Impedance Sensing in CMOS-Embedded Microfluidics Using BEOL Electrodes

• Published in: Journal of microelectromechanical systems Vol. 33; no. 1; pp. 110 - 117
• Main Authors: Weng, Wei-Yang, Chien, Jun-Chau
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: BEOL; CMOS; Diffusion rate; Electrodes; Etchants; Etching; Hydraulic pressure; Hydraulic systems; Impedance; impedance spectroscopy; Microfluidics; Process parameters; Sensors; Surface treatment; top-down; vias; Wet etching
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2023.3326973

This paper describes a novel CMOS-embedded microfluidics platform featuring on-chip impedance-sensing electrodes. The platform employs a single-step wet etching process, removing the CMOS back-end-of-line (BEOL) routing metals, to create hollow fluidic channels that can be closely integrated with active circuits. We optimize the process parameters and improve the etch rate by 10Í through screening different metal etchants and applying hydraulic pressure to enhance the etchant byproduct diffusion rates. To integrate on-chip electrodes for impedance sensing, we explore various strategies and present "via" electrodes that maintain their integrity in the etching process while preserving detection sensitivity. We also investigate the long-term reliability of the platform. Finally, we demonstrate the efficacy of impedance sensing using ionic solutions of varying strengths. [2023-0119]