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Many substrates for microelectronic systems contain ceramic/glass layers and metal features (e.g. electrodes, vias, metal pads) built up in a complex 3D architecture. The combination of different materials with distinct thermo-elastic properties may yield significant (local) internal stresses, which are to be superimposed to external thermo-mechanical loads in service. Due to the various material junctions, interfaces, etc, failure of these multilayer systems can hardly be predicted. In this work, a strategy is proposed to quantify the effect of architecture and loading conditions on the mechanical reliability of ceramic-based substrates. Model ceramic structures containing important design features (e.g. inner electrode, via, top metallization) were fabricated and tested in different environments (i.e. humid or dry conditions) under uniaxial as well as biaxial bending. Significant difference in the characteristic strength between ∼260 MPa and ∼620 MPa were measured, associated with the particular architectural feature, type of loading, and/or environment.

[EN] The processing and characterization of laminates based on TiAlC MAX phase, as matrix, and triaxial alumina braids, as reinforcing phase, are presented. TiAlC powders with a mean particle size below 1 µm are synthesized, while commercial 3M Nextel 610 alumina fibers are braided in a three-stage process consisting of spooling, braiding with an angle of 0° and ±60° and the separation to single-layer fabric. The laminates are processed by layer-by-layer stacking, where 3 two-dimensional alumina braids are interleaved between TiAlC layers, followed by full densification using a Field-Assisted Sintering Technology/Spark Plasma Sintering. The multifunctional response of the laminates, as well as for the monolithic TiAlC, is evaluated, in particular, the thermal and electrical conductivity, the oxidation resistance, and the mechanical response. The laminates exhibit an anisotropic thermal and electrical behavior, and an excellent oxidation resistance at 1200℃ in air for a week. A relatively lower characteristic biaxial strength and Weibull modulus (i.e., σ = 590 MPa and m = 9) for the laminate compared to the high values measured in the monolithic TiAlC (i.e., σ = 790 MPa and m = 29) indicates the need but also the potential of optimizing MAX-phase layered structures for multifunctional performance., Germany’s Federal Ministry of Education and Research (“Bundesministerium für Bildung und Forschung”), Grant/Award Number: 03SF0534; Spanish Ministry of Science and Innovation (MICINN/AEI) and FEDER (UE), Grant/Award Number: RTI2018- 095052- BI00; European Research Council (ERC), Grant/Award Number: 817615

In this work we demonstrate the feasibility of fabricating textured alumina employing a lithography-based ceramic manufacturing process. The combination of vat rotation and platform immersion contributes to the alignment of alumina templates during printing. Templated Grain Growth during sintering provides a high degree of texture (Lotgering Factor ​~ ​0.80) with relatively low porosity (approx. 7%). A comparable characteristic biaxial strength of 640 ​MPa and 570 ​MPa was measured for textured and equiaxed alumina samples, opening the path for 3D printing textured ceramics of complex architectures for structural and functional applications.

The strength distribution and fracture behaviour of miniaturized Lithium niobate (LiNbO 3 ) and Lithium tantalate (LiTaO 3 ) single crystals were assessed under biaxial bending. The susceptibility of these materials to environmental assisted cracking (SCCG) was studied by means of constant cross-head displacement rate experiments in air and in water. Two different sample sizes were tested and compared to assess the Weibull volume effect. Experimental results showed a significant difference in strength, LiNbO 3 being weaker than LiTaO 3 . No apparent SCCG and no volume effect on strength were found. A different distribution to Weibull behaviour was observed in LiNbO 3 . Fractography showed differences in the fracture patterns, due to the different cutting orientation of the two investigated materials with respect to the loading plane. New cleavage planes were identified as {10.1} for LiNbO 3 and {1 2 ¯ .3} for LiTaO 3 . Fracture surfaces of LiNbO 3 revealed surface damage, which may be responsible for the lower strength compared to LiTaO 3 .

Free-standing Li1.5Al0.5Ti1.5P3O12 electrolyte sheets with a thickness of 50–150 μm were prepared by tape casting followed by sintering at 850–1000 °C in air. While a sintering temperature of 850 °C was too low to achieve appreciable densification and grain growth, a peak relative density of 95% was obtained at 920 °C. At higher sintering temperatures, the microstructure changed from a bimodal grain size distribution towards exclusively large grains (> 10 μm), accompanied by a decrease in relative density (down to 86% at 1000 °C). In contrast, ionic conductivity increased with increasing sintering temperature, from 0.1 mS/cm at 920 °C to 0.3 mS/cm at 1000 °C. Sintering behavior was improved by adding 1.5% of amorphous silica to the slurry. In this way, almost full densification (99.8%) and an ionic conductivity of 0.2 mS/cm was achieved at 920 °C. Mechanical characterization was carried out on the almost fully densified material, yielding elastic modulus and hardness values of 109 and 8.7 GPa, respectively. The fracture strength and Weibull modulus were also characterized. The results confirm that densification and reduction of grain size improve the mechanical properties.

This work demonstrates the use of additive manufacturing to design and fabricate alumina ceramics with strength as high as 1 ​GPa. A multi-material approach is employed by embedding alumina-zirconia layers between outer pure alumina layers with significant compressive residual stresses. Biaxial bending is performed both on the 3D printed multi-material and monolithic alumina parts. Results are analysed in the framework of Weibull statistics. A characteristic biaxial strength higher than 1 ​GPa is measured on the multilayers, compared to 650 ​MPa in monolithic alumina, the difference corresponding to the magnitude of compressive residual stresses due to the thermal mismatch between material regions during cooling from sintering. This is the first report of employing additive manufacturing to tailor the strength of alumina ceramics, taking advantage of the layer-by-layer printing process. Designing complex-shaped ceramic architectures with residual stresses through additive manufacturing opens a new path for fabrication of technical ceramics with tailored mechanical properties.