The first working 3D NAND flash memory at sub-40nm feature sizes will be described by Macronix researchers at this year’s International Electron Devices Meeting (IEDM). They used vertical gates having horizontal channels to create a new architectural layout that dramatically decreases feature sizes in the wordline direction and improves manufacturability. The new architecture also enables the use of a novel “staircase” bitline contact formation method to minimize fabrication steps and cost. The result is an eight-layer device with a wordline feature size of 37.5nm, bitline feature size of 75 nm, 64 cells per string and a core array efficiency of 63%. The researchers say the technology not only is lower cost than conventional sub-20nm 2D NAND, it can provide 1 Tb of memory if further scaled to 25nm feature sizes. At that size the Macronix device would comprise only 32 layers, compared to 3D stackable NANDs with vertical channels that would need almost 100 layers to reach the same memory density.

A previously proposed 3D vertical gate NAND architecture.

An overview of the proposed architectural layout that is said to be an improvement.

A cross-sectional views of the new device.

TEM electron microscope views of the staircase bitline contacts.