Structure Of Silicon Nitride Research Articles

Fabrication of Graphene/Porous Silicon Nitride Material for Field-Effect Transistors

Graphene, a novel material, has attracted significant attention due to its distinctive band structure and fascinating physical properties. These unusual properties have caused the emergence of tantalizing potential applications, ranging from field effect transistors to chemical and biochemical sensors. Due to their low mass, high quality factor, and good optical properties, silicon nitride micromembrane resonators are widely used in force and mass sensing applications. However, for practical graphene devices, many problems need to be solved, such as morphology control, interfacial engineering between graphene and silicon nitride substrate. Here, we transfer graphene to the silicon nitride substrates with two different morphologies (holes and grooves). Monolayer graphene film can be prepared on the copper via chemical vapor deposition (CVD) process as previous reported method. Next step is transfering graphene to the substrate. The morphologies of graphene on the substrate were obtained by SEM (Fig. 1a,b). As shown , the graphene in the hole and groove is not suspended, but directly exposed to the substrate. The graphene’s Raman information in hole is achieved by the micro-Raman spectrometer (Fig. 1c), which shows good quality . Such hybrid Graphene/Porous Silicon Nitride structures can be used to fabricate field-effect transistors. Figure 1

Design and fabrication of suspended Si3N4 nanobeam cavities

We report on the design, theoretical simulations and fabrication details of photonic crystal nanobeams (PhCNB) in air-bridge silicon nitride structures. The PhC nanobeams consist of a one-dimensional photonic crystal lattice of circular air holes. The design of structures that show band gaps for the waveguide modes will allow the creation of suspended photonic nanobeam cavities in a second step. The silicon nitride layer is deposited on top of a thermally oxidized silicon wafer with LPCVD followed by e-beam lithography and proper wet etching to release the suspended structures.

Improved multicrystalline silicon ingot quality using single layer silicon beads coated with silicon nitride as seed layer

We propose to utilize single layer silicon beads (SLSB) coated with silicon nitride as cost-effective seed layer to grow high-quality multicrystalline silicon (mc-Si) ingot. The texture structure of silicon nitride provides a large number of nucleation sites for the fine grain formation at the bottom of the crucible. No special care is needed to prevent seed melting, which would lead to decrease of red zone owing to decrease of feedstock melting time. As we expected, mc-Si ingot seeded with SLSB was found to consist of small, different grain orientations, more uniform grain distribution, high percentage of random grain boundaries, less twin boundaries, and low density of dislocation clusters compared with conventional mc-Si ingot grown under identical growth conditions. These results show that the SLSB seeded mc-Si ingot has enhanced ingot quality. The correlation between grain boundary structure and defect structure as well as the reason responsible for dislocation clusters reduction in SLSB seeded mc-Si wafer are also discussed.

A study of the effect of the structure of plasma-chemical silicon nitride on its masking properties

Dependence of the chemical composition of a film of plasma-chemical silicon nitride on the technological parameters of the deposition process is studied. The stages in which the process parameters are optimized in order to improve the masking properties of the film are described. A systematic study of the Fourier-transform infra-red (IR) spectra of plasma-chemical silicon-nitride films is carried out. It is found that the chemical resistance of a silicon-nitride film depends on the configuration in which hydrogen is incorporated into chemical bonds.

Transparent silicon nitride films prepared by surface wave plasma chemical vapor deposition under low temperature conditions

Highly transparent silicon nitride films with a low absorption coefficient of only 200cm-1 or lower were prepared under high NH3/SiH4 source gas ratio conditions at 80°C or lower temperature using surface wave plasma chemical vapor deposition (SWP-CVD). Rutherford backscattering measurements indicated that a silicon nitride structure Si3Nx (x>5) with excess nitrogen could be prepared with the SWP-CVD method under high NH3/SiH4 source gas ratio conditions. X-ray photon spectroscopy (XPS) analysis provided verification that the excess nitrogen combined with the oxygen contained in the SiNx film during low-temperature film formation and that the atomic ratio of Si and N was almost stoichiometric, i.e., Si3N4.XPS study also revealed that the Si3N<4 structure contained suboxides, which presence may reduce the transparency of the films. In contrast, suboxides were not observed in the Si3N4 structure obtained under high NH3/SiH4 source gas ratio conditions. Fourier-transform infrared spectroscopy study confirmed that the SiNx film becomes more stable when the SiNx structure approaches the stoichiometric ratio. Achieving a near-transparent Si3N4 structure requires a sufficient amount of N atoms in the periphery of the Si atom, i.e., an adequate amount of NH3 is necessary in the presence of the SiH4.

