Nizn Ferrite Thin Films Factors Influencing The Performance

NiZn ferrite thin films can be used as planar inductor, miniature transformer, electromagnetic noise suppressors because of its high resistivity, high Curie temperature, low temperature coefficient, and excellent properties of high frequency. In this dissertation, effects of ZnFe₂O₄ underlayers and different substrates on microstructure and magnetic properties of NiZn ferrite thin films were investigated.NiZn ferrite thin films and ZnFe₂O₄ underlayers were prepared by radio frequency(RF)magnetron sputtering technique, respectively. The phase structure of deposited films and bulk were characterized by X-ray diffractometer (XRD). Magnetic property of deposited films was characterized by vibrating sample magnetometer(VSM),and the magnetic property of bulk was measured by B-H analyzer (SY-8232). The surface morphology of films was characterized by atom force microscopy (AFM),and cross-section morphology of bulk were observed by scanning electron microscope (SEM).ZnFe₂O₄ underlayers were deposited firstly, and the as-deposited films were annealed at differernt temperatures. Suitable annealing temperature was decided by investigating the phase structure of the film annealed at different temperatures. Then Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ ferrite thin films were deposited on Si(100) substrates buffered with different thicknesses of ZnFe₂O₄ underlayers, and the effects of ZnFe₂O₄ underlayer on the property of NiZn ferrite thin films were investigated. Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ ferrite thin films were deposited on Si(100), Si(111), MgAl₂O₄(100), MgAl₂O₄(111), MgO(100) substrates, respectively. Eventually, the effects of Mn-substitution and annealing process on the property of NiZn ferrite thin films were investigated.The result indicates that the saturation magnetization Ms of Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ ferrite thin films annealed at 800℃increases firstly and then decreases with the increase of ZnFe₂O₄ underlayer thickness, while the coercive force Hc decreases. When the thickness of ZnFe₂O₄ underlayers is 40nm Ms of Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ reaches the maximum value about 379 kA/m. Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ thin films deposited on the MgAl₂O₄(111) substrate show a saturation magnetization as high as 385kA/m, while the films deposited on the MgO (100) substrate show a coercive force as low as 1.75kA/m. With the increase of Mn content, Ms of Ni0.5-xZn0.5MnxFe₂O₄ ferrite thin films increases firstly and then decreases, while Hc decreases monotonously. When x=0.15 the Ms reaches the maximum value about 453kA/m. Ms and Hc of Ni_0.45Zn_0.5Mn_0.05Fe₂O₄ increase with the increase of annealing temperature, while Ms increase firstly and then decreases with the increase of duration time, but Hc changes contrarily.