N.V Masalsky1

1 Federal State Institution “Scientific Research Institute for System Analysis of the Russian Academy of Sciences” (Moscow, Russia)

For biomedical applications, there is currently a tendency to integrate extensive chemical sensing capabilities with electronic components on a chip for subsequent processing of experimental results. An approach to increasing the sensitivity of biosensors above the Nernst limit is considered. The approach is based on the use of complementary ion-sensitive transistors based on silicon nanowires with cylindrical geometry made using standard CMOS technology. In this case, the pH level of the solution will regulate the threshold voltage of the sensor device. As a result, the amplitude and pulse width of the output signal is modulated by the pH level of the solution. The use of complementary devices for the formation of a pH converter in time provides the best compactness for widespread implementation, since the built-in ADC and other analog units can be excluded. Theoretical foundations and a 3D TCAD model of a complementary sensor have been developed. Its numerical characteristics are numerically optimized using 3D modeling performed by the TCAD computer-aided design software package, depending on the topological parameters of the transistors and the level of control voltages. As a result, a sensor with optimized parameters was developed: the length and radius of the sensitive zone of 1860 nm and 22.6 nm, respectively, and the doping concentration of 1x1015 cm−3. Its sensitivity is above the Nernst limit by about 30% at a supply voltage of 1.2 V. At the same time, the sensitivity is almost constant in a wide pH range – from 3 to 11. The average offset value is 74.8 mV/pH. It is almost the same in the entire pH range. The total offset is 598.4 mV from 684 to 1282.4 mV. The output voltage is immune to the individual sensitivity of single transistor, the leakage current and power consumption are quite low. The modulation of the output pulse duration ranges from 74.5 microseconds for pH =3 to 58 microseconds for pH = 11. The change in the pulse response duration is 2 microseconds per pH. In this approach, both high sensitivity and linear conversion of the output current to the output voltage is achieved simultaneously. And also this approach is characterized by a good noise suppression ability. This opens the way for the effective integration of complementary biosensors with signal processors based on industrial CMOS technology due to the high output voltage and low supply voltage.

Masalsky N.V. Sensory properties of a complementary pair of silicon field-effect nanotransistors with cylindrical geometry. Biomedicine Radioengineering. 2022. V. 25. № 6. Р. 67-75. DOI: https://doi.org/10.18127/j15604136-202206-08 (In Russian)

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