Dense SiOC Research Articles

SiOC(N) Cellular Structures with Dense Struts by Integrating Fused Filament Fabrication 3D Printing with Polymer‐Derived Ceramics

Great advances have been made in various 3D printing methods for ceramics. Fabrication of Si‐based ceramics using polymer‐derived ceramics (PDCs) is gaining popularity. Using this route, preceramic polymers can be shaped in the polymer state and then pyrolyzed to produce different types of ceramics. Cellular ceramics can be manufactured using this technique. Herein, the novel fabrication of cellular ceramics with a two‐step process using PDCs is reported. First cellular structures are 3D printed with fused filament fabrication (FFF) using thermoplastic polyurethane and impregnated with preceramic polymer polysilazane. Second, pyrolysis of the impregnated structure produces a self‐similar ceramic cellular structure. The impact of 1) catalysts, 2) curing environment, and 3) pyrolysis sequence optimization to form cellular ceramics with fully dense SiOC(N) struts are systemically evaluated. The resultant custom ceramic components can tolerate operating temperatures of 1500 °C and can be manufactured for less than 5% of the cost of competing methods. The ceramic material is shown to be biocompatible and promotes fast cell adhesion. Finally, early‐stage cell activation on the SiOC(N) structure is shown to be tunable by adjusting the porosity with this 3D printing to mimic the bone tissue geometry for bone regeneration.

Fabrication of SiOC ceramic with cellular structure via UV-Assisted direct ink writing

In this study, polysiloxane resin was modified at the molecular scale to make it amenable to ultraviolet-curing and suitable for direct ink writing. The characterization results regarding the rheological properties and infrared spectra demonstrated that the conversion of CC is proportional to the viscosity and modulus of ink. As a result, three-dimensional cellular structures with a certain span and tailored porosity were obtained. The printed structures were then subjected to pyrolysis at temperatures higher than 1000°C to form uniform, crack-free, dense SiOC cellular ceramic structures, with ceramic yield of up to 70% and linear shrinkage as low as 25%. This technique enables the inexpensive and fast fabrication of SiOC ceramic products with relatively complex shapes.

Oxidation behavior of dense SiOC monolithics: The oxide scale development

Forming stable and continuous oxide scale is the key to resist oxidation by acting as a surface-diffusion barrier to reduce further oxygen attack. Oxidation behavior of dense SiOC monolithics was studied from 900 °C to 1200 °C for up to 18 h. The oxide scale formed at 1000 °C and 1200 °C was ∼106 μm and ∼81 μm in thickness, respectively. High thermal misfit strain induced by the large thickness and volume shrinkage originated from crystallization of silica resulted in the scale cracking with oxidation time. However, the scale formed at 1100 °C remained dense and thin (∼43 μm) without any visible defects, protecting the SiOC base effectively.

Highly micro- and mesoporous oxycarbide derived materials from HF etching of silicon oxycarbide materials

Abstract Highly micro-mesoporous silicon oxycarbide-derived carbon materials (SiOC-DC) with elevated specific surface area up to 895 m 2 g -1 and high pore volumes of mesopores (0.3 cm 3 g -1 ) and micropores (0.2 cm 3 g -1 ) have been obtained by direct etching of SiOC with HF. Initial organic-inorganic hybrids were synthesized by the sol-gel method employing triethoxysilane and polydimethylsiloxane (PDMS) of different molecular weights (550, 1750 and 4200 gmol -1 ). These hybrids were pyrolyzed from 1100 to 1400 °C. Short PDMS chains (550 gmol -1 ) within the hybrid structure rendered dense SiOC materials after pyrolysis, however long PDMS chains (1750 and 4200 gmol -1 ) produced highly micro-mesoporous SiOC materials up to 1300 °C. The etching of SiOC employing HF produced the selective removing of silica nano-domains and as a result highly micro-mesoporous SiOC-DC materials were created. In dense SiOC the HF attack is favored at the highest temperatures (1400 °C) when the SiOC is more phase separated. On the other hand, in porous SiOC there is an agreement between the pyrolysis temperature and the porosity and, therefore the SiOC materials are etched easier at 1200 °C. SiOC-DC materials are composed by a porous glassy network enriched with carbon (graphene-like carbon and turbostratic carbon) and SiC which present an incipient crystallization.

