28.7: pairwise coupled hybrid vanadium dioxide-mosfet (hvfet

28.7: Pairwise Coupled Hybrid Vanadium Dioxide-MOSFET (HVFET) Oscillators for Non-

Boolean Associative Computing N. Shukla1, A. Parihar2, M. Cotter1, H. Liu1, M. Barth1, X. Li1, N. Chandramoorthy1, H. Paik3, D. G. Schlom3, V. Narayanan1, A. Raychowdhury2, and S. Datta1

1The Pennsylvania State University, University Park, PA, USA 2Georgia Tech, Atlanta, Georgia, USA 3Cornell University, Ithaca, NY, USA

Wednesday: 11:35 AM Session: CDI

1

Associative Computing

degree of match or association between [X] and [Y]

PSU Memorized pattern Input Pattern

[X] [Y]

Ø Applications: Data recognition, mining and classification

-Pattern / Image recognition -Visual Saliency 2

Distance norm for Associative processing

Distance Calculator [X] [Y]

Fractional distance (Lk; k<1)

Absolute value difference (L1)

Square of distance (L2)

Ø An associative computing platform must compute distance

[X: p1, q1] [Y: p2, q2]

q q q

p p p

X

Y Y

X

Y

X

3

--

-

-

P1

C

P2C

P359C

P360C

--

P3C

P4

C

+

+

+

+

+

+ √

Euclidean Distance Calculation using CMOS Accelerator

Ø Boolean bottleneck in Adder tree and Square root (500,000 gates!) Ø Evaluate an alternate non-Boolean architecture to overcome bottleneck

32nm CMOS accelerator

Adder tree, subtractors and multipliers: A power

bottleneck

C P1 P2 P3

P6 P7 P8

P4 P5

4

13.1mW &

~500,000 gates

46% 48% 1% 5%

-+ +

√ Control logic

Non-Boolean Computing with Synchronized Oscillators

resonant freq

time

V Frequency

Ø Use synchronization dynamics (phase, frequency) of coupled oscillators as computational state variable

V1

V2

ϕ

time

V Phase

V1

V2

V1 V2

5

Coupled Oscillatory Systems Synchronization of Metronomes

Spin Torque Oscillators

CMOS

Zhang, Mian, et al. "Synchronization of micromechanical oscillators using light." Physical review letters 109.23 (2012): 233906.

Opto-mechanical Oscillators

6

https://www.youtube.com/watch?v=JWToUATLGzs; (Ikelguchi Lab)

Kaka, Shehzaad, Matthew R. Pufall, William H. Rippard, Thomas J. Silva, Stephen E. Russek, and Jordan A. Katine. "Mutual phase-locking of microwave spin torque nano-oscillators." Nature 437, no. 7057 (2005): 389-392.

Shibata, Tadashi, et al. "CMOS supporting circuitries for nano-oscillator-based associative memories.“ CNNA, 2012 13th International Workshop on. IEEE, 2012.

Fixed layer

Free layer

Ø Vanadium dioxide (VO2) based relaxation oscillators

§ Phase transition in VO2 § Oscillator demonstration via resistive feedback

§ Hybrid VO2-MOSFET (HVFET) oscillator

Ø Pairwise Coupled HVFET Oscillators

Ø Computing with HVFET Oscillators § Phase as computation state variable

Ø Power Consumption and benchmarking

Ø Summary

Outline

7







Ø Summary

Outline

8

9

Insulator-metal phase transition in VO2

Ø Abrupt change in VO2 resistivity through electron correlation dynamics in ultra-thin VO2 films.

240 270 300 33010-‐4

10-‐3

10-‐2

10-‐1

100

T emperature (K )

Res

istiv

ity (Ω.cm) insulator

metal

monoclinic

Metallic VO2

rutile Insulating VO2

M. Huefner, R. Ghosh, E. Freeman, N. Shulka, H. Paik, D. G. Schlom, and S. Datta "Hubbard Gap Modulation in Vanadium Dioxide Nanoscale Tunnel Junctions", Nano Letters, October 2014.

Ø Abrupt, hysteretic phase transition can be electrically triggered

Electrically induced phase transition

0 20 400.0

0.5

1.0

1.5

2.0

Current (m

A)

E lec tric F ield (kV /cm)

insulator

metal

10

VDC

VO2 based Oscillators

Ø  Series resistance (RS) can enable oscillations

V1

VDC

RSV1

t

VDC t

V1

IàM

VO2

C

VDC

V1

MàI

VO2

C

VDC

RS RS

V1 V1

t t

11

0 50 100 1506

8

10

12

V 1 (V)

T ime (µs )

experiment

VGS

D S

V1

VDC

Si substrate

0.0 0.2 0.4 0.6 0.80

20

40

60

80

100

Frequ

ency

(kH

z)

VG S (V )

Hybrid VO2-MOSFET (HVFET) oscillator

0 50 100 150

5

10

15

T ime (µs )

V1 (V

)

Ø  Voltage controlled VO2 oscillator realized by replacing RS with a MOSFET (HVFET Oscillator)

VDC t

V1

t

12







Ø Summary

Outline

13

VGS,1VGS,2

Si substrate

VDC VDC

V2 (output) V1 (output)

