Poornendu Chaturvedi

Impact of gate leakage considerations in tunnel field effect transistor design

In this paper, we have presented the impact of the gate leakage through thin gate dielectrics (SiO2 and high-? gate dielectric) on the subthreshold characteristics of the tunnel field effect transistors (TFET) for a low operating voltage of 0.5 V. Using calibrated two-dimensional simulations it is shown that even for such a low operating voltage, the gate leakage substantially degrades several subthreshold parameters of the TFET such as the off-state current, minimum subthreshold swing and average subthreshold swing. While the drain-offset as well as the short-gate are effective methods for reducing the gate leakage, we show that if the gate tunneling leakage is not considered, even for these two methods, the overall TFET off-state current will be significantly underestimated. Our results demonstrate the need to carefully account for the gate leakage in the design of TFETs just as it is done for the conventional nanoscale MOSFETs.

Functionalization Of Carbon Nanotubes With Metal Phthalocyanine For SELECTIVE Gas Sensing Application

Composites of hydroxylated single-walled carbon nanotubes and copper phthalocyanine (CuPc) has been obtained. Phthalocyanines get noncovalently adsorbed onto CNTs surface by π–π stacking. Conversion of β-form of phthalocyanine to α-form gives clear evidence of composite formation. Only carboxyl and hydroxyl CNTs react with phthalocyanine while no reaction occurs for amided CNTs. High selectivity in the thin film resistors of SWNT–OH + CuPc composites toward NOx gases is observed. The response for NOx is 10 times and 100 times more then that of ammonia and Sox, respectively. This makes the SWNT–OH + CuPc composite a candidate for detection of NOx—a common pollutant.

Effect of gate dielectric thickness on gate leakage in tunnel field effect transistor

Gate leakage is one of the important parameter expected to limit the performance of Tunnel FETs. We have simulated the effect of gate dielectric thickness on gate leakage in Tunnel FETs, using two dimensional numerical simulations. It has been observed that gate leakage considerably affects the subthreshold characteristics of TFETs. It was found to be most important component of off-state current and should be considered in future TFET device design. Effects of gate metal workfunction on device characteristics, particularly, gate leakage and origin of reverse tunneling at drain have also been discussed.

Optimization of Vertically Aligned Nature of CNTs for Improved Field Emission Behavior

For improved field emission behavior, we demonstrate the PECVD technique to grow highly ordered, selectively grown, vertically aligned carbon nanotubes (CNTs) with optimum density. We report the optimization of vertically aligned CNTs by optimizing catalyst thickness, dot size of catalyst and the spacing between them. We made an attempt to optimize the catalyst thickness to understand the effect over density, diameter and height of CNTs. SEM images reveal that the catalyst thickness as well as the dot size and the spacing is helpful in optimizing the vertical alignment of CNTs. The vertically aligned CNTs provide a large number of tips as compared to horizontally aligned CNTs over an area. Also, the high value of the enhancement factor required to achieve a better FE behavior is also plausible with vertical CNTs. The field emission results confirm that the vertically aligned CNTs bring a large current density at relatively low threshold field. We were able to achieve a current density of 100 mA/cm2 at a field of 6 V/µm. Density and therefore screening effect also becomes important factors that hinder the performance of CNT‐based emitters. However, in our typical samples we observed less discrepancy in the density, and the density so calculated was in the order of 109/cm2.

Graded silicon-germanium channel tunnel field effect transistor (G-TFET), an approach to increase I ON without compromising I OFF

As we move towards building low power and more energy efficient devices along with scaling channel length, leakage current and standby power dissipation are becoming major issues. Many alternative device structures have been proposed in the recent years and TFET is one of the promising candidate which has been studied extensively using not only numerical simulations [1], [2] but prototypes have also been fabricated [3]. TFETs can compete with conventional MOSFETs owing to their excellent sub threshold characteristics, reduced short channel effects and low OFF state current. Superior sub threshold swing characteristics below 60mV/decade make TFET a suitable candidate for low power design in comparison to conventional CMOS devices, that have a theoretical subthreshold swing limit of 60mV/decade. One of the biggest challenges in the TFET research is to improve their ON state current without compromising on OFF state current. In recent past, several groups have proposed several modification in TFET structure for improving their performance, such as using double gates, high-k gate materials and high-k spacers for effective gate control, Si1−xGex channel with uniform composition and small Si1−xGex pocket near the source to improve tunneling probability by having better band to band alignment.

Estimation and Reduction of Macroscopic Nonuniformity in CNT Thin Film Resistors

Carbon nanotube (CNT) thin film-based devices are expected to have better uniformity and reproducibility compared with single-tube devices due to statistical averaging. In this work, thin film resistors (TFR) were prepared from CNT dispersions and their nonuniformity estimated by multipoint, two-terminal resistance (TTR) measurements. I-V measurements were done for determining the nature of metal-CNT contact. For estimation of contact resistance, transmission line measurements (TLM) were carried out. Reduction of CNT-TFR nonuniformity was achieved using di-methyl formamide (DMF). Scanning electron microscopy and electrical measurements imply that DMF improves debundling of single-walled nanotubes, reduces the resistance and improves homogeneity of subsequently prepared thin films.