Thickness-dependent switching behavior of 0.8(Bi0.5Na0.5)TiO3-0.2SrTiO3 lead-free piezoelectric thin films

0.8(Bi0.5Na0.5)TiO3-0.2SrTiO(3) (BNT-0.2ST) thin films, with thicknesses ranging from 90 to 364 nm, were fabricated on platinized silicon substrates by sol-gel method. These films were investigated by switching spectroscopy piezoresponse force microscope (SS-PFM) as a function of frequency at room temperature, revealing the enhanced ferroelectric response in similar to 210 nm film at all frequencies (0.1 Hz - 1.5 Hz). This enhancement was ascribed to the largest thermally-activated stress at such thicknesses generated during film fabrications. As the temperature of the investigated films increases from room temperature to 200 degrees C, the piezoelectric parameters were obtained from SS-PFM, such as switching polarization (R-s), coercive bias (V-0), work of switching (A(s)), maximum strain (S-max), and negative strain (S-neg), indicating an occurrence of phase transition from ferroelectrics to relaxors. This work revealed that thickness plays a crucial role for ferroelectric response and temperature-dependent phase transition in BNT-0.2ST films, since it affects the stress state and switching behavior.