Summary of UNDERSTANDING FLASH MEMORY AND HOW IT WORKS
NAND Flash is a non-volatile memory technology replacing disk drives, utilizing modified transistors with an added "floating gate" to store data. By applying high voltage, electrons tunnel through an oxide layer to the floating gate, changing the transistor's threshold voltage to represent binary 1s or 0s. Data is stored in strings of cells organized into blocks, requiring erasure before writing since programming only changes bits from 1 to 0.
Parts used in NAND Flash:
- Modified transistor
- Control gate
- Floating gate
- Oxide insulating layer
- Dielectric layers
- Bit lines
- Strings (32 to 128 cells)
- Blocks
Flash memory is one of the most widely used types of non-volatile memory. NAND Flash is designed for modern file storage which replaced old disk drives. This article provides a brief understanding of how NAND Flash technology works.
The basic storage component used in Flash memory is a modified transistor. In a standard transistor, the flow of current through a channel between two contacts is turned on by a voltage applied to the gate. The channels are separated by an insulating layer of Oxide. In a Flash storage cell, there is an extra electrically isolated gate called “floating gate”. It is added to the control gate and the channel of the modified transistor.
High voltage is applied to the control gate of The Flash cell to program it. This pushes electrons to pass through the oxide layer to the floating gate (a process known as tunneling). The presence of these trapped electrons on the floating gate changes the required voltage to turn on the transistor. Thus, a transistor with no charge on the floating gate can easily turn on at a certain voltage, representing a 1, while a programmed cell will not turn on, representing a 0.
This kind of memory is non-volatile because the floating gate is surrounded by dielectric layers, it traps the electric charge even when the power is removed. Erasing a cell reverses this process by introducing a large negative voltage to the control gate to force the electrons to tunnel out of the floating gate.
A number of cells, typically 32 to 128, are connected in a string. Strings are organized in blocks. To program cells in a block, the data is put on the bit lines and a high voltage is applied. Because programming can only change a cell from a 1 to a 0, any cells where the new data is a 1, will be left in their current state. Therefore, all the cells must be erased before writing. This process ensures that any cells that will not be programmed already contain a 1.
Read More: UNDERSTANDING FLASH MEMORY AND HOW IT WORKS
- What replaces old disk drives?
NAND Flash is designed for modern file storage which replaced old disk drives. - How is data programmed in a Flash cell?
High voltage is applied to the control gate to push electrons through the oxide layer to the floating gate via tunneling. - Why is this memory considered non-volatile?
The floating gate is surrounded by dielectric layers that trap electric charge even when power is removed. - How does a cell represent a 1 versus a 0?
A transistor with no charge on the floating gate turns on easily to represent a 1, while a programmed cell with trapped electrons represents a 0. - How are Flash cells organized?
A number of cells, typically 32 to 128, are connected in a string, and strings are organized in blocks. - Why must all cells be erased before writing?
Programming can only change a cell from a 1 to a 0, so all cells must be erased to ensure unprogrammed cells contain a 1. - How is a Flash cell erased?
Erasing reverses the process by introducing a large negative voltage to the control gate to force electrons to tunnel out.
