  Ferroelectric domain walls (DWs) are promising structures for assembling
future nano-electronic circuit elements on a larger scale, since reporting
domain wall currents of up to 1 mA per single DW. One key requirement hereto is
their reproducible manufacturing by gaining preparative control over domain
size and domain wall conductivity (DWC). To date, most works on DWC have
focused on exploring the fundamental electrical properties of individual DWs
within single shot experiments, with emphasis on quantifying the origins for
DWC. Very few reports exist when it comes to compare the DWC properties between
two separate DWs, and literally nothing exists where issues of reproducibility
in DWC devices have been addressed. To fill this gap while facing the challenge
of finding guidelines achieving predictable DWC performance, we report on a
procedure that allows us to reproducibly prepare single hexagonal domains of a
predefined diameter into uniaxial ferroelectric (FE) lithium niobate (LN)
single crystals of 200 and 300 micrometers thickness, respectively. We show
that the domain diameter can be controlled with an error of a few percent.
As-grown DWs are then subjected to a standard procedure of current-controlled
high-voltage DWC enhancement, repetitively reaching a DWC increase of 6 orders
of magnitude. While all resulting DWs show significantly enhanced DWC values,
subtle features in their individual current-voltage (I-V) characteristics hint
towards different 3D shapes into the bulk, with variations probably reflecting
local heterogeneities by defects, DW pinning, and surface-near DW inclination,
which seem to have a larger impact than expected.
