Structural and electrical properties of evaporated Cr-Ni films as a function of gas pressure

Electrical measurements of 60 Cr-40 Ni films evaporated in UHV or at a definite partial pressure of N₂ and He showed that all continuous films have a positive temperature coefficient of resistivity (TCR). The electron diffraction pattern of these films could be indexed tetragonal (c/a=1.36; a=5.2 Å). Chromium was precipitated after annealing the films for 6 h at 300 °C in UHV.On evaporating Cr-Ni films at an oxygen partial pressure of 1 x 10^-6 torr the TCR became negative. The films had a structure corresponding to a distorted b.c.c. Cr lattice, which did not change even after annealing for several hours at 300 °C. This is given as a reason for the better electrical stability of these films. Possible explanations for the negative TCR of films evaporated in the presence of oxygen are also discussed.     

The ohmic stability and low temperature coefficient of resistance of Cu-Ni/Au-Ni multilayers obtained in ultrahigh vacuum by controlled co-evaporation

For compositions around 43 at.% Ni, thin films of CuNi alloys more than 1200 Å thick deposited in ultrahigh vacuum (UHV) onto a fused silica substrate by controlled co-evaporation from two separate copper and nickel sources show low negative temperature coefficients of resistance (TCRs) (-10^-4 to -10^-6 °C^-1) and a satisfactorily high stability in the temperature range 20–300 °C in UHV. In the atmosphere, however, the ohmic behaviour of the films shows hysteresis and appreciable instability due to oxidation.Thin Au-Ni films (38 at.% Ni) have a higher positive TCR (+2 × 10^-4 °C^-1) but they have the advantage of being less oxidized in atmospheric air up to 150 °C.In order to obtain unoxidizable multilayers with a low TCR we prepared CuNi films 1300 Å thick and stabilized them by annealing. AuNi films 200 Å thick were then deposited onto the CuNi films by controlled co-evaporation.After the annealing process the TCR was about -3 × 10^-6 °C^-1 from 20 to 150 °C. The ohmic stability tested from 20 to 150 °C in nitrogen and then in the atmosphere showed no appreciable zero balance drift or ohmic instability.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Properties of TiNxfilms reactively sputtered in an argon-nitrogen atmosphere

The dependence of the resistivity and temperature coefficient of resistivity (TCR) of TiN_x films on nitrogen pressure is described. The partial nitrogen pressure was varied from 10^?5 Torr to 2×10^?4 Torr. The maximum value of the resistivity (216 μΩ cm) and the lowest negative value of TCR (?33ppmK^?1) were obtained in the nitrogen pressure range (2?4)×10^?5 Torr. The minimum value of the resistivity (44 μΩ cm) and the highest positive value of the TCR (1160 ppm K^-1 were obtained in the nitrogen pressure range (4?10)×10^?5 Torr. The influence of aging temperature up to 573 K on the resistance changes are shown. X-ray diffraction analysis indicated the presence of oriented or non-oriented TiN in these films.     

Surface morphological investigation of iron films during oxidation

Different stages of iron films evaporated under a vacuum of about 10⁻⁵ torr were investigated with and without the addition of aluminium impurity at different percentages. Micrographs of such films heated at 623 K for 2 h show similar network spreading of oxide growth. Addition of aluminium significantly improves the oxidation resistance of iron films by the formation of Al₂O₃ layer.     

On the growth of cuprous oxide films

{lcub;001}rcub; cuprous oxide (Cu₂O) films were epitaxially grown. From the two methods which were used (the oxidation of copper films and the direct evaporation of bulk Cu₂O) only the oxidation of copper yielded good single-crystal films. It was found that the optimum conditions were an oxidation temperature of 450°C with a partial pressure of oxygen of 2×10^-5 Torr and, after oxidation, a further annealing at a pressure of 10^-8 Torr.     

Negative capacitance of native oxide films on (0001) InSe fracture surfaces

A negative capacitance has been found at low frequencies (1 × 10⁵ to 3.7 × 10⁷ Hz) in native oxide films grown in air on InSe(0001) fracture surfaces. The films have the form of a dielectric Se₂O₅ matrix containing indium metal nanoinclusions. Resistivity and capacitance measurements at frequencies from 100 Hz to 37 MHz have been used to study the polarization mechanisms for the native oxide films in In/native oxide/InSe structures. The results indicate that a negative capacitance (inductive impedance) of native oxide films may be due to carrier capture at traps located at the many metal—dielectric interfaces.     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

Annealing effect on the structural,electrical and 1/f noise properties of Mn–Co–Ni–O thin films

