Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O₃ thin films using second harmonic piezoresponse force microscopy

Here, we present a direct observation of fatigue phenomena in epitaxially grown Pb(Zr_0.2Ti_0.8)O₃ (PZT) thin films using second harmonic piezoresponse force microscopy (SH-PFM). We observed strong correlation between the SH-PFM amplitude and phase signals with the remnant piezoresponse at different switching cycles. The SH-PFM results indicate that the average fraction of switchable domains decreases globally and the phase delays of polarization switching differ locally. In addition, we found that the fatigue developed uniformly over the whole area without developing region-by-region suppression of switchable polarization as in polycrystalline PZT thin films.