Microfluidic packaging of high-density CMOS electrode array for lab-on-a-chip applications

Effective packaging and integration of microfluidic components with a small electronic chip, such as a complementary metal–oxide–semiconductor (CMOS) chip, is crucial for the ultimate realization of lab-on-a-chip (LOC) devices. Hence, the methods and materials used for the integration should provide good reproducibility, reliability, biocompatibility, and capability for mass production. This paper introduces a new concept that allows the miniaturization of microfluidic packaging and the integration of CMOS chips. The photosensitive polymer material used in this study serves not only as a photoresist to pattern diverse shapes of microfluidic structures at the wafer level, but also as an adhesive to bond the Indium-Tin-Oxide (ITO) coated glass chip to the CMOS die. The patterning process, using conventional photolithography, was demonstrated with a wide range of thicknesses from 10 μm to 80 μm, and reliable seamless bonding was achieved with a conventional flip-chip bonder. We also validated that the proposed packaging can be utilized in biological experiments by culturing live cells (MCF-7) for three days and by measuring the auto-fluorescence from the polymer material in the test-vehicles. In addition, the performance of the proposed packaging method was demonstrated by applying it to the microfluidic/CMOS hybrid chip for preliminary electrochemical testing (impedance measurement), and particle entrapment testing (dielectrophoresis experiment). The proposed fabrication procedure is expected to facilitate the wide adoption of CMOS technology in LOC applications.