Towards novel Mott FET: Concept, Present Status, and Future

1Isao H. Inoue

Towards novel Mott FET: Concept, Present Status, and Future

National Institute of Advanced Industrial Science & Technology (AIST) (Tsukuba, Japan)

[email protected] http://staff.aist.go.jp/i.inoue/Seminar @ Universitat Autnoma de Barcelona, Spain 9 Dec 2014

Tem

p

Ordered State

Classical Critical Point

Super

CeCu2Si2Te

mp

Antiferro

Pressure

Quantum Critical Point

Physical Parameters

Quantum critical phenomena

Pressure

Super

UGe2

Tem

p

Ferro

2


Phys. Parameters are alwayseither Pressure or Mag. Field

UGe2

Saxena et al., Nature 406, 587 (2000) [ Coleman, Nature 406, 580 (2000) ]

Ferro

Super

Pressure

Tem

p

Yuan et al., Science 302, 2104 (2003)

CeCu2Si2

AFSuper

Pressure

Tem

p

3


Continuous and reversible control of electronic states on the verge

of the quantum critical point

Randomness-free method: quantum critical phenomena is

so vulnerable to disorders

4

For QCP study, we need

[email protected] http://staff.aist.go.jp/i.inoue/Seminar @ Universitat Autnoma de Barcelona, Spain 9 Dec 2014 5

Electrostatic Carrier Doping

6Quantum critical phenomena

Electrostatic carrier doping

Mott transistor Exotic phonomena

7Quantum critical phenomena


Mott transistor Exotic phonomena

9Before explaining what is Mott FET, lets revisit the basics of electrostatic carrier doping


Field effect to an insulator

Channel material (insulator)

Gate electrode (metal)

Gate insulator+

-

+

-

+

-

+

-

+

-

Gate insulator


++ + ++ + + ++

- -- -

--

-- -

--

-- -

- ---

- -- -- --

-h+

h+h+

h+ h+

h+h+

h+h+h+

h+

h+

h+

h+h+

h+ h+

depletion layer

- --

- - -

-- -

--

-- -

- ---

- -- -- --

-h+

h+

h+h+

h+ h+

h+

h+ h+

h+

h+

h+

h+h+

h+h+

h+

h+h+

h+

h+h+

h+

h+

h+h+

- acceptorh+ hole

Gate electrode (metal)

Channel material (doped p-type Si)

Conventional MOSFET


+++

+++

+++

--

--

- -

---

--

--

-

-- -

-

---

--

--

-h+

h+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

h+h+

depletion layer (~m)

VG =V ins +

V ins

chemical potential

E C

E int

E V

How "Channel" is created

+++

+++

+++

--

--

- -

---

-

--

-

-- -

-

---

--

--h

+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

+ - -

++

--

--

++

++ -+

-+


chemical potential

V ins

inversion layer (~nm) = channel

VG =V ins +

E C

E int

E V

However, present Metal - Oxide - Semicondoctor FET is faced with a fatal

problem

13


H. Takamizawa et al., Appl. Phys. Express 4, 036601 (2011)

Laser-assisted atom probe tomography (LAPT) picture

14

Dopants in Si MOSFET


20nm device has only ~10 carriers.

15

H. Takamizawa et al., Appl. Phys. Express 4, 036601 (2011)

Laser-assisted atom probe tomography (LAPT) picture

20nm

20nm

5nm

M. R. Castell et al., Nature Materials 2, 129 (2003)3D atom probe (3DAP) picture

Dopants in Si MOSFET in 2020


Present MOSFET++

+++

++

++

--

--

- -

---

-

--

-

-- -

-

---

--

--h

+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

+ - -

++

--

--

++

++ -+

-+

V ins



chemical potential

VG =V ins +

E C

E int

E V


Present MOSFET vs. Future one

++

++

+

-

--

--

-

+ -

++ -

+ -

+++

+++

+++

--

--

- -

---

-

--

-

-- -

-

---

--

--h

+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

+ - -

++

--

--

++

++ -+

-+


Channel is hardly created for small dopant density

++

++

+

- h+

--

--

-

too large accumulation layer no effective channel

VG =V ins+

V ins

chemical potential

E C

E int

E V

++

++

+

-

--

--

-

+ -

++ -

+ -

V ins

chemical potentialVG =V ins+

E C

E int

E V


Present MOSFET vs. Future one

++

++

+

-

--

--

-

+ -

++ -

+ -

no effective channel

VG =V ins+

V ins

chemical potential

E C

E int

E V

+++

+++

+++

--

--

- -

---

-

--

-

-- -

-

---

--

--h

+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

+ - -

++

--

--

++

++ -+

-+

V ins



chemical potential

VG =V ins +

E C

E int

E V

Miniaturisation Limit!!

