Piezoelectrics are an incredibly useful family of materials that are used in sensors and actuators. In sensing, when they are deformed an electric charge is created in proportion to the deformation; for actuation, when they are subjected to an electric field a shape change is induced in proportion to the applied field. This behavior leads to applications such as ultrasonic imaging, fuel injection, micropositioning, energy harvesting, and microelectromechanical systems (ink jet print heads, microsensors, etc.). Unfortunately the most ubiquitous piezoelectric materials contain lead. The toxicity of lead has resulted in its elimination in paints and solders. Worldwide efforts are now underway to eliminate lead from all devices, including piezoelectrics. The aim of this research is to develop piezoelectric materials that do not contain lead for use in small-scale sensing and actuation applications. The elimination of lead is highly desirable in terms of processing and device fabrication, disposal at end-of-life, as well as opening up new application areas (in vivo sensing and actuation). In addition, this project acts as a vehicle for both recruiting and retaining a future generation of engineers and scientists that is diverse in terms of both gender and ethnicity. By integration with two mentoring programs that bring Oregon high school, undergraduate and graduate students, and the professor together, a pyramid of mentorship in the laboratory is being created and diversity is increased.
TECHNICAL DETAILS: The most prevalent piezoelectric material is based on Pb(Zr1-xTix)O3 (PZT). Recent worldwide regulatory restrictions on the use of lead have resulted in numerous groups searching for and examining lead-free replacement piezoelectric materials. The primary candidates to replace PZT are Bi, Na, and K based perovskites. However, to date research has largely neglected taking a thorough approach to thin film implementation of these materials, which is ultimately desired. Therefore a major opportunity exists to provide insight to the significant thin film processing issues and defect-related phenomena in these complex, volatile, multi-cation systems (which are exacerbated by the anisometric nature of thin film architectures). This work is designed to develop synthesis methodologies to high performing lead-free piezoelectric thin films using chemical solution and physical vapor routes. Novel elemental and structural characterization methods are used to understand the stoichiometry and defect equilibria present in these complex materials, and their impact on the ultimate ferroelectric and piezoelectric properties. Finally, this program acts as a critical vehicle for both recruiting and retaining a future generation of engineers and scientists that is diverse in terms of both gender and ethnicity. A culture of mentoring in the professor's laboratory is being fostered that enhances the connection of students to the field while also reaching out to recruit high school level students and attracting them to engineering and the sciences. This goal is being accomplished by collaborating with two programs at Oregon State University that bring underrepresented high school students to campus every summer to participate in research projects that are based on deposition and characterization of lead-free piezoelectric thin films.
