An Annealing Accelerator for Ising Spin Systems Based on In‐Memory Complementary 2D FETs

• Published in: Advanced materials (Weinheim) Vol. 34; no. 4; pp. e2107076 - n/a
• Main Authors: Sebastian, Amritanand, Das, Sarbashis, Das, Saptarshi
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.01.2022
• Subjects: 2D materials; Algorithms; Antiferromagnetism; Combinatorial analysis; Computer simulation; Ferromagnetism; Field effect transistors; Hardware; Heuristic methods; Ising model; Ising spin lattices; Metastable state; Optimization; Searching; Simulated annealing; Spin glasses; Temperature dependence; simulated annealing; Ising spin lattices; field-effect transistors; 2D materials
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202107076

Metaheuristic algorithms such as simulated annealing (SA) are often implemented for optimization in combinatorial problems, especially for discreet problems. SA employs a stochastic search, where high‐energy transitions (“hill‐climbing”) are allowed with a temperature‐dependent probability to escape local optima. Ising spin glass systems have properties such as spin disorder and “frustration” and provide a discreet combinatorial problem with a high number of metastable states and ground‐state degeneracy. In this work, subthreshold Boltzmann transport is exploited in complementary 2D field‐effect transistors (p‐type WSe2 and n‐type MoS2) integrated with an analog, nonvolatile, and programmable floating‐gate memory stack to develop in‐memory computing primitives necessary for energy‐ and area‐efficient hardware acceleration of SA for Ising spin systems. Search acceleration of >800× is demonstrated for 4 × 4 ferromagnetic, antiferromagnetic, and spin glass systems using SA compared to an exhaustive search using a brute force trial at miniscule total energy expenditure of ≈120 nJ. The hardware‐realistic numerical simulations further highlight the astounding benefits of SA in accelerating the search for larger spin lattices. Energy‐ and area‐efficient hardware acceleration of simulated annealing for the Ising spin system is achieved by exploiting subthreshold conduction and programmability of 2D field‐effect transistors based on p‐type WSe2 and n‐type MoS2. Search acceleration of >800× for 4 × 4 ferromagnetic, antiferromagnetic, and spin glass systems is demonstrated with a miniscule energy dissipation of ≈120 nJ.