Fabrication Of Nanoelectronic Devices Research Articles

Combining thermal scanning probe lithography and dry etching for grayscale nanopattern amplification

Grayscale structured surfaces with nanometer-scale features are used in a growing number of applications in optics and fluidics. Thermal scanning probe lithography achieves a lateral resolution below 10 nm and a vertical resolution below 1 nm, but its maximum depth in polymers is limited. Here, we present an innovative combination of nanowriting in thermal resist and plasma dry etching with substrate cooling, which achieves up to 10-fold amplification of polymer nanopatterns into SiO2 without proportionally increasing surface roughness. Sinusoidal nanopatterns in SiO2 with 400 nm pitch and 150 nm depth are fabricated free of shape distortion after dry etching. To exemplify the possible applications of the proposed method, grayscale dielectric nanostructures are used for scalable manufacturing through nanoimprint lithography and for strain nanoengineering of 2D materials. Such a method for aspect ratio amplification and smooth grayscale nanopatterning has the potential to find application in the fabrication of photonic and nanoelectronic devices.

Selectivity and Growth Rate Modulations for Ruthenium Area‐selective Deposition by Co‐Reagent and Nanopattern Design

AbstractArea‐selective deposition (ASD) is a bottom‐up technique that provides numerous opportunities for nanoelectronic device fabrication. For example, advanced nano‐interconnect structures with barrierless metals like Ru in the contact holes can be created by Ru ASD with the bottom metals as growth surfaces and dielectrics as non‐growth surfaces. This work investigates Ru ASD by chemical vapor deposition (CVD) on industrially relevant substrates and nanopatterns and reveals how selectivity and growth rate are modulated by the CVD conditions and type of nanopattern. For low‐k dielectric/Cu substrate combinations, the selectivity reverses from metal‐on‐metal to metal‐on‐dielectric upon only changing the CVD co‐reagent from H2 to NH3. In contrast, NH3 is the preferred co‐reagent for SiO2‐TiN line patterns with critical dimension (CD) of 40 nm due to the more favorable adsorption and diffusion kinetics that cause growth rate and selectivity enhancement. Consistent with a diffusion‐mediated mechanism, the growth rate enhances even more for Ru CVD on nanoscale contact holes with CD of 10.5 nm, becoming 2.4 times higher as compared to unpatterned substrates. Thus, the ASD process changes drastically when pattern dimensions reach the nanoscale. The reported insights facilitate rational design of metal ASD processes for multiple applications in nanofabrication.

Studying the effect of addition of lithium titanate on crystallinity and electrical properties of PPY-C /PVA nanocomposite for optoelectronic applications

This study involved the preparation of novel samples of polypyrrole-doped carbon/polyvinyl alcohol/lithium titanate nanocomposites, PPY-C/PVA/LiO, with a tuning of LiO concentration using the casting technique to be applicable in different applications. Various analytical procedures were employed to examine their optical, morphological, structural, and electrical properties. It was decided that the PPY-C/PVA is an amorphous structure that became crystalline when LiO NPs were added. This happened because the functional groups of the PPY-C/PVA and LiO NPs interacted with each other. It confirmed that by appearing the new characteristic diffraction peaks of LiO and the new vibrational stretching peak at 588 cm−1 of the metal-O bond and deducing the uniform distribution of the blend matrix with an increase in the number of white dots, it served as evidence of the impact of surface roughness on tuning the electrical properties of the nanocomposite. Also, studies on conductivity showed that as the concentration of LiO goes up, AC conductivity, dielectric constant, and dielectric loss all go down. This is because more nanofiller is added, more immobile ions form in clumped areas, and dipole polarization goes down. Also, adding LiO NPs to the polymeric matrix makes the matrix's chains less flexible, which raises the crystallinity ratio. The obtained results suggest that the prepared PPY-C/PVA/LiO nanocomposite is promising candidates in the fabrication of nano-electronic devices.

Modulating the Performance of MoS2-Based Nanocrystal Memory via Ag Ion Implantation

Nonvolatile flash memory is an important component of the semiconductor memory device, which is widely used in a variety of portable electronic equipment. As traditional flash memory approaches its physical limit, reduced reliability and performance degradation have become unavoidable. Two-dimensional (2D) layered materials exhibit excellent electronic properties even at the atomic level and have been considered as a promising development direction for future flash memory. Here, we report a MoS2-based Ag nanocrystal memory. The fabricated memory device can form the memory stack in one step through metal ion implantation, omitting tedious deposition steps compared to the conventional process. The fabricated silver nanocrystal memory exhibits a 9 V memory window and a high ON/OFF current ratio (>107). In addition, the device also exhibits good endurance characteristics of more than 104 cycles. The ion implantation technology and the 2D nature of the channel can be used for the fabrication of flexible nanoelectronic memory devices with large-scale integration.

