Development of an integrated RF impedance matching device with LPF function using a CoFeB magnetic/polyimide dielectric hybrid thin-film coplanar-line

In this study, the CoFeB/polyimide hybrid thin-film coplanar transmission-line for RF impedance matching was fabricated and its transmission characteristic was evaluated. The device has a thin-film coplanar structure with a CoFeB amorphous magnetic film with a relative permeability of 180, a polyimide dielectric film with a relative permittivity of 3.5, a top and bottom copper conductor film on a glass substrate. The quarter wavelength device with a 100 μm width magnetic film consisting of 0.3 μm × 2 layers had an insertion loss of 2 dB and a line length of 6 mm. The device functioned as a low pass filter with a GHz cut-off frequency, which was due to the eddy current loss and FMR absorption in the magnetic film. Therefore, the hybrid thin-film coplanar-line is expected to apply for GSM cellular phone with non-linear power amplifier.