Spintronics & AI Integration
Research Process
Design and fabrication of the MultiSpin.AI post-von Neumann architecture
The design and fabrication of the MultiSpin.AI post-von Neumann architecture involves a systematic process. Beginning with simulations to understand magnetic characteristics, researchers fabricate the Single-Layers Magnetic (SLMMS) using techniques like e-beam lithography, ion beam milling, and specific open processes.
Subsequently, multi-level magnetic tunnel junctions (M2TJs) are created, optimising different characteristics essential for meeting both magnetic and electrical requirements, with the incorporation of SLMMS.
The final stage includes the fabrication of a 4×4 array of 4-level M2TJs using an Application-Specific Integrated Circuit (ASIC). Guidelines for monolithic integration with Complementary Metal Oxide Semiconductor (CMOS) technology are established, and a comparative analysis assesses bit density against competing memory technologies, demonstrating advancements beyond traditional von Neumann architecture.
Characterization and Testing of SLMMS and M2TJs
The characterization and testing phase of the MultiSpin.AI architecture involves validating the designed properties of the Single-Layer Multistate Magnetic Structures (SLMMS) and multi-level Magnetic Tunnel Junctions (M2TJs). Researchers employ simulations to analyse SLMMS magnetic properties, assessing the impact of fabrication variability on writing error and inference disturbance. Magnetic characterization includes evaluating spin-orbit torque efficiency and measuring switching speeds, with SLMMS featuring two switchable magnetic crossing ellipses (2CE) and three magnetic crossing ellipses (3CE) supporting different discrete magnetic states.
Simultaneously, magnetic state tests on M2TJs involve PHE measurements on SLMMS and assessing M2TJs resistance to understand its impact on tunnel resistance, considering reliability and cross-field immunity. Characterization efforts focus on high-speed spin memory, examining the linearity of weight update and the number of usable states crucial for neural network training, providing essential insights into the performance of neural synaptic building blocks in matrix-vector multiplication operations and learning protocols.
AI algorithm design, validation and specs
The integration of an n-ary cell-based crossbar architecture in the MultiSpin.AI framework presents a challenge in adapting the Multiply-Accumulate (MAC) operation algorithm due to inherent variability in the physical n-ary cells. To overcome this, error correction algorithms are under development to address variations in Magnetic Tunnel Junctions (M2TJs) within the crossbar, aiming to enhance the reliability and reproducibility of the MAC operation.
This ongoing effort extends into the application phase, where the refined MAC operation co-processor design is tested in solving standard machine learning tasks, incorporating crossbar design expertise and end-user perspectives for a comprehensive evaluation of its capabilities and performance. In advancing the 4-level cell 4×4 crossbar, a tailored pattern recognition problem is actively designed and tested to match its limited computational capacity. Subsequent simulation involves large network inference using MultiSpin.AI, benchmarking its performance, and assessing viability for real-life neural networks, particularly in IoT applications. An evaluation framework is applied to gauge efficiency and ethical considerations, ensuring a holistic assessment of the MAC operation co-processor design in both technical and practical dimensions.
PoC demonstration
The Proof of Concept (PoC) demonstration is centred on the integration of the crossbar into a standard real-time AI computing architecture and the validation of the performance of the miniature demonstrator crossbar equipped with the multi-level spintronic cell. Collaboratively, we combine the previously fabricated 4×4 crossbar matrix of 4-level Magnetic Tunnel Junctions (M2TJs) with essential building blocks to create an efficient neuromorphic processor in the form of a miniature PCB prototype. Upon assembly and operationalization, this board serves to validate the n-ary computation capabilities.
To establish connectivity with a PC or microcontroller and enable algorithm control and the demonstration of neural network inference tasks, we develop the MCU driver and control software. Finally, the crossbar’s read-write capabilities are characterized, parameters for a full-scale device are estimated through modelling and experiments with the recently developed PCB, and the execution performance of new algorithms is assessed to ensure optimal functionality.
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