Boosting Stochasticity in Ovonic Threshold Switches Through Cryogenic First Firing for Fast and Reliable Entropy Generation

Abstract

As encryption demands at the edges grow, volatile switching devices have emerged as promising candidates for entropy sources because of their inherent stochastic properties, offering fast, energy-efficient operation and a minimal footprint. Although most studies have focused on exploiting inherent stochasticity, efforts to analyze and optimize these devices to enhance their randomness remain scarce. In this study, the stochastic switching characteristics of Ovonic Threshold Switch (OTS) devices by controlling the first firing temperatures to amplify their inherent stochasticity are explored. It is demonstrated that firing at cryogenic temperatures (77 K) induces field-dominant firing and a considerable increase in traps within the device. These additional traps lead to a substantial enhancement in switching variability, with the switching time fluctuation increasing up to four times compared to the first firing temperature of 298 K. Furthermore, a reference-free entropy-harvesting method is proposed that ensures robust and stable operation even under cycling degradation. Based on this approach, the OTS devices that undergo first firing at cryogenic temperatures achieve stable entropy generation at speeds exceeding 20 Mbit s−1. This study demonstrates the potential of optimizing OTS devices to satisfy the increasing demand for fast and energy-efficient entropy sources in advanced cryptographic systems.