Epitaxial (Pb,La)(Zr,Ti)O 3 thin films on buffered Si(100) by on-axis radio frequency magnetron sputtering Ø. Nordseth ⁎, T. Tybell, J.K. Grepstad Department of Electronics and Telecommunications, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway abstract article info Article history: Received 14 January 2008 Received in revised form 26 September 2008 Accepted 14 October 2008 Available online 25 October 2008 Keywords: Epitaxy Sputtering X-ray diffraction X-ray photoelectron spectroscopy In this study, we discuss the case for integration of epitaxial (Pb,La)(Zr,Ti)O 3 (PLZT) thin films with silicon for electro-optic device applications. PLZT films, approximately 500 nm thick, were grown by on-axis radio frequency magnetron sputtering on CeO 2 /YSZ-buffered Si(100) substrate with a SrRuO 3 electrode layer embedded between CeO 2 and PLZT. The structural properties and surface topography of the different oxide layers were examined with X-ray diffraction analysis and atomic force microscopy. The perovskite thin films were predominantly (001)-oriented, with a (002) rocking curve halfwidth of approximately 0.3° and a surface roughness compatible with requirements for application in optical devices. The PLZT cation stoichiometry was assessed from quantitative X-ray photoelectron spectroscopy. These measurements uncovered a substantial depletion of lead in the film surface for layers deposited at substrate temperatures above ~600 °C, whereas the surface concentration of La, Zr and Ti remained virtually unaffected over a wide range of growth temperatures. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In order to meet the increasing demand for high performance, low- cost integrated circuits in optical communication systems, introduction of materials with versatile functional properties is being explored [1–6]. The ferroelectric perovskite (Pb,La)(Zr,Ti)O 3 (PLZT) offers several functional properties attractive to optical device applications, such as a large electro-optic coefficient and high transparency at optical frequen- cies [7]. The electro-optic properties of PLZT are mainly governed by the chemical composition. The PLZT target used in the present study was (Pb 1 - x ,La x )(Zr y ,Ti 1 - y )O 3 , with x =0.08 and y =0.4, which exhibits tetra- gonal ferroelectric phase at room temperature and linear (Pockels) electro-optic characteristics [8]. This composition renders hysteresis loops of high coercivity and linear electro-optic response for applied fields below the coercive field. Such characteristics near zero applied field are considered attractive for optical devices operating without a biasing field, such as light modulators. The properties of ferroelectric perovskite thin films are strongly dependent on the crystalline structure. In order to facilitate epitaxial growth of PLZT on Si(100), a buffer layer structure of CeO 2 and yttria-stabilized zirconia (YSZ) is commonly adopted [9–11]. More- over, to add functionality to this thin film stack, a layer of SrRuO 3 is interposed between CeO 2 and PLZT [12]. The metallic properties of SrRuO 3 provide an electrode for subsequent polarization of the PLZT film. The perovskite structure of SrRuO 3 ensures an epitaxial relationship between this layer and PLZT. For applications of PLZT in optical devices, it is essential that highly crystalline and uniform films can be prepared with sufficient thickness to support propagation of optical modes. A number of deposition techniques were adopted to this end, such as chemical solution processing [13], pulsed laser ablation [14], metal-organic chemical vapor deposition [15], ion beam sputtering [16], magnetron sputtering [17], spin-coating pyrolysis [18], and sol–gel processing [19]. In the present communication, we report on deposition of epitaxial (Pb,La)(Zr,Ti)O 3 thin films on buffered Si(100) using radio frequency (rf) magnetron sputtering. An on-axis target geometry was adopted in order to attain high deposition rates, compared to that for films deposited by off-axis sputtering in a preceding growth effort [20]. Deposition of homogeneous films with several hundred nanometer thickness, required for application in integrated optics, is demonstrated. Moreover, it is shown that the cation stoichiometry of such films, notably their lead content, depends critically on the substrate temperature during growth. 2. Experimental details Buffer layers of YSZ (13 mol% Y 2 O 3 ) and CeO 2 were initially deposited on n-type Si(100) wafers (Siltronix) by electron beam evaporation. The silicon wafers were one-sided polished, with a thickness of 350 μm and resistivity 2–20 Ω cm. A 200 nm thick titanium layer was predeposited on the reverse of the polished silicon wafers to allow for radiative heating of the substrate during oxide film Thin Solid Films 517 (2009) 2623–2626 ⁎ Corresponding author. E-mail address: ornulf.nordseth@iet.ntnu.no (Ø. Nordseth). 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.10.038 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf