Reviewed by Lexie CornerDec 3 2024
In a study published in Materials Horizons, researchers at North Carolina State University developed a new method for self-assembling electronic devices. The proof-of-concept work produced diodes and transistors, demonstrating the potential for self-assembly of more complex electronic devices without relying on traditional computer chip manufacturing processes.
D-Met fabricated patterns produce components for potential use in microelectromechanical systems (MEMS). Image Credit: Julia Chang
Existing chip manufacturing techniques involve many steps and rely on extremely complex technologies, making the process costly and time-consuming. 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.
Martin Thuo, Study Corresponding Author and Professor, North Carolina State University
Thuo added, “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.”
Thuo refers to the novel self-assembling method as a directed metal-ligand (D-Met) reaction. This is how it operates.
The process begins with liquid metal particles. For proof-of-concept experiments, the researchers used Field’s metal, an alloy of indium, bismuth, and tin. These liquid metal particles are placed near a mold, which can be customized to any size or pattern. A solution is then poured over the liquid metal.
The solution contains ligands, molecules made of carbon and oxygen. These ligands attract ions from the liquid metal’s surface and organize them into a precise geometric pattern. As the solution fills the mold, the ion-bearing ligands begin to self-assemble into more complex, three-dimensional structures. As the liquid part of the solution evaporates, these structures become packed more closely together.
“Without the mold, these structures can form somewhat chaotic patterns. But because the solution is constrained by the mold, the structures form in predictable, symmetrical arrays,” Thuo added.
When a structure reaches the proper size, the mold is removed and the array heated. This heat degrades the ligands, releasing carbon and oxygen atoms. Metal ions combine with oxygen to make semiconductor metal oxides, whereas carbon atoms form graphene sheets. These ingredients form a well-organized structure composed of semiconductor metal oxide molecules wrapped in graphene sheets. The researchers employed this method to make nanoscale and microscale transistors and diodes.
The graphene sheets can be used to tune the bandgap of the semiconductors, making the semiconductor more or less responsive, depending on the quality of the graphene.
Julia Chang, Study First Author and Postdoctoral Researcher, North Carolina State University
By using bismuth during the proof-of-concept phase, the researchers were able to create photo-responsive structures. This allows for the modification of semiconductor properties using light.
“The nature of the D-Met technique means you can make these materials on a large scale – you’re only limited by the size of the mold you use. You can also control the semiconductor structures by manipulating the type of liquid used in the solution, the dimensions of the mold, and the rate of evaporation for the solution,” Thuo noted.
“In short, we have shown that we can self-assemble highly structured, highly tunable electronic materials for use in functional electronic devices. This work demonstrated the creation of transistors and diodes. The next step is to use this technique to make more complex devices, such as three-dimensional chips.”
The study’s first author is Julia Chang, a postdoctoral researcher at NC State. It was co-authored by Andrew Martin, a postdoctoral researcher at NC State; Alana Pauls and Dhanush Jamadgni, Ph.D. students at NC State; and Chuanshen Du, Le Wei, Thomas Ward, and Meng Lu from Iowa State University.
Chang, Martin, and Thuo are pursuing a patent for their D-Met findings. Chang, Ward, and Du have a separate patent pending for their D-Met study.
The study received funding from the National Science Foundation's Center for Complex Particle Systems under grant 2243104.
Journal Reference:
Chang, J. J. et. al. (2024) Guided Ad infinitum Assembly of Mixed-Metal Oxide Arrays from Liquid Metal. Materials Horizons. doi.org/10.1039/D4MH01177E