Correlation between microstructure, DC resistivity and magnetoresistance of SrRuO 3 films.
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Correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 films. K. Khamchane, R. Gunnarsson Z.G. Ivanov Department of Microelectronics and Nanoscience, Chalmers University of Technology and Göteborg University, SE -412 96 Göteborg, Sweden. A. Vorobiev1,2, P. Rundqvist' S. Gevorgian1,3 1 Department of Microelectronics, Chalmers University of Technology, SE-4 1296 Göteborg, Sweden 2 lnstitute for Physics of Microstructures RAS, N. Novgorod, GSP-105, 603600, Russia 3 Microwave and High Speed research Centre, Ericsson Microwave Systems, 431 84 Mölndal, Sweden ABSTRACT
We have investigated the correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 thin films. The films were epitaxially grown by pulsed laser deposition on (001) SrTiO3 substrates in a temperature range of 690–8100C. According to x-ray measurements, the structure of all films is a mixture of highly oriented domains of strained orthorhombic phases (ortho-I and ortho-II) with different lattice parameters. Films deposited at 7800C show a minimum resistivity (270!mWcm at 300!K) and a maximum magnetoresistance (8% at 5!K). These films consist mainly of ortho-I phase (a=0.393!nm). Films deposited at 6900C (predominantly ortho-II) have the highest resistivity (up to l700!mWcm at 300 K) and lowest magnetoresistance (3% at 5!K). INTRODUCTION
The properties of ferroelectric (dielectric) thin films, such as the perovskite SrTiO3 (STO), are such that they have a key role in microwave applications like electrically tunable capacitors, i.e. varactors. One important component of these varactors is the electrodes. The requirements set on these are that they must be grown epitaxially, be in lattice match, and be chemically stable with the ferroelectric thin film. The perovskitestructured itinerant ferromagnet SrRuO3 (SRO, Tc ~ 150!K) shows these features when grown on STO (cubic, a = 0.3905!nm). SRO exhibits the GdFeO3 orthorhombic structure with lattice parameters a = 0.557!nm, b = 0.553!nm and c = 0.784!nm, for simplicity often referred to as pseudocubic (a = 0.391!nm) [1,2]. It has previously been demonstrated that low-resistivity SRO films must be grown under precise deposition conditions [3]. Resistance and magnetoresistance have previously been measured for single crystals as well as for thin films [4,5]. However, most previous studies have focused on optimally grown thin films, i.e. films with lowest resistivity. We have carefully mapped the deposition conditions for SRO, and are able to relate the deposition temperature to microstructure. The films grow predominantly in
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one of two orthorhombic phases. Further, we have measured the magnetic and resistive behaviour for the different phases. EXPERIMENTAL
A KrF excimer laser beam (l = 248!nm, t = 30!ns) operating at 10!Hz, was focused to a spot size of 1 x 3!mm with an energy density of 1.5!Jcm-2. An on-axis deposition configuration with target-to-substrate distance of 4!cm was used. Substrates were fixed to the surface of a resistive heater bl
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