mottfet

Report
ITRS Workshop on Emerging Research Logic Devices
Bordeaux, France, September 21, 2012
Mott FET
A. Sawa1,2
S. Asanuma,1,2 P.-H. Xiang,1,2 I. H. Inoue,1,2
H. Yamada,1 H. Sato,1,2 and H. Akoh1,2
1National
Institute of Advanced Industrial Science and Technology (AIST)
2JST-CREST
Outline
・Correlated electron system
・Mott metal-insulator transition
・Mott field effect transistor
Feature/potential
Issues/challenges
・Experiments
Mn-oxides
Ni-oxides
V-oxides
・Summary
Correlated electron system
Band insulator
Mott insulator
electron
orbital
t
electron
Pauli’s rule
No more than 2 electrons
in an orbital
E
One electron in an orbital due to
on-site Coulomb repulsion (U > t)
t: Transfer
U: Coulomb
E
EF
E
EF
upper Hubbard
band (UHB)
U
EF
lower Hubbard
band (LHB)
Mott insulator-metal transition
Mott insulator
Electron
solid
electron
Resistivity [cm]
104
Electron
liquid
x=0
0
Mott transition
Huge resistance change
(t < U)
W
Ce MnO 3
CarrierCa
doping,
1-x
x
magnetic field,
light, ・・・
102
W < U10
Decrease in U (band gap)
10-2
E
Correlated-electron metal
W>U
(t > U)
x=0.02
E
W: band width
x=0.03
U: Coulomb
energy
U
10-4
EF 0
t
100W ∝ 200
300
t
Temperature
[K]
Y. Tomioka, unpublished
W
U
EF
Electronic phases
T
T
Critical
point
Antiferromagnetic
insulator
Antiferromagnetic
insulator
Ferromagnetic
metal
Carrier density
Carrier density
Quantum
CP
Optical property
(La,Sr)MnO3
insulator
metal
250
ab (cm)
Magnetizum
Paramagnetic
metal
Superconductivity
200
150
100
La2-xBaxCuO4
x=0.09
9T
50
0
0
0T
20
40
T (K)
Changes in electronic, magnetic, and optical properties
60
Mott FET
Mott FET
Mott FET can control electronic, magnetic, and
optical properties by electric field
Gate
Drain
Source
Correlated-electron material
“ON”
“ON”
“electronic”
“ON”
“OFF”
“magnetic”
“optical”
Mott transition/transistor‐Scaling?‐
Electron
solid
Insulator
Electron
liquid
Mott
transition
OFF
Metal
ON
In principle, a nanometer-scale Mott insulator
shows the Mott transition
103 electrons
Number of electrons
4 nm
No one has demonstrated
Mott transition/transistor‐Nonvolatile?‐
First order phase transition
Hysteretic behavior
Nonvolatile(?)
Kotliar et.al PRL 89, 046401 (2002).
V>0
electrode
doped-Mott ins.
V<0
Oka, Nagaosa, PRL95, 266403 (2005)
No one has demonstrated
Mott transition/transistor‐Fast switching?‐
Ultrafast optical pump‐probe spectroscopy
Sample: Gd0.55Sr0.45MnO3
Reflectcance
Electronic state
Karr rotation
Magnetic state
Matsubara et al., PRL99, 207401 (2007)
Mott transition takes place within a few picoseconds
Challenges
conventional gate dielectric (SiO2): ~1013/cm2
Ahn, Triscone, Mannhart,
Nature 424, 1015 (2003).
