Anup Lohani

Electrical detection of hybridization and threading intercalation of deoxyribonucleic acid using carbon nanotube network field-effect transistors

The authors study deoxyribonucleic acid (DNA) sensing characteristics of carbon nanotube network field-effect transistors (CNNFETs) by monitoring their electrical responses upon immobilization with a DNA probe, hybridization with DNA analytes, and intercalation with a N,N′-bis(3-propylimidazole)-1,4,5,8-naphthalene diimide modified with Os(2,2′-bipyridine)2Cl+ pendants. The CNNFETs immobilized by single-stranded DNA molecules demonstrate the selective sensing of its complementary and single-base mismatched DNA (difference of ∼16% in reduction of normalized drain current Id). Subsequent intercalation demonstrates a further sensitivity enhancement (difference of ∼13% in Id reduction) due to specific binding between hybridized DNA and intercalators, corroborated by the x-ray photoelectron spectroscopy study.

Tuning of electrical characteristics in networked carbon nanotube field-effect transistors using thiolated molecules

The authors examine the effects of adsorption of four thiolated molecules (HS–C10H21, HS–C11H22OH, HS–C10H20COOH, and HS–C2H4C4F9) on the electrical characteristics of single-walled carbon nanotube network FETs (SNFETs). Work function of the electrodes was measured before and after molecule adsorption. Schottky barrier energy extraction for SNFETs was also performed and the results provide direct evidence that the device characteristics of SNFETs after SAM adsorption are altered primarily due to the change in energy-level alignment between the Au and SWNTs, which thus provides an effective methodology for the tuning and performance optimization of these devices in a controllable way.

Achieving Sub- 0.1 eV Hole Schottky Barrier Height for NiSiGe on SiGe by Aluminum Segregation

Nickel germano-silicide (NiSiGe) contact was formed on silicon-germanium (Si 1-x Ge x or SiGe) epilayer with 26% Ge, grown on p-Si (100) substrate. We report the tuning of the effective Schottky barrier height (SBH) of holes at the NiSiGe/SiGe junction to sub-0.1 eV by the introduction of aluminum (Al) using ion implantation and its segregation at the NiSiGe/SiGe interface after germano-silicidation. The effective SBH decreases with increasing concentration of Al at the NiSiGe/SiGe interface. We demonstrate the achievement of one of the lowest reported hole SBHs for NiSiGe on SiGe of 0.068 eV, which is extremely promising for application in p-type metal oxide semiconductor field-effect transistors. The presence of Al does not affect the sheet resistance or the low-resistivity nickel mono-germano-silicide phase of the NiSiGe film. Our results indicate the possibility of an electric dipole at the NiSiGe/SiGe interface, introduced by Al atoms, which is responsible for the SBH modulation. Increase in thickness of nickel used for germano-silicidation increases the effective SBH. The increase in the Al implant dose reduces the effective SBH but degrades the SiGe epilayer by amorphizing it to a greater depth. Thus, a trade-off exists in choosing the Al implant dose and the nickel thickness needed to consume the amorphized SiGe for maximum device performance.

Low-Temperature-Processed Inorganic Gate Dielectrics for Plastic-Substrate-Based Organic Field-Effect Transistors

Low-temperature-processed inorganic gate dielectrics were employed here to yield high-performance organic field-effect transistors (FETs) on flexible plastic substrates. SiNx dielectrics deposited at room temperature and SiNx/sol-gel silica dielectric bilayer processed below 100degC were demonstrated to be viable gate dielectric materials, with the latter yielding effective field-effect mobilities of ~ 1 cm2/Vldrs at operating voltages of under -5 V with an on-off current ratio in the range of 105. The enhancement in device performance was attributed to an improved semiconductor-dielectric interface and a larger grain size of the pentacene deposited on the bilayer dielectrics. The flexibility of FETs fabricated on polyester substrates was also demonstrated with insignificant changes in device performance upon subjecting the devices to strains of 2.27%.