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24 August 2004

Magnetic Random Access Memory (MRAM)Magnetic Random Access Memory (MRAM)

Jimmy ZhuABB Professor in Engineering

Department of Electrical and Computer EngineeringCarnegie Mellon University

J. Zhu, 18-200 Lecture, Fall 2004 2

Computer SystemComputer System

DRAM

SRAM

Disk Drive

CPU

SRAM

TLB

SRAM

DRAM

L1 Cache

L2 Cache

Main Memory

Archival Memory

Volatile Memory

Non-Volatile Memory

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J. Zhu, 18-200 Lecture, Fall 2004 3

Static RAM (SRAM)

6-Transistor CMOS SRAM Access time: < 1 ns

Expensive:

Fast:

Cache Memory

$100 / MByte

Low Density:

>120 F2

F -- minimum fabrication feature size

= 10-9 second

J. Zhu, 18-200 Lecture, Fall 2004 4

Field Effect Transistor (FET)

symbol

D

S

G Source

Gate

Drain n+n+ p

n-channel FET

Conducting metal plate

Insulating oxide layer

Semiconductor

Conducting ground

MOSFET: Metal-Oxide-semiconductor-FET

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J. Zhu, 18-200 Lecture, Fall 2004 5

electron with charge e

http://www.pbs.org/transistor/science/info/transmodern.html

TGG VV >

Source

Gate

Drain

n+n+

++ + + + + + +

DI

p

DDV

GGV

n-channel FET

S D

G

Active condition:

TGS VV >i.e.

S

D

GDR

DDV

Drain current will be a function of gate voltage.

Di

How a FET Works: Transistor On

J. Zhu, 18-200 Lecture, Fall 2004 6

How a FET Works: Transistor Off

Source

Gate

Drain n+n+ p

electron with charge e

No current

S

DG

DDD VV =

DR

DDV

TGS VV