field effect experiments on transition metal...
TRANSCRIPT
Field effect experiments on Field effect experiments on transition metal oxidestransition metal oxides
E. E. BellingeriBellingeri
CNRCNR--INFM INFM -- LAMIA LAMIA CorsoCorso PerronePerrone 24 16152 24 16152 GenovaGenova ItalyItaly
Oxide Electronics Group Oxide Electronics Group
Director Director A.S. A.S. SiriSiri**
D. MarrD. Marréé**, , I. Pallecchi, L. PellegrinoI. Pallecchi, L. Pellegrino
G. Canu, A. G. Canu, A. CavigliaCaviglia
**UniversitUniversitàà didi GenovaGenova DipartimentoDipartimento didi FisicaFisica
Via Via DodecanesoDodecaneso 33 16146 33 16146 GenovaGenova
ItalyItaly
0
5
1015
20
2530
3540
45
50
Film 1 Film 2 Film 3 Film 4 Film 5 Film 6 Film 7 Film 8
μ 0Hc2
// ( T
esla
)
0 5 10 15 20 25 30 35 400
5
10
15
20
25
μ 0Hc2⊥ (
Tes
la )
T ( K )
0.0 0.2 0.4 0.6 0.8
1.5
2.0
2.5
3.0
Ani
sotro
py
T / TC
0
5
1015
20
2530
3540
45
50
Film 1 Film 2 Film 3 Film 4 Film 5 Film 6 Film 7 Film 8
μ 0Hc2
// ( T
esla
)
0 5 10 15 20 25 30 35 400
5
10
15
20
25
μ 0Hc2⊥ (
Tes
la )
T ( K )
0.0 0.2 0.4 0.6 0.8
1.5
2.0
2.5
3.0
Ani
sotro
py
T / TC
Superconductivity & technological transferThin films of superconductingmaterials – MgB2 with extremely high upper critical fields
Superconducting fault current limiterfabricated at LAMIA for CESI SpA
Superconducting resonator fabricatedat LAMIA for ESAOTE SpA
Spin-off company for MgB2 :Columbus Superconductors srl:
Km length MgB2 superconducting tapes and wires
Synthesis of superconducting oxidesStructural refinement and HRTEM analysis
Single crystal growth of superconducting
and magnetic oxides
HPHT Combustionsynthesisof nitrides Mechanical alloying
of metallic and ceramicnanopowders
Synthesis of intermetallic alloysfor hydrogen storage
and ceramics for fuel cells
Oxide Electronics: new materials and nanodevices
Channel dim: 0.7 μm x 8 μm
120 130 140 150
5.4x107
5.6x107
5.8x107
TMI=134.33KVgate = +/- 40 Volts => ΔTMI~ 1K
R (o
hm)
T (K)
Field Effect Nanotransistorson Functional Oxides
0 50 150 2001.0x104
1.5x104
2.0x104
2.5x104
3.0x104
3.5x104
Cha
nnel
Res
ista
nce
(Ω)
Time (min.)
30
-15
15
-30
0 Gat
e Vo
ltage
FerroelectricMemories Colossal
Magnetoresistance based devices
Outline
• Transition metal oxides
• Field effect geometries
• Experiments
Traditional
Ferroelectric
StackedBack GateSide Gate
Stacked
Local (AFM)Oxide Semiconductor
Manganites
Superconductor
Perovskite
Wurzite
Transition Metal oxides
• Transparent semiconductor • High mobility• Wide-band gap• Doped with magnetic ions (Co, Mn…): dilute magnetic semiconductors
ZnO HexagonalLattice parametersa=3.24 Å, c=5.19 Å
A: Alkaline Earth B: Transition Metal
Lattice Parameter (3.9 ± 0.1)Å
(Pseudo)cubicMany physical properties depending on cations• High Tc superconductivity• Ferroelectricity• Ferromagnetism, Colossal Magnetoresistance• Semiconductors, Insulators
ABO3
Wurzite
Perovskite
Dielectrics and semiconductors:
SrTiO3, LaVO3 , ZnO
0 50 100 150 200 250 30010-8
10-7
10-6
10-5
10-4
10-3
10-2
ρ (O
hm c
m)
Temperature (K)
M-I transition in titanates
Colossal magnetoresistance:
La1-xSrxMnO3, La1-xBaxMnO3
120 180 240 3000
10
20
30
40
50
60
70
80
90
R (K
Ω)
T (K)
B=0 B=0.1 T B=0.2 T B=0.5 T B=1 T B=2 T B=3 T B=5 T B=7 T B=9 T
0 50 100 150 200 250 3000.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
3.5x106
4.0x106
4.5x106
R (Ω
)
T (K)
Continuos flow P(O2) 10-2 mbar P(O2) 10-3 mbar P(O2) 10-4 mbar
Superconductivity:
YBCO, LaSCO, infinite layers…0 20 40 60 80 100
0
5
10
15
20
(La1.85Sr0.15)CuO4 thin film
Res
ista
nce
[Ω]
Temperature [K]
n Band filling factor proportional to the chargeW Band width proportional to d and p orbital overlapping
BANDWIDTH CONTROL
FILLING CONTROL
Isovalent atomic substitution(different radius)
Pressure
Orbital overlappingEterovalent atomic substitution
Field effect
Fermi level variationCell deformation
How to change n and W?
Properties are controlled by:
Problem: the phase diagram depends not only on the carrier concentration but also on the lattice structure; chemical doping affects both carrier concentration and lattice structure and it is very difficult to discriminate between these two contributions.Field effect tunes the carrier concentration only, thereby it is a powerful tool to study this correlated system
Illustration of the zero-temperature behaviour of various correlatedmaterials as a function of charge density. Silicon is shown as a reference. The examples for high-Tc superconductors and for colossal magnetoresistive (CMR) manganitesreflect YBa2Cu3O7- and (La,Sr)MnO3, respectively. AF, antiferromagnetic; FM, ferromagnetic; I, insulator; M, metal; SC, superconductor; FQHE, fractional quantum Hall effect; Wigner, Wigner crystal.
Electric field effect in correlated oxide systemsC. H. Ahn, J.-M. Triscone and J. Mannhart
Nature 424, 1015-1018 (28 August 2003) doi: 10.1038/nature01878
102010181014 101610121010 1022 (e cm-3)
Many of interesting physical properties in these material occur at 1019-1021 e-/cm3
(for 100 nm film => 1014 – 1016 e/cm2 => 10 – 1000 μC/cm2)Very high q value!
High polarizationUltrathin films
λε ε
DS
ext
kTe n
= 02
20
2
0
2
342
3
neE
k
Enek
Fr
TFTF
FrTF
εεππλ
εε
==
=
The characteristic width of accumulation or depletion layer is given by the electrostatic screening length
Thomas-Fermi for metal
Debye for semiconductors
≈1 A
≈10 nm
Lower carrier density larger λ
3.8 nm12 nm20 nm1018 (e/cm3)
1.2 nm3.8 nm6.5 nm1019 (e/cm3)
0.38 nm1.2 nm2.0 nm1020 (e/cm3)
εr =10 εr =100 εr =300 N(e/cm3)
3.8 nm12 nm20 nm1018 (e/cm3)
1.2 nm3.8 nm6.5 nm1019 (e/cm3)
0.38 nm1.2 nm2.0 nm1020 (e/cm3)
εr =10 εr =100 εr =300 N(e/cm3)
Debye length at room temperature
Field effect devices: Stacked Geometry
MIS heterostructureMetal-Insulator-Semiconductor
• Growth of the dielectric layer on the channel• Compatibility problems• Leakage
ChannelSTO single crystalGate
Source Drain
Gate
Back gate geometry
• Very good dielectric properties of the oxide (single x-tal)
• Very thick High voltage
Side gate devices
E
I
Source Drain
gatesgates
I
E
gategate
Active Active channelchannel
Source
Drain
Gate
Gate
Source Drain
Advantages of the side gate geometry
• Easy: 2-layers structure (film/substrate)
• High quality substrates Best Dielectric Properties
• Low voltage required
•Possibility to study the surface by Scanning Probe Microscopy
Planar Geometry Side Gate Geometry
Side gate field effect devices fabrication by AFM
First step: patterning by optical lithography and wet etching in 10-20 μm wide crossing channels
with bond pads
Conducting silicon W2C coated tip
0.12N/m
Second step: sub-micron patterning by Atomic Force Microscope anodization: the AFM biased tip triggers a local chemical and morphological transformation. Nanoxidation of siliconJ.A.Dagata,et al., Appl. Phys. Lett. 56, 2001 (1990)
Fabrication of constrictions as narrow as 40 nm.
