Dynamics of ferroelastic domains in ferroelectric thin films

Abstract

Dynamics of domain interfaces in a broad range of functional thin-film materials is an area of great current interest. In ferroelectric thin films, a significantly enhanced piezoelectric response should be observed if non-180 degrees domain walls were to switch under electric field excitation. However, in continuous thin films they are clamped by the substrate, and therefore their contribution to the piezoelectric response is limited. In this paper we show that when the ferroelectric layer is patterned into discrete islands using a focused ion beam, the clamping effect is significantly reduced, thereby facilitating the movement of ferroelastic walls. Piezo-response scanning force microscopy images of such islands in PbZr0.2Ti0.8O3 thin films clearly point out that the 90 degrees domain walls can move. Capacitors 1 microm2 show a doubling of the remanent polarization at voltages higher than approximately 15 V, associated with 90 degrees domain switching, coupled with a d33 piezoelectric coefficient of approximately 250 pm V-1 at remanence, which is approximately three times the predicted value of 87 pm V-1 for a single domain single crystal.

Ferroelectrics at the nanoscale

“…Despite this level of consensus, recent experimental work hints that parasitic dielectric dead-layers might not be intrinsic at all, or if they are, their presence is much less obvious than originally thought: Initially in response to concerns that permittivity suppression might result from microstructural imperfections [34][35][36] or from substrate clamping [37], Saad et al [38,39] made small parallelplate capacitors using 'thin films' that were directly milled from bulk single crystals using a Focused Ion Beam Microscope (FIB). Almost free-standing single crystal lamellae of BaTiO 3 down to ~75 nm were machined, and their functional properties tested, with the remarkable observation that bulk-like permittivities persisted, even in the thinnest films.…”

Effect of elastic domains on electromechanical response of epitaxial ferroelectric films with a three-domain architecture

“…It is clearly demonstrated that elastic domains can be sufficiently mobile in constrained ferroelectric films, and the relatively small extrinsic piezoeffect in the epitaxial films can be explained by elastic interactions between the clamped film and substrate. The extrinsic piezoeffect can be increased significantly by reducing the elastic clamping, as is supported by the experimental results on polydomain ferroelectric thin film "islands" with a lateral size comparable to their thickness [13,23].…”

“…Transmission electron microscopy (TEM) [25] and piezoelectric force microscopy (PFM) [13,23] studies of tetragonal PZT 20/80 films thicker than 300 nm show that they have a cellular architecture that completely relaxes the internal stresses. An optical microscopy study of epitaxial tetragonal BaTiO 3 thick films also illustrates similar morphology of a three-domain structure [14].…”

“…Particularly, the switching of elastic domains increases the compliance of polydomain phases to external mechanical, electrical or magnetic fields. The concept of elastic domains has been successfully applied to the analysis of polydomain microstructures in epitaxial films [4], and numerous polydomain structures in epitaxial films of superconductors [5], semiconductors [6], ferromagnetic [7] and ferroelectrics [8][9][10][11][12][13][14][15] have been studied experimentally and theoretically.…”

“…The elastic domain structure in epitaxial films has been studied extensively in theory [11,[18][19][20][21][22] and in experiment [12,13,23] during the last two decades. However, the theoretical work, including the comprehensive analysis based on homogeneous theory [10,18], construction of domain stability map based on theories of elastic domains and coherent phases [19], phase field modeling [11], and exact analytical solutions [20,21], mainly concentrated on elastic domain assemblies consisting of two domain variants (polytwins), except a few by Slutsker et al [22].…”