NiCr Films Research Articles

Nickel-chromium (Ni–Cr) coatings deposited by magnetron sputtering for accident tolerant nuclear fuel claddings

Nickel-chromium coatings were deposited on Zr1Nb alloy using magnetron sputtering systems with «hot» Ni and cooled Cr targets. The effect of coating composition on high-temperature oxidation resistance and hydrogen uptake of Zr1Nb was studied. Hydrogen uptake of the alloy was measured in situ under gas-phase hydrogenation at 633 K. High-temperature oxidation was performed in air atmosphere at 1173–1373 K for 20 min. It was shown that the coating with high Ni content (83 at.%) drastically increases hydrogen uptake of the Zr1Nb alloy and demonstrates low oxidation resistance even at 1173 K. The coatings with Cr content ≥45 at.% have low hydrogen permeability which reduces the rate of hydrogen uptake of the alloy. The oxidation resistance of the NiCr coatings increases with Cr content in the as-deposited coatings. The pure Cr coating exhibits the best oxidation resistance: only 8 μm-thick oxide layer was observed. There is also found the intensive diffusion of nickel into the alloy during high-temperature oxidation of the samples coated by NiCr films with 55 and 17 at.% Ni. The as-deposited NiCr coatings are less brittle than the pure Cr coating, but their mechanical properties degrade stronger than for the Cr coating after the oxidation test.

Effect of seed layers and rapid thermal annealing on the temperature coefficient of resistance of Ni[sbnd]Cr thin films

In this research, we studied the integration of radio frequency (RF)-sputtered NiCr resistors to improve the resistor behavior so that the resistance can be independent of temperature, or the temperature coefficient of resistance (TCR). The deposited NiCr (80/20 at.%) films were annealed with or without a seed layer, such as Ti, Cr, and Ni, by rapid thermal annealing (RTA) in the temperature range from 550 °C to 850 °C with 150 °C intervals for 90 s in nitrogen ambient to get obtain films with higher thermal stability. The TCR was dramatically increased after RTA at a higher temperature of 700 °C. The higher RTA temperature showed a larger grain size of the NiCr film and more diffusion of Cr and Ni atoms. The NiCr film deposited on the seed layers showed a lower TCR than that without the seed layer after the RTA process. The TCR values of the 10-nm-thick Cr/100-nm-thick NiCr (top) film were 35.8 ppm/K (at 125 °C) and 56.2 ppm/K (460 °C), respectively, before and after RTA at a temperature of 550 °C for 90 s. This shows the potential of sputtered NiCr film as the resistor for a pressure sensor in CMOS applications considering a back-end-of-line (BEOL) annealing temperature.

Investigation of the Speed of a SINIS Bolometer at a Frequency of 350 GHz

We have measured the time of the optical response of a 350-GHz radiation detector based on a superconductor–insulator–normal metal–insulator–superconductor tunnel structure with a suspended normal-metal bridge integrated into a planar log-periodic antenna. The transient characteristics of the detector were recorded when irradiated by a fast cryogenic blackbody source with a rise time of the order of microseconds. For this purpose, a short intense heating pulse was fed to an emitting NiCr film radiation source with a low heat capacity. The measured response time was 1.8 ± 0.5 μs at a bolometer electron temperature of 0.17 K, with a detection sensitivity of 10–17–10–18 W Hz–1/2 being potentially achievable.

A study on the NiCrMnZr thin film resistors prepared using the magnetron sputtering technique

We prepared two types of thin film, a NiCrMn resistive thin film was prepared using direct current and radio frequency magnetron co-sputtering from Ni0.6Cr0.4 casting alloy and manganese targets. A NiCrMnZr resistive thin film was prepared based on the optimum NiCrMn film composition, which was made using direct current and radio frequency magnetron co-sputtering from NiCrMn casting alloy and zirconium targets. The electrical properties and microstructures of the resistive films under different annealing temperatures were investigated. The results indicated that the NiCr film resistivity can be enhanced by adding manganese. When the annealing temperature was set to 300 °C, the NiCrMn films exhibited a resistivity ~400 μΩ-cm with the smallest temperature coefficient of resistance of −6.6 ppm/°C. For NiCrMnZr films, there are some Ni7Zr2 Nano crystalline phases observed when the annealing temperature was set to 400 °C. However, the NiCrMnZr film annealed at 300 °C still has an amorphous structure by transmission electron microscopy analysis. NiCrMn films with 16.7 at.% Zr exhibited the smallest temperature coefficient of resistance (+53 ppm/°C) with the resistivity ∼510 μΩ-cm after annealing at 300 °C in air.

