Batch-Fabricated α-Si Assisted Nanogap Tunneling Junctions

This paper details the design, fabrication, and characterization of highly uniform batch-fabricated sidewall etched vertical nanogap tunneling junctions for bio-sensing applications. The device consists of two vertically stacked gold electrodes separated by a partially etched sacrificial spacer layer of sputtered α-Si and Atomic Layer Deposited (ALD) SiO₂. A ~10 nm wide air-gap is formed along the sidewall by a controlled dry etch of the spacer. The thickness of the spacer layer can be tuned by adjusting the number of ALD cycles. The rigorous statistical characterization of the ultra-thin spacer films has also been performed. We fabricated nanogap electrodes under two design layouts with different overlap areas and spacer gaps, from ~4.0 nm to ~9.0 nm. Optical measurements reported an average non-uniformity of 0.46 nm (~8%) and 0.56 nm (~30%) in SiO₂ and α-Si film thickness respectively. Direct tunneling and Fowler-Nordheim tunneling measurements were done and the barrier potential of the spacer stack was determined to be ~3.5 eV. I-V measurements showed a maximum resistance of 46 × 10³ GΩ and the average dielectric breakdown field of the spacer stack was experimentally determined to be ~11 MV/cm.