Sub-3nm Quantum Tunneling Nanogap Electrodes for Reliable Molecular Devices

We report on advanced sub-3nm nanogap electrodes with quantum tunneling characteristics, designed for use in molecular devices. Compared to current technologies, our quantum tunneling nanogap electrodes exhibit high controllability, satisfactory yield, stability, and reliability in single-molecule detection. Starting with a suspended SiN film on a wet-etched Si substrate, focused ion beam (FIB) milling triggers the release of internal tensile stress stored within the SiN film, inducing self-breaking behavior. We discuss various milling parameters that enable precise control over SiN nanogap sizes, ranging from 5 nm to 35 nm. The local metallization of the SiN gap using Pt ultimately defines the sub-3nm quantum tunneling nanogap electrodes.Electrical characterizations were recorded using the two-probe method, and quantum tunneling behavior was confirmed through Simmons model fitting, with the nanogap electrodes measured to have an average size of 1.51 ± 0.25 nm. The scalability of our methods was demonstrated by fabricating arrays of quantum tunneling nanogap electrodes.The reliability of the quantum tunneling nanogap electrodes as molecular devices was validated in multiple environments. Firstly, we confirmed the formation of single-molecule junctions using conjugated p-terphenyl-4,4’’-dithiol (TPDT) molecules in both air and vacuum, even at cryogenic temperatures (100K-250K), revealing a conductance of the Pt-TPDT-Pt molecular junction at 2.8 × 10^-3 <i>G₀</i>. Additionally, we demonstrated the statistical identification of single DNA nucleotides in solution based on their electrical conductivity, which followed the trend dGMP &gt; dAMP &gt; dCMP &gt; dTMP. The readout of short 5-mer DNA oligomers was also confirmed, with the conductance signals of the bases corresponding well to the measured conductance of individual nucleotides.We believe that our technology overcomes the challenges associated with fabricating sub-3nm quantum tunneling devices, opening new prospects for molecular electronics applications.