  In this work, we design and implement a strong physical uncloneable function
from an array of individual resonant tunnelling diodes that were previously
described to have a unique response when challenged. The system demonstrates
the exponential scalability of its responses when compared to the number of
devices present in the system, with an expected large set of responses while
retaining a 1:1 relationship with challenges. Using a relatively small set of
16 devices, 256 responses are shown to have promising levels of distinctness
and repeatability through multiple measurements.
