Processing effects for integrated PZT: Residual stress, thickness, and dielectric properties.

摘要

This dissertation focuses on the integration of lead zirconate titanate (PZT) films on Pt/Ti/SiO2//Si, and the effect of on properties. Direct deposition of PZT on Si will lead to on-chip power capacitors, non-volatile memory cells, and vibration sensors. However, previous research indicates that the dielectric, ferroelectric and piezoelectric response characteristics for the devices are often inferior to bulk specimens. Property variations have been attributed to changes in several major variables including, chemical composition, phase content, grain size, crystallographic orientation, film thickness, and stress, each of which, in turn, can depend on processing.; The first goal of this work was to design a sol-gel processing methodology to control all major variables except film thickness and stress, thus isolating their respective effects on properties. All specimens were verified to be of the Pb(Zr0.53Ti0.47)O3 composition, in the perovskite structure, with a constant grain size of 110nm, and with (111) fiber texture. PZT film thickness was varied from 95nm to 500nm and residual stress was measured to be either 150 or 180MPa, biaxial tensile, depending on thickness. These specimens allowed for new insights into the fundamental differences between bulk materials and thin films.; A series-capacitor model accounted for the observed dilution in room-temperature K from >900 to ∼600 as film thickness decreased, but could not account for the absence of the expected dielectric anomaly at high temperatures. Instead, a stress-induced distributed phase transformation related to the polycrystalline nature of the film was proposed to account for the observed behavior. Residual stress reduced the spontaneous polarization values in these specimens to 32muC/cm 2 from the predicted stress-free value of 50muC/cm2. An increase in coercive field was attributed to interfacial capacitance and residual stress, whereas a decrease of 30MPa tensile stress resulted in an increase of d33 from 33 to 65pm/V, irrespective of changes in film thickness. These results isolated, for the first time, the effects of stress and thickness on the dielectric, ferroelectric and piezoelectric properties of PZT films without convolution from the other major variables. The research provides a guideline for the tailoring of properties by modifying mechanical stress in polarizable and deformable thin films.