Highly Sensitive pH Sensing based on a Complementary pair of Silicon Field-Effect Ion-Sensitive Transistors

A method for increasing the sensitivity of the pH sensor above the Nernst limit based on a complementary pair of silicon field-effect band ion-sensitive transistors is discussed. Based on experimental studies using 3D TCAD modeling, the design of the sensitive element of the pH sensor has been optimized. It was found that complementary structures with a length of 1400...1500 nm, a width of 175...186 nm and a thickness of 36...42 nm, with a reduced level of doping, provide an opportunity to improve sensitivity to pH above the Nernst limit. The prototype of the pH sensor developed using simulation revealed sensitivity above the Nernst limit by 33 % in a wide pH range from 3 to 12 at low control voltages. In the dynamic mode of determining the pH level, when triangular pulses are applied to the input, the duration of the output pulses decreases linearly with increasing pH. The characteristics of the studied structure are almost linear in a wide range of pH values. The output voltage may be immune to the individual sensitivity of single transistors, the leakage current and power consumption are quite low. The considered methodology opens up an effective approach to scaling the pH sensor, providing high resolution with minimal power consumption. At the same time, high sensitivity and linear conversion of the output current to the output voltage can be achieved. This opens the way for the effective integration of complementary sensors into an analytical laboratory on a chip.