Polarization Offsets of Non Graded and Graded Ferroelectric Films

Abstract

ABSTRACT Shifts of hysteresis loops along polarization axis are observed on non graded Pb(Zrx,Ti1-x)O3 ferroelectric films using a Sawyer-Tower circuit. The offsets become significant providing that the sense capacitor is large enough and the input resistance of the measurement set up is artificially increased. The offsets, consisting in DC voltages rather than DC polarizations, are thus not the exclusive feature of graded ferroelectric devices (GFD's). Our observations are consistent with the charging up of the sense capacitor by asymmetrical leakage currents in the film and strongly suggest that rectifying effects are probably involved in most of the vertical offsets observed on ferroelectric thin film capacitors. Assuming blocking contacts at the electrode—ferroelectric interfaces, we propose that the composition gradient in GFD's produces a variation of the band gap energy leading to potential barrier with different heights at the two interfaces. Such asymmetry of the energy band diagram is consistent with our hypothesis of asymmetrical leakage currents.