Amorphous Silicon Carbide is Ten Times Stronger Than Kevlar and Great to Microchips

Researchers at Delft University of Technology, led by assistant professor Richard Norte, have unveiled a remarkable new material with potential to impact the world of material science: amorphous silicon carbide (a-SiC). Beyond its exceptional strength, this material demonstrates mechanical properties crucial for vibration isolation on a microchip. Amorphous silicon carbide is therefore particularly suitable for making ultra-sensitive microchip sensors.

Amorphous silicon carbide boasts a yield strength 10 times greater than Kevlar, renowned for its use in bulletproof vests. IF you could make duct tape out of Amorphous silicon carbide you would need to hang about ten medium-sized cars end-to-end off that strip before it breaks.

The range of potential applications is vast. From ultra-sensitive microchip sensors and advanced solar cells, to pioneering space exploration and DNA sequencing technologies. The advantages of this material’s strength combined with its scalability make it exceptionally promising.

Nanostrings of Amorphous Silicon Carbide

The researchers adopted an innovative method to test this material’s tensile strength. Instead of traditional methods that might introduce inaccuracies from the way the material is anchored, they turned to microchip technology. By growing the films of amorphous silicon carbide on a silicon substrate and suspending them, they leveraged the geometry of the nanostrings to induce high tensile forces. By fabricating many such structures with increasing tensile forces, they meticulously observed the point of breakage. This microchip-based approach not only ensures unprecedented precision but also paves the way for future material testing.

Why the focus on nanostrings? “Nanostrings are fundamental building blocks, the very foundation that can be used to construct more intricate suspended structures. Demonstrating high yield strength in a nanostring translates to showcasing strength in its most elemental form.”

From micro to macro
And what finally sets this material apart is its scalability. Graphene, a single layer of carbon atoms, is known for its impressive strength but is challenging to produce in large quantities. Diamonds, though immensely strong, are either rare in nature or costly to synthesize. Amorphous silicon carbide, on the other hand, can be produced at wafer scales, offering large sheets of this incredibly robust material.

“With amorphous silicon carbide’s emergence, we’re poised at the threshold of microchip research brimming with technological possibilities,” concludes Norte.

Advanced Materials – High-Strength Amorphous Silicon Carbide for Nanomechanics

Abstract
For decades, mechanical resonators with high sensitivity have been realized using thin-film materials under high tensile loads. Although there are remarkable strides in achieving low-dissipation mechanical sensors by utilizing high tensile stress, the performance of even the best strategy is limited by the tensile fracture strength of the resonator materials. In this study, a wafer-scale amorphous thin film is uncovered, which has the highest ultimate tensile strength ever measured for a nanostructured amorphous material. This silicon carbide (SiC) material exhibits an ultimate tensile strength of over 10 GPa, reaching the regime reserved for strong crystalline materials and approaching levels experimentally shown in graphene nanoribbons. Amorphous SiC strings with high aspect ratios are fabricated, with mechanical modes exceeding quality factors 108 at room temperature, the highest value achieves among SiC resonators. These performances are demonstrated faithfully after characterizing the mechanical properties of the thin film using the resonance behaviors of free-standing resonators. This robust thin-film material has significant potential for applications in nanomechanical sensors, solar cells, biological applications, space exploration, and other areas requiring strength and stability in dynamic environments. The findings of this study open up new possibilities for the use of amorphous thin-film materials in high-performance applications.

Introduction
Advances in nanotechnology have revolutionized various fields, with the development of tensile-loaded, thin-film mechanical devices playing a pivotal role in state-of-the-art force, acceleration, and displacement sensing. Two approaches are used to boost the sensitivity of nanomechanical resonators under tensile loads. One approach fabricates the resonators using different materials in pursuit of films with inherent high-stress and low mechanical loss tangents (i.e high mechanical quality factors). In room temperature environments, high-tensile amorphous silicon nitride (a-Si3N4) nanomechanical resonators have marked some of the best performing devices in ultrasensitive mechanical detectors. Crystalline thin film materials (e.g. crystalline silicon (c-Si), crystalline silicon carbide (c-SiC)) and graphene are expected to have higher theoretical limits, but their projected performance relies on having perfect crystal structures with no defects (including edge defects). Additionally, it is difficult to attain crystalline films that can be easily deposited, have good film isotropy, and few lattice imperfections.

The other approach to boost sensor performance involves innovative resonator designs that concentrate stress in key areas. These designs are constrained by the thin film materials’ tensile fracture limits or ultimate tensile strength (UTS). Nanostructuring reduces the UTS due to introduced crystalline defects. For example, the UTS of a-Si3N4 thin film has been shown to be 6.8 GPa. To date, only crystalline and 2D materials have experimentally demonstrated UTS surpassing 10 GPa after being top-down nanofabricated. Among 2D crystalline materials, graphene harbors one of the highest theoretical UTS, but practically reaching the limit is also challenging due to lattice imperfections, atomically irregular edges, or sparser grain boundaries resulting from nanostructuring processes, which lead to a reduced fracture limit when it is tensile-loaded. In this regard, amorphous thin films with high UTS offer more design freedom for free-standing nanostructures, due to their lack of both crystalline defects and sensitivity to notches. Apart from allowing the enhancement of the Q factor of nanomechanical resonators, higher material UTS can enable the devices to perform better in diverse and harsh vibrational environments.

Amorphous SiC (a-SiC) thin film is gaining traction due to its remarkable mechanical strength and versatile properties. It holds unique advantages over its crystalline counterparts, such as lower deposition temperature and adaptability to various substrates, enabling deposition on large wafer scales. This material stands out in applications requiring protective coatings and in the development of MEMS sensors and integrated photonics, due to its resilience to mechanical wear and chemical corrosion. Its potential in high-yield production of diverse devices paves the way for advancements in sensing and quantum technology.

Delft researchers demonstrate wafer-scale amorphous films that harbor an ultimate tensile strength over 10 GPa after nanostructuring, a regime that is conventionally reserved for ultrastrong crystalline and 2D materials. Using delicate nanofabrication techniques, we produce several different nanomechanical resonators that can accurately determine the mechanical properties of SiC thin films such as density, Young’s modulus, Poisson ratio, and ultimate tensile strength. Notably, our highest measured tensile strength (>10 GPa) is comparable to the values shown for c-SiC and approaching the experimental values obtained for double-clamped graphene nanoribbon. They achieve mechanical quality factor up to 2 × 10^8 with a-SiC mechanical resonators, and measure loss-tangents on par with other materials used in high-precision sensors. Beyond sensing, these strong films open up new possibilities in high-performance nanotechnology, including thin solar cell technologies, mechanical sensing, biological technologies and even lightsail space exploration.