Transcript
Page 1: Data retention extraction methodology for perpendicular

Data retention extraction

methodology for perpendicular

STT-MRAM

Luc Tillie1,2, E. Nowak1, R. C. Sousa2, M.-C. Cyrille1, B. Delaet1,

T. Magis1,A. Persico1, J. Langer3 ,B. Ocker3 , I-L Prejbeanu2 and L. Perniola1

1CEA-LETI, Minatec Campus, Grenoble, France, email: [email protected], Univ. Grenoble Alpes / CEA / CNRS, Grenoble, France

3Singulus Technologies AG, Kahl am Main, Germany

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IntroductionIn Perp STT-MRAM, retention time 𝝉 at a given temperature is

related to the Thermal Stability factor 𝚫 [Feng et al. JAP 95] :

Application Retention

Time 𝝉Bit Error

Rate (N=1)

Thermal

Stability 𝚫 [𝐀𝐛𝐓]

Cache 10 ms 10βˆ’9 36 @85Β°C

Soldering ~9 min 10βˆ’5 38 @260Β°C

Storage (SCM) 1 month 10βˆ’9 56 @85Β°C

Automotive 10 years 10βˆ’5 51 @150Β°C

Consumer 10 years 10βˆ’5 51 @85Β°C

𝝉 = π‰πŸŽπ’†π’™π’‘(𝚫)

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Each application has a different temperature and retention target

𝚫 = π₯𝐨𝐠 βˆ’π‰πŸŽπ‘΅π‰

π’π’π’ˆ 𝟏 βˆ’ 𝑩𝑬𝑹

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Introduction

5% error ~ factor 10 in retention time

Thermal Stability must be extracted with high precision

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-5% +5%

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Outline

β€’ Perp-STT description

β€’ Direct retention time measurement

β€’ Delta extraction methods

β€’ Accuracy and precision

β€’ Delta dependence

β€’ Conclusion

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MAD Leti test chipStandard Foundry Wafer

CMOS 130nm + 4 Cu Metal

TiN Bottom Electrode

Definition

Perpendicular magnetic stack

deposition by Singulus

Ta/FeCoB/MgO/FeCoB/Ta/Co

/5x[Pt/Co]/Ru/Co/13x[Pt/Co]/Pt/Ta

Ø100nm Mesa Patterning

Encapsulation and CMP

M5

CMP touch (RMS ~ 2Γ…) TiN

AlCu M5

Cu M4

Fixed Layer

Oxide Layer

Free Layer

MAD Leti test chip : Multi back-end

memory platform

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Resistance Hysteresis Cycle

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Switching by current polarity

Parallel state : Low Resistance State

Anti-Parallel state : High Resistance State

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Resistance Distribution

7

4kbit matrix shows fully separated distributions

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~πŸ•(πˆπ‘Ήπ’‚π’‘ + πˆπ‘Ήπ’‘)

𝑹𝒑 [𝛀] 𝑹𝒂𝒑[𝛀]

Average 825 980

𝜎 9.53 11.37

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TMR Temperature dependence

𝑻𝑴𝑹 =𝑹𝒂𝒑 βˆ’ 𝑹𝒑

𝑹𝒑

The resistance window stays stable up to 235Β°C

Good state differentiation

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Sharrock’s Model

Sharrock’s model [Sharrock, IEE Trans. On Magnetism, 35 ,1999] :

Two stable states, Parallel (P) and Anti-Parallel (AP), separated

by an energy barrier πœŸπ‘¬

Parallel

StateAnti-Parallel

State

πœŸπ‘¬π‘· 𝒕𝒐 π‘¨π‘·πœŸπ‘¬π‘¨π‘· 𝒕𝒐 𝑷

𝜟~πœŸπ‘¬

π’Œπ’ƒπ‘»

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Outline

β€’ Perp-STT description

β€’ Direct retention time measurement

– On single devices

– On matrices

β€’ Delta extraction methods

β€’ Accuracy and precision

β€’ Delta dependence

β€’ Conclusion

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Switching Time Probability (STP) on single device

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Voltage pulse AP state P state

Objective : How much time before it switches thermally?

