Realizing a Low Noise Amplifier with Carbon Nanotube Technology

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

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

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

5. Channel Fabrication Most common today is CVD Chemical Vapor Deposition – ‘grow’ CNTs Can have a single CNT channel

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

7. Parasitics/Contacts(Capacitances & Resistances) Problems: Contact resistance High Cpd/Cps

8. Contacts/Parasitics Impedance from diffusive transport Parasitic capacitances from extra metals Can reduce length to improve this New layout: multiple gate fingers Limited by spacing

9. Contacts/Parasitics Use same drain/source/gate contacts, dielectrics, etc Integrable with CMOS Serious mismatch between contact resistance and channel resistance Schottkey barrier contacts instead of ohmic contacts Reduce channel resistance with self-aligning CNTs

10. Measurement Mismatch between device and apparatus Techniques Calibration and de-embedding techniques Time intensive DC measurements translated to RF Less accurate Difficult to compare results, especially for ?? ?? , ?? ??????

11. DC Characteristics Max reported gm currently ~50 ????/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

12. Transit & Max Frequency

13. 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

14. Conclusions Solutions 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?

15. Summary of Issues Parasitic capacitances from extra metals Contact resistances/diffusive behavior All these lead to Low gain, low operation frequency Gain/current tradeoff Worst case scenario: Schottky contacts with diffusive CNFETs with lower quality arrays

16. Summary of solutions Can solve all our problems at once 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?

17. Thank you! Questions?

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