data retention extraction methodology for perpendicular
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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: luc.tillie@cea.fr2SPINTEC, Univ. Grenoble Alpes / CEA / CNRS, Grenoble, France
3Singulus Technologies AG, Kahl am Main, Germany
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IntroductionIn Perp STT-MRAM, retention time π at a given temperature is
related to the Thermal Stability factor π« [Feng et al. JAP 95] :
Application Retention
Time πBit Error
Rate (N=1)
Thermal
Stability π« [π€ππ]
Cache 10 ms 10β9 36 @85Β°C
Soldering ~9 min 10β5 38 @260Β°C
Storage (SCM) 1 month 10β9 56 @85Β°C
Automotive 10 years 10β5 51 @150Β°C
Consumer 10 years 10β5 51 @85Β°C
π = πππππ(π«)
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Each application has a different temperature and retention target
π« = π₯π¨π βπππ΅π
πππ π β π©π¬πΉ
Introduction
5% error ~ factor 10 in retention time
Thermal Stability must be extracted with high precision
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-5% +5%
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
Γ100nm 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
Resistance Distribution
7
4kbit matrix shows fully separated distributions
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~π(ππΉππ + ππΉπ)
πΉπ [π] πΉππ[π]
Average 825 980
π 9.53 11.37
TMR Temperature dependence
π»π΄πΉ =πΉππ β πΉπ
πΉπ
The resistance window stays stable up to 235Β°C
Good state differentiation
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Sharrockβs Model
Sharrockβs model [Sharrock, IEE Trans. On Magnetism, 35 ,1999] :
Two stable states, Parallel (P) and Anti-Parallel (AP), separated
by an energy barrier ππ¬
Parallel
StateAnti-Parallel
State
ππ¬π· ππ π¨π·ππ¬π¨π· ππ π·
π~ππ¬
πππ»
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Outline
β’ Perp-STT description
β’ Direct retention time measurement
β On single devices
β 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?
Switching Time Probability (STP) on single device
π· π = π β ππππ
πππππ π«
+ Simple Method
+ Exact value of Retention time
- Impractical for long retention time
- Extrapolation for low temperature
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1000 events
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
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)
πΊπͺπ« π° =π«
πππ π«ππ©ππ±π© β
ππ©
π(π«)[Huai et al, JAP 98, 2005]
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T Ξ [kbT] Ic [mA]
ππΒ°π
(1/3) Switching Current Density (SCD)
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T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. π
πΊπͺπ« π° =π«
πππ π«ππ©ππ±π© β
ππ©
π(π«)[Huai et al, JAP 98, 2005]
(1/3) Switching Current Density (SCD)
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T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. π
πππΒ°π ππ π. π
πΊπͺπ« π° =π«
πππ π«ππ©ππ±π© β
ππ©
π(π«)[Huai et al, JAP 98, 2005]
(1/3) Switching Current Density (SCD)
T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. π
πππΒ°π ππ π. π
πππΒ°π ππ π. π
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+ Fast Method
+ Standard measurement
πΊπͺπ« π° =π«
πππ π«ππ©ππ±π© β
ππ©
π(π«)[Huai et al, JAP 98, 2005]
(2/3) Switching Pulse Width (SPW)
πΊπ·πΎ ππ = π°π π βπ
π«πππ
ππ
ππ
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In thermally activated regime :
[Koch et al, Phys. Rev. Lett. 92, 2004]
T Ξ [kbT] Ic [mA]
ππΒ°π
(2/3) Switching Pulse Width (SPW)
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[Koch et al, Phys. Rev. Lett. 92, 2004]
T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. ππ
πΊπ·πΎ ππ = π°π π βπ
π«πππ
ππ
ππIn thermally activated regime :
(2/3) Switching Pulse Width (SPW)
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[Koch et al, Phys. Rev. Lett. 92, 2004]
T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. ππ
πππΒ°π ππ π. ππ
πΊπ·πΎ ππ = π°π π βπ
π«πππ
ππ
ππIn thermally activated regime :
(2/3) Switching Pulse Width (SPW)
T Ξ [kbT] Ic [mA]
ππΒ°π ππ π. ππ
πππΒ°π ππ π. ππ
πππΒ°π ππ π. ππ
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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]
πΊπ·πΎ ππ = π°π π βπ
π«πππ
ππ
ππIn thermally activated regime :
(3/3) Switching Field Density (SFD)
πΊππ« π― =π
πΉπ―πππππ β
π―π
ππππΉπ―
π
πππππ π π β
π―
π―ππππ βπ π β
π―
π―π
π
[Feng et al. J.A.P 95, 2004]
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T Ξ [kbT] Hk [mT]
ππΒ°πͺ
(3/3) Switching Field Density (SFD)
πΊππ« π― =π
πΉπ―πππππ β
π―π
ππππΉπ―
π
π«ππππ π« π β
π―
π―ππππ βπ« π β
π
ππ€
π
[Feng et al. J.A.P 95, 2004]
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T Ξ [kbT] Hk [mT]
ππΒ°πͺ ππ π. ππ
(3/3) Switching Field Density (SFD)
πΊππ« π― =π
πΉπ―πππππ β
π―π
ππππΉπ―
π
π«ππππ π« π β
π―
π―ππππ βπ« π β
π
ππ€
π
[Feng et al. J.A.P 95, 2004]
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T Ξ [kbT] Hk [mT]
ππΒ°πͺ ππ π. ππ
ππΒ°πͺ ππ π. ππ
(3/3) Switching Field Density (SFD)
πΊππ« π― =π
πΉπ―πππππ β
π―π
ππππΉπ―
π
π«ππππ π« π β
π―
π―ππππ βπ« π β
π
ππ€
π
[Feng et al. J.A.P 95, 2004]
T Ξ [kbT] Hk [mT]
ππΒ°πͺ ππ π. ππ
ππΒ°πͺ ππ π. ππ
ππΒ°πͺ ππ π. ππ
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+ No degradation (only for reading)
- Involves magnetic field (Setup compatibility)
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 π« extraction
and high variability
High number of cycles needed
Measurement parameters
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Two main measurement conditions :
- Number of significant points for curve fitting
- Number of events measured
Delta β 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 β
1 yr
+ Simple method
+ Most precise
- Impractical for long retention time
SCD
Current
pulse
(amplitude)β₯3 β₯6 β₯200 β₯ πππ ns
+ Fast method
+ Typically no degradation
SPW
Current
pulse width
(length)
β₯3
(per
pts)
β₯5
(per
pts)
β₯10 β₯100ns β
ms
+ Fast method
- Requires to be in thermally
activated regime
- Degradation due to long pulses
SFDMagnetic
Fieldβ₯6 - β₯300 β₯ πππ
Β΅s β
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
β Diameter dependence
β 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 84β]
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Stability dependence with temperature
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STP at high temperature : Reference values
Stability dependence with temperature
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SCD on all range : Coherent with reference values
Stability dependence with temperature
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SPW Measurements : Coherent at high temperature,
deviates from SCD below 100Β°C
Stability dependence with temperature
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SFD at low temperature : noisy but coherent with SCD
Stability dependence with temperature
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 πBit Error
Rate (N=1)
Thermal Stability π«[π€ππ]
Cache 10 ms 10β9 36 @85Β°C
Soldering ~9 min 10β5 38 @260Β°C
Storage (SCM) 1 month 10β9 56 @85Β°C
Automotive 10 years 10β5 51 @150Β°C
Consumer 10 years 10β5 51 @85Β°C
Stability dependence with temperature
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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Luc.tillie@cea.fr
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