Ab initio design of nanostructures for solar energy conversion: a case study on silicon nitride nanowire.

Design of novel materials for efficient solar energy conversion is critical to the development of green energy technology. In this work, we present a first-principles study on the design of nanostructures for solar energy harvesting on the basis of the density functional theory. We show that the indirect band structure of bulk silicon nitride is transferred to direct bandgap in nanowire. We find that intermediate bands can be created by doping, leading to enhancement of sunlight absorption. We further show that codoping not only reduces the bandgap and introduces intermediate bands but also enhances the solubility of dopants in silicon nitride nanowires due to reduced formation energy of substitution. Importantly, the codoped nanowire is ferromagnetic, leading to the improvement of carrier mobility. The silicon nitride nanowires with direct bandgap, intermediate bands, and ferromagnetism may be applicable to solar energy harvesting.

Effects of rare earth adsorption on electronic structure and optical properties in β-Si3N4 ceramics from first principles

Electronic structure and optical properties of silicon nitride adsorbed by rare earths are explored by density functional theory.

Structure and composition of silicon nitride and silicon carbon nitride coatings for joint replacements

SiNx and SiCxNy coatings were fabricated with high power impulse magnetron sputtering (HiPIMS). The coatings microstructure, growth pattern, surface morphology, composition, and bonding structure were investigated by AFM, SEM, GIXRD, TEM, EDS as well as XPS, and related to the deposition parameters target powers and substrate temperature. Cross-sections of SiCxNy coatings showed either dense and laminar, or columnar structures. These coatings varied in roughness (Ra between 0.2 and 3.8nm) and contained up to 35at.% C. All coatings were substoichiometric (with an N/Si ratio from 0.27 to 0.65) and contained incorporated particles (so called droplets). The SiNx coatings, in particular those deposited at the lower power on the silicon target, demonstrated a dense microstructure and low surface roughness (Ra between 0.2 and 0.3nm). They were dominated by an (X-ray) amorphous structure and consisted mainly of Si–N bonds. The usefulness of these coatings is discussed for bearing surfaces for hip joint arthroplasty in order to prolong their life-time. The long-term aim is to obtain a coating that reduces wear and metal ion release, that is biocompatible, and with wear debris that can dissolve in vivo.

Integrated Long-Range Thermal Bimorph Actuators for Parallelizable Bio-AFM Applications

Atomic force microscope (AFM)-based cell force spectroscopy is an emerging research method that has already enhanced our understanding of the structural changes that take place in a cell as it becomes cancerous. However, the method is limited as it is not time-efficient in its current state of development. This paper presents the fabrication of an integrated long-range thermal bimorph actuator that controls the z-position of an AFM cantilever in liquid. Multiplied in arrays, such individually actuated probes can parallelize cell force spectroscopy measurements, thereby drastically reducing the time per measured cell. The need to accommodate differences in tip-sample distance implies an individual device actuation range of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\geq}{\rm 10}~\mu{\rm m}$</tex></formula> out-of-plane. In addition, any cross-talk, i.e., between actuators or between the actuator and the force sensor, must be minimized. To meet these requirements, we design and fabricate a novel thermal bimorph actuator that is paired with a force sensing cantilever. In order to keep temperatures in a bio-friendly range, the design is optimized for high thermomechanical sensitivity. Finite element model simulations confirmed that the surrounding liquid constitutes a large thermal reservoir that absorbs the generated heat without any dramatic temperature increase. Furthermore, given that a cell substrate material of high thermal conductivity is chosen, e.g., Si, the thermal coupling between the cell and the substrate, dominates over that between the cell and the actuator. Suspended silicon nitride structures with platinum electrodes are microfabricated through standard techniques. The finalized actuator is able to displace the cantilever out-of-plane by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 17}~\mu{\rm m}$</tex></formula> in air, corresponding well to estimations.

