Effect of top electrode thickness on the piezoresponse of polycrystalline ferroelectric capacitors

The domain images of ferroelectric capacitors with different top electrode thicknesses in the as-grown and poled states were obtained by piezoresponse force microscopy (PFM). In poled capacitors, a uniform piezoresponse with the same contrast was obtained for top electrodes of different thicknesses. For capacitors in the as-grown state, a lower piezoresponse was observed with thicker top electrodes, due to the different domain orientations, suppression effect of the ferroelectric domains and the damping effect of the electrode. It is shown that the piezoresponse decreases nonlinearly with the increase in electrode thickness. When the top electrode thickness is above 75 nm, the piezoresponse value is almost zero. When the top electrode thickness is increased from less than 10 to 75 nm, the piezoresponse is reduced rapidly to a very small value. Details of the domain wall, grain boundary and defects gradually become indistinguishable. Our investigation suggests that to obtain clear domain information by PFM based on global excitation, the top electrode thickness should be less than 10 nm.