PHOTOPOLYMERIZATION OF ION-SELECTIVE MEMBRANES ONTO SILICON-NITRIDE SURFACES FOR ISFET FABRICATION

A silicon nitride surface has been chemically modified with an ion-sensitive membrane consisting of a styrene-vinylbenzo-[18]-crown-6 copolymer (monomer ratio 4:1). The ionophore is therefore covalently bound to the polystyrene backbone so as to prevent gradual loss to the analyte solution. Silylation of the Si3N4 surface with vinyltrimethoxysilane allows the polymer film itself to be attached to the substrate via chemical bonding by in situ copolymerisation with the surface vinyl groups. The method chosen is that of photoinitiated polymerisation through a mask to be used for ISFET fabrication at wafer stage. The response to potassium ions observed with a 0.1 μm thick membrane is 37 mV per pK+ unit between 10-3 and 10-1 mol dm-3. © 1990.