High gain νMOS ISFET front end

The maximum theoretical sensitivity of ion sensitive field effect transistors (ISFETs) is known to be 59.2 mV/pH at 25°C. Devices built using standard CMOS processes generally have less sensitivity. Using floating gate νMOS concepts it is possible, without using additional circuitry or processing steps; to increase it when reflected to the input. That is by using a second electrical input that is capacitively coupled to ISFETs floating gate via a small capacitance. The ratio between the chemical sensitive passivation capacitance and this small capacitance becomes the amplification ratio of pH sensitivity referred to this input. A sensitivity of 459.17 mV/pH referred to the second input was measured. The same device had a sensitivity of 46.17 mV/pH referred to the reference voltage.