Electronic Department, Swiss Federal Institute of Technology Lausanne, 1015 Lausanne, Switzerland.
DPIA Department, University of Udine, 33100 Udine, Italy.
Sensors (Basel). 2021 Mar 4;21(5):1779. doi: 10.3390/s21051779.
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 µm, 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.
离子敏场效应晶体管（ISFET）形成了一类高灵敏度和可扩展的传感器，与先进的互补金属氧化物半导体（CMOS）工艺兼容。尽管之前已经有很多关于其作为低功耗集成传感器优点的演示，但在液体栅极配置下工作时，对其噪声特性的了解却很少。了解其在各种工作模式下的噪声特性对于选择最适合信噪比（SNR）和功耗的条件非常重要。本工作对后端工艺（BEOL）改进的工厂制造 ISFET 作为 pH 传感器的直流、瞬态和噪声特性及模型进行了系统的研究。目的是确定传感器对 pH 值变化的灵敏度和分辨率，并校准数值和集总元件模型，以支持对实验结果的解释。实验灵敏度约为 40 mV/pH，归一化分辨率为每 µm 5 mpH，与文献中的现有技术水平一致。同一器件的 ISFET 和 MOSFET 配置在低电流（弱反型）下漏极电流噪声谱之间的差异表明，传感器表面上 H 离子随机结合/解吸产生的化学噪声很可能是该区域的主要噪声源。相比之下，在高电流（强反型）下，两种配置提供了相似的漏极噪声水平，这表明噪声源于基础 FET 而不是传感区。
