NOC Symposium, May 9th 2012, Lyngby, Denmark Modeling and Power Evaluation of On-Chip Router Components in Spintronics Pierre Schamberger & Zhonghai Lu Xianyang Jiang Meikang Qui Dept. of Electronics Systems, School for ICT Institute of Microelectronics and IT Dept. of ECE KTH Royal Institute of Technology, Sweden Wuhan University, China University of Kentucky, USA
Agenda Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • Spintronics o Motivation o Overview • Magnetic Tunnel Junction (MTJ) o Theory o Research status o Reading and Writing MTJs o Switching energy o Simulation model • Results for on-chip routers components o Buffers o Crossbars Kungliga Tekniska Högskolan, 2 2012-05-09 Stockholm, Sweden
Spintronics & MTJ Magnetic Tunnel Junction
Spintronics ? Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • Motivations: o CMOS drawbacks A new • Static current technology • High dynamic current is required o Routers become essentials • Power consuming • Spintronics: o Tunneling effect o Spin and magnetic moment of the electron vs charge o Potential applications : Memory, Logic elements, … Kungliga Tekniska Högskolan, 4 2012-05-09 Stockholm, Sweden
Magnetic Tunnel Junction (MTJ) Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • Sandwich structure: o Ferromagnetic/Insulator/Ferromagnetic • 2 States: (1) (0) o Parallel & Anti-parallel (resp. 1 & 0) o 2 Resistances (High & Low) • Main parameter: o Tunnel Magnetoresistance Ratio (TMR) 𝑼𝑵𝑺 = 𝑺 AP − 𝑺𝑸 𝑺 𝑸 • Voltage dependency on the resistance values Kungliga Tekniska Högskolan, 5 2012-05-09 Stockholm, Sweden
MTJ: State of the Art Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • TMR up to 600% • Material: o Amorphous AlO barrier o MgO crystal barrier • Main parameters: o Thickness of the free layer o Thickness of the insulated layer Kungliga Tekniska Högskolan, 6 2012-05-09 Stockholm, Sweden
Pros & Cons Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion Advantages Drawbacks o Good integration o Perturbations at high concentration rate o Good scalability (MRAM) o Power failure safe o High switching (write) o No static current energy o Power stand-by Kungliga Tekniska Högskolan, 7 2012-05-09 Stockholm, Sweden
MTJ: Read circuitry Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion Evaluation request • 2 implementations: o 2 MTJs Logic “0” o 1 MTJ & 1 reference resistor Logic “1” 𝑺 𝑺𝑭𝑮 = 𝑺 AP + 𝑺 𝑸 2 MTJ 𝟑 Mixed 1MTJ-1Resistor Kungliga Tekniska Högskolan, 8 2012-05-09 Stockholm, Sweden
MTJ: Write (Switching) circuitry Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • Different switching methods: o Spin-Torque Transfer (STT) o Perpendicular magnetization Kungliga Tekniska Högskolan, 9 2012-05-09 Stockholm, Sweden
Switching energy Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • 3 types of switching: o Precessional Switching o Dynamic Reversal o Thermally Activated Switching • 2011 results : Direction Energy Time Anti-parallel state to parallel state 0.286pJ 1.54ns Parallel state to Antiparallel state 0.706pJ 0.68ns Switching power at 500MHz: o Actual: 125µW o Actual CMOS: 8µW o Expected: 0.1µW Kungliga Tekniska Högskolan, 10 2012-05-09 Stockholm, Sweden
Simulation models and results When applied to On-Chip Routers components
MTJ Model Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • Simulation choices: Res value ( Ω ) o Reading power only o Total power = reading power + writing power • Reading model: Crossing voltage (V) o Simple model : Variable resistance o Corrected model : 𝑆 = 1 1 1 𝑑 + 𝑏 ∗ exp −b. V • Writing power computation: o Extrapolated from 1fJ/switching Kungliga Tekniska Högskolan, 12 2012-05-09 Stockholm, Sweden
