Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale

Abstract

The nanoscale mechanism of retention behavior in SrBi 2 Ta 2 O 9 ͑SBT͒ thin films has been investigated by means of piezoresponse scanning force microscopy. It has been found that SBT films with Pt electrodes ͑SBT/Pt͒ exhibit a strong dependence of retention characteristics upon domain polarity: positive domains with the polarization vector pointing to the bottom electrode exhibit excellent stability in sharp contrast to the negative domains which show poor retention. The backswitching of the negative domains proceeds via sidewise motion of the domain walls and shows a log-time dependence. The strong effect of the poling voltage parameters ͑duration and amplitude͒ and the previous switching pattern on domain retention behavior is reported. On the other hand, in SBT films with IrO 2 electrodes ͑SBT/IrO 2 ), the written domains of both polarities show no sign of relaxation to the original state irrespective of the parameters of the poling voltage. The difference in retention behavior of opposite domains in SBT/Pt films is explained by the presence of the polarization-independent built-in bias at the SBT/Pt interface pointing to the bottom electrode. This built-in bias triggers the backswitching of a negative domain by generating positive nuclei at the interface. The forward growth of the nuclei is further governed by the field of the space charge which screens the original polarization state. The symmetric retention behavior and the stability of domain in SBT films with IrO 2 electrodes are attributed to the inhibition of the nucleation process at the SBT/IrO 2 interface.

Piezoelectric properties of PbTiO3 thin films characterized with piezoresponse force and high resolution transmission electron microscopy

“…6 gave Im= −0.63 V and coercive bias V c = 4.9 V. For this sample, the imprint Im varies in the range ϳ−1.6-+ 0.5 V over the film surface and V c between ϳ3.5 and 4.9 V. The imprint Im is comparable to imprint values of ϳ1 V for PTO films in former studies. 24 It can be explained by the different work functions of the bottom SRO electrode and of the Si doped PFM tip acting as top electrode 25,26 and/or by the presence of a depolarizing field caused by charge redistribution due to interface disorder ͑Figs. 2 and 3͒.…”

Direct Observations of Retention Failure in Ferroelectric Memories

“…The increased spatial resolution of TEM over electronic [5,[8][9][10] or surface probe studies [6,7,15] and the access to depth-dependent structural information provides a complete picture of the stable and metastable domain structure in the film during switching. [22][23][24] The switching induced by a surface probe is characterized using piezoresponse force microscopy (PFM) and by in situ TEM in Figure 1.…”

“…[1][2][3][4] However, the written polarization often suffers from a gradual backswitching leading to data loss. [5][6][7][8][9][10] At larger scales this process can be attributed to a thermodynamic instability of the written polarization due to electrostatic or elastic energy from built-in electric fields [6,[11][12][13][14] and strain. [15,16] However, we find that in writing nanosized domains, such as for memory bits in high bit-density storage, the domain wall itself can drive backswitching.…”

In-Plane 90∘ Rotation of Lamellar Domains in PbTiO3 Grains Revealed by Piezoresponse Force Microscopy

“…The quick development of scanning force microscopy (SFM), especially the piezoresponse force microscopy (PFM), provides a powerful tool to image ferroelectric domains and study switching dynamics of ferroelectric domains in the nanoscale [2,3]. Most of SFM investigations were concerned on the reversal of 180 • domains in ferroelectric films for the development of ferroelectric memories [4][5][6][7]. Study on the rotation of 90 • domains was limited, until Eng and coworkers [8][9][10][11] developed three-dimensional PFM, which enable to observe the in-plane component of the polarization.…”