Thin resistive film with temperature coefficient of resistance close to zero

A new structure of a thin resistive film based on NiCr with a temperature coefficient of resistance (TCR) close to zero is described. The resistor is formed from two nitrogen-doped NiCr films with a sputtered aluminium film between them. This structure, deposited on glass or alumina substrates, has a sheet resistance of 100 Ω, a TCR value less than ±10×10⁻⁶K⁻¹, low tracking of the TCR on the individual substrates and high long-term stability of the sheet resistance. The deposition process is characterized by high reproducibility of electrical properties. The surface and bulk chemical composition of the films have been monitored by secondary ion mass spectrometry and electron spectroscopy for chemical analysis.     

Electrical resistance drift of molybdenum silicide thin film temperature sensors

For a thermometer to be of practical use, its accuracy of temperature indication must be within a tolerable range. In this paper, patterned molybdenum disilicide (MoSi₂) thin film temperature sensors were fabricated to study their thermoresistance, i.e. resistance vs. temperature (R-T) characteristics. The R-T characteristic of MoSi₂ thin films exhibits a positive deviation from linearity (termed “superlinearity”) instead of showing a simple linearity as for most metals. This superlinear behavior was attributed to thermal expansion and the consequent decrease in the Debye characteristic temperature of MoSi₂. For long-term duration at elevated temperatures, the variation in thickness and composition of the sensor film due to oxidation and other factors may produce drift in the electrical resistance. In this study, the electrical resistance drifts of the sensors as a function of time at temperatures of 1200, 1300 and 1350 °C are presented. For the sensor film tested at 1300 °C, the resistance drift due to the thickness change of the sensor layer was well corrected with the help of an analysis of the oxidation rate of the sensor material. On the other hand, the in-depth composition profile analyzed by Auger electron spectroscopy (AES) indicated no significant composition variation, implying that we could neglect the correction factor for the composition variation in the present study. After the thickness factor was corrected for, a minor drift was still observed; this was also found for the same sensor film tested in an Ar ambient. The exact source of the minor drift is not well understood; further investigations are required.     

The thermoelectric power and the temperature coefficient of resistance of thin polycrystalline antimony films

Starting from the Mayadas-Shatzkes equations for the conductivity of a metal film, the temperature coefficient of resistivity and the thermoelectric power for polycrystalline semi-metal films were calculated.From the data obtained for various grain sizes D in the range 200–2000 Å, the concentrations n of electrons and p of holes, as well as the respective mobilities μ_n and μ_p, were determined without assuming n = p. Good agreement was found between experimental results and the theoretical equations we proposed.     

Absolute thermoelectric power and temperature coefficient of resistance of thin continuous metal films

General expressions are derived in terms of a function F(K), which is equal to the ratio of film to bulk conductivity, for the following: the ratio of film to bulk resistivity, the absolute thermoelectric power of the film material and the ratio of film to bulk temperature coefficient of resistance. The exact and approximate forms of the function F(K) for various theories of the scattering mechanism at the film surfaces are reported. Also plots of the derived expressions using some of these forms are given.     

薄膜低温热膨胀系数测量方法研究

热膨胀系数是材料在低温应用中最重要的力参数之一,薄膜材料的许多性质与其同种块材差别较大.针对预应力大小对测试结果的可能影响,提出了两种薄膜低温热膨胀系数的测量方法,直接测量法和间接测量法.测试温度范围为室温至77 K,可以进行施加不同预应力和在更低温度下进行测量.     

The effect of linear thermal expansion on the temperature coefficient of resistance of double-layer thin metallic films

A general theoretical expression for the temperature coefficient of resistance of double-layer thin metallic films, based on the well known Fuchs-Sondheimer model, is derived. This expression includes the linear thermal expansion coefficients and Poisson's ratios of the double layers and the substrate, also the film dimensions and temperature coefficient of resistance of the double-layer thin film, with and without the thermal expansion of both the film layers and the substrate. Numerical calculations are carried out for gold-silver double-layer films deposited on a glass substrate, where variations in the temperature coefficient of resistance depending on thermal expansion are studied as a function of reduced film thickness. The computed numerical results, using the derived new expression for the temperature coefficient of resistance of the double-layer thin metallic films, show that the thermal expansion decreases the value of the temperature coefficient of resistance.     

Wide temperature range negative temperature coefficient thermistor of a Y2O3 modified LaMnO3 bilayer thin film

Journal of Materials Science: Materials in Electronics - A bilayer architecture was established to modify the negative temperature coefficient (NTC) properties of LaMnO3 thin films. By...     

The Poole-Frenkel conduction mechanismin Mo-Cu2O-Au thin film structures

Thin films of cuprous oxide (4.6 μm) were electrodeposited on molybdenum. Gold contacts were vacuum evaporated on the films to form devices. These films showed relatively low electrical resistivities at around 10⁶ Ω cm and a charge transport mechanism which is different from the space charge limited current conduction previously reported for the 10¹¹ Ω cm films. The charge transport mechanism in these films was determined by isothermal measurements of the devices current-voltage (I–V) characteristics at some selected temperatures in the range of 78–321 K. In this temperature range the dominant transport mechanism can be explained by the Poole-Frenkel effect through the relation I = VG₀exp(−φ_0L/kT)exp(B_LV^1/2)+I₀exp(−φ_0H/kT)exp(B_HV^1/2) where the numerical values of the parameters are measured. φ_0L = 0.12 eV is the zero-field ionization energy of a shallow acceptor-type level (measured from the edge of the valence band) which has the dominant effect in the range of 78–230 K. Similarly φ_0H = 0.70 eV corresponds to a deep level dominant in the high-temperature range 230–321 K. In the high-temperature region a 2.7 μm thick hole accumulation layer forms beneath the oxide-gold interface, assuming the ionized deep level is doubly charged. This revised version was published online in July 2006 with corrections to the Cover Date.     

