Effect of Interfaces on the Properties of Polycrystalline Thin-Film PZT Ferroelectric Capacitors
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0966-T13-02
Effect of Interfaces on the Properties of Polycrystalline Thin-Film PZT Ferroelectric Capacitors Lyuba Delimova1, Igor Grekhov1, Dmitri Mashovets1, Ilya Titkov1, Valentin Afanasjev2, Petr Afanasjev2, Galina Kramar2, and Anatolii Petrov2 1 Solid State Electronics Division, Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya 26, St.Petersburg, 194021, Russian Federation 2 Microelectronics Department, St.Petersburg Electrotechnical University "LETI", Prof. Popov str. 5, St.Petersburg, 197376, Russian Federation ABSTRACT A photocurrent directed opposite to ferroelectric (FE) polarization is observed in shortcircuit thin-film polycrystalline Pt/PZT/Ir(Ti/SiO2/Si) structures. The direction and magnitude of photocurrent are defined by the sign and magnitude of the FE polarization. A model based on a photovoltaic effect with characteristics determined by polarization of PZT grains is proposed. The model considers the field interaction of FE polarization charge with the charge carriers in intergranular PbO channel. Thin-film FE capacitor is considered as a photosensitive heterogeneous medium, where the conduction of PbO channels along PZT grain boundaries is controlled by FE polarization. INTRODUCTION Studies of optical and photoelectrical properties of thin-film ferroelectric (FE) structures in a wide spectral range are of great interest for physics of FE and applications of FE structures. The rate of relaxation processes in a structure can be modified under illumination, and novel photovoltaic devices can be based on photoelectric effects in these structures. Properties of thinfilm FE structures of different types and destination were studied in [1-5]; thin-film PZT structures were investigated in [6-10]. However, only few complex studies of the effect of illumination including a visible spectral range on properties of submicron capacitors have been performed [11], but no unambiguous explanation has been offered. A comprehensive study of thin-film FE capacitors including investigation of the charge state at both interfaces, elemental content across thickness, FE properties, and effect of illumination on the structure properties is necessary. This study is devoted to a detailed investigation of thin-film Pt/PZT/Ir(Ti/SiO2/Si) structures [12-15]. The bottom 100-nm-thick Ir electrode was produced by dc magnetron sputtering onto Ti(10-nm)/SiO2(200-nm)/Si substrate at 2000C. PZT films of 100 nm in thickness were deposited onto this electrode by MOCVD. Input ratio in the Zr : Ti precursor was ~ 40 : 60. Postgrowth annealing was done in oxygen atmosphere for 1 min at 6000C. EXPERIMENTAL TECHNIQUE The elemental and phase distribution across the structure was studied by the Auger electron spectroscopy [14] using an AES-3 spectrometer. The electron beam area was ~ 5 µm2, the layerby-layer ion-beam milling was performed by 1-mm2-beam of Ar+ ions (3 keV energy, ~ 3 µA
current) [15]. The dielectric loss and capacitance-voltage characteristics at frequencies 100 Hz – 1 MHz were studied for di
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