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.     

Influence of the substrate nature on the properties of ZnO thin films

Zinc metallic films, deposited onto different substrates, were submitted to a thermal oxidation process, in air, in order to obtain ZnO thin films. X-ray diffraction patterns revealed that as-obtained ZnO thin films were polycrystalline and have a wurtzite (hexagonal) structure. The temperature dependences of the electrical conductivity during some heating/cooling cycles were studied and the conduction mechanism was interpreted in terms of Seto model. The sensitivity of ZnO thin films, at five gases, was investigated and it was established that ethanol is the test gas that produces the most significant changes in the electrical resistance of all the studied films. Some correlations between the oxidation temperature and the substrate nature and the parameters which characterize the structural and electrical properties of ZnO thin films have been established.     

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.     

Direct current reactive magnetron sputtered zinc oxide thin films —the effect of the sputtering pressure

ZnO thin films were deposited onto glass substrates by d.c. reactive magnetron sputtering from a metallic zinc target. A systematic study has been made on the influence of sputtering pressure in the range from 0.2 Pa to 3 Pa on the film structural and optical properties. At low sputtering pressure (0.2–0.4 Pa), the film was inhomogeneous, non-stoichiometric and had low refractive index and an almost amorphous structure. At high sputtering pressure (0.6–0.8 Pa), the film was homogeneous, stoichiometric and had high refractive index and the crystallinity was improved. As the sputtering pressure was further increased (1–3 Pa), the homogeneity and the refractive index of the film had no clear variation, but the crystallinity of the film went down. As the sputtering pressure was increased from 0.2 Pa to 3 Pa, the transmittance of the film increased and the deposition rate of the film decreased.     

Dual electrical properties of quench-condensed mercury films. Dependence on the substrate material

It is shown that the conductivity onset in cold deposited Hg films on glass substrates covered with a SiO layer corresponds to te film thickness of 4–5 Å in a contrast to films deposited on pure glass, where the conductivity onset can be observed only at 10–15 times higher thicknesses. Study of superconducting properties of films is also presented. We believe that chemical bonds between metallic atoms themselves and their chemical interaction with atoms of the substrate are very important for formation of the film structure and responsible for a completely different behavior of films deposited onto different substrates.     

C-Ti nanocomposite thin films: Structure, mechanical and electrical properties

Carbon-titanium nanocomposite thin films were deposited by DC magnetron sputtering on oxidized silicon substrates in argon. The films were prepared at different deposition temperatures between 25 and 800 °C. Transmission electron microscopy was used to determine the structure of the films. All the C-Ti nanocomposites consisted of columnar TiC structure with average column width ∼10 and 20 nm and a thin carbon matrix. The thickness of the carbon matrix between adjacent TiC columns was ∼2-5 nm.Mechanical properties (hardness, reduced modulus) of C-Ti films showed a distinct variation depending on the deposition temperature. Films deposited at 200 °C had the highest hardness ∼18 GPa and the highest reduced modulus ∼205 GPa.Temperature dependence of the film resistance was measured between 80 and 330 K. C-Ti nanocomposites have a non-metallic conduction mechanism characterized by a negative temperature coefficient of resistivity (TCR). The most negative TCR was observed for films showing high hardness and reduced modulus of elasticity.     

Influence of the nitrogen partial pressure on the properties of d.c.-sputtered titanium and titanium nitride films

The properties of titanium and titanium nitride films deposited onto biased substrates in a d.c. sputtering system were studied as a function of the partial nitrogen pressure. The deposition rate was deduced from film thickness measurements. The film composition was determined by Rutherford backscattering analysis and the structure was studied using X-ray diffraction. The resistivity was measured by the four-probe method and the temperature coefficient of resistivity (TCR) was determined in the temperature range from ?196 to 25 °C.Around a critical nitrogen pressure p_c of 4 × 10^-2 Pa the deposition rate decreases rapidly, the film structure changes from h.c.p. titanium to nearly stoichiometric f.c.c. TiN. At the same pressure, the film resistivity and the TCR present minimum values.A general sputtering model which takes into account the gettering action of the deposited material is proposed. This model allows the calculation of the surface coverage of the target by the reactive gas or the metallic compound and the determination of the deposition rate as a function of the reactive partial pressure. A good agreement is found with the deposition rates measured experimentally.     

DC electrical conduction of zinc telluride thin films

Zinc telluride (ZnTe) thin films were deposited by thermal evaporation onto glass substrates kept at room temperature. X-ray diffraction studies showed that the films were polycrystalline and of cubic structure. The current-voltage (I-V) characteristics of the Au/ZnTe/Au thin film sandwich system at different temperatures were studied. The DC conduction was explained using the Schottky or Jonscher-Ansari modified Pool-Frenkel mechanism.     

