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I Presentation of MIEC - Context and Definition

Impedance spectroscopy of Cu-containing Mixed Ionic Electronic Conduction (MIEC) material. 09-19-12. I Presentation of MIEC - Context and Definition. II Impedance Spectroscopy - Method description. Author : Benjamin Meunier Supervisors : Geoffrey W. Burr Kumar Virwani.

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I Presentation of MIEC - Context and Definition

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  1. Impedance spectroscopy of Cu-containing Mixed Ionic Electronic Conduction (MIEC) material 09-19-12 I Presentation of MIEC - Context and Definition II Impedance Spectroscopy - Method description Author : Benjamin Meunier Supervisors : Geoffrey W. Burr Kumar Virwani III Results Presentation - Impedance Models - Complementary studies Conclusion

  2. Outline Outline Outline I Presentation of MIEC - Context and Definition I Presentation of MIEC - Context and Definition II Impedance Spectroscopy - Method description II Impedance Spectroscopy - Method description III Results Presentation - Impedance Models - Complementary studies III Results Presentation - Impedance Models - Complementary studies Conclusion Conclusion Outline I Presentation of MIEC

  3. Context:Flash NAND Limitations Distributions of cells Non – Volatile Memory : candidate devices NAND Unlike to match HDD $/GB Endurance loss Phase Change Memory (PCM) Resistive RAM Bit line Price per Gigabyte Word line SLC 100Kcycles $ 103 0 1 Voltage $ 101 MLC 10Kcycles 11 10 01 00 NOR NAND $ 10-1 Voltage 2000 2004 “Oxygen exchange layer” (Ti,Zr,Hf,La) TLC 1Kcycles 111 101 010 000 110 100 011 001 Voltage VO VO HfOx VO VO VO VO VO VO VO VO VO Bigger Capacity = Less Endurance VO VO VO VO VO VO VO VO VO O2- VO VO O2- VO O2- VO VO VO BEC 2008 2012 Scaling Barrier Oxide sidewall (→ 40nm node ) Control gate Dielectric ONO Floating gate Tunneling oxide n+ n+ p-type silicon wafer It starts to be hard to keep shrinking flash devices Source : Objective-Analysis (Understanding the NAND Market) K.Kim and J.Choi, Conference 2006 3 6/14/12

  4. NVM– non-volatile memory ND– ‘Novel Diode’ access device Overall Vision:3Dmulti-layer Storage class memory Access Device specifications • ON state: high currents PCM needs ~ 107 A/cm2 @ 30 nm CD • OFF state: low leakage to enable large & efficient arrays • Back-End-Of-the-Line compatible (< 400oC processing) for stacking above metal wires • Bipolarity: to access bipolar RRAM (more reliable than uni-polar RRAM) Conventional silicon diodes do not meet all these requirements! Mixed Ionic-Electronic Conduction (MIEC)-based access device Source : G. W. Burr, VLSI paper 2012 4 6/14/12

  5. IV measurements :first characterization L 110 nm metal metal MIEC 30 nm Current (A) 50 nm < 10 pA leakage Ec TEC Voltage (V) 110 nm Ev 30 nm Current (A) 70 nm 70 nm < 10 pA leakage TEC Voltage (V) IV :General behavior – Double Diode • MIEC theory is an area of active research • We assume a n-doped semiconductor behavior because of the Cu+ ions (donors) • Two Schottky junctions 5 6/14/12

  6. + + 3 + Jtun Jtun + + 2 1 IV :Details of the Different States Prediction from electronic transport equations : Solid-state model : n depending of the defect model 1 OFF State : Equilibrium large barrier for holes → accumulation tunneling current due to the electrons 2 ON State : lowest barrier → hole injection 3 Saturation Current only limited by space-charge effects Source : I. Riess, J. Phys. Chem. Solids, vol.47, no.2, p129-138 (1986) 6 6/14/12

  7. um 0 2 4 6 8 10 12 14 0 um 2 4 6 8 10 12 14 Voltage margin @ 10nA I-V :Voltage Margin and Yield Current (A) Voltage Margin =1.5V Sufficient for cross-point arrays of HfO2 RRAM Voltage Margin @ 10 nA Voltage (V) 92 % : 1.35 V +/- 0.18 V Number of devices 100 % > 0.48 V 7 6/14/12

  8. Endurance : Previous Results 100% Yield : Source : G. W. Burr, VLSI paper 2012 8 6/14/12

  9. Outline I Presentation of MIEC - Context and Definition Outline I Presentation of MIEC - Context and Definition II Impedance Spectroscopy - Method description III Results Presentation - Impedance Models - Complementary studies Conclusion I Presentation of MIEC II Impedance Spectroscopy

  10. ZMIEC Impedance :MIEC – expectations - Amplitude - Phase Voltage (V) Va exp behavior of the current and single-sine → need small Va 10 6/14/12

  11. I Generator ... V Sample Impedance :BioLogic SP-300 Frequency Response Analysis (FRA) : Generation of Perturbation and Reference Signal Response of the sample : - Transfer Function - Harmonics of non-linearity - Noise coefficient Homodyne detection (lock-in) In the frequency domain :Real and Imaginary parts function of the frequency 11 6/14/12

  12. Bode Diagram of R+R/C frequency : Zup = Zdown A Equivalent circuits : Same electrical behavior→ Different physical phenomena Solutions : - Physical intuition/model must be involved - Different sets of measurements in different conditions Impedance :Example and Limitation OR 12 6/14/12

