Highly selective etching of SiNxover SiO2using ClF3/Cl2remote plasma.

Highly selective etching of silicon nitride over silicon oxide is one of the most important processes especially for the fabrication of vertical semiconductor devices including 3D NAND (Not And) devices. In this study, isotropic dry etching characteristics of SiNxand SiO2using ClF3/Cl2remote plasmas have been investigated. The increase of Cl2percent in ClF3/Cl2gas mixture increased etch selectivity of SiNxover SiO2while decreasing SiNxetch rate. By addition of 15% Cl to ClF3/Cl2, the etch selectivity higher than 500 could be obtained with the SiNxetch rate of ∼8 nm min-1, and the increase of Cl percent to 20% further increased the etch selectivity to higher than 1000. It was found that SiNxcan be etched through the reaction from Si-N to Si-F and Si-Cl (also from Si-Cl to Si-F) while SiO2can be etched only through the reaction from Si-O to Si-F, and which is also in extremely low reaction at room temperature. When SiNx/SiO2layer stack was etched using ClF3/Cl2(15%), extremely selective removal of SiNxlayer in the SiNx/SiO2layer stack could be obtained without noticeable etching of SiO2layer in the stack and without etch loading effect.

Selective etching of silicon nitride over silicon oxide using ClF3/H2 remote plasma.

Precise and selective removal of silicon nitride (SiNx) over silicon oxide (SiOy) in a oxide/nitride stack is crucial for a current three dimensional NOT-AND type flash memory fabrication process. In this study, fast and selective isotropic etching of SiNx over SiOy has been investigated using a ClF3/H2 remote plasma in an inductively coupled plasma system. The SiNx etch rate over 80 nm/min with the etch selectivity (SiNx over SiOy) of ~ 130 was observed under a ClF3 remote plasma at a room temperature. Furthermore, the addition of H2 to the ClF3 resulted in an increase of etching selectivity over 200 while lowering the etch rate of both oxide and nitride due to the reduction of F radicals in the plasma. The time dependent-etch characteristics of ClF3, ClF3 & H2 remote plasma showed little loading effect during the etching of silicon nitride on oxide/nitride stack wafer with similar etch rate with that of blank nitride wafer.

Gate-controlled gas sensor utilizing 1D-2D hybrid nanowires network.

Novel gas sensors that work at room temperature are attracting attention due to their low energy consumption and stability in the presence of toxic gases. However, the development of sensing characteristics at room temperature is still a primary challenge. Diverse reaction pathways and low adsorption energy for gas molecules are required to fabricate a gas sensor that works at room temperature with high sensitivity, selectivity, and efficiency. Therefore, we enhanced the gas sensing performance at room temperature by constructing hybridized nanostructure of 1D-2D hybrid of SnSe2 layers and SnO2 nanowire networks and by controlling the back-gate bias (Vg = 1.5 V). The response time was dramatically reduced by lowering the energy barrier for the adsorption on the reactive sites, which are controlled by the back gate. Consequently, we believe that this research could contribute to improving the performance of gas sensors that work at room temperature.

Effect of Nb Doping on Chemical Sensing Performance of Two-Dimensional Layered MoSe2.

Here, we report that Nb doping of two-dimensional (2D) MoSe2 layered nanomaterials is a promising approach to improve their gas sensing performance. In this study, Nb atoms were incorporated into a 2D MoSe2 host matrix, and the Nb doping concentration could be precisely controlled by varying the number of Nb2O5 deposition cycles in the plasma enhanced atomic layer deposition process. At relatively low Nb dopant concentrations, MoSe2 showed enhanced device durability as well as NO2 gas response, attributed to its small grains and stabilized grain boundaries. Meanwhile, an increase in the Nb doping concentration deteriorated the NO2 gas response. This might be attributed to a considerable increase in the number of metallic NbSe2 regions, which do not respond to gas molecules. This novel method of doping 2D transition metal dichalcogenide-based nanomaterials with metal atoms is a promising approach to improve the performance such as stability and gas response of 2D gas sensors.

Printing Highly Controlled Suspended Carbon Nanotube Network on Micro-patterned Superhydrophobic Flexible Surface.

Suspended single-walled carbon nanotubes (SWCNTs) offer unique functionalities for electronic and electromechanical systems. Due to their outstanding flexible nature, suspended SWCNT architectures have great potential for integration into flexible electronic systems. However, current techniques for integrating SWCNT architectures with flexible substrates are largely absent, especially in a manner that is both scalable and well controlled. Here, we present a new nanostructured transfer paradigm to print scalable and well-defined suspended nano/microscale SWCNT networks on 3D patterned flexible substrates with micro- to nanoscale precision. The underlying printing/transfer mechanism, as well as the mechanical, electromechanical, and mechanical resonance properties of the suspended SWCNTs are characterized, including identifying metrics relevant for reliable and sensitive device structures. Our approach represents a fast, scalable and general method for building suspended nano/micro SWCNT architectures suitable for flexible sensing and actuation systems.

Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of -sp2 carbon.

