Study On ZrW₂O₈,Al₂O₃ And Their Composite Films Prepared By Radio Frequency Magnetron Sputtering

Negative thermal expansion (NTE) material becomes a new branch of materials science in recent years. Particularly, ZrW₂O₈ has stimulated considerable interest in this topic, because it exhibits large isotropic NTE property over its entire stability range from 0.3K to 1050K, the thermal expansion coefficient is -9×10^-6K^-1. It has various potential applications in electronics, optics, biomedicine, sensor etc. But recently more powders and composites with other materials were studied and less reports on films or composite films were seen in the international wide. Al₂O₃ films were fully studied and have been used in many fields, but further studied on the dense structure, dielectric property, friction property and the dead device of the Al₂O₃ films due to the thermal coefficient mismatch with the substrate were necessary. So the preparations of ZrW₂O₈ films, Al₂O₃ films and their composite films were studied in this paper.ZrO₂:WO₃=1: 2.8,pure ZrW₂O₈, ZrO₂ and WO₃ ceramic targets were used to prepare the ZrW₂O₈ films by radio frequency magnetron sputtering in this work. The influence of heat-treating temperature on the film phase, morphology, cohesion between the film and the substrate and the negative thermal coefficient were studied. Al₂O₃ films were prepared with theα-Al₂O₃ ceramic targets by Radio frequency magnetron sputtering as well. The influence of processing parameter on the film preparation, dielectric constant and friction property was studied. The ZrW₂O₈/Al₂O₃ composite films were deposited by alternating radio frequency magnetron sputtering. We also study the preparation method and effect of post-deposition annealing on the microstructure and morphology of the composite films.The microstructure and morphology of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and atomic force microscope (AFM). The negative thermal expansion coefficient was calculated using the lattice constants obtained by Powder X software using the data collected at different temperatures by in Situ X-ray measurement. The thicknesses, friction and cohesion of the samples were measured by surface profilometer (ET350), surface performance test instrument (MS-T3000) and scratching adhesion tester (WS-2000). The dielectric properties of Al₂O₃ films were investigated with impedance analyzer (HP4294A).The results indicated that, the surfaces of the Al₂O₃ films obtained at low power were smooth and compact. The dielectric constant was about 3.2. the dielectric constants were increased and the dielectric losses were decreased with the increase of the applied RF power. With the increase of the frequency, the dielectric constants at a high frequency were found to reduced and become invariable gradually. With the increase of the frequency, the dielectric losses of the Al₂O₃ films obtained at 140W and 190W were found to reduce and the Al₂O₃ films obtained at 70W were found to increase, finally become invariable gradually as well. Al₂O₃ films have a fine wearing performance, the friction was about 0.18.The trigonal and cubic ZrW₂O₈ films were successfully prepared with different targets. The as-deposited film is amorphous. The trigonal ZrW₂O₈ films prepared with ZrO₂: WO₃=1:2.8 and target crystallized at around 740℃for 3 min in oxygen and cubic ZrW₂O₈ films crystallized at around 1200℃for 8min in a closed device. The preferred growing ZrW₂O₈ films prepared with pure ZrW₂O₈ target crystallized at around 740℃for 3 min in oxygen, and cubic ZrW₂O₈ films crystallized at around 1200℃for 8min in closed device. The cubic ZrW₂O₈ films deposited by alternating radio frequency magnetron sputtering with ZrO₂ and WO₃ targets crystallized at around 1200℃for 100s in ambient air. With the increase of the temperature, the grain size of the films increased but the tightness decreased. The cubic ZrW₂O₈ films prepared on the quartz, and then the Al₂O₃ film deposited on the ZrW₂O₈/SiO₂ substrate, after heat-treated at 500℃for 72h, we successfully prepared the ZrW₂O₈/Al₂O₃ composite films. Meanwhile, the Al₂(WO₄)₃ films crystallized at around 950℃for 10min were successfully prepared by alternating radio frequency magnetron sputtering with Al₂O₃ and WO3 targets, the surface of the film was multihole and had a fine cohesion between the film and the substrate.