Growth temperature dependent dielectric properties of BiFeO 3 thin films deposited on silica glass substrates Taimur Ahmed ⁎, Andrei Vorobiev, Spartak Gevorgian Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden abstract article info Article history: Received 31 January 2011 Received in revised form 14 February 2012 Accepted 23 February 2012 Available online 3 March 2012 Keywords: Bismuth ferrite Thin films Amorphous silica glass substrate Growth temperature Secondary phases Permittivity Ex-situ annealing We have studied the dependence of dielectric properties on the deposition temperature of BiFeO 3 thin films grown by the pulsed laser deposition technique. Thin films have been grown onto amorphous silica glass sub- strates with pre-patterned Au in-plane capacitor structures. It is shown that on the amorphous glass sub- strate, BiFeO 3 films with a near-bulk permittivity of 26 and coercive field of 80 kV/cm may be grown at a deposition temperature of about 600 °C and 1 Pa oxygen pressure. Low permittivity and higher coercive field of the films grown at the temperatures below and above 600 °C are associated with an increased amount of secondary phases. It is also shown that the deposition of BiFeO 3 at low temperature (i.e. 500 °C) and post deposition ex-situ annealing at elevated temperature (700 °C) increases the permittivity of a film. The ap- plied bias and time dependence of capacitance of the films deposited at 700 °C and ex-situ annealed films are explained by the de-pinning of the ferroelectric domain-walls. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Perovskite ABO 3 oxides are of great interest in many applications due to their multifunctional (semiconducting, electrochromic, mag- netoresistive, dielectric, multiferroic etc.) properties [1]. Specifically, the ionic conductivity and presence of oxygen vacancies make perovskite oxides useful for different sensing devices. For gas sensitivity, an oxide material should contain at least one readily reducible ion together with one that is readily oxidizable [2]. In recent years, multiferroic BiFeO 3 (BFO) has been the focus of extensive study due to its potential use in nonvolatile ferroelectric or magnetoelectric memories, sensors, terahertz devices and photonic devices [3,4]. BFO, both in bulk and nanoparticle form, is suitable for gas sensing because it contains two metals (Bi and Fe) that provide two relatively easily accessible oxidation states [2]. Moreover, BFO is characterized by high thermal and chemical stability in comparison with simple metal oxides [5]. In this work, BFO thin films are deposited by pulsed laser deposition (PLD) and their growth temperature dependent dielectric properties are measured to study the feasibility of fabricating a disposable and inexpensive device that could be later used in gas sensing applications. The focus of our studies is the optimization of permittivity because permittivity is assumed to be the potential sensing parameter in BFO thin film gas sensors. Amorphous silica glass (SiO 2 ) is used as a substrate because it is cheaper than the single crystal substrates (like SrTiO 3 , DyScO 3 , sapphire, etc.) and SiO 2 can also withstand high deposition temperatures during the PLD process. The challenge of growing BFO films on amorphous SiO 2 substrates is addressed by A. Vorobiev et al. [6] where buried coplanar Au electrodes are used as nucleation centers. Following the same configuration as in [6], we pattern Au electrodes as interdigitated capacitors (IDC) and grow BFO films on top of the electrodes. This configuration – featuring buried interdigital electrodes instead of parallel plate configuration with electrodes on top of the BFO film – facilitates the growth of BFO films on the amorphous substrates and also provides a larger active area for the gas sensing, thereby increasing the device sensitivity. It has already been reported that, on single crystal substrates, single-phase BFO thin films with limited thicknesses (25–240 nm) can only be grown in a narrow range of deposition temperature (550–600 °C) and pressure (around 1 Pa) [7–9]. It is not obvious whether these deposition conditions are also applicable for the growth of BFO films on the amorphous SiO 2 substrates. The present work seeks to address this uncertainty, by growing a number of BFO films at different temperatures while keeping the oxygen pressure constant at 1 Pa. 2. Experimental details Bottom Au (500 nm)/TiO 2 (50 nm) IDC electrodes are deposited by DC magnetron sputtering on amorphous SiO 2 substrates and subsequently patterned by photolithography and ion beam milling. Thin Solid Films 520 (2012) 4470–4474 ⁎ Corresponding author. E-mail address: taimur@alumni.chalmers.se (T. Ahmed). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2012.02.082 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf