for lead-free positive temperature coefficient of resistivity （PTCR） materials with a higher Curie temperature, has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature, Tc = 155℃, which is higher than that of BaTiO3 （≤ 130 ℃）. Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current （AC） resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data, the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature, indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency, the conduction mechanism is also discussed for a BB-BT ceramic system.

Negative Temperature Coefficient of Resistivity in Bulk Nanostructured Ag

The change of the temperature coefficient of resistivity (a) with the particle size, dp, and the grain size, dc, in the nanostructured Ag bulk samples was investigated. dp and dc were controlled by heating the nano-Ag powders over the temperature range from 393 to 453 K. The electrical resistance measurements of the nanostructured Ag bulk samples obtained by compacting the Ag powders after heat treatments showed a change in the sign of a with dP and dc. When dp and dc are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respectively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative a arises mainly from the high resistivity induced by the particle interfaces with very lowly ordered or even disordered structure, a large volume fraction of interfaces and impurities existing in the interfaces, and the quantum size effect appearing in the nano-Ag grains.

Influence of Zirconium Addition on Magnetic Properties and Temperature Coefficient for Nanocomposite Nd_(10)Fe_(78.5-x)Co_5Zr_xB_(6.5) Magnets

The influence of Zr addition on magnetic properties and temperature coefficient for nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 (x=0～4) bonded magnets was investigated. It was found that the room-temperature magnetic properties were remarkably improved with Zr addition due to the grain refinement and increasing volume fraction of the hard magnetic phase. The optimal magnetic properties of Jr=0.689 T, iHc=769.4 kA·m-1 and (BH)max=84 kJ·m-3 were obtained for 2.5% Zr addition. The temperature coefficient of remanence (α) increases slightly and the temperature coefficient of coercivity (β) decreases obviously with increasing Zr content for nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 (x=0～4) bonded magnets.

Study on Low Temperature Coefficient Rare-Earth Magnets

The rare-earth hard magnets with lower temperature coefficient, including Nd_2Fe_ 14B/Fe_3B-ferrite compound bonded magnets and Sm_ 0.8RE_ 0.2 (Co_ balFe_ 0.22Cu_ 0.06Zr_ 0.03)_ 7.4(RE=Gd, Er) sintered magnets, were studied. The result shows that the addition, that dope ferrite magnetic powder to double-phase nanocomposite Nd_2Fe_ 14B/Fe_3B magnetic powder, can make β_ jH_c to be obviously decreased. Similarly, the effect of homogeneous heating treatment on magnetic properties was studied. Doping heavy rare earth elements to the 2∶17-type SmCo magnet material powders shows that the sintered magnets obtained lower temperature coefficient, and enhanced magnets temperature stability.

An AlGaN/GaN HEMT with enhanced breakdown and a near-zero breakdown voltage temperature coefficient

An AlGaN/GaN high-electron mobility transistor（HEMT） with a novel source-connected air-bridge field plate（AFP） is experimentally verified.The device features a metal field plate that jumps from the source over the gate region and lands between the gate and drain.When compared to a similar size HEMT device with a conventional field plate（CFP） structure,the AFP not only minimizes the parasitic gate to source capacitance,but also exhibits higher OFF-state breakdown voltage and one order of magnitude lower drain leakage current.In a device with a gate to drain distance of 6 μm and a gate length of 0.8 μm,three times higher forward blocking voltage of 375 V was obtained at VGS =-5 V.In contrast,a similar sized HEMT with a CFP can only achieve a breakdown voltage no higher than 125 V using this process,regardless of device dimensions.Moreover,a temperature coefficient of 0 V/K for the breakdown voltage is observed.However,devices without a field plate（no FP） and with an optimized conventional field plate（CFP） exhibit breakdown voltage temperature coefficients of-0.113 V/K and-0.065 V/K,respectively.

Temperature coefficient of seawater pH as a function of temperature,pH,DIC and salinity

pH is a measure of the hydrogen ion activity in a solution,which is a function of temperature.Under normal seawater conditions,it is well constrained.Nowadays,with an increasing interest in complex environments(e.g.,sea ice),a better understanding of the temperature change on pH under extreme conditions is needed.The objective of this paper was to investigate the temperature coefficient of the seawater pH(△pH/△T)over a wide range of temperature,pH,dissolved inorganic carbon(DIC)and salinity by a method of continuous pH measurement with the temperature change,and to verify the application of CO2SYS for pH conversion under extreme conditions(on the National Bureau of Standards(NBS)scale and the total proton scale).Both experimental results and CO2SYS calculations showed that△pH/△T was slightly affected by temperature over the range of 0℃ to 40℃ and by pH(at 25℃)from 7.8 to 8.5.However,when pH was out of this range,△pH/△T varied greatly with pH value.According to the experimental results,changes in DIC from 1 mmol/kg to 5 mmol/kg and salinity from 20 to 105 had no significant effect on△pH/△T.CO2SYS calculations showed a slight increase in△pH/△T with DIC on both the NBS scale and the total proton scale;and underestimated△pH/△T at high salinity(i.e.,beyond the oceanographic range)on the NBS scale.Nevertheless,CO2SYS is still suitable for pH conversion even under extreme conditions by simply setting the input values of DIC and salinity in CO2SYS within the oceanographic range(e.g.,DIC=2 mmol/kg and S=35).

