Nano Elecrode Structures

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A group presentation on the work I did over the Summer of 2009

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Nano Elecrode Structures

  1. 1. MitgliedderHelmholtz-Gemeinschaft 2009 iNNIN REU Electrochemical Deposition of Polyaniline on Nanoelectrode CrossBar Structures José Guevarra Department of Mechanical Engineering University of California, Santa Barbara PI: Dr Dirk Mayer Mentor: Nils Sanetra
  2. 2. 29. Januar 2015 Folie 2 Outline • Motivation Molecular bioelectronics • The crossbar structure • Polyaniline (PANI) • Goals • Methods • Crossbar Structure Fabrication • Electrochemical deposition of PANI on Au • Summary and Outlook • Acknowledgments
  3. 3. 29. Januar 2015 Folie 3 Molecular electronics What is molecular bioelectronics? • Miniaturization • Alternative to CMOS Bioelectronics • Biomolecule as active part • Totally new functions (e.g. sensor)
  4. 4. 29. Januar 2015 Folie 4 The crossbar architecture What is a crossbar? • Two parallel planes of nanoscale wire arrays • Propterties of the crossbar determined by interjunction layer • Metal-Bridge-Metal (MBM) • For bioelectronics: Interjunctionlayer: SAM [Snider et al 2005]
  5. 5. 29. Januar 2015 Folie 5 Polyaniline (PANI) • Well documented conducting polymer • Can be acid-doped to form conducting salt (emeraldine) • Can be electrochemically deposited • Cheap Can it be used to close the interjunction gap?
  6. 6. 29. Januar 2015 Folie 6 Goals • Fabricate crossbar structures using a soft mold and lift-off process • Characterize pattern fidelity and compare to other methods • Electrochemically deposit a conducting polymer (Polyanaline) to bridge the junction gaps between crossbar junctions • Electronic characterization of polyaniline, electrodes, and junctions
  7. 7. 29. Januar 2015 Folie 7 Methods
  8. 8. 29. Januar 2015 Folie 8 Crossbar Structure Fabrication
  9. 9. 29. Januar 2015 Folie 9 Fabrication Process (NanoImprint Lithography) CF4 Etch O2 Etch Gold Deposition Lift-Off Using a soft mold (Surlyn) allows one to imprint a pattern from a rigid mold multiple times, this extends the life of the rigid mold Soft mold must be rigid enough to survive imprint process and transparent to allow crosslinking of photoresist
  10. 10. 29. Januar 2015 Folie 10 Transmission Characteristics • NXR-2010 crosslinks between 220nm and 300nm • Multiple layers of Surlyn and Surlyn with PDMS backplane should allow crosslinking of photoresist
  11. 11. 29. Januar 2015 Folie 11 Embossing Results • 1 layer of Surlyn – hard to handle (flimsy and curls on itself) • 2 layers of Surlyn – easier to handle • 3 layers of Surlyn – semi-rigid • 4 layers – difficult to emboss (many corrugations) • Surlyn from SONY (130-170 microns) – fairly rigid PDMS backplane must be spin coated to get uniform thickness Embossing is easier with Surlyn squares that fit within radius of wafer although the entire pattern may not be transfered
  12. 12. 29. Januar 2015 Folie 12 Imprinting Results • Attempted to use several types of underlayers (TI-Prime/PMMA/NXR-3010) • Used NXR-2010 undiluted and NXR-2010 + MMA(1:1) Typically, ended with two results • Photoresist ripped off, leaving few or no structures • No crosslinking, leaving no structures (Bikini-Waxing)
  13. 13. 29. Januar 2015 Folie 13 Imprinting Results: Ripping of Photoresist
  14. 14. 29. Januar 2015 Folie 14 Imprinting Results: Bikini-Waxing