The modified regions are swollen, porous and electrically insulating
•Nanoscale GaAs/AlGaAsheterostructures
Local “anodic oxidation” of oxides:
11 μm x 11 μm
11 μm x 11 μm
11 μm x 11 μm
Voltage controlled etching depthVoltage controlled etching depth !!!!!!
Modified regions are selectively etched in HCl solutionModified regions are selectively etched in HCl solution
HCl HCl solutionsolution
11 μm x 11 μm11 μm x 11 μm
Etched sub-micron wide insulating barriers can sustain applied voltages up to ±80 Volts without appreciable leakage (<100pA).
-80 -40 0 40 80
-0.4
-0.2
0.0
0.2I g (
nA)
Vg (Volts)
T=20K T=100K T=200K
Gate Gate
Source
Drain
Side gate field effect devices by AFM
-400 -300 -200 -100 0 100 200 300 400
107
108
X [nm]
Elec
tric
Fiel
d (V
/m)
-1 nm -20 nm -50 nm
AIR εr =1
Substrate εr
Gate Gate
Channel
Channel width 600 nm
Gap 1200 nm, Thickness 10 nm
Applied Voltage V = 10V
EstimatedEstimated capacitancecapacitance:C/m = 8.8 * εr pF/m
)/(10 210 VcmedV
dnr
g
sheet ×= ε
εr = 25 (LAO)
dnsheet= 2.5 1012 (e/cm2)
εr = 1000 (STO)
dnsheet= 1014 (e/cm2)
Vg=10Volts
Electric field profile and capacitance calculation
Ferroelectric Field effect Induced charge proportional to the ferroelectric remnant polarization
Ferroelectric
Channel
GatePulse
Ferroelectric properties:
-10 -5 0 5 10-40
-20
0
20
40
P (μ
C/c
m2 )
V (V)
Pb(Zr0.20,Ti0.80)O3
Remnant polarizationPr ~ 10÷60 μC/cm2
Coercive fieldEc~ 100 kV/cm
Pr~ 20 μC/cm2
σ~1014charges/cm2
c-axis= 4.13-4.16 Å
Pb
Pb
O
Pb
O
Pb
O
Ti
O
Pb
O
Pb
O
Pb
Pb
• No V applied during measurements• No leackage
• Only 2 states available
Perovskite films growth and structural properties
0 20 40 60 80 100 120 140180
190
200
210
220
230
240
Inte
nsity
(a.u
.)
Time (sec.)
Layer by layer growth
0 2 4 μmAtomically
smooth surfaces“Sharp” interface reflectivity
0 45 90 135 180 225 270 315
LAO 110
Cou
nts
[a.u
.]
φ [Deg]
STO 110
“Cube on cube”
epitaxial growth
20 25 30 35 40 45 500
1x104
2x104
3x104
4x104
5x104
6x104
7x104
8x104
44 45 4 6
10 3
10 4
10 5
2θ [D e g ]
Cou
nts
2Θ [deg]
Oxides Semiconductors
ZnOSTO single crystalAg (ZnO)
Source Drain
Gate
Easy case :ZnOBack-gate devices
Double side polished SrTiO3 110 substrate
10 20 30 40 50 60 70 80 90 100105
106
107
108
RS
D [Ω
]
T[K]
VG [V] +100 +50 0 -50
-15 -10 -5 0 5 10 150
100
200
300
400
T=300 K
RS
D (k
Ω)
E G (kV /cm )-5 -4 -3 -2 -1 0 1 2 3 4 5
1 0 5
1 0 6
1 0 7
1 0 8
1 0 9
1 0 1 0
RS
D (Ω
)
E G (K V /c m )
IS D 1 n A 1 0 n A 1 0 0 n A
Channel thickness 70 nm
T=50 K
Channel thickness 270 nm
• More then 5 order of magnitude RSD modulation at 50K
n = 5 1016 e/cm3
0 2 4 60
2
4
6
8
10
-3 -2 -1 0 1 2 3
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1 V
2 V
3 V
4 V
VG=5 V
I SD [μ
A]
VSD [V]
0.25 0.5 1 2 3
Vg [V] -1 -0.5 -0.25 0
VSD [V]
I SD [μ
A]
0 5 10 15 20 2505101520253035
10-11
10-10
10-9
10-8
10-7
10-6
0
2
4
6
8
10
12
-20 -10 0 1010-10
10-9
10-8
10-7
10-6
μFE
[cm
2 /Vs]
Vg [V]
77K
I SD [A
]
μ EF [c
m2 /V
s]
VG [V]
300K
I SD [A
]Gate
Gate
Source Drain
5 μm
Vds= 0.3 V
n = 6 1018 e/cm3
77 K
Transfer characteristics & field effect mobility
Characteristic curves
ZnOSide gate devices
20 nm thick ZnOfilm by two-step
method
