Multifunctional Nanostructure for Magnetoelectric and Spintronics ApplicationR.S. Katiyar, M. Gomez, G. Morell, L. Fonseca, W. Otano^, O. Perales+, M.S. Tomar+, Y. Ishikawa, R.Palai, R. Thomas, A. Kumar, V. Makrov

University of Puerto Rico, Rio Piedras, Mayaguez+, Cayey^, Puerto Rico.

Abstract: CMOS compatible Multifunctional Materials to meet the near future demand of miniaturization of Si based technology and beyond Si, were the goals of this project. We designed and optimized

multiferroic nanostructures for data storage and logic systems, due to high speed, low power consumption, radiation hardness, and low costs. Many of these devices need a stack of thin film

nanostructures (superlattices and heterostructures) and therefore, major part of our efforts in this period focused on demonstrating the feasibility of fabricating multiferroic thin film heterostructures

along with finding new multiferroic material at room temperature. Some of the materials screened so far showed multifunctional properties especially for spintronics and magnetoelectric applications.

NEW MAGNETOELECTRIC MULTIFERROICS MULTIFERROICS INTEGRATION WITH SILICON SPINTRONIC MATERIALS

As main memory??

Challenge!!!

FeRAM advantages

Lower power usage,

Faster write speed

Radiation resistance

Realizing the high density, like DRAM and FLASH, FeRAM is an interesting option for

“universal memory” candidate

1969 on-chip memory

(volatile)

1972

off-chip memory (volatile)

1992

(non volatile)

1987

(nonvolatile) Secondary

Den

sity 256 MB

128 MB

GB??

Toshiba and Fujitsu news

2009

PZT, SBT, BLT

2008

Fe-RAM Current Status

FeRAM currently used in

SONY PS2, Electronic power meters, automotive systems, smart cards, test

instrumentation, factory automation, laser printers, security systems, and other

systems that require reliable storage of data without an external power source

TransistorFE Capacitor

1. In 1T-1C 3-D structured nanocapacitor can

improve the density,

- 3D deposition is very difficult with multi-

component ferroelectric thin films!!.

Top electrode

Bottom Electrode

FE

3D FE capacitor

Currently used materials : PZT, SBT, and BLT ( Pr in

the range 20 to 35µC/cm2)

2. Introduce a better material with high Pr e.g. BFO-

60-150 µC/cm2

- BFO will leak the stored information!!

Ferroelectric

2D FE capacitor

Si

FE

Metal

Source DrainGate

Schematic of the IT-FeRAM

+ Buffer layer can solve this problem

But what it should be?

-12 -8 -4 0 4 8 120

20

40

60

80

100

120 Chigh

Clow

Ca

pa

cit

an

ce

(p

F)

Bias Volatge (V)

Accumluation

Inversion

- But ferroelectric directly on Si

difficult- interdiffusion

Insulating buffer disadvantage.

Generate depolarization field in the ferroelectric

film

Increase the operation voltage by weakening the

electric field across the ferroelectric layer.

To overcome these disadvantages:

Ferroelectric with low r

insulating buffer layer with high r

A High-k gate-oxide may be the ideal choice as a buffer

layer

oLarge band gap

oThermal and electrical stability

oGood interface between Si

1T-1C HIGH DENSITY FeRAM 1T

Multiferroic BFO based MFIS Diode P –type Si (100)

DyScO3

BFO

BiFeO3

+ High remnant polarization.

- Large dielectric loss and high leakage current

High band offset of DyScO3 and Si will reduce the leakage current through

BFO based MFIS structures and hence of great interest for the possible

memory applications.

100

101

102

103

0

40

80

120

160

Ca

pa

cit

an

ce

(p

F)

Retention time (s)

MIM P-E Hysteresis was leaky

MFIS showed ferroelectric hysteresis with reasonable memory window (1.7V)

Data retention is not really good..Severely loose the charge after 100 s.

- high leakage current BFO

Dynamic FeRAM??..

Ferroelectric BNT based MFIS

P –type Si (100)

DyScO3

BNT

Aurivillius phase Bi4Ti3O12 (BTO)

Lead free ferroelectric, Low coercive field, Less fatigue, Low processing temperatures.

Rare-earth substituted derivatives (Bi3.25Nd0.75Ti3O12) have attracted much attention in recent years for non-volatile memory

Large memory window of about 4.0V compared to

1.7 V of BFO

MFIS structures showed excellent data retention

compared to BFO

Low leakage current compared to BFO based

MFIS

Improved interfacial quality between DSO/Si

and DSO/BNT.

Resulted Publications:

1. R. Thomas, D. K. Pradhan, R. E. Melgarejo, J. J. Saavedra-Arias, N. K. Karan, R. Palai, N. M. Murari, and R.S. Katiyar ECS Transactions 13,363 (2008).

