Philip Kim Department of Physics Columbia University Toward Carbon Based Electronics Beyond CMOS Devices

End of the Road map: Quest for Beyond Si CMOS Era

SP 2 Carbon: 0-Dimension to 3-Dimension Fullerenes (C 60 ) Carbon Nanotubes Atomic orbital sp 2   GraphiteGraphene 0D1D2D3D

Outline: Carbon Based Electronics Material Platform: Low dimensional graphitic systems 1-D: Carbon Nanotubes (since 1991) 2-D: Graphene (since 2004) Device Concepts Conventional: (extended or ultimate) CMOS, SET Non-Conventional: Quantum Interference, Spintronics, valleytronics

Graphene : Dirac Particles in 2-dimension Band structure of graphene (Wallace 1947) kxkx kyky Energy kx'kx' ky'ky' E Zero effective mass particles moving with a constant speed v F hole electron

Single Wall Carbon Nanotube kyky kxkx kxkx kyky Allowed states Metallic nanotube E k 1D E Semiconducting nanotube E g ~ 0.8 ev / d (nm)

Length (  m) Resistance (k  ) T = 250 K  = 8 k  /  m Extremely Long Mean Free Path in Nanotubes Multi-terminal Device with Pd contact * Scaling behavior of resistance: R(L) L (  m) R (k  ) T = 250 K R (k  ) L (  m) R ~ R Q R ~ L l e ~ 1  m M. Purewall, B. Hong, A. Ravi, B. Chnadra, J. Hone and P. Kim, PRL (2007) Room temperature mean free path > 0.5  m

Nanotube FET Band gap: 0.5 – 1 eV On-off ratio: ~ 10 6 Mobility: ~ 100,000 cm 2 ~ nm Fermi velocity: 10 6 m/sec Max current density > 10 9 A/cm 2 V sd (V) I sd (  A) Ph. Avouris et al, Nature Nanotechnology 2, 605 (2007) Schottky barrier switching

Advantages of CNTFET Novel architecture -> Band-to-band tunneling FET: subthreshold slop ~ 40 No-dangling bond at surface -> high k-dielectric compatible C g ~ C Q can be attainable; small RC, low energy Thin body (1-2 nm) -> suppressed short channel effect channel length ~ 10 nm has been demonstrated Javey et al. PRL (2004). Appenzeller et al., PRL (2002)

Rodgers, UIUC Aligned growth of Nanotubes Nanotube Electronics: Challenges Pros: High mobility High on-off ratio High critical current density Small channel length Small gate capacitance Large Fermi velocity Con: Controlled growth Artistic dream (DELFT) IBM, Avouris group Nanotube Ring Oscillators graphene

Discovery of Graphene Large scale growth efforts: CVD, MBE, chemical synthesis

Number of Graphene Publications on arXiv /month Oct 05 Jun 05Feb 05 Oct 04 Feb 07 Oct 06 Jun 06Feb 06Feb 08 Oct 07 Jun 07 Dec 05 Aug 05 Apr 05 Dec 04 Apr 07 Dec 06 Aug 06 Apr 06Apr 08 Dec 07 Aug 07 Growth of Graphene Research Jun 08 factor 4 / year

Graphene Mobility n (10 12 cm -2 ) Mobility (cm 2 /V sec) TC17 TC12 TC145 TC130 Mechanically exfoliated graphene Tan et al. PLR (2007) Scattering Mechanism? Ripples Substrate (charge trap) Absorption Structural defects Modulate Doped GaAs: Pfeiffer et al. GaAs HEMT

High mobility materials have been under intensive research as an alternative to Silicon for higher performance mobility: Si (1,400 cm2/Vsec), InSb (77,000 cm2/Vsec) Graphene mobility: > 100,000 cm 2 room temperature unsuspended best before annealing after annealing Density ( cm -2 ) Mobility (cm 2 /V sec) Enhanced Room Temperature Mobility of Graphene SEM image of suspended graphene graphene

Low temperature direct atomic layer deposition (ALD) of HfO 2 as high-κ gate dielectric Top-gate electrode is defined with a final lithography step. I-V measurements at two different back gate voltages show a distinct “kink” for different top-gate voltages Transconductance can be as high as g m = 328μS (150μS/μm) Poor on-off ratio: ~ 5-10 due to zero gap in bulk Graphene FET characteristics Meric, Han, Young, Kim, and Shepard, Nature Nanotech (2008)