0 10 20 30 40 50 60 70 80 90 100106
107
108
109
R
[Ω]
T [K]
-4 -2 0 2 4 6 8 10 12
0.00
0.05
0.10
0.15
0.20
ΔE [e
V]
Vg [V]
C ExpDec1 fit of Data1_C
Thermal activated behaviour
MIT driven εr of the STO substrateCompetition between T and V dependences of εr Estimation of the density of state
(impurity band)
D(E)∝1/(E-Ec)
Time stable 20 % change in channel resistance
modulated by polarization pulses
Ferroelectric Field Effect0 50 150 2001.0x104
1.5x104
2.0x104
2.5x104
3.0x104
3.5x104
Ferroelectric field effect on SrTiO3 channel
Cha
nnel
Res
ista
nce
(Ω)
Time (min.)
30
-15
15
-30
0 Gat
e Vo
ltage
Consistent withchannel thickness
and channel carrierdensity
Strontium titanate resistance modulation by ferroelectric field effectD. Marré, A. Tumino, E. Bellingeri, I. Pallecchi, L. Pellegrino, A.S. Siri,
J. Phys. D: Appl. Phys. 36 No 7 896-900 (2003)
Ferroelectric
SrTiO3:La Channel
GatePulse
Substrate
S D
First example of side gate devices (SrTiOFirst example of side gate devices (SrTiO33 on LaAlOon LaAlO33))
Fabrication of submicron-scale SrTiO3 devices by an atomic force microscope L. Pellegrino, at al Appl. Phys. Lett. 81, 3849 (2002)
0 50 100
15.6
15.7
15.8 d)
10 nA
100 nA1 μA
Res
ista
nce
(MO
hm)
Time (s)
1 μm x 1 μm
200 nm
Drain
Source Gate
Ground
3 μm x 3 μm
Successive Modification of the channel by the AFM tip
950 1000 1050 1100 1150 1200
-10-505
10
23.0
23.2
23.4
Gat
e V
olta
ge (V
)
Time (Sec)
Res
ista
nce
(MO
hm)
Temperature Temperature characterizationcharacterization of the side FET of the side FET
0 30 60 90 120 150 180 210 240 270 3000.92
0.94
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1
10
100
Res
ista
nce
(MO
hm)
R(V
) / R
(0)
Temperature (K)
+44V/0V -44V/0V
0 V +44V - 44V
-60 -40 -20 0 20 40 600.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
R(V
)/R(0
)
Applied Gate Voltage (V)
300K (1micAmp) 200K (100nA) 100K (100nA) 80K (20nA) 60K (20nA)
-40 -20 0 20 400.92
0.94
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
R(V
)/R(0
)
Applied Voltage (V)
300 K 200 K 100 K 50 K 30 K 20 K 10 K 11 μm x 11 μm11 μm x 11 μm
HCl HCl solutionsolution
Nonlinearities in the I vs V channel behavior
VVgategate=0=0
-100V
+100V
Linear to Nonlinear
characteristics at low Ttransition of the SD
Gate modulation of Gate modulation of the SD linearitythe SD linearity
-20 -15 -10 -5 0 5 10 15 20
-0.6
-0.4
-0.2
0.0
0.4
0.6
0.2
Sour
ce D
rain
Vol
e (V
)
Source Drain Current (nA)
tag
200K 100K 50K 20K
-50 -40 -30 -20 -10 0 10 20 30 40 50-0.4-0.3-0.2-0.10.00.10.20.30.4 50 K
Sour
ce D
rain
Vol
tage
(V)
Source Drain Current (nA)
0V +22V +44V -22V -44V
-20 -10 0 10 20-0.8-0.6-0.4-0.20.00.20.40.60.8
20 KS
ourc
e- D
rain
Vol
tage
(V
)
Source Drain Current (nA)
-100V -44V 0 V +44V +100V
0 100 200 300 400 500 60020.0
22.5
25.0
27.5
30.0
32.5
35.0
37.5
- 100 V
0 V
- 100 V
- 88 V- 100 V
- 88 V
- 66V
- 44 V
-22 V0 V
Res
ista
nce
(MO
hm)
Time (s)
Observation of EObservation of E--Field Induced DriftField Induced Drift
Low Gate fieldLow Gate field High Gate field High Gate field
No No hysteresishysteresis Memory effectsMemory effects
20 Kelvin
0 200 400 600 800 1000 1200 1400 160018
20
22
24
26
28
3020 Kelvin
0 V
- 44 V - 44 V