A First-Principles Investigation of the Driving Forces Defining the Selectivity of TiO2 Atomic Layer Deposition

Area-selective deposition (ASD) is a technique to deposit material only on a defined area of a prepatterned surface, while no deposition occurs on adjacent surface areas. It is the subject of intense investigations by the scientific and engineering communities as it offers the prospect to simplify and improve patterning processes for fabrication of nanoelectronic devices as well as to reduce the manufacturing costs. Numerous efforts have been dedicated to identify process conditions for highly selective ASD processes. Still, the search for optimal conditions is often an empirical process due to the limited understanding of the mechanisms that take place at the atomic scale. Understanding the links between precursor reactivity, surface treatments, and the reactor operating conditions could greatly contribute to the development of highly selective ASD processes. In this paper, we therefore combine first-principles calculations with statistical thermodynamics to understand the role of the precursors in area-selective TiO2 atomic layer deposition (ALD). First, we investigate the selectivity loss mechanisms for TiCl4/H2O ALD on SiO2 nongrowth surfaces with different surface terminations (e.g., OH groups and trimethylsilyl groups). We link the resulting thermodynamic driving forces to experimental reports. Subsequently, we extend the investigation to a total of 26 commercially available titanium precursors and to three different oxygen sources and rank their potential for TiO2 ASD for the SiO2 surfaces with different surface terminations (OH groups and trimethylsilyl groups). We find that the combination of TiCl4 with H2O offers the best performance in terms of selectivity. The theoretical approach proposed here is expected to greatly assist and accelerate the design of precursors for different ASD approaches.

HBN-Layer-Promoted Heteroepitaxy in Reactively Sputter-Deposited MoSx≈2(0001)/Al2O3(0001) Thin Films: Implications for Nanoelectronics

We show that van der Waals (vdW)-bonded hexagonal boron nitride (hBN) promotes heteroepitaxial growth of semiconducting MoSx(0001) (x = 2.0 ± 0.1) thin films on Al2O3(0001) substrates. hBN layers are grown on Al2O3(0001) via pyrolytic cracking of borazine (∼6 × 104 L) at 1373 K and the MoSx layers are deposited in an ultrahigh-vacuum system via reactive direct-current magnetron sputtering of Mo in an Ar/H2S gas mixture at 1073 K on bare and hBN-covered Al2O3(0001). Using in situ low-energy electron diffraction and Auger electron spectroscopy along with ex situ X-ray diffraction, X-ray photoelectron and Raman spectroscopies, and transmission electron microscopy, we determine the as-deposited MoSx layer composition and crystallinity. We obtain highly 0001-oriented, ∼20-nm-thick, 2H-structured MoSx multilayers with better crystalline quality on hBN/Al2O3(0001) than on Al2O3(0001). We suggest that hBN buffer layer enhances surface diffusion of depositing species, compared to bare Al2O3(0001), leading to an observed improvement in the crystallinity of MoSx layers. We expect that our results are likely to have broad implications in nanoelectronic device fabrication.

Tunable Schottky contact at the graphene/Janus SMoSiN2 interface for high-efficiency electronic devices

The electrical contacts formed between the channel materials and the electrodes play a vital role in the design and fabrication of high-performance optoelectronic and nanoelectronic devices. In this work we propose combining metallic single-layer graphene (SLG) and a Janus SMoSiN2 semiconductor and investigate the electronic properties and contact types of the combined heterostructures (HTSs) using first-principles calculations. The effects of electric fields and interlayer coupling are also examined. The combined SLG/SMoSiN2 and SLG/N2SiMoS HTSs are both structurally and thermodynamically stable at equilibrium interlayer coupling. The combination between SLG and a Janus SMoSiN2 semiconductor generates a p-type or n-type Schottky contact, depending on the stacking configuration. The SLG/SMoSiN2 HTS generates a p-type Schottky contact while the SLG/N2SiMoS HTS forms an n-type one. Furthermore, applied electric field and strain can adjust the electronic features and contact types of the HTSs. An applied negative electric field and tensile strain lead to conversion from a p-type to an n-type Schottky contact in the SLG/SMoSiN2 stacking configuration, whereas a positive electric field and compressive strain give a transformation from an n-type to a p-type Schottky contact in the SLG/N2SiMoS stacking configuration. Our findings provide rational evidence for the fabrication and design of electrical and optical devices based on SLG/SMoSiN2 HTSs.

