The asymmetric behaviors of PZT thin film capacitors with different top electrode metals

In this study, Metal-PZT-Pt test capacitors were prepared in order to investigate the effect of top electrode materials on the ferroelectric properties. The PZT capacitors with noble metals (Pt, Au) show symmetric P-E hysteresis loops, while the capacitors with non-noble metal (W, Ti and TiN) top electrodes exhibit asymmetrical hysteresis loops, which can be explained by a net positive internal field induced by the metal work function differences between top and bottom electrodes. This bias may cause larger -Q(c)' than +Q(c)'. The external bias (V-appl) is needed in order to compensate the internal field and V-appl leads to a symmetrical ratio of +Q(c)'/-Q(c)'. It is found that the V-appl correlates with the metal work function difference between top and bottom electrodes.