CNTFET

CNTFET Substitute of MOSFET

Gonugunta Saiphani kumar M.Tech VLSI 2nd sem 14219008 NIT Jalandhar-144011

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IntroductionWhen further scaling down MOSFET, serious limits in fabrication& performanceIn 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 electronsAnd also self oscillation of MOSFET due to parasitic capacitances

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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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Carbon nano tubes

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Role of chirality vectordepending on angle of arrangement along the tubeIf n=m or n-m = 3i then it behaves like a metalOtherwise it behaves like a semiconductorDiameter SWCNT(~1nm) ; where a0 = 0.142nm

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CNTFETFormed by CNT connecting two metal electrodes.Gate electrode is separated CNT by thin oxide film.There is no scattering in the CNT channellThe net current is carried by carriers with energy between 1 and 2 that travel from contact 1 to contact 2. L = |Ch| = a *

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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-sExcellent electrostatics Excellent gate control.

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advantagesBetter control overchannel formation

Betterthreshold voltage

Bettersubthreshold slope

Highelectron mobility

Highcurrent density

Hightransconductance

Good stiffness, strength

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I-V Characteristics

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Implementation of full adder using 10nm CNTFET

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Results w.r.t MOSFET

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Drawbacks of CNTFETManufacturing 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 wont happen in the single-channeled ones.

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