Transcript ECG 453/653 Introduction to Nanotechnology

ECG 453/653
Introduction to Nanotechnology
Topic: Nanoparticles based Flash Memory
By : Sri Rama Krishna
Over View :
• Flash Memory
Introduction,
Types,
Principle of operation,
Applications.
• Nanoparticles
Definition,
Properties,
Fabrication Methods.
• Flash memory using Nanoparticles.
Flash Memory- Introduction
• Flash memory is non-volatile computer memory that can
be electrically erased and reprogrammed.
• It is a technology that is primarily used in memory cards
and USB flash drives for general storage and transfer of
data between computers and other digital products.
Flash Memory- Types
• Two major forms of Flash memory are NAND Flash and NOR
Flash
• NOR Flash:
Cross Section View of single Flash Cell =>
The characteristics of NOR Flash are lower
density, high read speed, slow write speed,
slow erase speed, and a random
access interface
NOR flash memory wiring and structure on silicon
Flash Memory- Types
• NAND Flash:
NAND flash memory wiring and structure on silicon
The characteristics of NAND Flash are:
high density, medium read speed, high write speed, high
erase speed, and an indirect or I/O like access.
Flash Memory- Types
Selection Between NOR & NAND Flash:
• For a system that needs to boot out of Flash, execute
code from the Flash, or if read latency is an issue, NOR
Flash is the choice of selection.
• However, for storage applications, NAND Flash’s higher
density, and high programming and erase speeds make it
the best choice.
Flash Memory- Principle of Operation
•In NOR gate flash, each cell resembles a standard MOSFET, 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.
•A single-level NOR flash cell in its default state is logically
equivalent to a binary "1" value, because current will flow
through the channel under application of an appropriate voltage
to the control gate.
Programming of NOR Flash
A NOR flash cell can be programmed, or set to a binary "0" value, by the
following procedure:
• an elevated on-voltage
(typically >5 V) is applied to
the CG
• the channel is now turned on,
so electrons can flow from the
source to the drain (assuming
an NMOS transistor)
• the source-drain current is
sufficiently high to cause some
high energy electrons to jump
through the insulating layer
onto the FG, via a process
called hot-electron injection.
Erasing of NOR Flash Memory cell
A NOR flash cell can be erased, or set back to a binary “1" value, by the
following procedure:
• To erase a NOR flash cell
(resetting it to the "1" state), a
large voltage of the opposite
polarity is applied between the
CG and source, pulling the
electrons off the FG through
quantum tunneling.
Flash Memory - Applications
• Applications include PDAs
(personal digital assistants),
laptop computers, digital
audio players, digital
cameras, mobile phones and
memory sticks.
Nanoparticles:
• Definition: "A particle having one or more dimensions of
the order of 100nm or less".
• Nanoparticles in a wide variety of
different shapes and sizes .
Nanoparticles are
often referred to as
Clusters, Nanospheres,
Nanorods, and
Nanocups.
Nanoparticles - Properties
• Size-dependent properties are observed such as “quantum
confinement” in semiconductor particles.
• Nanoparticles have a very high surface area to volume ratio. This
provides a tremendous driving force for diffusion especially at
elevated temperatures.
• Nanoparticles smaller than 50 nm are considered super hard
materials that do not exhibit the same malleability and ductility as
bulk material.
• Nanoparticles often have unexpected visible properties because they
are small enough to confine their electrons and produce quantum
effects.
Nanoparticles- Fabrication Methods
• “Attrition” and “Pyrolysis” are common methods
for creating Nanoparticles.
• In attrition, macro or micro scale particles are
ground in a ball mill, a planetary ball mill, or other
size reducing mechanism. The resulting particles are
air classified to recover Nanoparticles.
• In pyrolysis, a vaporous precursor (liquid or gas) is
forced through an orifice at high pressure and
burned. The resulting solid (a version of soot) is air
classified to recover oxide particles from by-product
gases.
Flash memory using Nanoparticles:
•
Current flash Memory manufacturing
technology forecasts no further developments in
terms of density after 2012.
• Flash memory Technology enters another
dimension with the Research being started to
construct flash memory using nanoparticles.
• Researchers in Korea and Australia have used
stacked layers of gold nanoparticles to boost the
storage density of flash memory.
Flash memory using Nanoparticles:
• The nanoparticles are deposited
onto an insulating surface over a
transistor in a first distribution of
the nanoparticles.
• A field is applied to the
nanoparticles on the surface that
applies a force to the particles,
rearranging the nanoparticles on
the surface by the force from the
field to form a second
distribution of nanoparticles on
the surface.
• A protective and enclosing
insulating layer is deposited on
the nanoparticle second
distribution. The addition of a
top conductive layer completes a
basic flash memory structure.
Flash memory using Nanoparticles:
•By this Method the size of
the oxide layer can be
decreased to very small
scale for each flash
memory cell.
• This way density(cells for
unit area) of the flash
memory is increased.
Thank You.