Pulsed laser deposition and characterization of conductive RuO 2 thin films
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Pulsed laser deposition and characterization of conductive RuO2 thin films A. Iembo, F. Fuso, and E. Arimondo Istituto Nazionale per la Fisica della Materia, Dipartimento di Fisica, Universit`a di Pisa, Piazza Torricelli 2, I-56126 Pisa, Italy
C. Ciofi and G. Pennelli Dipartimento di Ingegneria dell’Informazione: Elettronica, Informatica, Telecomunicazioni, Universit`a di Pisa, Via Diotisalvi 2, I-56126 Pisa, Italy
G. M. Curr`o, F. Neri, and M. Allegrini Dipartimento di Fisica della Materia e Tecnologie Fisiche Avanzate, Universit`a di Messina, Salita Sperone 31, I-98166 Messina, Italy, and Istituto Nazionale per la Fisica della Materia, Unit`a di Messina, Messina, Italy (Received 5 July 1995; accepted 19 November 1995)
RuO2 thin films have been produced on silicon-based substrates by in situ pulsed laser deposition for the first time. The electrical properties, the surface characteristics, the crystalline structure, and the film-substrate interface of deposited samples have been investigated by 4-probe resistance versus temperature technique, scanning electron microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy, respectively. The films show good electrical properties. The RuO2 -substrate interface is very thin (ø3 nm), since it is not degraded by any annealing process. These two characteristics render our films suitable to be used as electrodes in PZT-based capacitors.
A great amount of research is at present devoted to the application of ferroelectric materials in nonvolatile random access memories (NVRAM). Very promising candidates for such devices are capacitors based on PbTix Zr12x O3 (PZT) thin films,1,2 whereas Pt is currently used as capacitor electrodes. The use of Pt has some drawbacks, such as capacitor shorting due to Pt hillocks,3 severe polarization fatigue and aging,4 or diffusion of Pb5 and oxygen6 through Pt layers. Recently, conductive oxides have been investigated as alternative electrodes in PZT-based multilayer capacitors. In particular, ruthenium dioxide (RuO2 ) constitutes a suitable choice for this purpose thanks to its low resistivity (36 mV cm)7 and to its good thermal stability up to 800 ±C, which makes it an excellent interdiffusion barrier.3 Moreover, ferroelectric capacitors with RuO2 electrodes have shown an improvement of approximately 3 orders of magnitude in the fatigue behavior.4 Various deposition methods are available to produce thin films of such materials. Among them, pulsed laser deposition (PLD) has attractive features, including the production of polycrystalline-stoichiometric films without post-deposition annealing, and easy control of the deposition parameters, and a simple experimental setup, which can be adopted for in situ depositions of multilayer structures. We have already deposited thin films of PZT by PLD,8 and at present we are investigating the feasibility of producing RuO2 /PZT/RuO2 multilayer capacitors on silicon-based substrates, by in situ PLD. In this work we
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