In the era of the Internet of Things, hardware security is of critical importance. One way to achieve enhanced device security with a minimal increase in cost is using a physical unclonable function (PUF), which exploits the intrinsic randomness in a process. Though PUFs typically rely on manufacturing variability, Finocchio et al. developed a PUF using spin-orbit torque magnetoresistive random access memory (SOT-MRAM).

By using a current pulse to induce a random positive or negative magnetic orientation in a ferromagnetic dot, the authors demonstrated a SOT-based method of generating a cryptographic key. When the pulse is removed, the magnetization in the dot relaxes into one of the two perpendicular states, which the SOT-MRAM device structure then reads.

In testing the method, the group evaluated the approach for a single dot, a composition of three dots and a 16-by-16 array of SOT-MRAM cells with consistent outcomes. They found the likelihood of a dot transitioning into either state is about 50%, regardless of its initial orientation. This is a promising result, as a 50% probability is crucial for ensuring the randomness and unpredictability.

Additionally, the prediction is robust to changes in the amplitude of the pulse, which offers a substantial advantage, due to the difficulty of ensuring a uniform field in a large array of SOT-MRAM cells.

According to author Mario Carpentieri, a roadmap is already in place to integrate the technique into devices for hardware authentication purposes.

“Once the SOT-MRAM technology will be ready for the market, its application for hardware identification will be trivial,” he said.

Source: “Spin-orbit torque based physical unclonable function,” by G. Finocchio, T. Moriyama, R. De Rose, G. Siracusano, M. Lanuzza, V. Puliafito, S. Chiappini, F. Crupi, Z. Zeng, T. Ono, and M. Carpentieri, Journal of Applied Physics (2020). The article can be accessed at