2. R. Thomas, R.E. Melgarejo, N.M. Murari, S.P. Pavunny, R.S. Katiyar, Solid State Communications 149, 2013 (2009)

3. N. M. Murari, R. Thomas, R. S. Katiyar, J. Appl. Phys. 105, 084110 (2009)

4. N. M. Murari, R. Thomas, S. P. Pavunny, J. R. Calzada, and R. S. Katiyar, Appl. Phys. Lett. 94, 142907 (2009)

5. N. M. Murari, R. Thomas, R. E. Melgarejo, S. P. Pavunny, and R. S. Katiyar J. Appl. Phys. 106, 014103 (2009)

Current size 45 nm

<16 nm ~ 2015

Optics

Magnetism

Electronics

Semiconductor host

Magnetic impurity

Integration of magnetic functionality with electronic and optical

properties of semiconductor

Magnetic impurity doped ZnO based diluted magnetic semiconductors (DMS) can

serve as a source of spin-polarized electrons for the Spintronics applications

(Co, Al) co-doped ZnO based DMS thin films

Cu-doped ZnO based DMS thin films

The interface of the Al2O3/Zn0.99Cu0.01O

is epitaxial; (b) the film is nearly single

crystalline and defects free

Al2O3

(a) Zn0.99Cu0.01O

-6 -4 -2 0 2 4 6-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

M (/C

u)

Field (kOe)

Zn0.99

Cu0.01

O

Zn0.97

Cu0.03

O

Zn0.95

Cu0.05

O

T = 300 K

All thin films shows ferromagnetism at 300K

Maximum magnetization ~ 0.76 B/Cu in 3%

Cu doped sample

100 200 300 400 500 600 700

S

SE

high

2

5%Cu

3%Cu

In

ten

sity

(a

br. u

nits)

Raman shift (cm-1)

ZnO

1%Cu

*

Ag

Elow

2

Raman spectra confirms the

substitution of Cu2+ up to 3%

Resulted Publications:

1. K. Samanta, P. Bhattacharya, and R. S. Katiyar, J. Appl. Phys. 105, 113929 (2009)

2. K. Samanta, P. Bhattacharya, J. G. S. Duque, W. Iwamoto, C. Rettori, P. G. Pagliuso, and R. S. Katiyar, Solid State Communications 147, 305 (2008)

PZT

PF

N

PbZr0.53Ti0.47O3/PbFe2/3W1/3O3 (PZT/PFW)

Electrical control for magnetization

-10 -5 0 5 10

-16

-8

0

8

16

Ma

gn

eti

za

tio

n (

em

u/c

m3

)

Magnetic Field (kOe)

(c)

(b)

(a)

-300 -150 0 150 300

-63

-31

0

31

63

-300 -150 0 150 300-0.3

-0.1

0.0

0.1

0.3

Po

lari

za

tio

n ( C

/cm

2)

Electric field (kV/cm)

Po

lari

za

tio

n (C

/cm

2)

Electric field (kV/cm)

without field

1000 Oe

2000 Oe

3000 Oe

4000 Oe

5000 Oe

Recovery after

removal of field

Strong ME coupling in multiferroic thin film at room temperature resulted in resulted in three polarization states

Two with electric field and one with magnetic field.

Magnetic hysteresis at room temperature in PFW/PZT samples for 0.2PFW (a), 0.3PFW (b), and 0.4PFW (c)

Better hysteresis with 20/80 composition

Polarization flop under the application of external magnetic field

FE hysteresis studies under the application of external magnetic field from 0 to 0.5 T. The flopped

“hysteresis” at 0.5 T is given in the inset; It indicates -1, 0 and 1 three logic state for memory applications

0.1 1 10 100 1000

0

300

600

900

1200

1500

0

300

600

900

0.85 T

0.70T0.80T

Ima

gin

ary

pe

rmit

tiv

ity

(``

)

Re

al

pe

rmit

tiv

ity

(`)

Frequency (kHz)

0.85 T

0 T

100 200 300 400 500 600720

960

1200

1440

1680

100 200 300 400 500 600

0.01

0.1

1kHz

10kHz

100kHz

500kHz

1MHz

Ta

ng

en

t lo

ss

()

Temperature (K)

Die

lec

tric

co

ns

tan

t (

)

Temperature (K)

1kHz

10kHz

100kHz

500kHz

1MHz

Magnetic field induced Debye Relaxation

0 450 900 1350 1800

0

150

300

450

600

1 MHz

0.60 T

0.85 T

``

`

0 T

100 Hz

• High dielectric constant ~ 1450 and low dielectric loss < 0.03 from 100 to 500 K

• Dielectric constant varied due to the magnetic field dependence of the relaxation peak

• Dielectric relaxation was induced by applied external magnetic field above 0.6T (evident from the well defined Cole

- Cole plots).

