Analysis of the degradation of PZT and SrBi₂Ta₂O₉ thin films with a reductive process

Abstract

Electrical properties, crystal structure and composition were analyzed about ferroelectric PZT and SBT thin films with a reductive heat treatment. PZT films annealed in the atmosphere containing H₂ turned into paraelectric, while SBT films were shorted. Ferroelectricity of these degraded films recovered by a subsequent anneal in oxygen. Oxygen content in PZT and SBT films decreased by the reductive heat treatment and was compensated by the subsequent anneal in oxygen. Residual hydrogen was also detected in reduced SBT films. The loss of ferroelectricity or short of capacitor would be due to the oxygen defects and the residual hydrogen in ferroelectric thin films. A TiN layer covering ferroelectric capacitors acted as an H₂ barrier. Pt top electrode also played a role in preventing the reduction. This effect was enhanced by using a Pt electrode thicker than 300 nm and by anneal it at 600 °C.