prospects for ultrafast (

Prospects for Ultrafast (<10 psec) MRAM

5 TH E3S SYMPOSIUM 2017BERKELEY, CA

PROF. JEFFREY BOKOREECS DEPARTMENT

UNIVERSITY OF CALIFORNIA, BERKELEYLAWRENCE BERKELEY NATIONAL LABORATORY

“For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.”

STT-MRAM is “slow”

2J. BOKOR, E3S SYMPOSIUM 2017

Fastest Precessional Switching

3

120 psec switching of STT device ~ ½ precessional period

Rowlands, et al. APL (2012) [Irvine, UCLA, Minnesota, Hitachi]

J. BOKOR, E3S SYMPOSIUM 2017

Ultrafast Demagnetization Discovered in 1996

• Beaurepaire, et al., PRL (1996)

620 nm laser, 60 fs, 7 mJ/cm2

J. BOKOR, E3S SYMPOSIUM 2017 4

Ultrafast All-Optical Switching (AOS) in GdFeCo

5

Shot 1 Shot 2 Shot 3 Shot 4 Shot 5 …

20 mm

Ostler, et al., Nat. Comm. 3, 666 (2012)

Radu, et al., Nature 472, 205 (2011)


Ultrafast, all-optical magnetic recording (Radboud Univ. group)

ps e-pulse magnetic device

Ultrafast, all-electrical switching?

6

SpeedNon-volatility, functionality,

low energy

femto-magnetism

Scalable, integrable

spin-electronics

Disadvantages: scalabilty, need for femtosecond lasers…


What pulsewidth is needed for ultrafast magnetic switching of

GdFeCo?


GdFeCo switching dynamics up to 10 ps

J. Gorchon, et al., Phys. Rev. B94, 184496 (2016)


9

HI-AOS weakly dependent on pulsewidth



Is electronic heat current effective for ultrafast magnetic switching?


“Remote Heating”


Remote heating switches GdFeCo

57 nm Au / 11.5 nm GdFeCo bilayer

R. Wilson, et al., Phys. Rev. B95, 180409 (2017)


How to generate ps electrical pulses?


Ultrafast photoconducting switch

Ketchen, et al., APL (1986)

14

Oxygen-implantedSOS

Deconvoluted pw = 0.6 ps


CMOS can produce sub-5 ps pulses

15

OFF CURRENT (na/mm) [VARIES WITH THRESHOLD VOLTAGE]

Mistry, et al. IEDM 2007 (Intel)


Can ps electrical pulses induce ultrafast demagnetization?


Magnet resistive load

17

Magnet load(4 mm X 4 mm)

Ta(1)/Pt(1)/[Pt(0.7)/Co(0.86)]x8/Pt(1.7)

~14 pJ energy absorbed



Current Induced Ultrafast Demagnetization of Pt/Co

2 ps laser excitation 3.6 ps electrical excitation

18

Sample structure:Ta(1)/Pt(1)/[Pt(0.7)/Co(0.86)]x8/Pt(1.7)



Can ultrafast electrical pulses induce single-shot switching in GdFeCo?


Electrically excite, optical probe

20

20 mm

20 mm

4 X 5 mmTa(5)/Gd30Fe63Co7(20)/Pt(5)

Y. Yang, et al., Sci. Advances (in press)


Current pulse waveform

heating pulse ∝ I2

heating pulse width ~ 6 ps

~9 ps

GdFeCo electrically induced switching

Ultrafast electric current induced magnetic switching

Completely new magnetic switching mechanism21


5 mm


Electrical switching dynamics

• Current density ~ 7 X 108 A/cm2

(peak)

• Over 1010 switching cycles!

• For (20nm)3 cell estimate:Scaled switching energy ~3.5fJ, switching current ~10s of mA

22



Can we read out electrically?


GdFeCo MTJ from U. Minnesota

24

Chen, et al., Phys. Rev. Appl. (2017)


Can we switch a ferromagnet in an MTJ with high TMR?


Single-shot all-optical switching of a ferromagnet

Single-Shot switching of Co/Pt! J. Gorchon, et al., Appl. Phys. Lett. 111,042401 (2017)


Exchange coupling to GdFeCo

Conclusions

27

• Ultrafast (<10 ps) all-electronic switching of

magnets demonstrated

• Many building blocks investigated

• Opens up completely new regime of

ultrafast spintronics

• Possibilities for many new very practical

applications


Next Steps

28

• More complex magnetic heterostructures to reduce switching current even further

→ Deterministic switching?

• Integrate electrical readout

• Integrate magnetic structures on high-performance CMOS to “get rid of the laser”

• Further theory and simulation to better understand ultrafast switching physics

Acknowledgements

Yang Yang1, Jon Gorchon1,2, Akshay Pattabi1, Charles-Henri Lambert1, Richard Wilson1,2, Prof. Sayeef Salahuddin1,2

1EECS Dept., UC Berkeley; 2Lawrence Berkeley National Laboratory

This work supported by:

US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05-CH11231.

Center for Energy Efficient Electronics Science (E3S), National Science Foundation


Te depends strongly on pulsewidth

30



GdFeCo switches with full optical absorption in Au layer

3 10 30 100 3000.1

0.3

1

3

10

30

Au

GdFeCo

Total

Abs

orbe

d F

lue

nce

(J m

-2)

Au Thickness (nm)

31



Calculated heat currents

0.01 0.03 0.1 0.3 1 3 100.1

0.3

1

3

10

30

100

91 nm Au

From Au Electrons

Optical Heating

He

at

Cu

rre

nt

(TW

m-2)

Time (ps)

38 nm Au

32



TR-MOKE indicates electron thermal diffusion mechanism

-2.0 -1.0 0.0 1.0 2.0 3.0

0.00

0.25

0.50

0.75

1.00

Au(75 nm)

Au (30 nm)

No

rma

lize

d P

ola

r K

err

Ro

tatio

n

Delay (ps)

Au (0 nm)

33

Pt(5)/Au(h)/GdFeCo(10)/Ta(2)/MgO(170)/Au(10)

Pt(5)/Au(75)/MgO(3)/Au(10)/GdFeCo(10)/Ta(2)/MgO(170)/Au(10)→ no switching

[50 fs ballistic]



Electrically induced ultrafast magnetism


Electrical pulse measurement

35

~5 ps

heating pulse ∝ I2

heating pulse width ~ 3.6 psElectrical pulse energy ~200 pJ

R. Wilson, et al., Phys. Rev. B96 (2017)


Coupled GdFeCo/FM MTJ

36

55% TMR

Nishimura, et al., JAP (2002)


“For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.”

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