Study on film resistivity of Energy Conversion Components for MEMS Initiating Explosive Device

Resistivity of Plane-film Energy Conversion Components is a key parameter to influence its resistance and explosive performance, and also it has important relations with the preparation of thin film technology, scale, structure and etc. In order to improve the design of Energy Conversion Components for MEMS Initiating Explosive Device, and reduce the design deviation of Energy Conversion Components in microscale, guarantee the design resistance and ignition performance of MEMS Initiating Explosive Device, this paper theoretically analyzed the influence factors of film resistivity in microscale, through the preparation of Al film and Ni-Cr film at different thickness with micro/nano, then obtain the film resistivity parameter of the typical metal under different thickness, and reveals the effect rule of the scale to the resistivity in microscale, at the same time we obtain the corresponding inflection point data.

Experimental study of a SINIS detector response time at 350 GHz signal frequency

Response time constant of a SINIS bolometer integrated in an annular ring antenna was measured at a bath temperature of 100 mK. Samples comprising superconducting aluminium electrodes and normal-metal Al/Fe strip connected to electrodes via tunnel junctions were fabricated on oxidized Si substrate using shadow evaporation. The bolometer was illuminated by a fast black-body radiation source through a band-pass filter centered at 350 GHz with a passband of 7 GHz. Radiation source is a thin NiCr film on sapphire substrate. For rectangular 10÷100 μs current pulse the radiation front edge was rather sharp due to low thermal capacitance of NiCr film and low thermal conductivity of substrate at temperatures in the range 1-4 K. The rise time of the response was ~1-10 μs. This time presumably is limited by technical reasons: high dynamic resistance of series array of bolometers and capacitance of a long twisted pair wiring from SINIS bolometer to a room-temperature amplifier.

Study of the formation of thermochemical laser-induced periodic surface structures on Cr, Ti, Ni and NiCr films under femtosecond irradiation**Presented at the Fundamentals of Laser Assisted Micro- and Nanotechnologies (FLAMN-16) International Symposium (Pushkin, Leningrad oblast, 27 June to 1 July 2016).

The formation of femtosecond laser-induced periodic surface structures (LIPSS’s) on Cr, Ti, Ni and NiCr films (with different Cr contents) is investigated. It is established that thermochemical LIPSS’s with periods of 950, 930 and 980 nm are formed, respectively, on the surfaces of titanium, chromium, and nichrome (with a chromium content of 20%); however, thermochemical LIPSS’s are not formed on the surfaces of nickel and nichrome with a low chromium content, although Raman data indicate that oxidation occurs in all cases. A weakly ordered ablated structure with a period of 250 – 300 nm is found to be formed on oxidised areas of thermochemical LIPSS’s in the case of chromium and nichrome (80/20). Experimental data on selective etching of thermochemical LIPSS’s on titanium and chromium films are presented.

Improvement in Cr Nanoparticle Content in Ni–Cr Film by Co-deposition with Combined Surfactant HPB and CTAB

The effects of single surfactant hexadecylpyridinium bromide (HPB) and cetyltrimethylammonium bromide (CTAB) and the combination of HPB and CTAB on the Cr nanoparticle content in the Ni–Cr film prepared by co-deposition were investigated. Single HPB/CTAB addition inhibited the oxidation and amorphous transformation of the Cr nanoparticles in the plating bath and effectively stabilized the Cr nanoparticles content at approximately 10 mass% as a function of time. Moreover, the combination of HPB and CTAB formed a cylindrical micelle structure on the Cr nanoparticle surface, which prompted the formation of a layer of NiCr2O4. As a result, the Cr nanoparticle content increased sharply to 20 mass%.

