At the present time, newly developed, engineered thin-film materials, which have unique properties, are used in RF applications. Thus, it is important to analyze these materials and to characterize their properties, such as permittivity and permeability. Unfortunately, conventional methods used to characterize materials are not capable of characterizing thin-film materials. Therefore, on-wafer characterization methods using planar structures must be used for thin-film materials. Furthermore, most new, engineered materials are usually wafers consisting of thin films on a thick substrate.
The first step of this study was the development of a novel, on-wafer characterization method for isotropic dielectric materials using the T-resonator method. Although the T-resonator method provides highly accurate measurement results, there is still a problem in determining the effective T-stub length, which is due to the parasitic effects. Our newly developed method uses both the resonant effects and the feed-line length of the T-resonator. In addition, performing the TRL calibration provides the exact length of the feed line, thereby minimizing the uncertainty in the measurements. As a result, our newly developed method showed more accurate measurement results than the conventional T-resonator method, which only uses the T-stub length of the T-resonator.
The second step of our study was the development of a new on-wafer characterization method for isotropic, magnetic-dielectric, thin-film materials. The on-wafer measurement approach that we developed uses two microstrip transmission lines with different characteristic impedances, which allow the determination of the characteristic impedance ratio. Therefore, permittivity and permeability can be determined from the characteristic impedance ratio and the measured propagation constants. In addition, this method involves Thru-Reflect-Line (TRL) calibration, which is the most fundamental calibration technique for on-wafer measurement, and it eliminates the parasitic effects between probe tips and contact pads.
The third step of this study was the development of an on-wafer characterization method for magnetic-dielectric material using T-resonators. This method allows the determination of the ratio of the characteristic impedance to the effective refractive index of the magnetic-dielectric materials at the resonant frequency points. Therefore, permittivity and permeability can be determined. Although this method does not provide continuous extractions of material properties, it provides more accurate experimental results than the transmission line methods.
The last step of this research was the evaluation and assessment of an anisotropic, thin-film material. Many of the new materials being developed are anisotropic, and previous techniques developed to characterize isotropic materials cannot be used. In this step, we used microstrip line structures with a mapping technique to characterize anisotropic materials, which allowed the transfer of the anisotropic region into the isotropic region. In this study, we considered both uniaxial and biaxial anisotropic material characterization methods. Furthermore, in this step, we considered a characterization method for biaxial anisotropic material that has misalignments between the optical axes and the measurement axes. Thus, our newly developed anisotropic material characterization method can be used to determine the diagonal elements in the permittivity tensor as well as the misalignment angles between the optical axes and the measurement axes.