This thesis describes the development of sputter-deposited piezoelectric lead zirconate titanate for sensing and actuation in microelectromechanical systems (MEMS). Piezoelectricity, the coupling of mechanical stress or strain and electric polarization observed in certain dielectric ceramics, is attractive for converting between electrical and mechanical energy in MEMS devices. While piezoelectric ZnO is currently used in MEMS devices such as the flexural plate wave device (FPW), replacing this layer with piezoelectric PZT should improve the performance of these devices due to PZT’s substantially larger piezoelectric coupling.
Our efforts have focused, in part, on optimizing and understanding our sputter deposition process consisting of co-deposition from three independently powered targets in a reactive environment. We found our as-deposited film composition was affected by the resputtering of lead atoms in the target plasmas, and because of this the deposition rate of lead depended not only on the power applied to its target, but on the power level of the other targets. This meant that in order to obtain films of a desired composition, usually the morphotropic phase boundary composition with excess lead (Pb1.3Ti0.48Zr0.52O3), we had to characterize the composition change induced by changing the power level on a single target during the co-deposition process. We have also characterized the thickness variation across our wafers due to the geometry of our deposition system, and use this thickness variation while examining the effect of film thickness on the delamination of the PZT films.
We have examined the relationship between the piezoelectric PZT film and the electrode and adhesion layers in experiments where we varied different processing parameters. It was discovered that while a nitrogen annealing atmosphere yielded highly oriented PZT films, annealing in oxygen produced better ferroelectric and piezoelectric properties. The random orientation in our PZT films has been correlated with the formation of Pt grains oriented in the  direction in the underlying electrode layer during anneals in oxygen. Delamination in these films is a continuing problem and failure surfaces were examined by scanning electron microscopy and optical methods. Films with a low temperature oxide (LTO) adhesion layer were found to exhibit a jagged crack path, indicating better adhesion than films with a phosphorous-doped silicon glass (PSG) adhesion layer where the crack path was much smoother.
May 31, 2001
Knollenberg, C. F. (2001). Sputter Deposition of Piezoelectric Lead Zirconate Titanate Thin Films for Use in MEMS Sensors and Actuators. United States: University of California, Berkeley.