Investigation of Nonswitching Regions in Ferroelectric Thin Films Using Scanning Force Microscopy

Abstract

Nonswitching regions which degrade the electrical properties of ferroelectric thin films were investigated by scanning probe microscopy. An 80-nm-thick PbZr 0.5 Ti 0.5 O 3 (001)(PZT) ferroelectric thin film and a YBa 2 Cu 3 O 7−δ (100) bottom electrode were grown on SrTiO 3 (100) substrates by the pulsed laser deposition method. We successfully detected nonswitching regions in the PZT thin films by measuring ferroelectric hysteresis loops using a scanning probe microscope, and the hysteresis loops showed an asymmetric shift toward negative remanent polarization. It is suggested that the nonswitching regions originate from dislocations caused by a lattice mismatch between the PbZr 0.5 Ti 0.5 O 3 (001) and the YBa 2 Cu 3 O 7−δ (100). The effective thickness of the nonswitching regions is estimated to be 20 nm from the amount of the shift of the hysteresis loops.

Piezoresponse force spectroscopy of ferroelectric-semiconductor materials

“…[36][37][38][39][40][41] Recently, PFM spectroscopy has been extended to an imaging mode using an algorithm for fast ͑100-300 ms͒ hysteresis loop measurements developed by Jesse et al 42 The progress in experimental studies has stimulated a parallel development of theoretical models to relate PFM hysteresis loop parameters and materials properties. A number of such models are based on the interpretation of phenomenological characteristics of PFS hysteresis loops similar to macroscopic P-E loops, such as slope, imprint bias, coercive bias, remanent response, and work of switching, 43,44 as illustrated in Fig. 1.…”

Mechanisms of imprint effect on ferroelectric thin films

“…7 As a result of clamping-induced electrode-film interaction 19,20 and the corresponding thermal or lattice mismatch 21 interfacial stress is always present at the surface. Müller and Thomas investigated the thickness dependence of early-stage stress development in two-dimensional solid film growth and obtained the following exponential stress distribution function:…”

“…[45][46][47] Such degradation of ferroelectric properties 19 has been suggested to occur for reasons such as: ͑a͒ interdiffusion between a ferroelectric thin film and electrode, 48 ͑b͒ insufficient flatness of bottom electrode and film, and ͑c͒ vacancies of Pb and/or oxygen. 49 It is justifiable to model the surface layer as a graded one in which the permittivity and remanent polarization decrease gradually from the bulk values ͑Fig.…”

Properties of epitaxial BaTiO3 deposited on GaAs

“…28 It is also possible that a small imprint effect from epitaxial strain at the BTO/GaAs interface could contribute. 29 The PFM signal was indeed dominated by the piezoresponse of ferroelectric domains and not by coupling to surface or interface charges, 30 which is demonstrated by the fact that domains of opposite polarity routinely had a 180 phase difference (Figs. 5(c) and 5(e)).…”