Fabrication Process Of Silicon Nitride Solid-State Nanopores And Its Signal-to-Noise Ratio Research

Solid-state nanopores have achieved rapid development by virtue of their stable mechanical properties,adjustable pore size,ease of integrated design,and ability to adapt to variable buffer environments.The development of dielectric breakdown technique has been able to fabricate small-sized nanopores efficiently and stably,but its noise problem still needs to be further explored.This topic explores the rapid fabrication process of silicon nitride nanopores based on dielectric breakdown technique and investigates the signal-to-noise ratio problem of nanopores.The main studies are as follows:(1)Experimental platform for fabrication of solid-state nanopores by dielectric breakdown technique.The experimental platform for preparing solid-state nanopores was built based on the experimental principle of dielectric breakdown,including the deployment of the hardware platform and the development of the control program based on Lab VIEW software.Various material instrumentation,specific experimental procedures and characterization methods required for the experiments are summarized.(2)Rapid fabrication process and size control of silicon nitride nanopores.The effect on the nanopore fabrication process was explored by surface oxygen plasma treatment of silicon nitride films,and the current threshold parameters of the procedure were improved to finally enable rapid preparation of small-sized nanopores.Pulsed voltage was used to expand the pores to achieve size control of the nanopores and SEM characterization was performed after expansion,and the prepared silicon nitride nanopores were characterized by λ-DNA molecules.(3)Analysis and improvement of detection system and chip intrinsic noise.First,the main noise sources of silicon nitride nanopores in the signal detection process are analyzed in conjunction with the literature,including the noise sources of the external detection environment and the noise sources of the chip itself(including the noise of each part of low,medium and high frequencies).Then,for the noise sources of the silicon nitride chip itself in the high-frequency region,the film capacitance of the chip is reduced by increasing the thickness of the oxide layer,replacing the original silicon substrate material,or reducing the effective contact area between the chip and the solution,and in addition,the amplifier noise at the input can be reduced by means of low-pass filtering.(4)Detection noise analysis and improvement of silicon nitride nanopores.Different nanopore modification measures were used to improve the signal-to-noise ratio of the chip according to different nanopore fabrication methods.For the nanopores fabricated by dielectric breakdown,a slow nanopore expansion modification by applying a constant low voltage or immersing the chip in a specific concentration of Li Cl solution for a sustained period of time eventually improved the rectification effect of the nanopores and reduced the noise.For the nanopores fabricated by FIB,the wall surface was modified by using square wave type voltages with different frequencies of positive and negative cycles,and the appropriate parameters of modification voltage,frequency and time were determined,and in addition,the electrical model of silicon nitride nanopores was numerically fitted to analyze the effect mechanism of different frequency voltages.