Thin films of Mn_1.4Co_1.0Ni_0.6O₄ (MCN) spinel oxide are grown by radio frequency (RF) magnetron sputtering method on amorphous Al₂O₃ substrate. We investigate the annealing effect on the micro structural and electrical properties of RF sputtered MCN films. It is found that the crystallinity of MCN film is improved with increasing annealing time at 750 °C, and the annealed films present excellent cubic spinel (220) preferred orientation in X-ray diffraction patterns. Comparing to as-sputtered thin film, the annealed films show a decrease of 60 to 70 % in resistivity at 300 K. The annealed samples with post annealing time longer than 18 min acquire a negative temperature coefficient of resistance of about ?3.73 %K^?1 and resistivity of about 210–220 Ω cm at 300 K. 1/f noise of MCN films are also studied and the Hooge’s parameters (γ/n) are calculated. After annealing for 18 to 90 min, the γ/n values of the films are on the order of 10^?21 cm³, which ranks about two orders lower than that of amorphous silicon.     

Effect of annealing time on the structural,optical and electrical characteristics of DC sputtered ITO thin films

Using an Indium tin oxide (ITO) ceramic target (In₂O₃:SnO₂, 90:10 wt%), ITO thin films were deposited by conventional direct current magnetron sputtering technique onto glass substrates at room temperature. The obtained ITO films were annealed at 400 °C for different annealing times (1, 2, 5, 7, and 9 h). The effect of annealing time on their structural, optical and electrical properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM), ultra violet–visible (UV–Vis) spectrometer, and temperature dependence Hall measurements. XRD data of obtained ITO films reveal that the films were polycrystalline with cubic structure and exhibit (222), (400) and (440) crystallographic planes of In₂O₃. AFM and Scanning Electron Microscopy SEM have been used to probe the surface roughness and the morphology of the films. The refractive index (n), thickness and porosity (%) of the films were evaluated from transmittance spectra obtained in the range 350–700 nm by UV–Vis. The optical band gap of ITO film was found to be varying from 3.35 to 3.47 eV with the annealing time. The annealing time dependence of resistivity, carrier concentration, carrier mobility, sheet resistance, and figure of merit values of the films at room temperature were discussed. The carrier concentration of the films increased from 1.21 × 10²⁰ to 1.90 × 10²⁰ cm^?3, the Hall mobility increased from 11.38 to 18 cm² V^?1 s^?1 and electrical resistivity decreased from 3.97 × 10^?3 to 2.13 × 10^?3 Ω cm with the increase of annealing time from 1 to 9 h. Additionally, the temperature dependence of the carrier concentration, and carrier mobility for the as-deposited and 400 °C annealed ITO films for 2 and 9 h were analysed in the temperature range of 80–350 K.     

The electrical resistivity and resistance-temperature characteristics of thin titanium films

In this communication are described the results on the electrical resistivity and resistance-temperature characteristics of titanium films, measured in vacuum. They were evaporated onto soda glass microscope slides at room temperature in a sputter-ion pumped glass belljar vacuum system at about 5×10^-8 torr. The films varied in their thickness from 50 to 1100 Å, and the resistivity was very high for the thinnest films but for the thickest ones it approached approximately double the bulk value. The measured resistivities for the continuous freshly prepared films are too high to be explained on the basis of the Fuchs-Sondheimer theory^{1, 2} for diffuse scattering, and are attributed to porosity and the gaseous impurities taken down during and after their formation. The temperature coefficient of resistance (TCR) was negative for films less than 50–60 Å thick but positive for thicker ones. A bulk mean free path of 285 Å in titanium was calculated at room temperature.     

Subject index

Transparent conducting films of cadmium-tin oxide were prepared by d.c. reactive sputtering from a CdSn alloy target in an ArO₂ atmosphere. The electrical and optical properties of the films were found to depend on the oxygen concentration in the gas mixture. The lowest resistivity obtained was 4 × 10^?4 Ω cm and the average optical transmission was 90% over the visible region. The structure of the films was examined by X-ray diffraction. The thick films exhibited CdSnO₃ (200) or Cd₂SnO₄ (001) and (130) peaks but most of the thin films were amorphous. The post-deposition annealing of the films in an argon atmosphere affected their electrical and optical properties.     

Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Back-scattering investigation of the low temperature stability of the aluminum-silver system

The large angle elastic scattering of 2.9 MeV ⁴He₂ has been used to investigate the Al-Ag system. This system has important optical applications and affords an opportunity to study directly chemical kinetics. Heretofore, only indirect measurements of the system have been made. The samples consisted of thick Si substrates covered by a 5000 Å thermal SiO₂ layer. Then 2000 Å Al and 3000 Å Ag films were deposited in both sequences without raising the system vacuum above 2 × 10^-5 torr. The back-scattering measurements were performed after each step of a sequence of isothermal annealing treatments at 135°C for times up to 6 h. This study shows that the Si-SiO₂-Al-Ag system is stable after such a treatment. Thus, for Al first depositions, no intermediate metal is necessary for a diffusion barrier at room temperature. Indirect evidence is presented which suggests that the acting diffusion barrier in the Al first depositions is probably the thin natural aluminum oxide layer expected to be formed for the deposition conditions used. However, the adherence of these films to one another is shown to require further characterization if hifh bonding values are required. By comparison in Ag first depositions, extensive intermixing of the Al and Ag has occurred after as little as 105 min at 135°C. The back-scattering measurement correlated with the previous reflectivity measurements suggest that the interdiffusion of Ag and Al without significant compound formation plays a significant role in at least the initial changes in the reflectivity of thin films of Ag and Al. Finally, this study shows that a 500 Å Cr deposition between the Ag and Al depositions serves as an adequate diffusion barrier after an anneal treatment of 60 min at 300°C.     

