Computational Associative Memory with Amorphous Metal‐Oxide Channel 3D NAND‐Compatible Floating‐Gate Transistors

Abstract

Abstract3D NAND has been enabling continuous NAND density and cost scaling beyond conventional 2D NAND since sub‐20‐nm nodes. However, its poly‐Si channel suffers from low mobility, instability caused by grain boundaries, and large device‐to‐device variations in electrical characteristics at highly scaled device dimensions. These drawbacks can be overcome by introducing an amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) channel, which has the advantages of ultralow OFF current, back‐end‐of‐line compatibility, higher mobility than poly‐Si, and free of grain boundaries due to the amorphous nature. In this work, ultrascaled floating‐gate (FG) transistors with a channel length down to 60 nm are reported, achieving the highest ON current of 127 µA µm−1 among all reported a‐IGZO‐based flash devices for high‐density, low‐power, and high‐performance 3D NAND applications. Furthermore, a nonvolatile and area‐efficient ternary content‐addressable memory (TCAM) with only two parallel‐connected a‐IGZO FG transistors is experimentally demonstrated to address the TCAM scalability issue. Experimentally calibrated array‐level simulations show that this design achieves at least a 240 × array‐size scalability and a 2.7‐fold reduction in search energy than TCAMs based on complementary metal‐oxide‐semiconductor technology using 16 transistors, two‐transistor‐two‐resistive random access memory, and two‐ferroelectric field‐effect‐transistor.