Optoelectronic and magnetic properties of transition metals-adsorbed GeC monolayer

The optoelectronic and magnetic behaviors of GeC monolayer after transition metals (TMs) adsorption have been systematically discussed using density functional theory. The calculated data illustrates that the optimal adsorption sites of Sc-, Ti-, V-, Cr-, Mn-, Fe-, and Co-GeC systems are all located at [Formula: see text] site, while the Ni- and Cu-GeC systems are situated in [Formula: see text] site. The band structures of Ti-, Fe-, and Ni-GeC systems still remain nonmagnetic semiconductors, while the Sc-, Cr-, and Cu-GeC systems exhibit magnetic semiconductor behaviors, and the band gaps are 0.11 eV (Sc), 0.30 eV (Cr), and 0.57 eV (Cu), respectively. In particular, V- and Mn-GeC systems exhibit half-metallic characteristics, and Co-GeC system exhibits magnetic metal characteristics. And the magnetic moments of Sc-, V-, Cr-, Mn-, Co-, and Cu-GeC structures have been obtained to be 0.08, 1.00, 2.00, 1.00, 0.04, and 1.00 [Formula: see text], respectively. Furthermore, the charge transfer was exhibited between the GeC and TM. Especially, the work function of GeC can decrease greatly after TM adsorption, among them, the work function of Sc-GeC is 37.9% lower than that of GeC. Consequently, it indicates the usefulness of the TM-GeC system for the fabrication of spintronic and nanoelectronic devices.

Coherent control of electron spin qubits in silicon using a global field

Silicon spin qubits promise to leverage the extraordinary progress in silicon nanoelectronic device fabrication over the past half century to deliver large-scale quantum processors. Despite the scalability advantage of using silicon technology, realising a quantum computer with the millions of qubits required to run some of the most demanding quantum algorithms poses several outstanding challenges, including how to control many qubits simultaneously. Recently, compact 3D microwave dielectric resonators were proposed as a way to deliver the magnetic fields for spin qubit control across an entire quantum chip using only a single microwave source. Although spin resonance of individual electrons in the globally applied microwave field was demonstrated, the spins were controlled incoherently. Here we report coherent Rabi oscillations of single electron spin qubits in a planar SiMOS quantum dot device using a global magnetic field generated off-chip. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer.

Quantum pumping through the surface states of a topological insulator

We investigate quantum charge pumping through the surface states of a topological insulator (TI), i.e., ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. We consider a device with two oscillating potentials for the generation of a dc current in the adiabatic pumping regime. Applying the exchange magnetic field, we show that the device can work as a memory read-out. Also, we show that by applying a static gate voltage the pumping device can work as a field-effect transistor. In addition, the pumped current obtained in our proposed device is significantly (more than three orders of magnitude) greater than the pumped current obtained previously for TI-based devices. These properties show that ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ can be considered a good candidate for the fabrication of nanoelectronic devices based on TI as well as low-power and low-energy consumption devices in quantum computing.

Catalytic Growth of Ultralong Graphene Nanoribbons on Insulating Substrates.

Graphene nanoribbons (GNRs) with widths of a few nanometers are promising candidates for future nanoelectronic applications due to their structurally tunable bandgaps, ultrahigh carrier mobilities, and exceptional stability. However, the direct growth of micrometer-long GNRs on insulating substrates, which is essential for the fabrication of nanoelectronic devices, remains an immense challenge. Here, the epitaxial growth of GNRs on an insulating hexagonal boron nitride (h-BN) substrate through nanoparticle-catalyzed chemical vapor deposition is reported. Ultranarrow GNRs with lengths of up to 10µm are synthesized. Remarkably, the as-grown GNRs are crystallographically aligned with the h-BN substrate, forming 1D moiré superlattices. Scanning tunneling microscopy reveals an average width of 2nm and a typical bandgap of ≈1eV for similar GNRs grown on conducting graphite substrates. Fully atomistic computational simulations support the experimental results and reveal a competition between the formation of GNRs and carbon nanotubes during the nucleation stage, and van der Waals sliding of the GNRs on the h-BN substrate throughout the growth stage. Thisstudy provides a scalable, single-step method for growing micrometer-long narrow GNRs on insulating substrates, thus opening a route to explore the performance of high-quality GNR devices and the fundamental physics of 1D moiré superlattices.