Alternative of MOSFET is an urgent necessity.

But what can replace S?

20


Mott FET may be the only choice

First transistor (Bell Lab 1947)

Ge junction transistor (Bell Lab 1950)

Mott transistor (2020 ?)

22

Then, what is the Mott insulator?


Band of electrons kinetic energy


Valence Band

Conduction Band

Energy vs momentum plot


when you are sleepy

Energy vs momentum plotEnergy vs momentum plot


Density of States (DOS)


Valence Band

Conduction Band

EF

DOS of the normal band insulator

D(E)

EE

k


Conduction Band

EF

D(E)

E

k

DOS of the normal metal

EEF


EF

D(E)

E

k


EEF


D(E)

E

k


EEFEF

* *

m*


D(E)

E

k


EEFEF

* *

m* still metallic !!

heavy mass. "no" move.

32

Disappear !?

wheres Britney gone?

33

But before answering, we need to know

what enhances the effective mass?


Electrons with a spin degree of freedom

Orbital of an atomic site: size = kinetic energy = band width

band width = W

AIST Aris AIST Tls

34

couch

Naive model of the Mott transition


Pauli principle

Electron Correlations

= 0Electron

Correlations = U

35

Hubbard Model


transfer is not available

transfer is available

W (>U)

Competition between U and W

W (


U < W U > W

37



U On-site Coulomb Repulsions Energy W One-electron BandwidthKinetic Energy

Charge fluctuation is completely suppressed (as if it were a fully-filled band insulator)


38


Charge fluctuation is completely suppressed (as if it were a fully-filled band insulator)


39

U On-site Coulomb Repulsions Energy W One-electron BandwidthKinetic Energy

40

What is an answer for "Disappear !?"


Evolution of the density of states

G. Kotliar and D. Vollhardt Phys. Today 57, 53 (2004).

41

U/W = 0

U/W = 0.5



42


a renormalized band heavy-mass electrons (holes) forms a band.

incoherent states discrete energy levels of

localised electrons (holes).

U/W = 0

U/W = 0.5

U/W = 1.2



43


U/W = 0

U/W = 0.5

U/W = 1.2

U/W = 2

Finally the gap opens!! between the Hubbard bands though they are not the bands


Correlated Metal

Mott Insulator


44


[email protected] http://staff.aist.go.jp/i.inoue/China-Japan-Korea RRAM and FO WS@Beijing 16 Jan. 2014

ex

p(

) (a

rb. u

nits

)-3.0 -2.0 -1.0 0.0 1.0

(eV)

Quasi-particle spectra of Ca1-xSr xVO3

obtained by UPS

band calc. x=0.9 x=0.8 x=0.4 x=0.3

Isao H. Inoue et al., Phys. Rev. Lett. (1995)



First experimental evidence


MOSFET in 2020On State Off State

Mott FETVG

M. R. Castell et al., Nature Materials 2, 129 (2003)

3D atom probe (3DAP) picture

20nm device has more than 100,000 carriers. Carrier density is independent of device sizes.

No miniatur. prob. in Mott FET

20nm device has only ~20 carriers. Almost the end of the miniaturisation

47

Mott FET ?!

Mott insulator is an insulator How can you dope it carriers

by electric field?