  15. 15. 29. Januar 2015 Folie 15 Imprinting Results: Not a Total Loss Some larger, partial structures can be produced
  16. 16. 29. Januar 2015 Folie 16 Imprinting Results Conclusions: 1. Surlyn is too sticky 2. Thicker layers of Surlyn are not transparent Recommendations: 1. Surlyn requires silanization or appropriate treatment 2. Create a rigid, negative mold using SiO2 wafer and NXR-2010 [1]
  17. 17. 29. Januar 2015 Folie 17 Electrochemical Deposition of PANI on Au
  18. 18. 29. Januar 2015 Folie 18 PANI Electrodeposition on Au Basic Technique: • Immerse electrodes in Aniline + H2SO4 solution • Apply voltage bias across electrodes • PANI will oxidize on cathode, grow, and “bridge” gap to the next electrode Deposition Parameters: • Voltage bias between electrodes (0.95V, 0.97, 1 V) • Aniline Concentration (0.1 or 0.2 M Aniline) • Deposition Times Problems: • Use of small drops to immerse electrodes can result in concentration variation • Little to no control of immersed electrode area
  19. 19. 29. Januar 2015 Folie 19 PANI Electrodeposition on Au Deposition Characteristics: • Bridging times range from 45 minutes to 1.5 hours and more • Conductance may grow steadily or rapidly in orders of magnitude • Bridging usually indicated by spikes in current or relatively large current • Current during deposition never exceeds 10-4 A
  20. 20. 29. Januar 2015 Folie 20 PANI Deposition on Au: Sample 5 Before Deposition PANI Depositions 1. +0.95V, 1:10 hrs 2. +0.95V, 10 min 3. +0.95V, 5 min Samples rinsed in Milli-Q water, blown dry, and fresh Aniline solution added before each deposit After Deposition After 3 depositions no current between electrodes when measured in air
  21. 21. 29. Januar 2015 Folie 21 PANI Deposition on Au: Sample 5 No conduction because no bridging
  22. 22. 29. Januar 2015 Folie 22 PANI Deposition on Au: Sample 5 Short period of low conductance to a jump in four orders of magnitude in about 1 hr
  23. 23. 29. Januar 2015 Folie 23 PANI Deposition on Au: Sample 5 Current on the order of 10-6 A, implies Aniline bridging between electrodes Non-linear characteristics
  24. 24. 29. Januar 2015 Folie 24 PANI Deposition on Au: Sample 5 Some bridging between electrodes Conductance ~ 10-6 A
  25. 25. 29. Januar 2015 Folie 25 PANI Deposition on Au Sample Average Deposition Conductance (S) Bridging Observed Conductance Near +1V (S) measured in Air 3 10-9 No - 4 10-9 Yes 10-6 5 10-10 No - 5b 10-4 Yes 10-6 6 10-9 Yes 10-7 7 10-7 Yes 10-6 8 10-9 No -
  26. 26. 29. Januar 2015 Folie 26 PANI Deposition on Au: Voltage Dependence 0.1M Aniline, 0.95V 0.1M Aniline, 0.97V 0.1M Aniline, 1V 0.1M Aniline, 1V
  27. 27. 29. Januar 2015 Folie 27 PANI Deposition on Au: Concentration Dependence 0.2M Aniline, 0.97V 0.2M Aniline, 0.95V
  28. 28. 29. Januar 2015 Folie 28 Summary Conclusions: Surlyn soft molds need silanization An SiO2 + NXR-2010 rigid mold may be an alternative to the soft mold Deposition process not very predictable Bridging will take 45 minutes or more Use a funnel to control surface area and concentration
  29. 29. 29. Januar 2015 Folie 29 Acknowledgments Dr. Dirk Mayer Dr. Andreas Offenhäusser Nils Sanetra Lynn Rathbun Everyone from IBN-2 National Science Foundation National Nanotechnology Infrastructure Network Jennifer, Adam, and Kishore Thanks For the Best Summer Ever!
  30. 30. 29. Januar 2015 Folie 30 References [1] Cross-linked Polymer Replica of a Nanoimprint Mold at 30 nm Half-pitch, Nano Lett., Vol. 5, No. 1, 2005

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