Monolithic Silicon Nitride Research Articles

A novel thermally matched conductive phase of silicon nitride ceramics

Tungsten was first proposed as a conductive phase that better matches the thermal expansion of silicon nitride ceramics. Silicon nitride ceramics containing 20 vol% tungsten particles were fully densified via gas pressure sintering under a following nitrogen atmosphere. After introducing the tungsten particles, the thermal conductivity is increased two-fold and thermal expansion coefficient (CTE) almost remains as low as the monolithic silicon nitride ceramics. Most importantly, the composite ceramics achieve good electrical conductivity and a small and complex shape was machined via wire-electrode cutting to confirm its good wire-electrical discharge machinability. Tungsten particles have been proven to be a new ideal conductive phase for silicon nitride ceramics, and a new wire-electrical discharge machinable silicon nitride-based ceramic was prepared.

Towards monolithic low-loss silicon nitride waveguides on a mature 200 mm CMOS platform

Silicon nitride photonics has enabled a broad class of low-loss integrated devices and chip-scale solutions that benefit from transparency over a wide wavelength range and compatibility with complementary metal-oxide-semiconductor process, allowing applications of tele/datacom, artificial intelligence, sensing and bio-photonics. As a complimentary platform to silicon-on-insulator photonics, low-loss silicon nitride waveguide technology was present to extend the capabilities of silicon photonics platform. Silicon nitride films prepared by low pressure chemical vapor deposition have low intrinsic loss and good repeatability, but silicon nitride film is prone to crack when the thickness is no less than 300 nm. In order to reduce high stress, the wafer-level silicon nitride waveguides with 400 nm thickness were fabricated by two-step deposition method on 200-mm complementary metal-oxide-semiconductor pilot-line. Due to the different linewidth change between single-stripe and multiple-stripe structure after the same layer etch process, the layout compensation is needed to correct this deviation. But the linewidth sensitivity for silicon nitride waveguides is relatively low, propagation losses in the C-band were slightly reduced from 0.66 dB/cm for 0.9 µm width down to 0.62 dB/cm for 1 µm width.

Silicon nitride–silicon carbide micro/nanocomposites: A review

AbstractThis paper reviews investigations of silicon nitride–silicon carbide micro–nanocomposites from the original work of Niihara, who proposed the concept of structural ceramic nanocomposites, to more recent work on strength and creep resistance of these unique materials. Various different raw materials are described that lead to the formation of nanosized SiC within the Si3N4 grains (intragranular) and at grain boundaries (intergranular). The latter exert a pinning effect on the amorphous grain boundary phases in the silicon nitride and also act as nucleation sites for β‐Si3N4, which limits grain growth during sintering. This finer microstructure results in strengths higher than for the monolithic silicon nitride. Intragranular SiC particles enhance strength and fracture toughness as a result of residual compressive thermal stresses within the nanocomposites. High temperature strength and creep resistance are also much higher than for monolithic silicon nitride and a few investigations of these topics are briefly reviewed and the proposed mechanisms are described. Within the context of other studies cited, work on Si3N4–SiC micro–nanocomposites by the current authors describes an aqueous processing route for better dispersion of commercial powders prior to sintering.

Overcoming the quantum limit of optical amplification in monolithic waveguides.

Optical amplifiers are essential in numerous photonic applications. Parametric amplifiers, relying on a nonlinear material to create amplification, are uniquely promising as they can amplify without generating excess noise. Here, we demonstrate amplification based on the third-order nonlinearity in a single chip while, in addition, reporting a noise figure significantly below the conventional quantum limit when operated in phase-sensitive mode. Our results show the potential of nanophotonics for realizing continuous-wave parametric amplification that can enable applications in optical communications, signal processing, and quantum optics across a wide range of frequencies.

Silicon Nitride, a Close to Ideal Ceramic Material for Medical Application

This topical review describes the salient results of recent research on silicon nitride, a ceramic material with unique properties. The outcome of this ongoing research strongly encourages the use of monolithic silicon nitride and coatings as contemporary and future biomaterial for a variety of medical applications. Crystallographic structure, the synthesis and processing of monolithic structures and coatings, as well as examples of their medical applications that relate to spinal, orthopedic and dental implants, bone grafts and scaffolds, platforms for intelligent synthetic neural circuits, antibacterial and antiviral particles and coatings, optical biosensors, and nano-photonic waveguides for sophisticated medical diagnostic devices are all covered in the research reviewed herein. The examples provided convincingly show that silicon nitride is destined to become a leader to replace titanium and other entrenched biomaterials in many fields of medicine.

