Manufacture of Biodegradable Electronic Sensors Systems using Additive Manufacturing

The world’s ever-increasing demand for high performance electronics will inevitably result in a growing problem of waste as products reach the end of their lifetimes. The “tsunami of electronic waste” (e-Waste), which reached more than 53.6 million tonnes in 2019, requires a step-change in the design and fabrication of electronics for disposal, reuse or recycling. The issue is exasperated as during the manufacture of electronics, a significant amount of chemical waste is generated as by-products, and the combined impact of by- and end-products is leading to long term environmental and social damage that will outlast many generations. As electronics underpins a lot of future ICT including smart packaging, internet of things (IoT), displays (inc. VR/XR), smart packaging), the e-Waste issue needs to be resolved by realising electronic systems that inherently have end-of-life (cradle to cradle) solutions built in and thus do not require the same complexity of waste management. To this end, this challenge requires a new approach in the manufacture of electronic devices that emphasises low material use and makes end-of life recycling and disposal as simple and environmentally friendly as possible, while also keeping up with the difficult performance metrics required for operating modern devices.<br/><br/>The use of biodegradable materials is on the rise as practical difficulties related to e-waste requires greater attention. A large proportion of a Printed Circuit Board Assembly (PCBA), goes directly to landfill or incineration. It is feasible to recycle PCBAs as shown in several papers and there are many businesses recycling of e-waste. However, it is not a straightforward process. Consequently, the use of electronic materials that are more easily repurposed or recycled are being considered for future electronic systems. Most academic work on such electronics so far has focused on metal oxide or organic semiconductors, however, the modest performance offered by such materials, would not satisfy the demands of current consumer electronics.<br/><br/>In this talk, we will report on the development of new manufacturing platforms that offer a viable alternative to conventional silicon-based devices. Firstly, we have demonstrated fully biodegradable thin-film transistors (TFTs) arrays of up to 200 TFTs based on zinc oxide (ZnO) active layer using molybdenum (Mo) source, drain, and gate electrodes. The developed TFTs show a low positive threshold Voltage, a high average field-effect mobility in the saturation region and show stable device performance under stability tests. These have been used to make logic circuits (inverter and both NAND and NOR gate circuits) and simple memory devices such as SRAM cells. However, as mentioned, the performance is limited by the semiconductor, so a new additive manufacturing technique based on inkjet printing and hybrid ultrathin silicon and metal oxide devices is demonstrated and we show that the biodegradable devices and circuits can match conventional circuit boards on key metrics such as switching speed, level of integration and power consumption. We demonstrate the effectiveness of this process by producing a flexible and biodegradable Integrated circuits and use this to power a sensor array for agricultural applications for measuring pH and temperature.<br/><br/>Finally, we perform a detailed life cycle assessment of devices made using this method and compare their environmental impact to conventional ICs and PCBAs. We find that the reductions in material use and minimised end-of-life footprint can more than offset the costs associated with the increased complexity of manufacturing required by our process. We hope these results will show the potential of how new approaches in device production can greatly enhance the sustainability of electronic products.