Highly Performant Integrated pH-Sensor Using the Gate Protection Diode in the BEOL of Industrial FDSOI

This is the first demonstration of a CMOS pH-sensor using the gate protection diode of standard FDSOI transistors in the BEOL. The extremely steep switching of the drain current induced by an exploitation of the DIBL effect is used for fabrication of extremely sensitive pH-sensors. The back gate voltage at which the abrupt switching of drain current occurs depends on the potential at the gate protection diode. Integrating the pH sensing film on this diode BEOL metal, the shift depends on the pH value of the liquid which creates a proportional potential. The abrupt switching (as small as 9 mV/decade) of the drain current can give a theoretical maximum sensitivity of 6.6 decade of drain current change per unit pH. In this paper, we report an experimental sensitivity of 1.25 decade/pH which is superior to state-of-the-art CMOS pH sensors which have a maximum sensitivity of 0.9 decade/pH.