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 alpha-Si and Atomic Layer Deposited (ALD) SiO2. A similar to 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 similar to 4.0 nm to similar to 9.0 nm. Optical measurements reported an average non-uniformity of 0.46 nm (similar to 8%) and 0.56 nm (similar to 30%) in SiO2 and alpha-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 similar to 3.5 eV. I-V measurements showed a maximum resistance of 46 x 10(3) G Omega and the average dielectric breakdown field of the spacer stack was experimentally determined to be similar to 11 MV/cm.