Reduction of the Sintering Temperature for the Manufacturing of Carbon‐Rich Dense SiOC Bulk Ceramics

A major challenge in the processing of compact polymer derived ceramics is the removal of pores. Even after field‐assisted sintering (FAST) under pressure, a certain level of porosity remains within samples and parts. In order to reduce the porosity, a novel route is developed making use of the addition of trimethyl borate to a polysilsesquioxane‐type preceramic polymer system; trimethyl borate is a molecular boron oxide precursor. It is found that boron‐oxide free samples show a high compression rate during field‐assisted sintering between 1400 and 1600 °C, boron oxide and boron oxide/alumina containing samples show this effect already between 1350 and 1500 °C. In a tentative reaction mechanism, this effect is assigned to the formation of a borosilicate glass by chemical reactions of boron oxide with the silica component of the polysiloxane‐derived ceramic; this glassy phase assists the densification process by viscous flow. The porosity in boron oxide‐containing samples is found to be between 0.3% and 1.4% while boron oxide‐free samples show a total porosity of ≈38% after processing under identical conditions.

High-temperature creep behavior of a SiOC glass ceramic free of segregated carbon

In this study we present the high-temperature creep behavior of a dense SiOC glass ceramic free of segregated carbon. Solid-state NMR spectroscopy, XRD and TEM investigations indicate that the sample consists of β-SiC nanoparticles homogeneously dispersed in an amorphous silica matrix. Compression creep experiments were performed at 1100–1300°C and stresses of 50–100MPa. The calculated creep viscosity of SiOC is two orders of magnitude higher than that of pure silica. Whereas the activation energy for creep (696kJ/mol) is close to that determined in pure silica glass. However, a stress exponent of 1.7 was calculated, suggesting that other mechanisms might contribute to the creep in addition to the Newtonian viscous flow. The strong difference in the creep rates and creep mechanism of the SiOC glass ceramic and amorphous silica is discussed in terms of possible contributions of the interface between the silica matrix and the β-SiC nanoparticles.

Flexural Strength of Polysiloxane-Derived Strontium-Doped SiOC Ceramics

The effect of Sr addition on the flexural strength of bulk SiOC ceramics was investigated in polymer-derived SiOC ceramics prepared by conventional hot pressing. Crack-free, dense SiOC discs with a 30 ㎜ diameter were successfully fabricated from commercially available polysiloxane with 1 ㏖% strontium isopropoxide derived Sr as an additive. Agglomerates formed after the pyrolysis of polysiloxane led to the formation of domain-like structures. The flexural strength of bulk SiOC was strongly dependent on the domain size formed and Sr addition. Both the minimization of the agglomerate size in the starting powders by milling after pyrolysis and the addition of Sr, which reinforces the SiOC structure, are efficient ways to improve the flexural strength of bulk SiOC ceramics. The typical flexural strength of bulk Sr-doped SiOC ceramics fabricated from submicron-sized SiOC powders was ~209 ㎫.

Facile one-pot formation of ceramic fibres from preceramic polymers by pressurised gyration

This paper reports for the very first time a facile and simple method, consisting of simultaneous centrifugal spinning and solution blowing, to mass produce ceramic fibres from preceramic polymers. Solutions of two different commercially available silicone resins and a mixture of a silicone resin and graphene were used, and a polymer (polyvynilpyrolidone) was added to aid the fibre generation process. The fibre diameter and the morphology of the spun and the pyrolysed fibres were shown to be influenced by rotating speed, working pressure and the polymer concentration. Non-porous fibres were obtained using a low volatility binary solvent system and, after pyrolysis at high temperature, dense SiOC ceramic fibre bundles were produced. This fabrication method based on pressurised gyration shows great promise in the mass production of ceramic fibre bundles.