Investigation of percolation thickness of sputter coated thin NiCr films on clear float glass

Percolation thickness of reactively sputtered nickel chromium (NiCr) thin films is reported in this study. Nickel-chromium films with the thicknesses in between 1 and 10nm were deposited on 4mm clear glass substrate by dc magnetron sputtering. Optical properties such as refractive index, extinction coefficient and also sheet resistance, carrier concentration and mobility of NiCr films were determined by a combination of variable-angle spectroscopic ellipsometry and four point probe measurements. We show both the percolation phenomena in atmosphere and critical percolation thickness for thin NiCr films by both electrical and optical techniques. The two techniques gave consistent results with each other.

Capacitively coupled pickup in MCP-based photodetectors using a conductive metallic anode

We have designed and tested a robust 20×20cm2 thin metal film internal anode capacitively coupled to an external array of signal pads or micro-strips for use in fast microchannel plate photodetectors. The internal anode, in this case a 10nm-thick NiCr film deposited on a 96% pure Al2O3 3mm-thick ceramic plate and connected to HV ground, provides the return path for the electron cascade charge. The multi-channel pickup array consists of a printed-circuit card or glass plate with metal signal pickups on one side and the signal ground plane on the other. The pickup can be put in close proximity to the bottom outer surface of the sealed photodetector, with no electrical connections through the photodetector hermetic vacuum package other than a single ground connection to the internal anode. Two pickup patterns were tested using a small commercial MCP-PMT as the signal source: 1) parallel 50Ω 25-cm-long micro-strips with an analog bandwidth of 1.5GHz, and 2) a 20×20cm2 array of 2-dimensional square ‘pads’ with sides of 1.27cm or 2.54cm. The rise-time of the fast input pulse is maintained for both pickup patterns. For the pad pattern, we observe 80% of the directly coupled amplitude. For the strip pattern we measure 34% of the directly coupled amplitude on the central strip of a broadened signal. The physical decoupling of the photodetector from the pickup pattern allows easy customization for different applications while maintaining high analog bandwidth.

Improving the wet chemical patterning of nichrome film by inserting an ultrathin titanium layer

We studied how to improve the quality of nichrome (NiCr) films patterned with wet chemical etching by inserting an ultrathin titanium film. The experimental results showed that inserting a 20-nm Ti layer between the photoresist (PR) and NiCr greatly improved the quality of the resultant pattern, which had minimal undercut and smooth edges. We attributed this improvement to the improved mask/NiCr interface, which we confirmed by scanning electron microscopy (SEM). In addition, we found that the undercutting of NiCr comprised two stages—an initial, relatively slow undercut stage and a second, faster stage—separated by the critical time point, the time at which the unmasked NiCr film etched away completely.

Enhanced thermoelectric property and stability of NiCr–NiSi thin film thermocouple on superalloy substrate

Thin film thermocouples (TFTCs) can provide fast and accurate surface temperature measurement with minimal impact on the physical characteristics of the supporting components. In this study, NiCr and NiSi films were prepared with radio frequency (RF) magnetron sputtering and the influences of vacuum annealing on the resistivity of the films were investigated. Afterward, NiCr–NiSi films were deposited on Ni-based superalloy substrates to form TFTCs. The overall dimension of the thermocouple is 64 mm in length, 8 mm in width and 30 μm in thickness. Compared with those of as-deposited sample, the thermoelectric property and stability of the TFTC are significantly improved by vacuum annealing of NiCr and NiSi films. The variation of the Seebeck coefficient of TFTC was discussed based on the size effect of NiCr and NiSi films. And a lower Seebeck coefficient of TFTC of 38.4 μV·°C−1 is obtained.