  13. ZMIEC ZMIEC Impedance :First measurement Like 1st order behavior → Same if withdraw the tip Ctip Ctip 13 6/14/12

  14. 110 nm 200 um AFM Testing Probe First tests :Adopted Solution Preliminary tests : Resistance device Capacitance device MIEC top gold electrode (before and after annealing) 14 6/14/12

  15. 50.92 Ohms Resistance Sample : • The force that must be applied to assure good contact with the sample without damage. • Need to add serial resistance in order to avoid explosion • Test the regularity of the results Rsample = 20.6 +/- 0.5 Ohms 15 6/14/12

  16. Cut-off frequency We cannot see the cutoff frequency 50 MOhms We can see the cutoff frequency Capacitance Sample : 16 6/14/12

  17. Capacitance (pF) Area (um2) C// : same order of magnitude than Ctip(ie. slide 15) The characterization of the apparatus is done let's do IS of MIEC device Capacitance Sample : C = a x S + b b = C//parasitic capacitance 1T. Goto and T. Hirai, J. Mater. Sci. 24, 821 (1989) and references therein. 2 D. Fischer et all. , Phys. Rev. Lett. 92, 236405 (2004). 17 6/14/12

  18. Outline I Presentation of MIEC - Context and Definition II Impedance Spectroscopy - Method description III Results Presentation - Impedance Models - Complementary studies Conclusion II Impedance Spectroscopy III Results Presentation

  19. Measurements :First results Phase Diagram Phase (degree) vs frequency (Hz) 19 6/14/12

  20. Ccont Ccont Rel Rs Rel Rion CDeb /2 CDeb Rion CDeb MIEC Impedance :Band Diagram–based model Electrical model Impedance Equation Ccont: Due to the metal contact Rel: Tunneling electrons generating a current Rion : Resistance due to the ions CDeb : proportional to (λD)-1 which correspond to the 0-charged region close to contact Rs : Serial resistance added in order to reduce the current flowing through the device. + fix the high frequency impedance Source : A. Leshem, E. Gonen and I. Riess, Nanotechnology 22 (2011) 254024 20 6/14/12

  21. 0.2 V - 0.2V - 0.4 V Ccont Rs Rs Rel Rion CDeb Measurements :First Analysis Phase Diagram Bode Diagram Rel CDeb Rion Low frequency : High frequency : Summarize of the results : Z = Rs + Rel Z = Rs 21 6/14/12

  22. Ccont Rs Rel Rion CDeb /2 Measurements :Matching with the model Phase Diagram Phase (degree) vs frequency (Hz) 22 6/14/12

  23. P Equivalent circuit : Ps For a constant electric field : and P'(t) P∞ C1 t = 0s t R C2 Theory :Relaxation Process Polarization (P) : - Ps : long time polarization - P∞ : high frequency polarization Source : E. Barsoukov and J. R. MacDonald, Impedance Spectroscopy, Second Edition, Wiley (2005) p30-34 23 6/14/12

  24. Theory :Electrolyte Model Current through an electrolyte : We can neglect the concentration gradient. Correct assumption for High Frequency Chemical Electrical Jonscher : “[…] the origin of the frequency dependance of the conductivity [is] due to relaxation of the ionic atmosphere after the movement of the particles. “ Almond and West : Conductivity when several relaxation process are involved : With : Deriving from the previous relations Ref : Jonscher [1977, 1980] ; Almond and West [1983a, b], Almond et al. [1982, 1983, 1984] 24 6/14/12

  25. Ccont (nF) log | I (uA) | Rel (kOhms) CDebye(nF) Applied Voltage Results :Effect of Bias 30nm Voltage - 0.5V + 0.5V 25 6/14/12

  26. 120 nm 90 nm 60 nm Results :Effect of Thickness -0.2V 0.2V 26 6/14/12

  27. Summarize :Promising but … • Unexplained asymmetry • Explore transient/higher frequency behavior. • Add circuit elements that match empirical “turn-on” behavior. • Measure transient current directly. • Connect Impedance Spectroscopy to device modelling. Much additional work will be required before a complete understanding 27 6/14/12

  28. before annealing after annealing Au TEC Cu TEC To Do List : for future experiments • AFM measurement with the same sample (IV not the same than small MIEC samples) Effect of post-annealing • Gold diffusion upon anneal? → SIMS? Effect of electrode material • Evolution of frequency shape from negative to positive … • Temperature dependance 28 6/14/12

  29. Outline I Presentation of MIEC - Context and Definition II Impedance Spectroscopy - Method description III Results Presentation - Impedance Models - Complementary studies Conclusion II Impedance Spectroscopy III Results Presentation Conclusion

  30. Impedance Spectroscopy performed on MIEC devices • New IS setup established, independent of C-AFM • Large-area MIEC samples allow measurement of sample impedance rather than “tip” impedance. • Impedance Spectroscopy spectra matched to RC circuits from MIEC literature, at multiple bias conditions • Fitting procedure developed for circuit parameter extraction • Introduced extensions to existing circuit models • Showed connection between circuit models & relaxation processes • Preliminary experiments performed vs. thickness, top-electrode material, and anneal conditions • Numerous future experiments identified and initiated Conclusion

  31. Thanks for your attention Acknowledgements : Rohit Shenoy, Alvaro Padilla, Bulent N. Kurdi, for their involvement and interest. Luisa Bozano, Carl Larson and Spike Narayan without whom I would never have been here Liz Fedde, Jane Frommer, Leslie Krupp, Larissa Clark for their help and advice Amy Bowers, Mark Jurich, Bill Risk and all those who have contributed to the achievement of these results

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