[email protected] http://staff.aist.go.jp/i.inoue/China-Japan-Korea RRAM and FO WS@Beijing 16 Jan. 2014

J. Chakhalian, A. J. Millis and J. Rondinelli, Nature Materials 11, 92 (2012)


Apply E to a Mott insulator


++

++

+

--

--

- + -


VG =V ins+

V ins

E int

VG =V ins+

V ins

E int

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

E UHB

E LHB

E UHB

E LHB

chemical potential


++

++

+

--

--

- + -+ -+ -

+ -+ -

+ -+ -

+ -+ -

+ -


VG =V ins

V insE UHBE int

VG =V ins+

V ins

E int

sudden appearance of metallic state

E LHB

E UHB

E LHB

screening length (~nm)

chemical potential

Mott insulators ionic crystals (because of the strong electron correlations)

Defects form easily under large electric field.

51

Largest obstacle to realise the Mott FET


TiO2-x Co1-xO, Fe1-xO, Ni1-xO valence electron

1st electron ionisation

2nd electron ionisation

neutral composite

neutral composite

valence electron

Defects in transition-metal oxides


M. Janousch et al., Adv. Mat. 19, 2232 (2007)

0.2 mol% Cr-doped SrTiO3

By applying 0.1MV/cm for about 30 min

Pt

Pt

Vo are created, distributed in the channel, and form a metallic path.

VO creation by electric-field


Electrochemical reaction?

Science 339, 1402 (2013)VO2VO2


Hydrogen doping?

Nano Letters 12, 2988 (2012)

Modulation of the Electrical Properties of VO2 Nanobeams Using anIonic Liquid as a Gating MediumHeng Ji, Jiang Wei, and Douglas Natelson*

Department of Physics and Astronomy, MS 61, Rice University, 6100 Main Street, Houston, Texas 77005, United States

ABSTRACT: Vanadium dioxide (VO2) is a strongly corre-lated transition metal oxide with a dramatic metalinsulatortransition at 67 C. Researchers have long been interested inmanipulating this transition via the eld eect. Here we reportattempts to modulate this transition in single-crystal VO2nanowires via electrochemical gating using ionic liquids.Stray water contamination in the ionic liquid leads to large,slow, hysteretic conductance responses to changes in the gatepotential, allowing tuning of the activation energy of theconductance in the insulating state. We suggest that thesechanges are the result of electrochemical doping via hydrogen. In the absence of this chemical eect, gate response is minimal,suggesting that signicant eld-eect modulation of the metalinsulator transition is not possible, at least along thecrystallographic directions relevant in these nanowires.KEYWORDS: Vanadium dioxide, single crystal nanowire, ionic liquid, electrochemical doping, hydrogen doping

VO2 is a classic strongly correlated material that exhibits adramatic metal to insulator transition1 (MIT) whencooled through 67 C, accompanied by a simultaneousstructural transition from a high-temperature rutile to a low-temperature monoclinic structure. Temperature, pressure, andchemical doping can signicantly aect the phase transition2,3

by shifting the transition temperature or even stabilizing otherphases (M2 and triclinic phases).There has long been interest in electrostatic modulation of

the MIT in VO2, but this has remained a challenge. First, therelatively high carrier density observed by Hall measurementssuggests that VO2 has a very short screening length

4,5 thatlimits the electrostatic gating eciency, conning the eect ofthe gate to an extremely thin channel layer. Second, withconventional oxide gate dielectrics such as SiO2, Al2O3, andHfO2

5 leakage current often appears with applied high gatevoltage, and this current can cause self-heating and aect theMIT. Inhomogeneity of the sample due to strain and grainboundaries can also complicate matters. Gating during thephase coexistence portion of the transition in polycrystallinethin lms has shown some eect on the percolation of themetallic phase.6 Recent measurements with conventional gatedielectrics show indications of switching in the Raman responseas a function of gate,7 and small gate modulations of theconductance with long time constants5 and slow hysteresis.8

Recently, electrolytic gating with a very high inducedconcentration of carriers9 (8 1014cm2) has been realizedsuccessfully on various materials by using an ionic liquid as theelectrolyte. A gate-driven insulator-to-metal transition has beenachieved on wide band gap (3.3 eV) semiconductor ZnOtransistor.10 In the insulators SrTiO3

