Fabrication of micromachined piezoelectric diaphragm pumps actuated by interdigitated transducer electrodes

Micromachined pump structures were fabricated using surface micromachining. The structures consisted of three or five connected chambers. Sequential actuation of the diaphragms on these chambers will yield peristaltic pumping. As the actuation material, lead zirconate titanate (PZT [53/47]) thin films were employed and actuated by interdigitated transducer (IDT) electrodes. First, chambers and channels on the 4" (100) silicon wafers were defined by reactive ion etching (RIE) and thermally oxidized. The etched structures were then filled with amorphous silicon. Low temperature (silicon) oxide (LTO) and PZT films were then deposited. The I-TO and PZT layers act as passive and active layers in a piezoelectric unimorph, respectively. A ZrO2 layer was employed to prevent reaction between SiO2 and PZT layers. A Cr/Au electrode was evaporated on top of the PZT layer and patterned into ring-shaped IDT electrodes. Finally, a porthole at each end of the pump structures was defined by ion milling and the whole micropump structure was released by removing the sacrificial amorphous silicon using XeF2. Completely released 500 mum diameter pump structures were fabricated. The remanent polarizations of the PZT films on released diaphragms were similar to20 muC/cm(2) and their coercive fields were similar to50 kv/cm. 500 mum diameter diaphragms were deflected as much as 2 mum with 120 V applied. The shape and behavior of the diaphragm deflection can be explained by considering both d(31) and d(33) piezoelectric coefficients of the PZT films.