Nav: Home

Surprisingly strong and deformable silicon

June 10, 2020

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. Their results have recently been published in the scientific journal Nature Communications.

Ten-year effort

"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.

Striking results

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.
-end-
Youtube clip https://youtu.be/o4ufjHpJ64s

Reference

Chen, M., Pethö, L., Sologubenko, A.S. et al. Achieving micron-scale plasticity and theoretical strength in Silicon. Nat Commun 11, 2681 (2020).

ETH Zurich

Related Silicon Articles:

Single photons from a silicon chip
Quantum technology holds great promise: Quantum computers are expected to revolutionize database searches, AI systems, and computational simulations.
For solar boom, scrap silicon for this promising mineral
Cornell University engineers have found that photovoltaic wafers in solar panels with all-perovskite structures outperform photovoltaic cells made from state-of-the-art crystalline silicon, as well as perovskite-silicon tandem cells, which are stacked pancake-style cells that absorb light better.
Surprisingly strong and deformable silicon
Researchers at ETH have shown that tiny objects can be made from silicon that are much more deformable and stronger than previously thought.
A leap in using silicon for battery anodes
Scientists have come up with a novel way to use silicon as an energy storage ingredient.
Flexible thinking on silicon solar cells
Combining silicon with a highly elastic polymer backing produces solar cells that have record-breaking stretchability and high efficiency.
No storm in a teacup -- it's a cyclone on a silicon chip
University of Queensland researchers have combined quantum liquids and silicon-chip technology to study turbulence for the first time, opening the door to new navigation technologies and improved understanding of the turbulent dynamics of cyclones and other extreme weather.
Black silicon can help detect explosives
Scientists from Far Eastern Federal University (FEFU), Far Eastern Branch of the Russian Academy of Sciences, Swinburne University of Technology, and Melbourne Center for Nanofabrication developed an ultrasensitive detector based on black silicon.
2D antimony holds promise for post-silicon electronics
Researchers in the Cockrell School of Engineering are searching for alternative materials to silicon with semiconducting properties that could form the basis for an alternative chip.
Silicon technology boost with graphene and 2D materials
In a review published in Nature, ICFO researchers and collaborators report on the current state, challenges, opportunities of graphene and 2D material integration in Silicon technology.
Light and sound in silicon chips: The slower the better
Acoustics is a missing dimension in silicon chips because acoustics can complete specific tasks that are difficult to do with electronics and optics alone.
More Silicon News and Silicon Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.