Dielectric moculated field effect transistor (DMFET) with vertical nanogap for biosensor applications

Abstract

In this work, we present a dielectric modulated field effect transistor (DMFET) and label-free electrical detection of protein-ligand binding by using DMFET. The device was fabricated by standard CMOS process, except for the Cr/Au gate deposition. Au was chosen as a gate electrode because of high affinity between Au layer and bio-molecules. The 15 nm of vertical nanogap was successfully fabricated by the wet-etching Cr layer which was deposited as an adhesion layer between Au gate and gate oxide. The nanogap was modified with biotin and streptavidin. After binding streptavidin to biotin on the gold surface, the drain and gate current was measured with various gate voltages. The large threshold voltage was observed when biotin-streptavidin binding was achieved. It is because the total gate capacitance is increased as the nanogap is filled with biotin and streptavidin. The gate current was also increased after biotin-streptavidin binding. It means that when the nanogap was densely filled with biotin and streptavidin after forming the binding, it provides the current path that electrons tunneled from the inversed channel can flow through the binding to the gate. To confirm that the dramatic current and threshold voltage changes are due to the biotin-streptavidin binding, the nanogap of the device was analyzed with 6 different groups. As a result, only biotin-streptavidin binding is absolutely the most effective factor for changing electrical characteristics of DMFET device and the device also shows high specificity for detecting biotin-streptavidin binding. Furthermore, the threshold voltage was returned to its initial state, before modification when the biotin-streptavidin binding was reversibly broken. We also verified the presence of SAM, biotin, and streptavidin by using AFM. The proposed device showed much better sensitivity than previously reported FET-type biosensors for detecting bio-molecules, especially protein-ligand binding. In addition, it is expec...