Impact of solution chemistry on successfully depositing sol-gel PZT films directly on copper surfaces

The integration of ferroelectric oxide thin films with base metal electrodes is both enticing for manufacturing development and intriguing for scientific investigation. Traditionally, the ferroelectric lead zirconate titanate (PZT) has been considered incompatible with base metal technology because its PbO volatility makes conventional thermodynamic processing impractical. However, recent advances in sol-gel processing science have shown that during film deposition, reactions at the PZT/Cu interface can be avoided if organic constituents are strategically removed. Strategic organic removal requires both careful design of process variables and solution chemistry. Thermal and atmospheric processing conditions are constrained to kinetically maintain an unoxidized copper substrate. Solutions processed within these confined conditions must form gels with sufficiently reduced organic content and properly consolidated gel networks such that phase-pure and crack-free ceramic films can be crystallized. The current work explores three solution chemistries that use different chelating ligands: alkanolamines, acetylactone, and acetic acid. It is found that the alkanolamine solution frustrates perovskite formation and is prone to cracking under processing conditions compatible with the copper substrate. The introduction of water vapor into the processing atmosphere is only moderately successful at resolving these issues. Using a more volatile chelating agent (acetylacetone) shifts the thermal process window nearer a copper compatible regime. Because of its weaker chelation strength, acetic acid solutions are observed to be the most compatible with the processing constraints imposed by the copper substrate.