Deposition by plasma-assisted laser ablation and maskless patterning of YBa 2Cu 3O 7−x superconducting thin films

Abstract

YBa 2Cu 3O 7− x superconducting thin films were deposited in situ by plasma-assisted laser ablation onto polycrystalline yttria-stabilized-zirconia (YSZ) substrates at 700 °C in a low pressure (200–400 mTorr) O 2 discharge (−300 V). The laser operated at 5–50 Hz repetition rate and was focused onto a superconducting target with a typical energy density of 2.5–4 J cm −2. An in situ annealing step in 1 Torr O 2 atmosphere at 425 °C for 1–2 h was followed by slow cooling of the films to room temperature. The YBa 2Cu 3O 7− x films grew preferentially oriented with the c-axis normal to the substrate surface. They exhibited metallic behaviour in the normal state and superconducting transitions with typical onset of 91 K and zero resistance between 82 and 87 K. The transport critical current densities J c were 10 2 A cm −2 for 1μm thick films and two orders of magnitude higher, J c = 3 × 10 4 A cm −2, for 0.08 microm thick films. Maskless patterning was achieved by utilizing the ArF laser beam to induce etching selectivity of the superconducting thin films. For this purpose, the central part of the the beam was apertured by a slit and focused onto the sample by means of a 15 x Schwarzschild microscope objective to give an irradiated area on the sample of approximately 10 × 150 μm 2. The laser energy density on the sample was typically 10 3 J cm −2, while the repetition rate was varied between 10 and 20 Hz. Microbridges of different geometrics with a maximum resolution of 10 microm and high edge definition were obtained at 20 microm s −1 scan rate using this technique.