Bottom and top electrodes nature and PZT film thickness influence on electrical properties

Abstract

Using platinum (Pt) and LaNiO 3 (LNO) as both top and bottom electrodes, the investigation of their effect on structural, dielectric, ferroelectric and piezoelectric properties of PbZr 0.54Ti 0.46O 3 thin films with different thicknesses (200, 400, 600 and 800 nm) was made. Four different structures (Pt/PZT/Pt, LNO/PZT/LNO, Pt/PZT/LNO and LNO/PZT/Pt) were processed on silicon substrate for comparison. So a total of 16 structures available. X-ray diffraction (XRD) analyses revealed that the use of Pt or LNO as bottom electrode changes the PZT crystallographic orientation. Dielectric measurements showed that for the films grown on either Pt or LNO electrodes, lower values of ɛ r were always obtained when Pt was used as top electrode in comparison of LNO for which ɛ r reached maximum value. The crystallographic orientation of the bottom electrode also was found to influence the dielectric constant of the film. Concerning the ferroelectric properties it was observed that, for a given bottom electrode, the use of LNO as top electrode systematically reduces both positive and negative coercive fields, when compared with top Pt electrode. On the other hand, for a given top electrode, utilization of LNO as bottom electrode still leads to the lowering of coercive field values when compared to Pt bottom electrode, however in smaller proportions with respect to what was observed when substituting Pt by LNO as top electrode. Moreover it was observed that the thickness dependence of the coercive fields almost vanished each time, and only when, LNO was used as top electrode. The piezoelectric response, measured thanks to laser doppler vibrometer, is increased when LNO is used as the top electrode, in proportions depending to the film thickness.