Memory Technologies

Vivek Asthana

13th Mar 2013

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Memory Usage (2025)

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Outline

What is a Memory

Current Memory technologies

• SRAM

• DRAM

• Flash

Upcoming Memory technologies

• MRAM

• PCRAM

• FeRAM

• …

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What is a Memory

Memory cell:

Binary data

storage element • Charge

• Physical property

Memory Array

Control

A<>, CK

Decoder

Read and write circuitry

D<>, Q<>

WL

BL

Current Memory Technologies

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Current Memory Technologies

SRAM

Very fast

Low Density

Volatile

DRAM

Slow

High Density

Volatile

Flash

Very Slow

High Density

Non-volatile

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Memory Application Areas

Control

Datapath

Main

Memory

(DRAM)

Processor

Reg

isters

Second

Level

Cache

(SRAM)

Lev

el-1

Cach

e

Secondary

memory

(Non-

Volatile

Storage:

Disk)

size:

speed:

200 B

1 ns

Register Cache Main Memory Disk Memory

32KB -4MB

4 ns

2GB

60 ns 200 GB

8 ms

SoC

Board

Computer memory Hierarchy

USB Flash Drive

Memory Cards

Flash

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SRAM

8

BL BLB

WL

GND

VDD

blti blfi

0 1

Read Operation

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SRAM

9

BL BLB

WL

GND

VDD

blti blfi

0->1 1->0

Write Operation

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10

DRAM

• Refresh needed every ~100us

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Flash Memory

Floating gate transistor

Read

Upcoming Memory Technologies

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MRAM – Magnetoresistive RAM

Free electrode

Applied magnetic

field

Reference electrode

Metal-Insulator-Metal junction with ferromagnetic electrodes

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PCRAM – Phase Change RAM

Change of chalcogenide material from amorphous to crystalline structure

Applied current

pulse

Amorphous (high R) Crystalline (low R)

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FeRAM – Ferroelectric RAM

Change of polarisation in ferroelectric material on applying E-field

Applied electric

field

Pb Ti/Zr Oxygen

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Other Emerging Memories

• Emerging Ferroelectric memory

• Nano-mechanical memory

• Redox memory

• Mott memory

• Macromolecular memory

• Molecular memory

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ITRS: International Technology Roadmap for Semiconductors

Ref: www.itrs.net

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References

ITRS: www.itrs.net

Searching for the Dream Embedded Memory Sreedhar Natarajan, Shine Chung, Lluis Paris, Ali Keshavarzi; IEEE Solid-State Circuits Magazine, 2009

Introduction to Flash Memory Roberto Bez, Emilio Camerlenghi, Alberto Modelli, Angelo Visconti Proceedings of the IEEE, Volume: 91 , No.4 , Apr. 2003

Emerging non-volatile memory technologies Muller, G.; Nagel, N.; Pinnow, C.-U.; Rohr, T.; European Solid-State Circuits, 2003. ESSCIRC '03. Conference on , 16-18 Sept. 2003

A survey of circuit innovations in ferroelectric random-access memories Sheikholeslami, A.; Gulak, P.G.; Proceedings of the IEEE , Volume: 88 , Issue: 5 , May 2000

“Prozessintegration und Bauelementearchitekturen (LEB)”, lecture Notes, Prof. Ryssel