Synthesis and Crystal Structure of Cubic Ca16Si17N34

Since the late 1960s, the exact structure of cubic calcium silicon nitride has been a source of debate. This paper offers evidence that the cubic phase CaSiN(2) described in the literature is actually Ca(16)Si(17)N(34). Presented here is a method for synthesizing single crystals of cubic-calcium silicon nitride from calcium nitride and elemental silicon under flowing nitrogen at 1500 °C. The colorless millimeter-sized crystals of Ca(16)Si(17)N(34) with a refractive index (n(25)) = 1.590 were found to be cubic (a = 14.8882 Å) and belong to the space group F43m (216). The synthesis of bulk, powdered cubic-Ca(16)Si(17)N(34) from calcium cyanamide and silicon is also discussed. Ca(16)Si(17)N(34) is a relatively air-stable refractory ceramic. In contrast to the orthorhombic phase of CaSiN(2), in which Ca(2+) sits in octahedral sites, this cubic phase has Ca(2+) in cubic sites that makes it an interesting host for new phosphors and gives rise to unique crystal field splitting.

Impact of oxygen bonding on the atomic structure and photoluminescence properties of Si-rich silicon nitride thin films

The atomic structure and optical properties of Si-rich silicon nitride thin films have been for decades the subject of intense research, both theoretically and experimentally. It has been established in particular that modifying the chemical composition of this material (e.g., the Si excess concentration) can lead to dramatic differences in its physical, optical, and electrical properties. The present paper reports on how the incorporation of oxygen into silicon nitride networks influences their chemical bonding and photoluminescence properties. Here, by using a combination of analytical scanning transmission electron microscopy and x-ray photoelectron spectroscopy it is demonstrated that the structure of Si-rich silicon nitride with low O content can be described by the co-existence of Si nanocrystals in a Si3N4 matrix, with occasional localized nano-regions of a Si2ON2 phase, depending on the amount of excess Si. Furthermore, it is shown that the structure of silicon nitride with high O content can be adequately described by a so-called random bonding model, according to which the material consists in bonded networks of randomly distributed tetrahedral SiOxN4−x (where x = 0, 1, 2, 3, and 4). Photoluminescence measurements indicate that the effect of O is to introduce a gap state in the band gap of Si3N4 matrix. When a large amount of O is introduced, on the other hand, the photoluminescence measurements are in agreement with a shifted conduction band minimum in the dielectric. For both cases (high and low O content), Si dangling bonds were found to give rise to the deep level in the band gap of the nitride matrix, causing the dominant emission band in the photoluminescence of the films.

Electronic structure of silicon nitride

Amorphous oxide SiO2, oxynitride SiOxNy, and silicon nitride Si3N4 are the three key dielectric materials of silicon device technology. Silicon nitride is currently finding use in a variety of applications, in particular, as a storage medium in next-generation flash memory devices. Varying the chemical composition of nonstoichiometric silicon-rich SiNx allows a wide-range control of its optical and electrical properties. In this review, an analysis of the electronic structure of silicon nitride of varying composition is presented.

Effect of topological disorder on structural, mechanical, and electronic properties of amorphous silicon nitride: An atomistic study

We present a first-principles study of the effect of atomic variability on the structural, mechanical, and electronic properties of amorphous silicon nitride. Using a combination of molecular dynamics and density functional theory calculations, we predict an ensemble of statistically independent, well-relaxed, and stress-free amorphous silicon nitride structures. We analyze the short-, intermediate-, and long-range orders of the structures generated using radial distribution functions, ring statistics, bond angle distributions, and translational invariance parameters. Though energetically very similar, these structures span a wide range of densities (2.75--3.25 g/cm${}^{3}$) and bulk moduli (115--220 GPa) in good agreement with the fabrication-dependent experimental range. Chemical bonds and atomic defects are identified via a combination of bond distance cutoff and maximally localized Wannier function analysis. A significant number of the amorphous structures generated ($\ensuremath{\sim}$30$%$) are defect free providing an ideal reference to characterize the formation energy of the various point defects and their defect energy levels. An analysis of the Kohn-Sham density of states and energetics of the structures reveals that defects in amorphous dielectrics have a distribution of associated properties (e.g., formation energies and electronic energy levels) due to variations in local atomic structure; this should be taken into consideration in physics-based continuum models of these materials.

