Oscillator-Based Electrochemical Capacitance Imager with Frequency-Division-Multiplexed Readout

Abstract

Electrochemical biosensors, built using complimentary-metal-oxide semiconductor (CMOS) technology, have shown promise for various applications in health-care diagnostics, disease detection, and life science research. Unlike traditional bench-top instrumentation, CMOS-based platforms offer large-scale integration of sensor pixel arrays and readout electronics on the same chip, yielding improved spatial resolution, throughput, and signal-to-noise ratio (SNR) compared to non-integrated systems.

In this thesis, we present the design and electronic characterization of a CMOS oscillator- based electrochemical capacitance imager for biosensing. The imager features both time- division multiplexed (TDM) and frequency-division-multiplexed (FDM) readout, and is suitable for overcoming Debye-length-screening effects in integrated electrochemical biosensors. The implementation of FDM readout enables improved frame rate or improved signal-to-noise ratio (SNR) when compared to an imager that employs standard TDM readout. Each pixel in the array contains a 5-MHz–180-MHz capacitance-to-frequency converter (CFC) to detect changes in the interfacial capacitance at an in-pixel working electrode, ranging in area from 2×2-µm 2 to 200×200-µm 2.

We report experimental results from electronic characterization of a 420-pixel, 3.0×2.5 mm 2 capacitance imager, fabricated in a 1.8-V, 0.18-µm mixed-signal CMOS process. To the best of our knowledge, our work is the first demonstration of a CFC-based CMOS capacitance imager for biosensing with both TDM and FDM readout.