A physical unclonable function based on variations of write times in STT-MRAM due to manufacturing defects

A physical unclonable function (PUF) utilizes the unclonable random variations in a device’s responses to a set of inputs to produce a unique “biometric” for authentication. The random variations are caused by unpredictable and unclonable defects introduced during manufacturing. They are unique to a given device and act as a fingerprint. Here, we show that the switching time of a magnetic tunnel junction injected with a spin-polarized current generating spin transfer torque is sensitive to the nature of the manufacturing defects and hence can be the basis of a PUF. We use micromagnetic simulations to study the switching times and their probability distribution at room temperature under a constant current excitation for six different (commonly encountered) defect morphologies in spin-transfer-torque magnetic random access memory (STT-MRAM) to establish the viability of a PUF. We also study the challenge-response set of a small ensemble of STT-MRAMs with different defect morphologies and find that the associated inter-Hamming distance is close to the ideal value of 0.5.