Carbon forms one of nature's strongest chemical bonds; its allotropes having provided some of the most exciting scientific discoveries in recent times. The possibility of inter-allotropic transformations/hybridization of carbon is hence a topic of immense fundamental and technological interest. Such modifications usually require extreme conditions (high temperature, pressure and/or high-energy irradiations), and are usually not well controlled. Here we demonstrate inter-allotropic transformations/hybridizations of specific types that appear uniformly across large-area carbon networks, using moderate alternating voltage pulses. By controlling the pulse magnitude, small-diameter single-walled carbon nanotubes can be transformed predominantly into larger-diameter single-walled carbon nanotubes, multi-walled carbon nanotubes of different morphologies, multi-layered graphene nanoribbons or structures with sp(3) bonds. This re-engineering of carbon bonds evolves via a coalescence-induced reconfiguration of sp(2) hybridization, terminates with negligible introduction of defects and demonstrates remarkable reproducibility. This reflects a potential step forward for large-scale engineering of nanocarbon allotropes and their junctions.

High-performance H(2)S detection by redox reactions in semiconducting carbon nanotube-based devices.

Here we report the highly effective detection of hydrogen sulfide (H2S) gas by redox reactions based on single-walled carbon nanotubes (SWCNTs) functionalized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a catalyst and we also discuss the important role of water vapor in the electrical conductivity of SWCNTs during the sensing of H2S molecules. To explore the H2S sensing mechanism, we investigate the adsorption properties of H2S on carbon nanotubes (CNTs) and the effects of the TEMPO functionalization using first-principles density functional theory (DFT) and we summarize current changes of devices resulting from the redox reactions in the presence of H2S. The semiconducting-SWCNT (s-SWCNT) device functionalized with TEMPO shows a very high sensitivity of 420% at 60% humidity, which is 17 times higher than a bare s-SWCNT device under dry conditions. Our results offer promising prospects for personal safety and real-time monitoring of H2S gases with the highest sensitivity and low power consumption and potentially at a low cost.

Carbon nanotube-nanocup hybrid structures for high power supercapacitor applications.

Here, we design and develop high-power electric double-layer capacitors (EDLCs) using carbon-based three dimensional (3-D) hybrid nanostructured electrodes. 3-D hybrid nanostructured electrodes consisting of vertically aligned carbon nanotubes (CNTs) on highly porous carbon nanocups (CNCs) were synthesized by a combination of anodization and chemical vapor deposition techniques. A 3-D electrode-based supercapacitor showed enhanced areal capacitance by accommodating more charges in a given footprint area than that of a conventional CNC-based device.

Highly organized two- and three-dimensional single-walled carbon nanotube-polymer hybrid architectures.

Single-walled carbon nanotube (SWCNT) network architectures combined with flexible mediums (especially polymers) are strong candidates for functional flexible devices and composite structures requiring the combination of unique electronic, optical, and/or mechanical properties of SWCNTs and polymer materials. However, to build functional flexible devices with SWCNTs, it is required to have abilities to assemble and incorporate SWCNTs in desired locations, orientations, and dimensions on/inside polymer substrates. Here, we present unique two- and three-dimensional SWCNT network-polymer hybrid architectures by combining unprecedented control over growth, assembly, and transfer processes of SWCNTs. Several SWCNT architectures have been built on polymer materials ranging from two-dimensional suspended SWCNT microlines on PDMS microchannels to three-dimensional "PDMS-vertically aligned SWCNTs-PDMS" sandwich structures. Also a combined lateral SWCNT microline and vertically aligned SWCNT flexible device was demonstrated with good electrical conductivity and low junction resistance. The results reported here open the pathway for the development of SWCNT-based functional systems in various flexible device applications.

Accelerated reliability testing of highly aligned single-walled carbon nanotube networks subjected to DC electrical stressing.

We investigate the electrical reliability of nanoscale lines of highly aligned, networked, metallic/semiconducting single-walled carbon nanotubes (SWCNTs) fabricated through a template-based fluidic assembly process. We find that these SWCNT networks can withstand DC current densities larger than 10 MA cm(-2) for several hours and, in some cases, several days. We develop test methods that show that the degradation rate, failure predictability and total device lifetime can be linked to the initial resistance. Scanning electron and transmission electron microscopy suggest that fabrication variability plays a critical role in the rate of degradation, and we offer an empirical method of quickly determining the long-term performance of a network. We find that well-fabricated lines subject to constant electrical stress show a linear accumulation of damage reminiscent of electromigration in metallic interconnects, and we explore the underlying physical mechanisms that could cause such behavior.

Highly aligned scalable platinum-decorated single-wall carbon nanotube arrays for nanoscale electrical interconnects.

We present the fabrication and characterization of nanoscale electrical interconnect test structures constructed from aligned single-wall carbon nanotubes using a template-based fluidic assembly process. This CMOS-friendly process enables the formation of highly aligned parallel nanotube interconnect structures on SiO(2)/Si substrates of widths and lengths that are limited only by lithographical limits and, hence, can be easily integrated onto existing Si-based platforms. These structures can withstand current densities of approximately 10(7) A.cm(-2), comparable or better than copper at similar dimensions. Both the nanotube alignment and failure current density improve with decreasing structure width. In addition, we present a novel Pt nanocluster decoration method that drastically decreases the resistivity of the test structures. Ab initio density functional theory calculations indicate that the increase in conductivity of the nanotubes is caused by an increase in conduction channels close to their Fermi levels due to the platinum nanocluster decoration, with a possible conversion of the semiconducting single-wall carbon nanotubes into metallic ones. These results reflect a huge step toward the proposed replacement of copper-based interconnects with carbon nanotubes at gigascale integration levels.