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Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
Nowak SSDM\'09
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Nowak SSDM\'09

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Presentation done at IEEE SSDM in October 2009

Presentation done at IEEE SSDM in October 2009

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  • 1. Charge Localization During Program and Retention in NROM-like Non Volatile Memory Devices Etienne Nowak, Elisa Vianello*, Luca Perniola, Marc 2007 Bocquet, Gabriel Molas, Rabah Kies, Marc Gely, Gerard Ghibaudo+, Barbara De Salvo, Gilles Reimbold, Fabien Boulanger CEA/LETI-Minatec, 38054 Grenoble, France * DIEGM, University of Udine, Italy +IMEP/INPG Grenoble, France etienne.nowak@cea.fr Etienne Nowak et al. – SSDM 2009 1
  • 2. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 2
  • 3. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 3
  • 4. Motivation (1/2) 12V NROM -14V 0V 4.5V 0V 7V e- h+ Write (CHE) Erase (HHI) 4bit/cell 8Gbit product R.Sahar et al, ISSCC 2008 Benefit: 2007 Higher information density thanks to physically separated bits Purpose of the work: Extract information on pocket of trapped charges in alternative trapping materials for NROM devices Etienne Nowak et al. – SSDM 2009 4
  • 5. Motivation (2/2) Retention of cycled and uncycled Si3N4 devices has been well studied M. Janai et al., IEEE IRPS Tech. Dig., 2008, pp417-423 Few works have been done on different trapping layers T.Sugizaki et al., VLSI Tech Dig., 2003, pp.27-28. 2007 Intrinsic trapping properties of Si3N4, HfO2, Al2O3 still not well understood Maximum amount of trapped charge Localization of the trapped charge ∆Vt loss mechanisms on different material Etienne Nowak et al. – SSDM 2009 5
  • 6. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 6
  • 7. Devices under analysis Control N+ Poly N+ Poly N+ Poly Gate HTO HTO Blocking 10nm HTO 10nm 10nm oxide 6nm 6nm Trapping 6nm Si3N4 HfO2 Al2O3 layer 5nm SiO2 5nm SiO2 5nm SiO2 Tunnel oxide 2007 W/L=10/0.27 µm Three different trapping layers are compared LPCVD Si3N4 / ALCVD HfO2 / ALCVD Al2O3 Etienne Nowak et al. – SSDM 2009 7
  • 8. Method to extract trapped charges information Virgin Written 1E-4 VS=1.5V Reverse Read VG Source Current IS [A/um] VD=1.5V Forward Read 1E-6 SiO2 ∆VtR Si3N4/HfO2/Al2O3 Qcharged 1E-8 SiO2 1E-10 ∆VtF VS y x Lcharged VD L 1E-12 1E-14 2007 0 2 4 6 8 10 Gate Voltage VG [V] 1 - Measure ∆VtR and ∆VtF from the experimental results L. Perniola et al., IEEE TNANO, 2005 Etienne Nowak et al. – SSDM 2009 8
  • 9. Method to extract trapped charges information ∆VtF Charge Density Q charged [10 12cm -2] VG SiO2 Si3N4/HfO2/Al2O3 Qcharged SiO2 VS y x Lcharged VD L Virgin Written 1E-4 VS=1.5V Reverse Read Source Current IS [A/um] VD=1.5V Forward Read 1E-6 ∆VtR 1E-8 1E-10 ∆VtF 2007 ∆VtR 1E-12 1E-14 0 2 4 6 8 10 40 60 80 100 120 140 Gate Voltage VG [V] Effective charged Length 2L[nm] [nm] Charged Length L charged 2 - Extrapolate the values of Lcharged and Qcharged from an analytical map calculated through the ψS approach L. Perniola et al., IEEE TNANO, 2005 Etienne Nowak et al. – SSDM 2009 9
  • 10. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 10
  • 11. Program HfO2 Al2O3 Si3N4 Programming Window ∆VtR [V] Programming Window ∆VtR [V] 12 Stress Stress 12 V =V =0V VS=VB=0V 10 S B 10 VG=10V VG=12V 8 V =5V 8 D VD=5V 6 6 4 4 2 2 2007 0 0 -6 -4 -2 0 -6 -4 -2 0 10 10 10 10 10 10 10 10 Stress Time t [s] Stress Time t [s] Programming windows over 10 V for the 3 materials Etienne Nowak et al. – SSDM 2009 11
  • 12. Charge localization Charge Density Qcharged [10 cm-2] 18 Gate 16 12 14 12 10 t ~ 0.01s Source Drain 8 Gate Vg=10V Vg=12V ; Vd=5V 6 HfO2 4 Al2O3 2 Source Drain Si3N4 2007 0 0 50 100 150 200 250 Effective charged Length Lcharged[nm] 1. Charge “initially” localizes at ~40-60 nm next to drain 2. After t~10 ms, Qcharged saturates, then Lcharged broadens 3. Not significant difference between the trapping layers Etienne Nowak et al. – SSDM 2009 12