Electrical resistivity of thin bismuth films

For quantitative and reproducible observation of the quantum size effect (QSE) 78 samples of thin bismuth films were deposited at one time onto three muscovite substrates in ultrahigh vacuum. The electrical resistivity of these films, either in step-up series or a fixed thickness, was measured between 4.2 and 320 K. The experiments covered a thickness range from 300 to 3350 Å. The measured resistivities had a large scatter among simultaneously deposited samples of a fixed thickness. This scatter became more pronounced with decreasing temperature and it was due to the variation of the TCR above liquid nitrogen temperature. The thickness dependence of the ratio of resistivities at 4.2 K and 77 K (?_4.2/?₇₇), which had a relatively small scatter, did not show the oscillatory behavior predicted by Sandomirskii.     

Ultra-thin silver films obtained by sequential quench-anneal processing

We have used the “two-step” growth technique, quench condensing followed by an anneal, to grow ultra-thin films of silver on glass substrates. As has been seen with semiconductor substrates this process produces a metastable homogeneous covering of silver. By measuring the in situ resistance of the film during growth we are able to see that the low temperature growth onto substrates held at 100 K produces a precursor phase that is insulating until the film has been annealed. The transformation of the precursor phase into the final, metallic silver film occurs at a characteristic temperature near 150 K where the sample reconstructs. This reconstruction is accompanied by a decrease in resistance of up to 10 orders of magnitude.     

Rotation Speed-Induced Uniaxial In-Plane Anisotropy in Thin Films Deposited Onto a Rotating Substrate

The Rotating Cryostat system consists of a rapidly rotating, liquid-nitrogen-cooled drum, around which a substrate can be placed. The possibility of using multiport sources gives the system wide capabilities for producing new materials. The effects of various rotation speeds of 1900, 1500, 1000, 500, and 0 rpm on the magnetic properties of thin iron films deposited on different (glass, silicon, and Kapton) substrates from a resistively heated evaporation source and a dc sputtering source have been investigated. Magnetic measurement showed that the films have an in-plane magnetic anisotropy for all films deposited at high speeds on all types of substrates and the degree of magnetic anisotropy decreased with decreasing rotational speed for flexible Kapton substrate. While the glass and silicon substrates was stationary, in-plane magnetic anisotropy of the films dropped down to zero. The films deposited on Kapton showed the rotational-speed-dependent magnetic properties. Estimation of magnetic anisotropy confirms in-plane anisotropy in the films. Furthermore, as expected for all iron films no magnetic anisotropy perpendicular to film plane was observed irrespective of rotation speed and type of substrate used.     

2.24 Structural and electrical properties of discontinuous gold films on glass

In the present work thin gold films are investigated in the thickness interval 10–160 Å. The films are deposited in UHV on to glass substrates at room temperature and with an electric field in the substrate plane. In the thickness interval 10–45 Å the film is discontinuous and the size distribution of the islands as determined from electron micrographs is described with a log-normal distribution function. The onset of the in situ electrical conduction at the average thickness 45 Å makes it possible to measure the film resistance as a function of the film thickness during the condensation. At the thickness 53 Å stable metallic continuous paths are formed and the film achieves metallic properties. The fraction of the surface covered with material and the island density are measured 20 h after the deposition. Both these entities change rapidly at the stage when the film grows to be metallic continuous.     

Measurement of the Temperature Coefficient of Resistance in Metallic Films with Nano-thickness

The temperature coefficient of resistance (TCR) values of gold and aluminum films deposited on glass substrates were obtained in the range of thickness from 20 nm to 200 nm at 298 K and atmospheric pressure conditions. Applying an electrical current and measuring simultaneously the corresponding changes of voltage (i.e., electrical resistance), and the change of temperature on the thin films, the TCR value was estimated. The measured TCR values show a decrement with the film thickness reduction, and their values are approximately 13.0 % lower than their corresponding bulk values mainly for thinner films. A comparison with previously reported cooper TCR values and the values estimated with the Tellier–Tosser model show good agreement with differences of about 5.0 % between them.     

射频溅射工艺参数对AZO薄膜结构和性能的影响

采用射频磁控溅射法制备了掺铝氧化锌(AZO)薄膜,研究了衬底温度及溅射工作压强对沉积薄膜的晶体结构、表面形貌及电学性能的影响。结果显示,随衬底温度增加,薄膜的结晶结构发生显著变化,而溅射工作气压增加主要影响沉积薄膜(103)面与(002)面的相对强度。薄膜的表面形貌受温度影响严重,而气压对形貌的影响相对较小。衬底温度增加,薄膜的电阻率急剧降低,迁移率和载流子浓度都显著增加,而工作气压增加则导致电阻率先减小后增大。     

The structure of reactively sputtered metal carbide and metal silicide solar selective absorbers

Transition metal carbide and metal silicide films have recently been reported to produce excellent solar selective absorbers when deposited as interference layers onto metal substrates by d.c. reactive sputtering. These films, with a graded or multilayered profile, typically have solar absorptances greater than 0.90 and thermal emittances less than 0.05. In this paper we report the results of electron diffraction and electron microprobe studies on uniform titanium carbide and titanium silicide films produced by d.c. magnetron sputtering titanium in an atmosphere of argon plus methane or silane.The films were found to be rich in the non-metallic component and to consist of small particles of a metallic titanium carbide or silicide embedded in a porous matrix of carbon or silicon. The ratio of non-metal to metal increases with the reactive gas pressure in the sputter discharge, as does the film resistivity.Films which had been annealed in vacuum for sufficient time to change their optical properties showed no observable structural changes but it is inferred that the changes in optical properties are caused by a precipitation of carbon or silicon from the metallic particles into the matrix, causing the deposits to become more dielectric.     

The electrical conductance of continuous thin metallic double-layer films

The dependence of changes in the electrical conductance of continuous thin metallic double-layer films on changes in the thickness of the overlayer deposited onto the base layer was calculated. We took into consideration the influence on the electrical conductance of a double-layer film (apart from the background mechanism of the scattering of conduction electrons) of scattering at the external surfaces of the layer and at the interface. It was found that when the diffuse scattering of the conduction electrons by the layer surface system comprising the interface, the overlayer and the external surface increases in comparison with scattering at the external surface of the uncovered base film, the total conductance of the double- layer film first decreases and then increases with increasing overlayer thickness.     

Reactive sputtering of titanium and properties of titanium suboxide films for photochemical applications

The effect of oxygen partial pressure on the deposition rate, crystalline structure and optical absorption of thin film titanium suboxides prepared by the reactive sputtering of a titanium metal target is given. A wide variety of films ranging from metallic through semiconducting to dielectric specimens were deposited in a reproducible manner simply by controlling the oxygen content in the sputtering plasma atmosphere. In addition, polycrystalline stable semiconducting TiO₂ electrodes were deposited onto heated glass substrates. The spectral response was investigated; a main absorption edge of about 410 nm was obtained. The design of a special substrate table with a unique mask changer that allowed for the fabrication of different geometrical film patterns is also given.     

Electrochemical bath deposition technique: Deposition of CdS thin films

Cadmium sulphide thin films have been deposited onto chromium plated stainless steel substrates under the influence of electric field. The various deposition parameters such as speed of rotation of the substrates, temperature of the chemical bath, molar concentrations of solution and the strength of the electric field were kept at optimized conditions. The electrochemical photovoltaic (ecpv) cells are formed with CdS film electrodes. The properties of CdS films andecpv cells are monitored with selective values of the electric field employed in the controlled precipitation technique. This relatively new technique is described and the possible film formation mechanism suggested.     

Large area ZnO:Al films with tailored light scattering properties for photovoltaic applications

Aluminum-doped zinc oxide films on glass are promising substrates for use in thin film solar cells based on amorphous and amorphous/microcrystalline silicon absorber material. The films can be produced by magnetron sputtering on large scale at relative low cost. Especially reactive sputtering of metallic Zn/Al compound targets is a cheap way to produce films at high deposition rate. One drawback of amorphous silicon is the low absorption in the near infrared spectral range. Wet chemical etching has been used to produce a rough TCO surface that enables light trapping in the absorber. The etching behaviour of ZnO:Al films can be tuned by changing oxygen partial pressure during deposition. The etching behaviour is compared to ZnO structure and discussed regarding the performance of solar cells deposited onto the etched films.     

Control of oxidation state of copper in flame deposited films

The deposition of thin copper based films onto carbon steel surface is described, using premixed flames with different oxygen/methane ratios doped with aqueous copper nitrate as precursor. We investigated the chemical properties of the copper as a function of oxygen/methane ratio. Using fuel rich flames (equivalence ratio 0.665), the deposited copper film was entirely metallic. When the equivalence ratio was increased to 0.850 or greater the copper film contained predominantly Cu^2 +. Furthermore, the flame can be used for post deposition modification, as demonstrated by reduction of Cu^2 + containing films to Cu metal. All the films were characterised by X-ray diffraction, Raman and scanning electron microscopy (SEM). A rotating sample holder was employed to avoid over heating of the sample and the critical variables such as sample height in the flame and deposition time were optimised. Deposition for 20 min, which translated to a total residence time in the flame of approx. 76 s, produces metallic copper films of thickness 169 ± 18 nm as determined by anodic stripping and SEM. The microstructure of the metallic films was clearly composed of fused copper spheres of 100-150 nm, which are probably formed in the flame and subsequently deposited on the surface with good adhesion.