A Hot Topic
Printed electronics is a field that is most likely going to be responsible for the next wave of technological advancement. While quantum computers look promising and nanofeature transistors are being developed, printed electronics is not only compatible with modern technology but can be applied in many different environments.
For example, current technology does not allow for true wearable electronics as the electronic parts, themselves, are rigid and bulky. Some may argue that this is not the case with a typical example being the Apple watch. However, while such devices are worn, they do not move and bend with the wearer nor are they washable. True wearable electronics would be a device that could be glued or stuck into a piece of material (such as a t-shirt) and then worn without discomfort, behaving in a similar fashion to the material that it is attached to.
Many passive components have already been developed into being printable, including wires, resistors, capacitors, and even inductors. Scientists are even working on flexible semiconductors which could lead to flexible processors and microcontrollers using organic polymers.
A flexible semiconductor. Image credit: (c) Nature (2016). DOI: 10.1038/nature20102
There is, however, one problem with printed electronics. For an electronic circuit to function properly, conductors need to have low resistances.
Currently, nanoparticles of silver can be used on surfaces which are then heated to allow the silver particles to bond and provide a good conductive material. However, this heating means that the substrate which is holding onto the printed material also has to be able to tolerate the heat. Therefore, most common cheap packaging materials such as thin plastic and paper are not suitable for use.
This means that most items in shops cannot have cheap, printed RFID tags and instead need to use the more expensive, sticky pre-made tags.
A Silver Nano Lining
They say every cloud has a silver lining. Well, a team of Researchers from Duke University have a nanowire solution that may allow cheap materials to use printed electronics. The idea is to use silver nanowires instead of silver nanoparticles. They can then use a curing temperature of 70°C (a temperature that most packaging materials can handle).
Types of nanoparticle and wire. Image credit: Ian Stewart
Benjamin Wiley, an assistant chemistry professor at Duke, notes that the nanowires have considerably higher conductivity than do typical printed antennas for RFID tags which use silver nanoparticles—around 4,000 times higher, in fact.
What makes silver nanowires special is their length and the fact that they contain fewer boundaries for electrons to encounter. Flakes and particles typically have a roundish shape and this results in electrons “bumping” into many grain boundaries (which have a much higher resistance than silver). Nanowires, being much longer, result in fewer boundaries which allow electrons to travel a greater distance before encountering resistance from a boundary.
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The printable electronics industry is still in its infancy with niche applications but has a huge potential to change the face of electronics. Printable electronics will allow for entire electronics circuits and designs to be prototyped in hours without the need for a PCB or population line to create the circuit. And if a component printer could be fed with silver nanowire ink, household paper could be fed in as a substrate medium with the result being fully-populated circuits on a piece of paper.
Read more about the research in ACS Applied Materials and Interfaces.