The effects of irradiations on MOSFET and bipolar junction transistors are well known though irradiation mechanisms in two-dimensional graphene and related devices are still being investigated. In this work, we investigate irradiation mechanism based on a semi-empirical model for the graphene back-gate transistor and quantitatively analyze the irradiation influences on electrical properties of the device structure. The irradiation shifts the current which changes the region of device operation, degrades the mobility and increases the channel resistance which can increase the power dissipation. The main mechanism causing the degradation in performance of devices is the oxide trap charges near the SiO2/graphene interface and graphene layer traps charges.
In our earlier work1, we have developed an analytical current transport model of a p-channel Tunnel Field Effect Transistor (T-FET) made from 2D atomically thick Graphene Nanoribbon (GNR). Considering drain-source voltage (VDS), gate-source voltage (VGS), carrier mobility (μ) and top gate dielectric (tOX), the model demonstrates an ON current of 1605 μA/μm for a GNR width of 5nm at 0.275eV band gap. The calculated ON/OFF current ratio of 107 with a very steep Subthreshold-Slope (SS) of 7.07mV/decade is obtained from the I-VGS transfer characteristics. In the present work, current transport mechanism of graphene T-FETs considering constant and variable electric fields are proposed and corresponding I-V characteristics are obtained. The constant electric field model is based on tunneling mechanism of Esaki tunnel diode. The variable electric field model exhibits linear (Ohmic) I-V characteristics. Contrary to a variable electrical field, constant field model exhibits both linear and saturation regions of operation. Using back gated biasing, the n-channel TFET exhibits negative differential conductivity (NDC) for the variable electric field. The performance of GNR T-FET under constant electric field model is compared with the projected model of nMOSFETs in 2011 ITRS and found that the proposed model exhibits seven times lower power and eight times higher intrinsic speed in the upper GHz range. Such high performance makes graphene T-FET extremely suitable for design of ultra-low power RF integrated circuits.
Carbon nanotubes have exhibited excellent molecular adsorption properties and their dimensions are comparable to
typical bio-molecules such as the DNA. Carbon nanotube field effect transistors (CNT-FETs) and integrated circuits are
being explored for electrical sensing of bio-materials and gases. The adsorbed molecules by the carbon nanotube and the
CNT-FET result in a change of the CNT conductance and electronic properties of the CNT-FET which can be easily
monitored. It thus becomes very important to better understand electronic transport and model its behavior in relation to
bio- and chemical sensing. Some of the recently developed compact analytical models for current transport in CNT-FETs
are compatible with EDA tools for analysis and design of CNT-FET based integrated circuits but these are limited to
applications in non-ballistic region. Since applications requiring a large number of bio-sensing using CNT-FETs are in 2-
20 nm range, in this work, the current transport model of CNT-FETs has been suitably modified for operation in the
ballistic region for use in integrated circuit design and sensing applications.
The surface potentials in a CNT-FET have been coupled with the current transport equations to obtain compact electronic
current transport models for operation in the ballistic region. A p-type CNT-FET is considered for the analysis which can
be easily applied in n-type CNT-FETs. The work is also compared with other electronic transport models and
experimental measurements. A close agreement establishes the validity of our electronic transport model of the transistor
operation in the ballistic region. It is also shown that two subbands in the valance band of CNT are sufficient for
computation of current in CNT-FETs. The current transport model characterizing CNT-FET in the ballistic region is
simple and compatible with EDA tools for bio-sensing chip design.
We investigated the application of one-dimensional fluid model in modeling of electron transport in carbon nanotubes and equivalent circuits for interconnections and compared the performances with the currently used copper interconnects in very-large-scale integration (VLSI) circuits. In this model, electron transport in carbon nanotubes is regarded as quasi one-dimensional fluid with strong electron-electron interaction. Verilog-AMS in Cadence/Spectre was used in simulation studies. Carbon nanotubes of the types single-walled, multiwalled and bundles were considered for ballistic transport region, local and global interconnections. Study of the S-parameters showed higher transmission efficiency and lower reflection losses. Theoretical modeling and computer-aided simulation studies through a complimentary CNT-FET inverter pair, interconnected through a wire, exhibited reduced delays and power dissipations for carbon nanotube interconnects in comparison to copper interconnects in 22 nm and lower technology nodes. The performance of CNT interconnects was shown to be further improved with increase in number of metallic carbon nanotubes. Our study suggests the replacement of copper interconnect with the multiwalled and bundles of single-walled carbon nanotubes for the sub-nanometer CMOS technologies.
Current transport in carbon nanotube field effect transistors (CNT-FETs) has been modeled from charge distributions
and the potential inside the carbon nanotube. Analytical equations describing I-V characteristics of the CNT-FETs have
been obtained from the combination of diffusion and drift mechanisms in the channel region for normal and sub-threshold
operations. It is shown that the electronic transport in semiconducting single-walled carbon nanotubes and
field effect transistors can provide better understanding of their bio- and chemical sensing for the detection of traces of
agents at molecular levels.