In Situ Graded Ceramic/Reduced Graphene Oxide Composites Manufactured by Spark Plasma Sintering

The present work merges two key strategies for the manufacturing of advanced ceramics, in particular, the development of functionally graded materials (FGMs) and the addition of graphene-based fillers into a ceramic matrix. A silicon nitride/reduced graphene oxide FGM composite is produced, in one step, from a single powder composition using the spark plasma sintering (SPS) technique with an asymmetric setting of the punches and die to create a continuous temperature gradient along the cross section of the powder compact. A deep microstructural and mechanical characterization has been done across the specimen thickness. The FGM composite exhibits bottom-top gradients in both the matrix grain size (150% increase) and α-phase content (89→1%). The FGM bottom surface is 10% harder than the top one and, on the other hand, the latter is 15% tougher. The presence of reduced graphene oxide sheets homogeneously distributed within the ceramic composite reduces the mechanical gradients compared to the monolithic silicon nitride FGM, although allows reaching a maximum long-crack toughness value of 9.4 MPa·m1/2. In addition, these graphene-based fillers turn the insulating ceramics into an electrical conductor material.

Enhanced bioactivity of Si3N4 through trench-patterning and back-filling with Bioglass®.

Using a simple and innovative sandblasting process, disks of monolithic biomedical silicon nitride (β-Si3N4) were texturized with a matrix of regular, discrete square trenches with a total depth in the range of hundreds of microns. The process consisted of sandblasting Si3N4 substrates through a stainless-steel wire-mesh (150 or 200 μm) using abrasive silicon carbide powders (α-SiC, ∼40 μm) under 1,034 kPa (150 psi) of gas pressure. The depth of the porosities could be controlled varying both the treatment time and the distance from the surface. Part of the samples were then filled with 45S5 Bioglass® powders to improve the osteointegration and stimulate the production of bone tissue. Due to the increased macroscopic and microscopic roughness, biological testing using human osteosarcoma cells (SaOS-2) showed improved cell proliferation and greater production of both mineral (hydroxyapatite) and organic (collagen) phases on the patterned surfaces compared to untreated β-Si3N4 or to the biomedical titanium control samples. Both of these effects were further enhanced when the porosities were filled with Bioglass®.

Microcavity-based narrowband parametric amplifier for carrier recovery in optical coherent self-homodyne detection.

We demonstrate all-optical carrier recovery exploring optical parametric amplification (OPA) in a monolithic high-finesse silicon nitride microring cavity. Compared to a nonresonant OPA process in nonlinear waveguides, cavity-based OPA allows a much narrower gain bandwidth by manipulating the intracavity light interactions with a controllable parametric gain, thus facilitating high-resolution carrier extraction without needing a large guard band between the carrier tone and data spectrum. Here, we achieve narrowband OPA with a 22.0dB peak gain and a bandwidth as low as 15.2MHz in a 100μm radius microring cavity, which is applied to implement carrier recovery of a 16QAM optical orthogonal-frequency-division-multiplexing data signal. A highly coherent phase is conserved between the recovered carrier tone and the original data, enabling self-homodyne detection with high data quality and minimized electrical compensation. Our study holds potential to constitute energy-friendly coherent receivers.

Absolute Deflection Measurements in a Micro- and Nano-Electromechanical Fabry-Perot Interferometry System.

Fabry-Perot laser interferometry is a common laboratory technique used to interrogate resonant micro- and nano-electromechanical systems (MEMS/NEMS). This method uses the substrate beneath a vibrating MEMS/NEMS device as a static reference mirror, encoding relative device motion in the reflected laser power. In this work, we present a general approach for calibrating these optical systems based on measurements of large-amplitude motion that exceeds one half of the laser wavelength. Utilizing the intrinsic nonlinearity of the optical transduction, our method enables the direct measurement of the system's transfer function (motion-to-detected-voltage). We experimentally demonstrate the use of this technique to measure vibration amplitudes and changes in the equilibrium position of a MEMS/NEMS device using monolithic silicon nitride and silicon cantilevers as sample systems. By scanning the laser along a cantilever surface, we spatially map static and dynamic deflection profiles simultaneously, and then compare the static profile against results from a commercial optical profilometer. We further demonstrate extension of our calibration technique to measurements taken at small amplitudes, where the optical transduction is linear, and to those taken in the frequency domain by a lock-in amplifier. Our aim is to present a robust calibration scheme that is independent of MEMS/NEMS materials and geometry, to completely negate the effects of nonlinear optical transduction, and to enable the assessment of excitation forces and MEMS/NEMS material properties through the accurate measurement of the MEMS/NEMS vibrational response.

