Abstract
For ion sensitive field effect transistors (ISFETs) built using a standard CMOS process, it is possible for more than one device to share the same ion sensitive membrane (passivation layer). Using floating gate MOS concepts, a complementary pair of ISFETs (n and p devices) can share the same ion sensitive membrane forming an ISFET based chemical switch. It is shown here that, using FG-ISFET and Neuron MOS concepts, a second electrical input may be capacitively coupled to their floating gate.
Through properly sizing this coupling capacitor, it is possible to enhance pH sensitivity referred to its input more than a hundredfold. This forms an ISFET based νMOS chemical inverter with enhanced input referred sensitivity. This circuit was simulated, built, and tested. Its switching threshold voltage; referred to reference electrode, shifted by 31.26mV per pH. This was increased to 3.7V/pH when referred to the second electrical input. This is the highest ever reported chemical signal amplification for such a minimum component ISFET circuit.