11 and KTaO3,12 super-

conductivity was observed in ionic liquid-gated single-crystaldevices. Very recent ionic liquid gating experiments on

sputtered VO2 lms13 have shown a reduction in channel

resistance at positive gate potentials in the monoclinic phasewith a slow time dependence to the response.In this paper, we report our examination of ionic liquid

gating of single crystal VO2 nanowires and nd that even withwhat should be extremely large accumulation of ionic charge onthe VO2 surface, when dry ionic liquid is employed, there is noobservable electrostatically induced phase transition. Withwater-containing ionic liquid or other hydrogen-containingliquids used as electrolytes, we observe large, slow, hystereticgate response. Following positive gate bias applied attemperatures above the transition, the low-temperatureconductance is strongly increased, and this increase is persistentfollowing the removal of any gate voltage. We ascribe thesechanges to electrochemical doping of the bulk of the VO2crystals, most likely with hydrogen, that can signicantly changeVO2s electrical properties.Rather than polycrystalline lms, in this work we used

individual single-crystal VO2 nanobeams grown by vapor phasetransport.14 These crystals possess a highly homogeneoussurface (1 nm roughness) and minimal lattice defectscompared to conventionally deposited VO2 lms. From ourprevious research, the electric transport properties based ontwo-terminal VO2 nanostructures have been well character-ized.15 A typical single-crystal nanowire has a width and athickness of a few hundred nanometers, and a length of tens ofmicrometers. The contacts for the three-terminal devices werepatterned by electron-beam lithography and Ti/Au (typically 5

Received: February 22, 2012Revised: April 6, 2012Published: May 11, 2012

Letter

pubs.acs.org/NanoLett

2012 American Chemical Society 2988 dx.doi.org/10.1021/nl300741h | Nano Lett. 2012, 12, 29882992

Modulation of the Electrical Properties of VO2 Nanobeams Using anIonic Liquid as a Gating MediumHeng Ji, Jiang Wei, and Douglas Natelson*

Department of Physics and Astronomy, MS 61, Rice University, 6100 Main Street, Houston, Texas 77005, United States

ABSTRACT: Vanadium dioxide (VO2) is a strongly corre-lated transition metal oxide with a dramatic metalinsulatortransition at 67 C. Researchers have long been interested inmanipulating this transition via the eld eect. Here we reportattempts to modulate this transition in single-crystal VO2nanowires via electrochemical gating using ionic liquids.Stray water contamination in the ionic liquid leads to large,slow, hysteretic conductance responses to changes in the gatepotential, allowing tuning of the activation energy of theconductance in the insulating state. We suggest that thesechanges are the result of electrochemical doping via hydrogen. In the absence of this chemical eect, gate response is minimal,suggesting that signicant eld-eect modulation of the metalinsulator transition is not possible, at least along thecrystallographic directions relevant in these nanowires.KEYWORDS: Vanadium dioxide, single crystal nanowire, ionic liquid, electrochemical doping, hydrogen doping

VO2 is a classic strongly correlated material that exhibits adramatic metal to insulator transition1 (MIT) whencooled through 67 C, accompanied by a simultaneousstructural transition from a high-temperature rutile to a low-temperature monoclinic structure. Temperature, pressure, andchemical doping can signicantly aect the phase transition2,3

by shifting the transition temperature or even stabilizing otherphases (M2 and triclinic phases).There has long been interest in electrostatic modulation of

the MIT in VO2, but this has remained a challenge. First, therelatively high carrier density observed by Hall measurementssuggests that VO2 has a very short screening length

4,5 thatlimits the electrostatic gating eciency, conning the eect ofthe gate to an extremely thin channel layer. Second, withconventional oxide gate dielectrics such as SiO2, Al2O3, andHfO2

5 leakage current often appears with applied high gatevoltage, and this current can cause self-heating and aect theMIT. Inhomogeneity of the sample due to strain and grainboundaries can also complicate matters. Gating during thephase coexistence portion of the transition in polycrystallinethin lms has shown some eect on the percolation of themetallic phase.6 Recent measurements with conventional gatedielectrics show indications of switching in the Raman responseas a function of gate,7 and small gate modulations of theconductance with long time constants5 and slow hysteresis.8

Recently, electrolytic gating with a very high inducedconcentration of carriers9 (8 1014cm2) has been realizedsuccessfully on various materials by using an ionic liquid as theelectrolyte. A gate-driven insulator-to-metal transition has beenachieved on wide band gap (3.3 eV) semiconductor ZnOtransistor.10 In the insulators SrTiO3

