HTSC thin film growth by inverted cylindrical magnetron sputtering

Inverted cylindrical magnetron sputtering (ICM) is a reliable and reproducible method for the production of HTSC thin films. This allows systematic studies of film growth as a function of various deposition parameters, including film thickness, substrate material, or buffer layers. After describing in some detail the special demands on sputtering devices for HTSC thin film growth, we report the growth conditions and growth quality of 1–2–3 films of different orientation on substrates such as SrTiO₃ and MgO. Furthermore, we report on the growth of buffer layers of YSZ onR-plane sapphire. Epitaxial GdBa₂Cu₃O₇ films grown on these buffer layers showed critical current densities of 3×10⁶ A/cm² at 77 K and a zero resistance transition temperature of 92.5 K.     

A method for preparation of a high-quality high temperature superconducting ceramics

An improved method for hot pressing of high temperature superconducting (HTSC) powders prepared by conventional solid phase synthesis of the initial BaCO₃, CuO and Ln₂O₃ allows one to obtain HTSC targets and magnetic shields possessing a high degree of homogeneity. By sputtering such targets HTSC films with critical current density of 3.3·10⁶ A/cm² have been deposited. Shields, prepared according to this method, show a shielding coefficient of 10⁵ andH _c of 79 Öe in the constant magnetic field and in the alternating magnetic field the amplitude is 90 Öe in the frequency range of 70–3000 Hz.     

Preparation and magnetic properties of SrFeO3−x (x = 0.25 ∼ 0.5) using RF magnetron sputtering optimized through sputtering plasma analysis

We investigated the preparation and the magnetic properties of SrFeO_3−x using conventional RF magnetron sputtering. Photoluminescence spectrum analyses of the sputtering plasma revealed that the film composition was changed even using the stoichiometry target. After fixing the composition of the targets from an intensity ratio of the Sr and Fe plasma, the polycrystalline SrFeO_3−x films with different oxygen deficiencies were able to prepare using the various sputtering gas ratio. The magnetic properties of the samples were also changed with changing the sputtering gas ratio. This magnetic property change was likely due to the suppression of the oxygen deficiency in the film.     

In situ grown superconducting YBCO films on buffered silicon substrates for device applications

Thin films of YBa₂Cu₃O_7?δ (YBCO) have been grownin situ on silicon single-crystal (100) substrate by using SrTiO₃ as a buffer layer. The deposition has been carried out by on-axis rf magnetron sputtering method. The deposition condition have been optimized by studying the plasma characteristics and correlating them with the superconducting performance of the film. Films deposited at substrate temperature in the range of 680–700°C from stoichiometric YBCO targets in an argon + oxygen mixture (3∶1) are superconducting and showc-axis epitaxy. Compositional confirmation has been carried out using Rutherford backscattering. Scanning tunneling microscopy of the films reveal formation of well-defined layered structure with some defects in the initial stages ofin situ growth of the films. Films grown on SrTiO₃ substrates have excellent crystalline quality (XRD), transition temperatureT _c0=81 K and the critical current densityJ _c >2×10⁵ A/cm² for unpatterned films at 77 K. On silicon substrates using buffer layers thein situ deposited YBCO films shows a higher transition width andT _c0 is also slightly less (71 K).     

Ultra-thin TaN Films for Superconducting Nanowire Single-Photon Detectors

Ultra-thin films of superconducting tantalum nitride are deposited by reactive magnetron sputtering on heated sapphire substrates. The critical temperature T _C=10.25 K is reached for films thicker than 10 nm. A superconducting nanowire single-photon detector in the form of a meander line with a width of 110 nm was made from 5 nm thick TaN film. The detector had a transition temperature of 8.3 K and a critical current density of 4 MA/cm² at 4.2 K. A photon detection efficiency of 20% has been obtained for the detector with a filling factor of 0.55 at wavelengths up to 700 nm.     

High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target

We have deposited Ti-Si-C thin films using high-power impulse magnetron sputtering (HIPIMS) from a Ti₃SiC₂ compound target. The as-deposited films were composite materials with TiC as the main crystalline constituent. X-ray diffraction and photoelectron spectroscopy indicated that they also contained amorphous SiC, and for films deposited on inclined substrates, crystalline Ti₅Si₃C_x. The film morphology was dense and flat, while films deposited with direct-current magnetron sputtering under comparable conditions were rough and porous. We show that, due to the high degree of ionization of the sputtered species obtained in HIPIMS, the film composition, in particular the C content, depends on substrate inclination angle and Ar process pressure.     

Comparative study of zinc oxide and aluminum doped zinc oxide transparent thin films grown by direct current magnetron sputtering

Pure and aluminum (Al) doped zinc oxide (ZnO and ZAO) thin films have been grown using direct current (dc) magnetron sputtering from pure metallic Zn and ceramic ZnO targets, as well as from Al-doped metallic ZnAl2at.% and ceramic ZnAl2at.%O targets at room temperature (RT). The effects of target composition on the film's surface topology, crystallinity, and optical transmission have been investigated for various oxygen partial pressures in the sputtering atmosphere. It has been shown that Al-doped ZnO films sputtered from either metallic or ceramic targets exhibit different surface morphology than the undoped ZnO films, while their preferential crystalline growth orientation revealed by X-ray diffraction remains always the (002). More significantly, Al-doping leads to a larger increase of the optical transmission and energy gap (E_g) of the metallic than of the ceramic target prepared films.     

