3D NAND Flash Memory Based on Double-Layer NC-Si Floating Gate with High Density of Multilevel Storage

As a strong candidate for computing in memory, 3D NAND flash memory has attracted great attention due to the high computing efficiency, which outperforms the conventional von-Neumann architecture. To ensure 3D NAND flash memory is truly integrated in the computing in a memory chip, a new candidate with high density and a large on/off current ratio is now urgently needed. Here, we first report that 3D NAND flash memory with a high density of multilevel storage can be realized in a double-layered Si quantum dot floating-gate MOS structure. The largest capacitance-voltage (C-V) memory window of 6.6 V is twice as much as that of the device with single-layer nc-Si quantum dots. Furthermore, the stable memory window of 5.5 V can be kept after the retention time of 10⁵ s. The obvious conductance-voltage (G-V) peaks related to the charging process can be observed, which further confirms that the multilevel storage can be realized in double-layer Si quantum dots. Moreover, the on/off ratio of 3D NAND flash memory with a nc-Si floating gate can reach 10⁴, displaying the characteristic of a depletion working mode of an N-type channel. The memory window of 3 V can be maintained after 10⁵ P/E cycles. The programming and erasing speed can arrive at 100 µs under the bias of +7 V and -7 V. Our introduction of double-layer Si quantum dots in 3D NAND float gating memory supplies a new way to the realization of computing in memory.