Organic Charge Trapping Memory Transistors

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Under a Compulsory Course of "Materials Physics and Technology for Nanoelectronics" a team of BE Students of Nanotechnology, Nanoelectronics and Bionnotechnology prepared this seminar for Prof. Marc Heyns, [email protected] Kapeldreef 75, B-3001 Heverlee IMEC Building IV, room 2.33Tel: 016 281 348

Transcript of Organic Charge Trapping Memory Transistors

  • 1. Organic Charge Trapping Memory Transistors Dries Agten Erik Bury Andr Cardoso Evelien Mathieu Pieter Weckx

2. Overview

  • Introduction
    • Memory types
    • FET-based memories
  • Working principle
    • Charge trapping
    • Band diagram analysis
    • Programming sequence
  • Comparison of two devices
    • PVA & PCBM
    • P MS & Pentacene
  • Conclusion

3. Memory types Q.D. Ling et al,Progr. Polym. Sci .2008 , 33, 92 Introduction 4. FET-based memories

  • Floating Gate
  • Ferroelectric

Charge Trapping Cyferz, Wikipedia,2007,Flash_cell_structure Cyferz, Wikipedia,2008,1T_FeRAM_cell_structure Introduction 5.

  • SONOS/MONOS
  • Dielectrics

Cyferz, Wikipedia,2007,SONOS_cell_structure L. Forbes,free patents onl .2005 ,10/775908Charge Trapping Introduction 6. Charge Trapping Organic field-effect transistors with polarizable gate insulators Howard E. Katz et al.,Appl. Phys.2002 , 91, 15726 There is growing appreciation of the capability to fabricate various kinds of electronic circuits from organic materials. Introduction 7. From MOS toFG MOS

  • Based on MOSFET transistor
  • Gate is uncoupled, memory is non-volatile
  • Charges are trapped in the floating gate
  • Data sensed by V thshift of MOSFET

Data represented by carriers stored in the floating gate J. D. Casperson et al., CIT, Journal of Applied Physics,2009 , 92, 261Working principle 8. Influences on V th Traps close to/in the channel Charge injection from the semiconductor into the dielectric Slow reactions of charge carriers in the organic semiconductor Mobile ions in the semiconductor Ferroelectric effect Mobile ions in the dielectric Charge injection from the gate electrode M. Egginger et al.,Monatsh Chem, 2009 ,140,735 Working principle 9. Band diagram analysis (1) Vgs=0V Vgs=-5V -> accumulation -> depletion Working principle 10. Band diagram analysis (2) Vgs=-5V Vgs=-10V -> accumulation -> inversion Working principle 11. Working principle

  • When applying an external voltage to the gate, charges tunnel from the channel to the interface (~10 4carriers to represent 1 bit)
  • Both electrons and holes

Programming sequence 12. Measurement setup S.Y. Chou, Princeton University,Publication on website Working principle 13. Measurements Shift in threshold voltage M. Debucquoy et al,Organic electronics 2009 , 10, 1252 Working principle 14. Ambipolar vs unipolar

  • Ambipolar semiconductor: both p-type and n-type operations are realised (eg. program by holes and erase by electrons)
  • ->Balanced mobility (n and p) and ON/OFF operation needed

Insufficient electron mobility -> Trapped holes cannot be erased Wide memory window Working principle 15. Stacking holes for memory usage

  • Example: electrons tunnel back too easy -> poor retention time
  • Negative part of memory window is useful

M. Debucquoy et al ,Organic electronics 2009 , 10, 1252 Working principle 16. Search for improvement in terms of Materials and Scheme Singh et al, 2004 Heremans et al, 2009 Comparison of two devices Comparison of two devices 17. Comparison - Structure

  • PVA polyvinylalcohol
  • PCBM methanofullerene

T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409Organic components

    • Size: channel length W=1000um L=10um

Comparison of two devices

  • Pentacene polyaromatichydrocarbon
  • P MS polystyrene
  • Thiol monolayer fluorinated thiols

18. Comparison - Semiconductor

  • PCBM
  • p-type
  • High mobility
  • High ON/OFF current ratio

T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409

  • Pentacene (~14 )
    • 5 benzene rings
    • Crystal Structure
  • p-type
  • High Mobility
  • Reasonable ON/OFF current ratio