11 and KTaO3,12 super-

conductivity was observed in ionic liquid-gated single-crystaldevices. Very recent ionic liquid gating experiments on

sputtered VO2 lms13 have shown a reduction in channel

resistance at positive gate potentials in the monoclinic phasewith a slow time dependence to the response.In this paper, we report our examination of ionic liquid

gating of single crystal VO2 nanowires and nd that even withwhat should be extremely large accumulation of ionic charge onthe VO2 surface, when dry ionic liquid is employed, there is noobservable electrostatically induced phase transition. Withwater-containing ionic liquid or other hydrogen-containingliquids used as electrolytes, we observe large, slow, hystereticgate response. Following positive gate bias applied attemperatures above the transition, the low-temperatureconductance is strongly increased, and this increase is persistentfollowing the removal of any gate voltage. We ascribe thesechanges to electrochemical doping of the bulk of the VO2crystals, most likely with hydrogen, that can signicantly changeVO2s electrical properties.Rather than polycrystalline lms, in this work we used

individual single-crystal VO2 nanobeams grown by vapor phasetransport.14 These crystals possess a highly homogeneoussurface (1 nm roughness) and minimal lattice defectscompared to conventionally deposited VO2 lms. From ourprevious research, the electric transport properties based ontwo-terminal VO2 nanostructures have been well character-ized.15 A typical single-crystal nanowire has a width and athickness of a few hundred nanometers, and a length of tens ofmicrometers. The contacts for the three-terminal devices werepatterned by electron-beam lithography and Ti/Au (typically 5

Received: February 22, 2012Revised: April 6, 2012Published: May 11, 2012

Letter

pubs.acs.org/NanoLett

2012 American Chemical Society 2988 dx.doi.org/10.1021/nl300741h | Nano Lett. 2012, 12, 29882992

56

Mott insulators ionic crystals (because of the strong electron correlations)

Defects form easily under electric field.

Can we apply electric field to Mott insulators without causing

electrochemical reactions?

57

Isao H. Inoue Neeraj Kumar Ai Kitou

Use Parylene to suppress

the defects formation


58

Isao H. Inoue Ai Kitou

Use Parylene to suppress

the defects formation


Neeraj Kumar (AIST)

Pablo Stoliar (CIC nanoGUNE)

59

Parylene !?


"Biocompatible glass is coated with protective substances for anti-migration and insulating properties and this is where the Parylene C coating comes.

It also protects the microchip from natural substances in the body, that may penetrate through micro-cracks caused by mechanical damages."

From "moving a pet to Australia" website

by ParyleneProtect surface

Parylene coated rotors and stators are used to control the Canadian arm for NASA Space Shuttle.

Parylene coated circuit boards provides excellent resistance to moisture, chemicals, and mold. Circuit boards for medical equipment can be steam and gamma sterilised. Parylene can also prevent dendrite and tin whisker growth.

From "Paratronix Inc." website

Parylene coating of paper documents, autographs, and photos retards the aging process and protects from moisture, mold, and chemicals.

60


Creation of oxygen vacancies is suppressed. Channel is kept clean.

P.-J. Chen et al., Lab on a Chip 6, 803 (2006)

conformal coating

by ParyleneProtect oxide surface

oxides

61

62

High-k/Parylene bilayer to accumulate more carriers

must be very thin


"Biocompatible glass is coated with protective substances for anti-migration and insulating properties and this is where the Parylene C coating comes.

It also protects the microchip from natural substances in the body, that may penetrate through micro-cracks caused by mechanical damages."

From "moving a pet to Australia" website

In General, Parylene film is very thick

Parylene coated rotors and stators are used to control the Canadian arm for NASA Space Shuttle.

Parylene coated circuit boards provides excellent resistance to moisture, chemicals, and mold. Circuit boards for medical equipment can be steam and gamma sterilised. Parylene can also prevent dendrite and tin whisker growth.

From "Paratronix Inc." website

Parylene coating of paper documents, autographs, and photos retards the aging process and protects from moisture, mold, and chemicals.

Parylene film in most of the literatures are more than ~1m thick.