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Switching Time Probability (STP) on single device

𝑷 𝝉 = 𝟏 βˆ’ 𝒆𝒙𝒑𝝉

π‰πŸŽπ’†π’™π’‘ 𝚫

+ Simple Method

+ Exact value of Retention time

- Impractical for long retention time

- Extrapolation for low temperature

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1000 events

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Switching Time Probability (STP) on matrix

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+ Simple Method

+ Exact value of Retention time

- Impractical for long retention time

- Extrapolation for low temperature

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Outline

β€’ Perp-STT description

β€’ Direct retention time measurement

β€’ Delta extraction methods

1. Switching Current Density

2. Switching Pulse Width

3. Switching Field Density

β€’ Accuracy and precision

β€’ Delta dependence

β€’ Conclusion

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(1/3) Switching Current Density (SCD)

𝑺π‘ͺ𝑫 𝑰 =𝚫

πˆπœπ‰ 𝚫𝐭𝐩𝐞𝐱𝐩 βˆ’

𝐭𝐩

𝝉(𝚫)[Huai et al, JAP 98, 2005]

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T Ξ” [kbT] Ic [mA]

πŸπŸ“Β°π‚

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(1/3) Switching Current Density (SCD)

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T Ξ” [kbT] Ic [mA]

πŸπŸ“Β°π‚ πŸ‘πŸ• 𝟐. πŸ’

𝑺π‘ͺ𝑫 𝑰 =𝚫

πˆπœπ‰ 𝚫𝐭𝐩𝐞𝐱𝐩 βˆ’

𝐭𝐩

𝝉(𝚫)[Huai et al, JAP 98, 2005]

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(1/3) Switching Current Density (SCD)

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T Ξ” [kbT] Ic [mA]

πŸπŸ“Β°π‚ πŸ‘πŸ• 𝟐. πŸ’

πŸπŸπŸ“Β°π‚ πŸπŸ– 𝟐. 𝟐

𝑺π‘ͺ𝑫 𝑰 =𝚫

πˆπœπ‰ 𝚫𝐭𝐩𝐞𝐱𝐩 βˆ’

𝐭𝐩

𝝉(𝚫)[Huai et al, JAP 98, 2005]

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(1/3) Switching Current Density (SCD)

T Ξ” [kbT] Ic [mA]

πŸπŸ“Β°π‚ πŸ‘πŸ• 𝟐. πŸ’

πŸπŸπŸ“Β°π‚ πŸπŸ– 𝟐. 𝟐

πŸπŸπŸ“Β°π‚ πŸπŸ– 𝟏. πŸ–

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+ Fast Method

+ Standard measurement

𝑺π‘ͺ𝑫 𝑰 =𝚫

πˆπœπ‰ 𝚫𝐭𝐩𝐞𝐱𝐩 βˆ’

𝐭𝐩

𝝉(𝚫)[Huai et al, JAP 98, 2005]

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(2/3) Switching Pulse Width (SPW)

𝑺𝑷𝑾 𝒕𝒑 = 𝑰𝒄 𝟏 βˆ’πŸ

πš«π’π’π’ˆ

𝒕𝒑

π‰πŸŽ

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In thermally activated regime :

[Koch et al, Phys. Rev. Lett. 92, 2004]

T Ξ” [kbT] Ic [mA]

πŸ–πŸ“Β°π‚

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(2/3) Switching Pulse Width (SPW)

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[Koch et al, Phys. Rev. Lett. 92, 2004]

T Ξ” [kbT] Ic [mA]

πŸ–πŸ“Β°π‚ πŸ•πŸ’ πŸ‘. πŸ“πŸ•

𝑺𝑷𝑾 𝒕𝒑 = 𝑰𝒄 𝟏 βˆ’πŸ

πš«π’π’π’ˆ

𝒕𝒑

π‰πŸŽIn thermally activated regime :

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(2/3) Switching Pulse Width (SPW)

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[Koch et al, Phys. Rev. Lett. 92, 2004]

T Ξ” [kbT] Ic [mA]

