Complex Permittivity Measurements in 1–30 GHz Using a MEMS Probe

An open-ended coplanar waveguide (CPW) structured probe was implemented for the measurement of dielectric properties of liquids using microelectromechanical systems (MEMS) technology. The MEMS probe, fabricated on sapphire substrate, consists of an open-ended CPW, where the conducting layers were made using Cr/Al. A dielectric layer using SU-8 was added to protect the metal layer. An aperture at the end of the probe was added where the CPW contacts with the material under test. The size of the probe is 180 μm (width) × 660.2 μm (thickness) × 6000 μm (length), aperture size is 100 μm × 100 μm, and thickness of SU-8 is 10 μm. The permittivities of ethanol-water mixtures measured using the MEMS probe in the 1-30 GHz agreed well with the values presented in the literature. The low cost, small, lightweight, and portable probe described in this paper can be used to measure dielectric properties of very small volume of samples.