Simulation and fabrication of silicon nanowire BioFETs

Abstract

In recent years, numerous researches on the silicon nanowire biologically sensitive field effect transistors (BioFETs) have been done since Charlse Lieber group at Harvard University disclosed the pioneering experiment results. It is well known that the silicon nanowire BioFETs is fast, label free, inexpensive and ultrahigh sensitive compared to other existing bio sensor technologies. Thanks to these advantages, we expect that one can use them to implement early diagnosis of cancers, AIDS (HIV), etc. with detecting specific bio-molecules such as antigen from the pure blood. In addition, the BioFETs can be applicable for the many areas where the highly sensitive and precise sensors are needed. In this thesis, we have developed an in-house simulation tool for silicon nanowire BioFETs solving the three-dimensional drift-diffusion equation and Poisson-Boltzmann equation, self-consistently, and also fabricated some samples and measured their characteristics. Because BioFETs have buffer solution with many ions, the simulation of them should take it into account: the BioFETs are simulated using the Poisson-Boltzmann equation instead of usual Poisson equation. After figuring out how to apply the Poisson-Boltzmann equation for buffer solution of different pH and concentration, we have built the simulator and analyzed the characteristics of BioFETs. Especially, we have confirmed experimentally and simulation-wise, the change of drain current or conductance with respect to the change of pH buffer solution. In the simulations of the BioFETs, the charge of bio-molecules such as protein, DNA etc. was determined by difference between their isoelectric point (pI) and pH of buffer solution. Various probe and target bio-molecules charges, due to different pH of buffer solution, result in the change of the sensitivity of Bio-FETs. With the aid of the simulation works, the sensitivity of BioFETs can be optimized with the pH of buffer solution, which is close to pI of probe b...