Characterization of Lead Zirconate-Titanate Thin Films Prepared by Pulsed Laser Deposition
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CHARACTERIZATION OF LEAD ZIRCONATE-TITANATE THIN FILMS PREPARED BY PULSED LASER DEPOSITION
C.K. CHIANG, W. WONG-NG, P.K. SCHENCK, L.P. COOK, M.D. VAUDIN National Institute of Standards and Technology Gaithersburg, MD 20899 P.S. BRODY, B.J. ROD, and K.W. Bennett Harry Diamond Laboratories Adelphi, MD 20783
ABSTRACT Dense smooth lead zirconate-titanate thin films have been prepared by excimer laser deposition. The as-deposited films are amorphous as indicated by x-ray powder patterns. Differential scanning calorimetry studies show that the film has a glass transition at 301 *C, and the amorphous to crystalline transformation takes place above 350'C to 650'C. Phase formation as a result of post-deposition heat treatment is described. INTRODUCTION For electrical and electronic applications of ceramic materials, we have applied pulsed laser deposition to produce various thin films, including barium titanate and lead zirconatetitanate (PZT). " The PZT films produced in our laboratory using a Nd/YAG laser showed ferroelectric hysteresis, indicating potential for application as non-volatile memories and related devices. However, these films had unsuitable microstructure, including large ejected particles and rough surfaces. 2 One cause of this morphology may be the thermal energy produced by the Nd/YAG laser during the sputtering. To improve these films we have since used an excimer laser, and in this paper we report the effect of post-depositional annealing on PZT films deposited by pulsed eximer laser deposition. EXPERIMENTAL The thin film deposition system was the same as reported earlierl, except that we used an ArF excimer laser (193 nm). The deposition was done at a repetition rate of 10 Hz and nominal pulse width of 23 ns. The laser beam was focused to produce a fluence of typically 10-30 J/cm2 . A commercial PZT target (PZT 5A, 47% PbTiO 3 and 53% PbZrO 3) was used. During the deposition, the target was rotated and the laser beam was rastered across the target to maintain uniform material removal. A rotating substrate holder was used to hold substrates directly over the target surface at distances 3.0 cm from the target surface. The reaction chamber was continuously evacuated to < 1 mTorr by oil free pumps. During deposition, oxygen was metered into the chamber to produce a background pressure of 100 mTorr. The growth rate of PZT film was about 50 nm/min. Typical thickness of the thin film was from 150 nm to 500 nm. Mat. Res. Soc. Symp. Proc. Vol. 230. c1992 Materials Research Society
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For electronic studies we used silicon < 100> single crystal wafers as substrates which were coated with 500 nm platinum. For the materials processing studies, we used platinum substrates. After deposition, the films were annealed in air at various temperatures and times. To determine the crystallization temperatures of the as-deposited PZT films differential scanning calorimetry (DSC) measurements were made. A platinum substrate similar to that upon which the film was deposited was used as the reference. DSC curves were meas
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