Simulate Carbon Nano-Tube Mosfet for Different Conditions

ICT ASSIGNMENT NO. 2

Q) Simulate carbon nano-tube mosfet for different conditions (eg: gate/drain voltage sweep, threshold voltage). Comment on results obtained.

ANS.:

Carbon nanotubes (CNTs) are being explored as a structure that may play a leading role in future electronic systems. CNTs are planar graphite sheets (graphene) that are seamlessly wrapped into tubes, as shown in Fig. 2. CNTs possess favorable electrical characteristics and can be fabricated in dimensions as small as 4-8Å in diameter. The electrical characteristics of a CNT vary with its diameter and the wrapping angle of the graphene. Both the diameter and the wrapping angle can be described by the tube’s fundamental indices (n,m). Theory indicates that CNTs can be metallic or semiconducting depending on the fundamental tube indices (n,m), and bandgap depends on the diameter. Analysis shows semiconducting CNTs have very high low-field mobilities, with peak drift electron velocities that can be as much as five times higher than that of silicon. Tubes can be doped by donors and acceptors. CNTs facilitate devices with large transconductances and high drive currents. Experiments have demonstrated the viability of CNT-based FETs and CNT-SOI type MOSFETs. Preliminary research has been done to model, design CNT embedded bulk MOSFETs.

[pic 1]

CNT MOSFET Cross section

[pic 2]

Id vs. Vd for gate & drain voltage sweep, threshold voltage = 0.2V

[pic 3]

Id vs. Vd for gate & drain voltage sweep, threshold voltage = 0.32V

[pic 4]

Id vs. Vd for gate & drain voltage sweep, threshold voltage = 0.5V

[pic 5]

Id vs. Vd for gate & drain voltage sweep, threshold voltage = 0.75V

It is observed that as Gate voltage increases, drain current increases. Also, as threshold voltage increases, drain current decreases.