In this paper, we report an ion sensitive field effect transistor (IS-FET) sensor on anodic aluminum oxide (AAO) substrate, which can directly detect nitrate in water without a buffer solution. The free-standing AAO substrate has a highly ordered porous structure, which supports graphene and Au electrodes. The AAO substrate increases the exposed area of graphene in water. We describe the surface structure of the AAO substrate with scanning electron microscopy in each fabrication process. The device structure and mechanism are also explained in the paper. Graphene is used for the sensing material for its sensitivity in response to the surroundings. The nitrate selective membrane is synthesized and applied to the surface of graphene. The performance of the IS-FET sensors is characterized by a semiconductor analyzer. In the results, the performance of the device is significantly enhanced due to the porous structures of AAO. We successfully demonstrate the superior sensitivity and selectivity of the sensors. The detection limit is 0.05 ppm, and the response time is less than 3 seconds. [2020-0131]
Bibliographical noteFunding Information:
Manuscript received May 6, 2020; revised June 21, 2020; accepted July 4, 2020. Date of publication July 17, 2020; date of current version October 7, 2020. This work was supported by the Legislative-Citizen Commission on Minnesota Resources under Grant LCCMR-2016-051-B. Subject Editor R. Ghodssi. (Corresponding author: Tianhong Cui.) Jungyoon Kim and Tianhong Cui are with the Mechanical Engineering Department, University of Minnesota, Minneapolis, MN 55455 USA (e-mail: firstname.lastname@example.org; email@example.com).
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- selective membrane