Pulsed Laser Deposition of High-Epsilon Dielectrics: PMN and PMN-PT
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PULSED LASER DEPOSITION OF HIGH-EPSILON DIELECTRICS: PMN AND PMN-PT K.L. SAENGER, R.A. ROY, D.B. BEACH, and K.F. ETZOLD IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY. ABSTRACT In this study we report on the KrF excimer laser deposition of crystalline films of lead magnesium niobium oxide (PMN) and solid solutions of PMN and lead titanate (PT) in a 65:35 ratio. These materials have potential microelectronic applications as thin film capacitors due to their high dielectric constants (cPMN(bulk) Z 10,000). Films were typically deposited in an oxygen background at elevated substrate temperatures (T, = 525 °C) on substrates of Pt(l 1l)/Si0 2/Si or Pt(l I1)/glass. The deposited films were characterized by Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction, and capacitance/loss measurements. Films prepared from a nearly stoichiometric commercial PMN target were low in Mg and Pb and yielded only the low-c pyrochlore phase (measured rr,,m-_ 100), even after cx-situ annealing at temperatures up to 650'C. Films deposited from Pb,Mg-rich targets prepared by a sol-gel process (tailored to produce the desired film stoichiometry) contained mixtures of perovskite and pyrochlore, with typical r values of order 600-1200. INTRODUCTION High dielectric constant (high-&) materials arc of interest to the semiconductor industry due to their potential value as thin film capacitors in microelectronic devices. In the case of DRAM, shrinking device dimensions coupled with roughly constant capacitance requirements have already driven the development of non-planar (higher effective area) capacitors and forced the use of increasingly thinner dielectrics (i.e., - 50 A SiO 2). Since the capacitance of a parallel plate capacitor is proportional to r, x area/thickness, the selection of a higher-r material results in a less demanding requirement for the area/thickness ratio, and consequently a greater flexibility in the overall chip design. In this study we focus on the preparation of crystalline films of lead magnesium niobium oxide (PMN) and 65:35 solid solutions of PMN and lead titanate (PT) by pulsed laser deposition (PLD). While these materials have been deposited in thin film form by sol-gel techniques [1, 2], little work has been done with physical vapor dePMN-bascd materials have several similarities to the position techniques. ferroelectric lead zirconate titanatc (PZT) materials, which have also been successfully deposited by PLD [3, 4]. Both have a high-r perovskite phase (eg.I PbNb0.667Mg0.333O3 ) and a low-c pyrochlore phase (e.g., Pb 2Nb,.75 Mg 0.25O 6.625 [5]. Both also have a propensity for lead loss at the deposition temperatures (T,, 525°C) which are required to obtain the pcrovskite phase in-situ. The successful synthesis of these materials thus requires a careful control of both film stoichiometry and crystal structure. Our interest in PMN-bascd materials stems from their extremely high permittivity. Pure PMN in the pcrovskite phase has a maximum E of nearly 20,000 at -0°C and an t of aroun
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