Nanoscale control of ferroelectric polarization and domain size in epitaxial Pb(Zr0.2Ti0.8)O3 thin films

Abstract

We demonstrate that atomic force microscopy can be used to precisely manipulate individual sub-50 nm ferroelectric domains in ultrahigh density arrays on high-quality epitaxial Pb͑Zr 0.2 Ti 0.8 ͒O 3 thin films. Control of domain size was achieved by varying the strength and duration of the voltage pulses used to polarize the material. Domain size was found to depend logarithmically upon the writing time and linearly upon the writing voltage. All domains, including those written with ϳ100 ns pulses, remained completely stable for the 7 day duration of the experiment. © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1388024͔Increasing demand for ultrahigh density ͑uhd͒ information storage has fueled significant interest in the use of atomic force microscopy ͑AFM͒ for nanoscopic read/write operations. General requirements of nonvolatile uhd memories are fast operating times, small bit size, and long-term data retention. Nonreversible AFM lithography by local oxidation and thermomechanical processes has been extensively researched. 1-3 Solutions incorporating parallel processing have also been explored, increasing the scan range and speed of possible applications. 4,5 A particularly appealing approach, allowing dynamic memory as well as data storage, is to locally modify the reversible and nonvolatile polarization of ferroelectric oxides with an AFM-generated electric field, 6-12 a technique recently extended to ferroelectric/silicon heterostructures. 13 Detailed studies of domain switching behavior in these materials, focusing on domain size and stability in relation to writing time, writing voltage, and the shape of the AFM tip, are therefore important for the development of memory applications. Such studies would also aid in understanding the fundamental physics of domain dynamics in thin films. The perovskite Pb͑Zr x Ti 1Ϫx )O 3 ͑PZT͒, a stable compound with high remanent polarization, has been widely recognized as an attractive candidate for memory applications. Epitaxially grown monocrystalline films of this material are particularly suitable for domain behavior studies due to the uniformity of their switching properties over the sample surface. 10 Although desirable long-term stability has been found for standard 100 nm sized capacitors in 1000-Å-thick films of related ferroelectric compounds, 11 studies of retention loss in sub-100 nm PZT domains using the AFM approach, with the tip itself serving as a mobile top electrode, present contradictory results. The extrapolation of temperature dependence data for epitaxial PZT films gives polarization retention estimates of decades at RT, 9 while other groups report spontaneous reversal of polarization after a few hours. 8 In this letter we demonstrate nanoscopic control of read/ write operations in uhd arrays, and report on the time dependence of domain switching behavior for domains as small as 40 nm, over eight orders of magnitude in writing time, down to ϳ100 ns. We also discuss how different applied voltages affect the size of the polarized domains. Final...

Screening and size effects on the nanodomain tailoring in ferroelectrics semiconductors

“…Such "threshold" domain formation is similar to the well-known first order phase transition and correlates with recent experimental [2], [3] and theoretical [16], [22], [23] results.…”

“…The correlation length cannot be smaller than the several lattice constants, i.e. for LiNbO 3 we obtained . Keeping in mind this limitation, we obtained rather low value of critical voltage about 1 V that corresponds to the atomic scale domains with radius 1.4 nm and length 18 nm.…”

“…This result seems quite reasonable, because usually stable ferroelectric nanodomains in thin films can be recorded only above some critical voltage 3-6V (see e.g. [2], [3]), on the other hand threshold voltage was calculated in other models (see e.g. [16], [23]).…”

“…It is clear from general point of view that domains formation can be caused by strong local electric fields with definite polarity. Recently one and two dimensional arrays of spike-like nano-domains have been fabricated in LiNbO 3 [1], LiTaO 3 [2], Pb(Zr,Ti)O 3 [3], BaTiO 3 [4], RbTiOPO 4 and RbTiOAsO 4 [5] ferroelectric crystals with the help of electric fields caused by atomic force microscope (AFM) tip. Obtained nano-domain arrays could be successfully used in modern large-capacity memory devices and light converters based on second harmonic generation.…”

Ferroelectrics at the nanoscale

“…Domains were written perpendicular to the axis of a series of nanowires, by applying a voltage through a scanning probe microscopy tip, as has been done in previous nanoscale polarisation studies [19][20][21]. Non-contact electric force microscopy (EFM) was then used to image the field emanating from the written domains.…”