Electrical transport properties of nickel chromium alloy films

The effect of the electron–phonon interactions on the electrical transport properties of NiCr alloy films is studied. The resistivity of the NiCr films is measured between 2 and 300 K, and reveals an overall metallic conduction behavior. The resistivity–temperature curves of NiCr films are successfully interpreted using the traditional electron–phonon coupling theory. The results reveal that the electrons coupling with the acoustic-mode phonons dominate the electrical properties of NiCr films over the entire temperature range investigated, and weak corrections by the electron–optical–phonon interactions are present in the high temperature regime. The dominance of the electron–phonon interactions on the transport behavior of NiCr films is further confirmed by the magnetotransport analysis. The electron–phonon interaction constant of NiCr films is also discussed.

Room temperature, very sensitive thermometer using a doubly clamped microelectromechanical beam resonator for bolometer applications

We propose a room temperature, all electrical driving and detecting, very sensitive thermometer structure using a microelectromechanical (MEMS) resonator for bolometer applications. We have fabricated a GaAs doubly clamped MEMS beam resonator whose oscillation can be excited and detected by the piezoelectric effect. When a heating power is applied to a NiCr film deposited on the MEMS beam surface, internal thermal stress is generated in the beam, leading to a reduction in the resonance frequency. The present device detects the shift in the resonance frequency caused by heating and works as a very sensitive thermometer. When the resonator was driven by a voltage slightly below the threshold for the nonlinear, hysteretic oscillation, the thermometer showed a voltage responsivity of about 3300 V/W, while keeping a low noise spectral density of about 60 nV/Hz1/2, demonstrating a noise equivalent power of <20 pW/Hz1/2 even at room temperature. The observed effect can be used for realizing high-sensitivity terahertz bolometers for room-temperature operation.

Phenomenological model for prediction of complex ablation geometries in metal films using ultrashort laser pulses

Ablation of thin metal films with laser pulses having a pulse duration shorter than the electron-phonon relaxation time, so called ultrashort laser pulses, enables melt-free patterning of arbitrary geometries. Ablation with ultrashort laser pulses is an emerging process and is currently used in the field of microelectronics for the repair of photolithography masks and in the photovoltaic industry for patterning of indium tin oxide (ITO). Another current field of investigation is the patterning of thin film strain sensors. In order to achieve the desired ablation quality, a multipulse irradiation is often required. Currently, there is no “simple” model to predict line and more complex ablation geometries created by multipulse irradiation. Within this paper, an incubation threshold is introduced to enhance an existing incubation model, which is restricted to the prediction of point ablations. The resulting phenomenological model is experimentally verified on thin NiCr films using 10 ps laser pulses. The usability of the derived model is significantly higher than other existing models due to concentrating on the relevant criterion for patterning of electronic circuits: the removal threshold as well as an easy to handle procedure to determine the model parameters, which can be determined on a machining setup in industrial conditions.

Microhardness and Adhesion Strength of PMC’s Coatings by NiCr Alloy

The use of polymer matrix composites (PMCs) in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance but their useful lifetime is limited by their poor environmental resistance. Flame sprayed NiCr graded coatings are being investigated as a method to address this technology gap by providing high temperature and environmental protection to polymer matrix composites. In this research coating was spread with two configuration, coating with bound coat and coating without bound coat. In general the coating with bound coat and coating without bound coat showed increase in micro hardness and adhesion with increase curing temperature; this is due to the microstructural changes the physical splat structure of the coating also changes with heat treatment. All coating failed at the interface between the composites and the coating, failure occurs along the weakest plane within the system, some of the coating systems that have presented fracture at the bond coat/top coat interface. The surface topography of NiCr films was further examined by using AFM atomic force microscopy as a function of curing temperature at 100,200 and 300°C for 1 h each, it can be clearly seen that the island structure was observed and the Rmax increase, the surface became rougher with increasing curing temperature. The surface morphology and microstructure of the coating were examined using SEM.