Investigation of the Effect of Temperature Coefficients on Mono-Crystalline Silicon PV Module Installed in Kumasi, Ghana

The performance of solar PV modules is significantly affected by temperature. This paper focuses on the determination of the effect of temperature on a commercial mono-crystalline silicon PV module whose temperature coefficients were not provided by the manufacturer for installation in Kumasi, Ghana, Sub-Saharan Africa (SSA) ambient. In order to determine the effect of temperature on the output characteristics of the module, the temperature coefficients of current, voltage and power were determined. First of all, the module was cooled to a temperature between 10°C - 15°C in a cooling chamber, covered with cardboard paper before the outdoor electrical tests using Daystar I-V Curve tracer. The results show that as temperature increases, irradiance decreases significantly leading to a decrease in output power (Pmax). The open circuit voltage (Voc) also decreases, whilst short circuit current (Isc) increases slightly. The temperature coefficients were obtained from the slopes of the plots of temperature against Pmax, Isc and Voc. The slopes were used to determine how the respective output characteristics are affected as the module’s temperature rises. The temperature coefficients for power, voltage and current were obtained from the slopes of the graphs using the IVPC software and found to be −0.313 W/°C, −0.11 V/°C and 0.004 A/°C respectively. The results indicate that output power is a decreasing function of temperature (that is power decreases when temperature increases). This information will be useful to system developers, manufacturers and investors seeking to procure PV modules for installation in Kumasi, Ghana. The temperature coefficients of commercial PV modules could be independently verified using the technique employed in this study. Future work will focus on the long-term effect of temperature on the electrical performance characteristics.

Temperature-Irradiance Matrix and Determination of Temperature Coefficients of a Monocrystalline PV Module

Photovoltaic (PV) modules performance testing and energy rating as described in IEC 61853-1 standard depend on electrical performance parameters (short-circuit current, open-circuit voltage, maximum-power) of PV modules as a function of temperature and irradiance. In this work, in order to precisely determine the effects of temperature on the electrical parameters of a monocrystalline PV module, the temperature controlled, xenon light based solar simulator system with irradiance attenuating masks was used. This solar simulator, according to the IEC 60904-9 standard in terms of spectral match, spatial non-uniformity and temporal instability has A+A+A+ classes which are two times better than the standard requirements for a solar simulator to be used in PV module measurements. Moreover, the thermal chamber used in this work is a closed type chamber with fast opening door for not allowing the distortion of temperature uniformity over the surface of PV modules under test. Within about 2 m × 2 m area within 15°C to 75°C temperature interval, the temperature uniformity obtained for this system is less than 1.0°C which is almost two times better than the IEC 60891 standard requirements (±2.0°C). The temperature and irradiance dependent measurements of the electrical performance parameters of a mono-crystalline PV module at various irradiance levels and the evaluation of its temperature coefficients [α (% °C-1), β (% °C-1) and δ (% °C-1)] were done by implementing the interpolation method described in IEC 60891 standard.

Improvement of the electrical resistivity of epoxy resin at elevated temperature by adding a positive temperature coefficient BaTiO3-based compound

The DC electrical resistivity-temperature characteristic is an important property for insulating materials to operate at a high stress level.In order to improve the DC electrical resistivity at elevated temperature in a targeted way,a positive temperature coefficient(PTC)material(Ba Ti O3-based compound(BT60))was selected as the filler in this paper,whose electrical resistivity has a PTC effect when the temperature exceeds its Curie temperature.The BT60 was treated with hydrogen peroxide and(3-Aminopropyl)triethoxysilane.Epoxy composites with different loadings of BT60 fillers(0 wt%,0.5 wt%,and 2 wt%of epoxy)were prepared,denoted as EP-0,EP-0.5,and EP-2.It was shown that BT60 was able to maintain the DC breakdown strength when its loading was less than 2 wt%of epoxy.As the temperature exceeds 60°C,BT60 will compensate for the negative temperature coefficient effect of epoxy resin to some extent.The electrical resistivity of EP-2 was improved by 55%compared with that of neat epoxy at 90°C.It was found that the potential barrier at the grain boundary of BT60 and the deep traps in the interface between BT60 and the epoxy resin hinder the migration of carriers and thus increase the electrical resistivity of epoxy composite.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 type thin film chip resistors when the deposition time was about 11 min and deposition films were annealed at 500 ℃ for 120 min.The morphologies of Cr-Si-TaAl film surfaces were examined by scanning electron microscopy(SEM).The analysis suggests that Ta and Al may be distributed in CrSi2 film with mixed form of several structures(e.g.,bridge-like,capillary-like or island-like structures),and such a structure distribution is responsible for high film resistance and low TCR of Cr-Si-Ta-Al film.

