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This paper demonstrates the first-of-its-kind additively manufactured microfluidics-based flexible RF sensor, combining microfluidics, inkjet-printing technology, and soft lithography, which could potentially enable the first “real-world” wearable “smart skin” applications. A low-cost, rapid, low-temperature, and zero-waste fabrication process is introduced, which can be used to realize complex microfluidic channel networks with virtually any type of sensing element embedded. For proof-of-concept purposes, a reusable and flexible microfluidics sensor was prototyped using this process, which only requires 0.6- \mu \text L fluid volume to produce a 44% frequency shift between an empty ( \epsilon r=1 ) and a water-filled channel ( \epsilon r=73 ), demonstrating a sensitivity that is higher than most previously reported microfluidics-based microwave sensors. Seven different fluids were used to measure the sensitivity of the prototype and an overall sensitivity of 24\%/ \log (\epsilon r) was observed. The “peel-and-replace” capability of the presented sensor not only facilitates the cleaning process for sensor reusability, but it also enables sensitivity tunability. For bent/conformed configurations, the sensor’s functionality is good even for a bending radius down to 7 mm, demonstrating its great flexibility. After bending multiple times, the sensor still exhibits a very good performance repeatability, which verifies its reusability feature. The introduced additively manufactured RF microfluidics-based sensor would be well suited for numerous wearable and conformal fluid sensing applications (e.g., bodily fluids analyzing and food monitoring), while it could also be utilized in a variety of microfluidics-reconfigurable microwave components. [ABSTRACT FROM AUTHOR]

This work introduces the material and electrical characterization of two dielectric inks for use with inkjet printing fabrication and the realization of fully-printed multilayer electronic structures. The dielectric inks are categorized by the thickness of their per-layer profiles, where SU-8 polymer and poly(4-vinylphenol)-based solutions are utilized to realize thick (>4 μm) and thin (< 400 nm) inkjet-printed dielectric films, respectively. The material formulations for each ink are outlined in detail in order to achieve the desired viscosity and surface tension for optimal printing with a Dimatix inkjet printing system. Once printability and processing techniques are tuned and established, various material and electrical characterizations are performed, including printed profile measurement, multilayer profile tendencies, thermal reflow processing, UV-ozone surface energy modification, relative permittivity extraction, leakage current density, and dielectric breakdown voltage. Finally, the demonstration of fully-printed post-processed on-chip capacitors utilizing both thin and thick dielectric inks in conjunction with a silver nanoparticle-based metallic ink is presented and compared with other inkjet-printed capacitors. [ABSTRACT FROM AUTHOR]