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Murickassery, India

Aparna P.,Mahatma Gandhi University | Varughese M.,Mahatma Gandhi University | Varghese M.K.,Mahatma Gandhi University | Varghese M.K.,Pavanatma College | And 2 more authors.

yDNA is a base-modified nucleic acid duplex containing size-expanded nucleobases. Base-modified nucleic acids could expand the genetic alphabet and thereby enhance the functional potential of DNA. Unrestrained 100 ns MD simulations were performed in explicit solvent on the yDNA NMR sequence [5′(yA T yA yA T yA T T yA T)2] and two modeled yDNA duplexes, [5′(yC yC G yC yC G G yC G G)2] and [(yT5′ G yT A yC yG C yA yG T3′)•(yA5′ C T C yG C G yT A yC A3′)]. The force field parameters for the yDNA bases were derived in consistent with the well-established AMBER force field. Our results show that DNA backbone can withstand the stretched size of the bases retaining the Watson-Crick base pairing in the duplexes. The duplexes retained their double helical structure throughout the simulations accommodating the strain due to expanded bases in the backbone torsion angles, sugar pucker and helical parameters. The effect of the benzo-expansion is clearly reflected in the extended C1′-C1′ distances and enlarged groove widths. The size expanded base modification leads to reduction in base pair twist resulting in larger overlapping area between the stacked bases, enhancing inter and intra strand stacking interactions in yDNA in comparison with BDNA. This geometry could favour enhanced interactions with the groove binders and DNA binding proteins., 2016. © 2015 Wiley Periodicals, Inc. Source

Joseph S.,Pavanatma College | George James T.,Pavanatma College | Mathew V.,Thomas College
Journal of Semiconductor Technology and Science

Double Gate MOSFETs (DG MOSFETs) with doping in one or two thin layers of an otherwise intrinsic channel are simulated to obtain the transport characteristics, threshold voltage and leakage current. Two different device structures- one with doping on two layers near the top and bottom oxide layers and another with doping on a single layer at the centre- are simulated and the variation of device parameters with a change in doping concentration and doping layer thickness is studied. It is observed that an n-doped layer in the channel reduces the threshold voltage and increases the drive current, when compared with a device of undoped channel. The reduction in the threshold voltage and increase in the drain current are found to increase with the thickness and the level of doping of the layer. The leakage current is larger than that of an undoped channel, but less than that of a uniformly doped channel. For a channel with p-doped layer, the threshold voltage increases with the level of doping and the thickness of the layer, accompanied with a reduction in drain current. The devices with doped middle layers and doped gate layers show almost identical behavior, apart from the slight difference in the drive current. The doping level and the thickness of the layers can be used as a tool to adjust the threshold voltage of the device indicating the possibility of easy fabrication of ICs having FETs of different threshold voltages, and the rest of the channel, being intrinsic having high mobility, serves to maintain high drive current in comparison with a fully doped channel. Source

James T.G.,Pavanatma College | Joseph S.,Pavanatma College | Mathew V.,Thomas College
Journal of Nanoelectronics and Optoelectronics

With the continued scaling of the SiO 2 thickness below 2 nm in Double Gate MOSFET devices, a large direct-tunneling current flows between the gate electrode and silicon substrate is highly affecting device performance. Therefore, higher dielectric constant materials are desirable for reducing the gate leakage while maintaining transistor performance for very thin dielectric layers. The counter doped (p-type) Double Gate MOSFETs with high-κ gate dielectric material is modeled to obtain the transport characteristics, DIBL, / on// off ratio, threshold voltage and subthreshold leakage current. Reduction of short channel effects are observed in counter doped (p-type) DG MOSFET with high-κ dielectrics. Drain induced barrier lowering (DIBL) is reduced to ≈25%, subthrehold leakage current is decreased to ≈50%, / on// off ratio is increased to ≈75% and threshold voltage (V t) is increased to ≈6% in 1 nm dielectric thickness T ox. Results show that counter doped DG MOSFETs with high-κ gate dielectric material is an effective method to reduce the short channel effects. Copyright © 2010 American Scientific Publishers All rights reserved. Source

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