0 V
+ 44 V
0 V
-44 V
0 V
+ 44 V
0 V
Res
ista
nce
(MO
hm)
Time (s)
……ExploitingExploiting the the DielectricDielectric ConstantConstant of the of the SubstrateSubstrateMaximumMaximum resistanceresistance modulationmodulation observedobserved on on
homoepitaxialhomoepitaxial STO STO devicesdevicesSTO:LaSTO:La on STOSTO
STO substrate
-10 -8 -6 -4 -2 0 2 4 6 8 10
-50
0
50
100
150
200
ΔR/R
(%)
VGate (V)
2K 5K 10K 20K 50K
0 10 20 30 40 500
5
10
15
20
25
30
-10 -5 0 5 100.1
1
10
R (M
Ω)
Temperature (K)
VGate (V) +9 0 -9
50K
20K
10K
5K
2K
Res
ista
nce
(MΩ
)
VGate (V)
• Homoepitaxial thin films have better conductivity
• Higher effect at lower gate voltages
Drain-source current IDS plotted against the drain-source bias VDS of the Al2O3/SrTiO3 FET at 300 K. A channel length and a width of the FET device were 25 and 300 µm, respectively. The inset shows the blow-up of the IDS–VDS curve for VGS = 0 V
. (a) The gate-source bias VGS dependence of the drain-source current IDS for a fixed drain-source bias VDS = +1 V of the same device used for Fig. 2. The on–off ratiobetween VGS of 0 and 4 V for VDS of 1 V exceeds 100. (b) VGS dependence of the field effect mobility µFE. µ and µ were deduced from Fig. 3(a) by using Eqs. (1) and (2), respectively. Both increase monotonically with VGSand no saturation was observed even for large gate bias
Fig. 1. (a) Drain-source currentIDS plotted against the drain-source bias VDS of the Al2O3/KTaO3 FET for various gate voltages VGS at 300 K. TheKTaO3 single crystal was annealed at 700 °C prior to thedevice fabrication.
Manganites
SideSide--gate devices in a Lagate devices in a La0.670.67BaBa0.330.33MnOMnO33 exhibiting metallic behaviorexhibiting metallic behavior
Reversible shift of the metal-semiconductor transition temperature by 3.2K
120 128 136 144 152 160 168 1762021222324252627282930
Vgate = -66 V
0 VVgate = +66 V
TMI=147.84 K at Vgate =0ΔTMI=3.2 K at Vgate =+/- 66 V
R (M
Ω)
T (K)Comparison of the effects of electric and magnetic fields
Channel width 2.3 mmGate barrier width 1.4 mm
100 110 120 130 140
30
40
50
30 60 90 120 150
Vg = 0 V
T (K)
Vg = 0 VVg = -40 V
Vg = +40 V
R (M
Ω)
T (K)
B=0ΔTMI≈1.3K
190 200 210 220
3.9
4.0
4.1
4.2
90 120 150 180 210
Vg = 0 V
T (K)
Vg = -40 VVg = 0 V
Vg = +40 V
R (M
Ω)
T (K)
B=9TΔTMI≈1K
For εr≈1000, the equivalent charge per unit volume accumulated/depleted by a gate voltage
of ±66V in the channel is 6.2•1019 cm-3
Reversible shift of the transition temperature of manganites in planar field-effect devices
patterned by atomic force microscope I. Pallecchi et al., Appl. Phys. Lett. 83, 4435 (2003)
Film thickness 22 nm ⇒C≈7.6•εr pF/m
Field effect on planar devices made of epitaxial manganite perovskites I. Pallecchi et al., J. Appl. Phys. 95, 8079 (2004)
-80 -60 -40 -20 0 20 40 60 80
2832364044
30
33
3636
37
3817.0
17.2
17.4
17.6
Rds
(MΩ
)
Vg (Volts)
T=50K
Rds
(MΩ
)
T=100K
Rds
(MΩ
)
T=150K
Rds
(MΩ
)
T=190KThe relative change in channel resistance behavior as a function of the applied electric field is odd and linear at T>100K; at lower temperature the observed non-linearitiesmay be due to non-linear dielectric permittivity of the SrTiO3 substrate.
