Noise and structural properties of reactively sputtered RuO2 thin films

Ruthenium dioxide thin films were reactively rf sputtered on SiO₂/Si substrates and annealed in the temperature range from 150 to 500 °C. The structural and morphological properties of the films were investigated using Raman spectroscopy, transmission electron microscopy and atomic force microscopy. The increase of grain size was improved with annealing temperature. After annealing at 500 °C, the roughening of the RuO₂/SiO₂ interface was observed. The electrical behaviour was analysed by resistivity, thermal coefficient of resistance and low frequency noise. Good correlation between structural and electrical properties of RuO₂ films was established.     

Ta thin film resistors reactively sputtered onto substrates mounted on a rotating carousel

Ta thin film resistors have been reactively sputtered in 1.5×10^–5 Torr oxygen and 1.5×10^–5 Torr nitrogen simultaneously, using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For non-heat-treated films the resistivity increases and the TCR becomes more negative as the carousel rotation speed increases. These changes in electrical properties are attributed to the observed increase in the oxygen concentration and a simultaneous decrease in the nitrogen concentration in the films. The electrical properties are further perturbed by an elongation of the physical structure of the films as a result of carousel rotation. This elongation, which can produce an increased resistivity for a given TCR, is attributed to oblique incidence effects as the substrate rotates into, and out of the discharge. Changes produced in the electrical and structural properties of the films during heat-treatment at 500 C are shown to depend on carousel rotation speed: recrystallization and surface oxidation occur for films deposited onto a rotating carousel, whereas films deposited onto a stationary carousel undergo surface oxidation only, as indicated by the kinetics of the conductance change and the lack of structural changes as shown by transmission electron microscopy.     

Electrical and structural properties of ion beam sputtered silver-SiO2 cermet films

Thin silver-SiO₂ cermet films containing 55–92 wt.% silver were deposited by co-sputtering using ion beam techniques. The resistivity and its temperature coefficient varied from 10^-6 to 10¹ Ω m and from +600 to -3500 ppm K^-1, respectively. Electron microscope examination revealed that films with a high silver content are of the capillary type whereas with increasing proportions of SiO₂ a transition to island structure is observed. In the latter case good agreement between measured and calculated electrical parameters was found.     

Microstructural analysis and modeling of RuO2 thin film resistors

The microstructural properties of RuO₂ thin film resistors with different temperature coefficients of resistance (TCRs) were analyzed using X-ray diffraction, scanning electron microscopu and Auger electron spectroscopy. A model based on microstructure of the films was developed to explain the experimental results, such as the negative, positive and near-zero TCRs of the resistors. The grain size controlled the resistivity of the resistors. However, the chemical composition of the film was more likely to control the TCR of the resistors. A layer-like structyre was required to fabricate near-zero-TCR resistors. The modeling based on the electrical measurement of the resistors provided valuable guidance in designing and fabricating near-zero-TCR resistors.     

Structural, optical and electrical properties of reactively sputtered Ag2Cu2O3 films

Ag₂Cu₂O₃ thin films were deposited on glass substrates by RF magnetron sputtering of an equiatomic silver-copper target (Ag_0.5Cu_0.5) in reactive Ar-O₂ mixtures. The reactive sputtering was done at varying power, oxygen flow rate and deposition temperature to study the influence of these parameters on the deposition of Ag₂Cu₂O₃ films. The film structure was determined by X-ray diffraction, while the optical properties were examined by spectrophotometry (UV-vis-NIR) and photoluminescence. Furthermore, the film thickness and resistivity were measured by tactile profilometry and 4-point probe, respectively. Additional mobility, resistivity and charge carrier density Hall effect measurements were done on a few selected samples. The best films in terms of stoichiometry and crystallography were achieved with a sputtering power of 100 W, oxygen and argon flow rates of 20 sccm (giving a deposition pressure of 1.21 Pa) and a deposition temperature of 250 °C. The optical transmittance and photoluminescence spectra of films deposited with these parameters indicate several band gaps, most prominently, a direct one of around 2.2 eV. Electrical characterization reveals charge carrier concentrations and mobilities in the range of 10²¹-10²² cm^− 3 and 0.01-0.1 cm²/Vs, respectively.     

