Thermal Inkjet Pumping and Flow Rate Estimation for Microfluidics in Lab-on-CMOS Packages

In this work, we present the use of a thermal inkjet (TIJ) die as an active micropump for lab-on-CMOS applications, with the goal of replacing off-chip syringe pumps with in-package fluidic control. A combination of wafer-level molding and 3D-printing is used to co-locate a TIJ integrated circuit (IC) pump with package-level microfluidics and electrodes for impedance sensing in a single planar package. The TIJ IC acts as a pull-pump, ejecting waste solution and pulling new solution across a set of gold electrodes on the package surface; flow rate is controlled directly by the TIJ firing rate. These electrodes can be used to measure impedance, such as for electrical cell counting, and we further characterize the ability to electrically estimate volumetric flow rate from transient signals and known geometry. To demonstrate, impedance measurements of 3, 4.5, and 6 μm polystyrene beads in solution were performed at droplet ejection rates ranging from 63-500 Hz, and an adjustable flow rate of 29.4 pl/s/Hz is shown, estimated using both electrical and optical tracking methods. Long-term, this approach can provide integrated pumping, adjustable flow rate control, and integrated flow rate measurement for multi-chip lab-on-CMOS systems.