We consume portable electronics at an alarming rate in the pursuit of having the newest gadgets at our fingertips. Electronic devices become outdated at an increasingly fast pace—so much so that discarded laptops, mobile phones, and electronic goods are becoming the world’s biggest waste problem. Global electronic waste (e-waste) is predicted to hit 49.8 million tonnes this year. In fact, it’s been reported that only 20% of e-waste is documented to be properly collected and recycled. As the waste is non-renewable and non-biodegradable, it equates to a massive problem. To add to the sheer volume, most of the waste is toxic, and the electronic waste heaps are constantly leaking dangerous levels of toxic chemicals into the environment.
The obvious solution might be to try to improve how e-waste is disposed of and to increase the number of components that are recycled. However, scientists at the University of Wisconsin-Madison, alongside researchers in the U.S. Department of Agriculture Forest Products Laboratory (FPL), have discovered a surprising solution by producing a wooden semiconductor chip that is almost entirely biodegradable.
How Are Biodegradable Computer Chips Made?
Computer chips are sophisticated devices that form the brains behind our prototypes and project—they can include up to 30 layers of complex circuitry. In conventional chip manufacturing, electronic components like transistors are made on the surface of a rigid wafer comprised of semiconducting materials like silicon. The silicon is purified, melted, and cooled to form an ingot, which is then sliced into discs called wafers. The chips use petroleum-based polymers for their substrates. These polymers are non-biodegradable, depend on non-renewable resources for support, contain toxic compounds, and aren’t flexible.
The interesting thing about the current production method of chips is that the majority of the material is support. Zengiang Ma from the University of Wisconsin-Madison, the team responsible for creating the new chips, stated that less than a couple of micrometres is needed for everything else. This is what led to the search for a replacement support layer, or substrate, within the computer chip. However, the difficulty was producing a smooth-enough surface that also had the capacity for thermal expansion. The final product evolved from the concept of breaking wood down further from individual fibre, at the micron stage, to the nanoscale. The result is a material which is very strong, transparent, flexible, and, most-importantly, biodegradable—cellulose nanofibril (CNF). An epoxy coating is added to the surface to ensure a smooth layer and eliminate the hydroscopic nature, both of which were previously barriers for using wood-derived materials.
The support layer is made by adding water to cellulose-containing materials using high-pressure homogenisers or microfluidisers to reduce the fibres to the nanoscale. The gel that is produced is freeze-dried to remove water and leave the long interconnected nanofibers. The devices undergo protective anchor patterning using photoresist, and the underlying sacrificial layer is etched away using diluted hydrofluoric acid. This protects the devices and allows them to be tethered to the support layer. Other than this, the electronic components in the CNF chips are made in the same way as traditional types, but they are lifted from the wafer using a rubber stamp and transferred across to the CNF.
How Good Is the Performance Of Biodegradable Computer Chips?
An obvious concern of the use of green flexible electronics is their performance. The work carried out by the team at Wisconsin-Madison has demonstrated that the replacement substrate is efficient for use in high-performing radio frequency circuits. This is especially relevant for microwave chips made with gallium arsenide, as it is especially difficult to fabricate on foreign substances. Key findings regarding performance include:
- The replacement support layer reduces the amount of semiconducting material required by a factor up to 5000, without sacrificing performance.
- The CNF didn’t undergo any electrical breakdown, even at high voltages of up to 1,100 V, which is beyond what is required for consumer electronics.
- The dielectric constant was similar to that of polyester films, but the biodegradable properties of CNF easily make it the superior product.
- A decay of current was observed at increasing voltages due to the comparably low thermal conductivity of CNF, but not to the point of affecting the practical usage for amplifiers in mobile devices with cellular frequencies of around 800 to 2500 MHz.
In summary, the study demonstrated that high-performance flexible microwave and digital electronics could be produced using CNF. These circuits perform similarly to those traditionally used in technology such as smartphones and tablets. There is also an opportunity to increase performance in certain areas by, for example, including materials with high thermal conductivities such as boron nitride.
Will Biodegradable Chips Be Used in Mainstream Technology Production?
As the production method demonstrated uses only the smallest amount of toxic materials, the use of the biodegradable CNF could make a massive environmental impact if it were widely used. The chips are so safe that they would be naturally degraded by fungus if they were left in a forest.
However, it will likely take further pressure for this to happen, as it is difficult for an industry to change its existing practices without incentives, increased costs, or penalties. Currently, mass-production of toxic semiconductor chips is cheap and accessible. If the rare semiconductor materials, such as gallium, increase in price, this would likely force a change.
Another potential driver for the use of CNF or a change in production may come from the military. Certainly, having transient electronics that degrade and thereby protect sensitive information would have some serious benefits. However, the most significant change has to be driven by the overall environmental benefits.
The trend for constantly changing electronic devices shows no signs of slowing down, and the problem of e-waste isn’t going anywhere. There are many initiatives in place to try to isolate valuable parts, extend the life of various components and find low-cost ways to automate recycling of our technical gadgets. However, if we could reduce the waste at the source and not chance so much toxic waste ending up in a landfill, wouldn’t the world be a better place? If biodegradable computer chips could become the first step in the mainstream adoption of environmentally friendly electronic materials, then we could have a chance to vastly reduce the volume of e-waste and its environmental impact.