A Physical Unclonable Function With Bit Error Rate < 2.3 $\times$ 10-8 Based on Contact Formation Probability Without Error Correction Code

This article proposes a physical unclonable function (PUF) based on the contact formation probability. The contact here is the interconnect layer between the metal and the silicon in a chip. As the contact is designed smaller than the size given in the design rule, the contact formation becomes stochastic in a certain range of contact hole sizes and can be a random source for the PUF. Consequently, once the contact state is determined to be either open or short, its connectivity does not change over time under noisy environmental conditions, such as temperature, supply voltage, humidity variations, and so on. The reliability of the proposed contact PUF is verified through seven reliability tests defined by the Joint Electron Device Engineering Council (JEDEC) standards. No bit errors occur in any of the 366 chips tested. The bitcell is designed using a digital standard cell structure and scattered throughout the chip embedded in other logic gates. This makes it difficult to find the bitcell position. The proposed contact PUF is fabricated using 0.13- $\mu \text{m}$ CMOS technology. It achieves 49.99% uniqueness and 0.99973 entropy and passes all applicable randomness tests given by the National Institute of Standards and Technology (NIST) SP 800-22.