Growth of Ferroelectric PbZr x Ti 1-X O 3 (PZT) Thin Films by Liquid-Delivery Metalorganic Chemical Vapor Deposition
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Growth of Ferroelectric PbZrxTi1-XO3 (PZT) Thin Films by Liquid-Delivery Metalorganic Chemical Vapor Deposition S. Matichyn, M. Lisker and E. P. Burte Institute of Micro and Sensor Systems, Otto-von-Guericke University of Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
ABSTRACT In this study lead zirkonat titanate (PZT) thin films were deposited using direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD). The chemical states and the stoichiometry of PZT-films were characterized using X-ray photoelectron spectroscopy (XPS). The crystal structure of the films was investigated by X-ray diffraction (XRD). The surface composition of the films was Pb : Zr : Ti = 1.05 : 0.52 : 0.48, which indicates that the deposited films had a stoichiometric PZT composition. 130 nm thick PZT films deposited on Ir showed preferred orientation. The main role for formation of the perovskite PZT films plays the content of the lead in the deposited films. Lead deficiency causes the formation of the pyrochlore phase with poor electrical properties. In films with a significant excess of lead a second PbO phase appeared that can be observed even with naked eyes. Negligible excess of lead can be reduced by postdeposition annealing at 500-600 °C. The Ir/PZT/Ir capacitor showed large values of the remanent polarisation of about 60µC/cm2 at an applied voltage of 3 V. So high value of the remanent polarisation can be induced by structural stress in the films. After ten switch impulses the values of the remanent polarisation have significantly decreased. This is probably due to a relaxation of crystal cells. INTRODUCTION In the last decade, many ferroelectric materials have been intensively studied for application into ferroelectric random access memory (FeRAM) devices [1-5]. Among these ferroelectrics, thin films of a perovskite type Pb(ZrxTi1-x)O3 (PZT) and bismuth-layered SrBi2Ta2O9 (SBT) are the most promising materials. Due to its high polarizability PZT is considered to be more suitable for mega-bit density FeRAMs. Furthermore, to promote phase transformation in SBT films from the non-ferroelectric fluorite to the ferroelectric Aurivillius phase a high temperature annealing in oxygen ambient is required [6]. Sputtering [7,8] and sol-gel [9,10] methods are the most commonly used techniques for depositing these ceramic films. Unfortunaly, both of these techniques have a severe drawback. Growth of homogeneous layers on three-dimensional structures cannot be realised by these methods. Using MOCVD (metal organic chemical vapor deposition) allows to overcome this drawback. MOCVD offers advantages on film quality, step coverage, and uniformity over a large area [11]. The direct liquid injection (DLI)-metal organic chemical vapor deposition (MOCVD) employed in this study is an attractive method to use solid precursors dissolved in a solvent. In
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this process, the solution is directly injected into a flash evaporator and the vaporized mixture is introduced into the deposition chamber. DLI-MOC
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