Random pn-junctions for physical cryptography

In this paper, we report on high-rectification pn-diodes (rectification ratios up to 2×107) prepared by aluminum-induced crystallization on crystalline Si-wafers, which exhibit highly random I(V) characteristics. We argue that arrays of such diodes can be employed as physical uncloneable functions for cryptography. To resolve the structure of the active diode area, focused-ion beam imaging was used. The I(V) curves of the diodes reveal that both a smaller polycrystalline silicon film thickness and a smaller diode size lead to increasing randomness due to the increasing inhomogeneity of thinner films and due to more pronounced grain boundary effects for smaller diodes.