X-Ray Analysis on Ceramic Materials Deposited by Sputtering and Reactive Sputtering for Sensing Applications

Abstract

Piezoelectric materials have been extensively studied and employed over the last decades with the aim of developing new sensors and actuators to be applied in a wide range of industrial fields. The continuous increase of miniaturization requirements led also to an increasing interest in the synthesis of piezoelectric materials in the form of thin films. As an example, the growth of wireless mobile telecommunication systems favored the expansion of the design and fabrication of high-frequency oscillators and filters (Huang et al., 2005). Within this context, conventional surface acoustic wave (SAW) filters were gradually replaced by film bulk acoustic resonator (FBAR) devices. Their advantage in comparison with SAW devices resides in a higher quality factor (Lee et al., 2003) and lower fabrication costs (Huang et al., 2005). These kinds of devices are based on piezoelectric materials. Thus, an improvement in such material properties can have a strong impact in communication performances. A similar situation exists in the field of sensing. The increase of the sensitivity in piezoelectric sensors is one of the main targets which could be achieved by improving material characteristics. Therefore, the interest in this class of materials is not decreasing with time. On the contrary the enhancement of the piezoelectric material performances, together with the synthesis of new lead-free piezoelectric materials and the integration of ceramic materials with flexible substrates (Akiyama et al., 2006; Wright et al., 2011), is one of the latest research goals. Most piezoelectric materials are metal oxide and few metal nitride crystalline solids and can be single crystals or polycrystalline materials. In both cases, piezoelectric materials are anisotropic and the determination of the response of the material to an external mechanical stress induced along a certain direction on its surface must be performed along different crystallographic axes. Quantitative information about how the material responds to external stresses is given by the piezoelectric constants. Thus, the efficiency of the piezoelectric response can strongly vary with the crystal orientation of the material, and this occurs for bulk materials and thin films (Du et al., 1999; Yue et al., 2003).