Fabrication And Charaterization Of The Radio-frequency Micro-inductors With Magnetic-films

High performance RF integrated micro-inductor is a highly desired passive component for wireless communication applications. To date, lack of miniature IC inductors with low lost and high performance hinders realization of single chip RF SoC. Magnetic materials integrated into micro-inductors can not only heighten the inductance but also reduce the magnetic loss of inductors. It is a promising way to realize the high performance integrated micro-inductors through the integration of magnetic materials into inductors. In this thesis, the magnetic performance and fabrication processes of ferrite thin-films for high frequency have been studied. Based on these studies, the RF planar micro-inductors with ferrite thin-films are first fabricated by using standard Si integrated technology. The experimental results show the integration of magnetic materials into inductors can enhance the whole performance of RF planar micro-inductors effectively. Firstly, a physical model of planar inductor is introduced. Based on this model, analytical formulas used for the calculation of Q factor and inductance is obtained, and the analysis of the impact factors, such as inductor size and material parameters, to the inductor L and Q value are further performed. Considering the high resistivity of ferrite, an equivalent circuit model of planar inductor with magnetic thin-films and the formulas for the calculation of L and Q value of the inductors are achieved. Based on the equivalent circuit model, the affection of ferrite magnetic thin-films on the performance of RF planar micro-inductors are investigated systematically, which is the theoretical foundation for realizing the integrated inductor with ferrite thin-films. The simulated results show that high-frequency dielectric constant is the same important as the high-frequency permeability of the magnetic materials that are applied for the RF integrated inductors. The ferrite materials with high permeability and low dielectric constant are suitable to the integrated inductors. Using partial element equivalent circuit method provides an accurate means used for the calculation of metal loss in RF frequency meantime. Secondly, the high-frequency properties of NiCuZn, YIG and CoZrO ferrite that fabricated by using a sol-gel auto-combustion process are investigated. The experimental results indicate the materials possess low magnetic loss and dielectric loss. The resonant frequency of NiCuZn and CoZrO ferrite is higher than 1 GHz, which is suitable to RF integrated inductors. Based on the studies, high quality NiCuZn and YIG ferrite thin films are fabricated by using sol-gel method and rapid thermal processing. The effects of the film composition and the fabricated processing parameters on the phase identification, the surface morphology and magnetic properties of the ferrite thin-films are investigated systematically. A set of optimal processing parameters is obtained. The experimental results show that sol-gel method can lower the crystallization temperature effectively and the magnetic properties of thin-films are almost identical with the bulk materials when the sol concentration for the fabrication of the thin-films is enough. Using sol-gel method in conjunction with RTP is useful to achieve the low-temperature integrated fabrication of magnetic thin-films, which is the fundament for the realization of the integrated inductor with ferrite thin-films. To realize the designed planar RF micro-inductor with ferrite thin-films, several key processes have been developed, among which are the etching of magnetic thin-films, polyimide layer preparation and dry etching, and copper electroplating. In the course of research, the etching process suitable for ferrite magnetic films is obtained through the comparison of several etching techniques. Meanwhile, we studied the formation and dry etching of polyimide films, which is used as dielectric layer between inductor coils and underpass lead. To fabricate thick copper coils, a selective copper electroplating on seed layer with resist as structural mold is established. The main process steps include seed layer sputtering, lithography of thick photoresist, copper electroplating and seed layer removal. These key processes are compatible with standard Si integrated process. Based on the structure design and technology process, the planar micro-inductor patterns based on magnetic films with the single metal layer or dual metal layers are designed separately. The fabricated processes course compatible with Si integrated process is developed for the planar micro-inductors with magnetic thin-films. The successful planar micro-inductors is fabricated. The process results show the integration of magnetic films into micro-inductors for IC is quite viable. Finally, the high frequency testing of the micro-inductor samples is performed. The effects of PAD style for measuring, the structure and material parameters of inductors on high-frequency performance of inductors are investigated systematically by using the obtained experimental data. Comparison with the simulated results shows the equivalent circuit model can satisfy design accuracy of planar inductor below 5 GHz. The comparison between the samples based on YIG, NiCuZn and CoZrO ferrite magnetic thin-films withthe referential inductors that don't include magnetic thin-films is carried out. A typical inductor sample with CoZrO thin-film is presented. The inductance is raised by 25% and the quality factor is raised by 23%, compared with the inductor, which doesn't include ferrite thin-film.