13-07-2012, 11:35 AM
FLASH MEMORY
FLASH MEMORY.pptx (Size: 339 KB / Downloads: 29)
Introduction
Flash memory is a non-volatile computer storage chip.
Developed from electrically erasable programmable read only memory(EEPROM).
Has fast access time.
Faster than dynamic RAM.
But slower than static RAM.
Used in personal computers , digital audio player , digital cameras , scientific instruments , medical electronics , etc.
Principle of operation
Flash memory stores information in an array of memory cells made from floating-gate transistors.
In traditional single-level cell (SLC) devices, each cell stores only one bit of information.
Some newer flash memory, known as multi-level cell (MLC) devices, can store more than one bit per cell by choosing between multiple levels of electrical charge to apply to the floating gates of its cells.
Floating-gate transistor
In flash memory, each memory cell resembles a standard MOSFET ,except the transistor has two gates instead of one.
On top is the control gate (CG), as in other MOS transistors, but below this there is a floating gate (FG) insulated all around by an oxide layer. The FG is interposed between the CG and the MOSFET channel. Because the FG is electrically isolated by its insulating layer, any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years.
Programming NOR
Elevate the on-voltage applied to CG.
Electrons start flowing from source to drain.
With this source-to-drain flow some electrons have enough energy to penetrate the insulating layer around floating gate.
FLASH MEMORY.pptx (Size: 339 KB / Downloads: 29)
Introduction
Flash memory is a non-volatile computer storage chip.
Developed from electrically erasable programmable read only memory(EEPROM).
Has fast access time.
Faster than dynamic RAM.
But slower than static RAM.
Used in personal computers , digital audio player , digital cameras , scientific instruments , medical electronics , etc.
Principle of operation
Flash memory stores information in an array of memory cells made from floating-gate transistors.
In traditional single-level cell (SLC) devices, each cell stores only one bit of information.
Some newer flash memory, known as multi-level cell (MLC) devices, can store more than one bit per cell by choosing between multiple levels of electrical charge to apply to the floating gates of its cells.
Floating-gate transistor
In flash memory, each memory cell resembles a standard MOSFET ,except the transistor has two gates instead of one.
On top is the control gate (CG), as in other MOS transistors, but below this there is a floating gate (FG) insulated all around by an oxide layer. The FG is interposed between the CG and the MOSFET channel. Because the FG is electrically isolated by its insulating layer, any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years.
Programming NOR
Elevate the on-voltage applied to CG.
Electrons start flowing from source to drain.
With this source-to-drain flow some electrons have enough energy to penetrate the insulating layer around floating gate.