Novel Materials Applications of Pulsed Laser Deposition
- PDF / 3,226,296 Bytes
- 10 Pages / 576 x 777.6 pts Page_size
- 15 Downloads / 254 Views
Figure 1. Schematic diagram of an electrical polarization hysteresis loop measured for a ferroelectric capacitor cell with applied voltage E and measured polarization P, showing the coercive voltage Ec and remnant polarization Pr.
44
superlattices that have been laser evaporated. Over 75 of these materials were deposited as thin films. The goal of this article is to provide an introduction to some of the newer applications of PLD for thin film fabrication. Four classes of materials are highlighted: ferroelectrics, bioceramics, ferrites, and tribological materials. Ferroelectric materials are structurally related to the hightemperature superconducting oxides and therefore are a direct extension of the recent superconducting oxide work. Bioceramics are dissimilar in structure and application to both ferroelectrics and superconducting oxides, but they are complex multicomponent oxides and, therefore, benefit from the use of PLD. Ferrites, also complex, multicomponent oxides, represent another exciting, but only lightly explored opportunity for PLD. In contrast, tribological materials are typically neither complex nor multicomponent. Nevertheless, interesting structures and properties have been produced by PLD. A few of the more important ones will be discussed. These different types of materials demonstrate the diversity of capabilities offered by PLD. Ferroelectrics Ferroelectric materials possess a wide array of interesting physical and electrical properties, as has recently been described.2 By definition, they will retain an electrical polarization generated by an applied electrical field after the field is removed. Figure 1 schematically demonstrates this behavior in an electrical polarization hysteresis loop with a coercive voltage £c, and a remnant polarization Pv. This polarizability imparts other useful properties as
well, namely, piezoelectric, pyroelectric and electrooptic behavior, and in some cases a very large (—1,000) dielectric constant. In thin film form, materials with such properties offer tremendous potential for use in sensors, displays, actuators, and various elements of electrical and optical integrated circuits. This potential has long been recognized (see review by Francombe3), but has been difficult to realize. The enthusiasm of the early 1970s foi applying ferroelectric thin films diminished largely due to problems in fabricating economical and high-quality thin films of ferroelectric materials. Such difficulties arose because these materials are typically multicomponent oxides and frequently contain a volatile constituent. Haertling4 and Roy5 both recently published reviews on the history and difficulties of fabricating thin films of ferroelectric oxides. An increasing need to use the properties of ferroelectric materials in integrated circuit devices, and improved thin film deposition techniques have rekindled interest in developing ferroelectric thin films for applications. The growing number of well-attended conferences on thin film ferroelectrics (e.g., References 6-9) attests to this
Data Loading...
