ISFET's with ion-sensitive membranes fabricated by ion implantation

Ion sensitive FETs (ISFETs) for sodium ions (Na/sup +/) fabricated by ion-implantation are investigated. The sensing layers are produced by implanting Na/sup +/ ions into the surface of an oxidized Si/sub 3/N/sub 4/ layer through an Al buffer layer deposited beforehand, in order to reduce the damage to the gate insulator of the ISFET during ion implantation. The Na/sup +/ sensitivity, selectivity, repeatability, thermal characteristics, and long-term stability are evaluated. The ISFET responds to Na/sup +/ ions independent of pH within the range of pH 7-10, and the Na/sup +/ sensitivity is nearly Nernstian. The ISFETs repeatability and long-term stability (about 1300 h), suggests that the ion-implantation technique is a suitable method for fabricating a stable ion-sensing layer.<
>