On-chip router components Agenda Spintronics MTJ On-chip Components Conclusion • 3 main parts: o Arbiter o Buffers o Crossbar • Speed: o 500MHz – 2GHz • Data width: o Up to 128 bits Kungliga Tekniska Högskolan, 13 2012-05-09 Stockholm, Sweden
Buffer implementation Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion o CMOS Flip-flops • Classic flip-flop model o MTJ reader circuitry • Random Access Type • Only 1evaluation circuit/module • 1 MTJ to store a each state Kungliga Tekniska Högskolan, 14 2012-05-09 Stockholm, Sweden
Buffer implementation Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion o CMOS Flip-flops • Classic flip-flop model o MTJ reader circuitry • Random Access Type • Only 1evaluation circuit/module • 1 MTJ to store a each state • Branch transistor for depth>50 Kungliga Tekniska Högskolan, 15 2012-05-09 Stockholm, Sweden
Buffer implementation: Results Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion Full Power Consumption = Switching probability: 50% Reading power + Switching power Frequency: 250MHz Duty Cycle: 25% Switching energy (est.): 1fJ Key depth = 10 (over which the MTJ implementation is less power consuming) Power saving = up to -56% (Trend for deep buffer implementation, 56% of the CMOS power consumption is saved) Kungliga Tekniska Högskolan, 16 2012-05-09 Stockholm, Sweden
Crossbar implementation Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • CMOS implementation: o Tri-state buffers o CMOS Flip-flop for the control bits • MTJ implementation 1: o Tri-state buffers o MTJ reader for the control bits Kungliga Tekniska Högskolan, 17 2012-05-09 Stockholm, Sweden
Crossbar implementation Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion • MTJ implementation 2: o No CMOS tri-state buffer o Logic-in-Memory device CMOS Flip-flop: 0.6uW MTJ reader: 2.27uW Logic-In-Memory Mux: 2.5uW Kungliga Tekniska Högskolan, 18 2012-05-09 Stockholm, Sweden
Conclusion Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion Spintronics • o About electron’s spin , not charge MTJ switching methods • o Energy magnitude vs. Switching speed MTJ reader concepts • o Resistance value comparison Buffer MTJ implementation • o Very scalable o Power efficient Crossbar MTJ Implementation • o Hardly scalable o Not yet power efficient Extensions • o Router Arbiter with MTJ o Scalable Logic-in-Memory Multiplexer structure (Crossbar) Kungliga Tekniska Högskolan, 19 2012-05-09 Stockholm, Sweden
Questions Agenda Spintronics MTJ On-chip Buffer On-chip Crossbar Conclusion Thank you for your attention! Any questions ? Kungliga Tekniska Högskolan, 20 2012-05-09 Stockholm, Sweden
Annexes Magnetic Tunnel Junction
Annex: MTJ Reader DyCML DyCML: • o Dynamic Current Model Logic CCK: • o Cross-Coupled Keeper DCS: • o Dynamic current source Kungliga Tekniska Högskolan, 22 2012-05-09 Stockholm, Sweden
Annex: Crossbar Logic-in-Memory Kungliga Tekniska Högskolan, 23 2012-05-09 Stockholm, Sweden
Annex: Buffer impl. results 1000 Total Power = Using (reading) power + Switching power Switching probability : 50% 408 Frequency : 250MHz Duty Cycle : 25% 205 180 MTJ switching energy (est.) : 1fJ 100 92,5 Power (uW) 45 P flip-flop P MTJ P MTJ (group) 20 19,8 11,8 10 4,65 4,6 3,3 2,35 2,6 1,1 1 1 10 100 1000 Size (in bits) Kungliga Tekniska Högskolan, 24 2012-05-09 Stockholm, Sweden
Annex: Extensions • MTJ Arbiters • Switching energy enhancements • Resizing buffers more power efficiently • Scalable Logic-in-Memory Multiplexer Kungliga Tekniska Högskolan, 25 2012-05-09 Stockholm, Sweden
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