As the CMOS-based ion-sensitive field-effect transistor (ISFET) is scaling down to achieve a compact sensing array with high spatial resolution, reduction of sensing layer capacitance attenuates capacitive coupling efficiency of environmental input signals and decreases sensitivity performance. To address this issue, a concept of three-dimensional (3D) sensing structure is proposed and examined in this study. This can increase the sensing layer capacitance for a given footprint area. Based on our designs, a series of 3D sensing structures can be implemented with a standard CMOS foundry service and CMOS-compatible post processes. Our experimental results show that an $8.5^{2}\mu \text{m}^{2}$ footprint design of the 3D sensing structure can obtain approximately 2-fold increase in transconductance compared with a traditional ISFET with the same footprint. This enables pH sensitivity to be improved 1.5-fold in current response and 1.15-fold in voltage response. Therefore, the proposed 3D-structure ISFET can pave the way toward an ISFET sensing array with high sensitivity and high spatial resolution.

中文翻译：

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具有三维扩展栅极架构的基于CMOS的ISFET的传感特性增强

随着基于CMOS的离子敏感场效应晶体管（ISFET）的规模缩小，以实现具有高空间分辨率的紧凑型感应阵列，感应层电容的减小会削弱环境输入信号的电容耦合效率，并降低灵敏度性能。为了解决这个问题，本研究提出并研究了三维（3D）感应结构的概念。对于给定的占位面积，这可以增加感测层的电容。根据我们的设计，可以通过标准的CMOS代工服务和与CMOS兼容的后期处理来实现一系列3D感测结构。我们的实验结果表明 $ 8.5 ^ {2} \ mu \ text {m} ^ {2} $ 与具有相同覆盖区的传统ISFET相比，3D感测结构的覆盖区设计可以使跨导增加大约2倍。这样可使pH灵敏度在电流响应中提高1.5倍，在电压响应中提高1.15倍。因此，所提出的3D结构的ISFET可以为具有高灵敏度和高空间分辨率的ISFET感测阵列铺平道路。