Size-dependent Metal-insulator Transition Random Materials Crystalline & Amorphous Purely Electronic Switching

Transcription

1 Nanometallic RRAM I-Wei Chen Department of Materials Science and Engineering University of Pennsylvania Philadelphia, PA Nature Nano, 6, 237 (2011) Adv Mater,, 23, 3847 (2011) Adv Func Mater,, 22, 546 (2012)

2 Size-dependent Metal-insulator Transition Random Materials Crystalline & Amorphous Purely Electronic Switching

3 A Metal? An Insulator?

4 Periodic System With a band gap, or without Insulator: : infinite resistivity at 0K Metal: : finite resistivity at 0K

5 Random System Aperiodic: No sharp band edge Mott : Mobility edge (k space) Anderson: = diffusion i 0K (elastic tunneling) = extent of wave function Metallic if if < Metal: Insulator: < < Insulating if > Sample size (thickness) =

6 An insulator, small enough, is a metal! Conducting Insulating

7 Long- Random Insulator Atomically mixing metal into insulator

8 Nanometallic Thin Film: Crystalline Top electrode Nanometallic Film Bottom electrode Substrate [001] 10 [100] I (m ma) nm 20 nm Voltage (V) 75%CaZrO 3-25%LaNiO 3 Insulator Metal

9 After switching (0) 1M ( ) Resis stance ( 100k 10k HR 1k Voltage-controlled MIT ~ ~ 25 nm 10 6 LR Thickness (nm) As fabricated (1) ( ) Res sistance 20 nm 10 5 Thickness nm nm 10 nm nm Voltage (V) (1) Low resistance Ohmic I (A) Voltage (V) (0) High resistance non-ohmic

10 Mechanism for Switching (on/off) LRS TE HRS TE T2 T2 T3 T3 T1 electron flow T1 electron flow BE BE Free electron path ( > ) Isolated traps Filled traps < Repulsion Change Diffusion Length: on/off

11 Switching: A Metal-Insulator Transition rrent ( A A) Cu High resistance HR state Insulating K 100 K 7K Temp Cu urrent (m ma) Low resistance LR state Metallic Voltage (V) Voltage (V) Resistan nce ( ) K 300K Voltage (V) 7K 100 K Temp 300 K Temp

12 Nanometallic Glasses SiO 2 :Pt SrRuO 3 15 Pt Si Random SiO 2 :f Pt alloy Insulator Metal 10 I [ma A] nm 21 nm V [V] 2 293K I (ma) K V (V)

13 -triggered (SiO 2 :0.2 Pt) Nanoscale MIT 100M f-triggered ( ~20 nm) ) R ( 1M 10k 7 nm nm V (V) 21 nm 100M 12 nm 9 nm 1M R ( ) 10k 7% 13% 20% 25% 30% V (V)

14 Random Nanometallic Materials Insulator : Metal [001] LaAlO 3 :LaNiO 3 [100] LaAlO 3 :SrRuO 3 CaZrO 3 :LaNiO 3 CaZrO 3 :SrRuO 3 Si 3 N 4 :metal A LaNiO 3 -CaZrO 3 Si 3 N 4 :metal B Si 3 N 4 :metal C Si 3 N 4 :Pt SiO 2 :Pt Oxide A:Pt etc. SiO 2 :Pt

15 Nanometallicity Percolation (kohm-c cm) Res sistivity %Pt 45%Pt SiO 2 :Pt f c (mol %) f Percolation (mol%) 30%Pt SiO 2 :Pt Temperature (K) Bulk percolation: f ~ 0.4 SiN 3/4 :Pt <<38 38 SiN 3/4 :metal A <<40 40 LaAlO 3 :LaNiO LaAlO 3 :SrRuO CaZrO 3 :LaNiO CaZrO 3 :SrRuO Not percolation-induced induced d metallicity it

16 f- Map for MIT Percolation Threshold (nm) Insulating f Conducting Nanometallicity I (ma) V-triggered MIT 20 1M R-V I-V 100k 10k 1k V (V) R ( )

17 Nanostructure?

18 SiN:metal A System: 10 nm TEM Films Insulating Switching Switching Switching 5 nm SiN SiN+ x1% metal SiN+x2% metal SiN+x3%metal SiN+x4% metal SiN+x5% metal SiN+x6% metal metal Switching Switching Conducting Metal-rich Nanoparticles (Percolating) Conducting

