Process for producing a surface gate of an integrated electro-chemical sensor, consisting of a field-effect transistor sensitive to alkaline-earth species and sensor obtained

A process for making a surface gate of an integrated electrochemical sensor comprising a field-effect transistor having two doped zones comprising a source and a drain and a median surface on which a surface gate is to be formed, wherein the process comprises the steps of:

• subjecting the median surface to a treatment of hydroxylation in order to obtain 10.sup.14 to 10.sup.15 OH sites per cm.sup.2,
• washing and drying the surface, and further comprising the steps of:
• grafting the median surface with a grafting product in order to produce grafts on some or all sites on the median surface,
• preparing phosphonate-based iono-sensitive molecules,
• making operative one or more of the grafts using the iono-sensitive molecules.