An effective method of pH-metry based on a complementary scheme of ion-sensitive nanotransistors

A method for increasing the pH sensitivity of a sensor above the Nernst limit based on a complementary pair of silicon ribbon field ion-sensitive nanotransistors is discussed. In this work, three stages are combined - TCAD modeling, crystal fabrication and testing. Thus, we excluded the search for optimal technological parameters of silicon ribbon posts and additional research to optimize the manufacturing process. We also reduced the setup time of the software and measurement complex and obtained an assessment of the systematic measurement error. The volt-ampere characteristics of complementary transistors are optimized using 3D modeling performed using the TCAD Sentaurus instrument-technology modeling system using Sentaurus Devicee.2010.12. The numerical optimization strategy is to determine the size ranges of the ribbon sensitive region of an ion-sensitive transistor, where its current sensitivity is constant with the largest number of samples, implying that one sample is equivalent to one pH level. For further research, a prototype was taken with the dimensions of a sensitive area with a length of 1452 nm, a width of 184 nm and a height of ts = 38.5 nm, which has the maximum sensitivity of single transistors in the range of 14 samples. An experimental approbation has been carried out confirming the practical applicability of the method of pH-metry of liquid solutions based on a complementary scheme of ion-sensitive nanotransistors. The experimental sample developed using TCAD modeling revealed sensitivity above the Nernst limit by about 25% in the pH range from 3 to 12 with a sensitivity of 0.001 pH. 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 the studied pH range. 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.