An ISFET-based calcium sensor using a photopolymerized polysiloxane membrane

A. van den Berg*, A. Grisel, E. Verney-Norberg

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

35 Citations (Scopus)
133 Downloads (Pure)


In this paper an on-wafer fabrication technique for membrane-covered calcium-sensing ISFETs is presented. The complete structure consists of a standard Al2O3 pH-ISFET, covered with a hydrogel membrane and a second polysiloxane-type calcium-sensing membrane. Both membranes are deposited and photolithographically structured on the wafer. The adhesion of the membranes to the ISFET surface is ensured by presilylating the surface prior to the deposition of the membranes, and has been confirmed by tests in an ultrasonic bath. The on-wafer fabrication of calcium-sensitive ISFETs with a 25 μm thick poly (hydroxyethyl methacrylate) (polyHEMA) membrane covered with a 80 μm thick polysiloxane membrane is described and illustrated. The structural membrane definition for both membranes is better than 20 μm. The calcium-sensing properties of three completed devices have been investigated. A reproducible sensitivity of 28.7 mV/pCa and a detection limit of 10-6.4 M calcium are found upon titration of CaCl2 in demineralized water. The selectivity coefficients with respect to magnesium, sodium, and potassium are found to be log KCaMg Pot = -4.9, log KCaNa Pot = -4.5, and log KCak Pot = -4.1 respectively, which are comparable with the literature values.

Original languageEnglish
Pages (from-to)235-238
Number of pages4
JournalSensors and Actuators: B. Chemical
Issue number3-4
Publication statusPublished - 1 Jan 1991
Externally publishedYes


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