1.
Electrical Properties Factors <ul><li>Contact: </li></ul><ul><ul><li>Number of concentric layers in contact with electrode [19] </li></ul></ul><ul><ul><li>Contact geometry (side vs tip) [20] </li></ul></ul><ul><ul><li>Contact area [23] </li></ul></ul><ul><ul><li>Electrode materials used [21, 22] </li></ul></ul><ul><ul><li>Interface coupling (scattering induced by defects; tunneling) [24, 25] </li></ul></ul><ul><li>CNT: </li></ul><ul><ul><li>Consistency across different samples </li></ul></ul><ul><ul><li>Semiconducting vs metallic [19] </li></ul></ul><ul><ul><li>Outer-layer vs inner-layer [26, 27] </li></ul></ul><ul><ul><li>Defect density [28] </li></ul></ul><ul><li>Literature: 34 Ω to ~10 MΩ </li></ul>

2.
I-V characteristics <ul><li>9 CNTs connections </li></ul><ul><li>Ohmic response </li></ul><ul><li>~ 480 kΩ </li></ul><ul><li>Stable, repeatable response </li></ul>

3.
I-V characteristics <ul><li>Unstable at same pressure </li></ul><ul><li>~100x reduction in conductivity after SEM </li></ul>

4.
I-V characteristics <ul><li>~ 7 kΩ ( > 10 CNT connections) </li></ul><ul><li>No electrical connection after some CNT breakage </li></ul>

5.
I-V characteristics

6.
Si-CNT contact <ul><li>Assumptions: </li></ul><ul><ul><li>Outercell contributes most current </li></ul></ul><ul><ul><li>d > 16nm => bandgap smaller than 0.026eV </li></ul></ul><ul><ul><li>Metallic </li></ul></ul>

7.
Si-CNT contact <ul><li>W ~ 9 nm </li></ul><ul><li>Tunneling dominate </li></ul><ul><li>Specific contact resistance ~10 -4 Ωcm 2 </li></ul><ul><li>Contact area ~ 2.5x10 -11 cm 2 </li></ul><ul><li>Contact resistance (~0.5-5 MΩ) vs overall resistance of ~ 2.5 MΩ </li></ul>

8.
Native oxide <ul><li>~10Å thickness </li></ul><ul><li>Breakdown field ~3x10 7 V/cm </li></ul><ul><li>Voltage applied (V2~5V, V1~7V) </li></ul>

9.
Non-ohmic I-V characteristics <ul><li>Non-ohmic </li></ul><ul><li>Lacks apparent “turn-on” voltage </li></ul><ul><li>Somewhat symmetrical about origin </li></ul>

10.
Non-ohmic I-V characteristics <ul><li>~8x10 -7 A at 1V (tunneling through 10Å oxide) </li></ul><ul><li>Tunneling current exponential with applied voltage </li></ul>a) [30], b) [31]

11.
Non-ohmic characteristics <ul><li>At low bias (<0.25 V) </li></ul><ul><ul><li>Limited by tunneling current density ~10 A/cm 2 , exponentially increasing) </li></ul></ul><ul><li>At high bias (>0.3 V) </li></ul><ul><ul><li>Limited by combination of CNT and contacts resistance, ohmic) </li></ul></ul><ul><li>Symmetrical about origin </li></ul>

12.
Native oxide <ul><li>Breakdown voltage ~3x10 7 V/cm </li></ul><ul><li>Oxide thickness < 20Å </li></ul><ul><li>Gradient past breakdown => ~270 kΩ </li></ul>

13.
Si-CNT-Au system

14.
Si-CNT-Au system <ul><li>Overall resistance ~170 kΩ, ~6.7 MΩ </li></ul>

15.
Pressure-sensing <ul><li>Pressure-sensing observed in ohmic device </li></ul>

16.
Pressure-sensing <ul><li>Negative resistance coefficient of temperature </li></ul>

17.
Contact annealing <ul><li>Electrically heat up secondary heater </li></ul><ul><li>Fragments of CNTs observed post-heating </li></ul>

