Spatially Resolved Spectroscopic Mapping of Polarization Reversal in Polycrystalline Ferroelectric Films: Crossing the Resolution Barrier

The mesoscopic reversible and irreversible polarization dynamics in polycrystalline PZT thin film capacitors are studied using local spectroscopic mapping and macroscopic first-order reversal curve measurements. The transition from a regime of short range domain wall motion to the formation of mesoscopic clusters to complete switching is observed. The fractal dimension of the clusters is consistent with the random-bond disorder model. The combination of macroscopic and local measurements allows the characteristics length scales corresponding to the transition from Rayleigh to Preisach behaviors and onset of macroscopic averaging to be determined.

Figure 1

(a) Rayleigh-like dielectric response and (b) Preisach density measured using large capacitor structures. (c) Minor and major hysteresis loops calculated from the irreversible part of the Preisach density, assuming the sample was depoled prior to the field excitation. (d) Averaged local SS-PFM loops for similar excitation windows. (e) The dispersion$\sigma P(V)$ and (f) $RV(L)$ for different excitation windows.

Figure 2

(a)–(f) Evolution of the hysteresis loop as a function of the applied bias voltage. (a) and (b) show the remanent piezoresponse maps, RP. (c)–(f) are switchable response maps with increasing excitation windows [units : PFM amplitude (a.u)].

Figure 3

(a) Distribution of remanent piezoelectric response for different excitation windows. (b) Distribution of switchable response showing Gaussian profiles. Evolution of (c) average SR and (d) deviation with excitation window. The intercept in (c) is $\sim 1\mathrm{V}$ (error bars are invisible). The red dots in (c) illustrate the normalized switched polarization calculated from macroscopic (global) Preisach measurements. $A$, $B$, and $C$ denote three different sets of data on the same film.

Figure 4

Topography of (a) bare film and (b) electroded film in comparison with (c) the switchable response map at an excitation window of 7 V. (d) Comparison of the correlation widths from the SR images with the electrode and bare PZT topography images. (e) Spatial autocorrelation functions $CF$ at different bias voltages. (f) Fractal analysis of SR images for different bias windows. (g) Bias window dependence of fractal dimensionality.