IBM Zurich,AFM ImagePenacene Aug 2009 Campbell, 1961molecular packing Prof. Takao Someya Comparison of two devices 19. Comparison - Electret

  • Charge trapping within bulk or at interface
  • Hydrophilic

T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409

  • P MS (poly alpha - methylstyrene)
  • Hydrophobic
  • (Insulator coated with a very thin-layer)
  • Reduces: trapped electrons at the interface between the pentacene and the gate dielectric
  • To suppress the degradation of the onoff ratio
  • High-quality,electron-trap freesurface allowing excellentelectron transport

Comparison of two devices 20. Comparison - Adjacent materials

  • Cr for source & drain:
    • No diffusion into PCBM
  • ITO gate
  • No insulator layer
  • Heptadecauoro-1-decanethiol
  • ( Thiol monolayer )
  • Other materials:
    • Au;SiO 2 ;n++Si

Improved interface: Improves pentacene layer growth Reduces interface states

  • Mobility increases
  • Threshold voltage approaches zero

Appl. Phys. Lett.88, 222103(2006) Improve the interfaceContacts Semiconductor layer Comparison of two devices 21. Performance measurements (Singh)Comparison of two devices T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409 T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409 22. Performance Measurements ( Herem.) -pulse (write) htrapped Programming voltageTransistors mobility e - trapped dielectric V on= 2V Gate Decrease 1.9V->1.4V h mobility decrease Shift V ON+& V ON- Retention time Memory Window + pulse (erase) etrapped Saturation Comparison of two devices 23. Performance Comparison [a] R. Bez et al,Proc. of the IEEE2003 , 91, 4, 489 [b] S. Kolliopoulou et al,Microel. Eng.2004 , 73-74, 725 [c] R.C.G. Naber et al,Nat. Mater. 2005 , 4, 243 [d] T.B. Singh et al,Appl. Phys. Lett. 2004 , 85, 22, 5409 [e] P. Heremans et al,Appl. Phys. Lett. 2009 , 95, 103311 Comparison of two devices FLASH [a] Floating Gate [b] Ferroelectric [c] PVA & PCBM [d] PMS & pentacene [e] Retention time (h) ~ 3 years ~ 11 ~ 168 > 15 > 3 months Programming time (s) 0.8 1 0.3e-3 500 1.5e-3 Programming/erasing voltage (V) +8/-8 +6/-6 +77.5/-77.5 +50/-50 -15/+15 24. Conclusion

  • Conclusion from Singhorganic memory:
    • The combination of PVA & PCBM
    • does not make a good memory-element
  • Conclusion fromHeremansorganic memory:
    • It is possible to fabricate a device with reprogrammable nonvolatile organic memory usable in Plastic Logic.

Organic Transistor/Memory devices will reach $21.6 Billion in 2015, NanoMarkets (2001) Conclusion 25. References

  • K.J. Baeg et al, Adv. Funct. Mater.2008 , 18, 3678-3685
  • T.B. Singh et al, Appl. Phys. Lett.2004 , 85, 5409-5411
  • K.J. Baeg et al, Adv. Mater.2006 , 18, 3179-3183
  • Q.D. Ling et al,Progr. Polym. Sci.2008 , 33, 917-978
  • R. Bez et al, Proc. of the IEEE2003 , 91, 4, 489-502
  • S. Kolliopoulou et al, Microel. Eng.2004 , 73-74, 725-729
  • R.C.G. Naber et al, Nat. Mater.2005 , 4, 243-248
  • P. Heremans et al, Appl. Phys. Lett.2009 , 95, 103311
  • J.Kang et al, J. Am. Chem. Soc.,2008 , 130 (37), 1227312275
  • K. Myny et al, Appl. Phys. Lett.2006 , 88, 222103
  • K. Asadi et al, Nature Materials2008 , 7, 547
  • Forbes, free patents onl.2005 , 10/775908
  • H.E. Katz et al, Appl. Phys.2002 , 91, 15726
  • Cyferz, Wikipedia2007 , Flash_cell_structure
  • Cyferz, Wikipedia2008 , 1T_FeRAM_cell_structure
  • Cyferz, Wikipedia2007 , SONOS_cell_structure