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Electrothermal Model-based Analysis for Novel Phase-Change
Memory Structure with Decoupled Program and Read Paths
Date : 2021. 03. 31
Inhyuk Choi
Neuromorphic Materials and Devices Laboratory (NMDL)
Department of Materials and Science and Engineering, Seoul National University
1
Outline 2
Introductionβ’ Phase Change Memory (PCM)β’ Issues on conventional PCM structure
Novel PCM structureβ’ Conceptβ’ Electrothermal model: Joule heating β’ Electrothermal model: Joule heating + Thermoelectric effectsβ’ Possibility of cyclic endurance enhancement
Summary
Outline 3
Introductionβ’ Phase Change Memory (PCM)β’ Issues on conventional PCM structure
Novel PCM structureβ’ Conceptβ’ Electrothermal model: Joule heating β’ Electrothermal model: Joule heating + Thermoelectric effectsβ’ Possibility of cyclic endurance enhancement
Summary
Introduction 4
Storage Class Memory Neuromorphic Computing
A. Lotnyk et al., Nanoscale Adv., (2019)
Q. Z. Wan et al., Adv. Mater. Technol. Rev., (2019)
Introduction 5
Non-Volatile
Memory
Key properties Endurance
Power consumption
Write & Read Speed
PRAM RRAM MRAM
S. Bhatti et al., Materials Today, (2017)
G. W. Burr et al., Adv. Physics X, (2017)
Motivation 6
Issues in conventional PCM structures: 1) ππππππππππππ π―π―π―π― ππππππππ Trade-off
Reduction of RESET power by increasing πΉπΉππππ Contact / Cell size reduction increases both π π π‘π‘π‘ & π π ππππ Material doping increases both πππ‘π‘π‘ & ππππππ (by W-F Law)
However, for fast readout (< ππππππππ),
πΉπΉπΊπΊπΊπΊπΊπΊ < ~ππππππππππ is required!Boniardi, M. et al., IEDM, (2014)
Lacaita, A. L. et al., Microelectron. Eng., (2013)
7Motivation
β’ Stuck SET: Gradual elemental segregation
β’ Stuck RESET: Void formation near the contact
Burr, G. W. et al., J. Vac. Sci. Technol., (2010) Yang, T-Y. et al., Appl. Phys. Lett., (2009)
High electric fields in phase change material is one of the main driving forces.
Due to integrated program and read paths
Issues in conventional PCM structures: 2) Cyclic Endurance Failure
Outline 8
Introductionβ’ Phase Change Memory (PCM)β’ Issues on conventional PCM structure
Novel PCM structureβ’ Conceptβ’ Electrothermal model: Joule heating β’ Electrothermal model: Joule heating + Thermoelectric effectsβ’ Possibility of cyclic endurance enhancement
Summary
Novel PCM structure 9
Separated program and read paths.
Breaks out of the π°π°πΉπΉπΊπΊπΊπΊπΊπΊπΊπΊ vs πΉπΉπΊπΊπΊπΊπΊπΊ trade-off.
Enhancement of the cyclic endurance.: Significant reduction of the electromigration.
Thermoelectric effects can be maximized.: Reduction of the power consumption.
Concept
Model-based Analysis 10
Geometry Equations
π»π» οΏ½ π½π½ = βπ»π» οΏ½ ππ π»π»π»π» = 0
πππΆπΆππππππππππ β π»π» οΏ½ (π π π»π»ππ) =
π½π½ οΏ½ π½π½ππ
2D Axisymmetric analysis
The heater needs to be stable at high temperatures (e.g. Refractory metals)
Comparison of π°π°πΉπΉπΊπΊπΊπΊπΊπΊπΊπΊ ππππ πΉπΉπΊπΊπΊπΊπΊπΊ curve with reducing βrβ of heating materials
Electrothermal model: Joule Heating effects
π½π½: Current densityππ: Electrical Cond.π»π»: Electric potentialππ: Mass densityπΆπΆππ: Heat capacityπ π : Thermal Cond.
Results 11
(πΌπΌπ π π π π π π π π π : when π π π π π π π π π π π π /π π π π π π π π β 103)
Consistent πΉπΉπΊπΊπΊπΊπΊπΊ while reducing π°π°πΉπΉπΊπΊπΊπΊπΊπΊπΊπΊ.: Cell scaling no longer affects read speed.
Energy efficiency should be improved.: Thermoelectric effects for additional heat.
Thermoelectric effects- Seebeck + Peltier + Thomson effect.- Conversion between heat and electricity.
Comparison of ππππππππππππ π―π―π―π― ππππππππ Trend
12Model-based Analysis Electrothermal model: Joule heating + Thermoelectric effects
Geometry Equations
π»π» οΏ½ π½π½ = βπ»π» οΏ½ ππ π»π»π»π» + πππ»π»ππ = 0
πππΆπΆππππππππππ
β π»π» οΏ½ π π π»π»ππ =π½π½ οΏ½ π½π½ππ
β πππ½π½ οΏ½ βππ β πππ½π½ οΏ½ππππππππ
π»π»ππ
Assumption: Two heater materials
π½π½: Current densityππ: Electrical Cond.
πΆπΆππ: Heat capacityπ π : Thermal Cond.
π»π»: Electric potentialππ: Mass density
Results 13
R-I curve change according to the βSβ value
< Seebeck effect only > < Peltier effect only >
14
Temperature distribution
Joule Heating(JH)
JH + PH(βπΊπΊ = ππππππ)
JH + PC(βπΊπΊ = βππππππ)
(Under positive polarity)
πΊπΊπ¨π¨ > ππ, πΊπΊπ©π© < ππ Heaters become resistive by
the Seebeck effect.
βπΊπΊ = πΊπΊπ¨π¨ β πΊπΊπ©π© > ππ βππ > 0: Peltier Heating(PH). βππ < 0: Peltier Cooling(PC).
Reduction of ππππππππππππ
(Under the same voltage)
Results
πππ¦π¦π¦π¦π¦π¦ = πππππππππππππ¦π¦π¦π¦π¦π¦ = ππππππππππ πππ¦π¦π¦π¦π¦π¦ = ππππππππππ
15ResultsComparison of ππππππππππππ π―π―π―π― ππππππππ Trend, Power consumption
101 102 10310-1
100
101
102
R(I)
/R(I=
200Β΅
A)
IRESET [Β΅A]
Confined cell Confined cell (+TE) Novel cell Novel cell(+TE) Ref. 1 Ref. 2
r = 4nm, πΊπΊππ= 100 β 500
Discussions 16
Possibility of cyclic endurance enhancement
Summary 17
Based on the electrothermal model, the novel PCM structure with the separated program and read paths no longer has a ππππππππππππ π―π―π―π― ππππππππ trade-off of the existing PCM structures.
Energy efficiency can be greatly improved by maximizing the thermoelectric effects in the novel PCM structure.
Cyclic endurance can be enhanced in the novel PCM structure since the electromigration in the phase change material is expected to be significantly reduced during the program.