N.V. Masalsky1

1 Federal State Autonomous Institution Federal Scientific Center Scientific Research Institute of System Research of the National Research Center “Kurchatov Institute” (Moscow, Russia)
1 volkov@niisi.ras.ru

A method of highly sensitive pH sensing with sensitivity above the Nernst limit in a wide pH range is discussed. The prototype sensor is based on a silicon combined ion-sensitive field-effect transistor with a cylindrical geometry and an elliptical channel section of the transistor. In fact, in the well-known design of the pH sensor on complementary ion-sensitive transistors, this pair was replaced by one combined ion-sensitive transistor. At the same time, the main function – the formation of the "pH-voltage" converter, which provides efficient signal processing with good noise immunity and the best compactness for widespread adoption, is fully preserved. The choice of design is due to the aggressive scaling of sensor elements and low power consumption. A model of a combined ion-sensitive field-effect transistor has been developed in the environment of the TCAD Sentaurus instrument technology modeling system using the Sentaurus Devicee.2010.12. The numerical optimization strategy is to determine the geometry ranges of the sensitive region of the transistor, where its output voltage sensitivity is constant with the largest number of samples, meaning that one sample is equivalent to one pH level. For further research, a prototype was taken with the dimensions of the sensitive area: length 2248 nm, the major axis of the ellipse 72.4 nm, the smaller axis 18.5 nm, the thickness of the sensitive membrane 8 nm, which has the same highest sensitivity of 86.4/pH in the range of 9 samples from 3 to 12 pH at a supply voltage of 1.0 V and a voltage variation on the reference electrode from 0 to 1.0 V.

Internal noise can reduce the resolution of the device. In this case, the noise produced by the field-effect transistor is dominated by flicker noise. A flicker noise model of a silicon combined ion-sensitive transistor has been developed. As a result of the simulation, it is shown that taking into account this mechanism increases the lower detection threshold by about two times relative to the ideal case. The influence of the geometry of the sensitive area on the noise level is investigated. As a result, a 1% change in the length of the sensitive area leads to a proportional change in the noise level by 0.25%, and a 1% change in the thickness of the sensitive membrane leads to a proportional change in the noise level by about 1%.

Masalsky N.V. A method of highly sensitive pH sensing based on a silicon combined ion-sensitive nanotransistor // Biomedicine Radioengineering. 2026. V. 29. № 4. P. 99–110. DOI: https:// doi.org/10.18127/ j15604136-202604-09

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