πŸ–πŸ“Β°π‚ πŸ•πŸ’ πŸ‘. πŸ“πŸ•

πŸπŸ•πŸ“Β°π‚ πŸ“πŸ 𝟐. πŸ–πŸ

𝑺𝑷𝑾 𝒕𝒑 = 𝑰𝒄 𝟏 βˆ’πŸ

πš«π’π’π’ˆ

𝒕𝒑

π‰πŸŽIn thermally activated regime :

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(2/3) Switching Pulse Width (SPW)

T Ξ” [kbT] Ic [mA]

πŸ–πŸ“Β°π‚ πŸ•πŸ’ πŸ‘. πŸ“πŸ•

πŸπŸ•πŸ“Β°π‚ πŸ“πŸ 𝟐. πŸ–πŸ

πŸπŸ‘πŸ“Β°π‚ πŸ’πŸ– 𝟐. πŸ‘πŸ–

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+ Fast Method

+ Requires to be in thermally activated regime

- Degradation due to long pulses

[Koch et al, Phys. Rev. Lett. 92, 2004]

𝑺𝑷𝑾 𝒕𝒑 = 𝑰𝒄 𝟏 βˆ’πŸ

πš«π’π’π’ˆ

𝒕𝒑

π‰πŸŽIn thermally activated regime :

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(3/3) Switching Field Density (SFD)

𝑺𝑭𝑫 𝑯 =𝟏

π‘Ήπ‘―π‰πŸŽπ’†π’™π’‘ βˆ’

π‘―π’Œ

πŸπ‰πŸŽπ‘Ήπ‘―

𝝅

πœŸπ’†π’“π’‡π’„ 𝜟 𝟏 βˆ’

𝑯

π‘―π’Œπ’†π’™π’‘ βˆ’πœŸ 𝟏 βˆ’

𝑯

π‘―π’Œ

𝟐

[Feng et al. J.A.P 95, 2004]

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T Ξ” [kbT] Hk [mT]

πŸ‘πŸŽΒ°π‘ͺ

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(3/3) Switching Field Density (SFD)

𝑺𝑭𝑫 𝑯 =𝟏

π‘Ήπ‘―π‰πŸŽπ’†π’™π’‘ βˆ’

π‘―π’Œ

πŸπ‰πŸŽπ‘Ήπ‘―

𝝅

πš«π’†π’“π’‡π’„ 𝚫 𝟏 βˆ’

𝑯

π‘―π’Œπ’†π’™π’‘ βˆ’πš« 𝟏 βˆ’

𝐇

𝐇𝐀

𝟐

[Feng et al. J.A.P 95, 2004]

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T Ξ” [kbT] Hk [mT]

πŸ‘πŸŽΒ°π‘ͺ πŸ”πŸ— 𝟎. πŸπŸ–

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(3/3) Switching Field Density (SFD)

𝑺𝑭𝑫 𝑯 =𝟏

π‘Ήπ‘―π‰πŸŽπ’†π’™π’‘ βˆ’

π‘―π’Œ

πŸπ‰πŸŽπ‘Ήπ‘―

𝝅

πš«π’†π’“π’‡π’„ 𝚫 𝟏 βˆ’

𝑯

π‘―π’Œπ’†π’™π’‘ βˆ’πš« 𝟏 βˆ’

𝐇

𝐇𝐀

𝟐

[Feng et al. J.A.P 95, 2004]

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T Ξ” [kbT] Hk [mT]

πŸ‘πŸŽΒ°π‘ͺ πŸ”πŸ— 𝟎. πŸπŸ–

πŸ“πŸŽΒ°π‘ͺ πŸ’πŸ‘ 𝟎. πŸπŸ—

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(3/3) Switching Field Density (SFD)

𝑺𝑭𝑫 𝑯 =𝟏

π‘Ήπ‘―π‰πŸŽπ’†π’™π’‘ βˆ’

π‘―π’Œ

πŸπ‰πŸŽπ‘Ήπ‘―

𝝅

πš«π’†π’“π’‡π’„ 𝚫 𝟏 βˆ’

𝑯

π‘―π’Œπ’†π’™π’‘ βˆ’πš« 𝟏 βˆ’