Influence of 235U enrichment on the moderator temperature coefficient of reactivity in a graphite-moderated molten salt reactor

To optimize the temperature coefficient of reactivity(TCR)for a graphite-moderated and liquid-fueled molten salt reactor,the effects of fuel salt composition on the fuel salt temperature coefficient of reactivity(FSTC)were investigated in our earlier work.In this study,we aim to provide a more comprehensive analysis of the TCR by considering the effects of the graphite-moderator temperature coefficient of reactivity(MTC).The effects of^235U enrichment and heavy metal(HM)proportion in the salt mixture on the MTC are investigated from the perspective of the six-factor formula based on a full-core model.For the MTC(labeled“αTM”),the temperature coefficient of the fast fission factors(αTM(ε))is positive,while those of the resonance escape probability(αTM(p)),the thermal reproduction factor(αTM(η)),the thermal utilization factor(αTM(f)),and the total non-leakage probability(αTM(A))are negative.The results reveal that the magnitudes ofαTM(ε)andαTM(p)for the MTC are similar.Thus,variations in the MTC with^235U enrichment for different HM proportions are mainly dependent onαTM(η),αTM(A),andαTM(f),but especially on the former two.To obtain a more negative MTC,a lower HM proportion and/or a lower 235U enrichment is recommended.Together with our previous studies on the FSTC,a relatively soft neutron spectrum could strengthen the TCR with a sufficiently negative MTC.

A novel Na_(1−x)K_(x)TaO_(3)perovskite microwave dielectric ceramic with high permittivity and high positive temperature coefficient

A novel Na_(1−x)K_(x)TaO_(3)(x=0,0.025,0.05,0.075,0.1,and 0.15)ceramic with high permittivity and high positive temperature coefficient was synthesized via the conventional solid-state method.All samples were determined to be pure phase orthorhombic NaTaO3 structure of space group Pmcn,and larger grain and lower porosity were observed after adding an appropriate amount of K+ions.The Q×f value is majored by the packing fraction and grain size,while the value ofτf is influenced by Ta–O bond valence.The Na_(0.95)K_(0.05)TaO_(3) ceramic possesses excellent dielectric properties ofεr=164.29,Q×f=9091 GHz(f=3.15 GHz),tanδ=3.46×10^(–4),τf=+809.52 ppm/℃,sintered at 1550℃.Compared with NaTaO_(3) ceramics,the Na_(1−x)K_(x)TaO_(3)ceramics prepared in this study demonstrate higher dielectric constants and higher positive temperature coefficients,which are promising for device miniaturization andτf compensators.

Temperature-insensitive reading of a flash memory cell

The temperature characteristics of the read current of the NOR embedded flash memory with a 1.5T-per-cell structure are theoretically analyzed and experimentally verified.We verify that for a cell programmed with a“10”state,the read current is either increasing,decreasing,or invariable with the temperature,essentially depending on the reading overdrive voltage of the selected bitcell,or its programming strength.By precisely controlling the programming strength and thus manipulating its temperature coefficient,we propose a new setting method for the reference cells that programs each of reference cells to a charge state with a temperature coefficient closely tracking tail data cells,thereby solving the current coefficient mismatch and improving the read window.

Temperature coefficients of grain boundary resistance variations in a ZnO/p-Si heterojunction

Heteroepitaxial undoped ZnO films were grown on Si （100） substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃ （Sample 1, S1） and 02-800℃ （Sample 2, S2） for 1 h, respectively. The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S 1 were positive （positive temperature coefficients, PTC） while that of both the as-grown sample and S2 were negative （negative temperature coefficients, NTC）. Second, the I-V properties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S 1 had double Schottky barrier behaviors, which were in contradiction with the ideal p-n heterojunction model. Combined with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary. This resulted in adjustment electrical properties ofZnO/p-Si heterojunction that may be suitable in various applications.

Fabrication of nano-grained negative temperature coefficient thermistors with high electrical stability

Dense nano-grained Ni_(0.7)Mn_(2.3O4) negative temperature coefficient(NTC) thermistors were fabricated by a novel two-step sintering approach that combines rapid sintering and principle of conventional two-step sintering technique.Samples were sintered at 1042℃ for 30 s in the first rapid step and then at 850-950℃ for 20 h in the second soaking step.Crystal phase,microstructure and electrical properties of sintered samples were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),resistance temperature relationship and aging performance.Sintered samples show a single-phase cubic spinel structure and indicate a high relative density ranging from 84% to 91% of the theoretical density.Moreover,average grain sizes of sintered samples under SEM are distributed between 254 and 570 nm.Meanwhile,the resistivity and the aging coefficient significantly decrease when soaking sintering temperature rises.In addition,the obtained material constant(B) ranges from 3931 to 3981 K.Ni_(0.7)Mn_(2.3)O_(4)-3(soaking at 900℃) and Ni_(0.7)Mn_(2.3O4)-4(soaking at 950℃) present little aging behavior,implying great electrical stability.