The world of electronics continues to prove Moore’s Law wrong, with breakthrough devices getting smaller and smaller. However, to stay on pace with the next generation of precision devices, engineers and developers remain at the mercy of the size of one component: the transistor.
Transistors are one of the main reasons for ICs having a footprint threshold. Hoping to discover alternatives, researchers have ventured into the nanoworld.
Some examples of nanowires that are used in electronic devices. Image used courtesy of Baraban et al
In this article, from 3D nanowire structures to gold-coated, silver nanowires, we shrink down to the nanoscale to investigate the recent research regarding nanowires and their push for flexible, precise, and miniaturized electronics.
Nanowire Architecture: A New Form of Transistor
Before getting too far, a nanowire is a unique structure with a nanoscale diameter and has been a research interest since the early 1990s.
These nanowires can be easily integrated into electronic, thermoelectricity, photovoltaic, mechanic, and optical applications. Research has shown that nanowire architectures can deliver large amounts of power thanks to the energy density. Take this recent announcement from the Norwegian University of Science and Technology (NTNU) that claims to improve solar cells using nanowires.
Another place of research comes from the Swiss Federal Institute of Technology Lausanne (EPFL) in Switzerland. EPFL is widely known for being one of the world’s most prominent natural sciences and engineering research universities.
Within the university is the institute of technology where scientist, Valerio Piazza, leads the Laboratory of Semiconductor Materials. This lab focuses on semiconductors on a nanoscale and has recently shared the news about creating new 3D architectures built from a new nanowire form.
A view at atomic levels of a network of vertical and horizontal nanowires with unique patterns to enhance the electrical performance of a device. Image used courtesy of EPFL
Piazza and his colleagues have written a couple of articles exploring nanowires further by etching nanoconductors on substrate surfaces to create different patterns.
These horizontal nanowires are comprised of group III and V atoms: gallium, aluminum, indium, nitrogen, phosphorus, and arsenic, which help make up a network of electrical current.
However, what stands in the way of commercial device scalability with nanowires revolve around the trade-offs between material properties and the desired device requirements.
The 3D geometry of nanowires, doping variations of the electrical junctions is changed when exposed to certain instances such as external heat, light, or moisture. This challenge is why their research on doping challenges discusses alternative methods that suggest a core shell-like coating could cover the nanowire structure to ensure the electrical properties do not diminish over time.
Despite the amount of research done by this team, more research is still required since the 3D architecture hasn’t narrowed in on a specific method that will lead to the best cost-effective route for semiconductor manufacturers.
However, the promising news is that Piazza’s horizontal nanowires can match the 10 nm footprint of current transistors, but the nanowire structure could yield an overall better electrical performance.
Along with this discovery, Piazza received recognition and funding from the 2020 Piaget Scientific award to help “move transistors beyond their saturation point” using nanowires and nanostructures.
Along with EPFL’s research into nanowire technology, another batch of researchers from the Terasaki Institute for Biomedical Innovation (TIBI) are also trying to find innovative ways to improve nanowire technology.
Researchers Develop Silver Nanowires with a Gold-Coated Shell
Precision devices are a technology that requires high-resolution scanning probe microscopes for clear visualization of surfaces at an atomic level.
These devices are commonly used in specific sensors for touch screen handhelds and in wearable biosensors that monitor chemical levels in our blood, muscle movement, breathing, and pulse rate.
The conventional method for creating these precision devices involves gathering electrodes that have applied thin coatings of conductive materials onto glass or ceramic substrates. This method leaves the electrode fragile and inflexible, making it difficult to fabricate.
The appeal of nanowires comes from many reasons, such as conductivity, stability, and flexibility. Unique characteristics of nanowires are that the diameter is one-thousandth of a millimeter and the malleability of the structure in various cross-sectional shapes. Add higher conductivity, and nanowires are now a potentially better option for flexible electronics and precision devices.
Gold-coated nanowires have yielded high results for high-resolution scanning images. Image used courtesy of TIBI
Nanowires haven’t fully made their way into commercial usage due to being at risk of corrosion brought on by heat, light, and moisture. This corrosion can occur in the etching of the nanowire surface, impacting the electrical, mechanical, and optical properties, causing a meltdown of the structure.
The idea to add a protective shell around the wire has been suggested by TIBI researchers, an ultrathin shell around silver nanowires to improve stability and prevent corrosion.
The research team chose gold as a shell since it can handle heat, light, and moisture. However, placing gold on silver nanowires creates potential problems when charged gold atoms react to silver and cause pores in the structure. To combat this, TIBI scientists found that optimized chemicals can interact with the charged gold atoms to suppress any holes or pores from forming.
The first author of TIBI’s nanowire project, Yangzhi Zhu, Ph.D. expressed comfort in knowing the team of researchers had addressed the main challenges that nanowire structures encounter. He mentions that they tried to consider as many possible challenges that face nanowires. This focus on mitigating errors, they hope, would help with designing an efficient method to increase the durability of silver nanowire-based devices.
TIBI continued to run experiments of silver uncoated nanowires and gold-coated nanowires when exposed to air, which resulted in the uncoated nanowires being damaged within a few days while the gold-coated nanowires prevailed for six months.
Though these are just two recent research ventures, the world of nanowires is still keeping the ball rolling towards finding better ways to become commercialized. It will be interesting to see how much further this technology advances and if it can finally take stronger steps out of research and into real-world applications.
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