Effect of Microstructure on the Sheet Resistance of Ion-Beam Deposited ZnO Thin Film
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EFFECT OF MICROSTRUCTURE ON THE SHEET RESISTANCE OF ION-BEAM DEPOSITED ZnO THIN FILM SALIMAN A. ISA, P.K. GHOSH AND P. G. KORNREICH Department of Electrical and Computer Engineering, Syracuse University, Syracuse, New York 13244 ABSTRACT ZnO thin films were deposited by ion-beam sputtering technique. Preliminary results show that the films are stoichiometric and crystalline in nature. The microstructure of ZnO films obtained depends very much on the process parameters. Among these parameters is the substrate temperature whose effect has been carefully examined. ZnO films were deposited with substrate temperatures ranging from 200*C to 350'C. We observed that the sheet resistance of the films varies with their microstructure. In this investigation, a sheet resistance of 6.6 Mega-ohms per square is measured on a dense film deposited at a substrate temperature of 325*C. We present in this paper a correlation between the film's microstructure and stoichiometry with some of it's electrical properties. Introduction Zinc Oxide material has long been recognized as having the strongest piezoelectric effect of any non-ferroelectric material. As a vacuum deposited thin film, it finds considerable application especially in piezoelectric transducers for the generation and detection of bulk and surface acoustic waves at microwave frequencies [1][2]. For this type of application, the piezoelectric quality film must meet the basic characteristic of high electrical resistivity and an oriented crystalline structure that yields a very strong piezoelectric effect. These properties in turn depend on the film's microstructure. The microstructural properties of the film are also dictated by the deposition parameters. The Zinc Oxide (ZnO) thin films discussed here have been deposited by an ion-beam bombardment sputtering technique. The adjustable parameters considered in this investigation are the sputtering gas composition (Argon + Oxygen), sputtering pressure, and substrate temperature. The effect of these parameters on the microstructure and the sheet resistance of the films have been investigated. The scanning Electron Microscopy (SEM) has been used to examine the microsctructure, and a four point probe also has been used to measure the sheet resistance of the films. Experimental Procedures ZnO thin films have been deposited by sputtering from a high grade (99.99) ZnO ceramic target. The sputtering system used is the Veeco 3-inch micro-etch system utilizing the Kaufman type of ion source. The ion source is located on a Vesco 7700 series high vacuum pumping station. Mat. Res. Soc. Symp. Proc. Vol. 128. ' 1989 Materials Research Society
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The ions needed for sputtering are provided by the ion source where an arc discharge between the cathode and the anode takes place. The positive ions of the plasma are extracted and accelerated by a special multi-grid system with the resulting homogenous, colliminated and monoenergetic ion beam bombarding the surface of the ZnO target located below the grid assembly in the vacuum chamber. Sputteri
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