The investigation of the switching of ferroelectric films BiFeO3 by second harmonic generation optical microscopy in a planar pattern of electrodes
In the most ferroelectric devices there used polarization switching in the direction which is perpendicular to the film plane. Planar geometry is optimal for the optical applications because it guarantees more effective interaction of electromagnetic wave and ferroelectric polarization as well as gives wide opportunities for elements integration and creation of the new generation of optical IC.
The switching of ferroelectric films BiFeO was investigated by second harmonic generation microscopy in a planar pattern of electrodes. Investigation data turned out indispensable for the revelation of the electric field distribution in the structure.
(a) (b) (c) (d)
Figure 1. Nonlinear optical image (mapping) of the BFO film with planar pattern of electrodes for different values of applied field: -25V (a), 0V (b), +25V (c), 0V (d). Image (a) shows the highlighted areas for which there was conducted an analysis of the switching parameters in local area.
Figure 1 represents the results of nonlinear optical mapping of ferroelectric films BiFeO3 when applying electric field to a planar pattern of electrodes with the range of 2 mkm and the width gap of 2 mkm.
As we know from the  the intensity of the SHG signal which is generated by metallic electrodes is very small in comparison with SHG intensity from the ferroelectric films especially when applying electric field. That’s why dark areas on the nonlinear optical image can be identified as electrodes.
It was shown in the , that the SHG intensity is proportional to ferroelectric polarization square, representing the sum of polarization terms depending and independing from the external electric field. SHG intensity will be equal when applying electric field with different signs with the small part on the unswitching polarization and it will be impossible to define oppositely polarized area on nonlinear optical image.
From the figure 1 it is obvious that the structure contains relatively big parts of unswitching polarization which may be linked to the formation of different kind defects (including mechanical strain) in near-electrode area.
Figure 2. Cross-section of nonlinear optical images built in selected areas for different parameters of applied field.
Figure 2 represents cross-section built in selected areas. It is seen that local switching parameters shows the high inhomogeneity of the polarization distribution in studied structure.
 Mishina E.D. et al. Local probing of the polarization state in thin Pb(ZrTi)O3 films during polarization reversal // Appl. Phys. Lett. 2001. Vol. 78, № 6. P. 796.