  Break junctions provide tip-shaped contact electrodes that are fundamental
components of nano and molecular electronics. However, the fabrication of break
junctions remains notoriously time-consuming and difficult to parallelize. Here
we demonstrate true parallel fabrication of gold break junctions featuring
sub-3 nm gaps on the wafer-scale, by relying on a novel self-breaking mechanism
based on controlled crack formation in notched bridge structures. We achieve
fabrication densities as high as 7 million junctions per cm$^{2}$, with
fabrication yields of around 7% for obtaining crack-defined break junctions
with sub-3 nm gaps of fixed gap width that exhibit electron tunneling. We also
form molecular junctions using dithiol-terminated oligo(phenylene ethynylene)
(OPE3) to demonstrate the feasibility of our approach for electrical probing of
molecules down to liquid helium temperatures. Our technology opens a whole new
range of experimental opportunities for nano and molecular electronics
applications, by enabling very large-scale fabrication of solid-state break
junctions.