𝐇

𝐇𝐀

𝟐

[Feng et al. J.A.P 95, 2004]

T Ξ” [kbT] Hk [mT]

πŸ‘πŸŽΒ°π‘ͺ πŸ”πŸ— 𝟎. πŸπŸ–

πŸ“πŸŽΒ°π‘ͺ πŸ’πŸ‘ 𝟎. πŸπŸ—

πŸ•πŸŽΒ°π‘ͺ πŸ‘πŸ 𝟎. 𝟐𝟏

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+ No degradation (only for reading)

- Involves magnetic field (Setup compatibility)

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Outline

β€’ Perp-STT description

β€’ Direct retention time measurement

β€’ Delta extraction methods

β€’ Accuracy and precision

β€’ Delta dependence

β€’ Conclusion

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Precision Measurement

SCD

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Low cycle number induces optimistic 𝚫 extraction

and high variability

High number of cycles needed

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Measurement parameters

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Two main measurement conditions :

- Number of significant points for curve fitting

- Number of events measured

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Delta – accuracy and precision

Delta extraction requires :

At least 5 points over the distribution

A high number of events measured

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Summary Table

Switching

Mechanism

Significant

points #Events #

Step

speedComments

Accuracy Precision

5% 1% 5% 1%

STPRetention

(thermal)- - β‰₯10 β‰₯20

1s –

1 yr

+ Simple method

+ Most precise

- Impractical for long retention time

SCD

Current

pulse

(amplitude)β‰₯3 β‰₯6 β‰₯200 β‰₯ πŸπŸŽπŸ’ ns

+ Fast method

+ Typically no degradation

SPW

Current

pulse width

(length)

β‰₯3

(per

pts)

β‰₯5

(per

pts)

β‰₯10 β‰₯100ns –

ms

+ Fast method

- Requires to be in thermally

activated regime

- Degradation due to long pulses

SFDMagnetic

Fieldβ‰₯6 - β‰₯300 β‰₯ πŸπŸŽπŸ“

Β΅s –

ms

+ No degredation

- Involves magnetic field

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Outline

β€’ Perp-STT description

β€’ Direct retention time measurement

β€’ Delta extraction methods

β€’ Accuracy and precision

β€’ Delta dependence

– Diameter dependence

– Temperature dependence

β€’ Conclusion

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Stability dependence with diameter

60Β°C 150Β°C 210Β°C

SCD

SPW

Non-quadratic behavior

Coherent with a constant sub-volume nucleation.

[Sun et al, Phys. Rev. B 84’]

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Stability dependence with temperature

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STP at high temperature : Reference values

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Stability dependence with temperature

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SCD on all range : Coherent with reference values

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Stability dependence with temperature

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SPW Measurements : Coherent at high temperature,

deviates from SCD below 100Β°C

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Stability dependence with temperature

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SFD at low temperature : noisy but coherent with SCD

Stability dependence with temperature

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Thermal stability modeling

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- MacroSpin and Domain-Wall models coherent at high temperature

- MacroSpin deviates below 100Β°C

- Domain-Wall close to SCD on all range

Up

Down

Uniform Magnetic Reversal

Β« MacroSpin Β»

Domain-Wall Propagation

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Application Retention

Time 𝝉Bit Error

Rate (N=1)

Thermal Stability 𝚫[𝐀𝐛𝐓]

Cache 10 ms 10βˆ’9 36 @85Β°C

Soldering ~9 min 10βˆ’5 38 @260Β°C

Storage (SCM) 1 month 10βˆ’9 56 @85Β°C

Automotive 10 years 10βˆ’5 51 @150Β°C

Consumer 10 years 10βˆ’5 51 @85Β°C

Stability dependence with temperature

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Conclusion

β€’ 4 retention time methods have been compared in

diameter and temperature

β€’ Accuracy and precision study showed the need of

measuring enough events with a minimum number of

significant points

β€’ The 4 extractions gave similar results except the SPW

which deviates significantly below 100Β°C

β€’ Extrapolating from high temperature to a certain value

has to be done with care

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Thank you for your attention

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[email protected]


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