%0 Journal Article
%T Epitaxial Piezoelectric Pb( ) Thin Films on Silicon for Energy Harvesting Devices
%A A. Sambri
%A D. Isarakorn
%A A. Torres-Pardo
%A S. Gariglio
%A Pattanaphong Janphuang
%A D. Briand
%A O. St¨¦phan
%A J. W. Reiner
%A J.-M. Triscone
%A Nico F. de Rooij
%A C. H. Ahn
%J Smart Materials Research
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/426048
%X We report on the properties of ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) thin films grown epitaxially on (001) silicon and on the performance of such heterostructures for microfabricated piezoelectric energy harvesters. In the first part of the paper, we investigate the epitaxial stacks through transmission electron microscopy and piezoelectric force microscopy studies to characterize in detail their crystalline structure. In the second part of the paper, we present the electrical characteristics of piezoelectric cantilevers based on these epitaxial PZT films. The performance of such cantilevers as vibration energy transducers is compared with other piezoelectric harvesters and indicates the potential of the epitaxial approach in the field of energy harvesting devices. 1. Introduction In the last decade, studies on epitaxial ferroelectric thin films have led to many interesting results and exciting discoveries [1]. The possibility of tailoring or even enhancing some physical parameters via epitaxial strain engineering [2¨C4] has suggested the idea of the exploitation of such thin films for several technological applications [5]. Nevertheless, the benefits of the epitaxial approach on the performances of ferroelectric thin film-based devices have to compensate the hurdles related to the epitaxial growth on industrial substrates such as silicon, the modern technological platform. It is in fact well known that the basic requirements for the epitaxy, that is, a good lattice match between substrate and film and a reciprocal chemical stability, are not easily fulfilled in the case of oxide growth on silicon. Beside the difference in lattice parameters and thermal expansion coefficients, the main problem is the surface reactivity of silicon to oxygen, with the formation of an amorphous layer of silicon dioxide that hints any further epitaxy. Moreover, the cations of most ferroelectric compounds interdiffuse into the silicon substrate, forming spurious extra phases at the interface [6]. In order to overcome such difficulties, a suitable buffer layer is needed that acts as a barrier for cations migration and as a structural template for the growth of the ferroelectric epitaxial film [7¨C9]. PZT is one of the most investigated ferroelectric materials, due to its high values of remnant polarization and piezoelectric coefficients. In the bulk form, it displays a complex phase diagram versus the Ti/Zr content: for the stoichiometry of our choice, that is, Pb( )O3 (PZT 20/80), it is ferroelectric with a tetragonal structure up to a transition temperature of 460ˇăC [10]. It
%U http://www.hindawi.com/journals/smr/2012/426048/