[paper] A Compact Model of Gate Capacitance in Ballistic GAA-CNFET

A. Dixit, N. Gupta

A Compact Model of Gate Capacitance 

in Ballistic Gate-all-around Carbon Nanotube Field Effect Transistors 

IJE TRANSACTIONS A: Basics Vol. 34, No. 7, (July 2021) 1718-1724 

DOI: 10.5829/ije.2021.34.07a.16

* Nanomaterial Device Laboratory, Department of Electrical and Electronics Engineering,
Birla Institute of Technology and Science, Pilani, Rajasthan, India

Abstract: This paper presents a one-dimensional analytical model for calculating gate capacitance in Gate-All-Around Carbon Nanotube Field Effect Transistor (GAA-CNFET) using electrostatic approach. The proposed model is inspired by the fact that quantum capacitance appears for the Carbon Nanotube (CNT) which has a low density of states. The gate capacitance is a series combination of dielectric capacitance and quantum capacitance. The model so obtained depends on the density of states (DOS), surface potential of CNT, gate voltage and diameter of CNT. The quantum capacitance obtained using developed analytical model is 2.84 pF/cm for (19, 0) CNT, which is very close to the reported value 2.54 pF/cm. While, the gate capacitance comes out to be 24.3×10-2 pF/cm. Further, the effects of dielectric thickness and diameter of CNT on the gate capacitance are also analyzed. It was found that as we reduce the thickness of dielectric layer, the gate capacitance increases very marginally, which provides better gate control upon the channel. The close match between the calculated and simulated results confirms the validity of the proposed model.

Fig. Schematic view of CNFET for modelling gate capacitance (a) front view (b) side view

Acknowledgements: Authors acknowledge the financial support of Defence Research and Development Organisation (DRDO), Govt. of India [ERIP/ER/DGMED&OS/990416502/ M/01/1657] and Nanomaterial device laboratory, BITS Pilani for carrying research out work reported this paper.

[paper] Carbon Nanotube Detectors and Spectrometers for the Terahertz Range

Junsung Park¹, Xueqing Liu¹, Trond Ytterdal²

and Michael Shur^1,3 

Carbon Nanotube Detectors and Spectrometers for the Terahertz Range 

Crystals 2020, 10, 601

DOI:10.3390/cryst10070601

¹Department of Electrical, Computer, and Systems Engineering, RPI  Troy, NY 12180, USA
²Department of Electronic Systems, NUST, O.S. Bragstads plass 2a, 7034 Trondheim, N
⁴Electronics of the Future, Inc., Vienna, VA 22181, USA

Abstract: We present the compact unified charge control model (UCCM) for carbon nanotube field-effect  transistors  (CNTFETs)  to  enable the accurate  simulation  of  the  DC  characteristics  and plasmonic terahertz (THz) response  in the  CNTFETs. Accounting for  the ambipolar  nature of the carrier transport (n-type and p-type conductivity at positive and negative gate biases, respectively), we use n-type and p-type CNTFET non-linear equivalent circuits connected in parallel, representing the ambipolar  conduction in the  CNTFETs.  This allows us to present a realistic non-linear  model that is valid across the  entire voltage  range  and is therefore suitable  for  the  CNTFET design. The important  feature  of  the  model  is that  explicit equations for gate  bias,  current,  mobility,  and capacitance with smoothing parameters accurately describe the device operation near the transition from above- to below-threshold regimes, with scalability in device geometry. The DC performance in  the proposed  compact CNTFET  model  is  validated  by  the  comparison between  the  SPICE simulation and the experimental DC characteristics. The simulated THz response resulted from the validated CNTFET model is found to be in good agreement with the analytically calculated response and  also  reveals  the  bias  and  power  dependent  sub-THz  response  and  relatively  wide  dynamic range   for   detection   that   could   be   suitable   for   THz   detectors.   The   operation   of   CNTFET spectrometers  in the THz  frequency  range  is  further  demonstrated  using  the  present  model.  The simulation exhibits that the CNT-based spectrometers can cover a broad THz frequency band from 0.1 to 3.08 THz. The model that has been incorporated into the circuit simulators enables the accurate assessment  of  DC  performance  and  THz  operation.  Therefore,  it  can  be  used  for the design  and performance estimation of the CNTFETs and their integrated circuits operating in the THz regime.  

Fig: Schematic illustration of the simulation circuit for the CNTFET THz detection

with the open boundary condition at the drain.

Funding: This  work  at  RPI  was  supported  by  the  U.S.  Army  Research  Laboratory  under  the  Cooperative Research Agreement (Project Monitor Dr. Meredith Reed) and by the US ONR (Project Monitor Dr. Paul Maki).