Epitaxial Pb(Zr 0.52 Ti 0.48 )O 3 /La 0.7 (Pb,Sr) 0.3 MnO 3 Ferroelectric/CMR Memory Optimized for Room Temperature Oper
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ABSTRACT Epitaxial ferroelectric/colossal magnetoresistive PbZro.s2Tio.480 3/Lao. 7(Pb,Sr)o. 3MnO 3 (PZT/LPSMO) thin film heterostructures have been grown onto SrTiO 3 single crystals by KrF pulsed laser deposition technique to fabricate nonvolatile magnetosensitive memory. Colossal magnetoresisitivity (CMR) in LPSMO film has been tailored to room temperature by compositional control to get the maximum temperature coefficient of resistivity of 7.3 %K" @ 295 K and maximim magnetoresistivity of 27% @ 7 kOe and 300 K. The main processing parameters have been optimized to preserve CMR performance in LPSMO film after deposition of the top ferroelectric layer. Vertical Au/PZT/LPSMO/STO capacitor cell possesses very high dielectric permittivity about 1500 and rather low loss of 5% at 1 kHz, saturation polarization of 40.4 ýtC/cm 2 , remnant polarization of 20.6 ýiC/cm 2, coercive field of 22.8 kV/cm, and no visible fatigue after 1.33.108 reversals. Three top contact metals: Au, Pt, and Ta, deposited at room temperature, have been examined. As compared with Ta, Pt and Au top contacts show superior performance regarding to combined properties: high remnant and saturation polarization, low loss and no fatigue while top Ta contacts have been found to be more efficient to reduce leakage in ferroelectric film.
INTRODUCTION Perovskite ferroelectric thin films have a tremendous potential for data storage, sensor, and microelectromechanical system technologies. Recently, doped rare-earth manganites exhibiting colossal magnetoresistivity have been proposed to be used as semiconductor channel material for Ferroelectric Field Effect Transistors (FET). 1The operation of the FET is based on the depletion and accumulation of hole carriers in compounds of mixed valence, such as manganites with low Mn3- content, by an electric stray field of reversed polarization in adjacent ferroelectric. Furthermore, colossal magnetoresistivity (CMR) of manganite can endow such FET with high magnetosensitivity. We have already demonstrated magnetosensitive nonvolatile memory (MSM) based on epitaxial ferroelectric/colossal magnetoresistive heterostructures made by pulsed laser deposition. 2 In this paper we report new PbZro. 52Tio.480 3/Lao. 7(Pb,Sr)o. 3MnO 3 film structure optimized for room temperature MSM operation.
EXPERIMENTAL A description of the processing technique is as follows: at first a 248 nm KrF excimer laser (Lambda Physik-300) was used to ablate two ceramic targets with the composition La0.7 5 Sr0 .2 5 MnO 3
371 Mat. Res. Soc. Symp. Proc. Vol. 602 © 2000 Materials Research Society
Films of and Latous sebrie 3. continuous series of solid solutions with the basic chemical formula (1x)wLa 0,Pb 4r0. 0 3Mn0 . 3 + x7La0. 75 25Mn0 3 with x = 0, 0.3, 0.37, 0.4, 0.5, 0.6, and I have been fabricated and LPSMO film with x = 0.37 has been chosen for
further
processing.
Deposition
of
LPSMO onto SrTiO 3 (001) single crystal was carried out in an oxygen pressure of about 300 mTorr at substrate temperature of 730 'C, was followed by annealin
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