NAND Architecture - Strings and Arrays

Diagram of a Single NAND Flash Cell:

Combining Individual NAND Flash Cells into a String:

All by itself, a single flash cell would not be of much value. But combining many of them is what allows the storage of significant amounts of data. The first step in combining individual NAND cells is the NAND String.

The Image above shows the NAND String depicted in both a diagram form and in schematic form. Schematic form is typically used to show much larger arrays.

NAND cells are connected end to end to form a string of cells. Typically 32 or 64 cells are connected together in series with each other, with each cell representing a bit of data (0 or 1).

Combining NAND Strings into Arrays:

While a NAND String can store 32 bits of data, this still only translates into 4 bytes of data or enough for 4 characters. So, strings are combined into larger arrays to achieve some useful amounts of storage.

The Image above shows the NAND String schematic repeated several times in an array. Notice the additional connections made to the NAND strings which serve to tie the array together. The red line connects the Sources (S) of the individual strings.

The yellow lines connect the Control Gates of the NAND strings. In the array, the control gates are connected horizontally, but not vertically. In addition, the Drain (D) lines are not showing connections since they will be used separately in the array.