nram: high performance, highly reliable emerging memory · nano-ram, carbon nanotube based...

NRAM: High Performance, Highly Reliable Emerging Memory Sheyang Ning1,2, Tomoko Ogura Iwasaki1,

Darlene Viviani2, Henry Huang2, Monte Manning2, Thomas Rueckes2,

Ken Takeuchi1

1Chuo University 2 Nantero Inc. Flash Memory Summit 2016 Santa Clara, CA

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Outline

Flash Memory Summit 2016 Santa Clara, CA

2

l Introduction of NRAM l  Single NRAM cell and cell array measurement setup l  NRAM characteristics

l  DC-IV curve l  Set and reset program characteristics l  Large on/off ratio l  High temperature program l  High endurance

l  Conclusion

Introduction of NRAM


3

DRAM

NRAM

NAND flash

Nano-RAM, Carbon nanotube based resistive memory

Performance

Compare with Conventional Memories


4

DRAM NAND flash NRAM

Performance

Scalability

Non-volatile

= bad = good

Endurance

20 ns pulse [1]

Single cell 15 nm [2]Single cell 1012 [3]1000 years@ 85ºC [2]

[1]. S. Ning et al., IEEE Symp. on VLSI Technology, Jun. 2014, pp. 96–97. [2]. Nantero Presentation for ITRS ERD/ERM, International Technology Roadmap for Semiconductors (ITRS), 2013. [3]. S. Ning et al., IEEE Trans. on Electron Devices (TED), vol. 62, no. 9, pp. 2837–2844, Sept. 2015.

Compare with Emerging Memories


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[1]. S. Ning et al., Solid-State Electronics, vol. 103, pp. 64–72, Jan., 2015. [2]. H. Y. Cheng et al., IEEE Int. Electron Devices Meeting, 2013, pp. 30.6.1–30.6.4. [3]. S. Ning et al., Symp. on VLSI Tech., 2014, pp. 96–97. [4]. S. Ning et al., Ext. Abstr. Solid State Devices and Materials (SSDM), Oct. 2015, pp. 1198-1199.

ReRAM [1] PRAM [2] NRAM [3]

Endurance 108 109 1012

High Current High Low

Resistive switching on

readPhase change

Filament size

Tunneling current

between CNTs

Material Carbon nanotube (CNT)AlxOy Ge2Sb2Te5

Physical Mechanism


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[1]. S. Ning et al., in VLSI Symp. Tech. Dig., Jun. 2014, pp. 120–121. [2]. Nantero presentation, Int. Tech. Roadmap for Semiconductors (ITRS), 2013.

Small distance

R cell 800 kΩ

R cell ≈ 1 GΩ

Large distance

≈

Physical Mechanism


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Set: attraction force

+

−

Reset: repulsive force

Electrical induction

Heat caused phonon vibration

[1]. S. Ning et al., IEEE Trans. on Electron Devices (TED), vol. 62, no. 9, pp. 2837–2844, Sept. 2015.

Outline


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l  Introduction of NRAM l Single NRAM cell and cell array measurement

setup l  NRAM characteristics


l  Conclusion

Single NRAM Cell and Cell Array Test


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[1]. S. Ning et al., IEEE Trans. on Electron Devices (TED), vol. 62, no. 9, pp. 2837–2844, Sept. 2015. [2]. G. Rosendale et al., Proceedings of the European Solid-State Circuits Research Conference (ESSCIRC), Sept. 2010, pp. 478–481.

140 nm NRAM single cell 116 nm, 4 Mbits NRAM cell array

NRAM testchip

SL0BL0

0 V+VSet

WL

+VReset0 VSet voltage

Reset voltage

SLNBLN

NRAM cell

BL SL

……

V d

V g

NRAM cell

Oscilloscope

Outline


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l  Introduction of NRAM l  Single NRAM cell and cell array measurement setup l NRAM characteristics

l DC-IV curve l Set and reset program characteristics l Large on/off ratio l High temperature program l High endurance

l  Conclusion

-3 -2 -1 0 1 2 3

ResetSet

Vd (V)

I d(µA)

100

1

10−2

10−4

10

10−1

10−3

DC-IV Curve


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0 1 2 3Vd (V)

051015

I d(µA) Trigger

voltage

[1]. S. Ning et al., IEEE Symp. on VLSI Technology, Jun. 2014, pp. 96–97.

Current vibration due to long term voltage stress on CNTs

Single cell bi-polar program

Butterfly curve

Same cell, reset curve

-20

0

20

40

Cur

rent

(µA

) Voltage (V)

0.72pJ

Low Program Current


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Single cell DC Icompliance = 5 µA, 30 µA, and 100 µA

Single cell AC Ipeak < 20 µA

[1]. S. Ning et al., IEEE Trans. on Electron Devices (TED), vol. 62, no. 9, pp. 2837–2844, Sept. 2015. [2]. S. Ning et al., IEEE Symp. on VLSI Technology, Jun. 2014, pp. 96–97.

