Microstructure And Properties Of NiZnCo Ferrite Magnetic Films Fabricated By RF Magnetron Sputtering

The soft magnetic film materials have small coercive force and high saturation intensity, so it is suitable for these materials to the developing trend of electronic products toward much smaller and micro-miniature electronic device. At present, the soft magnetic film material is becoming an important research field of the magnetic materials. In the present work, the nano-crystalline NiZnCo ferrites/SiO₂ composite powder is synthesized by Sol-gel method. The target is fabricated by isostatic cool pressing with NiZnCo ferrites/SiO₂ composite powder. The ferrite film is successfully deposited on silicon and glass substrate by using of radio frequency magnetron sputtering (RF-MS). With the help of modern analyzers, XRD,EPMA,AFM,TEM and DTA, the chemical composition phase constitution and morphology of the ferrite film are analyzed. The magnetic and mechanical properties of NiZnCo ferrites/SiO₂ composite film are studied. The forming mechanism of NiZnCo ferrites/SiO₂ composite film is also discussed preliminarily.Experimental results show that there is the optimal technical process and parameter to synthesize the NiZnCo ferrites/SiO₂ powder by sol-gel method. Pure nitrates of Ni, Zn and Co are dissolved in absolute alcohol, and then Si(OC₂H₅)₄(TEOS) is dropped into the solution. The hydrogen nitrate is used to adjust the PH value 1². The intermixture is heated for half an hour in water bath and gelatinized for 5 hours. The purple gel is dried at 85℃for 12 hours and heated at 800℃ for 2 hours. The chemical composition of ferrite powder is suitable to the quality requirements and the morphology of the powder is globular shape. The grain size is in the range of nanometer. The powder is spinel type of NiZnCo ferrites/SiO₂.The research of target and film indicates that the target is prepared by isostatic cool pressing with 99.5% pure NiZnCo ferrites/SiO₂ powder. PVA is used as cohesive material. The green target is sintered in the high temperature furnace and the shrinking of the target is over 14% and can meet the requirement of sputtering target. The sputtering technique of forming film and surface treatment of substrate is designed. The sputtering deposition rate and the morphology of the films are researched by adjusting technical parameters of magnetron sputter.With the help of modern analyzers XRD, EPMA, AFM, TEM and DTA, the chemical composition , phase constitution and morphology of the ferrite film are analyzed. Results show silicon substrate is more suitable to be used as the depositedsubstrate. The sputtering deposition rate increases with the increasing of sputtering power. But the microstructure of NiZnCo ferrites/SiCh ferrite film is changed from the well-distributed small rectangular grain to coarse flake grain. When the distance between target and substrate is 65mm, the sputtering deposition rate is maximum and the microstructure of NiZnCo ferrites/SiCh ferrite film is best. So The optimal sputtering parameters are as follows, 6X10⁵Pa (degree of vacuumX l.OXKT'Pa (sputter pressure)> 120W (sputtered power) and 65mm (the spacing of substrate-target) .The NiZnCo ferrites/SiO2 film deposited by magnetron sputter is amorphous and can be changed into crystalline by post-annealing treatment. The grain size of the film is refined and closely packed after post-annealing treatment. The oxygen component of film is lost during the sputtering deposition and it is refilled after post-annealing treatment.The magnetic hysteresis loops of NiZnCo ferrites/SiCh ferrite films are tested. Results indicate that NiZnCo ferrites/SiO2 films possess small coercive force (about 5.17 kA/m) and high saturation intensity (378.4kA/m). The saturation intensity drops slowly in the demagnetization because of the Co-doping method and the non-magnetic SiC"2. The influence of heat treatment and different substrates on the magnetic properties is studied. The film deposited on silicon substrate has higher saturation intensity than the film deposited on glass although they both have small coercive force. After post-annealing treatment, the saturation intensity is enhanced and the soft magnetism is improved.The interfacial adhesion strength between film and substrate is tested by scratch method. The results show that NiZnCo ferrites/SiCh film possesses the strong adhesive strength (force) with substrate. Because of the silicon substrate has better surface, the adhesive force of the film deposited on silicon substrate is stronger than that of the film deposited on glass substrate. The adhesive force increases with the increasing of film thickness because the adhesive force between the substrate and the film is probably related with adhesion capacity of interface.