1. CNTFET
Substitute of MOSFET
Gonugunta Saiphani kumar
M.Tech VLSI 2nd sem 14219008
NIT Jalandhar-144011
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2. Introduction
 When further scaling down MOSFET, serious limits in fabrication&
performance
 In particular five different short-channel effects can be distinguished:
1. drain-induced barrier lowering and punchthrough
2. surface scattering
3. velocity saturation
4. impact ionization
5. hot electrons
And also self oscillation of MOSFET due to parasitic capacitances
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3. Solutions to overcome
 Modification on existing structures & technologies
 High - K insulating material, metal gate electrode
 Using new materials to replace silicon MOSFETs
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4. Carbon nano tubes
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5. Role of chirality vector
depending on angle of arrangement along the tube
 If n=m or n-m = 3i then it behaves like a metal
 Otherwise it behaves like a semiconductor
 Diameter SWCNT(~1nm) ; where a0 = 0.142nm
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6. CNTFET
 Formed by CNT connecting
two metal electrodes.
 Gate electrode is separated
CNT by thin oxide film.
 There is no scattering in the CNT channell
 The net current is carried by carriers
with energy between μ1 and μ2 that
travel from contact 1 to contact 2.
L = |Ch| = a *
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7. Why carbon nanotubes?
 Single walled carbon nanotube is a potential channel material for future
high performance logic circuits.
 High carrier mobility from 3000 to 10000 cm2/v-s
 Excellent electrostatics
 Excellent gate control.
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9. advantages
 Better control over channel formation
 Better threshold voltage
 Better subthreshold slope
 High electron mobility
 High current density
 High transconductance
 Good stiffness, strength
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10. I-V Characteristics10

11. Implementation of full adder using
10nm CNTFET
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12. Results w.r.t MOSFET
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13. Drawbacks of CNTFET
 Manufacturing CNTFET-based circuits will differ from current practice with
conventional silicon Technologies so the fault/defect models must be
revisited.
 the defect and failure rate at device and circuit level is expected to be
much higher than with traditional CMOS.
 The carbon nanotube degrades in a few days when exposed to oxygen.
There have been several works done on passivating the nanotubes with
different polymers and increasing their lifetime.
 So many difficulties in mass production, production cost.
 The multi-channeled CNTFETs can keep a stable performance after several
months, while the single-channeled CNTFETs are usually out of work after a
few weeks in the ambient atmosphere.The multi-channeled CNTFETs keep
operating when some channels break down, this won’t happen in the
single-channeled ones.
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