18.
Contact annealing <ul><li>Heating in furnace ~500 0 C </li></ul><ul><li>No apparent physical change, though conductivity decreases </li></ul>

19.
CNT-based probe electrode <ul><li>Intracellular (~100mV) vs Extracellular (~100µV) </li></ul><ul><li>Patch cell (“gigaohm seal”) </li></ul>

20.
CNT-based probe electrode

21.
Fabrication steps <ul><li>Parylene-C </li></ul><ul><ul><li>high volume resistivity </li></ul></ul><ul><ul><li>Biocompatibility </li></ul></ul><ul><ul><li>conformal deposition </li></ul></ul><ul><ul><li>Melting temp (290 0 C) </li></ul></ul>

22.
Fabrication steps

23.
CNT-based probe electrode

24.
Impedence attempts

25.
Onion cell connection

26.
Conclusions <ul><li>Fine-tune localized growth of CNTs </li></ul><ul><li>In-situ monitoring and controlled growth of CNTs </li></ul><ul><li>Investigate the electrical properties of Si/CNT/Si system </li></ul><ul><li>Pressure-sensing & cell electrode probe </li></ul>

27.
Publications <ul><li>Takeshi Kawano, Dane Christensen, Supin Chen, Chung Yeung Cho , Liwei Lin, “Formation and characterization of silicon/carbon nanotube/silicon heterojunctions by local synthesis and assembly”, Applied Physics Letters , 89(1), (2006) </li></ul><ul><li>Takeshi Kawano, Chung Yeung Cho , Liwei Lin, “Carbon nanotube-based nanoprobe electrode”, IEEE International Conference of Nano/Micro Engineered and Molecular Systems Conference (2007) </li></ul><ul><li>Takeshi Kawano, Chung Yeung Cho , Liwei Lin, “In-situ controlled growth of carbon nanotubes by local synthesis”, IEEE International Conference on Micro Electro Mechanical Systems Conference (2007) </li></ul><ul><li>(Not related to this CNT work) Kyoungsub Shin, Weize Xiong, Chung Yeung Cho , C. Rinn Cleavelin, Thomas Schulz, Klaus Schruefer, Member, IEEE , Paul Patruno, Lee Smith, and Tsu-Jae King Liu, “Study of bending-induced strain effects on MugFET performance”, IEEE Electron Device Letters , 27 (8), 671-673 (2006) </li></ul>

28.
Acknowledgement <ul><li>Prof Lin, Prof King </li></ul><ul><li>Takeshi Kawano </li></ul><ul><li>Brian, Sha Li, Lei Luo, Ethan, Takashi </li></ul><ul><li>Other lab mates </li></ul><ul><li>EML folks </li></ul><ul><li>Tammy, my family </li></ul>

29.
References <ul><li>Eikos.com company info </li></ul><ul><li>Anyuan Cao et al., “ Super-compressive foamlike carbon nanotube films ”, Science, 310 , 1307-1310 (2005) </li></ul><ul><li>Nantero.com NRAM movie </li></ul><ul><li>Ray H. Baughman et al., “ Carbon nanotubes - the route toward applications ”, Science, 297, 787-782 (2002) </li></ul><ul><li>Nadine Wong Shi Kam et al., “ Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction ”, PNAS, 102 (33), 11600-11605 (2005) </li></ul><ul><li>T. D. Yuzvinsky et al., “ Engineering nanomotor components from multi-walled carbon nanotubes via reactive ion etching ”, AIP Conference Proceedings 723 , 512-515 (2004) </li></ul><ul><li>Mei Zhang et al., “ Strong, transparent, multifunctional, carbon nanotube sheets ”, Science 309 , 1215-1219 (2005) </li></ul><ul><li>Hongjie Dai, “Carbon nanotubes: opportunities and challenges”, Surface Science, 500, 218-241 (2002) </li></ul><ul><li>Dane Cristensen, “ Localized synthesis, assembly and application of carbon nanotubes ”, PhD dissertation in Mechanical Engineering in UC Berkeley (2005) </li></ul>

30.
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31.
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32.
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