Integration method of silicon sensors on SU‑8‑based microfluidic platforms
In this paper, a method of integration of silicon sensors in microfluidic platform is presented. In particular, impedimetric silicon sensors are used to make the proof of concept. These sensors are integrated in a FR4 substrate [component of a printed circuit board (PCB)] where the SU-8 microfluidic circuit is built. In order to generalize the application of this method, standard processes that are typical in the laboratories are used. The material to fabricate those microfluidic circuits is the negative photoresist SU-8. The method of fabrication consists on performing the typical SU-8 process over the silicon chips once they are inserted in the FR4 substrate. This method must provide flatness to avoid irregular microchannels. Also, the proposed process must ensure the insulation of the electric connections to avoid short-circuits when the sample fluid flows through the systems, and bondings robust enough to support a spinning step. In addition, the SU-8 process must be clean enough to keep the capability of measurement of the sensors. This cleanness has been studied using different conductivities of a KCl solution, providing good results. Finally, apart from integrating microfluidic and electronics in the same substrate, this method of integration provides an approach to the optimum between low cost, simplicity and precise measurements thank to the use of inexpensive PCB-based platforms and precise silicon sensors.