Presented by Anas Mazady, Cameron Fulton, Nicholas Williams

University of Connecticut

Department of Electrical and Computer Engineering

Thursday, April 28, 2011

Optimization of geometric properties concerning phase-change memory

(PCM) mushroom cells

Fast memory Believed capable

of replacing NAND flash

Capable of multi-bit storage Essential due to low

packing density

Significance

RESET (0) by heating PCM above melting point and quenching

SET (1) by heating PCM above crystallization temperature and below melting temperature

READ by applying very small voltage pulse and measuring current draw (V=IR) Large current in crystalline phase, smaller current in amorphous phase

General Operation

OXIDETiN

GST

TiN

Vpulse

Aluminum

Aluminum

θ

5 nm

40 nm

30 nm

20 nm

100 nm

25 nm

NOTE: Geometry is not drawn to scale

7 nm

Al High electrical conductivity Fabrication

SiO2 Poor thermal conductor Insulator

TiN Low thermal conductivity Adequate electrical conductivity Heater/heat sink

Materials

Ge2Sb2Te5 (GST) High crystallization temperature Low melting point Adequate Data retention (~10 years at 80°C-

90°C)

Phase-change material

CMOS compatible fabrication techniques Minimal thermal crosstalk (65 nm nodes) Multi-bit storage possible

GST

0° to 90° Large active region smaller active region High peak RESET current lower current

26% reduction High peak temperature lower peak

temperature Larger GST area at 90°

Heat diffuses over larger area Oxide confines heat

Variation of theta angle

4 nm to 20 nm Constant theta angle Constant 1.0 ns voltage pulse Increase in active region size

Must amorphize entire contact area Reduction in voltage pulse

Reduction in thermal resistance (oxide) 10.5 times more RESET current

Variation of heater contact

OXIDETiN

TiN

Vpulse

Aluminum

Aluminum

5 nm

40 nm

30 nm

20 nm

100 nm

25 nm

NOTE: Geometry is not drawn to scale

GST

7 nm

Lateral cross-section: 78.54 nm2

GST thickness: 20 nm Erase time: 1.0 ns Programming voltage: 0.512 V Read voltage: 150 mV Low read current: 3.25 nA High read current:1.04 µA RESET current density: 133.7 MA/cm2

Small contact area

Specifications

Low (0) resistance = 46.2 MΩ High (1) resistance = 144.2 kΩ ~320 times less resistance 2-3 orders of magnitude Large range

Multi-bit storage

Resistance Variation

READ operation

0.00 0.25 0.50 0.75 1.00 1.25 1.500

1

2

3

4

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

I

Cur

rent

(nA

)

Time (ns)

Rea

d V

olta

ge (

V) V

IPEAK = 3.25 nAR = 46.2 MΩ

IPEAK = 1.04 µAR = 144.2 kΩ

0.00 0.25 0.50 0.75 1.00 1.25 1.500.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

I

Cur

rent

(uA

)

Time (ns)

Rea

d V

olta

ge (

V) V

QUESTIONS or COMMENTS?