ECG 453/653 Introduction to Nanotechnology

1
ECG 453/653Introduction to Nanotechnology
Topic Nanoparticles based Flash Memory
By Sri Rama Krishna
2
Over View

• Flash Memory
• Introduction,
• Types,
• Principle of operation,
• Applications.
• Nanoparticles Definition,
• Properties,
• Fabrication Methods.
• Flash memory using Nanoparticles.

3
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.

4
Flash Memory- Types

• Two major forms of Flash memory are NAND Flash
  and NOR Flash
• NOR Flash

Cross Section View of single Flash Cell gt 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
5
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.
6
Flash Memory- TypesSelection 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 Flashs
  higher
• density, and high programming and erase
  speeds make it the best choice.

7
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.

8
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 gt5 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.

9
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.

10
Flash Memory - Applications

• Applications include PDAs (personal digital
  assistants), laptop computers, digital audio
  players, digital cameras, mobile phones and
  memory sticks.

11
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.
12
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.

13
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.

14
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. 

15
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.

16
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.

17
Thank You.