Highly Reliable Magnetic Memory-Based Physical Unclonable Functions.

Magnetic random-access memory (MRAM), which stores information through control of the magnetization direction, offers promising features as a viable nonvolatile memory alternative, including high endurance and successful large-scale commercialization. Recently, MRAM applications have extended beyond traditional memories, finding utility in emerging computing architectures such as in-memory computing and probabilistic bits. In this work, we report highly reliable MRAM-based security devices, known as physical unclonable functions (PUFs), achieved by exploiting nanoscale perpendicular magnetic tunnel junctions (MTJs). By intentionally randomizing the magnetization direction of the antiferromagnetically coupled reference layer of the MTJs, we successfully create an MRAM-PUF. The proposed PUF shows ideal uniformity and uniqueness and, in particular, maintains performance over a wide temperature range from -40 to +150 °C. Moreover, rigorous testing with more than 1584 challenge-response pairs of 64 bits each confirms resilience against machine learning attacks. These results, combined with the merits of commercialized MRAM technology, would facilitate the implementation of MRAM-PUFs.

Spintronic Physical Unclonable Functions Based on Field-Free Spin-Orbit-Torque Switching.

Physical unclonable function (PUFs) utilize inherent random physical variations of solid-state devices and are a core ingredient of hardware security primitives. PUFs promise more robust information security than that provided by the conventional software-based approaches. While silicon- and memristor-based PUFs are advancing, their reliability and scalability require further improvements. These are currently limited by output fluctuations and associated additional peripherals. Here, highly reliable spintronic PUFs that exploit field-free spin-orbit-torque switching in IrMn/CoFeB/Ta/CoFeB structures are demonstrated. It is shown that the stochastic switching polarity of the perpendicular magnetization of the top CoFeB can be achieved by manipulating the exchange bias directions of the bottom IrMn/CoFeB. This serves as an entropy source for the spintronic PUF, which is characterized by high entropy, uniqueness, reconfigurability, and digital output. Furthermore, the device ensures a zero bit-error-rate under repetitive operations and robustness against external magnetic fields, and offers scalable and energy-efficient device implementations.

Improved synaptic functionalities of Li-based nano-ionic synaptic transistor with ultralow conductance enabled by Al2O3barrier layer.

In this study, we investigated the effect of an Al2O3barrier layer in an all-solid-state inorganic Li-based nano-ionic synaptic transistor (LST) with Li3PO4electrolyte/WOxchannel structure. Near-ideal synaptic behavior in the ultralow conductance range (∼50 nS) was obtained by controlling the abrupt ion migration through the introduction of a sputter-deposited thin (∼3 nm) Al2O3interfacial layer. A trade-off relationship between the weight update linearity and on/off ratio with varying Al2O3layer thickness was also observed. To determine the origin of the Al2O3barrier layer effects, cyclic voltammetry analysis was conducted, and the optimal ionic diffusivity and mobility were found to be key parameters in achieving ideal synaptic behavior. Owing to the controlled ion migration, the retention characteristics were considerably improved by the Al2O3barrier. Finally, a highly improved pattern recognition accuracy (83.13%) was achieved using the LST with an Al2O3barrier of optimal thickness.