Interface roughness in Resonant Tunnelling Diodes for physically unclonable functions

Resonant Tunnelling Diodes with Interface Roughness (IR) were investigated for their potential as components of Physically Uncloneable Functions (PUFs). A comparison of an RTD with IR against a ‘smooth’ device without IR, showed a reduction in current and Peak to Valley Current Ratio (PVCR) between the resonant peak and valley currents I r / I v . Furthermore, IR resulted in a perturbation of the Negative Differential Region (NDR) of the IV characteristic to higher bias. This perturbation was due to IR effectively thickening barriers and thereby narrowing the Quantum Well (QW) and leading to a higher ground state QW energy. Variation of correlation length L C and roughness asperity Δ R M S for batches of 25 randomly generated RTDs with IR showed that increasing Δ R M S decreased mean PVCR and increased the standard deviation of the resonant peak voltage V r and current I r . 150 RTDs with an L C of 7.5 nm and Δ R M S of 0.3 nm resulted in a min-entropy of 1.275 bits, showing that 100 RTDs could idealistically compose a PUF encoding 127 bits. • A Resonant Tunnelling Diode (RTD) with Interface Roughness (IR) has a lower current and Peak to Valley Current Ratio (PVCR) compared to a smooth device without IR. • An RTD with IR also has an NDR perturbed to higher bias because of IR effectively narrowing the QW, and thus spacing out QW eigenvalues, leading to more bias needed to reach the resonant peak of an RTD. • The effects of varying correlation length and root mean square asperity of IR was studied for batches of 25 randomly generated RTDs with IR, showing that increasing asperity had the main effect. Increasing asperity decreased PVCR and increased standard deviation of current and voltage. • A 150 RTDs for correlation length of 7.5 nm and an asperity of 0.3 nm were generated, and their resonant peak current–voltage values were plotted on a scatterplot. By splitting the scatterplot into quadrants, it is possible to encode information in which quadrant the resonant peak appears. The min-entropy for such was 1.275 bits, so idealistically it is possible to compose a Physically Uncloneable Function composed of 100 RTDs that encodes 127 bits.