Steve Shen Ph.D.
Department of Mechanical Engineering
"PZT Thin-Film Micro Sensors and Actuators: Applications to Biomedical Engineering"


ABSTRACT

Lead-Zirconium-Titanium Oxide (or PZT) is a piezoelectric material widely used as sensors and actuators for bulk structures.  Advantages of PZT-based devices include high frequency bandwidth, fast response, and high sensitivity.  Miniaturization of PZT-based devices will not only perfect many existing products, but also open vast new biomedical applications, such as tiny biomedical diagnostic tools, minute hearing implants, and miniaturized surgical tools that are less invasive.

At the University of Washington, we fabricate PZT thin films using sol-gel processes.  Resulting PZT films have thickness in the order of 1 µm, and crack free area of the film can be as large as 4mm x 4mm .  For actuator applications, our design consists of a silicon diaphragm and a PZT film with bottom and top electrodes.  In addition, the silicon diaphragm can carry miniaturized "tools," which ranges from a single optical fiber (e.g., for scanning endoscopes) to millions of narrods (e.g., for micromixers).  Voltage applied to the PZT film drives the silicon diaphragm and its tools into an out-of-plane or an in-plane motion.  Currently, we are studying the feasibility of using the PZT thin-film microactuators for 2-D scanners and hybrid cochlear implants to combine acoustic and electric stimulations.  For sensor applications, our design consists of a stainless steel needle coated with a PZT thin film and a top electrode.  When the needle is subjected to compressive loads, the charge accumulated in the PZT thin film is proportional to the loads and can be measured through use of a charge amplifier.  The PZT microsensor, for example, can be used to monitor the pressure distribution in a knee joint during a walking cycle.