Recent Progress in Near‐Field Tip Enhancement: Principles and Applications

To meet the challenges raised by the fabrication of nanoelectronic devices on currently available micro/nano technologies, article number 2100456 by Jianlei Cui and colleagues reviews the essential principles and recent applications of near-field tip enhancement induced by laser-irradiated scanning probe microscope probe tips. Such key applications include nanofabrication, nano-joining, and nanomanipulation, which are expected to serve a critical role in the fabrication of nanoelectronic devices.

Controllable Melting and Flow of Ag in Self-Formed Amorphous Carbonaceous Shell for Nanointerconnection.

Nanointerconnection has been selected as a promising method in the post-Moore era to realize device miniaturization and integration. Even with many advances, the existing nanojoining methods still need further developments to meet the three-dimensional nanostructure construction requirements of the next-generation devices. Here, we proposed an efficient silver (Ag)-filled nanotube fabrication method and realized the controllable melting and ultrafine flow of the encapsulated silver at a subfemtogram (0.83 fg/s) level, which presents broad application prospects in the interconnection of materials in the nanometer or even subnanometer. We coated Ag nanowire with polyvinylpyrrolidone (PVP) to obtain core–shell nanostructures instead of the conventional well-established nanotube filling or direct synthesis technique, thus overcoming obstacles such as low filling rate, discontinuous metalcore, and limited filling length. Electromigration and thermal gradient force were figured out as the dominant forces for the controllable flow of molten silver. The conductive amorphous carbonaceous shell formed by pyrolyzing the insulative PVP layer was also verified by energy dispersive spectroscopy (EDS), which enabled the continued outflow of the internal Ag. Finally, a reconfigurable nanointerconnection experiment was implemented, which opens the way for interconnection error correction in the fabrication of nanoelectronic devices.

Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon.

Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.

(Invited) Role of Low-Energy Ions during Plasma-Enhanced Atomic Layer Deposition

This contribution will discuss the role and impact of ions during plasma-enhanced atomic layer deposition (ALD), in the context of the latest trends in nanoelectronic device fabrication. Due to the ongoing downscaling of semiconductor device structures, atomic-scale processing techniques such as plasma ALD are becoming increasingly important and more widely applied. Detailed insight into the role of ions is essential, now more than ever, for further advancing the atomic-level precision that plasma ALD offers.Among others, it will be presented that even ions with a low energy of <20 eV, as typical when using a grounded substrate and a remote plasma source, can considerably influence plasma ALD processes. This will be illustrated using plasma ALD of SiO2 and TiO2 as industry-relevant case studies. Specifically, it is observed that (low-energy) ions contribute to the film quality of SiO2,1 can induce crystallization during plasma ALD of TiO2,2 and can alter the growth per cycle by a factor of up to ~2 (for both SiO2 and TiO2). These effects can have important consequences for applications, for instance on the film conformality obtained on 3D nanostructures.Furthermore, the mechanisms governing the influence of ions on an elementary level will be discussed. An important topic here is the combined effect of ion energy, ion flux and plasma exposure time. These parameters can all have a different impact, depending on the plasma and material system. For plasma ALD of SiO2 and TiO2 the combined effect can be universally described by the ion energy dose (i.e., ion energy × flux × exposure time),3 where a minimal effect is obtained when supplying a dose of <1 eV nm-2 cycle-1, or a strong effect when supplying a dose of >100 eV nm-2 cycle-1.1,2 In conclusion, general insights into the role of ions during plasma ALD will be presented, which are particularly important for advancing the level of control over film thickness and material properties in the fabrication of (next-generation) nanoelectronics. Arts et al., Appl. Phys. Lett. 117, 031602 (2020).Arts et al., Impact of ions on film conformality and crystallinity during plasma-assisted atomic layer deposition of TiO2 (to be published).Faraz et al., Plasma Sources Sci. Technol. 28, 024002 (2019). Figure 1

Selectivity Enhancement for Ruthenium Atomic Layer Deposition in Sub‐50 nm Nanopatterns by Diffusion and Size‐Dependent Reactivity

