Investigation of thickness dependence of the ferroelectric properties of Pb(Zr_(0.6)Ti_(0.4))O_3 thin-film capacitors

摘要

The ferroelectric properties of Pt/Pb(Zr_(0.6)Ti_(0.4))O_3/Pt/TiO_2/SiO_2/Si thin-film capacitors with different thicknesses are investigated. According to the literature data, tilting of the hysteresis loops and marked increase of the coercive fields are observed when the thickness of the film is reduced. The degradation of the switching properties is fully reproduced by simulations including nonferroelectric space-charge layers at both ferroelectric/electrode interfaces. Based on the theoretical results, a converse model is constructed from which the overall interface capacitance, the total interface built-in potential, and both dielectric permittivity and polarization of the bulk ferroelectric layer are determined for each film. Remarkably the polarization loop due to the switching domains, calculated for each Pb(Zr,Ti)O_3 (PZT) capacitor, exhibited a squarelike shape with coercive fields in agreement with the bulk value. Moreover, a unique set of parameters was found whatever the film thickness. From our results it is concluded that the degradation of the ferroelectric properties of metal-PZT thin-film-metal capacitors, often encountered when their thickness is reduced, probably arises from a mechanism of modulation of density and sign of the space charge at both interfaces.