Herein this paper we propose a surface potential based analytical model for planar junctionless field effect transistor (JL-FET) for pH sensing. The electrolyte considered is phosphate buffer saline (PBS) solution which has been modeled as three layered stacked structure consisting of stern layer, ion-permeable membrane and bulk electrolyte. The proposed model has been deduced considering Poisson's equation in the channel region. Relative shift in threshold voltage ( $\rm V_{Th}$ ) and maximum drain current ( $\rm I_{DS,max}$ ) have been used as sensitivity metrics. The low concentrations of electrolyte (0.01), yielded higher $\rm V_{Th}$ sensitivity of $\text{63}\;mV/pH$ and $\text{59}\;mV/pH$ for bottom and liquid gate respectively as compared to higher molar concentrations of electrolyte. For 0.01 PBS the aggregate drain current shift has been found to be $52.8\ \mu A/pH$ and is larger for liquid gate operation while as for bottom gate, shift of $18.9\ \mu A/pH$ is observed. Further considering pH range of 1-14, we computed various figure of merits (FOMs) that include sensitivity, linearity and signal to noise ratio for the device. The FOMs were computed and analyzed for independent operation of liquid and bottom gate for three different molarities of PBS (1, 0.1, 0.01) each with pH range from 1 to 14. Signal to noise ratio of drain current is found maximum for low molar concentrations of electrolyte and also is highest at point of maximum transconductance. The results obtained from analytical model are in good coherence with the TCAD simulation model.

中文翻译：

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平面无结 pH 传感 BioFET 的表面电位分析建模和性能计算图

在本文中，我们提出了一种用于 pH 传感的平面无结场效应晶体管 (JL-FET) 的基于表面电位的分析模型。所考虑的电解质是磷酸盐缓冲盐水 (PBS) 溶液，该溶液已被建模为三层堆叠结构，由船尾层、离子渗透膜和本体电解质组成。考虑到通道区域中的泊松方程，推导出了所提出的模型。阈值电压的相对偏移 ( $\rm V_{Th}$ ) 和最大漏极电流 ( $\rm I_{DS,max}$ ) 已被用作敏感度指标。低浓度的电解质 (0.01)，产生更高的$\rm V_{Th}$ 敏感度 $\text{63}\;mV/pH$ 和 $\text{59}\;mV/pH$与更高摩尔浓度的电解质相比，分别用于底部和液体栅极。对于 0.01 PBS，已发现总漏电流偏移为$52.8\ \mu A/pH$ 并且对于液体浇口操作更大，而对于底浇口，偏移 $18.9\ \mu A/pH$被观察到。进一步考虑 1-14 的 pH 范围，我们计算了各种品质因数 (FOM)，包括设备的灵敏度、线性度和信噪比。对于三种不同摩尔浓度的 PBS (1, 0.1, 0.01) 的液体和底栅的独立操作计算和分析 FOM，每种 PBS 的 pH 范围为 1 到 14。发现低摩尔浓度的漏极电流的信噪比最大电解质，并且在最大跨导点处也是最高的。分析模型得到的结果与TCAD仿真模型具有良好的一致性。