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A SEMINAR ON

OVONIC UNIFIED MEMORY

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Contents:

Memory

Limitations of Present Memory Technologies

Emerging Memory Technologies

Ovonic Unified MemoryProgramming of OUM Device

Memory Structure

V-I CharacteristicsChiplet

Advantages

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CLASSIFICATIONS OFMEMORY:

Internal Processor Memory Main Memory

Secondary Storage Memory

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Memory Device Characteristics:

Cost

Access Time and Access Rate

Access Mode- Random and Serial

Alterability- ROMS

Permanence of Storage:

1) Destructive Read-Out

2) Dynamic Volatility3) Volatility

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Limitations of Present Memory

Technologies: Random Access Memory:

Volatile and expensive.

Dynamic RAM:Volatile and difficult to integrate.

Static RAM:

Expensive.

Erasable-Programmable Read Only Memory:

High Power Requirement, Poor Flexibility.

FLASH:

Limited number of Read and Write cycles.

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Challenges :

The ability to retain stored charge for long periodswith zero applied or refreshed power.

High speed of data writes.

Low power consumption.

Large number of write cycles.

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Emerging Memory

Technologies:Supports expansion in 3-dimensional spaces

Fe-RAM:

Data is stored by applying a very low voltage.

Polymer Memory:

Different conductivity states represents bits of information.NROM:

Stacks are used to store charges which writes into memory.

MRAM:

Data is stored by applying magnetic fields.OUM

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HISTORYR.G.NEALE , D.L.NELSON , GORDEN.E.ORIGINALLY

REPORTED PHASE CHANGE MEMORY

IT WAS BASED ON CHALCOGENIDE MATERIALS.THE IMPROVEMENTS IN PHASE CHANGE MEMORYLEAD TO OUM TECHNOLOGY.

THE PRESENT PHASE CHANGE MEMORY IS CALLED

OUM

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OUM

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OUM ATTRIBUTESNON VOLATILE IN NATURE

HIGH DENSITY ENSURES LARGE STORAGE OF DATA

WITHIN A SMALL AREAUSES VERY LOW VOLTAGE AND LOW POWER

FROM A SINGLE SOURCE

REDUCED COST

NON DESTRUCTIVE READ

HIGH SCALABLE MEMORY

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Ovonic Unified Memory:

The OUM is non-volatile memory that uses the reversible

structural phase-change in thin-film material (e.g.,

chalcogenides) as the data storage mechanism.

Electrical energy (heat) is used to convert the material between

crystalline (conductive) and amorphous (resistive) phases and

the resistive property of these phases is

used to represent0s and 1s.

Once programmed, the memory state of the cell is determined

by reading its resistance.

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morp ous aseCrystalline Phase

Electron

Diffraction

Patterns

Material Characteristics

Short-range atomic order

Low free electron density

High activation energy

High resistivity

TEM Images

Long-range atomic order

High free electron density

Low activation energy

Low resistivity

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Programming of OUM Device:

The OUM cell is programmed by application of a current pulse at a voltage

above the switching threshold. The programming pulse drives the memory cell into a high or low resistance

state, depending on current magnitude.

Information stored in the cell is read out by measurement of the cells

resistance.

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OUM ARCHITECTURE

resistance change is very large-more than a factor of 100.

Thermal insulators are also attached to the memory structure in order to avoid data loss due to

destruction of material at high temperatures.

To write data into the cell, the chalcogenide is heated past its melting point and then rapidly cooled

to make it amorphous.

To make it crystalline, it is heated to just below its melting point and held there for approximately

50ns, giving the atoms time to position themselves in their crystal locations.

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INTEGRATION WITH CMOS

y Its one of the main application of oum

yIts under the contract of space vehicle directorate of the air forceresearch laboratory

y Initial goal o this effort was to develop the process necessary toconnect the memory element to CMOS transistors and metal

wiring

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V-I Characteristics:The voltage is applied to

one of the two terminals of

the chalcogenide resistor and

the access transistor

The state of the memory

cell is read using the

difference in I-V

characteristics below VT.

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ABOUT CHALCOGENIDE ALLOY

y CHALCOGENIDE ALSOCALLEDPHASE CHANGEALLOYS

y ITS APART OF OUMS

STRUCTUREy ITS A TERNARY SYSTEMy IT CONSISTS OF GALLIUM

,ANTIMONY & TELLURIUMy CHEMICALLY CALLED

Ge2Sb2Te5

y PRODUCED BY MELTING&SUBSEQUENT MILLING OFRAW MATERIAL

y POWDERS ARE PROCESSEDBY HOT ISOTACTIC PRESSING

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Objectives of CTCV:Chalcogenide technology characterization vehicle

To make the read and write circuits robust with

respect to potential variations in cell electricalcharacteristics;

To test the effect of the memory cell layout on

performance; and

To maximize the amount of useful data obtainedthat could later be used for product design.

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Advantages:Cost/Bit Reduction

Near-Ideal Memory Qualities

Highly Scalable

Logic Process Compatible

Merged Memory Logic

System-on-chip Compatible

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Problems/Concerns of OUM

High voltage are required to write data

High temperature involved in themanufacturing process

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APPLICATIONS

stored as a structural phase impervious to ionizing radiation effects. tolerance of the chalcogenide material A radiation hardened semiconductor technology OUM allows the rewriting ofCD & DVDs

OUM has direct applicationso computers,o cell phones,o graphics-3D rendering,o GPS,o video conferencing,

o multi-media,o Internet networking and interfacing,o digital TV,o telecom,o PDA,o digital voice recorders,o modems,

o DVD,

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Conclusion:

Ovonic unified memory can be randomly addressed.OUM cell can be written 10 trillion times whencompared with conventional flash memory.OUM requires fewer steps in an IC manufacturingprocess resulting in reduced cycle times, fewer defects,

and greater manufacturing flexibility.These properties essentially make OUM an idealcommercial memory.All mechanisms depend on purity and compatibility of the

chalcogenide and surrounding materialsDetailed acceleration and atomic-levelmodels are areas for future work

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REFERENCESy OUM a 180 nm non volatile memory cell element

technology for stand alone and embedded applications Stefan Lai and Tyler Lowrey

y Current status ofPhase change memory Stefan Laiy

Computer Organization V Carl Hamacher, Zvonko GVranesic, Safwat G Zakyy Computer Architecture and Organization - John P Hayes.y Solid State Devices- Ben G Streetman,Sanjay Banerjeey www.intel.com

y www.ovonyx.comy www.baesystems.comy www.aero.orgy IEEE SPECTRUM, March 2003

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THANKS

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QUESTIONS?