S D D SCC

Pairwise Coupled HVFET Oscillators

Ø Capacitively coupled oscillators show frequency synchronization

0 10 20 30-‐50

-‐40

-‐30

-‐20

-‐10

0

F requency (kH z )

Pow

er (dB

)

Resonant frequency

V1 V2

CC= 2.2nF

VDC

t V2

t V1

t

14

-‐0.2 -‐0.1 0.0 0.1 0.25

10

15

20

ΔVG S (V )

Res

onan

t frequ

ency

(kH

z)

0.0 0.2 0.4 0.60

1

2

3

T ime (ms )

V1,2 (V

)

Synchronization of Pairwise Coupled HVFET Oscillators

Ø Resonant frequency can be tuned with ΔVGS Ø Oscillators show near anti-phase synchronization

ΔVGS= VGS,2-VGS,1 V1 V2

15







Ø Summary

Outline

16

Equivalent Circuit for coupled HVFET Oscillators

Ø Equivalent circuit to analyze HVFET oscillator synchronization dynamics

17

MOSFET

VMOS RVO

g0 gmVgs

C1 + g0

gmVgs C2

+

MOSFET

VMOS

VGS,1 VGS,2

CC

2 1

- -

RVO 2 2

Locked

Locked Unlocked

Unlocked

Phase Space Diagram (locking / unlocking)

VO

2 VDC

Vgs1

VO

2

VDC

Vgs2

CC

Ø Gate Input voltage difference decides synchronization

ΔVGS=VGS,2-VGS,1

ΔVGS=-0.2 V ΔVGS=-0.02 V

ΔVGS=0.2 V ΔVGS=0.02 V

18

Phase Space Diagram (Locked Case)

Ø Part of steady state periodic orbit in the XOR=0 region of the phase space depends on ΔVGS = VGS,2 - VGS,1

0.6 0.7 0.80.6

0.7

0.8

P

0.6 0.7 0.80.6

0.7

0.8

0.6 0.7 0.80.6

0.7

0.8

V1 (V)

V 2 (V

)

VGS,1 = 0.3V VGS,2 = 0.3V

VGS,1 = 0.3V VGS,2 = 0.32V

VGS,1 = 0.3V VGS,2 = 0.35V

XOR=0

19

Phase Difference measurement

Coupled Oscillator

Output

Output Threshold XOR Time

Average

V1

V2

20

Ø System implementation to measure steady state periodic orbit of the HVFET oscillators

-‐0.2 0.0 0.2

0.25

0.30

0.35

0.40

0.45

0.50

0.55

ΔVG S (V ) X

OR

-‐0.4 -‐0.2 0.0 0.2 0.4

0.1

0.2

0.3

0.4

0.5

0.6

0.7

XOR

ΔVG S (V )

simulation experiment ΔVGS= VGS,2-VGS,1 ΔVGS= VGS,2-VGS,1

Ø Degree of match between inputs can be measured with HVFET oscillators

21

Distance calculation using Coupled HVFET oscillators

Distance Norm (L) for pairwise coupled oscillators

Ø Synchronized HVFET oscillators follow a L1/2 distance norm Ø Distance computing hardware realized using synchronized HVFET oscillators

00.2

0.40.6

0.81

0 0.2 0.4 0.6 0.8 1

0.70.60.50.40.30.20.1

XOR

00.2

0.40.6

0.81

0 0.2 0.4 0.6 0.8 1

0.70.60.50.40.30.20.1

X (a.u.) X (a.u.) Y

(a.u

.)

Y (a

.u.)

22

L1/2 Fractional distance norm XOR output of Coupled Oscillators

Visual Attention

Ø Objects with high degree of contrast most salient to human eye

Visual attention using Coupled Oscillators and CMOS

23

CMOS

Visual Saliency using Coupled Oscillators and CMOS

Ø VO2 coupled oscillators an alternate hardware to do visual saliency

Coupled Oscillators

24







Ø Summary

Outline

25

26

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

~1500X

Pow

er C

onsu

mpt

ion

(W)

13.1 mW

8 µW 13.1mW

& ~500,000 gates

CMOS based Euclidean norm

Benchmarking

Ø Small number of oscillators required to a compute distance norm Ø Distance computing with oscillators results in ~1500X power reduction (fundamental distance computing hardware)

46% 48% 1% 5%

-+ +

√ Control logic

Power Analysis: HVFET based computational hardware

27

~259 µW

3% 12.39%

11.28%

39.06%

34.18%

Oscillator (8-Pairs) Threshold/Buffer XOR 5-bit Counter Averager

Peripheral circuitry~97%

~8 µW

8 oscillators + 752 gates Ø Peripheral circuitry a large power consumer

28

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

~50X Po

wer

Con

sum

ptio

n (W

)

Benchmarking

Ø ~50X power reduction enabled through a physics based computing approach!

13.1 mW

259 µW







Ø Summary

Outline

29

Summary Ø Experimental demonstration of coupled VO2 based re laxat ion osci l la tors wi th input programmable synchronization

Ø Demonstration of coupled oscillators as a fractional distance (L1/2) computing machine

Ø Application in Associative processing e.g. visual saliency

Ø ~50X power performance improvement with physics based computing approach!

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Thank you!

28.7: pairwise coupled hybrid vanadium dioxide-mosfet (hvfet

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