Measurement of thin film composites using microstrip line fixtures

We present a technique to measure the material parameters of a thin film composite over a broad frequency range (50 MHz to 2.5 GHz). Two different microstrip line fixtures are prepared for the in-plane permittivity and permeability measurements, respectively, and their geometries are optimized to uniformly excite the E-field and H-field on the film surface. With this, broadband S-parameter responses of the film can be captured and used in the material parameter retrieval process. The latter is based on the well-known Nicolson-Ross-Weir equations in conjunction with curve fitting a set of full-wave simulation data. A patterned magnetic film composite with thin (150 μm) and small (1 × 1 cm²) form factor is characterized using the proposed method. The measurement results demonstrate a constant in-plane permittivity but a dispersive in-plane permeability over the target frequency range.