Recent Advances in the Deposition of Multi-Component Oxide Films by Pulsed Energy Deposition

Abstract

Chapter x Recent Advances in the Deposition of Multi-Component Oxide Films by Pulsed Energy Deposition T. Venkatesan*, K. S. Harshavardhan, M. Strikovski and J. Kim Neocera, Inc., 10,000 Virginia Manor Road, Beltsville MD 20705, USA. (To be published in "Thin Films and Heterostructures for Oxide Electronics", edited by Dr. S. B. Ogale and published by Elsevier) 1. INTRODUCTION The potential of Pulsed Laser Deposition (PLD) was realized for the first time with the deposition of high temperature superconducting films of YBCO nearly 17 years ago [1]. It was shown that the non-equilibrium thermal evaporation process preserves the stochiometry of the target material in the film under material-specific window of laser energy density and collection angle of the evaporant [2,3]. Preservation of target stochiometry, a unique feature of PLD, is considered to be a result of the following two important factors. 1. The time scale of the evaporation process and the heat transfer to the target is short compared to the time scale in which the surface and bulk atomic species intermix. 2. Due to high evaporant density at the target surface, collisional processes dictate the angular distribution of the ejected species (atoms, neutrals and ions) and up to a specific distance from the target, the trajectories are species independent. This distance is specific to a target material, laser energy density and the deposition pressure. Besides preserving the target stochiometry in the deposited film, some of the attractive features of PLD include the following. 1. Since the energy source (pulsed laser) is external to the deposition chamber, film depositions can be undertaken over a wide dynamic range of chamber pressures and substrate temperatures. In RF sputtering for example, the chamber can not be at arbitrary pressures during the film deposition. Similarly, in Chemical Vapor Deposition (CVD), the substrate temperature is governed for example, by the precursor cracking temperature. 2 2. Multi-layers can be prepared by sequentially locating a target in the laser beam and this can be accomplished easily by using a multi-target carrousel and simple target manipulation schemes. Either manual or automated approaches can be used. 3. For exploring new materials, a target typically an inch or less in diameter, a few millimeters thick is adequate and such targets can be synthesized with relatively low investment and in short turn around times using standard ceramic processing routes. As a result, PLD has emerged as the technique of choice among researchers working in the area of multi-component oxide thin films, and is today the fastest route to prototyping films of novel materials. While the early PLD systems were simple, consisting of a target, substrate heater and a pumping stack, today’s systems have evolved considerably in their functionality and features. In this review we hope to capture the salient progress made to date and also speculate on what the future holds for this technique.