Cr-Si-Ni-N电阻薄膜的晶化与氧化特性

在PN2／PAr2分压比分别为0％，2．5％，5％，10％的溅射气氧化中制备了不同氮含量的Cr-Si-Ni-N薄膜，并研究了薄膜在热处理过程中的晶化，氧化行为以及电性能变化。结果表明，非晶Cr-Si-Ni-N薄膜在加热过程中，将析出晶化相CrSi2，随薄膜中氮含量增加，晶化相的形核与长大减缓，然而，薄膜的抗氧化能力得到提高。与低氮含量Cr-Si-Ni-N薄膜相比，高氮含量Cr-Si-Ni-N薄膜的电阻值在热处理过程中变化较小，欲获得较小电阻温度系数（TCR）需要更高的退火温度。     

Effect of silicon ion implantation on the properties of a cast Co–Cr–Mo alloy

The effect of silicon ion implantation upon the corrosion resistance and structure of the cast Co–Cr–Mo alloy of the Vitalium type, was examined. The silicon fluences were 1.5, 3.0 and 4.5 × 10¹⁷Si⁺ cm^-2. The surface layer of the Vitalium samples implanted with these silicon doses was found to become amorphous. Further annealing of the samples at 200 °C resulted in the Cr₃Co₅Si₂ phase being formed, whereas the amorphous layer was preserved. The Vitalium samples submerged in the 0.9% NaCl solution underwent mainly uniform corrosion, irrespective of whether or not they had been implanted with Si⁺ ions. With increasing doses of implanted silicon and after annealing at 200 °C (samples implanted with 1.5 × 10¹⁷Si⁺ cm^-2), the corrosion resistance increased. The thickness of the oxide layer formed during the anodic polarization depended on the implanted silicon doses. This revised version was published online in November 2006 with corrections to the Cover Date.     

High k dielectrics for low temperature electronics

In this work the electrical and structural properties of two high k materials as hafnium oxide (HfO₂) and tantalum oxide (Ta₂O₅) produced at room temperature are exploited. Aiming low temperature processing two techniques were employed: r.f. sputtering and electron beam evaporation.The sputtered HfO₂ films present a nanocrystalline structure when deposited at room temperature. The same does not happen for the evaporated films, which are essentially amorphous. The density and the electrical performance of both sputtered and evaporated films are improved after annealing them at 200 °C. On the other hand, the Ta₂O₅ samples deposited at room temperature are always amorphous, independently of the technique used. The density and electrical performance are not so sensitive to the annealing process. The set of data obtained show that these dielectrics processed at temperatures below 200 °C present promising properties aiming to produce devices at low temperature with improved interface properties and reduced leakage currents.     

Composition, surface morphology and electrical characteristics of Al2O3-TiO2 nanolaminates and AlTiO films on silicon

We propose and demonstrate Metal-Oxide-Semiconductor structures comprising Al₂O₃-TiO₂ nanolaminate and AlTiO films. Composition, structural and electrical characteristics were studied in detail and compared to TiO₂ thin film-based structures. All dielectric films were evaporated using an electron beam gun (EBG) system on unheated p-Si substrate without adding O₂. MOS structures were investigated in detail before and after annealing at up to 950 °C in O₂ and N₂ + O₂ environments. The nanolaminate films remain in an amorphous state after annealing at 950 °C. The smallest quantum mechanical corrected equivalent oxide thickness measured was ∼1.37 nm. A large reduction of the leakage current density to 1.8 × 10^− 8 A/cm² at an electric field of 2 MV/cm was achieved by the annealing process.     

Mass spectrometric determination of oxygen at partial pressures of less than 1.5 μPa (10−8 torr)

During an investigation of chemisorption and photodesorption reactions between oxygen and thin films of zinc oxide, the need arose for the determination of oxygen partial pressures in the range 1 μPa to 100 pPa (10^?8 to 10^?12 torr), in a static system, using a residual gas analyzer. Within this range the pumping actions for various components of the vacuum system were significant and this paper describes these actions and the techniques developed to lower the limit of detection of oxygen by mass spectrometric analysis to about 700 pPa .l (5 × 10^?12 torr .l)     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.