Micromachined strip line with SU-8 as the dielectric

For the first time this paper presents strip lines fabricated using SU-8 as the dielectric material. It shows the complete fabrication process of micromachined strip lines with a total height of 35.5µm as well as their characterization by on-wafer S-parameter measurements with frequencies up to the mm-wave range. Strip lines with a strip thickness of 2.5µm, a line length of 3mm and variations of strip width between 6 and 30µm were manufactured and measured. The characteristic impedance, the phase constant, the phase velocity and the attenuation constant of the lines were determined from the measured S-parameters. Characteristic impedance values between 86ohm and 38ohm were measured and on the 48ohm strip line an attenuation constant of 1.9dB and 0.58dB at 10GHz and 48GHz respectively were determined. Since the fabricated strip line is totally shielded and its dielectric consists solely of SU-8, determination of the relative dielectric constant and the loss tangent of SU-8 was performed from microwave measurements on the strip lines. A relative dielectric constant of 3.1 and a loss tangent of 0.043 for SU-8 was determined.