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1. Progress toward picosecond on-chip magnetic memory

   https://doi.org/10.1063/5.0083897  

   Polley, Debanjan ; Pattabi, Akshay ; Chatterjee, Jyotirmoy ; Mondal, Sucheta ; Jhuria, Kaushalya ; Singh, Hanuman ; Gorchon, Jon ; Bokor, Jeffrey ( April 2022 , Applied Physics Letters)

   We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed tomore »accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.

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2. Heterogeneous Technology Configurable Fabrics for Field-Programmable Co-Design of CMOS and Spin-Based Devices

   https://doi.org/10.1109/ICRC.2017.8123638  

   DeMara, Ronald F. ; Roohi, Arman ; Zand, Ramtin ; Pyle, Steven D. ( November 2017 , IEEE International Conference on Rebooting Computing)

   he architecture, operation, and characteristics of two post-CMOS reconfigurable fabrics are identified to realize energy-sparing and resilience features, while remaining feasible for near-term fabrication. First, Storage Cell Replacement Fabrics (SCRFs) provide a reconfigurable computing platform utilizing near-zero leakage Spin Hall Effect devices which replace SRAM bit-cells within Look-Up Tables (LUTs) and/or switch boxes to complement the advantages of MOS transistor-based multiplexer select trees. Second, Heterogeneous Technology Configurable Fabrics (HTCFs) are identified to extend reconfigurable computing platforms via a palette of CMOS, spin-based, or other emerging device technologies, such as various Magnetic Tunnel Junction (MTJ) and Domain Wall Motion devices. HTCFs are composed of a triad of Emerging Device Blocks, CMOS Logic Blocks, and Signal Conversion Blocks. This facilitates a novel architectural approach to reduce leakage energy, minimize communication occurrence and energy cost by eliminating unnecessary data transfer, and support auto-tuning for resilience. Furthermore, HTCFs enable new advantages of technology co-design which trades off alternative mappings between emerging devices and transistors at runtime by allowing dynamic remapping to adaptively leverage the intrinsic computing features of each device technology. SPICE simulations indicate 6% to 67% reduction in read energy, 21% reduction in reconfiguration energy, and 78% higher clock frequency versus alternative fabricatedmore »emerging device architectures, and a significant reduction in leakage compared to CMOS-based approaches.« less
3. A 3 pJ/bit free space optical interlink platform for self-powered tetherless sensing and opto-spintronic RF-to-optical transduction

   https://doi.org/10.1038/s41598-021-87885-6  

   Wheaton, Skyler ; Lopez-Dominguez, Victor ; Almasi, Hamid ; Cai, Jialin ; Zeng, Zhongming ; Khalili Amiri, Pedram ; Mohseni, Hooman ( April 2021 , Scientific Reports)

   Tetherless sensors have long been positioned to enable next generation applications in biomedical, environmental, and industrial sectors. The main challenge in enabling these advancements is the realization of a device that is compact, robust over time, and highly efficient. This paper presents a tetherless optical tag which utilizes optical energy harvesting to realize scalable self-powered devices. Unlike previous demonstrations of optically coupled sensor nodes, the device presented here amplifies signals and encodes data on the same optical beam that provides its power. This optical interrogation modality results in a highly efficient data link. These optical tags support data rates up to 10 Mb/s with an energy consumption of ~ 3 pJ/bit. As a proof-of-concept application, the optical tag is combined with a spintronic microwave detector based on a magnetic tunnel junction (MTJ). We used this hybrid opto-spintronic system to perform self-powered transduction of RF waves at 1 GHz to optical frequencies at ~ 200 THz, while carrying an audio signal across (see Supplementary Data for audio files).
4. EE-ACML: Energy-Efficient Adiabatic CMOS/MTJ Logic for CPA-Resistant IoT Devices

   https://doi.org/10.3390/s21227651  

   Kahleifeh, Zachary ; Thapliyal, Himanshu ( November 2021 , Sensors)

   Internet of Things (IoT) devices have strict energy constraints as they often operate on a battery supply. The cryptographic operations within IoT devices consume substantial energy and are vulnerable to a class of hardware attacks known as side-channel attacks. To reduce the energy consumption and defend against side-channel attacks, we propose combining adiabatic logic and Magnetic Tunnel Junctions to form our novel Energy Efficient-Adiabatic CMOS/MTJ Logic (EE-ACML). EE-ACML is shown to be both low energy and secure when compared to existing CMOS/MTJ architectures. EE-ACML reduces dynamic energy consumption with adiabatic logic, while MTJs reduce the leakage power of a circuit. To show practical functionality and energy savings, we designed one round of PRESENT-80 with the proposed EE-ACML integrated with an adiabatic clock generator. The proposed EE-ACML-based PRESENT-80 showed energy savings of 67.24% at 25 MHz and 86.5% at 100 MHz when compared with a previously proposed CMOS/MTJ circuit. Furthermore, we performed a CPA attack on our proposed design, and the key was kept secret.
5. Magnetic memory driven by topological insulators

   https://doi.org/10.1038/s41467-021-26478-3  

   Wu, Hao ; Chen, Aitian ; Zhang, Peng ; He, Haoran ; Nance, John ; Guo, Chenyang ; Sasaki, Julian ; Shirokura, Takanori ; Hai, Pham Nam ; Fang, Bin ; et al ( October 2021 , Nature Communications)

   Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 10⁵ A cm⁻²have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiencyθ_SHin TIs is quantified by both the SOT-induced shift of the magnetic switching field (θ_SH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θ_SH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.