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.

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.

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.

Resistivity-temperature Characteristics of Conductive Asphalt Concrete

The changes of resistivity of conductive asphalt concrete at different temperatures were studied,and positive temperature coefficient（PTC）modelwas established to estimate the influence of temperature on the resistivity quantitatively,which eliminated the interference with conductivity evaluation brought by temperature variation.Finally,the analysis of temperature cycling test results proves that the changes of percolation network structure caused by temperature variation prompt the emergence of PTC of conductive asphalt concrete.

Investigation on the Novel High-performance Copper/Graphene Composite Conductor for High Power Density Motor

High-performance Cu/Graphene composite wire synergistically strengthened by nano Cr_(3)C_(2) phase was directly synthesized via hot press sintering followed by severe cold plastic deformation, using liquid paraffin and CuCr alloy powder as the raw materials. Since graphene is in situ formed under the catalysis of copper powder during the sintering process, the problem that graphene is easy to agglomerate and difficult to disperse uniformly in the copper matrix has been solved. The nano Cr_(3)C_(2)-particles nailed at the interface favor to improve the interface bonding. The Cu/Graphene composite possesses high electrical conductivity, hardness, and plasticity. The composite wire exhibits high electrical conductivity of 96.93% IACS, great tensile strength of 488MPa, and excellent resistance to softening. Even after annealing at 400℃ for 1 h, the tensile strength can still reach 268 MPa with a conductivity of about 99.14% IACS.The wire's temperature coefficient of resistance(TCR) is largely reduced to 0.0035/℃ due to the complex structure,which leads the wire to present low resistivity at higher temperatures. Such Cu/Graphene composite wire with excellent comprehensive performance has a good application prospect in high-power density motors.

Influence of sintering schedule on the electrical properties of Mn(NO_3)_2-doped Ba_(0.92)Ca_(0.08)TiO_3 PTCR ceramics

The relationship of electrical properties of Mn-doped Ba_(0.92)Ca_(0.08)TiO_3PTCR (positive temperature coefficient resistance) ceramics with two sintering schedules wasdiscussed. Using TEM (transmission electron microscope) combined with EDS (energy dispersive X-rayspectrometer), the Mn ions distributed at grain boundaries were analyzed. The results show that thePTCR effect of Mn-doped PTCR ceramics is more dependent on the sintering schedule than those of Mnfree. The phenomenon may be caused by the valence states variance of Mn ions segregated at the grainboundaries.

Mn_(3)Ag_((1-x))Cu_((x))N antiperovskite thin films with ultra-low temperature coefficient of resistance

We demonstrate the first successful attempt to partially substitute Cu into the Mn_(3)AgN-antiperovskite system to form Mn_(3)Ag_((1-x))Cu_((x))N thin films with an ultra-low temperature coefficient of resistance(TCR)for fabrication of ultra-precise passive components.Films were grown by reactive magnetron sputtering on alumina and glass substrates and were found to be amorphous in nature with highly negative TCR of-233 to-351 ppm/℃in their as-grown state.Increasing Cu alloying from x=0 to 1,resulted in increased sheet resistance,a negative shift of TCR and a change of grain morphology from spherical to elongated.Post-deposition heat treatment at 300-375℃,resulted in a positive shift of TCR and an ultra-low TCR of-4.66 ppm/℃for films with x=0.6.The heat treatment induces grain growth,surface roughness and the formation of a manganese oxide upper surface layer up until temperatures of 350℃,after which surface oxidation begins to dominate.The growth rate of the surface layer is controlled by the Cu concentration and heat treatment temperature,which both play a central role in the development of these novel ultralow TCR Mn_(3)Ag_((1-x))Cu_((x))N thin film structures.

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.

La_(0.7)Ca_(0.3)MnO_(3-δ):Ag nanocomposite thin films with large temperature coefficient of resistance(TCR)

In this work, oxygen vacancy-regulated La_(0.7)Ca_(0.3)MnO_(3-δ):Ag (LCMO:A) nanocomposite thin films onLaAlO_(3) (001) substrates were investigated to obtain films with large temperature coefficient of resistance(TCR) values. LCMO:A nanocomposite thin films were synthesized using pulsed laser deposition, andoxygen pressures during film deposition and annealing steps were optimized. As oxygen pressuresincreased, lattice parameter increased from 70 Pa to 100 Pa, Tp increased monotonically from 168 K to282 K, and average Mn^(4+) concentration in the film increased as indicated by X-ray photoemissionspectroscopy data. Record high TCR value of ~37% K^(-1) was achieved in LCMO:A nanocomposite thin filmprepared with optimal oxygen pressures, making this film promising candidate for applications inbolometers.

