采用射频磁控溅射法制备的La0.5Sr0.5CoO3薄膜的结构和电学性能-英文文献

Journal of Alloys and Compounds449(2008)

68–72

Structural and electrical properties of La0.5Sr0.5CoO3thin

films prepared by rf magnetron sputtering

A.S.Asha a,M.T.Sebastian b,M.K.Jayaraj a,∗

a Optoelectronics Device Laboratory,Department of Physics,Cochin University of Science and Technology,Kochi682022,Kerala,India

b Regional Research Laboratory,Thiruvananthapuram695019,Kerala,India

Received4November2005;received in revised form28December2005;accepted15January2006

Available online19January2007

Abstract

La0.5Sr0.5CoO3thinfilms were prepared by rf magnetron sputtering from stoichiometric La0.5Sr0.5CoO3powder target.The rf power and the post deposition annealing conditions have been optimized to obtain conducting La0.5Sr0.5CoO3thinfilms.The dependence of conductivity,optical and structural properties of the thinfilms on the deposition and the post deposition annealing conditions has been investigated.The crystallinity of thefilms was found to improve with increase of rf power and annealing temperature.The variation in resistivity and band gap with rf power and annealing conditions are correlated.

©2006Elsevier B.V.All rights reserved.

Keywords:Ferroelectrics;X-ray diffraction;Absorption

1.Introduction

Ferroelectric thinfilm capacitors are of increasing interest due to their potential application in dynamic random access memory and non-volatile random access memory(NVRAM) [1].The desired perovskite phase of lead zirconium titanate (PZT)is produced at about600◦C in oxygen ambient,it is important that the bottom electrode should not suffer any delete-rious effects in its microstructure or electrical properties during the growth of PZT layer.Conventional ferroelectric capacitors using platinum electrodes have poor adhesion to SiO2.The Pt will react with Si to form a silicide in the absence of oxygen significantly below the600◦C,the deposition temperature of PZT[2].The PZT capacitors using Pt electrodes show a polar-ization fatigue due to the buildup of space charge within the PZT layer or at the PZT–electrode interface.The other source for the origin of space charge may be mobile oxygen vacancies and Schottky depletion region due to work function mismatch at the PZT–electrode interface[3].

The PZT capacitors with conducting oxide such as La0.5Sr0.5CoO3(LSCO)as electrode show outstanding fatigue

∗Corresponding author.Tel.:+914842577404;fax:+91484257595.

E-mail address:mkj@cusat.ac.in(M.K.Jayaraj).resistance[4,5].The improved fatigue behavior may be due to the controlled charged defects at the PZT–electrode interface by the oxide electrodes.LSCO electrode has a better work func-tion match to the PZT material[1].LSCO can be deposited at the same growth condition as PZT and its resistance is isotropic[5].The LSCO has perovskite structure and its lat-tice parameter matches with PZT.This promotes the growth of perovskite phase of PZT,minimizing the capacitor fatigue[6]. LSCO thinfilms may be prepared by both chemical and phys-ical methods.Chemical methods are the sol–gel process[7], metal organic chemical vapor deposition[8]and dipping pyrol-ysis[9].The sputtering[10,11]and pulsed laser depositions [12–14]are the physical methods used for the preparation of LSCO.

In this paper we report the preparation and characterisation of LSCO thinfilms by rf magnetron sputtering.The rf power and the annealing conditions of the as prepared thinfilms are optimised to get better conducting thinfilms.

2.Experimental

La0.5Sr0.5CoO3thinfilms were prepared by rf magnetron sputtering of the synthesized 0.5Sr0.5CoO3powder was prepared from stoichiometric mixtures of La2O3,SrCO3,and Co3O4.The powder was ball milled using ZrO2balls in de-ionized water for24h.It was dried and calcined for24h at1200◦C.

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