Influence of Reactive Ion Etching on THz Transmission and Reflection Properties of NiCr Film Deposited on a Dielectric Substrate

Enhanced terahertz (THz) absorption of NiCr film deposited on a dielectric substrate has been proven by applying a reactive ion etching (RIE) treatment to the dielectric film. Nano – scale nickel – chromium (NiCr) thin films are deposited on RIE treated silicon dioxide (SiO 2 ) dielectric substrates to study the transmission and reflection characteristics. Experimental results suggest that both transmission and reflection of NiCr film are weakened by the RIE treatment. The most significant decrease of transmission is observed in 1 ~ 4 THz while that of reflection occurs in 1.7 ~ 2.5 THz band. The decrease of both transmission and reflection is more significant for NiCr film with higher thickness. The RIE treatment, which induces nano – scale surface structures and increases the effective surface area of NiCr film, enhances the absorption and weakens the transmission and reflection of THz radiation. DOI: http://dx.doi.org/10.5755/j01.ms.21.2.6131

Study on Optical Properties of Nanostructured NiCr Film Prepared by Magnetron Sputtering and RIE for Terahertz Applications

Nanoscale NiCr thin film has been proven to be an effective metallic terahertz (THz) absorption layer. To prepare NiCr film with a small thickness and enhanced THz absorption, a combined process of magnetron sputtering and reactive ion etching (RIE) is suggested to obtain nanostructured NiCr film with different thicknesses by precise control of process parameters and etch time. Optical characteristics tests show that both transmission and reflection of NiCr film are weakened by the RIE treatment. NiCr absorption layer is prepared in 80 × 60 infrared focal plane arrays (IRFPAs) by a combination of substrate modification process and RIE thinning process. THz absorption is effectively enhanced by RIE processes applied to the dielectric substrate and NiCr film, which generates nanoscale structures on upper and lower surfaces of NiCr absorption film for an increased specific surface area. The noise equivalent power (NEP) of the THz detection unit achieves 162.8 pW/Hz1/2, which is suitable for the application of active THz imaging. The results indicate that nanostructured NiCr film is an effective THz absorption layer for applications in thermal sensing and its absorption performance can be further improved by RIE.

TCR control of Ni–Cr resistive film deposited by DC magnetron sputtering

The temperature coefficient of resistance (TCR) is a major and important characteristic of thin film resistors. In this study, we focus on the dependence of TCR on different Ni–Cr film thickness and different annealing conditions. The electron mean free path (MFP) of Ni–Cr film has been determinate. Field Emission Scanning Electron Microscopy (FE-SEM) has been used in studying the morphology of the Ni–Cr film; X-ray diffraction (XRD) has been similarly employed in studying the transformation of the crystallite phase. The TCR performance is stable as the Ni–Cr film thickness is thicker than the electron MFP, and increases slightly as the annealing temperature increases. The 30 nm thickness of Ni–Cr film was annealed at 300 °C; in this phase, metastable amorphous and crystalline film was formed. We obtained the thin film resistors of low TCR under ±5 ppm/°C at −55 and 125 °C.

Microstructural and mechanical characteristics of Ni–Cr thin films

Ni–Cr alloy thin films have been deposited using magnetron co-sputtering technique at room temperature. Crystal structure was evaluated using GIXRD. Ni–Cr solid solution upto 40at% of Cr exhibited fcc solid solution of Cr in Ni and beyond that it exhibited bcc solid solution of Ni in Cr. X-ray diffraction analysis shows formation of (111) fiber texture in fcc and (220) fiber texture in bcc Ni–Cr thin films. Electron microscopy in both in-plane and transverse direction of the film surface revealed the presence of columnar microstructure for films having Cr upto 40at%. Mechanical properties of the films are evaluated using nanoindentation. The modulus values increased with increase of Crat% till the film is fcc. With further increase in Crat% the modulus values decreased. Ni–Cr film with 20at% Ni exhibits reduction in modulus and is correlated to the poor crystallization of the film as reflected in XRD analysis. The Ni–Cr thin film with 80at% Ni and 20at% Cr exhibited the most distinct columnar structure with highest electrical resistivity, indentation hardness and elastic modulus.