Making Non-Volatile Nanomagnet Logic Non-Volatile

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Austin Chambers
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1 Slides by Lubaba Making Non-Volatile Nanomagnet Logic Non-Volatile Aaron Dingler, Steve Kurtz Michael Niemier, Xiaobo Sharon Hu, Joseph Nahas

2 PAPER OVERVIEW Issue: - Nanomagnet Logic: greatest feature non-volatility (even at gate level). - Externally supplied switching energy is needed to re-evaluate a magnet ensemble, which could be done by multiphase clocking inherently pipelined manner for high throughput. However, this could arise bit conflicts (agitate random walk )make Nanomagnet Logic Volatile. Objective: To make Nanomagnet Logic Non-Volatile. Approach and Comparative Study: IMPROVING NON-VOLATILITY: Eliminate Random Walk: ( aspect ratio): drawback -> external energy - Selective Latching: Selected device to hold the data, needed to be non-volatile - Use surrounding devices with higher permeability [µ =B/H] - Use Biaxial anisotropic (magnetic)device [K u cos2(θ) + ¼ K 1 sin2(2θ)] 2

3 PAPER OVERVIEW Issue: - Nanomagnet Logic: greatest feature non-volatility (even at gate level). - Externally supplied switching energy is needed to re-evaluate a magnet ensemble, which could be done by multiphase clocking inherently pipelined manner for high throughput. However, this could arise bit conflicts (agitate random walk )make Nanomagnet Logic Volatile. ->system building Objective: To make Nanomagnet Logic Non-Volatile. Approach and Comparative Study: IMPROVING NON-VOLATILITY: Eliminate Random Walk:( aspect ratio): quantum study -> design modification - Selective Latching: system study -> design optimization - higher permeability: knowledge of physics-> device selection - Use Biaxial anisotropic (magnetic)device : quantum study -> device selection 2

4 OUTLINE Background Root cause Approach Comparative Simulation 4

switching energy is needed to reevaluate a magnet ensemble Clk N Clk N+1 t (a) AF-lines move information; (b) an AF-line has a new input,

5 NANOMAGNET LOGIC & FIELD-DRIVEN CLOCKING Nanomagnet library: programmable majority gates, fanout, AND/OR, NAND/NOR logic, Register, Wire->Anti-Ferromagnetically coupled line - Single domain magnets can represent and store binary data Field-driven clocking: Externally switching energy is needed to reevaluate a magnet ensemble Clk N Clk N+1 t (a) AF-lines move information; (b) an AF-line has a new input, and an external clocking field is used to facilitate re-evaluation of the line; (c) as the field is removed, devices relax along their easy axes; 5

6 OUTLINE Background Root cause - Origins of volatility Approach Comparative Simulation 6

ORIGINS OF ENSEMBLE VOLATILITY Architectural-level bit conflicts can

Clk phase2 odd number of magnets per clock group 40 of, 40x60x20 nm3

5mT-> B required an even number of magnets per clock group Random

7 ORIGINS OF ENSEMBLE VOLATILITY Architectural-level bit conflicts can occur in defect free NML: ->pipelining (eg:3-phase clock) Clk phase2 Clk phase2 odd number of magnets per clock group 40 of, 40x60x20 nm3 supermalloy magnets spaced 8 nm apart. 5mT-> B required an even number of magnets per clock group Random walk <- field coupling and thermal noise alone could be sufficient to initiate a state destroying case 7

8 OUTLINE Background Root cause - Origins of volatility Approach - Eliminate Random Walk - Selective Latching - Enhanced permeability dielectrics - Biaxial anisotropy Comparative Simulation: OOMMF (Object Oriented MicroMagnetic Framework) 8

Eliminate Random Walk By increasing magnet s aspect ratio: Quantifying ensemble stability the probability per unit time of reversal over the EB is 1/τ, where τ a exp(eb/kt) 3-magnet

9 Eliminate Random Walk By increasing magnet s aspect ratio: Quantifying ensemble stability the probability per unit time of reversal over the EB is 1/τ, where τ a exp(eb/kt) 3-magnet Quantifying ensembles 40x60x20 40x80x20 Required fields will increase from 5 mt (40x60x20 nm 3 ) to 50 mt (40x80x20 nm 3 )-> (i.e., B ~ µi/l : Ohmic losses->i 2 R increase by a factor of 100) 9

10 OPTIMIZING EXTERNAL FIELD Selective Latching: EG. A line of 40x60x20 nm 3 devices where select devices are replaced by higher aspect ratio, 40x80x20 nm 3 devices. Ohmic loss could be reduced such that 1 out three clk will need 10 time current. +1 Enhanced permeability dielectrics: Use surrounding devices with higher permeability [B=µH; µ ; H = I /L ] Eg. relative permeabilities of ~4.5X(superparamagnetic CoFe) improve clock energy by ~20X 10

11 OPTIMIZING EXTERNAL FIELD Biaxial anisotropy: additional energy -90 o 0 o, 0 o 90 o, 2 maximas [K u cos2(θ) + ¼K 1 sin2(2θ)] Aspect Ratio-apart K1 required B nm3-nm kj/m3 mt 60x90x x90x x90x

12 PAPER OVERVIEW Issue: - Nanomagnet Logic: greatest feature non-volatility (even at gate level). - Externally supplied switching energy is needed to re-evaluate a magnet ensemble, which could be done by multiphase clocking inherently pipelined manner for high throughput. However, this could arise bit conflicts (agitate random walk )make Nanomagnet Logic Volatile. Objective: To make Nanomagnet Logic Non-Volatile. Approach and Comparative Study: IMPROVING NON-VOLATILITY: Eliminate Random Walk: ( aspect ratio): drawback -> external energy - Selective Latching: Selected device to hold the data, needed to be non-volatile - Use surrounding devices with higher permeability [µ =B/H] - Use Biaxial anisotropic (magnetic)device [K u cos2(θ) + ¼ K 1 sin2(2θ)] 2

13 Making Non-Volatile Nanomagnet Logic Non-Volatile 13

Systematic Design of Nanomagnet Logic Circuits

Systematic Design of Nanomagnet Logic Circuits Indranil Palit, X. Sharon Hu, Joseph Nahas, and Michael Niemier Department of Computer Science and Engineering, University of Notre Dame Notre Dame, IN 46556,