Effect of Quadruple Size Transistor on SRAM Physically Unclonable Function Stabilized by Hot Carrier Injection

This article presents a bitcell of a static randomaccess memory (SRAM)-based physically unclonable function (PUF) with quadruple-size transistor, which reduces the tail’ of mismatch distribution after hot carrier injection (HCI) burn-in. A statistical mismatch distribution model after HCI application for a certain time is proposed by combining native mismatch distribution before HCI and mismatch shift distribution after HCI. Model calculation shows that quadruple-size transistor SRAM PUF needs 15-min HCI burn-in time to achieve cryptographic level requirement, which is more than 3 times shorter than normal-size transistor SRAM PUF of 46-min. The effect of utilizing the quadruple-size transistor with respect to HCI burn-in for stability reinforcement is also confirmed by measuring chips fabricated in a 130-nm CMOS process. Experimental results show that the ‘tail’ in mismatch distribution is significantly eliminated after 18-min HCI burnin time of quadruple-size transistor SRAM PUF, which meets our expectations. The presented statistical model also matches the measurement data well.