ECG 453653 Introduction to Nanotechnology Topic Nanoparticles based

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 100 nm 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.