True Reference Nanosensor Realized with Silicon Nanowires

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• 作者：A. Tarasov ; M. Wipf ; K. Bedner ; J. Kurz ; W. Fu ; V. A. Guzenko ; O. Knopfmacher ; R. L. Stoop ; M. Calame ; C. Sch枚nenberger
• 刊名：Langmuir
• 出版年：2012
• 出版时间：June 26, 2012
• 年：2012
• 卷：28
• 期：25
• 页码：9899-9905
• 全文大小：318K
• 年卷期：v.28,no.25(June 26, 2012)
• ISSN：1520-5827

文摘

Conventional gate oxide layers (e.g., SiO₂, Al₂O₃, or HfO₂) in silicon field-effect transistors (FETs) provide highly active surfaces, which can be exploited for electronic pH sensing. Recently, great progress has been achieved in pH sensing using compact integrateable nanowire FETs. However, it has turned out to be much harder to realize a true reference electrode, which 鈥?while sensing the electrostatic potential 鈥?does not respond to the proton concentration. In this work, we demonstrate a highly effective reference sensor, a so-called reference FET, whose proton sensitivity is suppressed by as much as 2 orders of magnitude. To do so, the Al₂O₃ surface of a nanowire FET was passivated with a self-assembled monolayer of silanes with a long alkyl chain. We have found that a full passivation can be achieved only after an extended period of self-assembling lasting several days at 80 掳C. We use this slow process to measure the number of active proton binding sites as a function of time by a quantitative comparison of the measured nonlinear pH-sensitivities to a theoretical model (site-binding model). Furthermore, we have found that a partially passivated surface can sense small changes in the number of active binding sites reaching a detection limit of 未N_s 鈮?170 渭m^鈥?Hz^鈥?/2 at 10 Hz and pH 3.