• Relaxation peak shifted towards lower frequency at higher magnetic field.

• Critical field (~0.50T) and relaxation saturation at ~0.92T matched well with the theoretical calculations and

modified Vogel-Fulcher Equation

Room temperature multiferroic PZT/PFW Superlattices

-4000 -2000 0 2000 4000-60

-40

-20

0

20

40

60

Ma

gn

eti

za

tio

n (

em

u/c

m3)

Applied field (Oe)

300 K

40 400

1E-7

1E-6

1E-5

1E-4

1E-3

Cu

rre

nt

de

ns

ity (

A/c

m2)

Electric field (kV/cm)

250 K

300 K

350 K

400 K

PZT/PFW thin films of

~300nm thickness with 8:2

periodicity

The remanent polarization is

~ 33 µC/cm2

Very high breakdown field.

At 20 V (for 300 nm films) ~

60-100 MV/m,

-600 -400 -200 0 200 400 600

-100

-67

-33

0

33

67

100

Po

lari

zati

on

(C

/cm

2)

Electric field (kV/cm)

W. Eerenstein, N.D. mathur and J.F. Scott. Nature 442, 759, (2006); J

J.F. Scott , Ashok Kumar, R. Palai., M K Singh ,R.S. Katiyar et al. JACeS 91(6), 1762, (2008).

Spalding et. al., Science, Vol 309, 391-392 (2005)

M. Bibes and A. Barthélémy. Nature, 7, 425 (2008)Computational Nanoferronics Laboratory Marjana Ležaić (Germany)

Related Publications:

1. A. Kumar et al., J. Phys. Condens. Mat., August 29, 382204 (2009)]

2. A. Kumar et al., Applied Physics Letters, 94, 212903, (2009)

3. R. Pirc et al. Physical Review B 79, 214114 (2009)

4. A. Kumar et al. JMS, DOI 10.1007/s10853-009-3503-y

The magnetization in 10% Co doped ZnO

thin films reduces due to incorporation of

additional carriers

The decrease of magnetization may be due to

the degeneracy of the donor level to the

conduction band

-15 -10 -5 0 5 10 15

-1.0

-0.5

0.0

0.5

1.0

0 50 100 150 200 250 300

0

6

12

18

24

30

36

0 30 60 90 1200.0

0.3

0.6

0.9

1.2

1.5

Zn0.9-x

Co0.1 O:Al

x

M (

em

u/c

m3)

-1

p (

10

-3em

u/m

ole

-Z

nO

)-1

T (K)

T (K)

T = 300 K

x = 0

x = 0.005

x = 0.01

x = 0.015

M

(

B/C

o)

H (kOe)

a)

Al Co CW

% % K

0 11.0(5) -3.5(2)

0.5 8.0(5) -1.3(2)

1.0 7.0(5) -1.5(2)

1.5 8.0(5) -1.9(2)

b)

30 40 50 60 70 80

(0

00

4)

Inte

ns

ity

(a

. u

)

2 (degree)

(0

00

2)

Al 2

O3

0.5%Al:ZCO

1.0%Al:ZCO

1.5%Al:ZCO

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.60

20

40

60

80

3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.70

2

4

6

8

10

12

(

2) (

x10

9 c

m-2)

Al1.5%

Al1.0%

Tra

ns

mis

sio

n (

%)

Photon energy (eV)

Co10%

Al0.5%

d-d Transitions

1.88, 2.03, 2.18 eV

Films are highly c-axis oriented and free from impurity phase

Optical band gap increases up to 54 meV due to Al doping; this is due tothe Burstein-Moss (B-M) shift

Characteristic d-d transitions confirms the substitution of Co2+ in Zn2+

lattice site

Pb(Fe0.5Nb0.5)O3Pb(Fe0.5Ta0.5)O3

Pb(Fe0.66W0.33)O3Pb(Zr0.5Ti0.5)O3

Tc ~ 380 K

TN ~ 140-150 K

Tc ~ 180 K

TN ~ 380 K

Tc ~ 310 K

TN ~ 150 K

Tc ~ 620 K

Can solid solution of PZT with PFW results in novel

multiferroics at room temperature??

Low coercive field~ 400 Oe and high saturation magnetization ~ 60 emu/cm2 were obtained

Imprint in ferroelectric hysteresis either due to strain, difference in work function between to and bottom electrode and

existence of Polar nano regions Acknowledgements: This work was supported by DoE (#DE-FG02-08ER46526) and

partially by NSF-0531171 Grants.

MIMMFIS