Surprisingly strong and deformable silicon
The strength of lithographically produced silicon pillars even reached values that one would only expect only in theory
Laszlo Pethö / Empa
Since the invention of the MOSFET transistor sixty year ago, the chemical element silicon on which it is based has become an integral part of modern life. It ushered in the computer age, and by now the MOSFET has become the most produced device in history. Silicon is readily available, cheap, and has ideal electrical properties, but also one important drawback: it is very brittle and, therefore, breaks easily. This can become a problem when trying to make micro-electro-mechanical systems (MEMS) from silicon, such as the acceleration sensors in modern smartphones.
At ETH in Zurich, a team led by Jeff Wheeler, Senior Scientist at the Laboratory for Nanometallurgy, together with colleagues at the Laboratory for Mechanics of Materials and Nanostructures at Empa, has shown that, under certain conditions, silicon can be much stronger and more deformable than was previously thought.
“This is the result of a ten-year effort”, says Wheeler, who worked as a researcher at Empa prior to his career at ETH. To understand how tiny silicon structures can deform, within the framework of an SNF project, he took a closer look at a widely used production method: the focused ion beam. Such a beam of charged particles can mill desired shapes into a silicon wafer very effectively, but in doing so leaves behind distinct traces in the form of surface damage and defects, which cause the material to break more easily.
Lithography with final cleaning
Wheeler and his collaborators had the idea to try a particular type of lithography as an alternative to the ion beam method. “First, we produce the desired structures – tiny pillars in our case – by etching away un-masked material from the areas of the silicon surface using a gas plasma”, explains Ming Chen, a former PhD student in Wheeler’s group. In a further step, the surface of the pillars, some of which are narrower than a hundred nanometres, are first oxidized and then cleaned by completely removing the oxide layer with a strong acid.
Chen then studied the strength and plastic deformability of silicon pillars of different widths with an electron microscope and compared the two production methods. To that end, he pressed a tiny diamond punch into the pillars and studied their deformation behaviour in the electron microscope.
The results were striking: the pillars that had been milled with an ion beam collapsed at a width of less than half a micrometre. By contrast, the pillars produced by lithography only suffered brittle fractures at widths above four micrometres, while thinner pillars were able to withstand the strain much better. “These lithographic silicon pillars can deform at sizes ten times greater than what we’ve seen in ion beam-machined silicon with the same crystal orientation, with double the strength!”, Wheeler summarizes the results of his experiments.
The strength of the lithographically produced pillars even reached values that one would only expect only in theory, for ideal crystals. What makes the difference here, says Wheeler, is the absolute purity of the surfaces of the pillars, which is achieved by the final cleaning step. This results in a much smaller number of surface defects from which a fracture could originate. With the assistance of Alla Sologubenko, a researcher with the microscopy centre ScopeM at ETH, this additional deformability also allowed the team to observe a striking change in deformation mechanisms at smaller sizes. This revealed new details on how silicon can deform.
Applications in smartphones
The results obtained by ETH researchers could have an immediate impact on the fabrication of silicon MEMS, Wheeler says: “In this way, the gyroscopes used in smartphones, which detect rotations of the device, could be made even smaller and more robust.” That shouldn’t be too difficult to realize, given that industry is already using the combination of etching and cleaning Wheeler and his colleagues investigated. The method could also be applied to other materials having crystal structures similar to that of silicon, the researchers believe. Moreover, more elastic silicon could also be used to further improve the electrical properties of the material for certain applications. By applying a large strain of the semiconductor the mobility of its electrons can be increased, which can lead, for instance, to shorter switching times. So far, one had to produce nanowires to achieve that, but now this could be done directly using structures integrated into a semiconductor chip.
Other news from the department science
Blue-green algae sugar instead of glyphosate
Cooperation project develops environmentally friendly glyphosate alternative
Using clay to combat eternal toxins
TU Freiberg clarifies basis for innovative PFAS filter made of clay
Unveiling a new era of imaging: Boston University engineers lead breakthrough microscopy techniques
Researchers made significant advancements in the field of vibrational imaging
Phasing out fossil fuels could save millions of lives
The mortality burden attributable to air pollution from fossil fuel use is considerably higher than most previous estimates - a phaseout of fossil fuels would have tremendous, positive health outcomes
Replicating the structure of bird feathers
The new material could be used in batteries or filtration
Quantum tool opens door to uncharted phenomena
Method can contribute to a better understanding of quantum materials
Recovering instead of shredding: recycling batteries more efficiently
KIT researchers are working with industry to develop a more sustainable recycling process to recycle materials from lithium-ion batteries more effectively
Industry 4.0: No impact on energy consumption?
To what extent does the digitalisation of industrial and manufacturing processes (Industry 4.0) improve energy efficiency and thus reduce energy intensity?
