Investigation Of Automatic Measurement System For Microwave Permeability Spectrum Of Nanostructural Magnetic Thin Films

With the widespread use of wave-absorbing materials in the field such as microwave communication, microwave darkroom, electromagnetic antiradiation, electronic countermeasure, it become an important problem to research and develop wave-absorbing materials answering the above demand. FeCo-based alloy nano-granular films and nano-multilayer films are much accounted for their high permeability and high loss under microwave frequency to realize broadband absorbing of microwave. The exact knowledge of film permeability μ r is essential in the study of stealthy material. So the measurement of complex permeability of thin films at microwave frequencies is very important. Microstrip reflection method was selected to make measurement of complex permeability of a given film that based on comparison and analysis of the measurement methods for permeability at home and abroad. The complex permeability was deduced by an analytical approach from the measured reflection coefficient of a shorted microstrip line with and without a ferromagnetic film material inside using the transmission line theory and Maxwell equations. A shorted microstrip line is designed and fabricated as a prototype measurement fixture with the help of Ansoft-HFSS, and the process of the measurement is also simulated to testify correctness of the measurement method. A measurement system with GPIB bus structured is built up that consists of an 8722ES vector analyzer, personal computer, a shorted microstrip transmission-line home-made and an 82357USB/GPIB cable. Automatic application software is developed by virtual instrumentation and efficiency is improved greatly. By means of this system, a series of FeCo-based thin films with about 0.4micron thickness sputtered on silicon substrate are measured in 0.5-5GHz frequency range and the general correctness of the measurement results. Microstrip reflection method can make a high speeding measurement, and the measurement technique is fast, easy to implement because the test sample can be made and inserted easily into the test chamber. It is inferred that this method can't only be applied to planar isotropic nano-films but also to planar anisotropic nano-films.