Sensitivity, Noise and Resolution in a BEOL-Modified Foundry-Made ISFET with Miniaturized Reference Electrode for Wearable Point-of-Care Applications

Abstract

Ion-sensitive field-effect transistors (ISFETs) form a high sensitivity and scalable class of sensors, compatible with advanced complementary metal-oxide semiconductor (CMOS) processes. Despite many previous demonstrations about their merits as low-power integrated sensors, very little is known about their noise characterization when being operated in a liquid gate configuration. The noise characteristics in various regimes of their operation are important to select the most suitable conditions for signal-to-noise ratio (SNR) and power consumption. This work reports systematic DC, transient, and noise characterizations and models of a back-end of line (BEOL)-modified foundry-made ISFET used as pH sensor. The aim is to determine the sensor sensitivity and resolution to pH changes and to calibrate numerical and lumped element models, capable of supporting the interpretation of the experimental findings. The experimental sensitivity is approximately 40 mV/pH with a normalized resolution of 5 mpH per µm2, in agreement with the literature state of the art. Differences in the drain current noise spectra between the ISFET and MOSFET configurations of the same device at low currents (weak inversion) suggest that the chemical noise produced by the random binding/unbinding of the H+ ions on the sensor surface is likely the dominant noise contribution in this regime. In contrast, at high currents (strong inversion), the two configurations provide similar drain noise levels suggesting that the noise originates in the underlying FET rather than in the sensing region.

Multiscale simulation analysis of passive and active micro/nanoelectrodes for CMOS-based in vitro neural sensing devices

“…en=7.5 nV Hz−false(1/2false), in=2 fA Hz−false(1/2false)) . The model neglects chemical [74] and biological noise, and the 1/f noise of the (MOS)FET, which are present in the real system where semiconductor devices are in contact with electrolytes [75]. Therefore, the computed SNR is a best-case estimate, nevertheless still useful to compare the sensor/readout combinations.…”

Integration of Ultra-Low Volume Pneumatic Microfluidics with a Three-Dimensional Electrode Network for On-Chip Biochemical Sensing

“…Miniaturized reference electrodes (mRE) have been increasingly used to develop integrated electrochemical biosensors for various applications including POC scenarios. General approaches to fabrication of mRE involve post-processing of the chip [ 23 ] or PCBs [ 24 ] to co-integrate them with the sensing sites. These approaches are generally ad-hoc and lack scalability.…”

Stochastic Time Response and Ultimate Noise Performance of Adsorption-Based Microfluidic Biosensors

“…The random nature of the AD process coupled with MT cause number of adsorbed particles, which result in sensor signal stochastic as AD noise, binding/unbinding noise, biological or chemical noise [1 tuations in the sensor signal also depend on other kinds of noise origi sor transduction mechanism and the read-out circuitry, but the unavo termines the sensor's ultimate noise performance and poses fundam quantification limits inherent to all adsorption-based sensors. The noise to the total sensor noise can even be dominant [16,17,20,21]. T AD noise and related parameters of stochastic sensor response becom for the optimization of adsorption-based chemical and biological mi terms of reliable analyte detection and quantification, and also in term ing performance (i.e., higher signal-to-noise ratio and lower minimal d Figure 1.…”

“…The random nature of the AD process coupled with MT causes fluctuations in the number of adsorbed particles, which result in sensor signal stochastic fluctuations known as AD noise, binding/unbinding noise, biological or chemical noise [15][16][17][18][19]. The total fluctuations in the sensor signal also depend on other kinds of noise originating from the sensor transduction mechanism and the read-out circuitry, but the unavoidable AD noise determines the sensor's ultimate noise performance and poses fundamental detection and quantification limits inherent to all adsorption-based sensors.…”