Tensile deformation induced structural rearrangement in amorphous silicon nitride

Silicon nitride exhibits good mechanical properties and thermal stability at high temperatures. Since experiments have limitations in nanoscale characterization of the chemical structure and related properties, atomistic simulation is a proper way to investigate the mechanism of this unique feature. In this paper, the melt-quench method is used to generate the amorphous structure of silicon nitride; then the structural properties of silicon nitride under tensile deformation were studied by angular pair distribution functions. The corresponding mechanism of tensile stress induced structure rearrangement is explored.

Study of Silicon Nanoparticles Formation in Silicon Nitride

We present results of the study on the silicon nanoparticles formation in multilayer silicon nitride structures. These structures consist of pairs of stoichiometric silicon nitride dielectric layers (SiNx) and silicon rich nitride layers (SRN). Silicon nanocrystals precipitate from the SRN layer during annealing at high temperatures (1000 °C or 1100 °C). High resolution transmission electron microscopy has been applied for investigation of the nanocrystals formation. Surface photovoltage spectroscopy technique was used for the spectral characterization of prepared structures

A-SiNx:H Antireflective And Passivation Layer Deposited By Atmospheric Pressure Plasma

An Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD) is under development to deposit hydrogenated amorphous silicon nitride (a-SiNx:H) on silicon solar cells. Due to its inline integration capability, it is an alternative to the standard industrial Low Pressure Plasma Enhanced Chemical Vapor Deposition (LP-PECVD) process, allowing higher production throughput. The present work shows the correlation between the treatment head configuration and the antireflective properties of the thin film. The analysis of deposited silicon nitride chemistry and structure explains why the thin film has at first a too high extinction coefficient and gives solutions to solve the problem by improving the gas flow control and the plasma length. Silicon passivation is also discussed.

An algorithm for the generation of silicon nitride structures

Abstract Silicon nitride is used for demanding tasks due to its high stiffness, strength and, especially, its high fracture toughness. Examples include cutting tools, forming rolls and ball bearings. The microstructure is characterized by elongated β-Si 3 N 4 grains of different size and shape, which lead to the increased fracture toughness. Consequently, the paper will present an algorithm for the generation of three-dimensional and periodic silicon nitride-like microstructures, which will be used for micromechanical finite element simulations. The structure generation algorithm enhances the sequential adsorption technique with growth of particles and steric hindrance, which are motivated by experimental results. Results of the structure generator, such as the pseudo-time evolution and its statistical geometric distributions are presented and compared to literature data. With the finite element simulations, using a periodic unit cell, a validation of the model with literature values for Young's modulus and Poisson's ratio was possible.

Study of the atomic and electronic structures of amorphous silicon nitride and defects in it

The structure of amorphous silicon nitride obtained by cooling from a melt has been simulated by Car-Parinello molecular dynamics. Several types of Si-Si defect coordination have been revealed. It has been found that, in addition to normal Si-Si bonds, numerous double Si-Si bonds (Si-Si-Si defects) are present in the amorphous structure.

A new transparent Bio-MEMS for uni-axial single cell stretching

A novel, completely transparent bio-MEMS (bio-Micro Electro Mechanical System) device has been devised and manufactured using finite element analysis (FEA) and micro-fabrication techniques. The device has been designed to be used for testing the mechanical properties of single living cells, it is versatile and suitable for coupling with other analysis techniques. Furthermore, being completely transparent, it can be used with either transmission or reflection microscopes. The transparent bio-MEMS is based on a silicon dioxide–silicon nitride structure and, since the main goal is to test living cells, it is meant to work in a liquid environment and allow for cell stretching. Sensors for cell deformation and for platform displacement are also present and the required sensitivity for single cell analyses is granted. The device will moreover allow the recording of the stress–strain curve for single living cells.

Optical properties of multilayer silicon nitride structures with silicon quantum dots

AbstractIn our study we report the investigation of nanostructures embedded in silicon nitride films deposited by RF plasma enhanced chemical vapor deposition (PECVD). The multilayer structure consisting of fifty near‐stoichiometric silicon nitride layers followed by silicon–rich silicon nitride layers has been deposited and heated in 1100 °C in order to realize the quantum dot superlattice. The properties of the quantum dots are investigated using high resolution transmission electron microscopy (HRTEM) and spectroscopic ellipsometry. It has been observed that after annealing the photoluminescence that was previously observed in the sample is strongly suppressed. At the same time a new absorption peak in the dispersion of the extinction coefficient occurred almost at the same value of the wavelength. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)