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ITRS Workshop on Emerging Research Logic Devices Bordeaux, France, September 21, 2012. Mott FET. A. Sawa 1,2 S. Asanuma, 1,2 P.-H. Xiang, 1,2 I. H. Inoue, 1,2 H. Yamada, 1 H. Sato, 1,2 and H. Akoh 1,2 1 National Institute of Advanced Industrial Science and Technology (AIST) 2 JST-CREST.

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Mott FET


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    1. 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

    2. Outline ・Correlated electron system ・Mott metal-insulator transition ・Mott field effect transistor Feature/potential Issues/challenges ・Experiments Mn-oxides Ni-oxides V-oxides ・Summary

    3. Correlated electron system Band insulator Mottinsulator electron orbital t electron One electron in an orbital due to on-site Coulomb repulsion (U > t) Pauli’s rule No more than 2 electrons in an orbital t:Transfer U: Coulomb E E E upper Hubbard band (UHB) U EF EF EF lower Hubbard band (LHB)

    4. Mott insulator-metal transition Mottinsulator Correlated-electron metal Carrier doping, magnetic field, light, ・・・ Electron liquid Electron solid Huge resistance change W < U W > U electron Mott transition (t < U) (t > U) Decrease in U (band gap) E E W: band width U: Coulomb energy W U U W Y. Tomioka, unpublished EF EF W∝ t t

    5. Electronic phases T T Critical point Antiferromagnetic insulator Ferromagnetic metal Paramagnetic metal Antiferromagnetic insulator Quantum CP Carrier density Carrier density Magnetizum Superconductivity Optical property (La,Sr)MnO3 insulator metal Changes in electronic, magnetic, and optical properties

    6. Mott FET

    7. MottFET Mott FET can control electronic, magnetic, and optical properties by electric field Gate Drain Source Correlated-electron material “ON” “ON” “ON” “OFF” “electronic” “magnetic” “optical”

    8. 103electrons Number of electrons 4nm Motttransition/transistor‐Scaling?‐ Electron solid Electron liquid Metal Insulator Mott transition ON OFF In principle, a nanometer-scale Mott insulator shows the Mott transition No one has demonstrated

    9. Motttransition/transistor‐Nonvolatile?‐ First order phase transition Hysteretic behaviorNonvolatile(?) Kotliaret.al PRL 89, 046401 (2002). V > 0 V < 0 electrode doped-Mott ins. Oka, Nagaosa, PRL95, 266403 (2005) No one has demonstrated

    10. Motttransition/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

    11. 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

    12. Electric double layer transistor

    13. 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 mF/cm2 a large amount of carriers: 1014 – 1015 cm-2(@2V) J. T. Ye et al., Nature Mater. 9, 125 (2010)

    14. Electric double layer transistor (EDLT) VD VG IG ID Ionic Liquid Sepa- rator − − − − + + + + D S G − − − − CMO YAO substrate DEME+cation TFSI- anion + − CMO channel Thickness: ~30nm W/L: ~10μm/100μm 10mF/cm2@10-3Hz →1.5 × 1014 /cm2@VG= 2.5 V S. Asamuna, ASet al., Appl. Phys. Lett. 97, 142110 (2010) P-.H. Xiang, ASet al., Adv. Mater. 23, 5822 (2011)

    15. EDLT consisting of compressively strained CaMnO3 film Insulator Metal Thickness of channel : 40nm On/Off ratio: >10 @RT >103 @50K Nonvolatile change in resistance at “room temperature” P-.H. Xiang, ASet al., Adv. Mater. 23, 5822 (2011)

    16. New approach for Mott transistor non-doped (VG = 0) carrier doped (VG ≠ 0) Sheet Resistance (logarithmic scale) Sheet Resistance TMI Temperature Temperature “sharp” and “large” resistance change ·CMR-manganite, High TCcuprate ·1014~ 1015/cm2 carriers (Nd,Sm)NiO3TMI = 200–400 K VO2TMI = 300–340 K

    17. NdNiO3 EDLT R. Scherwitzlet al., Adv. Mater. 22, 5517 (2010). S. Asamuna, ASet al., Appl. Phys. Lett. 97, 142110 (2010)

    18. Nd0.5Sm0.5NiO3 EDLT NSNO(0.5)/NdGaO3 (110) (Thickness:~6 nm) Temperature (ºC) 10-5 -33 -13 7 27 10-6 @300 K 10-2 10-7 (Nd,Sm)NiO3 channel VG 0V 10-8 -2.3V ISD (A) -2.5V 10-9 10-10 10-3 Resistivity(Wcm) 10-11 10-12 -3 -2 -1 0 1 2 3 VG(V) 10-4 220 240 260 280 300 320 Temperature (K) Large resistance change (~105) at room temperature S. Asamuna, ASet al., unpublished

    19. VO2EDLT ¥ Nonvolatile Gate voltage VO2 insulator metal Nakano et al., Nature 487, 459 (2012)

    20. Oxide FET Operation temperature On/Offratio Mobility (cm2/Vs) Gate voltage (V) Channel Gate material References SrTiO3 R. T. ~105 2.5 ~10 a-CaHfO3 JJAP46, L515 (2007) SrTiO3 superconductivity:TC ~0.3K at VG=-3V electrolyte Nat. Mater. 7, 855 (2008) KTaO3 R. T. ~104 0.4 100 a-Al2O3 APL84, 3726 (2004) 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) GdBa2Cu3O7 50-300K <3 ±3 Science 284, 1152 (1999) La2CuO4 R. T.(?) <10 <8 SrTiO3 APL76, 3632 (2000) (La,Sr)MnO3 10-300K <3 ±1 PZT PRB74, 174406 (2006) Ionic liquid (La,Ca)MnO3 100-200K <10 ±3 PRL102, 136402 (2009) 77K <10 SrRu1-xTixO3 ±10 PZT APL82, 4770 (2003) R. T. <1 50K R. T. >103 ~10 CaMnO3 Ionic liquid ±2 Adv. Mater. 23, 5822 (2011) NdNiO3 ~100K >10 ±2.5 Ionic liquid APL97,142110 (2010) (Nd,Sm)NiO3 ±2.5 Ionic liquid R. T. ~105 unpublished VO2 260K ±3 Ionic liquid ~103 Nature 487, 459 (2012)

    21. 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 (>1014cm-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