Controlling the Reliability of SRAM PUFs With Directed NBTI Aging and Recovery

As the Internet of Things continues to spread, devices within it are given more personal information which must be protected. To provide this protection, a device known as a physical unclonable function (PUF) has been devised which takes advantage of natural variations in silicon to create a unique fingerprint which can be used for secret key generation and authentication. This fingerprint is often based upon settlement of a race condition in competing circuits which is decided by process variations and noise. In this paper, we focus on the SRAM PUF, whose fingerprint is determined by the tendency of each cell to contain a 0 or 1 after it powers on. These cells are susceptible to negative-bias temperature instability (NBTI) while storing data, which pushes their power-on tendencies away from the data they contain. We present a method by which the success rate of an SRAM to produce a correct fingerprint can be reduced to 0% in only one day using NBTI activated and accelerated by elevated voltage and temperature, followed by another method in which it can be restored to nearly 100% in less than two days using active, accelerated NBTI recovery with negative voltage and elevated temperature.