19 Oxide A:Pt System 5 nm Insulating Oxide Oxide+ x1% Pt Oxide+x2% Pt Oxide +x3% Pt Switching Switching Conducting (percolating) Metal-rich Nanoparticles Irrelevant for Nanometallic Switching

20 Metallic Nanoparticle? (SiO 2 :f Pt) Calibr rated Reflectio on (%) f Pt f ~ 0.2 Fused Silica f ~ 0.5 f ~ 0.37 f ~ 0.3 f ~ Wavelength (nm) Pt < 0.3: No Metallic Nanoparticle Plasmon Resonance: Signature of Metallic Nanoparticles

21 Capacitance (HR): SiN:Metal A f critical C = C diel + C met NP I C met NP ~ n met NP r 2 met NP r Switching % ~ n met NP r 3 met NP % Metal C met NP ~ %/r met NP f metal < f critical : No Metallic Nanoparticle

22 Reality Check Scaling: x nm times x nm Endurance: >10 7 cycles

23 Electronic Transition?

24 Fundamentally Different Features T Initial State Electrode s Work Functions, B UV R C Pulse Width,

25 Initial State No forming Initial state: metal High breakdown voltage >15 V

26 Top & Bottom Electrodes Must Be Different ø TE (ev) ø BE (ev) V s Polarity SiO 2 :Pt Pt 5.65 SRO Pt 5.65 Mo Mo 4.6 SRO I (ma) R ( ) Ag 4.26 Pt Pt 5.65 Ta V (V) + : Counter clockwise SiN 3/4 :Pt Pt 5.65 SRO LaAlO 3 : Pt 5.65 SRO LaNiO 3 Au 5.10 SRO Ag 4.26 SRO LaAlO 3 : Pt 5.65 SRO SrRuO 3 CaZrO 3 : Pt 5.65 SRO LaNiO 3 CaZrO 3 : Pt 5.65 SRO SrRuO 3 I (ma) V (V) -: Clockwise R ( )

27 UV Resets Memory: Electronic Pt, 5.6eV CaZrO 3 :LaNiO 3 SrTiO 3 SrRuO 3, 5.0eV Inten nsity UV light 4.2 ev 3.4 ev 3.0 ev Wavelength (nm) Res sistance ( ) UV off UV on LR UV off Time (sec) UV off UV on HR UV off Time (sec) Not an ionic effect

28 Electronic Transition: UV-triggered Pt SiO 2 :Pt Fused SiO 2 SrRuO 3 or Mo UV light 100k 100k R 10k UV on R ( 10k 1k UV on 1k Time (sec) Time (sec) Not an ionic effect

29 R HR Dependence Resis stance ( ) (100 m) 2 (60 m) 2 (40 m) 2 (20 m) 2 (10 m) Voltage (V) Resist tivity ( cm m) nm 20nm 17nm Area (cm 2 ) Obeys Ohm s law (R HRS 1/A) Extreme thickness dependence!

30 Non-Ohmic Thickness Dependence mm 2 ) A ( m R ~ exp(δ/ HR ) R x (nm) > (HR State) t Wave Function ~ exp(- / HR ) HR Violates Ohm s Law

31 ζ : Decreased by trapped charge mm 2 ) A ( m R ~ exp( / ) (nm) )20 10 R x (nm) Diffusion length ( ) : HR and LR f f ζ HR (nm) ζ LR (nm)

32 Symmetric Capacitance: Higher for HRS Equivalent Circuit 6000 Line & BE & Film / connecti interface Device on -Z im ( ) 3000 HRS@0V HRS@0.4V HRS@0.8V HRS@1.2V LRS Only at very high Z real ( ) No Interface Barrier: Symmetric C(V)

33 No Pulse Width Effect (>RC time) No Rate Dependence: Not AMemristor! > RC: Same switching voltage regardless of < < RC: Increasing switching voltage at smaller Same observations for HR-LR and LR-HR switching RC Time = R Line Line C Cell Cell ~ Cell Area Prediction: Same switching voltage down to ps in sub- m devices

34 Device Performance Retention Variance

35 Memory Retention Resist tance ( ) C HRS: >10ms 100ns LRS: >10ms 100ns Resist tance ( ) t retention /t write HRS: >10ms 100ns LRS: >10ms 100ns 10yr time (sec) t retention /t write Good retention regardless of programming speed

