Nanoscale switching in resistive memory structures

Transcription

1 Nanoscale switching in resistive memory structures D. Deleruyelle, C. Dumas, M. Carmona, Ch. Muller IM2NP UMR CNRS 6242 & Institut Carnot STAR Polytech Marseille, Université de Provence IMT Technopôle de Château Gombert Marseille Cedex 20 e mail: christophe.muller@im2np.fr Innovative Memory Technologies Minatec Grenoble France

2 Partners in EMMA* project MDM (Milano Italy) S. Spiga, A. Lamperti, and M. Fanciulli Numonyx (Milano Italy) I. Tortorelli, R. Bez IMEC (Leuven Belgium) R. Müller, L. Goux, D.J. Wouters * Emerging Materials for Mass storage Architectures FP6 IST no

3 Outline 1. Context 2. Nanoscale switching in CuTCNQ-based memory structures 3. Nanoscale switching in NiO film on top of pillar bottom electrode 4. Summary

4 Outline 1. Context 2. Nanoscale switching in CuTCNQ-based memory structures 3. Nanoscale switching in NiO film on top of pillar bottom electrode 4. Summary

5 Key players on resistive systems

6 Latest ITRS classification (partial) Types Nanothermal High resistance "0" Logical states Low resistance "1" Materials Transition metal oxide (TMO) Chalcogenide nanowires for PCM Nanomechanical Suspended CNT Nanowires Nanorods Nanoionic Organic complex Oxide Chalcogenide

7 Nanothermal devices (TMO) Fujitsu (TiO 2 ) Samsung (NiO) Matsushita (FeO x ) Hynix (TiO 2 ) Spansion (Cu 2 O) Fujitsu (Ti doped NiO)

8 Qimonda Nanoionic devices Ionic transport combined with redox process in a solid electrolyte o Anions (e.g. O 2 ) NIMS Memristor (HP), CMOx (Unity), o Cations (e.g. Ag + ) CBRAM (Qimonda, NIMS, Adesto, ) HP Unity Adesto 4F 2 /8 bits = 0.5F 2

9 Outline 1. Context 2. Nanoscale switching in CuTCNQ-based memory structures 3. Nanoscale switching in NiO film on top of pillar bottom electrode 4. Summary

10 Metal organic complex CuTCNQ Copper-tetracyanoquinodimethane CuTCNQ may grow in small dimension via holes o High density & low cost memory devices Gas/solid reaction or growth in solution Bipolar resistive switching Demolliens et al., J. Cryst. Growth, submitted

11 CuTCNQ nanowires on HfO 2 layer CuTCNQ nanowires Au (TE) HfO 2 (switching layer) Pt (BE) CuTCNQ nanowires grown on 3 nm thick HfO 2 "switching layer" (SL) o Copper transport within HfO 2 switching layer Creation/dissolution of conductive bridges o Improved electrical performances Muller et al., Solid-State Electronics, Submitted

12 Switching characteristics Bipolar resistance switching (RS) o Clockwise on pad-size devices o Anticlockwise at nanoscale At nanoscale, RS governed by a nano-gap between AFM tip and CuTCNQ nanowires

13 An additional proof Au Cu (BE) Complementary C-AFM experiments performed on CuTCNQ(nanowires)/Cu(BE) (without oxide switching layer) Basic local memory operations achieved under bias voltage o Set/Reset/Read Muller et al., Solid-State Electronics, Submitted

14 Redox process Cu + Nano-gap Cu Cu + Cu + Cu Cu Cu CuTCNQ Nano-gap Cu + Cu + Cu Cu Cu Cu CuTCNQ

15 Modeling V Top V Top Nano-gap = SL Cu + t CF tsl R SL Cu Cu Cu Cu CuTCNQ R CuTCNQ V Bottom Equivalent resistance of the stack t SL t CF R TOT = R SL + R CuTCNQ with R SL = SL Transport of Cu + ions governed by drift-diffusion mechanism J(x,t) = qµ Cu+ [Cu + ] D Cu+ [Cu + ] x + S SL Einstein relationship and continuity equation

16 Actual nanoionic device Satisfactory agreement between AFM measurements and model This model can be transposed to copper transport within HfO 2 switching layer Oxidation process at CuTCNQ surface o Cu Cu + + 1e Transport of Cu + ions from CuTCNQ to AFM tip Reduction process at AFM tip o Cu + + 1e Cu Growth of conductive filaments from AFM tip to CuTCNQ surface Redox set operation HRS LRS Deleruyelle et al., Appl. Phys. Lett., vol. 96, no. 26, pp (1-3), 2010

17 Outline 1. Context 2. Nanoscale switching in CuTCNQ-based memory structures 3. Nanoscale switching in NiO film on top of pillar bottom electrode 4. Summary

18 Memory devices Electrical characterization on conventional probe station Conductive AFM (C-AFM) measurements TE Pt NiO ALD Pt BE AFM tip NiO Silver paste SiO 2 SiO 2 Si 3 N 4 CoSi 2 Si 3 N 4 CoSi 2 Si Si W-plug Spiga et al., Proc. of MRS Spring Meeting, 2009 Demolliens et al., IEEE Proc. of Int. Memory Workshop, 2009

19 Microstructure TEM cross-section AFM topography Pt NiO 200 nm Imprint of underlying W-plug W (180 nm) SiO 2 Si 3 N 4 50 nm CoSi 2 Bending of NiO film due to a dishing of W-plugs during CMP process

20 Experimental protocol Program Set & Reset Read B-doped diamond Pt-Ir

21 Forming/set operation Superimposition of topography and current mapping Initial state V Prog = 1 V V Prog = 2 V V Prog = 3 V 1.5 µm V Read = 1 mv No conductive spots in initial state o High resistance state Gradual appearance and growth of highly conductive regions (around 20 to 30 nm) when increasing programming bias o Emulation of forming/set operation

22 Reset operation Superimposition of topography and current mapping Initial state V Prog = 5 V V Prog = 4.5 V 1.5 µm V Read = 1 mv Dissolution of conductive filaments at high voltage o Reset operation achieved! Some residual conductive regions still remain after local reset

23 Superimposition of topography and current mapping Retention 2 days 13 days 21 days 30 days 1.5 µm V Read = 1 mv Initial forming and read of programmed area Some conductive filaments remain after 30 days o Retention demonstrated at nanoscale Decrease of filament diameter in time

24 Actual nanothermal device Initial insulating state LRS: multiple conductive regions within NiO film HRS: only few residual conductive filaments after reset

25 Outline 1. Context 2. Nanoscale switching in CuTCNQ-based memory structures 3. Nanoscale switching in NiO film on top of pillar bottom electrode 4. Summary

26 Summary Memory cell structure Polarity of switching Switching classification Basic mechanism Size limits Reset operation NiO deposited on top of pillar W electrode Unipolar Nanothermal Filamentary Filament diameter (20 nm) Joule effect enabling filament dissolution CuTCNQbased memory elements Bipolar Nanoionic Filamentary Area around tip Redox process Switching demonstrated at nanoscale in both systems! o Scalabilty conditioned by a tight control of filaments

27 Thank you for your attention