New approach to the sensible utilisation of carbon dioxide from car exhaust gases
"A method has been discovered that uses impure CO2 streams and enables a breakthrough in the synthesis of valuable chemicals and pharmaceuticals"
Boosting PET recycling with higher standards for laboratory experiments
New study shows how enzymatic plastic degradation could be brought one step closer to commercialisation
Innovating Optoelectronic Components with Phosphorus
Significant breakthrough: phosphorus chemists develop new method to selectively introduce phosphorus and nitrogen atoms into polyaromatic systems
Artificial intelligence finds ways to develop new drugs
The chemists tested the process using borylation – a reaction that activates hydrocarbon scaffolds
X-rays reveal how glasses lose their stability
PETRA III experiment shows how atoms in glass behave as weaknesses appear
Most read news
Plastic-eating bacteria turn waste into useful starting materials for other products
Microbial Upcycling of Waste PET
Microbes could help reduce the need for chemical fertilizers
A coating protects nitrogen-fixing bacteria: Start-up to commercialise coated bacteria for large-scale use in regenerative agriculture
New designs for solid-state electrolytes may soon revolutionize the battery industry
Scientists achieve monumental improvements in lithium-metal-chloride solid-state electrolytes
Dow and Evonik announce startup of hydrogen peroxide to propylene glycol (HPPG) pilot plant
Innovative technology offer flexibility, lower costs, and a smaller environmental footprint
Inauguration of the world’s first pilot plant for the cost-efficient production of green methanol
Start-up C1 Green Chemicals AG and research partners develop fundamentally new production process
This is a battery
Two colored liquids bubbling through tubes: Is this what the battery of the future looks like?
Converting PFAS “forever chemicals” into valuable compounds
Scientists develop a new method to incorporate harmful perfluoroalkenes into N-heterocyclic carbene ligands
Not so silver lining: Microplastics found in clouds could affect the weather
Low-altitude and denser clouds contained greater amounts of microplastics
Graphene's proton permeability: A switch for future energy technologies
This discovery could lead to the development of more efficient hydrogen fuel cells and solar water-splitting devices
Lithium-ion batteries are no longer the gold standard in battery tech
On the way to safer and more powerful energy sources
CO2-free hydrogen: BASF receives funding approval for 54-megawatt water electrolysis plant
Proton exchange membrane (PEM) electrolyzer expected to produce up to 8,000 metric tons of hydrogen per year
More news from our other portals
Bowel cancer: aspirin activates protective genes
Researchers have identified a signaling pathway by which aspirin can inhibit colorectal cancer.
Dunning-Kruger effect with muesli bars
Those who know the least consider themselves highly competent
Autonomous measuring instruments systematically detect new materials
A new algorithm measures materials libraries up to four times faster than before: It’s based on machine learning
New drug delivery system could reduce daily diabetes shots to just three a year
Dietary management drugs have transformed Type 2 diabetes care, but daily injection routines are challenging for some patients
Naked Clams: The New Superfood Sensation Emerging from the Depths
Researchers found Naked Clams contain almost twice the amount of Vitamin B12 as blue mussels and have developed an efficient way to farm them
Researchers discover new ultra strong material for microchip sensors
A material that doesn't just rival the strength of diamonds and graphene, but boasts a yield strength 10 times greater than Kevlar
Pushers, overcrowded trains and phone zombies
Sprite presents the world's first vending machine that responds to the things that bother Generation Z the most
Aston University technology to combat the not-so sweet practice of honey fraud
Light technology to be used to detect if honey is blended with cheap additions
How stem cells and immune cells communicate
Lisec Artz Award for Simon Haas: Groundbreaking discovery of an unknown protective mechanism against blood cancer from stem cells
Scientists use quantum biology, AI to sharpen genome editing tool
"This study represents an exciting advancement toward, understanding how we can avoid making costly ‘typos’ in an organism’s genetic code"
From the trough to the plate - digitally calculated
Computer program "ConTrans" estimates how much of an undesirable substance is transferred from animal feed to food
Viral Impostors: Breakthrough for Virus Research
The penetration of viruses into cells can now be tracked with unprecedented accuracy thanks to innovative design for pseudoviruses
Fatty acid factory filmed at work
High-resolution images provide new insights into cellular fatty acid production: Potential for medicine and biotechnology
Textbook knowledge turned on its head: 3-in-1 microorganism discovered
Newly multifunctional bacterial species
Tönnies Group launches first nationwide "Meat Climate Platform"
100 guests at the Future Forum for Agriculture
Tracking down Environmental Toxins
Detection of per- and polyfluoroalkyl substances (PFAS) by interrupted energy transfer
Could eating turkey ease colitis?
According to data in mice, extra tryptophan could reduce the risk of future colitis flares
The weight of pollution: exposure linked to obesity
Chronic exposure to environmental pollutants found to increase risk of cardiovascular disease
Are healthy foods automatically sustainable, too?
Perceptions about sustainability and healthy food choices are closely linked