Structure and electrical properties of Ta films sputtered in ArO2

The effect of varying oxygen content upon structural and electrical properties of Ta films was investigated. The 2000 Å films were deposited by d.c. diode sputtering at 6.6 kV and 300 mA onto Corning 7059 glass, quartz, sapphire and Ta₂O₅ coated Corning 7059 glass substrates. Crystalline structure of the Ta deposits was studied by an X-ray film technique, and their oxygen contents were determined with an electron microprobe. The β-Ta phase is obtained for films containing no oxygen. Solubility of O₂ in the β-phase is about 5 at. %, after which a phase related to TaO_z appears. At 13 at. % O₂, b.c.c.-Ta diffraction lines appear and grow in intensity with increasing O₂ content as the amounts of the first two phases decrease. The three phase region extends up to 28 at. % O₂. At 30 at. % O₂ only b.c.c.-Ta remains, indicating a solubility much higher than that reported for the bulk phase. Resistivities increased from 180 μΩ cm for β-Ta to 350 μΩ cm at 30 at. % O₂. In addition, temperature coefficient of resistance and thermoelectric power were determined as a function of oxygen content.     

Electrical characteristics of Ti-O/Ta2O5 thin film sputtered on Ta/Ti/Al2O3 substrate

The electrical characteristics of Ti-O/Ta₂O₅ films sputtered on Ta/Ti/Al₂O₃ substrate were investigated. Ta (tantalum) was used for the bottom and upper electrodes for the purpose of simplifying the fabrication process and Al₂O₃ substrates were used, which are needed in integral passive devices. Ta/Ti-O/Ta₂O₅/Ta/Ti/Al₂O₃ capacitors were annealed at 700 °C for 60 s in vacuum. The X-ray diffraction pattern (XRD) results showed that as-deposited Ta had a highly preferred orientation, but Ta₂O₅ film had amorphous structure, which was transformed to crystallization structure by rapid thermal heat treatment. We examined the log J-E and C-V characteristics of the dielectric thin films deposited on the Ta bottom electrode. From these results, we concluded that the leakage current could be reduced by introducing a Ti-O buffer layer. The conduction mechanisms of Ta/Ti-O/Ta₂O₅/Ta/Ti/Al₂O₃ capacitors could be interpreted appropriately by hopping conduction in lower field (E<1×10⁵ V/cm) and space-charge-limited current in higher fields (1×10⁵ V/cm<E).     

Electrical properties of reactively sputtered carbon nitride films

Carbon nitride films with β-C₃N₄ crystals of 200 nm grain size were grown on Si (1 0 0) substrates using magnetron sputtering. These films were characterized by transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Carbon nitride films had low surface roughness. Maximum N/C ratio of 0.5 was achieved in the films. Chemical bonds of sp, sp² and sp³ coexisted in the films. The fraction of each bond was related to the deposition conditions. The resistivities of the films were measured, which ranged from 1×10³ to 1×10⁷ Ω cm. The measured resistivity results indicated that the carbon nitride films had semiconductive properties. The resistivity largely depended on the sp³/sp² ratio. Effects of N₂ fraction, target current and substrate bias were investigated. All these deposition parameters had influence on the chemical bonds of the films, and on the resistivities too. High sp³/sp² ratio resulted in high resistivity.     

Properties of thin film capacitors made with reactively sputtered Ta-Al

The dielectric properties of oxides formed on Ta-Al-N films were investigated. The capacitors made from these films exhibit excellent a.c. and d.c. properties and are comparable in performance with TaN capacitors. Owing to the high resistivity of Ta-Al-N films an aluminum underlayer was used for these capacitors to reduce losses at high frequencies. It is concluded that these capacitors are more desirable for applications in hybrid integrated circuits when used together with Ta-Al-N resistors.     

Sn1−x Pbx O2 sputtered thin films as photoanodes for photoelectrochemical cells

Pb_x Sn_1?x O₂ thin films have been prepared by glow discharge. These films have been characterized by X-ray and microprobe analysis. The photoelectrochemical behaviour shows anodic and cathodic corrosion either in the dark or under illumination. The onset of photocurrent is pH dependant. Photocurrent versus the wavelength is shifted to the visible range of the spectrum when lead content increases.     

Optical properties of thin film Au-MgF2 cermets

The preparation of thin films of cermets of gold in magnesium fluoride and the ellipsometric determination of the optical constants of the materials of the films are described. The results for materials of two compositions are compared with predictions based on the Maxwell Garnett expression for the complex refractive index of cermets in terms of the refractive indices of the constituents. It is shown that reasonable agreement between experimentally determined and theoretical values of the refractive indices of the cermets can be approached only if the restriction of the mean free paths of the conduction electrons in the gold particles is taken into account.     

