To catch up with growing complexity of artificial neural networks, hybrid integrated systems with high-density nanoscale memristive devices have been proposed as building blocks for the next generation computing hardware. In this Tutorial, we first introduce the methodologies in fabrication of memristor crossbars with a sub-10 nm feature size, including nanoimprint lithography that provides excellent resolution at low cost. Technical issues such as critical dimension control, overlay alignment accuracy, and reliable mold cleaning are discussed in detail. In the meantime, as lateral scaling becomes more challenging, three-dimensional (3D) integration presents an alternative solution to further increase the packing density and to provide new functionalities. Some early demonstrations of 3D hybrid memristor/complementary metal oxide semiconductor circuits are reviewed here, and their design and fabrication related issues are discussed. Successful implementation of large-scale 3D memristive systems with nanometer scale devices may provide ultimate solution to the hardware bottleneck for future computing applications.
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