Use of the solvent chemistry for the control of the critical thickness of PbTiO 3 ultrathin films
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Susana Holgado Escuela Polite´cnica Superior, Universidad Auto´noma de Madrid, Cantoblanco, E-28049 Madrid, Spain
Zhaorong Huang Department of Materials, School of Applied Sciences, Cranfield University, Bedfordshire MK43 0AL, United Kingdom
Maria L. Calzada and Jesu´s Ricotea) Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain (Received 27 September 2009; accepted 28 January 2010)
The preparation of high-quality ferroelectric PbTiO3-based ultrathin films by chemical solution deposition, using a diol-based sol-gel method, has proved to be successful. However, there is a critical thickness below which the films break up into isolated structures. According to previous studies, above a certain grain size to thickness ratio a microstructural instability occurs and the coatings are no longer continuous. We explore the use of the solvent chemistry to control this phenomenon, as an alternative to the more conventional variation of the crystallization parameters. The use of diols with short C chain lengths leads to films with smaller grain sizes, whose critical thicknesses are lower. A reduction from 40 to 15 nm is achieved by reducing the number of C of the diol used from 5 to 2. A critical value of G/t < 5.0 is necessary to obtain continuous ultrathin films with the processing conditions used.
I. INTRODUCTION
The present miniaturization trends in the microelectronics industry are demanding an ever-larger degree of integration. Device dimensions are now in the nanometer scale, and, thus, so are all the elements that are part of them. This size reduction can be a challenge in some cases, such as for nanoelectromechanical systems (NEMS), as most of the techniques used for transduction reach their limits in the nanoscale.1 The use of ultrathin ferroelectric films, with large piezoelectric coefficients, is a good option to be explored. Besides, ultrathin films are required for writing thermally stable domains for probebased data ferroelectric storage devices,2 which to be of a uniform size must be large relative to the grain size.3 So the challenge is producing ultrathin ferroelectric films with small grain size. However, further development in the fabrication methods of ferroelectric oxide nanostructures to be integrated in the new nanodevices is necessary, not only because of the potential technological interest,4 but also because of the unique properties of ferroelectrics with reduced dimensions.5–8 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0127
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 5, May 2010 Downloaded: 06 Apr 2015
Chemical solution deposition (CSD) presents clear advantages over other methods of preparation of highquality ferroelectric films for their integration in nanodevices. The high degree of compositional control achieved, the deposition of large uniform areas, and the low costs have made it the method of preparation of a wide range of oxide films for electronic applications.9 However, CSD
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