Substrate selection presents particular challenges for the production of high‐quality high‐temperature superconducting (HTS) thin films suitable for applications. Because the substrate is generally a passive component, it is often ignored and assumed to have a negligible effect on the structure residing on top of it. There is also a technological motivation to use substrates that conventional wisdom would argue are unlikely to support high‐quality HTS films. These facts have led to rediscovery of many of the fundamental issues governing the role of the substrate in determining the properties of the thin film(s) it supports. For this reason, the study of issues in substrate selection for HTS materials presents a microcosm for substrate selection more generally. We consider the major issues governing the role of the substrate in HTS thin‐film technology and discuss many of the material classes and specific materials that have been studied for their suitability as substrates for HTS films.

Substrate selection for high‐temperature superconducting thin films

The growth and characterisation of YBa2Cu3O7 thin films are reviewed. The discussion of growth is limited to the physical vapour deposition techniques of laser ablation, sputtering and evaporation. Emphasis is placed on the practical problems of growing epitaxial films in situ and characterising them.

https://iopscience.iop.org/article/10.1088/0953-2048/3/1/006/pdf

Physical vapour deposition techniques for the growth of YBa2Cu3O7 thin films

Superconducting nanobridges of YBa2Cu3O7 thin films with widths down to w=200 nm and lengths from 0.2 to 10 μm are patterned using metal masks fabricated by electron‐beam lithography and reactive ion etching. The YBa2Cu3O7 films were dry etched by ion beam milling at minimal energies of 250 eV on a liquid‐nitrogen‐cooled sample holder. Long bridges (l=10 μm) showed superconducting features similar to those of unstructured YBa2Cu3O7 films. Short nanobridges exhibited phase‐slip center behavior up to the transition temperature of 87–89 K. Shapiro steps were observed in the current‐voltage characteristics in applied microwave fields and the critical current decreased linearly with the amplitude of the microwave field.

Nanobridges of optimized YBa2Cu3O7 thin films for superconducting flux‐flow type devices

In situ epitaxial growth of YBa2Cu3O7−δ thin films on Y‐cut LiNbO3 substrates using a standard laser ablation technique is reported. Resistance of the films shows a normal metallic behavior and a very sharp (<1 K) superconducting transition with Tc(R=0) of 92 K. High critical current density of Jc(77 K)=2×105 A/cm2 is observed, which is in accordance with epitaxial growth. Film orientation observed from x‐ray diffraction spectra indicates that the c axis is normal to the substrate plane and the a axis is at 45° to the [11.0] direction of the hexagonal lattice of the substrate with two domains in mirror image to the (110) plane.

Epitaxial growth of YBa2Cu3O7−δ thin films on LiNbO3 substrates

Y‐Ba‐Cu‐O thin films have been prepared on MgO(100) substrates by rf reactive magnetron sputtering from a single ceramic target By adopting high total pressures, typically 280 mTorr, and relatively low substrate temperatures of approximately 650 °C, epitaxial films with the relations (001) YBa2Cu3Oy∥(001)MgO and [100]YBa2Cu3Oy∥[100]MgO can be reproducibly obtained A high degree of epitaxy is confirmed by x‐ray pole figure measurements and ion channeling These films require a brief rapid thermal oxygen anneal at typically 850 °C, to exhibit sharp superconducting transitions with zero resistance around 75 K Films deposited at higher temperatures above 700 °C show transitions as deposited with zero resistance near 80 K The quality of the transition is correlated with expanded lattice constants with the best transitions occurring in films whose lattice constants approach that of the bulk The films have high critical current densities of 1–5×106 A/cm2 at 42 K They also show good uniformity and excellen

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=905537

Epitaxial Y‐Ba‐Cu‐O thin films on MgO deposited by high‐pressure reactive magnetron sputtering

We present details about the deposition of thin Y1Ba2Cu3O7−δ films on single‐crystal LiNbO3 substrates by planar dc magnetron sputtering. Among other data, results of transition temperature (Tc(R=0) =88 K) and critical current density (jc >2×109 A/m2 at 77 K) plus some details about film‐to‐substrate orientation which is present in all three crystallographic directions are reported.

Fully textured growth of Y1Ba2Cu3O7−δ films by sputtering on LiNbO3 substrates

The preparation of high-quality thin Y1Ba2Cu3O7 − δ films on various substrates, particularly LiNbO3 and MgO, by d.c.-magnetron sputtering from a sintered stoichiometric target is investigated in some detail. Films are characterized according to their superconducting properties, crystallographic texture, surface smoothness, etc.

Preparation of thin YBa2Cu3O7 − δ layers on various substrates (LiNbO3, MgO, SrTiO3) BY d.c.-magnetron sputtering☆

Thin Y 1 Ba 2 Cu 3 O 7- δ films with smooth surfaces have been deposited directly crystalline by planar dc magnetron sputtering from a stoichiometric sintered target. Transition temperature achieved are about T c = 91K on MgO and SrTiO 3 , and 88K 2 on LiNbO 3 substrates with transport critical current densities j c exceeding 1×10 10 A/m 2 and 2×10 9 A/m 2 , resp., measured at T = 77K in zero field.

Preparation and characterization of thin Y1Ba2Cu3O7-δ films made by dc magnetron sputtering

The resistivity behavior of sputtered YBCO films has been investigated during anneal at temperatures up to 1175 K. Characteristic variations in resistivity under different experimental conditions are related to microstructural changes and corresponding superconducting properties. >

H. Neeb

Papers

Fully textured growth of Y1Ba2Cu3O7−δ films by sputtering on LiNbO3 substrates

Preparation of thin YBa2Cu3O7 − δ layers on various substrates (LiNbO3, MgO, SrTiO3) BY d.c.-magnetron sputtering☆

Preparation and characterization of thin Y1Ba2Cu3O7-δ films made by dc magnetron sputtering

Resistivity behavior during anneal of YBa/sub 2/Cu/sub 3/P/sub 7-x/ films