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The effect of re-sputtering on the in situ growth of superconducting YBa2Cu3Ou thin films

Abstract Radio frequency magnetron sputtering of a stoichiometric YBa 2 Cu 3 O 7− x target in an Ar/O 2 gas produces highly energetic neutral particles which bombared the growing films. This slows down the deposition rate and in some cases no deposition at all occurs. Some damage is caused to the film with no superconducting transtion properties observed. By placing the substrates off-axis and perpendicular to the target surface the deposition rate is imporoved. Moving the substrates towards towards the edge of the plasma improves the resistivity, transition and structural properties of the film.

A substrate heater design for high temperature deposition in an oxidizing plasma

Abstract A novel contact heater which can operate reliably in air, vacuum and highly oxidizing atmospheres has been designed and constructed. It uses a fully enclosed element which makes good thermal contact with a stainless steel plate on which the substrates are clamped. Adequate radiation shields are used to reduce heat loss. Power consumption is less than 200 W for an operational temperature of 750°C.

C-axis expansion in RF sputtered YBa2Cu3Ox thin films

The c-axis lattice parameter of YBa2Cu3Ox thin films deposited on SrTiO3(100) and MgO(100) has been carefully measured and compared with the critical temperature and normalized resistance of a number of films. The films were prepared in situ using RF magnetron off-axis sputter deposition in the high-pressure regime. The Tc dependence on the c-axis expansion has previously been reported to be much weaker in thin films than in bulk material and considered not to be entirely due to O deficiency in the chain sites. However, the change in c is less than 1% and conflicting results have previously been obtained. By comparing X-ray diffraction peak shifts relative to substrate peaks and also detailed analysis of (001) data we have obtained unambiguous evidence for the c-axis expansion. We find that the Tc versus c-axis expansion tends to follow bulk values for films on MgO(100) but for films sputtered onto SrTiO3(100) the Tc is fairly constant with c-axis expansion. In the latter films we also find a-axis-orientated grains, which account for higher resistance values and the shape of the R/T curves. The stability of Tc with c-axis expansion is considered to be partly due to the presence of the a-axis-orientated grains.

Preliminary measurements of the low frequency impedance of superconducting epitaxial Y-Ba-Cu-O films

The authors have produced epitaxial thin films of superconducting Y-Ba-Cu-O grown onto (110) and (100) oriented SrTiO3 and MgO substrates by in situ RF sputter deposition. The impedance of the films has been measured and the results compared with two-fluid theory. The impedance of the films depended strongly on crystallographic orientation. Between room temperature and the critical temperature Tc the film reactance was inductive for well orientated (100) films and capacitive for (013) orientated films. The films were purely inductive for temperatures below Tc, with a constant value equal to the film inductance after flux exclusion due to the Meissner effect.

Quasi-static impedance and penetration depth of YBCO thin films

Abstract The low frequency complex impedance and penetration depth of high temperature superconducting thin films has been investigated. Analysis of two-dimensional current density and impedance equations shows that when the penetration depth λ=δ/√2 (where δ is the skin depth) there is a crossover from superconductivity to normal conductivity which is observed experimentally. We also include the effects of the normal inductance and displacement current and show that negative (capacitive) reactance may arise if the latter is sufficiently large. The analysis is compared with measurements obtained from thin film YBCO grown epitaxially on SrTiO 3 and MgO substrates by RF Sputtering.

In situ growth of YBa2Cu3O7-x on SrTiO3 and MgO substrates by RF sputter deposition

The authors report on the optimization of the growth parameters: substrate temperature, off-axis substrate position and sputtering parameters, for the in situ growth of YBa2Cu3O7-x films condensed on (110) and (100) SrTiO3 and (100) MgO substrates by RF magnetron sputtering.

Thermodynamic aspects to the growth of thin films of superconducting YBa2Cu3Ox

Abstract The thermodynamic aspects of growth have been investigated for thin films of superconducting YBa 2 Cu 3 O x condensed on MgO(100) and SrTiO(110) substrates by in situ rf magnetron sputter deposition. On the MgO(100) substrates we observe highly c -axis orientated 160 nm grains with density 3.6 × 10 8 cm −3 . For simultaneous deposition on SrTiO 3 (110) lateral growth structures occur epitaxially orientated with (013) parallel to the substrate plane. It seems unlikely that the spiral growth features reported for YBCO sputtered on (100) surfaces will occur on the (110) substrates. The results suggest that the growth mechanisms are considerably different for the two orientations. Nucleation and island growth occur on the (100) surface and lateral epitaxial growth occurs on the (110) surface for films deposited under the same conditions.

Low frequency impedance and structural properties of YBCO thin films

Abstract This paper concerns work carried out on the ac electrical properties of YBCO thin films. The experiments were carried out in the low frequency range 100 kHz–13 MHz. Results show that the film impedance above T c is related to the orientation of the substrate used. It is the difference in film orientation which most likely leads to the difference in reactance observed. The film impedance also depended critically on the film quality. For temperatures below T c all films were purely inductive as expected.

YBCO thin film device fabrication using lithographic techniques

Abstract We have investigated the use of conventional lithographic techniques and chemical etching to form structures in thin film YBCO produced by rf magnetron sputtering. Micro Posit 1350 positive photoresist was used to put down patterns on untreated Y 1 B 2 Cu 3 O x surfaces. Etching was carried out in solutions of orthophosphoric acid or ferric nitrate. Using this procedure we produced Hall bars, and narrow constrictions. The narrow constrictions were used primarily for measuring critical currents. Critical current densities greater than 10 6 A cm −2 were measured for films deposited on SrTiO 3 (110) orientated substrates. A constriction, 200 μm wide, exhibited weak linking behaviour.