63


High-k (HfO2, Ta2O5, etc.)/Parylene bilayer

Hybrid gate insulator

high-k materials (~15 < < ~25) + Parylene-C (=3.2)

Isao Inoue and Hisashi Shima, Japan Patent Number: 5522688, Date of Patent: 18th April, 2014

64


SrTiO3

AlHfO2

Au

Ti

parylene

BF-TEM image

65


SrTiO3

Al

HfO2Ti

parylene

BF-TEM image

66

5nm


SrTiO3Al

HfO2

Au Ti

parylene

STEM-EDS mapping

67

68

Intel 4004 IC the original microprocessor or computer on a chip.

We are preparing FET devices using a conventional

photolithography

Source Drain

Gate

V+V

VH

VH+

4m12m

AIST 2014 designed for 4-probe and Hall effect measurements to study "physics of Mott FET.

Doped semiconductor case


+++

+++

+++

--

--

- -

---

--

--

-

-- -

-

---

--

--

-h+

h+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

h+h+


VG =V ins +

V ins

chemical potential

E C

E int

E V

+++

+++

+++

--

--

- -

---

-

--

-

-- -

-

---

--

--h

+h+

h+h+

h+h+

h+h+

h+

h+

h+

h+

h+h+

+ - -

++

--

--

++

++ -+

-+


chemical potential

V ins


VG =V ins +

E C

E int

E V


Large single crystals are commercially available

1cmStep-and-terrace surface is easily obtained

perovskite structure Insulator with ~3.3eV band gap

SrTiO3 as a benchmark

Not a Mott insulator, though.

5[nm

]0

0

400

800800

400

SrTiO3

From a catalog of SHIKOSHA Co.Ltd.

SrTiO3 is widely used as a substrate

of oxide thin-film growth


++

++

+

--

--

- + -

VG =V ins+

V ins

VG =V ins+

V ins

+ -

+ -

+ -

+ -

+ -

+ -

+ -

+ -

E C

E V

E C

E V

chemical potentialF

sub-threshold region ( < ) strongly inverted region ( > )

F


72

sub-threshold region ( < F )

strongly inverted region ( > F )

=175mV/decades

Cch/Cins = 1.8

F = 0.6eV

Vth= 1.6V

Very small sub-threshold swing


Very small sub-threshold swing

73


~1014cm-2 and ~10 cm2/Vs

74

10

0.1

0.001

10k

1M

1G

h/e2

@300K

breakdown

@300K

L = 12m W = 4m

HfO2(20nm)/Parylene-C(6nm)/SrTiO3

75

High-k/Parylene/SrTiO3

cleaner interface

continuous and large doping control

76

High-k/Parylene/Mott Insultor

cleaner interface

continuous and large doping control

Coming Soon!

77

Half-Time Summary1. Why we need the Mott transistor? - miniaturisation limit!

2. How to avoid defects formation at the interface - Parylene!

78



Mott transistor Exotic phonomena on the horizon!

79



Mott transistor Exotic phonomena on the horizon!

Several mor

e

slides to sho

w

if time allows

80

National Institute of Advanced Industrial Science & Technology (AIST) (Japan)

Christos Panagopoulos

Nanyang Technological University (Singapore)

Azar B. Eyvazov*

Isao H. Inoue

CNRS & Universit Paris Sud (France)

Pablo Stoliar** Marcelo J. Rozenberg***

*also AIST (now a PhD student in Cornell University, US)

**also Universidad Nacional de San Martin, Argentina, and Universit de Nantes, France

***also Universidad de Buenos Aires, Argentina


Unusual I-V curves

Hardly seen in Al2O3/SrTiO3 Al2O3/SrTiO3 has some amount of carriers from the first

K. Ueno et al., App. Phys. Lett. 83, 1755 (2003)

10-6

81

A. B. Eyvazov et al., Sci. Rep. 3, 1721 (2013)


When increasing VSD

10-6V/VSD

I SD

V/VSD

I SD

0.3mm/0.8mm = 0.375

increasing VSD for large fixed VG

0.3mm/0.8mm = 0.375

normal

abnormal !

increasing VSD for small fixed VG

82



10-6

When increasing VG

V/VSD

I SD

V/VSD

I SD

0.3mm/0.8mm = 0.375

0.3mm/0.8mm = 0.375

increasing VG for any fixed VSD

normal

abnormal !

not observed

83



Proc. Phys. Soc. 82, 954 (1963)

Nonlinear by E. Scholl, Cambridge Univ. Press (2001)

Negative Differential Resistance

84


V/VSD

I SD

0.3mm/0.8mm = 0.375

increasing VG for any fixed VSD

current path!

