Abstract
In-memory computing could enhance computing energy efficiency by directly implementing multiply accumulate (MAC) operations in a crossbar memory array with low energy consumption (around femtojoules for a single operation). However, a crossbar memory array cannot execute nonlinear activation; moreover, activation processes are power-intensive (around milliwatts), limiting the overall efficiency of in-memory computing. Here we develop an ultrafast bipolar flash memory to execute self-activated MAC operations. Based on atomically sharp van der Waals heterostructures, the basic flash cell has an ultrafast n/p program speed in the range of 20–30 ns and an endurance of 8 × 106 cycles. Utilizing sign matching between the input voltage signal and the storage charge type, our bipolar flash can realize a rectified linear unit activation function during the MAC process with a power consumption for each operation of just 30 nW (or 5 fJ of energy). Using a convolutional neural network, we find that the self-activated MAC method has a simulated accuracy of 97.23%, tested on the Modified National Institute of Standards and Technology dataset, which is close to the conventional method where the MAC and activation operations are separated.
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Data availability
The data that support the plots in this paper and other findings of this study are available from the corresponding authors on reasonable request. Source data are provided with this paper.
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The codes used for the simulation are available from the corresponding authors on reasonable request.
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Acknowledgements
This work was supported by the National Key Research and Development Program (grant number 2021YFA1200500), the Innovation Program of Shanghai Municipal Education Commission (grant number 2021-01-07-00-07-E00077) and the National Natural Science Foundation of China (61925402, 62090032 and 62004040), Science and Technology Commission of Shanghai Municipality (19JC1416600), Shanghai Pilot Program for Basic Research – FuDan University 21TQ1400100 (21TQ011), Shanghai Rising-Star Program (22QA1400700) and the young scientist project of the MOE innovation platform.
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C.L. and P.Z. conceived the idea. C.L., X.H. and Z.T. designed and conducted the experiments. S.Z. and S.W. provided valuable input in the experiments. X.H., C.L. and P.Z. co-wrote the manuscript and all authors contributed to the discussion and revision of the manuscript.
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Supplementary sections 1–10 containing Figs. 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, 2-2, 2-3, 2-4, 3-1, 4-1, 4-2, 5-1, 6-1, 6-2, 8-1, 8-2, 8-3, 8-4, 8-5 and 10-1, Tables 3-1, 7-1, 8-1, 8-2 and 9-1, and corresponding discussions.
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Huang, X., Liu, C., Tang, Z. et al. An ultrafast bipolar flash memory for self-activated in-memory computing. Nat. Nanotechnol. 18, 486–492 (2023). https://doi.org/10.1038/s41565-023-01339-w
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DOI: https://doi.org/10.1038/s41565-023-01339-w
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