Properties Of NiCuZn Ferrite Thin Films Prepared By Sol-gel Method

With the rapid development of technology of integrated semiconductor, electronic devices need to be miniaturized and used at high frequency. So thin films have caused wide public concern over the recent years. NiZn ferrite with large resistivity, high resonance frequency has been widely used for transformer, inductor in the field of communication, PC, EMI, TV and so on. We can regulate frequency of NiZn ferrite by adding suitable Cu to the ferrite. NiCuZn ferrite has become one important branch of the NiZn ferrite. In a word, it is of great significance to prepare NiCuZn ferrite thin films of good performance.In this thesis, we prepare NiCuZn ferrite thin films by sol-gel (spin-coating) method. The influence of quality of sol, annealing temperature, annealing time, raw material composition, magnetic vacuum rapid heat treatment and spin-coating process on the crystal structure, micromorphologies and magnetic properties of the NiCuZn ferrite thin films have been investigated in order to prepare films with high saturation magnetization Ms and low coercivity Hc. The NiCuZn ferrite thin films were investigated systematically by the X-ray diffraction, Vibrating sample magnetometer, field emission scanning electron microscope and atomic force microscope. The conclusions we draw as follows:(1) Observing from the TG-DTA plots, we choose 120℃and 300℃as the temperatures that evaporate the water and organics in the ferrite films. We can get uniform and good performance NiCuZn ferrite thin films with the speed of spin coater 4000 rpm, spin time 30 s and three layers ferrite films. The thickness of the thin films is about 240 nm.(2) The quality of sol was investigated. We found that we obtained high performance NiCuZn ferrite thin films when the concentration of sol was 0.2 mol/L, aging time 24 h and concentration of PEG about 25 g/L.(3) The Heating rate and annealing time were set to be 2℃/min and 2 h respectively during annealing process. The thin film has a single phase of spinel, when the temperature rised to 500℃.The a-Fe2O3 phase appeared, with the annealing temperature higher than 600℃, due to the volatilization of Zn. The saturation magnetization Ms and coercivity Hc increased firstly, then decreased with the increase of temperature. The maximum saturation magnetization Ms(355 emu/cc) was obtained when annealing temperature raised up to 800℃, which was close to the saturation magnetization of bulk, and the corresponding coercivity Hc was 150 Oe. The sol-gel method can lower the crystal temperature of NiCuZn ferrite, which could be able to realize low-temperature cofired ferrites.(4) The Ni0.8-xCuxZn0.2Fe2O4 thin films with different proportion of nickel and copper were investigated. All the films were annealed at 600℃for 2 h. The saturation magnetization Ms of ferrite thin films increased with x ranging from 0.2 to 0.4, then, decreased beyond x=0.4, while the coercivity Hc decreased monotonically. The compositions of Ni0.4Cu0.4Zn0.2Fe2O4 and Ni0.2Cu0.6Zn0.2Fe2O4 obtained a maximum saturation magnetization Ms of 284 emu/cc and a minimum coercivity Hc of 14 Oe respectively. We can regulate the Ms and Hc of NiCuZn ferrite films by adding suitable Cu content.(5) We tried to processe Ni0.4Cu0.2Zn0.4Fe2O4 thin films with magnetic vacuum rapid heat treatment. The results showed that the properties of thin films became worse because rapid heat treatment could not remove the stress in the ferrite thin films effectively.