An improvement of retention property by using surface treatment in SOL-GEL derived PZT films

Abstract

The retention property of PZT (PbTixZr1-xO3) films has been a major obstacle to commercial FRAM (Ferroelectric Random Access Memory) prodeucts. The retention phenomenon is mainly due to undesired interfacial layers or defects such as oxygen vacancy or Pb vacancy, which is generated by fabricating PZT films. In sol-gel process, the undesired layer is formed at the surface of the PZT films during the annealing process, which greatly degrades the retention property. It was found that the degradation of retention property is caused by a Pb-deficient and Zr-rich layer with high defect density on the surface of PZT film. The undesired surface layer was clearly removed by adopting a novel surface-cleaning technique. The surface-modified PZT films showed excellent Qos value of 34 μC/cm2 after baking for 175 hours at 125°C, which is about 4 times larger than that of as-grown PZT film. The Qos-rate of the surface-modified PZT film was about-9%, which is about one third of that of as-grown PZT film. In spite of the harsh pulse train, where Vwrite = 4.0 V, Vread = 3.1 V for switching charge and 3.3 V for non-switching, the Qos value and Qos-rate of surface modified PZT film were drastically improved.