New Aging Compensation Scheme for Ring Oscillator-Based PUFs

Physical Unclonable Functions (PUFs) are widely adopted for users’ authentication. They exploit process parameter variations occurring during chip fabrication to guarantee that only legitimate users are granted access to a considered resource. However, as proven [1], when implemented by scaled down technologies, they become vulnerable to aging, particularly Bias Temperature Instability (BTI), that may impact their correct operation in the field, due to the increasing conduction threshold of their transistors. Considering the case of PUFs implemented by Ring Oscillators (ROs), we here propose a new scheme to compensate the BTI-induced degradation affecting RO-based PUFs. Hereinafter, we refer to the proposed scheme as Compensator for Aging in RO-based PUFs (CARO-PUF). Concurrently with the PUF operation in the field, the proposed scheme generates a voltage signal proportional to transistors’ threshold voltage, by exploiting a circuit similar to that in [2]. This signal is then used to control voltage-controlled current generators, that inject an auxiliary current into the ROs to compensate for the BTI-induced variation of transistors’ threshold voltage. This way, the proposed approach enables to mitigate the aging effect on the ROs and to ensure the PUF correct operation over time. We will show that, if adopted for a standard RO-based PUF, our CARO-PUF scheme enables a reduction up to 90% in the oscillation frequency degradation caused by BTI. We show that, compared to a recent aging-robust RO-based PUF, the proposed CARO-PUF achieves a significantly higher reduction in frequency degradation over time, while requiring a lower area overhead and power consumption. Moreover, our proposed approach can be also applied to existing aging-robust RO-based PUFs (e.g., those in [1], [3], [4]), to further enhance their resilience against BTI-induced degradation.