Sheet charge or volume charge?How much in depth does the electric field penetrate in a film with more than 1020 carriers/cm3? Shall we invoke a phase separationscenario?
Is this true field effect?
Side-gate devices in a La0.7Sr0.3MnO3 below the percolation threshold
0 50 100 150 200 2502
4
6
8
10
B=9T
B=6T
B=3T
B=1T B=0
Vg=0
R (M
Ω)
T (K)
50 100 150 2000.0
0.1
0.2
0.3
0.4
0 3 6 90.0
0.1
0.2
0.3
0.4
ΔR/R
(T=1
00K)
B (T)
B=9T
B=6TB=3T
B=1TB=0
ΔR/R
T (K)
The electric field enlarges or shrinks the metallic ferromagnetic domains, while the magnetic field
enlarges and also polarizes them.
50 100 150 2002
4
6
4
6
8
4
6
8
4
6
8
104
6
8
10
B = 9 T
Vg= - 70 V
Vg= + 70 V
Vg= 0
R (M
Ω)
T (K)
B = 6 T
Vg= - 70 V
Vg= + 70 VVg= 0
R (M
Ω)
B = 3 T
Vg= - 70 V
Vg= + 70 V
Vg= 0
R (M
Ω)
B = 1 T
Vg= - 70 V
Vg= + 70 V
Vg= 0
R (M
Ω)
B = 0
Vg= - 70 V
Vg= + 70 V
Vg= 0
R (M
Ω)
Semiconducting behavior with incipient metallic
transition
In a phase-separation scenario, metallic ferromagnetic regions are embedded in a semiconducting
paramagnetic matrix and their volume fraction is below the percolation threshold
I.Pallecchi et al.
High Temperature Superconductors
Field effects in superconducting films. Changeof the DS resistance of an ,8-nm-thick YBa2Cu3O7-d channel with a ,300-nm-thick Ba0.15Sr0.85TiO3 gate insulator. The blue curve corresponds to depletion of the carrier density, and the red curve correspondstoenhancement of the carrier density in the DS (drain–source) channel.
Temperature and electric field dependence of the capacitance and dielectric constant of the STO single-crystal gate insulator. Inset: schematic of the device
Resistivity as a function of temperature of the PBCO/NBCO heterostructure close to the foot of the transition and over the wholetemperature range (inset) for different applied fields across the gate dielectric. The resistivity was calculated using the thickness of the NBCO layer. The arrow indicates the value of TKT for zero appliedfield.
Critical temperature TKT (the Kosterlitz–Thoulesstemperature), and Tc0, the temperature at whichR=0.1 of the NBCO layer as a function of the measured polarization at TKT or Tc0
Temperature dependence of the resistivity of Nd1.2Ba1.8Cu3Oy films having different thicknesses: 4 u.c. (closed squares), 8 u.c. (open squares), 10 u.c. (closed circles), and 110 cells (open triangles). In the inset a sketch of the field effect device is shown.
Sheet resistance measured as a function of temperature on an 8 u.c. FET for Vg = 0 (closed circles), Vg = –30 V (open diamonds), and Vg
= –34 V (open circles). The dashed line indicates the value of the quantum resistance RQ = 6.45 k . In the inset the insulating–
superconducting transition is shown
Conclusions• Field effect in transition metal oxides is possible
adopting new geometries and high-κ materials.
• Back and side gate geometry allow direct access to the channel under FE
• In ZnO the application is close
• FE proved to be a powerful tools for the study of strongly correlated electron system:– Magnetic transition and phase separation in manganites– Superconducting properties in HTCS