Piezoresponse force microscopy observations of switching behavior in Pb(Zr,Ti)O3 capacitors

We report on the polarization switching behavior in Pt/Pb(Zr,Ti)O-3 (PZT)/SrRuO3/SrTiO3(111) capacitors observed by piezoresponse force microscopy (PFM). Through PFM observations of capacitors partially switched by applying switching pulses shorter than the switching time, the nucleation behavior and domain growth were investigated. Polarization switching preferentially originated from preexisting latent nuclei and consequently, switched domains appeared at the same positions for various pulses with the same polarity. On the other hand, switched domains were observed at different positions for voltage pulses with different polarities. On the basis of a comparison of domain patterns with topography, it is suggested that switched domains are roughly associated with PZT grains and that each grain has preferred polarization directions. Switching current measurements revealed that a voltage drop across the series resistance of the SrRuO3 bottom electrode and PFM system occurred in our measurements because the switching currents were more than 10 mA. Due to this voltage drop, the effective voltage applied to PZT thin film (V-PZT,V-eff) was almost constant at 2.8 V when external pulse voltages were changed from +/- 4 to +/- 10V. For V-PZT,V-eff of 2.8V, the density of latent nuclei and the velocity of sideward domain growth were estimated to be similar to1 mum(-2) and 15 m/s, respectively.