8.7 Physically unclonable function for secure key generation with a key error rate of 2E-38 in 45nm smart-card chips

Physically unclonable function (PUF) circuits are for generating unique secure keys or chip IDs based on intrinsic properties of each chip itself [1-2]. PUFs are a step forward to improve the security level compared to traditional NVM (non-volatile memory) solutions (FUSEs, EEPROM/FLASH, etc.) because they resolve security issues, such as active data-probing, transferring the security key from outside, etc. Since the MOSFET mismatch (e.g. size, doping concentration, mobility and oxide thickness) due to process variations cannot be fully controlled, PUFs, which are based on such phenomena, cannot be replicated. Unfortunately, the PUF output is erroneous by nature, as caused by thermal noise, voltage/temperature influence, aging effects, etc. The stability issue must be overcome since standard security applications, such as data encryption and digital signatures, have zero error-tolerance. In this work, a PUF structure based on the threshold voltage (Vth) difference of inverting logic gates is presented, which is implemented for secure 24b key generation in a 45nm smart card chip. The key is used as part of an encryption key and achieves an error rate as low as 2.01×10-38. The PUF system is also scalable for a larger key size.