Influence of LaNiO 3 as an Electrode on the Properties of Ferroelectric Oxides
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Mat. Res. Soc. Symp. Proc. Vol. 623 © 2000 Materials Research Society
materials and hence no lattice mismatch is seen, thus facilitating the smooth growth of electrode/ferroelectric/electrode structures. In quite a few cases it is shown that the perovskite electrodes enhance the phase stability of the ferroelectric materials. In this paper we report our investigation on LaNiO 3 as an electrode to evaluate the ferroelectric properties of SBT and BaTiO 3. We have fabricated LaNiO 3/ferroelectric/LaNiO 3 structures on substrates like Pt coated Si (100) and LaA1O 3 (100) by the pulsed laser ablation technique. The ferroelectric properties have been evaluated by utilizing RT66A ferroelectric test instrument.
EXPERIMENTAL
Thin films of LaNiO 3 (LNO), SrBi 2Ta 2O9 (SBT) and BaTiO 3 (BT) were fabricated utilizing the pulsed excimer laser ablation technique. An excimer KrF laser with a wavelength of 248 nm was focussed onto the respective targets to produce a fluence of 2 J/cm 2. The LaNiO 3 films were deposited at 750'C with oxygen ambient pressure maintained at 200 mTorr during deposition. The substrate temperature for SBT growth was maintained at 600'C and the deposition carried out in 250 mTorr oxygen ambient. The BT films were deposited at 750C in an oxygen ambient of 2X10-3 Torr. The laser pulse repetition rate was maintained at 5 Hz for all the deposition cases. LNO and SBT were cooled in 760 Torr oxygen ambient, while the BT films were cooled in the oxygen ambient at which they were deposited. The electrode/ferroelectric/electrode structures were fabricated to evaluate the ferroelectric properties. The capacitor structures were grown on Pt coated Si(100) and LaA10 3 (100) (LAO) substrates. The bottom electrodes were approximately 1500 Athick and the ferroelectric layers were about 2500 A. The phases of the films deposited were identified by X-ray diffraction technique with CuKa radiation. The hysterisis loop and the fatigue of the ferroelectric structures were measured using the RT66A ferroelectric tester. RESULTS AND DISCUSSION LaNiO 3 is a metallic oxide having a provskite structure as that of most ferroelectric materials[9,10]. LaNiO 3 has an excellent crystallographic compatibility with several perovskite type materials (super-conducting as well as insulating). It is rhombohedral metal oxide with a lattice constant of 0.383 nm, and a surface resistivity of the order of 250 1 iQ cm. There are quite a few reports where LaNiO 3 has been utilized as an electrode to evaluate the ferroelectric properties of PZT and BST[3,5,1 1]. We have utilized LNO as an electrode to evaluate the ferroelectric properties of SBT and BT. As described in the previous section we have grown LNO on Pt coated Si(100) and LAO substrates and used as bottom and top electrodes to evaluate the ferroelectric properties of SBT and BT. The structural perovskite phase in the deposited films were determined by the X-ray diffraction. Fig. 1 shows the X-ray diffraction spectra of LNO films grown on Pt coated Si(100) and LAO substrates at 725°C. The
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