1. Mott FET ITRS Workshop on Emerging Research Logic Devices Bordeaux, France, September 21, 2012 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

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

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Carrier doping, magnetic field, light, ・・・ light, ・・・ Decrease in U (band gap) Huge resistance change Y. Tomioka, unpublished

5. T Carrier density Antiferromagnetic insulator Critical point Electronic phases T Carrier density Paramagnetic metal Quantum CP (La,Sr)MnO 3 Superconductivity Changes in electronic, magnetic, and optical properties Optical property Magnetizum Ferromagnetic metal Antiferromagnetic insulator metal

6. Mott FET

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

8. Mott transition/transistor ‐ Scaling? ‐ Metal ON Insulator OFF Mott transition Number of electrons 10 3 electrons 4 nm In principle, a nanometer-scale Mott insulator shows the Mott transition No one has demonstrated ElectronsolidElectronliquid

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

10. Matsubara et al., PRL99, 207401 (2007) Reflectcance Electronic state Karr rotation Magnetic state Mott transition takes place within a few picoseconds Sample: Gd 0.55 Sr 0.45 MnO 3 Mott transition/transistor ‐ Fast switching? ‐ Ultrafast optical pump ‐ probe spectroscopy

11. Challenges 10 13 10 15 conventional gate dielectric (SiO 2 ): ~10 13 /cm 2 For the realization of a practical Mott transistor, Correlated-electron materials with a MI transition attainable at significantly lower carrier concentrationsCorrelated-electron materials with a MI transition attainable at significantly lower carrier concentrations High-k gate materials with a large breakdown strengthHigh-k gate materials with a large breakdown strength Ahn, Triscone, Mannhart, Nature 424, 1015 (2003). 10 14 – 10 15 cm -2

12. Electric double layer transistor

13. Outer Helmholtz plane J. T. Ye et al., Nature Mater. 9, 125 (2010) S. Ono et al., APL 94, 063301 (2009) a large amount of carriers: 10 14 – 10 15 cm -2 (@2V) Electric double layer transistor Electrolyte/ionic liquid is used as gate dielectrics Large capacitance: > 10  F/cm 2

14. CMO channel Thickness: ~ 30 nm W/L: ~ 10μm/100μm + − DEME + cation TFSI － anion GDS ++++ − −−− Ionic Liquid Sepa- rator − − CMO IDID IGIG VDVD VGVG YAO substrate 10  F/cm 2 @10 -3 Hz →1.5 × 10 14 /cm 2 @V G = 2.5 V Electric double layer transistor (EDLT) S. Asamuna, AS et al., Appl. Phys. Lett. 97, 142110 (2010) P-.H. Xiang, AS et al., Adv. Mater. 23, 5822 (2011)

15. Insulator Metal Thickness of channel : 40nm On/Off ratio: >10 @RT >10 3 @50K >10 3 @50K P-.H. Xiang, AS et al., Adv. Mater. 23, 5822 (2011) Nonvolatile change in resistance at “room temperature” EDLT consisting of compressively strained CaMnO 3 film

16. New approach for Mott transistor Sheet Resistance Temperature ·CMR-manganite, High T C cuprate ·10 14 ~ 10 15 /cm 2 carriers non-doped (V G = 0) carrier doped (V G ≠ 0) Sheet Resistance (logarithmic scale) Temperature “sharp” and “large” resistance change (Nd,Sm)NiO 3 T MI = 200–400 K VO 2 T MI = 300–340 K T MI

17. NdNiO 3 EDLT S. Asamuna, AS et al., Appl. Phys. Lett. 97, 142110 (2010)R. Scherwitzl et al., Adv. Mater. 22, 5517 (2010).

18. Nd 0.5 Sm 0.5 NiO 3 EDLT NSNO(0.5)/NdGaO 3 (110) (Thickness:~6 nm) 10 -2 10 -3 10 -4 Resistivity(  cm) 320300240220 Temperature (K) 260280 0V -2.3V -2.5V (Nd,Sm)NiO 3 channel VGVG 27-33-137 Temperature (ºC) Large resistance change (~10 5 ) at room temperature S. Asamuna, AS et al., unpublished 10 -5 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12 10 -6 I SD (A) 3-3012-2 V G (V) @300 K

19. ￥ Nonvolatile insulator metal Gate voltage VO 2 VO 2 EDLT Nakano et al., Nature 487, 459 (2012)

20. Oxide FET Mott FET SrTiO 3 TiO 2 (anatase) In-Ga-Zn-O GdBa 2 Cu 3 O 7 (La,Sr)MnO 3 Operation temperature On/Off ratio Gate material SrTiO 3 References R. T. ~10 5 0.37a-LaAlO 3 /MgO R. T. Gate voltage (V) Mobility (cm 2 /Vs) 5 APL92, 132107 (2008) ~102.5~10 5 a-CaHfO 3 JJAP46, L515 (2007) La 2 CuO 4 R. T.(?)<10<8SrTiO 3 APL76, 3632 (2000) (La,Ca)MnO 3 SrRu 1-x Ti x O 3 77K R. T. <10 <1 ±10PZT APL82, 4770 (2003) superconductivity: T C ~0.3K at V G =-3Velectrolyte Nat. Mater. 7, 855 (2008) 100-200K<10±3 PRL102, 136402 (2009) PZT (ferroelectrics ） 50-300K<3±3 Science 284, 1152 (1999) 10-300K<3±1PZT PRB74, 174406 (2006) ~10 8 125 - 6a-Y 2 O 3 APL89, 112123 (2006) Channel KTaO 3 ~10 4 0.4a-Al 2 O 3 R. T.100 APL84, 3726 (2004) CaMnO 3 50K R. T. >10 3 ~10 ±2 Adv. Mater. 23, 5822 (2011) (Nd,Sm)NiO 3 ~100K>10±2.5Ionic liquid APL97,142110 (2010) Ionic liquid NdNiO 3 ±2.5Ionic liquid unpublished VO 2 260K ~10 3 R. T.~10 5 Ionic liquid±3 Nature 487, 459 (2012)

21. Feature/potential of Mott FET Functionality: electronic, magnetic, and optical switchesFunctionality: electronic, magnetic, and optical switches Scaling limit: < 10 nmScaling limit: < 10 nm Nonvolatile and fast switchingNonvolatile and fast switching Bottleneck/challenge A large number of carriers (>10 14 cm -2 ) is necessary to be doped in order to induce the Mott transition Summary For the realization of a practical Mott transistor (“solid”) Higk-k gate materials with a large breakdown strength(“solid”) Higk-k gate materials with a large breakdown strength expected from theoretical and experimental studies on correlated electron materials