Monolithic silicon nitride-based aerogels with large specific surface area and low thermal conductivity

Abstract C/silica (RF/SiO2) aerogel (RFSA) was synthesized via a one-step sol-gel process and supercritical fluid drying. Then, monolithic silicon nitride (Si3N4) aerogel (SNA) was prepared via carbothermal nitridation of the RFSA in flowing N2. The effects of the RFSA density and carbothermal temperature on the formation of the SNA were investigated. The evolution of the physical properties, chemical structure, morphology, pore structure, and thermal performance of the SNA was examined. Si3N4 nanocrystals were formed from the RFSA at a carbothermal temperature of 1500 °C. The as-prepared SNA had a low density (0.127 g/cm3), large specific surface area (445 m2/g) and low thermal conductivity (0.04909 W/(m·K)), which were far better than those of its state-of-art counterparts. Because of its good thermal stability, the SNA can be used as a thermal insulator and support at high temperatures.

Thermal Shock Resistance of Si<sub>3</sub>N<sub>4</sub>/hBN Ceramic Composites

Si3N4/hBN composites were fabricated by hot isostatic pressing at 1700°C/3h with 1, 3 and 5 wt. % micro-sized or nano-sized hexagonal boron nitride particles added to silicon nitride matrix. An indentation quench test method was used for estimation of thermal shock resistance of monolithic Si3N4 and Si3N4/hBN composites. Thermal shock resistance of the composites increased with the increase of size and volume of hBN particles. The critical temperature difference for the composites with micro-sized hBN was significantly higher (over 900°C) compared to the monolithic silicon nitride (580°C).

Effect of addition of micron-sized TiC particles on mechanical properties of Si3N4 matrix composites

Abstract The effect of micron-sized TiC particles on mechanical properties of Si 3 N 4 matrix composites was investigated. Si 3 N 4 TiC composites were fabricated by using powder metallurgy and gas pressure sintering (GPS) methods. In order to achieve high mechanical properties, the experimental data were carried out with five different Si 3 N 4 TiC contents. Hardness, fracture toughness and relative density of Si 3 N 4 TiC composites were characterized. The result indicated that the highest relative density (98.0%) and fracture toughness (K IC = 8.4 MPa m 1/2 ) were measured for monolithic silicon nitride and 5 wt% TiC, respectively. Qualitative and quantitative phase compositions were analyzed by X-ray diffraction (XRD). The experimental analyses indicated that the TiC phase reacted with Si 3 N 4 during the liquid phase sintering, resulting in formation of TiC 0.3 N 0.7 . The phase transition, crystal growth, microstructure and mechanical properties of composites were investigated by scanning electron microscopy (SEM). Due to the inhibition of the grain growth, the aspect ratio exhibited a higher value from SNT0 (aspect ratio = 4.54) to SNT5 (aspect ratio = 5.60). The toughening mechanism of Si 3 N 4 TiC composites was attributed to crack deflection and crack impedance by periodic compressive stress in the Si 3 N 4 matrix. However, the increase of the TiC content easily led to excessive connection microcrack, which would not be beneficial for the strength.

Modeling of two‐pump optical frequency comb generation in monolithic silicon nitride ring resonator

ABSTRACTThe two‐pump Four‐Wave‐Mixing (FWM) in the ring resonator promises more agile compact frequency comb generation than the traditional singe‐pump scheme regarding the convenient tuning of comb line space by modifying the two pumps’ space. The silicon‐nitride‐ring‐resonator‐based optical frequency comb generation system input with two pumps for the parametric process is simulated by an iterative process relying on the split‐step Fourier method. The influences of the coupling coefficient and pumps’ frequencies on the comb spanning are explained in terms of Q factor and resonance condition of the ring. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:919–921, 2016

Tribological characterisation of silicon nitride/multilayer graphene nanocomposites produced by HIP and SPS technology

Tribological performance of monolithic silicon nitride (Si3N4) and Si3N4 based composite ceramics containing 1wt% and 3wt% multilayer graphene (MLG) sintered by conventional hot isostatic pressing (HIP) and spark plasma sintering (SPS) have been investigated by ball-on-disc tests in dry sliding conditions at two different sliding speeds (v=20 and 200mm/s), using SiC and Si3N4 ball materials, as sliding counterparts to compare the wear behaviour of the differently produced ceramic materials. The wear performance was characterized by the specific wear rate (k), wear coefficient (K) and friction coefficient (μ), completing with the analysis of the wear track morphology and wear mechanisms. SPS composites showed improved wear behaviour that can be explained by the combined effect of SPS on the microstructure and mechanical properties resulting in modification of the controlling wear mechanism of the Si3N4/MLG composites.