Superconducting Y-Ba-Cu-O films by rf sputtering in axial magnetic field

Films of Y-Ba-Cu-O system have been prepared by rf sputtering from composite Y-Ba-Cu-O targets in an axial magnetic field in 4:1 Ar/O₂ mixture on 〈100〉 SrTiO₃ and 〈100〉 MgO substrates at 270°C and 450°C. Although back-sputtering caused due to negatively-charged oxygen ions was found to drastically vary the film composition about the centre of the sputtering axis, by properly orienting the substrates with respect to the sputtering axis near-stoichiometric films have been obtained. Films annealed at 900°C in oxygen have shown superconducting onset at 88°K and zero resistance transition at 72°K.     

Preparation and Characterization of Nanometer Grained High Temperature Superconducting High-Quality Epitaxial Bi-2223 Thin Films Grown by DC Sputtering

Bi₂Sr₂Ca₂Cu₃O_10+?? HTSC epitaxial thin films with thickness in the order of 6.0?nm were prepared onto (100) aligned SrTiO₃ single-crystal substrates by DC sputtering from stoichiometric targets. As-grown samples were characterized by X-ray diffraction, AC-susceptibility and scanning electron microscopy. X-ray diffraction patterns show that all obtained superconducting thin films were c-axis oriented with a Bi-2223 phase. All reflections (except the substrate ones) can be assigned to the (00l) reflections of the film material (h=k=0, l??0), indicating that the films were grown preferentially with the c-axis normal to the film plane. In order to investigate the crystal quality of these Bi-2223 films, the rocking curves of the (0012) peaks were explored by ??-scans. The rocking curve of the (0012) reflection had a full width at half maximum (FWHM) of 0.30??. This demonstrates that our prepared Bi-2223 thin films have good crystalline quality and high degree of c-axis orientation. The grain size has well known important effects in the magnetic, optical, and electrical properties of metals and alloys. High temperature superconducting thin films, obtained in this work, have nanometer grain size. The mean size of the grains of the samples were determined by X-ray diffraction (XRD) and found to be in the order of 34.8?nm. The superconducting transitions temperature of several Bi-2223 samples is about 103?K. Surface morphology of the films and chemical composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX).     

Preparation of YBa2Cu3O7 − δ Thin Films by the Self-Template Sputtering Method

Using the self-template technique, c-axis-oriented epitaxial YBa₂Cu₃O_{7 ? δ} thin films have been prepared in situ on LaAlO₃ substrate by the d.c. magnetron sputtering method. The properties of thin film dependence on the deposition conditions of the two-step self-template method have been systematically investigated. By optimizing the parameters, high-quality YBCO thin films with T _c0 ≥ 90 K, ΔT _c ≤ 1 K, R _s (77 K, 10 GHz)～500 μΩ were reproducibly obtained. The best sample grown under optimal conditions gave a low R _s of 330 μΩ at 77 K, 10 GHz, which can be used in a microwave field.     

Thermal Oxidation of Thin Cu–Ti Films

Thin Cu–Ti films are grown on single-crystal silicon substrates by magnetron sputtering, and their oxidation is studied between 420 and 670 K. A technique is proposed for producing Cu–Ti films of controlled composition using a composite target. The phase composition of the films oxidized in oxygen at atmospheric pressure is determined, and their microstructure is studied by scanning electron microscopy. The films are found to contain the intermetallic compounds Cu₃Ti and CuTi₂, which form during both magnetron sputtering and subsequent oxidation.     

Structure and characterization of magnetoresistance of La0.7Pb0.3MnO3−δ in bulk and films deposited on LaAlO3 (100), (110) and (111) substrates

The structure and properties of La_0.7Pb_0.3MnO_3−δ (LPMO) bulk and films, which are deposited onto (001), (110) and (111) LaAlO₃ (LAO) substrates using the direct current magnetron sputtering technique, are obtained. For bulk of LPMO, T_p is almost equal to T_c (252 K) and its R(T) curve has a bump in low temperature region. For films, the colossal magnetoresistance (CMR) of 28% at 155 K and in 0.5 T was observed on (001) oriented substrate under 9 Pa sputtering gas pressure and substrate temperature of 790 °C. The transport properties of the deposited films are slightly lower than that of the bulk.     

Growth parameter effect in superconducting YBa2Cu4O8 thin films by d.c. magnetron sputtering

High- T _c YBa₂Cu₄O₈ (124) thin films have been made by d.c. magnetron sputtering deposition on (100) MgO substrates. The effect of several processing variables, including the ratio of oxygen to argon, total pressure, and substrate temperature, on the superconducting properties of the thin films, were systematically investigated. The as-prepared films annealed in flowing oxygen at 800°C for 4 h under ambient pressure obtained nearly phase-pure 124 and exhibited superconducting onset transition at 75 K.     