Microstructure and electrochemical properties of magnetron-sputtered LiCoO2/LiNiO2 multi-layer thin film electrode

LiCoO₂ single-layer and LiCoO₂/LiNiO₂ multi-layer thin film electrodes were successfully fabricated by magnetron sputtering. Their microstructure and electrochemical properties were investigated. Once annealed, both films had the (0 0 3) preferred orientation to minimize the surface energy. The initial discharge capacity of the multi-layer thin film was approximately 53.1 μAh/cm² μm, which was higher than that of the LiCoO₂ single-layer thin film having similar thickness. The capacity retention of the multi-layer thin film was superior to that of the single-layer thin film. These findings indicate that the multi-layer thin film is a promising cathode material for the fabrication of high-performance thin film batteries.     

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al₂O₃) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 °C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al₂O₃-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.     

Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films

HfO₂ thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O₂/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO₂ grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO_x suboxide layer at the HfO₂/Si interface is unavoidable. The HfO₂ thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O₂/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO₂, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO₂ to form HfO₂, leaving Si-Si bonds behind.     

Electrical properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films on TiO2 buffer layer

Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ antiferroelectric thin films with thickness of 500 nm were successfully deposited on TiO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates via sol-gel process. Microstructure of Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was studied by X-ray diffraction analyses. The antiferroelectric nature of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was confirmed by the double hysteresis behaviors of polarization and double buffer fly response of dielectric constant versus applied voltage at room temperature. The capacitance-voltage behaviors of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films with and without TiO₂ buffer layer were studied, as a function of temperature. The temperature dependence of dielectric constant displayed a similar behavior and the Curie temperature (T_c) was 193 °C for films on both substrates. The current caused by the polarization and depolarization of polar in the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films was detected by current density-electric field measurement.     

Composition, structure and optical properties of sputtered thin films of CuInSe2

Thin films of copper indium selenide (CuInSe₂) were produced by radio frequency (RF) sputtering due to the ability of this technique to achieve stoichiometric layers and its scalability to large-area devices. Results of energy dispersive analysis of X-rays (EDAX) revealed that the sputtered films were near to stoichiometry for substrate temperatures T_Sub not exceeding 200 °C. X-ray diffraction (XRD) patterns indicate that the films exhibited some pattern similar to that of bulk crystals of tetragonal chalcopyrite, predominantly [112] oriented. Based on the XRD patterns, the lattice parameters and grain sizes were examined. The band gap E_g, estimated from optical absorption data, was between 0.6-1.08 eV, depending on sputtering conditions such as substrate temperature and bias voltage. High optical absorption coefficients (> 10⁴ cm^− 1) were found.     

Electrical,morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells

Molybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in “substrate configuration” thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films.     

Effect of structural transformation on the electrical properties for Ge1Sb2Te4 thin film

Dependence of electrical properties of phase change Ge₁Sb₂Te₄ thin film on structural transformation was investigated. The electrical resistivity of the film decreases with increasing annealing temperature with a steep drop at ∼ 230 °C (the second crystallization temperature), at which the structure of Ge₁Sb₂Te₄ changes from face-centered cubic to trigonal state. The steep drop of resistivity at the second crystallization temperature is mainly due to the increase of hole density within the p-type film, according to Hall measurement. The crystallization process has been followed by in situ resistance measurement at various annealing temperatures. Transmission electron microscope and atomic force microscope were also employed to study the film.     

Atmospheric pressure PECVD of SiO2 thin film at a low temperature using HMDS/O2/He/Ar

SiO₂-like thin films were deposited at a low temperature (< 50 °C) by a remote-type, atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using a pin-to-plate-type, dielectric barrier discharge with gas mixtures containing hexamethyldisilazane (HMDS)/O₂/He/Ar. The film characteristics were investigated according to the HMDS and O₂ flow rates. To obtain a more SiO₂-like thin film, an adequate combination of HMDS and oxygen flow rates was required to remove the -(CH₃)_x bonding in the HMDS and to oxidize the Si in HMDS effectively. At the optimized flow rates, the surface roughness of the SiO₂-like thin film was also the lowest. By using HMDS (50 sccm) and O₂ (500 sccm) flow rates in the gas mixture of HMDS/O₂/He (2 slm)/Ar (600 sccm), SiO₂-like thin films with a low impurity (< 6.35% C) were obtained at a deposition rate of approximately 10.7 nm/min.