Criteria for Crack Deflection-Penetration in EBC Coated Ceramics: A Parametric Study

This article discusses results obtained from a parametric study to analytically evaluate the impingement of a crack at the interface of an environmental barrier coating (EBC) and a monolithic Silicon nitride (Si3N4) layered ceramics substrate. The study establishes a correlation that leads to determine if the crack is arrested or advanced by either penetrating or deflecting along the EBC/substrate interface. A finite-element-based fracture mechanics methodology is utilized to perform these calculations. Critical parameters determining penetration-deflection conditions in relation to EBC's physical characteristics, such as porosity level, voids, and mini cracks, are determined for a single layer and multi-layered coating system coordinating the interactions between the EBCs (Mullite, Mullite mixture, Silicon nitride, etc.) and the substrate structure. Results showing thermo-mechanical stresses and stress/strain energy release relations with respect to crack penetration-deflection are presented and discussed as the crack is advanced.

Spark plasma sintering of Si3N4/multilayer graphene composites

Abstract Mulitlayer graphene reinforced silicon nitride composites were prepared by spark plasma sintering to investigate the effect of the graphene addition on mechanical properties. The composites contained multilayer graphene (MLG) in various (0, 1, 3 and 5 wt%) content. Significantly higher fracture toughness of 8.0 MPa m1/2 was obtained at 1% MLG content, however, on further increasing the graphene content the toughness did not increase, but dropped to the value of the monolithic silicon nitride. The maximum hardness of 18.8 MPa was also obtained at 1% MLG, while at higher MLG contents it gradually decreased.

Influence of processing on fracture toughness of Si3N4+graphene platelet composites

Abstract Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets’ addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si 3 N 4 grains with smaller diameter in comparison to the composites prepared by HIP. The indentation fracture toughness of the composites was in the range 6.1–9.9 MPa m 0.5 , which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3 MPa m 0.5 . The highest value of K IC was 9.9 MPa m 0.5 in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5 MPa m 0.5 . The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging.

Fracture behavior of silicon nitride ceramics subjected to hypervelocity impact

A new advanced ceramic thruster made of monolithic silicon nitride ceramics was developed for the planetary exploration spacecraft AKATSUKI (PLANET-C) at Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). To ensure its operation onboard the spacecraft, the reliability of the ceramic thruster against micrometeoroid hypervelocity impact has been investigated. Silicon nitride plates were impacted by spheres of stainless-steel and other materials with 0.2–0.8-mm diameters in the velocity range up to 8.0 km/s using a two-stage light-gas gun. Using crater depth data under various impact conditions, the penetration equation of silicon nitride was determined. The impacted samples showed fracture patterns of three types: cratering, cratering with spallation, and perforation. These fracture patterns were well categorized by the multiple forms of the penetration equation.

Wear resistance of hot-pressed Si3N4/SiC micro/nanocomposites sintered with rare-earth oxide additives

The wear resistance of hot-pressed silicon nitride/silicon carbide micro/nanocomposites as well as monolithic silicon nitrides sintered with the same rare-earth oxide sintering additives (La2O3 ,N d 2O3 ,Y 2O3, Yb2O3 and Lu2O3) has been investigated under dry sliding conditions. The friction coefficient decreased with a decreasing ionic radius of rare-earth elements in both the monoliths and the composites. The friction coefficient of composites was always lower in comparison with that of Si3N4 monoliths. Similarly, the specific wear rate significantly decreased with a decreasing ionic radius of rare-earths either in monolithic or composite materials. The composites always exhibited lower specific wear rate compared to the monoliths. Mechanical wear (micro-fracture) and tribochemical reaction were found as the main wear mechanisms in all investigated materials. The higher bonding strength in the case of materials sintered with additives of a smaller ionic radius restricts dropping of the individual silicon nitride grains during wear experiments. This high bonding strength and the high fracture toughness are the reasons why the ceramics doped by Lu exhibited the best wear resistance. The Evans and Marshall lateral-crack chipping model based on the fracture toughness and hardness values well describes the wear rate of the investigated micro/nanocomposites.

Evaluation of quasi-static fracture characteristics considering surface conditions of silicon nitride for a space component

ISAS/JAXA is now planning to adopt a thruster made of monolithic silicon nitride (SN282 manufactured by Kyocera Co.) onto a Venus exploration probe, PLANET-C, in replacement of conventional niobium heat-resistant alloy. Silicon nitride is still brittle and requires precise analysis on multiaxial thermal stresses induced during firing, though it has high toughness among other structural ceramics. This study evaluated quasi-static fracture characteristics of SN282 considering the surface conditions through compression-torsion biaxial fracture tests as well as the conventional four-point-bending tests. The samples were applied to the mechanical tests either as-ground or after annealing at 1300°C in air for 1 h, which formed an oxidation layer of more than 250nm on the specimen surface. Symmetry four-point-bending tests showed that annealing improves flexure strength and reduce the difference caused by grinding directions. Biaxial stress fracture tests showed the high compressive stress makes the influence of facial crack insensitive.