Time (ns)0 50 100 150

Time (ns)0 50 100 150

Reset

Set

-40

-20

0

20

Cur

rent

(µA

) Voltage (V)0.57pJ

Voltage

Cur

rent

(A)

10−8

10−4

10−6

10−2

10−10

10−12

100 µA30 µA5 µA

Set Reset

ResetB

ER(a

.u.) 2

1

0

1 10.8

0.60.40.8

0.6

Reset Characteristic


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l  Cell array measurement, Reset is driven by both voltage and current

[1]. S. Ning et al., Ext. Abstr. Solid State Devices and Materials (SSDM), Oct. 2015, pp. 1198-1199.

WL=0.4 a.u., SL from 0 to 1 a.u.

SL=VprogramBL = 0 V

WL= Vgate

Set and Reset Voltages


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l  Use incremental pulse programing on single cell


0.4

0.6

0.8

1

ResetvoltageSetvoltage(absolutevalue)

Write cycles106 107 108 109 101010111012

Prog

ram

vol

tage

s (a

.u.)

0.2

0.4

0.6

0.8

1

Write cycles106 107 108 109 101010111012

Prog

ram

vol

tage

s (a

.u.)

0%

20%

40%

60%

80%

100%

cell 1cell 2cell 3

Cum

ulat

ive

prog

ram

suc

cess

Reset voltage (V)Cum

ulat

ive

prog

ram

suc

cess

0%

20%

40%

60%

80%

100%cell 1cell 2cell 3

Cum

ulat

ive

prog

ram

suc

cess

Set voltage (V)Cum

ulat

ive

prog

ram

suc

cess

Reset Set

l  Three randomly chosen NRAM cells

Large On/Off Ratio


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l  Single cell measurement

[1]. S. Ning et al., IEEE Symp. on VLSI Technology, Jun. 2014, pp. 96–97.

Possible for multi-level cell (MLC) > 100 times on/off ratio

Read at 1 V

0 50 100 150 200Read cycles

Res

ista

nce

(Ω)

Resistance ≈ 1.3×107 Ω

≈ 105 Ω104

105

106

107

109

108

High Temperature Program


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l  Single cell measurement, stable program voltage at different temperatures


2585125

Reset voltage (a. u.)

Res

et fa

ilure

rate

(a.u

., lo

g sc

ale)

10 0.5

2585125

Set voltage (a.u.)

Set f

ailu

re ra

te (a

.u.,

log

scal

e)

10 0.5

Reset Set


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High Endurance Single cell

[1]. S. Ning et al., IEEE Trans. on Electron Devices (TED), vol. 62, no. 9, pp. 2837–2844, Sept. 2015. [2]. S. Ning et al., Ext. Abstr. Solid State Devices and Materials (SSDM), Oct. 2015, pp. 1198-1199.

Cell array

Write cycles

104

105

106

108R

esis

tanc

e (Ω

)

LRS ≤ 200kΩ

HRS ≥ 1.25MΩ

106 107 108 109 1010 10111012

107

Reset BERSet BER

Write cycles

Prog

ram

BER

(a.u

.)

5

4

3

2

1

0103 104 105 108106 107

High Endurance


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l  Cell array does not wear-out after 108 write cycles

[1]. S. Ning et al., Japanese Journal of Applied Physics (JJAP), vol. 55, no. 4S, 2016. [2]. S. Ning et al., Ext. Abstr. Solid State Devices and Materials (SSDM), Oct. 2015, pp. 1198-1199.

1 2 3 4 5

Set BERSet BER afterSet voltage

SetBL voltage (a.u.)

108 write cyclesafter 103 write cycles

1

0.8

0.6

0.5

0.7

0.9

1

0

0.8

0.6

0.4

0.2SetB

ER (a

.u.)

Verify-set pulses1 2 3 4 5

Reset BERReset BER afterReset voltage

Reset SL voltage (a.u.)

108 write cyclesafter 103 write cycles

1

0.8

0.6

0.7

0.9

1

0

0.8

0.6

0.4

0.2Res

etB

ER (a

.u.)

Verify-reset pulses

Outline


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l  Introduction of NRAM l  Single NRAM cell and cell array measurement setup l  NRAM characteristics


l Conclusion

Conclusion


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l  NRAM is an emerging nonvolatile memory cell which has performance between DRAM and NAND flash.

l  Compared with other emerging nonvolatile memories, NRAM has competitive characteristics, including, lower program current, large on/off ratio, large endurance, high temperature stability and long retention time.

nram: high performance, highly reliable emerging memory · nano-ram, carbon nanotube based...

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