1. Realizing a Low Noise Amplifier with Carbon Nanotube Technology
Kristen N. Parrish
May 3, 2010

2. What is a CNFET? Carbon Nanotube Field Effect Transistor
Semiconducting CNT channel
Fig 1 [1]
Fig 2 [2]

3. An exciting new field… but why do we care?
Ballistic operation
Better for this than CMOS – higher mean free path, less short-channel effects
Improved conductivity, mobility, transconductance, high frequency operation
THz performance predicted
Complimentary to existing CMOS technology
Continue scaling trends (Moore’s Law)
Nanoscale dimensions
Fig 3 [3]

4. LNA Metrics of Evaluation
Low Noise Amplifier
High ft and fmax
High gain
Sufficient current output
Low noise at RF
Fig 4. Standard Inductively
Degenerated LNA Topology

5. Channel Fabrication Most common today is CVD
Chemical Vapor Deposition – ‘grow’ CNTs
Can have a single CNT channel
22 uS with d=2nm
Unfortunately, occurs in ‘off’ mode
Solution: increase width
Fig 5 [4]

6. Channel Fabrication Increase width to take advantage of high densities
Semiconducting and metallic types
1/3 are metallic
Lose gate control
Solutions
Burn off metal CNTs
Chemical control
Fig 6 [5]

7. Parasitics/Contacts (Capacitances & Resistances)
Problems:
Contact resistance
High Cpd/Cps
Fig 7 [3]
Solutions:
Decrease length
Decrease metal areas
Fig 8 [6]

8. DC Characteristics Max reported gm currently ~50 𝜇𝑆/nanotube
Current output is low
low on/off ratio
Current/gain tradeoff
Improvements from
Increasing array purity
Increasing array density (CNT spacing)
Channel length & parasitic resistance

9. Transit & Max Frequency
Limited by parasitic capacitances
Still approaching THz
Fig 9 [1]
Fig 10 [5]

10. Noise Has not been characterized to GHz frequencies for CNFET
Have observed for CNTs:
Thermal: only dependent on resistance; limited by length
Flicker: 1/f; not generally a concern for high frequencies
Shot: orders of magnitude smaller than other contributions; makes ballistic transport more desirable
Fig 11 [7]
Fig 12 [8]

11. Conclusions Solutions What we want: Why aren’t we there yet?
Smaller channel length
Improved arrays (purer, denser)
New topologies (self alignment, introduce gate fingers, etc)
What we want:
Ohmic contacted Ballistic CNFETs with a dense self-aligned array of identical semiconducting nanotubes
Why aren’t we there yet?

12. Thank you!
Questions?

13. References
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