An equivalent circuit model of ion-selective membrane|insulator|semiconductor interfaces used for chemical sensors

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 1995-06, Vol.389 (1), p.71-78
• Main Authors: Demoz, Alebachew, Verpoorte, Elisabeth M.J., Harrison, D. Jed
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Ion selective electrodes; Ion selectivity
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/0022-0728(95)03836-6

The ac impedance characteristics of an ion-selective membrane|insulator|semiconductor (MIS) structure designed for chemical sensing applications have been modelled quantitatively for a frequency range from about 5 Hz to 40 kHz. When plasticized poly(vinylchloride)-based K +-selective membranes, nominally 100 μm thick, are used with 45 nm of Si 3N 4 and 50 nm of SiO 2 on a Si electrode, the impedance characteristics are dominated by the membrane above 100 Hz. Capacitance—voltage curves show a complex potential dependence below this frequency. The bulk resistance of the membrane contributes significantly to the equivalent capacitance below 1 kHz. Experiment and theory show that sensors based on ac or impedance measurements of changes in the Si space charge will be subject to significant errors if the membrane resistance is also a function of the solution conditions.