Highly precise Ti/Pt/Cr/Au thin-film temperature sensor embedded in a microfluidic device

A multilayer(Ti/Pt/Cr/Au)resistive temperature sensor was proposed and investigated to precisely measure the temperature characteristic in microfluidic devices.The Ti/Pt/Cr/Au sensor was fabricated by direct current(DC)sputtering,vacuum evaporation and liftoff process.The thermal annealing test was conducted in the temperature range of 200-800℃for obtaining an appropriate property of the multilayer.Based on the experimental results,400℃was selected as the experimental annealing temperature for the Ti/Pt/Cr/Au layer.The redistribution of structural imperfections and recrystallization promote the density and adhesion of multilayer during the annealing process.With the annealing temperature rising,the annealing process leads to through-thickness migration of chromium and partial depletion of the adhesive layer.The Ti also diffuses into the Pt,which makes the interface disappear.Nevertheless,the layer remains continuous.The temperature coefficient of resistance(TCR)of the sensors was investigated through the microfluidic testing system.The excellent stability and sensitivity of the Ti/Pt/Cr/Au thin-film temperature sensor are verified.Furthermore,the capability of the Ti/Pt/Cr/Au thin-film temperature sensor detecting the sudden temperature change caused by bubble effect is very meaningful to the microfluidic devices.

Influences of Film Thickness on the Electrical Properties of TaN_x Thin Films Deposited by Reactive DC Magnetron Sputtering

TaNx thin films were deposited on commercial polished Al2O3 ceramic substrates by reactive dc magnetron sputtering. The influences of the film thickness on the electrical properties of the samples were examined in detail. It is found that the film thickness does not influence the phase structures of the TaNx thin films. The sheet resistances of the samples shift from 173 Ω/sq. to 7.5 Ω/sq. with the film thickness shifting from 30 nm to 280 nm. With the increase of the film thickness from 30 nm to 280 nm, the temperature coefficient of resistance （TCR） of the samples shifts from negative value to positive value. When the film thickness is about 100 nm, TaNx thin films exhibits a near-zero TCR value （approximately -15×10^-6/℃）. This fact implies that TaNx thin films with a null TCR can be obtained by adjusting the film thickness. The variation in the electrical properties of the TaNx thin films with the film thickness can be qualitatively explained by the parallel connection of surface layer with high resistivity and negative TCR and TaNx layer with low resistivity and positive TCR.

The TCR of Ni24.9Cr72.5Si2.6 thin films deposited by DC and RF magnetron sputtering

The temperature coefficient of resistance（abbreviated as TCR） of thin film resistors on some sensor chips,such as thermal converters,should be less than several ppm/℃.However,the TCR of reported thin films is larger than 5 ppm/℃.In this paper,Ni（24.9）Cr（72.5）Si（2.6） films are deposited on silicon dioxide film by DC and RF magnetron sputtering.Then as-deposited films are annealed at 450 ℃ under different durations in N2 atmosphere.The sheet resistance of thin films with various thickness and annealing time are measured by the four probe resistivity test system at temperature of 20,50,100,150,and 200 ℃ and then the TCR of thin films are calculated.Experimental results show that the film with the TCR of only-0.86 ppm/℃ can be achieved by RF magnetron sputtering and appropriate annealing conditions.

Evaluation of structure,dielectric and electrical properties of(Li/Ta/Sb)modified(Na,K)NbO_(3) lead-free ceramics with excess Na concentration

Polycrystalline perovskite structured Li_(0.04)(Na_(0.54+x) K_(0.46))_(0.96)(Nb_(0.81)Ta_(0.15)Sb_(0.04))O_(3) ceramics with x¼0:00,0.005 and 0.01 mole excess Na concentration were prepared by solid state sintering method.The present study relates the role of excess Na addition with the stoichiometry,density,structure,dielectric and ferroelectric properties of the samples.X-ray diffraction(XRD)pattern exhibits single phase orthorhombic structure.The characteristic Raman modes were observed due to translational modes of cations and vibrational modes of NbO_(6) octahedra and no structural phase transition were observed.This confirms the formation of single phase perovskite structure and is consistent with XRD results.The dielectric permittivity increases about two times,while dielectric loss decreases by four times for χ=0.01 composition.The electrical measurements carried by Complex Impedance spectroscopic analysis suggest negative temperature coefficient of resistance(NTCR)behavior.

Dielectric relaxation and modulus spectroscopy analysis of(Na_(0.47)K_(0.47)Li_(0.06))NbO_(3) ceramics

We have investigated the structure,dielectric and electrical properties of lead-free polycrystalline (Na_(0.47)K_(0.47)Li_(0.06))NbO_(3) ceramics as a function of temperature and frequency in order to understand the intrinsic contribution of grain/bulk and grain boundary effects toward the dielectric response as well as the electrical conduction mechanism in the samples fabricated by microwave sintering method.X-ray diffraction analysis exhibits perovskite structure with orthorhombic symmetry,which is well supported by the Raman spectroscopic analysis.A minor secondary impurity phase of tungsten bronze structure was observed for samples sintered at 1050℃,which gets weaker for samples sintered at 1150℃.Dielectric permittivity was enhanced by 50%,although there was a reduction in the dielectric loss by about 50%at Curie temperature(450℃)for samples sintered at 1150℃.Complex impedance spectroscopic analysis indicated non-Debye-type dielectric relaxation present in the samples,and this phenomenon followed thermally activated process related to hopping mechanism.Nyquist plot showed the negative temperature coefficient of resistance,characteristic of the samples.