Effect of two types of surface sites on the characteristics of Si/sub 3/N/sub 4/-gate pH-ISFET's

Based on the site-binding model, the effects of two types of surface-sites (namely, silanol site and amine site) and their ratio on the characteristics of Si/sub 3/N/sub 4/-gate pH-ISFET are discussed. As the ratio /spl beta/ of silanol sites to amine sites is about 7/3, the maximum of the sensitivity of electrolyte-insulator (E-I) interfacial potential versus pH value, as well as of the range of linear response are theoretically obtained. The stability of pH-ISFET devices is partially determined by the total number of the two types of surface-sites and their ratio. The theoretical results are supported by experimental results.