Abstract
A complex deposition procedure of the hydrogel layer of modified poly(2-hydroxyethyl methacrylate) (polyHEMA) covalently linked to the silicon nitride surface and covering only the gate area of the ISFET, was optimized for photolithographic technology, using standard silicon wafers of 3” diameter. The influence of hydrogel composition and layer thickness on the sensors’ parameters was investigated. It was shown, that ISFETs covered with more than 100 μm thick polyHEMA layers in restricted pH-range could be practically insensitive to pH. Regarding mechanical stability of ion-selective sensors, a polyHEMA layer of ca. 20 μm thickness was found to be the best suitable for further manufacturing of durable ion selective sensors (Chemically modified Field-Effect Transistors – ChemFETs). The weak buffering properties of the thin polyHEMA layers had no disadvantageous influence on the sensors’ function.
Highlights
Progress in microelectronics and semiconductor technology enabled new capabilities in the field of sensor construction, of pH sensors based on field-effect transistors (FETs) as transducers of chemical signal
It turned out that the hydroxyethyl methacrylate (HEMA) mixture with PVP K-90 as a filler and 0.1 M KCl solution is excellent suitable for deposition of coatings by means of spin-off technique on the silanized silicon nitride substrates because it wets the wafer surface very good and it is possible to deposit a layer of demanded thickness by adjusting the spin rate and time
For ISFETs with polyHEMA coatings obtained by means of the above-described methods, pH-response characteristics were performed in order to verify the buffering properties of the polyHEMA
Summary
Progress in microelectronics and semiconductor technology enabled new capabilities in the field of sensor construction, of pH sensors based on field-effect transistors (FETs) as transducers of chemical signal. One. Sensors 2003, 3 of research lines has based on physical deposition of an ion-selective polymeric membrane onto the ISFET gate insulator. Influence of carbon dioxide as acidic agent on measurements is observed, which penetrates through the membrane to the gate surface and changes the potential of transistor transducer The problem of this ill-defined membrane-gate insulator interface has been solved by introducing poly(2-hydroxyethyl methacrylate) (polyHEMA) as a hydrogel material between the gate insulator and the sensing membrane. Chemical binding of the methacrylate layer with the support is achieved by photochemical polymerization of 2-hydroxyethyl methacrylate Further advantage of this material is the possibility of chemical binding of the ion-selective membrane to its surface. Inert gas for photopolymerization at UV-light: − nitrogen, technically pure (99,9%) - Praxair, Warsaw
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