Applied Surface Science 258 (2011) 1390–1394 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al h om epa g e: www.elsevier.com/locate/apsusc BiFeO 3 /Zn 1-x Mn x O bilayered thin films Jiagang Wu a,∗ , John Wang b , Dingquan Xiao a , Jianguo Zhu a a Department of Materials Science, Sichuan University, 610064, PR China b Department of Materials Science and Engineering, National University of Singapore, 117574, Singapore a r t i c l e i n f o Article history: Received 9 May 2011 Received in revised form 19 September 2011 Accepted 20 September 2011 Available online 24 September 2011 Keywords: BiFeO3/Zn1-xMnxO Bilayered thin films Magnetron sputtering Electrical properties a b s t r a c t BiFeO 3 /Zn 1-x Mn x O (x = 0–0.08) bilayered thin films were deposited on the SrRuO 3 /Pt/TiO 2 /SiO 2 /Si(1 0 0) substrates by radio frequency sputtering. A highly (1 1 0) orientation was induced for BiFeO 3 /Zn 1-x Mn x O. BiFeO 3 /Zn 1-x Mn x O thin films demonstrate diode-like and resistive hysteresis behavior. A rema- nent polarization in the range of 2P r ∼ 121.0–130.6 C/cm 2 was measured for BiFeO 3 /Zn 1-x Mn x O. BiFeO 3 /Zn 1-x Mn x O (x = 0.04) bilayer exhibits a highest M s value of ∼15.2 emu/cm 3 , owing to the presence of the magnetic Zn 0.96 Mn 0.04 O layer with an enhanced M s value. © 2011 Elsevier B.V. All rights reserved. 1. Introduction BiFeO 3 (BFO), which is well known to possess the simultane- ous ferroelectric and magnetic orderings and a giant polarization at room temperature, is among the ideal candidates for sensors, actuators, ferroelectric random access memories, and microelec- tromechanical systems [1–8]. Several recent attempts, such as by ion substitutions on either A-site or B-site or both sites of the lattice [9,10], formation of heterostructure structures [11–14], and control of film orientation [15], have been made in order to reduce the leakage current and enhance the multiferroic behavior of BFO. The heterostructure approach is among the most promis- ing approaches, whereby the interface coupling and interactions among the different functional layers in the heterostructure struc- ture can strongly influence the growth and physical behavior of the thin films [11–14,16,17]. Indeed, an appropriate combination of the layers differing in composition and structure can lead to a dramatic enhancement in the multiferroic behavior for BFO [11–14]. BFO thin films with a giant remnant polarization are ideal candi- dates for the high-density memories, where one of the fundamental problems in such devices is the scaling limit [18]. In contrast, the resistance-based random access memories (RRAM) have recently been given considerable attention because of their scaling-less limits [19], which undoubtedly have a significantly different tech- nological potential as compared to the charge based storages. Compared to other nonvolatile memories, RRAM has several ∗ Corresponding author. E-mail address: wujiagang0208@163.com (J. Wu). advantages, including a fast writing time, high density, and low operating voltage [19]. A generalized heterostructure model, namely the “conductive metal-ferroelectric-semiconductor-metal structure” was proposed [20], which has recently been given to considerable attention as field-effect transistors (FET) for mem- ory functionality and nondestructive readout behavior [21,22]. Zn 1-x Mn x O exhibits a piezoelectric wurtzite-structure and an irre- versible spontaneous polarization. It also has a low electrical resistivity, a wide spectral transparency, and strongly excitonic, direct electronic band-to-band transition, together with a room- temperature ferromagnetism [23]. It is therefore of considerable interest to investigate the bilayered thin films consisting of semiconducting ferromagnetic Zn 1-x Mn x O and multiferroic BFO layers, as a conductive metal-multiferroic-semiconductor-metal heterostructure in order to widen the practical application and improve the magnetic properties of BFO thin films. In this work, the bilayered thin films consisting of BFO and Zn 1-x Mn x O (BFO/Zn 1-x Mn x O) were deposited by radio fre- quency (rf) sputtering, and their film texture as well as electrical behavior are carefully investigated. A highly (1 1 0) orienta- tion and dense microstructure were well developed for the BiFeO 3 /Zn 1-x Mn x O thin films. Diode-like and resistive hysteresis behavior was observed, together with a high remanent polarization and improved magnetic properties. 2. Experimental procedure Bilayered BFO/Zn 1-x Mn x O (x = 0, 0.01, 0.02, 0.04, 0.05, and 0.08) thin films were deposited by rf sputtering from pre-fabricated BFO and Zn 1-x Mn x O ceramic targets, which were synthesized via a 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.09.083