Preparation and colossal magnetoresistance in a trilayer La0.67Sr0.33MnO3/La0.75MnO3/La0.67Sr0.33MnO3 device by dc magnetron sputtering

Epitaxial trilayer films of La_0.67Sr_0.33MnO₃ (LSMO)/La_0.75MnO₃ (L0.75MO)/La_0.67Sr_0.33MnO₃ (LSMO) have been prepared on (0 0 1) oriented LaAlO₃ substrates by dc magnetron sputtering. The structure and MR are studied. All as-deposited trilayer films exhibit a semiconductor to metal transition at temperature ranging from 116 to 185 K. The MR is also shown to be dependent on the thickness of the middle oxide layer. A maximum MR value of 32% (ΔR/R₀) has been obtained at 132 K under 0.4 T magnetic field for a LSMO (300 nm)/L0.75MO (70 nm)/LSMO (300 nm) trilayer film. The MR of trilayer film prefers to that of both LSMO and L0.75MO single layer films.     

The Structure and Properties of Ti–B–N, Ti–Si–B–N, Ti–Si–C–N, and Ti–Al–C–N Coatings Deposited by Magnetron Sputtering Using Composite Targets Produced by Self-Propagating High-Temperature Synthesis (SHS)

The microstructures and compositions of multicomponent Ti–B–N, Ti–Si–B–N, Ti–Si–C–N, and Ti–Al–C–N films deposited by reactive magnetron sputtering using composite targets and produced by self-propagating high-temperature synthesis (SHS) have been investigated by means of transmission electron microscopy. Auger spectroscopy, and X-ray diffraction. Depending on the chemical composition of the film deposited, different single-phase crystalline films were observed. The sputtering process included sputter cleaning prior to the DC magnetron sputter deposition of Ti and TiN interlayers prior to DC magnetron sputter deposition of the multicomponent films from multicomponent targets. The films produced were characterized in terms of their microhardness, wear resistance, high-temperature oxidation conducted in air. and corrosion resistance in a solution of 5NH₂SO₄ at room temperature.     

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa₂Cu₃O_7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature T _c ,off=89 K and a critical current density j _c =2 MA/cm² (at 77 K) and were free from secondary phase particles larger than 10 nm. Pis’ma Zh. Tekh. Fiz. 24, 80–85 (February 26, 1998)     

Low-cost ZnO:Al transparent contact by reactive rotatable magnetron sputtering for Cu(In,Ga)Se2 solar modules

Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se₂ (CIGS) module manufacturing. Although innovative concepts like rotatable magnetron sputtering from ceramic targets have been realised, costs are still high due to expensive ceramic targets. Significant cost reductions are expected by using reactive sputtering of metallic targets.Therefore, ZSW and industrial partners investigated the reactive sputtering of Al-doped zinc oxide (ZAO) as TCO on CIGS absorbers of high quality and industrial relevance. The reactive DC sputtering from rotatable magnetron targets is controlled in the transition mode by adjusting oxygen flow and discharge voltage. Optimisation leads to ZAO films with a TCO quality nearly comparable to standard films deposited by DC ceramic sputtering. Scanning electron microscopy, X-ray diffraction, and Hall analyses of the ZAO films are performed.Medium-size CIGS modules are coated with reactively sputtered ZAO, resulting in 12.8% module efficiency and surpassing the efficiency of the ceramic witness device. Cd-free buffered devices are also successfully coated with reactive TCO. Damp heat stability according to IEC61646 is met by all reactively sputtered devices.     

Electrical and optical properties of TiN thin films

TiN thin films have been grown by reactive magnetron sputtering. It has been shown that an Ohmic contact to TiN thin-film can be made from indium. The TiN thin films have been shown to be n-type semiconductors with a carrier concentration of 2.88 × 10²² cm^?3 and resistivity of ρ = 0.4 Ω cm at room temperature. The activation energy for conduction in the TiN films at temperatures in the range 295 K < T < 420 K is 0.15 eV. The optical properties of the TiN thin films have been investigated. The material of the TiN thin films has been shown to be a direct gap semiconductor with a band gap E _g = 3.4 eV.     

Influence of the target composition on reactively sputtered titanium oxide films

Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiO_x targets with different oxygen contents.The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.     

Synthesis and properties of superconducting lanthanum sulfide films

We report the structural and transport properties of La-S films prepared by reactive planar magnetron sputtering. The La-S (Th₃P₄ cubic structure) can be prepared over a range of compositions with the electronic properties varying from a low electron density superconductor (T_c≈ 7 K) to a semiconductor which shows thermally activated transport at low temperature. This method of deposition produces small grained (≈ 200 Å) polycrystalline films whose composition can be varied continuously by tuning the deposition parameters. We discuss the TEM and X-ray data as well as the resistivity, Hall effect and superconducting properties of these films. We find that the superconducting transition temperature of the films is the same as that of bulk single crystals; however the mobility is a factor of 2 to 300 lower than that found in bulk specimens.