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.

BiFeO 3 was studied as an alternative environmentally clean ferro/piezoelectric material. 200-nm-thick BiFeO 3 films were grown on Si substrates with SrTiO 3 as a template layer and SrRuO 3 as bottom electrode. X-ray and transmission electron microscopy studies confirmed the epitaxial growth of the films. The spontaneous polarization of the films was ϳ45 C/cm 2 . Retention measurement up to several days showed no decay of polarization. A piezoelectric coefficient ͑d 33 ͒ of ϳ60 pm/ V was observed, which is promising for applications in micro-electro-mechanical systems and actuators.

In this letter we report on the effect of thickness scaling in model PbZr 0.2 Ti 0.8 O 3 ͑PZT͒ / SrRuO 3 heterostructures. Although theoretical models for thickness scaling have been widely reported, direct quantitative experimental data for ultrathin perovskite ͑Ͻ10 nm͒ films in the presence of real electrodes have still not been reported. In this letter we show a systematic quantitative experimental study of the thickness dependence of switched polarization in (001) epitaxial PZT films, 4 to 80 nm thick. A preliminary model based on a modified Landau Ginzburg approach suggests that the nature of the electrostatics at the ferroelectric-electrode interface plays a significant role in the scaling of ferroelectric thin films. The effect of thickness scaling in ferroelectrics has recently been of immense interest. [1][2][3][4][5][6][7][8][9][10][11][12] As the dimensions (both lateral and vertical direction) of the perovskite layer decreases, the fundamental question of size dependence becomes crucial. From a theoretical point of view, two models have been traditionally used to describe size effects, namely an "intrinsic" effect 9,10,13 and a "depoling field" effect. 4,5,14,15 Experimentally Tybell et al. 8 qualitatively showed that even a 4-nm-thick epitaxial PbZr 0.2 Ti 0.8 O 3 (PZT) film on Nb:STO is ferroelectric. However a direct experimental quantification of the ferroelectric polarization, particularly for films in the sub-10 nm thickness range has not been reported. For such ultrathin films direct experimental quantification of size effects are complicated by extrinsic effects such as leakage and therefore methods other than the traditional P -E hysteresis loop have been reported to characterize the stability of the polar state. 1,7 This letter presents experimental measurements of the switched polarization in PZT films of thickness down to 4 nm, in the presence of real electrodes.A 70-nm-thick SRO layer was grown on STO at 650°C followed by the PZT layer via pulsed laser deposition. The deposition was carried out at 100 mTorr of oxygen and the sample was cooled down from growth temperature 1 atm of oxygen. In order to avoid complications from 90°domain formation the PZT films were grown in a thickness range from 4 to 80 nm, for which they are entirely c-axis oriented. The switchable polarization was measured using a Radiant Technologies Precision Premier system at 16 kHz (hysteresis loops) and an AFM based pulsed probing technique with conductive Pt-Ir tips was employed to measure the pulsed polarization. 16 We focused on the PZT ͑0/20/80͒ composition, since it has an in-plane lattice parameter of 3.94 Å, 17 which is closely lattice matched to SRO͑3.93 Å͒. Figure 1(a) is a low magnification TEM image of a 4 nm (nominal) thick film; the interfaces between SRO and PZT are sharp, identified as dashed lines in the high resolution image, Fig. 1(b). The electrode-ferroelectric interface shows a significantly reduced dislocation density, attributed to the small lattice mismatch (0.7%) at growth temperature of 600...

We report on the measurement of switchable pulse polarization of micron and submicron ferroelectric capacitors contacted using an atomic force microscope. Fast square pulses with rise time on the order of tens of nanoseconds are used to obtain the switchable polarization (ΔP) of discrete polycrystalline Pb(ZrTi)O3 capacitors of 21.5, 0.69, and 0.19 μm2 prepared by sputtering and reactive ion etching. Our studies show that the switching characteristics of these capacitors are well behaved, indicating that high-speed and high-density ferroelectric memory capacitors are not limited by scaling down the capacitor area.