Selective Enhancement of Randomness at the Materials Level: Poly-Si Based Physical Unclonable Functions (PUFs)

Physically Unclonable Functions (PUFs) were introduced over a decade ago for a variety of security applications. Silicon PUFs exploit uncontrollable random variations from manufacturing to generate unique and random signatures/responses. Existing research on PUFs has focused on either PUF design at the architectural level or optimization of lithography to increase sensitivity to random process variations. However, such sources of randomness may become limited during standard CMOS manufacturing as processes continue to mature especially with the advances in design for manufacturability. In this paper, poly-Si is proposed to improve PUF quality at the materials level. Compared to conventional single crystal Si (sc-Si), defects and trapped charges resulting from the random distribution of crystal grains and grain boundaries (GBs) in poly-Si offer considerable random variations. By using poly-Si only in the PUF region in devices, the randomness of the PUF can be enhanced without impacting other functional circuits and thus the IC yield can be maintained. RO-PUF simulation results based on a poly-Si field effect transistor (FET) model show that compared to sc-Si based PUFs, the reliability of poly-Si based PUFS can be improved from 89.18% to 98.82%.