Controlled creation and displacement of charged domain walls in ferroelectric thin films.

Charged domain walls in ferroelectric materials are of high interest due to their potential use in nanoelectronic devices. While previous approaches have utilized complex scanning probe techniques or frustrative poling here we show the creation of charged domain walls in ferroelectric thin films during simple polarization switching using either a conductive probe tip or patterned top electrodes. We demonstrate that ferroelectric switching is accompanied - without exception - by the appearance of charged domain walls and that these walls can be displaced and erased reliably. We ascertain from a combination of scanning probe microscopy, transmission electron microscopy and phase field simulations that creation of charged domain walls is a by-product of, and as such is always coupled to, ferroelectric switching. This is due to the (110) orientation of the tetragonal (Pb,Sr)TiO3 thin films and the crucial role played by the limited conduction of the LSMO bottom electrode layer used in this study. This work highlights that charged domain walls, far from being exotic, unstable structures, as might have been assumed previously, can be robust, stable easily-controlled features in ferroelectric thin films.

Velocity Control of 180° Domain Walls in Ferroelectric Thin Films by Electrode Modification.

The velocity of individual 180° domain walls in thin ferroelectric films of PbZr0.1Ti0.9O3 is strongly dependent on the thickness of the top Pt electrode made by electron-beam induced deposition (EBID). We show that when the thickness is varied in the range <100 nm the domain wall velocity is seen to change by 7 orders of magnitude. We attribute this huge range of velocities to the similarly large range of resistivities for the EBID Pt electrode as extrapolated from four-point probe measurements. The domain wall motion is governed by the supply of charges to the domain wall, determined by the top electrode resistivity, and which is described using a modified Stefan Problem model. This has significant implications for the feasibility of ferroelectric domain wall nanoelectronics, wherein the speed of operation will be limited by the maximum velocity of the propagating domain wall front. Furthermore, by introducing sections of either modified thickness or width along the length of a "line" electrode, the domain wall velocity can be changed at these locations, opening up possibilities for dynamic regimes.

Controlling domain wall motion in ferroelectric thin films.

Domain walls in ferroic materials have attracted significant interest in recent years, in particular because of the unique properties that can be found in their vicinity. However, to fully harness their potential as nanoscale functional entities, it is essential to achieve reliable and precise control of their nucleation, location, number and velocity. Here, using piezoresponse force microscopy, we show the control and manipulation of domain walls in ferroelectric thin films of Pb(Zr,Ti)O3 with Pt top electrodes. This high-level control presents an excellent opportunity to demonstrate the versatility and flexibility of ferroelectric domain walls. Their position can be controlled by the tuning of voltage pulses, and multiple domain walls can be nucleated and handled in a reproducible fashion. The system is accurately described by analogy to the classical Stefan problem, which has been used previously to describe many diverse systems and is here applied to electric circuits. This study is a step towards the realization of domain wall nanoelectronics utilizing ferroelectric thin films.