ANNEALING PROCEDURES AND THEIR EFFECTS ON PZT/NANOPARTICLE THIN FILMS VIA A MODIFIED SOL-GEL PROCESS

摘要

The development of lead zirconate titanate (PZT) films can be a fairly troublesome process when trying to obtain a viable thick crack-free film. Traditional methods for film fabrication via a pure sol-gel solution provide the best results, but still can have many problems. This paper maps out the specific spin-coating and annealing steps used in order to achieve a PZT film with minimal-to-no cracking and/or delamination. A seed layer of PbTiO_3 (PT) was used in order to create nucleation sites for the subsequent PZT layers, virtually eliminating any delamination. All layers, including the PT base layer, were spin-coated at 3000 rpm onto a 100-mm silicon wafer (previously sputtered with Ti and Pt for adhesive and conductive purposes, respectively) and soft-baked at 150 °C for 10 min. Initial annealing procedures produced severe cracking, a result of the relatively high cooling rates through the Curie temperature (～350 °C). The annealing process was refined, for individual layers, to 550°C for 120 s, with a cooling rate of 0.042 °/s between 400 and 300 °C. Final annealing was conducted at 600 °C for 30 min, with a cooling rate of 0.028 °/s between 400 and 300 °C. The resulting PZT layer was virtually crack-free. Platinum was sputtered again subsequent to PZT deposition in order to pole the piezoelectric material. A PZTanoparticle powder mixture was also investigated as the piezoelectric layer. PZT nanoparticles were suspended in the sol-gel precursor solution and then spin-coated also at 3000 rpm onto a 100-mm wafer and soft-baked at 150 °C for 10 min. The relatively slow cooling rate was extended between 500 and 100 °C in order to prevent any cracking that might occur along grain boundaries between the individual PZT nanoparticles. The resulting film was crack-free, however displaying areas of agglomerated nanoparticles.