All-Spin Logic

1. All-Spin Logic Behtash Behin-Aein Ph.D Supriyo Datta Research Group behinb@purdue.edu Electrical and Computer Engineering Purdue University, West Lafayette, IN

2. Basic ASL Device Operation (Nature Nanotech.)5, pp. 266 - 270 (2010). B. Behin-Aein, D. Datta, S. Salahuddin and S. Datta. Magnets are natural spin digitizers >0 < 0 spin-torque • Proposed all-spin logic: • Information: state of magnet • Communication: spin currents • Energy: supply voltage μ μ μ μ spin-current Vsupply (VDD) • CMOS logic: • Information: charge on capacitor • Communication: charge currents • Energy: supply voltage Input Capacitor Output Capacitor

3. Spin-Torque Switching in Lateral Devices Theory (Purdue) Experiment No fitting parameters • Spin-charge circuit: spin and charge voltages/currents • LLG: switching requirements and magneto-dynamics Yang et al. Nature Phys. 4, (2008)

4. Spin-Charge Circuit Model I1 I2 V V1 V2 g g0 g0 (V,0) (Ic,0) 5 5 1 1 3 (V,Vth) 4 3

5. Essential Characteristics of a Logic Switch Power gain Nonlinearity • Provides error correction • Maintains signal levels through • long chain of concatenated gates. Concatenability Boolean Logic • Provides the means • to compute. Feedback Prevention • Provides unidirectionality • of switching between corresponding inputs/outputs. • Ensures that input/output signals are of the same form and range.

6. Concatenability Same physical form and range Input Output • Input / Output: Electrical • Input / Output: Optical R Ouput Input R

7. All-Spin Logic (ASL) vs. Conventional Spintronics Logic Spin state variable is used internally 10’s micro-V 10’s milli-V >> Logic gate A Middle Circuitry Vsupply v Spin-to-charge conversion & amplification are required GND GND Logic gate B ASL: Information is in the magnet Spin state variable is used internally

8. Electrical Input | All-Spin Block |Electrical Output Electrical Write / Input Electrical Read / Output Device / ASL Block

9. Switching Energy: Intrinsic Mz = MsVcos(θ) MsV = NsμB Hz - Hc Hc - MsV Field generated by a current carrying wire θ [degress] Behin-Aein et al. IEEE TNANO 8, 2009

10. Spin Torque Switching:Switching Current / Switching Time • PMA • Sun, J.Z. PRB 62, 570 (2000)

11. Switching Energy: Joule Dissipation Yang et al. Nature Phys. 4. (2008) • Lowering Ns can reduce Es. • There are stable magnets with a few thousand spins at RT.

12. Energy-Delay metric Key Point: Low resistance, low voltage circuits, compared to CMOS Input Output Channel

13. Questions? Vsupply • Proposed all-spin logic • Information: state of magnet • Communication: spin current • Energy: supply voltage Input Output Channel GND • Possibility of a low power, low voltage architecture based on spin circuits. • Detailed models being developed to assess specific implementations.

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15. Non-Reciprocity (Feedback prevention) Vsupply Input Output Spin Channel Energy Energy GND 0 0 Vsupply 180 180 θ [degrees] θ [degrees] Vbias Vbias Spin Channel GND GND

16. Parameters extracted from Yang et al. Nature Phys. 4. (2008)

17. Spin-Torque switching in lateral devices Experiment Theory (Authors…) No fitting parameters • Spin-circuit model: gives the value of spin current for a given charge current. • Magneto-dynamics (LLG): Determines the switching • spin-current Yang et al. Nature Phys. 4, (2008)