  • 13. Ey evolution during program Normal Field EY [MV/cm] 1.4 Lcharged 1.4 Lcharged Normal Field EY [MV/cm] Vd=5V Vg=12V Vd=5V Vg=12V 1.2 1.2 Gate 1.0 Gate 1.0 0.8 12 Qcharged to 20x10 cm =0 -2 0.8 0.6 12 every 2.5x10 cm -2 0.6 EY 0.4 0.4 Source 12 -2 Drain Qcharged=17.5x10 cm Source 0.2 EY Drain 0.2 0.0 Effective LengthLeff Effective Length Leff 0.0 -0.2 -0.1 0.0 0.1 0.2 -0.2 -0.1 0.0 0.1 0.2 Source 2007 Position X [um] Drain Source Position X [um] Drain Maximum Qcharged and subsequent Lcharged broadening explained by: Decrease of Ey at the Si/SiO2 interface Ey peak shift towards the source side Etienne Nowak et al. – SSDM 2009 13
  • 14. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 14
  • 15. Gate Retention operation Source Drain Programming Window ∆VtR [V] 120 5 Total Charge Variation Qchargedx Lcharged [%] 4 100 3 2 T=25° T=125° C C 80 T=25° T=125° C C HfO2 HfO2 1 Al2O3 Al2O3 60 Si3N4 0 Si3N4 0 1 2 3 4 5 0 1 2 3 4 5 10 10 10 10 10 10 10 10 10 10 10 10 2007 Time t [s] Time t [s] Lateral charge migration is the main ∆VtR loss mechanism for the three materials at 25° C. Charge loss is relevant only for Al2O3 at 125° C Etienne Nowak et al. – SSDM 2009 15
  • 16. Retention Model to extract the ∆Lcharged Drift-Diffusion equations  ∂n ( x , t ) ∂ ∂ 2 n( x , t )  = [µeff n(x , t )E (x , t )] + D  ∂t ∂x ∂x 2   ∂E ( x , t ) = qn( x , t )  ∂x εr ε0 Charge density Shape1  Qcharged Drain Shape2 side Source Gate side 2007 Lcharged Position Source Drain ∂n( x, t ) V =0 =0 ∂x 1D model of nitride Drift-Diffusion of majority carriers Effective mobility coefficient µeff Etienne Nowak et al. – SSDM 2009 16
  • 17. Retention Model to extract the ∆Lcharged Effective charged Length 150 Drift-Diffusion, Shape1 increase∆ Lcharged [nm] Drift-Diffusion, Shape2 Charge density Qcharged Shape1 Drain 100 Diffusion, Shape1 Shape2 side Source side Lcharged Position ∂n( x, t ) 50 V =0 ∂x =0 ∆ Lcharged=A*ln(t) A=α µeffQtotal/εrε 0 2007 -3 -1 1 3 5 7 10 10 10 10 10 10 Timet [s] Drift predominant over Diffusion ∆Lcharged independent of the shape of the trapped charges Drift follows an empirical law: Lcharged=Lcharged0+A*ln(t) Etienne Nowak et al. – SSDM 2009 17
  • 18. Data vs model: lateral charge migration 25 HfO2 Effective Charged Length increase ∆Lcharged [nm] Al2O3 20 A=3.7 Si3N4 15 10 A=1.7 5 A=0.55 0 2007 3 4 5 10 10 10 Time t [s] Lateral migration for the three material follows a logarithmic law with different A coefficient Lowest drift observed for Si3N4 Etienne Nowak et al. – SSDM 2009 18
  • 19. Outline Motivation Methodology Program operation 2007 Retention Conclusion Etienne Nowak et al. – SSDM 2009 19
  • 20. Conclusion Comparative study of trapping properties in Si3N4, HfO2 and Al2O3 in program and retention conditions Large window (~10 V) possible for all trapping materials Maximum Qcharged is limited by electrostatics not by the trapping layer properties Method allows separating vertical vs lateral 2007 charge migration Lateral migration, due to charge drift, is the main Vt shift mechanism in retention mode for the three materials at 25°C Log(t) dependence of lateral migration, and Si3N4 shows the lowest drift Etienne Nowak et al. – SSDM 2009 20
  • 21. Thanks for your attention! 2007 Etienne Nowak et al. – SSDM 2009 21
  • 22. Extraction Method Analytical model Based on Liu Surface Potential model Calculate ∆VtR and ∆VtF for a given Qcharged and Lcharged Extract Qcharged and 2007 Lcharged from measured ∆VtR and ∆VtF [L. Perniola et al., IEEE Trans. on Nanotech., Vol. 4, No. 3, pp. 360- 368, May 2005] Etienne Nowak et al. – SSDM 2009 22
  • 23. Retention Model Drift-Diffusion equation  ∂n ( x , t ) ∂ ∂ 2n(x , t )  = [µeff n(x , t )E (x , t )] + D  ∂t ∂x ∂x 2   ∂E ( x , t ) = qn( x , t )  ∂x  εr ε0 Diffusion equation Drift equation 2007 D=0 µeff = 0 ∂n ( x , t ) ∂ 2n( x , t )  x n( x , t )dx  =D ∂n ( x , t ) ∂  ∫ ∂t ∂x 2 = A* n( x , t ) 0∞  ∂t ∂x  n( x , t )dx    ∫0   µeff q ∫ n( x , t )dx ∞ µeff Qtotal A = * 0 = εr ε0 εr ε0 Etienne Nowak et al. – SSDM 2009 23

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