https://newatlas.com/manufacturing/self-assembling-electronics/ [newatlas.com]
A remarkable proof-of-concept project has successfully manufactured nanoscale diodes and transistors using a fast, cheap new production technique in which liquid metal is directed to self-assemble into precise 3D structures.
In a peer-reviewed study due to be released in the journal Materials Horizons, a North Carolina State University team outlined and demonstrated the new method using an alloy of indium, bismuth and tin, known as Field's metal.
The liquid metal was placed beside a mold, which the researchers say can be made in any size or shape. As it's exposed to oxygen, a thin oxide layer forms on the surface of the metal. Then, a liquid is poured onto it, containing negatively-charged ligand molecules designed to pull individual metal atoms off that oxide layer as positively-charged ions, and bind with them.
These metal ions held in the ligands become a little like magnetic building blocks, attracted to one another, and as the ligand solution begins to flow through channels in the mold, driven by capillary action, it pulls these building blocks through with it. The mold essentially gets the blocks to line up into orderly structures, like wires, and stick to each other in place.
“Without the mold, these structures can form somewhat chaotic patterns,” says Martin Thuo, corresponding author and professor of materials science and engineering at North Carolina State University. “But because the solution is constrained by the mold, the structures form in predictable, symmetrical arrays.”
Once everything is in place, the liquid part of the ligand solution begins to evaporate, which has the effect of squeezing the ligands and metal ions even closer together in their channels. Then the mold is taken away, and the final shape is slowly heated to around 600 °C (1,112 °F) and kept there for an hour.
This heating process supplies enough energy to break the chemical bonds holding the ligand molecules together, so carbon and oxygen atoms are released.
The oxygen immediately bonds to the metal ions, forming semiconductor metal oxides that fuse together with one another in a sintering process to form wires. The carbon atoms, meanwhile, organize themselves into graphene, which wraps neatly around the wires to improve their electrical conductivity, protecting them from moisture or further oxidation.
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The team says the technique offers a faster, cheaper, more reliable way of making computer chips. “Existing chip manufacturing techniques involve many steps and rely on extremely complex technologies, making the process costly and time consuming,” says Thuo. “Our self-assembling approach is significantly faster and less expensive. We’ve also demonstrated that we can use the process to tune the bandgap for semiconductor materials and to make the materials responsive to light – meaning this technique can be used to create optoelectronic devices.
“What’s more, current manufacturing techniques have low yield, meaning they produce a relatively large number of faulty chips that can’t be used. Our approach is high yield – meaning you get more consistent production of arrays and less waste.”