HOW DOES FLASH MEMORY WORK?

By Sarat Bhargavaee13b1008

Table of Contents

Introduction to Flash Memory.

The Basic Storage element of a Flash Storage devices

How to read, write, erase data to a Floating gate Transistor(FGT) ?

Comparison between NOR and NAND architectures.

How to read , write , erase data in each of NOR , NAND architectures ?

Introduction to Flash Memory

What is Flash Memory ?

Flash memory belongs to the class of Electronic Non-volatile memories.

It was first introduced by Toshiba in 1984.

There are mainly 2 Types of Flash memory technologies• Nand Flash • Nor Flash

Floating-gate Transistor

The basic storage element of Flash memory is Floating gate Transistor.

Floating gate Transistor MOSFET

The Floating gate is electrically insulated on all sides

SLC (Single level cell)

MLC (Multi level cell)

Reading from Floating gate transistor

Writing to a Floating gate transistor

How to change the charge stored in Floating gate when it is electrically isolated ?

Hot electron injection

In this process we apply Very High Voltage (5V) at the Control gate

and across the Source and drain.

Quantum Tunnelling

In this process we apply very high Negative Voltage across the control gate

and the source.(Erasing making 1’s).

Very high Positive across Cg , Source for programming.

NOR and NAND Architectures

FGT’s are connected in parallel in NOR architecture

Have Low latency time or High read speed. Less bit density Used in places where Random access is

required

FGT’s are connected in series (8) Writing speed is much faster than

NOR at the cost relatively high latency.

More bit density Used in USB devices

Reading data

NOR Architecture:NAND Architecture:

Erasing data

NOR Architecture: NAND Architecture:

Writing data

NOR Architecture:NAND Architecture:

Conclusion

Now a days the flash memory technology is trying to replace the traditional Hard drives with SSD’s because of low latency and low power consumption.

But the challenge is the cost

In recent times there are attempts to replace them with DRAM.

But here the challenge the low access speed compared to DRAM.

Sources

http://en.wikipedia.org/wiki/Flash_memory#cite_note-32

https://www.youtube.com/watch?v=s7JLXs5es7I&index=211&list=WL

http://images.google.co.in/