Preferred orientation and microstructure of Ni-Zn-Cu ferrite thin films deposited by rf magnetron sputtering
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We have investigated the effects of process parameters such as rf power, substrate, and gas pressure Pp^ on preferred orientation, microstructure, and magnetic properties of N i - Z n - C u ferrite thin films deposited by conventional rf magnetron sputtering. The texture structure was developed in the ferrite films deposited on the SiO 2 /Si(100) substrate at low rf power conditions. The ferrite film on the S i ( l l l ) substrate always had (111) texture irrespective of process parameters due to lattice matching, but the texture of the ferrite film on SiO 2 /Si(100) changed from (111) to (100) and finally returned to (111) orientation again with decreasing PAr. Such behavior would occur presumably due to the characteristic atomic stacking sequence corresponding to a given condition of the ion bombardment. The ferrite films deposited at low PAl had a denser microstructure consisting of tightly packed columnar grains with a smoother surface, better adhesion to the substrate, and better crystallinity than those at high PAI- HC\\ of ferrite film deposited at low PAT was larger than that at high PM and also larger than Hcl of that deposited at the same PM because larger compressive stress was induced at low PAl than at high /\r-
I. INTRODUCTION The development of ferrite films and their devices, which can be compatible to monolithic microwave integrated circuit (MMIC), has been a major focus of current research in microwave magnetics.1 Ni—Zn ferrite, which is a ferrimagnetic oxide with a mixed spinel structure, is the most suitable material for device applications in the upper microwave and lower millimeter-wave range.2'3 Ni and Ni-Zn ferrite films have been prepared by ferrite plating,3"5 oxidation of metallic films,6 arc plasma method,7'8 chemical transport,9'10 chemical vapor deposition (CVD),11"14 and sputtering,15 but Cu-doped Ni-Zn ferrite film has not been reported. We doped Ni-Zn ferrite with Cu to reduce the crystallization temperature of ferrite film. This idea was deduced from the fact that the sintering temperature of bulk Ni-Zn ferrite can be reduced by 200 °C through the doping of Cu,2'16 and was confirmed by our previous work.17 It is well known that during the film deposition process various process parameters, such as composition of gas mixture, gas pressure, deposition rate, and negative bias on the substrate, can determine preferred orientation,18 microstructure,19"25 and the magnetic property of ferrite films. A number of authors have proposed their theories, which can provide a general relationship between the process parameters and the preferred orientation, based on their criteria such as critical nucleus,26 supersaturation and surface energy,27 ion channeling,28"31 plastic flow,32 and the competition between surface and J. Mater. Res., Vol. 9, No. 9, Sep 1994 http://journals.cambridge.org
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strain energy.33 However, no general rule has been successfully developed even for simple metal systems. In this paper, we have investigated the effects of some parameters such as rf
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