36 Retention per Constant Voltage Stressing Test (sec) LR to HR V + *= V 1.6V V 27V 2.7V V 5.5V V m+ (V) 2 ) ln( V m years 1.1V 1.6V V + *= 2.3V 2.7V 45V 4.5V 5.5V /V m+ (V -1 ) < 0.4 V >10 year data retention t Fowler-Nordheim Tunneling over Barrier d: 15nm~ nmthick 2.6

37 Retention per Constant Voltage Stressing Test HR to LR (sec c) V *= 1.25V V 2.6V 3.6V V m (V) < 0.4 V >10 year data retention

38 Switching Uniformity R distribution rrent (A) Cu k cycles Applied voltage (V).1V ( ) 10k 1k ±4V, 100ns # of switching F(x) Cumulative probability, LRS HRS Resistance, x ( ) Highly reproducible on-offoff Narrowly distributed resistance

39 Switching Uniformity: Weibull plot Weibull plot (R) F( x) 1 exp( ( x / x0) k ) Ln(-Ln(1-F(x) )) LRS HRS V off (LRS HRS) -V on (HRS LRS) Ln(x) () k /μ R HRS R LRS Higher Weibull exponent k: more uniformity (lower /μ)

40 Switching Uniformity: R HRS & V switching Weibull distribution (analytic relation) / [ (1 2 2 / k) (1 1/ (1 1/ k) k)] 1/ 2 k Our Device R HRS / TiO 2 (DC) [1] TiO 2 :Pt (DC) [1] HfO 2 (AC) [2] HfO 2 :Al (AC) [2] NiO (DC) [3] NiO (AC) [3] NiO:Ti (DC) [4] NiO:Ti (AC) [4] Cu x O (AC) [5] ZnO:Mn (DC) [6] TaO (AC) [7] x PCMO (DC) [8] our device Weibull plot k 100 TiO 10 2 [1] TiO 2 :Pt [1] HfO 2 [2] HfO 1 2 :Al [2] NiO [3] NiO:Ti [4] ZnO:Mn [6] our device (V off ) 0.1 our device (-V on ) Weibull plot V switching / 1.K. Tsunoda et al., Tech. Dig. International Electron Devices Meeting 2007, B. Gao et al., Tech. Dig. Symposium on VLSI Technology 2009, M.-J. Lee et al.,, Tech. Dig. International Electron Devices Meeting 2007, A. Chen et al., Tech. Dig. International Electron Devices Meeting 2005, Y. C. Yang et al., Nano Lett. 2009, 9, W.-Y. Chang et al., Appl. Phys. Lett. 2009, 95, Z. Wei et al., Tech. Dig. International Electron Devices Meeting 2008, D. -J. Seong et al., Tech. Dig. International Electron Devices Meeting 2009,

41 Intermediate States: Metals or Insulators?

42 Intermediate States Insulator or Metal? Cur rrent (ma) 15 L Voltage (V) Resis stance ( ) L L Temperature (K) Resis stance ( ) L Temperature (K) FIT: Fluctuation-induced Tunneling Elastic tunneling 0 0 l 2 =area R/2 R/2 G ( T) G exp GV ( ) G 0, T C n T w G (1/ ) 10-2 (1/ ) Experimental FIT fitting Experimental Fitting T T K 250K exp( V / V0 ) 1 h exp( V / V ) 1 V 0 G Voltage (V) T(K) FIT

43 Intermediate States Insulator or Metal? Cur rrent (ma) Resis stance ( ) 10 9 L2 15 L L1 Voltage (V) Temperature (K) Resist tance ( ) 10 9 L2 Temperature (K) Reduced Activation Energy 10 1 L2 0 Insulator W T dln ( T) dt W 10 0 Metal Temperature (K) Multi-step on-switching: insulator-bad metal-metal transition Multi-state Multi-filament

44 Nanometallic RRAM Size-dependent d Nanometallicity it Metal Insulator Transition Random Materials Purely Electronic Switching

45 Conclusions Nanometallicty t : a size effect unique to random materials MIT: : triggered via δ, f, V, & photon; switching due to changing localization length, direction controlled by electrode work function Thank You Device properties: highly reproducible switching parameters, short read/write time independent of voltage, long retention time, adjustable switching parameters Nanostructure: metallic nanoparticles irrelevant