Influence of high-temperature oxidation on photoluminescent properties of white Si[sbnd]O[sbnd]C(–H) ceramics

SiOC(–H) ceramics were prepared by pyrolyzing densely cross-linked polysiloxane particles in hydrogen at temperatures of 800, 900 and 1100°C. Thermogravimetric–differential thermal analysis (TG–DTA) curves of these SiOC(–H) ceramics in an air flow revealed that the oxidation resistance strongly depended on the decarbonization temperature. On the other hand, these decarbonized samples were oxidized in dry air flow at temperatures of 300, 500, 700, 1000 and 1200°C. After the oxidation in air, photoluminescent (PL) spectra and Fourier transform infrared (FTIR) spectra of the oxidized samples were investigated. In partly organic SiOC(–H) ceramics with high H/C ratios, the intensity of blue PL simultaneously decreased with rapid oxidation. Residual weak PL peaks are probably assigned to defects in silica formed on particle surfaces. In dense SiOC(–H) ceramics with a relatively low H/C ratio, the intensity of white PL gradually decreased with moderate oxidation and the PL peak position shifted to longer wavelengths. Intensity of phosphorescence of the dense SiOC(–H) ceramics was also weakened after oxidation. The decrease of phosphorescence intensity, however, began at a rather low temperature range as compared with that of the apparent PL.

The effects of UV radiation on SiC(O)N/SiOC(− H) thin films grown on Si substrates using plasma-enhanced atomic layer deposition

Multilayer Cu/SiC(O)N/dense SiOC(−H)/porous SiOC(−H)/p-Si(100) thin-film stacks were fabricated. A 200-nm-thick porous SiOC(−H) film was deposited on an Si substrate using plasma-enhanced chemical vapor deposition. Subsequently, a 60-nm-thick dense SiOC(−H) film followed by a 20-nm-thick SiC(O)N film was deposited using plasma-enhanced atomic layer deposition. These multilayer films were then irradiated with ultraviolet (UV) light at 400°C for various times in the range 5 to 20min to improve their structural, mechanical, and electrical properties. The effects of the UV radiation on the interfacial bonding configurations and the mechanical properties of the interface between the SiC(O)N etch stop layer and the porous low-k SiOC(−H) film were investigated. The elemental concentrations of Si, C, N, and O were determined at the SiC(O)N/SiOC(−H) interfaces using Auger electron spectroscopy depth-profile analysis, and the electrical properties of the Cu/SiC(O)N/SiOC(−H)/Si metal-insulator-semiconductor structures were investigated using capacitance–voltage and current–voltage profiling. Based on our experimental results, UV exposure for 5 to 10min is optimal for improving the characteristics of Cu/SiC(O)N/SiOC(−H)/Si multilayered films.

Lithium insertion into dense and porous carbon-rich polymer-derived SiOC ceramics

Two polymer-derived SiOC ceramics with different amount of carbon were synthesized either as dense or porous SiOC powders. The dense materials were produced up to a maximum temperature of 1400 °C and show a phase separated nanostructure consisting of SiO2-rich clusters, nanocrystalline SiC and nanocrystalline carbon phase. The corresponding porous materials were obtained by etching the silica phase of the dense SiOC with 20% HF solution. The electrochemical properties of the dense and porous SiOC ceramics in terms of lithium insertion/extraction were studied. Accordingly, the SiOC materials show a first lithium insertion capacity between 380 and 648 mAh g−1 followed by significantly lower extraction capacities between 102 and 272 mAh g−1. We consider the free carbon phase present in the ceramic as the major lithium intercalating agent. The porous samples show a stable electrochemical behavior up to 30 cycles while for the dense materials the efficiency drops to almost zero after 10 cycles.

Polymer‐Derived SiOC–barium–strontium aluminosilicate Coatings as an Environmental Barrier for C/SiC Composites

Polysiloxanes polymer coatings were formed on carbon fiber‐reinforced silicon carbide (C/SiC) composites at 100°C in air with barium–strontium aluminosilicate (BSAS) as fillers. After the polymeric coatings were pyrolyzed at 1350°C under argon, a dense SiOC–BSAS‐coated C/SiC composite was obtained. The oxidation test in dry air and the corrosion test in water vapor were carried out on the coated composites at 1250°C, respectively. The results indicated that the polymer‐derived SiOC–BSAS coatings could protect the C/SiC composites well both in dry air and water vapor. Even after corroded for 200 h in water vapor, the coated C/SiC composites showed little weight loss and high residual flexural strength.

