| Four different sizes of MEMS based piezoelectric ultrasonic transducers have been successfully fabricated at the University of Minnesota Micro-technology laboratory. The transducers operate at their fundamental resonance frequencies for maximum sensitivity.; The ultrasonic transducer elements consist of square silicon nitride membranes. A capacitor structure of piezoelectric material, lead zirconium titanate (PZT), was deposited on the top of the supporting nitride structure. The PZT structure enables the actuation and the sensing of the ultrasonic waves.; The thin film PZT for this work was spin-coated onto the device using a metalorganic deposition method, resulting in a PZT thickness of 0.4μ m. The average remanent polarization (+Pr) of the PZT thin film was measured at 23.5μCcm 2 with an average dielectric constant (K) of 1552. The membrane elements were individually released free by a deep reactive ion etching (DRIE) of the back of the silicon substrate, resulting in a structure with minimal cross talk between the different elements when fabricated in two dimensional arrays.; The transducers were also tested for impedance characteristics, average fundamental resonance modes were found at 15.6MHz, 9.52 MHz, 8.8MHz, and 8.7MHz, with the highest frequency registered for the smallest membrane size. Finally, the transducers were pulsed in per-fluorocarbon high dielectric strength solution and ethos were received from an air-solution interface.; Mechanical and electrical models were used to study the transducers behavior, simulations results agree well with the measured data suggesting that these models can be further used for optimizing future generations of transducers.; This thesis also suggests a novel ultrasonic micro-imaging system based on the integration of the transducer elements with micro-pumps for local contrast agent deployment. This method will overcome the toxicity, and absorption in circulation associated with the use of contrast agents. |