Unconventional thin film IV–VI photodiode structures

An account is given of IV–VI photodiode structures that are designed to exploit the unique properties of thin films. These devices include the low capacitance pinched-off photodiode and the photo field-effect transistor (which make use of the proximity of the depletion region to an insulating substrate), the lateral-collection photodiode (which uses confinement of photogenerated carriers) and a range of devices that use optical interference to modify the spectral quantum efficiency.     

The use of novel PtSi thin film structures in preferential sputtering measurements

The yields of silicon and platinum from the argon sputtering of PtSi films were measured by Rutherford backscattering techniques. Novel thin film structures of Al₂O₃ (substrate)/W/PtSi were employed to facilitate the measurements. Before steady state was reached, more silicon than platinum was sputtered off, in good agreement with platinum enrichment measurements in the sputtered samples. At steady state the silicon and platinum sputtering yields were equal.     

Nondestructive low-cycle fatigue characterization of multi-layer thin film structures

A multi-layered thin film structure (namely, electrodeposited Cu/sputtered Cr/Kapton substrate/sputtered Cr/electrodeposited Cu), utilized as a flexible component for computers, has been exposed to fatigue. Although a standardized testing method for fatigue ductility is available for a solid monolayer of electrodeposited foil, there is no method available for examining such a multi-layered thin film structure. In this study, four different methods were employed to characterize the low-cycle fatigue damage: (1) DC resistance measurement, (2) residual stress development by x-ray diffraction, (3) dislocation density calculation by using obtained x-ray diffraction line profiles, and (4) microscopic observations. Low-cycle fatigue was conducted at eight levels of applied total strain, i.e., _T =13.95%, 7.69%, 5.83%, 4.69%, 3.37%, 2.37%, 1.59%, and 1.19%. The number of fatigue cycles, when the crack was first observed on the outer Cu layer, was identical to that observed with the onset of increased resistance. This cycle number is thus designated as the number of cycles-to-fatigue crack initiation,N _c . AtN _c , the residual stresses also show a noticeable relaxation, and the dislocation density shows a remarkable increase. IfN _c is plotted against the applied total strain amplitudes, a Manson-Coffin's relationship is obtained with an exponent of 0.39. It is recommended that monitoring the continuous changes in DC resistance could provide a reliable nondestructive evaluation of low-cycle fatigue life of a multi-layered thin film structure.     

Finite element analysis of piezoelectric thin film membrane structures

Thin film structures have found a wide variety of applications in electromechanical technologies. As the design flexibility for these structures increases, so does the demand for design software that can provide some good insights into the behavior of the structure before it is fabricated. In this study, a finite element code based on a combination of equivalent single-plate theory and classical laminated plate theory was used to predict the dynamic response of thin film structures in micro length scale. As a benchmark for the code development, thin film structures were also fabricated using MEMS technology, and their fundamental frequencies were characterized. It was demonstrated that the model predictions matched fairly well with the experimental data for the small membranes with widths less than 200 microm, but underestimated them for large ones with widths greater than 500 microm. The model also demonstrated that the fundamental frequencies increased with the thickness of the layers. The areas that need to be investigated further in order to improve the predicative capability of the calculations include effects of residual stress, dc bias voltage, parasitic capacitance, interaction of membrane vibration with the supports of the structure, and accurate measurement of the dimensions and material properties of the thin films.     

The equivalent coefficient of thermal activity of floors

The heat transfer process between a human foot and a floor is examined. It is shown that the parameter determining the insulating quality of the floor is the equivalent coefficient of thermal activity. A method is given for determining this coefficient.     

Photostimulated polarization and depolarization in metal-GaSe-metal thin film structures

The processes of photostimulated polarization and photostimulated depolarization were discovered in metal-GaSe-metal thin film systems and investigated in detail. The peaks corresponding to the levels of 0.20, 0.40 and 0.62 eV measured from the valence band of GaSe films were observed in the spectral curves of the photodepolarization currents. The value of the forbidden gap is found to be 2.02 eV. The experimental dependence of polarization on an external electric field and on the polarization time were studied.     

Modifications in thin film structures by swift heavy ions

We review older and more recent work concerning modification of thin films during irradiation with heavy ions in the electronic energy deposition regime: loss of H₂ and N₂ from the bulk of several thin film materials, electronic sputtering of SiO₂ and oxygen diffusion across an interface in SiO₂.     

氧化钆掺杂纳米氧化铈薄膜的制备与烧结性能研究

以Ce(NO3)3·6H2O和Gd2O3为前驱体,六亚甲基四胺为沉淀剂,通过均相沉淀反应直接合成能长时间稳定悬浮的氧化钆掺杂纳米氧化铈(Ce0.8Gd0.2O1.9,GDC)母液.对合成的前驱粉体进行了XRD、BET、动态光散射等研究,XRD结果表明粉体具有氧化铈的立方萤石结构特征峰,BET结果表明粉体比表面积为68.3m2/g,当量粒径为约12nm,非等温烧结实验结果表明粉体具有良好的烧结活性.用浸渍-提拉法(dip-coating)在多孔NiO-YSZ阳极基底上制备GDC电解质薄膜,并利用场发射扫描电镜对薄膜的烧结行为进行了研究,薄膜在1300℃等温烧结后实现完全致密化.通过薄膜制备过程中制浆与成膜两个步骤的有机结合,探讨一条制备高性能GDC电解质薄膜的新途径.