{001} Textured Growth of Doped, Gradient Free, Lead Zirconate Titanate Thin Films by Chemical Solution Deposition

Restricted
Author:
Borman, Trent Mitchell
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 15, 2016
Committee Members:
  • Susan E Trolier-Mckinstry, Thesis Advisor
  • Clive A Randall, Committee Member
  • Srinivas A Tadigadapa, Committee Member
Keywords:
  • PZT
  • piezoelectrics
  • ferroelectrics
  • thin films
  • mems
Abstract:
This work studied means of enhancing the performance of PbZrxTi1–xO3 (PZT) thin films via {001} textured growth, doping, and reduction of Zr/Ti compositional gradients. The direct seeding of {001} PZT on platinized silicon substrates was studied in relation to the platinum characteristics, doping, solution Pb stoichiometry and layer thickness. High temperature platinum was observed to enhance PZT grain size and reduce surface coverage of the pyrochlore secondary phase when compared to room temperature platinum. Generally, no significant crystallographic difference was observed between seed layers deposited on high temperature or room temperature platinum. Increases in solution lead excess reduced surface pyrochlore significantly. Niobium doping was found to increase grain size and pyrochlore coverage while Mn doping exhibited a rosette microstructure with poor crystallization on High Temperature (HT) Pt (via XRD). A thickness regime of 30 – 70 nm was found to yield strongly {001} oriented PZT seed layers. Degradation of {001} orientation as a function of film thickness was attributed to surface pyrochlore converting to misoriented perovskite grains. Use of lead rich solutions (particularly at the top surface of each crystallization) provided a means of preventing pyrochlore formation. Niobium doped films with Lotgering factors in excess of 0.99 were attainable with solutions ranging from 10-20 at.% Pb excess in various stacking sequences. In addition to films with low, medium and high lead contents, a film with thin layers of manganese doping was deposited. No significant trend was observed in the dielectric or piezoelectric properties as a consequence of lead content. The film with Mn doped layers exhibited reduced dielectric properties (including Rayleigh coefficients) and small signal piezoelectric properties while exhibiting similar large signal piezoelectric performance (d33;f of ~120 pm/V). Films with higher lead contents were found to undergo dielectric breakdown in a tighter distribution at lower electric fields than films with a low lead content, which exhibited a larger spread of failures at a higher average field. All films tended to microcrack prior to dielectric breakdown events and material ejection occurring. Microcracks were found to propagate predominately in a straight line with throughout the entire film thickness ~1.4 μm.