Characteristics of PZT thin films as ultra-high density recording media

Scanning force microscopy (SFM) has been used to study nanoscale variations in switching parameters in layered perovskite films of SrBi2Ta2O9 and to investigate the effect of capacitor scaling on the standard deviation of the capacitors’ integral polarization signal. Ferroelectric poling and SFM piezoresponse imaging were performed in a number of regions on the film surface sized 2×2, 1×1, 0.5×0.5, and 0.3×0.3 μm2 with subsequent statistical analysis of the obtained data. It has been found that variations of the polarization signal can be approximated by the normal distribution function. The standard deviation increases with the decrease in the capacitor size, suggesting a stronger effect of grain misalignment in smaller capacitors. The obtained results imply that reliable high-density ferroelectric memories cannot be realized unless a certain capacitor size/grain size ratio is maintained.

Section: Alexei Gruverman A)mentioning

confidence: 99%

Scaling effect on statistical behavior of switching parameters of ferroelectric capacitors

Gruverman

1999

“…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.…”

mentioning

confidence: 99%

“…[1][2][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][7][8][9][10][11][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.…”

mentioning

confidence: 99%

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

Paruch

Tybell

Triscone

2001

196

136

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...

“…In contrast, studies of thermal domain evolution in PbZr x Ti 1−x O 3 showed an Arrhenius-type decay of domain size. 9 Thermally activated decay of naturally occurring domains in cleaved triglycine sulfate single crystals was also studied at room temperature and under heating, with independent observation of random-bond disorder-governed behavior. 10,11 In this letter we report the high stability of linear ferroelectric domains in epitaxial PbZr 0.2 Ti 0.8 O 3 thin films up to temperatures as high as 735°C, well above the bulk ferroelectric transition temperature ͑T c ͒.…”

mentioning

confidence: 99%

High-temperature ferroelectric domain stability in epitaxial PbZr0.2Ti0.8O3 thin films

Paruch

Triscone

2006

Using high-resolution atomic force microscopy, we have shown extremely high stability of linear ferroelectric domains in epitaxial PbZr 0.2 Ti 0.8 O 3 thin films heated up to 735°C, a significant advantage for technological applications. An elevated transition temperature ϳ785°C is observed even in relatively thick ͑91 nm͒ films, despite relaxation of in-plane film-substrate lattice-mismatch-induced strain. We also demonstrate the negligible role of the film surface in determining the written domain-wall configuration, both by direct comparison of the surface roughness with domain-wall position at successive thermal cycles, and by measurements of domain-wall dynamics before and after heating. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2196482͔The diverse electronic and mechanical properties of ferroelectric perovskites make them particularly interesting for multifunctional devices in which their piezoelectric and pyroelectric properties, as well as their switchable ferroelectric polarization, can be exploited. In addition, local control of polarization by atomic force microscopy ͑AFM͒, combined with oxide growth techniques by which epitaxial single-crystal quality thin films of these materials can be grown on numerous substrates, 1,2 including silicon, 3 allows significant gains to be envisaged in application parameters, such as frequency or information density. An important consideration for devices is thermal stability. For example, in surface acoustic wave ͑SAW͒ frequency filters, thermal effects are a primary cause of device failure, and there is great interest in developing temperature-compensated systems. 4 Recently, a prototype SAW filter was fabricated using ferroelectric domain structures in PbZr 0.2 Ti 0.8 O 3 as 1 -4 GHz range "piezoelectric interdigitated transducers" ͑PIT͒ ͑Ref. 5͒. This material, unlike many standard piezoelectrics, shows a positive temperature coefficient of delay of the transverse vibrational mode resonant frequency. Its use in combination with a negative-temperature-coefficient-of-delay substrate could thus allow compensation of quasistatic thermal effects, provided the ferroelectric domain structures remain stable in the −20-100°C range particularly important for applications. Investigating the effects of heating on ferroelectric domains in epitaxial thin films is thus of obvious practical importance. To understand these effects at the nanometer scale required for miniaturized devices, such studies should focus in particular on domain walls, whose static and dynamic behavior determines the stability and growth of domains in ferroelectric materials.We have recently shown that ferroelectric domain walls in epitaxial thin films are well described as elastic interfaces in the presence of random bond disorder and dipolar interactions, 6 within the theoretical framework developed for elastic objects in random media. 7 In such systems, domain walls are pinned by disorder, although a thermally activated nonlinear response is possible even for subcritical forces. However, the...