Compact modeling and characterization of carbon nanotube field-effect transistors and analog high- frequency circuit design
Final Report Abstract
A closed-form analytical drain current formulation based on the Landauer integral was developed that takes into account electron–phonon scattering in the channel and was successfully used for performance predictions from varying Schottky barrier (SB) height, characteristic length, electron mean free path and band gap of the channel material. The new formulation removes deficiencies in the treatment of the effective mean free path of electrons scattered by acoustic phonons in previously existing compact models. Unfortunately, project funding was insufficient for developing a complete CNTFET model with an accurate description of the model parameters as a function of CNT density and diameter as well as device geometry and substrate coupling and thermal effects. It was also shown that the generic formulations of a "virtual source" compact model, which has become popular for nanoscale silicon MOSFETs, is quite reasonably suited for capturing the measured DC and high-frequency (HF) characteristics of CNTFETs with different channel lengths as well as of 200 nm III-V (InGaAS) nanowire HFETs and 120 nm Si based MOSFETs. However, the physics of the source and drain SB are not included in this model, so it lacks predictive capability and is also not capable of handling the characteristics of high-linearity CNTFETs. Based on the developed compact models, which were calibrated on measured data, CNTFET- based high-frequency amplifiers were studied regarding the impact of transistor linearity and CNT inductor quality factor Q on maximum gain and low-noise applications at 2.4 GHz. The results of the designed single- and double-stage amplifiers indicate that the performance is not affected as long as Q is beyond 8. Hence CNT-based inductors appear to be feasible components for RF amplifiers. Comparing the noise and gain performance of these designs to other FET technologies and considering the linearity performance, CNTFET-based amplifiers turn out to be credible contenders for developing circuit applications at S-band frequencies using on-wafer stabilizing and matching networks. In addition, a CNTFET based oscillator operating at 461 MHz (−115 dBc/Hz phase noise at 1 MHz) was designed, implemented and characterized for the first time. The thermal resistance and capacitance of fabricated HF CNTFETs were determined for the first time. The extracted parameters, especially the short thermal time constant in the range of a few ps, confirm the thermal stability expected for these devices. The developed lumped element electro-thermal model agrees well with the experimental data obtained from pulsed measurements. The original plan in this project was to apply the models to a larger variety of HF CNTFETs with also significantly improved performance. Unfortunately, funding of CNTFET process development has been inadequate for implementing and running a stable wafer-scale process flow for test chip fabrication. This has so far limited the experimental data. Different channel materials were compared with the aim of identifying the potential of a CNT based FET technology. The results show that with improved contact resistance and tube density, CNTFETs can reach far higher cut-off frequencies than FETs with incumbent channel materials, including III-V channels. Along with their much higher transconductance and simple fabrication process, CNTFETs would then lead to superior circuit performance and hence become the FET technology of choice.
Publications
- "Contact resistance extraction methods for short- and long-channel carbon nanotube field-effect transistors", Solid-State Electronics, Vol. 125, pp. 161-166, 2016
A. Pacheco-Sanchez, M. Claus, S. Mothes, M. Schröter
(See online at https://doi.org/10.1016/j.sse.2016.07.011) - “Carbon nanotube field-effect transistor performance in the scope of the 2026 ITRS requirements”, Proc. SISPAD, pp. 270-280, 2016
A. Pacheco-Sanchez, D. Loroch, S. Mothes, M. Schröter, M. Claus
(See online at https://doi.org/10.1109/SISPAD.2016.7605201) - "A CNTFET Oscillator at 461 MHz", IEEE Microw. and Wireless Comp. Lett., Vol. 27, No. 6, pp. 578-580, 2017
A. Taghavi, C. Carta, T. Meister, F. Ellinger, M. Claus, M. Schröter
(See online at https://doi.org/10.1109/LMWC.2017.2701312) - “Analytical Drain Current Model of One-Dimensional Ballistic Schottky-Barrier Transistors”, IEEE Trans. Electron Dev., Vol. 64, No. 9, pp. 3904-3911, 2017
I. Bejenari, M. Claus, M. Schröter
(See online at https://doi.org/10.1109/TED.2017.2721540) - "Flexible virtual source compact model for efficient modeling of emerging channel materials and device architectures", TechConnect Briefs (Nanotech), Anaheim (CA), 244-248., May 13, 2018
S. Mothes, F. Wolf, M. Schröter
- “Three-dimensional transport simulations and modeling of densely packed CNT- FETs”, IEEE Trans. Nanoelectronics, Vol. 17, No. 6, pp. 1282-1287, Nov. 2018
S. Mothes and M. Schröter
(See online at https://doi.org/10.1109/TNANO.2018.2874109) - "Self-Heating Characterization and Thermal Resistance "Modeling in Multitube CNTFETs", Journal: IEEE Trans. Electron Devices, Vol 66, No. 11, pp. 4566-4571, 2019
A. Pacheco-Sanchez, I. Bejenari, M. Schröter
(See online at https://doi.org/10.1109/TED.2019.2942783) - "Gate Spacer Investigation for Improving the Speed of HF Carbon Nanotube-based Field-Effect Transistors", ACS Applied Materials & Interfaces, 2020
M. Hartmann, J. Tittmann-Otto, S. Böttger, G. Heldt, M. Claus, S. Schulz, M. Schroeter, S. Hermann
(See online at https://doi.org/10.1021/acsami.0c01171) - "High-frequency performance study of CNTFET-based amplifiers", IEEE Trans. Nanotechnol., vol. 19, no. 1, pp. 284-291, 2020
J. Ramos-Silva, A. Pacheco-Sanchez, L. Diaz-Albarran, L. Rodriguez-Mendez, M. Enciso-Aguilar, M. Schröter, E. Ramirez-Garcia
(See online at https://doi.org/10.1109/TNANO.2020.2978816)
