Estimation of the Depletion Layer Thickness in Silicon Nanowire-Based Biosensors from Attomolar-Level Biomolecular Detection

Abstract

Silicon nanowire (SiNW) biosensors have attracted a lot of attention due to their superior sensitivity. Recently, the dependence of biomolecule detection sensitivity on the nanowire (NW) width, number, and doping density has been partially investigated. However, the primary reason for achieving ultrahigh sensitivity has not been elucidated thus far. In this study, we designed and fabricated SiNW biosensors with different widths (10.8–155 nm) by integrating a complementary metal-oxide-semiconductor process and electron beam lithography. We aimed to investigate the detection limit of SiNW biosensors and reveal the critical effect of the 10-nm-scaled SiNW width on the detection sensitivity. The sensing performance was evaluated by detecting antiovalbumin immunoglobulin G (IgG) with various concentrations (from 6 aM to 600 nM). The initial thickness of the depletion region of the SiNW and the changes in the depletion region due to biomolecule binding were calculated. The basis of this calculation are the resistance change ratios as functions of IgG concentrations using SiNWs with different widths. The calculation results reveal that the proportion of the depletion region over the entire SiNW channel is the essential reason for high-sensitivity detection. Therefore, this study is crucial for an indepth understanding on how to maximize the sensitivity of SiNW biosensors.

The possibility of ultrasensitive detection of biomolecules using silicon nanowire biosensor with structural optimization

“…This observed trend in current changes aligns with the experimental results. 19,20,28,29) For calculating the resistance change ratio, the resistance of the SiNW biosensor at a ρ s of 0 C m −2 was designated as R 0 , while the resistances at other ρ s were denoted as R. The resistance change ratio was calculated by R R R 100%. 9…”

“…The SiNW biosensors, exhibiting diverse widths ranging from 10.8 to 155 nm, were meticulously fabricated through a CMOS-compatible topdown fabrication process, as detailed in our prior work. 19,20) The n-type SiNWs connected with Ti electrodes were formed on a 145 nm thick buried oxide layer (SiO 2 ). The dimensions of the SiNWs were precisely controlled, with a length of 14 μm and a thickness of 22 nm.…”

“…In our previous works, we investigated the influence of SiNW widths on the sensitivity of biosensors and revealed that narrower SiNWs increase the proportion of the depletion region in the entire SiNW channel, leading to highly sensitive detection. [18][19][20] In addition to experimental validation, theoretical studies are crucial for predicting sensing performance through the combination of multiple parameters, but they have been relatively scarce in the research of SiNW biosensors. Therefore, in this study, we developed a three-dimensional numerical model of SiNW biosensor using the finite-element method in COMSOL Multiphysics.…”