Integration of Thermal Inkjet into Over-Molded Substrates for Lab-on-CMOS Pumping Applications

Co-packaging microfluidics and integrated circuits (ICs) has allowed for increasingly integrated lab-on-chip and lab-on-CMOS systems. Many of these, however, still required external hardware for pumping. Here, a combination of wafer-level molding and 3D-printing is used to package an IC with thermal inkjet (TIJ) capabilities as a micropump, coupled with package-level microfluidics and electrodes for impedance sensing. Including TIJ dispense capability in the package eliminates the need for external pumps for delivering fluid to the sensor. The TIJ IC acts as a pull-pump, ejecting waste solution and pulling new solution from an input port across a set of gold electrodes on the package surface. These electrodes are situated on the floor of a microfluidic channel and can be used to measure impedance, such as for electrical cell counting, and also to electrically estimate volumetric flow rate from transient signals, given known electrode spacing. To demonstrate, impedance measurements of 4.5 μm poly beads were performed at droplet ejection rates ranging from 63-200 Hz, and an estimated flow rate of 1.77 nl/min/Hz is shown using both electrical and optical tracking methods. Long-term, this approach can provide integrated pumping for multi-chip lab-on-CMOS systems in overmolded substrates.