Abstract
Ion sensitive field effect transistors (ISFETs) have been used as analogue continuous time chemical sensor. A single ISFET, either an N or a P device, forms the sensitive part of the circuit that may condition the signal. Each ISFET had its own ion sensitive membrane as part of it. It is shown in this work that, for devices built using a standard CMOS process, it is possible for more than one ISFET to share the same ion sensitive passivation layer. Using floating gate devices concepts, a complementary pair of ISFETs (n and p devices) shared the same ion sensitive membrane forming a fully functioning chemical switch. Its switching threshold voltage shifted by 28.33 mV per pH change of the electrolyte under test.