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Giant Self-Polarization in FeRAM Element Based on Sol-Gel PZT Films

Published online by Cambridge University Press:  04 March 2015

L. A. Delimova
Affiliation:
Solid-State Electronics Division, Solid State Physics Division, Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
E. V. Guschina
Affiliation:
Solid State Physics Division, Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
V. S. Yuferev
Affiliation:
Solid-State Electronics Division, Solid State Physics Division, Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
I. V. Grekhov
Affiliation:
Solid-State Electronics Division, Solid State Physics Division, Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
N. V. Zaiceva
Affiliation:
Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
N. V. Sharenkova
Affiliation:
Division of Physics of Dielectric and Semiconductors, Ioffe Institute, Polytekhnicheskaya 26, St.Petersburg, 194021, Russian Federation.
D. S. Seregin
Affiliation:
Electronics Department, Moscow State Technical University of Radioengineering, Electronics and Automation, Vernadskogo 78, Moscow, 119454, Russian Federation.
K. A. Vorotilov
Affiliation:
Electronics Department, Moscow State Technical University of Radioengineering, Electronics and Automation, Vernadskogo 78, Moscow, 119454, Russian Federation.
A. S. Sigov
Affiliation:
Electronics Department, Moscow State Technical University of Radioengineering, Electronics and Automation, Vernadskogo 78, Moscow, 119454, Russian Federation.
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Abstract

Integrated ferroelectric capacitors Pt/PZT/Pt/Ti/SiO2/Si with sol-gel deposited PZT films are studied. The (111) textured polycrystalline films are shown to have nonconductive PZT grain boundaries. The short-circuited photocurrents measured under illumination of the films by light with the quantum energy of 2.7 eV indicate the polarization inside the film directed from the top to the bottom electrode. Using the modified method of depolarization hysteresis loops, we found a non-switchable part of polarization which was measured to be -16 μC/cm2 and directed from the top to the bottom electrode. We consider this result to be a giant self-polarization and explain it in terms of flexoelectricity caused by lattice mismatch between the PZT and bottom Pt layers. The strain gradient across the PZT film thickness is estimated from the in-plane lattice constants measured in Pt and PZT films to be ∼103cm-1, which can produce the downward flexoelectric polarization of ∼14 μC/cm2, coinciding well with the measured one. Nonsymmetrical depolarization loops are found in the films when the polarization switching itself becomes more difficult under the negative or positive driving voltage. We show experimentally how depolarization with compensating bias or film illumination can affect the film polarization switching.

Type
Articles
Copyright
Copyright © Materials Research Society 2015 

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References

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