Integrated Microwave Resonator for Detecting Microliter Liquid Mixtures

The design, fabrication, and measurement of a resonant microwave interdigitated sensing structure (MISS) fabricated using integrated circuit technology and able to detect microliter volumes of liquids mixtures are presented in this letter. The proposed device is based on interdigitated aluminum (Al) electrodes with a sensitive area of 1.3 mm × 2.6 mm delimited by a ring fabricated with SU-8 resin, which allows the accurate placement of the sample drop. An empty sensor was designed to present its intrinsic resonance at 16 GHz so that when deionized water is used as the sample, its resonance drops to 1.25 GHz due to the change in sample permittivity. Experimental validation was performed using isopropyl–water mixtures with different concentrations between 0% and 100%. From measurements, it is shown that by using the proposed resonator, a maximum sensitivity of 4.72% is obtained. Finally, results indicate the potential of the proposed structure for dielectric spectroscopy and the possibility of exploiting the use of this resonator as a biosensor, and also of integrating it into other type of sensors to improve their detection properties.