Formation and observation of ferroelectric domains in PbZr_1-xTi_xO₃ (PZT) thin films using atomic force microscopy

Very small-sized ferroelectric domains (<60 nm in diameter) were induced and observed using a modified atomic force microscopy (AFM). Bias voltage between a conductive AFM tip and a sol-gel processed PZT film caused the switching of small ferroelectric domains. Electrostatic forces between the polarized area and the tip provide the imaging of the polarized small domains. Applying voltage with the opposite sign can depolarize the polarized area and the formation of a series of data dots was demonstrated. In addition, the retention phenomena of micron size domains in PZT films were investigated. The polarized images disappeared within a few days even without an application of voltage - often called the retention loss or failure. An empirical relationship between relaxation time, bit size and poling time is established and verified. Two operative processes for the retention loss are either the stray charge accumulation on the polarized surfaces or the stress relaxation of the piezoelectric films. An effective way of improving the retention characteristics is suggested. The experimental results obtained in this study provide substantial insight into the mechanism for the retention failure of the polarized domains as well as the polarization behavior in PZT films with a nano-meter scale.