Dense SiOC cap for damage-less ultra low k integration with direct CMP in C45 architecture and beyond

Deposited on a porous a-SiOC:H intermetal dielectric (IMD), a dense a-SiOC:H cap was successfully integrated in a C45 dual damascene architecture. The paper demonstrates that, stopping the CMP with around 10 nm of the cap left, the IMD integrity is preserved. As a consequence, a 3.5% decrease in RC delay, a 7.3% decrease in IMD integrated k-value and an increase of the time to failure by a 100 factor are reached relative to direct CMP. The cap also allowed to achieve straight lines and to improve the lines height uniformity as if CMP stopped on the IMD.

Time-Dependent Dielectric Breakdown Characterization of 90- and 65-nm-Node Cu/SiOC Interconnects with Via Plugs

As the wiring-space decreases, the time-dependent dielectric breakdown (TDDB) of Cu/low-dielectric constant (k) interconnects becomes a critical reliability issue and more accurate prediction of the TDDB lifetime will be required. In this investigation, TDDB dependences on temperature and electric field are studied comprehensively for 90- and 65-nm-node Cu/SiOC interconnects using practical multilevel test structures with via plugs. Low-electric-field TDDB tests down to 1 MV/cm were carried out by a package TDDB method with high temperature up to 300 °C. Linear dependence of the TDDB lifetime on the electric-field is observed down to 1 MV/cm, and this suggests that the lifetime can be predicted using the E-model. The linear dependence of the TDDB lifetime on temperature is also observed up to 300 °C at 1.8 MV/cm. The activation energies for the 90 and 65 nm nodes are almost the same values, 0.76 eV for the 90 nm node and 0.74 eV for the 65 nm node. Failure is observed at the interfaces between the cap dielectric (SiCN) and the silicon dioxide layer with a surface polished by chemical-mechanical polishing (CMP) for both nodes. It is noted that no difference in the failure modes is seen between dense SiOC for the 90 nm node and porous SiOC for the 65 nm node, in spite of the different materials used for the intermetal dielectrics. This suggests that the polished interfaces greatly affect on the TDDB lifetime for both nodes. Improved TDDB lifetime is obtained by increasing the post-CMP cleaning time and the pretreatment time before the cap dielectric deposition. Sufficient TDDB lifetimes of over 10 years under practical operating conditions are obtained for both 90- and 65-nm-node Cu/low-k interconnects with via plugs.

Mechanical characterization of a polysiloxane-derived SiOC glass

Silicon oxycarbide glass with the composition Si 1.0O 1.6C 0.8 was synthesized from a commercial polysiloxane by polymer pyrolysis. Dense SiOC samples were obtained by cross linking of the polysiloxane followed by warm pressing to form cylindrical samples and subsequent pyrolysis of the shaped polymer at 1100 °C in Ar. Hardness ( H), Young's modulus ( E) and Poisson's ratio ( ν) of the as-prepared SiOC glass were evaluated from indentation studies and from acoustic microscopy. Indentation studies showed that E depends on the applied load and amounts to 90 GPa for low load and to 180 GPa for high load. Average values of 6.4 and 101 GPa were obtained for H and E, respectively, by the Vickers indentation method. Acoustic microscopy analysis yielded values of 96 GPa and 0.11 for E and ν, respectively. Compared to vitreous silica, the Young's modulus of the SiOC glass is about 1.3–1.5 times higher. To the knowledge of the present authors, the measured Poisson's ratio ( ν = 0.11) is the lowest reported so far for glasses and polycrystalline ceramics.

SiOC glass modified by montmorillonite clay

The addition of inexpensive montmorillonite clay to a silicone resin employed as preceramic polymer was found to be advantageous for the production of SiOC glass matrix composites. Dense SiOC based monoliths were achieved with the addition of a substantial amount of calcined clay (30 wt.%) to the preceramic polymer; these composites exhibited remarkable hardness and fracture toughness, higher than those of SiOC glasses reported in the literature, due to the very small dimensions of silica and mullite crystal inclusions deriving from the decomposition of clay. Microcellular SiOC glass based microcellular foams were also produced, from composites filled by both calcined and organically functionalized clay. The inclusions from the decomposition of clay provided for the retention of the microcellular structure even after oxidation at 1200 and 1450 °C. Functionalized clay showed a more pronounced effect in limiting the extent of the densification and collapse of microcellular shape than calcined clay. In both cases, the crushing strength after oxidation was found to be particularly remarkable.