The effect of electrode composition on rf magnetron sputtering deposition of Pb[(Mg 1/3 Nb 2/3 ) 0.7 Ti 0.3 ]O 3 films
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Ferroelectric Pb[(Mg1/3Nb2/3)o.7Tio.3]03 (abbreviated PMNT) thin films were prepared on silicon substrates by rf magnetron sputtering deposition with PbO-enriched PMNT targets. The effects of electrode composition and thin film growth conditions were investigated with grazing-incidence x-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. The dielectric property of perovskite films was also measured. The usage of a Pt/Ti electrode was observed to enhance the formation of perovskite PMNT films; in addition, the TiO2 rutile phase was formed at the interface between the PMNT film and Pt electrode due to the oxidation of out-diffused Ti atoms from the inner Ti electrode. It was then noticed that if a target containing a larger excess of PbO was used, a higher consumption of TiO2 occurred and more perovskite phase would be formed in the deposited films. Consequently, perovskite PMNT films having a uniform microstructure and satisfactory dielectric property close to the bulk value were obtained by rf magnetron sputtering deposition on the Pt/Ti/SiO 2 /Si substrate at 640 °C under appropriate working conditions.
I. INTRODUCTION Renewed interest has arisen during recent years in ferroelectric thin films for applications to integrated circuit (IC) memories because of their remanent polarization and dielectric properties.1 In terms of materials, lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 (abbreviated as PMN), lead titanate, PbTiO3 (abbreviated as PT), and their solid solutions, Pb[(Mg1/3Nb2/3)J;Tii_x]O3 (abbreviated as PMNT), provide a particularly versatile choice.2 For example, (i) PMNT films of a high x value have a high dielectric constant appropriate for dynamic random access memories (DRAM's) and integrated capacitor devices, and (ii) films of a low x value have a large remanent polarization appropriate for ferroelectric random access memories (FRAM's). 3 The preparation of PMN and PMNT thin films by the sol-gel process has been previously reported.2"8 According to the present authors' knowledge, the fabrication of PMNT films by rf magnetron sputtering or other physical deposition methods has seldom been found in previous literature. In our other work, the PMNT perovskite films of x = 0.3 and x = 0.5 were successfully deposited on Si(100) substrate at temperatures above 560 °C and 610 °C, respectively, by rf sputtering under appropriate working conditions; however, obtaining pure perovskite films of x 3= 0.7 was quite difficult. Having films for application in DRAM's and integrated capacitor devices would necessitate fabricating PMNT films of a high x value integrated with Si transistors. J. Mater. Res., Vol. 9, No. 7, Jul 1994
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Platinum is a material often used as an inner electrode in perovskite thin film devices. It is chosen not only because the lattice mismatching between perovskite materials and Pt metal is generally small,9 but also because it has good electric conductivity and superior resistance against chemical reactions.10
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