Silicon non-uniformly doped nanotransistor biosensors

Abstract

To implement effective biomedical diagnostics, it is important to evaluate the potential of non-uniformly doped silicon cylindrical field nanotransistors, which are comparable in size to biological nanoobjects. With such special engineering of the working region of the transistor, when high-doped zone is bordered by the source, and low-doped zone with drain, can significantly increase the sensitivity of the sensor, due to the fact that the gating mechanism of molecules associated on its surface, becomes more efficient due to the complete screening of carriers in the workspace. This improves the transistor's conductivity, which provides an acceptable electrical response. Research the detecting properties of longitudinally non-uniformly doped silicon transistor biosensors with cylindrical geometry, which function in the depletion mode, using computer modeling based on the developed mathematical model of the electric current of the transistor in the subthreshold mode, taking into account the requirements for conducting field experiments. Quasianalyticity model subthreshold current for silicon field-effect transistor with non-uniformly doping of the working area where high-doping zone bordered by the source and low-doping with drain, on the basis of analytical solution of 2D Poisson equation was designed. Several prototypes with different concentration conditions of doping between zones, ranging from three orders of magnitude to five times higher, were studied using the example of measuring the pH of solutions using computer modeling. In this case, the operating mode of biosensors was regulated by strobing the electrolyte. In all cases, the gating mechanism of molecules bound on the surface of sensors will be more effective due to the complete shielding of carriers in the working area. With a certain form of impurity concentration in the work area, it can potentially increase the sensitivity by a factor of ten and provide an acceptable level of response. Also, an important advantage of the non-uniformly doped sensors is their very low charge detection limit. It can be concluded that reducing the steepness of the sub-threshold characteristic is one of the main goals in the development of biosensors based on silicon field-effect transistors. And an effective approach is a special engineering of the working area of the transistor structure of the sensor, associated with its non-uniformly doping. The developed model and the results show that further optimization of the structure of silicon cylindrical field nanotransistor sensors can provide a significant improvement in their sensitivity, as well as obtain a reliable assessment of its limits, and serve as a factor for the development of equipment for biomedical diagnostics.