1013 1015
1014 – 1015 cm-2
For the realization of a practical Mott transistor,
• Correlated-electron materials with a MI transition attainable at
significantly lower carrier concentrations
• High-k gate materials with a large breakdown strength
Electric double layer transistor
Electric double layer transistor
Electrolyte/ionic liquid is used as gate dielectrics
Outer Helmholtz
plane
S. Ono et al., APL 94, 063301 (2009)
Large capacitance: > 10 F/cm2
J. T. Ye et al., Nature Mater. 9, 125 (2010)
a large amount of carriers:
1014 – 1015 cm-2(@2V)
Electric double layer transistor (EDLT)
VD
VG
IG
ID
Ionic Liquid
SepaD + + + + S rator
− − − −
− − − −
G
CMO
YAO substrate
+ DEME+ cation
−
TFSI- anion
CMO channel
Thickness: ~ 30 nm
W/L:
~ 10μm/100μm
S. Asamuna, AS et al., Appl. Phys. Lett. 97, 142110 (2010)
P-.H. Xiang, AS et al., Adv. Mater. 23, 5822 (2011)
10[email protected]
→1.5 × 1014 [email protected]= 2.5 V
EDLT consisting of
compressively strained CaMnO3 film
0.25
ID (A)
0.20
0.15
0.10
Insulator
0.05
IG (nA)
Metal
0.00
0.1
0.0
-0.1
-2
Thickness of channel : 40nm
On/Off ratio: >10 @RT
>103 @50K
-1
0
1
2
VG (V)
Nonvolatile change in resistance
at “room temperature”
P-.H. Xiang, AS et al., Adv. Mater. 23, 5822 (2011)
non-doped
(VG = 0)
carrier doped
(VG ≠ 0)
Temperature
·CMR-manganite, High TC cuprate
·1014~ 1015/cm2 carriers
Sheet Resistance
(logarithmic scale)
Sheet Resistance
New approach for Mott transistor
TMI
Temperature
“sharp” and “large” resistance change
(Nd,Sm)NiO3
TMI = 200–400 K
VO2
TMI = 300–340 K
NdNiO3 EDLT
S. Asamuna, AS et al., Appl. Phys. Lett. 97, 142110 (2010)
R. Scherwitzl et al., Adv. Mater. 22, 5517 (2010).
Nd0.5Sm0.5NiO3 EDLT
NSNO(0.5)/NdGaO3 (110) (Thickness:~6 nm)
(Nd,Sm)NiO3 channel
VG
0V
-2.3V
-2.5V
10-3
@300 K
10-5
10-6
10-7
ISD (A)
Resistivity(cm)
10-2
Temperature (ºC)
-33
-13
7
27
10-8
10-9
10-10
10-11
10-4
220 240 260 280 300 320
Temperature (K)
10-12
-3 -2
-1
0 1
VG(V)
2
3
Large resistance change (~105) at room temperature
S. Asamuna, AS et al., unpublished
VO2 EDLT
Nonvolatile
¥
Gate voltage
VO2
insulator
metal
Nakano et al., Nature 487, 459 (2012)
Oxide FET
Channel
Operation
On/Off
temperature ratio
SrTiO3
SrTiO3
R. T.
~105
Mobility Gate voltage
(cm2/Vs)
(V)
Gate material
2.5
~10
superconductivity: TC ~0.3K at VG=-3V
References
a-CaHfO3
JJAP46, L515 (2007)
electrolyte
Nat. Mater. 7, 855 (2008)
a-Al2O3
APL84, 3726 (2004)
KTaO3
R. T.
~104
0.4
100
TiO2 (anatase)
R. T.
~105
0.37
5
a-LaAlO3/MgO
APL92, 132107 (2008)
In-Ga-Zn-O
R. T.
~108
12
5-6
a-Y2O3
APL89, 112123 (2006)
Mott FET
PZT
(ferroelectrics)Science 284, 1152 (1999)
GdBa2Cu3O7
50-300K
<3
±3
La2CuO4
R. T.(?)
<10
<8
SrTiO3
(La,Sr)MnO3
10-300K
<3
±1
PZT
(La,Ca)MnO3 100-200K
<10
±3
Ionic liquid
77K
R. T.
50K
R. T.
~100K
<10
<1
>103
~10
>10
±10
PZT
±2.5
Ionic liquid
R. T.
~105
±2.5
Ionic liquid
unpublished
260K
~103
±3
Ionic liquid
Nature 487, 459 (2012)
SrRu1-xTixO3
CaMnO3
NdNiO3
(Nd,Sm)NiO3
VO2
±2
APL76, 3632 (2000)
PRB74, 174406 (2006)
PRL102, 136402 (2009)
APL82, 4770 (2003)
Ionic liquid Adv. Mater. 23, 5822 (2011)
APL97,142110 (2010)
Summary
Feature/potential of Mott FET
• Functionality: electronic, magnetic, and optical switches
• Scaling limit: < 10 nm
• Nonvolatile and fast switching
expected from theoretical and experimental studies on
correlated electron materials
Bottleneck/challenge
A large number of carriers (>1014 cm-2 ) is necessary to be
doped in order to induce the Mott transition
For the realization of a practical Mott transistor
• (“solid”) Higk-k gate materials with a large breakdown
strength

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