The effect of oxygen partial pressure during cooling on lead zirconate titanate thin film growth by using rf magnetron s
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The effect of oxygen partial pressure during cooling on lead zirconate titanate thin film growth by using rf magnetron sputtering method Dong Joo Kim, Tae Song Kim,a) Jeon Kook Lee, and Hyung Jin Jung Thin Film Technology Research Center, KIST, 39-1 Haweolgog-dong, Seongbuk-gu, Seoul 136-791, Korea (Received 6 July 1997; accepted 13 November, 1997)
The lead zirconate titanate (PZT) thin film was deposited on platinized silicon wafer substrate by the rf magnetron sputtering method. In order to investigate the effect of cooling ambient, oxygen partial pressure was controlled during cooling PZT films. The PZT films cooled at lower oxygen partial pressure had perovskite phase and pyrochlore phase in both as-grown and postannealed films, but in the PZT films cooled at higher oxygen partial pressure, pyrochlore phases were not detected by XRD. As the oxygen partial pressure became lower during cooling, the capacitors had low values of remanent polarization and coercive field for as-grown films. The PZT capacitor with such a low value was recovered by postannealing in air, but its electrical properties had the same tendency before and after annealing. Microstructure was also affected by cooling ambient. Higher oxygen partial pressure on cooling reduced the number of very fine grains, and enhanced uniform grain distribution. Fatigue characteristics were also enhanced by cooling at higher oxygen partial pressure. However, the imprint was negligible irrespective of oxygen partial pressure upon cooling. The cooling procedure at higher oxygen ambients is believed to reduce the amounts of nonferroelectric second phases and oxygen vacancies. We find that oxygen partial pressure during cooling is a considerable process parameter. Therefore, care should be taken in treating the parameter after depositing films.
I. INTRODUCTION
Recently, ferroelectric thin films have been studied extensively for memory devices such as nonvolatile ferroelectric random access memory (NvFeRAM)1 and dynamic access memory (DRAM),2 sensors and actuators.3 For using lead zirconate titanate (PZT) capacitors for memory applications, a single phase perovskite is highly desired. Small volume percentages of residual second phase can be especially detrimental for process integration due to its low ferroelectric properties and substantially different etch rates compared to the perovskite phase. One avenue to improve the ferroelectric properties of films is through the control of a synthesis process. Thus, there have been several studies to enhance the ferroelectric properties, such as remanant polarization and fatigue via controlling process parameters.4 In the case of sputtering deposition of ferroelectric thin films, most researchers reported the parameters of postannealing or oxygen pressure during deposition.5–8 Fox and Krupanidhi demonstrate that the oxygen content of as-sputtered lead lanthanum titanate films had a profound effect on the transformation to perovskite during subsequent annealing.9 Oxygen a)
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