V/VSD

I SD

0.3mm/0.8mm = 0.375

increasing VSD for small fixed VG

field domain!

Negative Differential Resistance

85



Numerical simulation: results

86



Comparison of Exp & Calc

10-6

87


Experiment Calculation


Simulation of path formation

88


Spatio-temporal current paths. All disappears when VG turns off. Not due to oxygen defects!!


Schematic picture of channel

89



High-k/Parylene/SrTiO3 FET

cleaner interface

filamentation90


1011 1012

H. Nakamura et al., Appl. Phys. Lett. 89, 133504 (2006)

h/e2=25.8k

92

Filamentation at 7K

93

Filamentation Occurs even at 7K!!

Then, what happens at ultra-low T

superconductivity?


34

SC at LaAlO3/SrTiO3 interface

S. Thiel et al., Science 313, 1942 (2006)

N. Reyren et al., Science 317, 1196 (2007)

TC ~ 200mK HC2 ~ 0.1T JC ~ 100A/cmnonvolatile


34

SC at electrolyte/SrTiO3 interface

K. Ueno et al., Nature Materials 7, 855 (2008)

TC ~ 400mK HC2 ~ 0.1T JC ~ 300A/cm


33

SC of bulk SrTiO3-

M. Jourdan et al., Eur. Phys. J. B 33, 25 (2003)

TC ~ 140mK HC2 ~ 0.3T JC ~ 100A/cm2 ~ 100A/cm (for t10nm) Good agreement in the orders with

1) SC at LaAlO3/SrTiO3 interface, 2) SC at electrolyte/SrTiO3 interface,

and

3) our gate-annealed SC (next slide).

31

Sample A

VG threshold is lowered. Nonvolatile metallic state.

Bulk-like superconductivity due to oxygen vacancies?

TC ~ 350mK HC2 ~ 0.1T

prolonged (one-day) applicationof large VG

SC was seen only after

Al electrode

Volta

ge (m

V)

0

0.2

Temperature (K)1.8 2.21.4

H. Nakamura et al., J. Phys. Soc. Jpn. 78, 083713 (2009).


SC in "gate-annealed" parylene/SrTiO3


32

Oxygen vacancy creation on SrTiO3

M. Janousch et al., Adv. Mat. 19, 2232 (2007)

0.2 mol% Cr-doped SrTiO3

By applying 105V/cm for about 30 min

Pt

Pt

Oxygen vacancies are created, and distributed in the channel, and form a metallic path.

99

All the superconductivity of SrTiO3 interface shown here might be caused by oxygen defects

Is this the conclusion?

100

Is this the conclusion?

No. we observed another

All the superconductivity of SrTiO3 interface shown here might be caused by oxygen defects

20mK

7K

39

1011 1012

Domain formation of doped carrier and percolation transition

h/e2=25.8k

1011 1012 1013

108

106

104

102

1

Gate-annealed superconductivity below 350mK



due to oxygen defects!!

Another Zero-R State

35

oxygen vacancies due to VG application hinder this fragile zero-R state.

Sample B

the first few applications of VGonly seen during


VG (V)

continuous & reversible control of normal zero-R transition!

TC? ~ 120mK HC2? ~ 0.01T JC ? ~ 0.1A/cm

TC ~ 400mK HC2 ~ 0.1T JC ~ 300A/cm

SC at electrolyte/SrTiO3 interface gate-annealed SC SC at LaAlO3/SrTiO3 interface bulk superconductivity

is Fragile

102

Zero-R State

103



Mott transistor Exotic phonomena on the horizon! Zero-R state


zzz

high-k/Parylene to protect surface

Filamentation

Summary

Date post:	19-Jul-2015
Category:	Science
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