AbstractArea‐selective deposition (ASD) is a promising bottom‐up approach for fabricating nanoelectronic devices. However, a challenge is to prevent the undesired growth of nanoparticles in the nongrowth area. This work uses kinetic Monte Carlo (KMC) methods to investigate the defectivity in ruthenium ASD by (ethylbenzyl)(1‐ethyl‐1,4‐cyclohexadienyl)Ru/O2 (EBECHRu) atomic layer deposition (ALD) in line‐space nanopatterns with different dimensions. Ru ASD is governed by adsorption as well as diffusion. The defectivity depends on the pattern dimensions, as nanoparticles can diffuse and reach the interface with the growth area where they aggregate. For linewidths of 50 nm and smaller, all Ru adspecies are captured at the growth interface before growth by precursor adsorption is catalyzed. The synergetic effect of diffusion and size‐dependent reactivity reduces defectivity below 1010 Ru atoms cm−2 for at least 1000 ALD cycles. This is more than 1000 times lower than for patterns with a linewidth of 200 nm and larger, where the Ru content decreases significantly only near the interface with the growth surface. The predicted depletion zone is confirmed by experiments in nanoscale line‐space patterns. Overall, this mechanism results in smaller and fewer Ru nanoparticles for smaller patterns, facilitating the development of passivation‐deposition‐etch ASD processes for nanoelectronic device fabrication.

Prediction of two-dimensional bismuth-based chalcogenides Bi2X3(X = S, Se, Te) monolayers with orthorhombic structure: a first-principles study

First-principles calculation is a very powerful tool for discovery and design of novel two-dimensional materials with unique properties needed for the next generation technology. Motivated by the successful preparation of Bi2S3 nanosheets with orthorhombic structure in the last year, herein we gain a deep theoretical insight into the crystal structure, stability, electronic and optical properties of Bi2X3 (X = S, Se, Te) monolayers of orthorhombic phase employing the first-principles calculations. The Molecular dynamics study, phonon spectra, criteria for elastic stability, and cohesive energy results confirm the desired stability of the Bi2X3 monolayers. From S, to Se and Te, the work function value as well as stability of the systems decrease due to the decline in electronegativity. Mechanical properties study reveals that Bi2X3 monolayers have brittle nature. The electronic bandgap values of Bi2S3, Bi2Se3 and Bi2Te3 monolayers are predicted by the HSE06 functional to be 2.05, 1.20 and 1.16 eV, respectively. By assessing the optical properties, it has been found that Bi2X3 monolayers can absorb ultraviolet light. The high in-plane optical anisotropy offers an additional degree of freedom in the design of optical devices. The properties revealed in our survey will stimulate and inspire the search for new approaches of orthorhombic Bi2X3 (X = S, Se, Te) monolayers synthesis and properties manipulation for fabrication of novel nanoelectronic and optoelectronic devices.

Ab initio investigation of physical properties of the graphene/As-F hetero-bilayer

In this paper, the physical properties of the graphene/As-F hetero-bilayer are investigated using first-principle calculations on the basis of density functional theory. It is found that the Dirac-cone properties of both graphene and As-F nanosheets are well preserved in this system, and that the two Dirac cones are symmetric about the Fermi level and their positions can be effectively tuned by the strained biaxial stretching. These findings are useful for the design and fabrication of novel nano-electronic devices formed by graphene-based hetero-bilayers. Improved optical properties are also observed in this system, displaying its potential photocatalytic and photovoltaic applications.

Complex Metal Nanostructures with Programmable Shapes from Simple DNA Building Blocks.

Advances in DNA nanotechnology allow the design and fabrication of highly complex DNA structures, uisng specific programmable interactions between smaller nucleic acid building blocks. To convey this concept to the fabrication of metallic nanoparticles, an assembly platform is developed based on a few basic DNA structures that can serve as molds. Programming specific interactions between these elements allows the assembly of mold superstructures with a range of different geometries. Subsequent seeded growth of gold within the mold cavities enables the synthesis of complex metal structures including tightly DNA-caged particles, rolling-pin- and dumbbell-shaped particles, as well as T-shaped and loop particles with high continuity. The method further supports the formation of higher-order assemblies of the obtained metal geometries. Based on electrical and optical characterizations, it is expected that the developed platform is a valuable tool for a self-assembly-based fabrication of nanoelectronic and nanooptic devices.

Sodium-Mediated Low-Temperature Synthesis of Monolayers of Molybdenum Disulfide for Nanoscale Optoelectronic Devices

Monolayers of molybdenum disulfide are of vital importance in the fabrication of optical and nanoelectronic devices. The development of thin and low-cost devices has increased the demand for synthe...