NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS
Though the concept of junctionless field effect transistor (JLFET) is old, it was not possible to fabricate a useful JLFET device, as it requires a very shallow channel region. Very recently, the emergence of new and advanced technologies has made it possible to create viable JLFET devices using nan...
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ndltd-siu.edu-oai-opensiuc.lib.siu.edu-dissertations-25312018-12-20T04:42:55Z NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS Muntahi, Abdussamad Though the concept of junctionless field effect transistor (JLFET) is old, it was not possible to fabricate a useful JLFET device, as it requires a very shallow channel region. Very recently, the emergence of new and advanced technologies has made it possible to create viable JLFET devices using nanowires. This work aims to computationally investigate the interplay of quantum size-quantization and random dopant fluctuations (RDF) effects in nanoscale JLFETs. For this purpose, a 3-D fully atomistic quantum-corrected Monte Carlo device simulator has been integrated and used in this work. The size-quantiza¬tion effect has been accounted for via a param¬eter-free effec¬tive potential scheme and benchmarked against the NEGF approach in the ballistic limit. To study the RDF effects and treat full Coulomb (electron-ion and electron-electron) interactions in the real-space and beyond the Poisson picture, the simulator implements a corrected-Coulomb electron dynamics (QC-ED) approach. The essential bandstructure and scattering parameters (energy bandgap, effective masses, and the density-of-states) have been computed using an atomistic 20-band nearest-neighbour sp3d5s* tight-binding scheme. First, an experimental device was simulated to evaluate the validity of the simulator. Because of the small dimension, quantum mechanical confinement was found to be the dominant mechanism that significantly degrades the current drive capability of nanoscale JLFETs. Surface roughness scattering is not as prominent as observed in conventional MOSFETs. Also, because of its small size, the performance of the device is prone to the effect of variability, for which a discrete doping model was proved essential. Finally, a new JLFET was designed and optimized in this work. The proposed device is based on a gate-all-around silicon nanowire. Source/drain length is 32.5 nm and channel length is 14 nm. Gate contact length is 9 nm. The EOT (equivalent oxide thickness) is 1 nm. It has a metal gate with a workfunction of 4.55 eV. The source, channel and drain regions are n-type with a doping density of 1.5×1019 cm-3. Detailed simulation shows that the two most influential mechanisms that degrade the drive capability are quantum mechanical confinement and Coulomb scattering. Surface roughness scattering is found to be very weak. In addition, thinner nanowire is more prone to Coulomb scattering exhibiting a reduced ON-current (ION). Simulation results show that silicon nanowires with a side length (width and depth) of 3 nm and a doping density of 1.5×1019 cm-3 produce satisfactory drive current. 2018-05-01T07:00:00Z text application/pdf https://opensiuc.lib.siu.edu/dissertations/1527 https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=2531&context=dissertations Dissertations OpenSIUC Device Simulation FET JLFET Monte Carlo Nanoscale Effect Transistor |
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Device Simulation FET JLFET Monte Carlo Nanoscale Effect Transistor |
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Device Simulation FET JLFET Monte Carlo Nanoscale Effect Transistor Muntahi, Abdussamad NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
description |
Though the concept of junctionless field effect transistor (JLFET) is old, it was not possible to fabricate a useful JLFET device, as it requires a very shallow channel region. Very recently, the emergence of new and advanced technologies has made it possible to create viable JLFET devices using nanowires. This work aims to computationally investigate the interplay of quantum size-quantization and random dopant fluctuations (RDF) effects in nanoscale JLFETs. For this purpose, a 3-D fully atomistic quantum-corrected Monte Carlo device simulator has been integrated and used in this work. The size-quantiza¬tion effect has been accounted for via a param¬eter-free effec¬tive potential scheme and benchmarked against the NEGF approach in the ballistic limit. To study the RDF effects and treat full Coulomb (electron-ion and electron-electron) interactions in the real-space and beyond the Poisson picture, the simulator implements a corrected-Coulomb electron dynamics (QC-ED) approach. The essential bandstructure and scattering parameters (energy bandgap, effective masses, and the density-of-states) have been computed using an atomistic 20-band nearest-neighbour sp3d5s* tight-binding scheme. First, an experimental device was simulated to evaluate the validity of the simulator. Because of the small dimension, quantum mechanical confinement was found to be the dominant mechanism that significantly degrades the current drive capability of nanoscale JLFETs. Surface roughness scattering is not as prominent as observed in conventional MOSFETs. Also, because of its small size, the performance of the device is prone to the effect of variability, for which a discrete doping model was proved essential. Finally, a new JLFET was designed and optimized in this work. The proposed device is based on a gate-all-around silicon nanowire. Source/drain length is 32.5 nm and channel length is 14 nm. Gate contact length is 9 nm. The EOT (equivalent oxide thickness) is 1 nm. It has a metal gate with a workfunction of 4.55 eV. The source, channel and drain regions are n-type with a doping density of 1.5×1019 cm-3. Detailed simulation shows that the two most influential mechanisms that degrade the drive capability are quantum mechanical confinement and Coulomb scattering. Surface roughness scattering is found to be very weak. In addition, thinner nanowire is more prone to Coulomb scattering exhibiting a reduced ON-current (ION). Simulation results show that silicon nanowires with a side length (width and depth) of 3 nm and a doping density of 1.5×1019 cm-3 produce satisfactory drive current. |
author |
Muntahi, Abdussamad |
author_facet |
Muntahi, Abdussamad |
author_sort |
Muntahi, Abdussamad |
title |
NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
title_short |
NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
title_full |
NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
title_fullStr |
NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
title_full_unstemmed |
NANOSCALE EFFECTS IN JUNCTIONLESS FIELD EFFECT TRANSISTORS |
title_sort |
nanoscale effects in junctionless field effect transistors |
publisher |
OpenSIUC |
publishDate |
2018 |
url |
https://opensiuc.lib.siu.edu/dissertations/1527 https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=2531&context=dissertations |
work_keys_str_mv |
AT muntahiabdussamad nanoscaleeffectsinjunctionlessfieldeffecttransistors |
_version_ |
1718803194714259456 |