A Physically Unclonable Function with 0% BER Using Soft Oxide Breakdown in 40nm CMOS

A physically unclonable function (PUF) utilizing the randomness of soft oxide breakdown (BD) locations in MOSFETs is presented. The so-called soft-BD PUF features a self-limiting mechanism to generate one single soft-BD spot in a pair of MOSFETs; the subsequent BD location is used as the source of entropy to generate a highly stable "0" or "1" bit with an equal probability of 0.5. The soft-BD PUF comprising all the essential periphery circuits are fabricated in a 40nm CMOS process. Experiments show that the PUF has no instability in most of the operating conditions using the proposed readout scheme. The native bit error rate remains zero from V_DD=0.8 V to 1.5 V at room temperature and from -20°C to 120°C at nominal V_DD=0.9 V. The throughput is shown to be at least 40 Mb/s and the PUF readout consumes only 51.8 fJ/bit. The randomness and uniqueness of the PUF are close to an ideal case, and no spatial correlation was observed.