Within the field of microelectronics, most of the novel innovations that are developed have been driven by Moore’s Law. This relates to the observation made by Gordon Moore in 1965 that the number of transistors in a dense integrated circuit doubles every two years. Ubiquitous silicon semiconductor integrated circuit technology has therefore been driven by this principle for decades. The scaling down of device dimensions allows the manufacture of nearly 60 billion devices onto a single chip, and at a reasonable cost in the economy of scale.

For niche applications that may require richer features, the more-than-Moore philosophy demands advanced functionality to be integrated onto a silicon chip with additional structures, which could be optical, micro-electromechanical, microfluidic or biological. For more than 40 years, the Carl and Emily Fuchs Institute for Microelectronics (CEFIM) in the University of Pretoria’s Faculty of Engineering, Built Environment and Information Technology has been making excellent contributions to the discipline of microelectronics by pursuing research that adheres to the more-than-Moore approach.

As a leader in this field since 1973, CEFIM’s flagship project on additive manufacturing for electronic systems (AMES) aspires to build on the Institute’s four decades of distinction. The quest is to challenge the establishment of electronic system integration strategies that best exploit modern additive manufacturing (3D printing) technologies at the micron scale.

The modern trend of deploying Internet of Things (IoT) at a massive scale creates opportunities in which more-than-Moore research and development are key. Technological innovation at CEFIM aims to develop low-cost, simple and efficient additive manufacturing processes, design techniques and modelling methods and tools that are collectively able to reliably integrate systems.

CEFIM’s team of researchers has identified AMES as an appropriate suite of technologies in the transdisciplinary domains of health, water, wireless communication and climate sciences. It enables the realisation of novel solutions in optical, electrochemical, mm-wave and microfluidic sensor systems that can make an impact on society, while contributing to and competing in the global knowledge ecosystem.

The additive technologies CEFIM currently uses include planar and 2½-D processes, but it is looking forward to the flexible, true 3D conformal printing of fine features with a wide range of materials, potentially moving towards fully printed integrated electronic devices. Expanding the use of materials and processes that facilitate sustainable and responsible production must be investigated as these approaches will contribute to the achievement of sustainable development. CEFIM’s consideration of low-cost, low-volume production technologies is envisaged to enhance scientific research and support domestic manufacturing infrastructure, extending to small-scale industrial enterprises.

Through the additive manufacturing of electronic systems, CEFIM is helping to innovate our tomorrow with more of its more-than-Moore microelectronics.

Case studies

Additive fabrication processes are explored to heterogeneously integrate CEFIM’s custom mixed-signal integrated circuit chips into microsystems. For example, the team is working on integrating complementary metal-oxide semiconductor (CMOS) sensor readout chips into a microfluidics lab-on-chip microsystem implementation on low-cost substrates. A growing demand for inexpensive, rapid, flexible, and easy-to-use point-of-care diagnostics – as exemplified by the COVID-19 pandemic – has resulted in the rapid growth of printed electronics globally.

One such design is a capacitive sensing array as part of a non-flow biosensing microsystem for a whole-cell counting application. A finite element analysis model is also presented to investigate the effects of electrode geometry, cell position and cell interaction on the measured capacitance. The microsystem will be employed for detecting water contamination by bacteria such as E. coli, which is the standard indicator organism of faecal pollution. A collaborative project has also been initiated where bacterial activity is monitored during the remediation processes of wastewater, contributing to the environmentally friendly aspects of a circular economy.

A low-cost microcontroller-based electronic nose (e-nose) was developed using an array of gas sensors and machine learning algorithms. The instrument must be portable and, therefore, battery powered. Equipping the device with IoT capabilities enables valuable distance monitoring. In future, CEFIM will use functional printed electronics to explore the component development of metal-oxide gas sensors for tighter integration and size, weight, and cost efficiency.

An application investigated for the e-nose is in the field of smart agriculture, namely the semi-quantitative monitoring of the Amitraz insecticide concentration in a cattle dip solution. On the one hand, inadequate concentration is ineffective as an insecticide, but on the other, careful concentration control is necessary because tick resistivity against the acaricide is becoming a problem. This device is not only useful at the dipping troughs of affluent farms, but can have a positive impact on rural African agriculture by making the monitoring of plunge dipping tanks accessible to rural farmers.

Another application of additive manufacturing that is addressed at CEFIM is the creation of low-cost, lightweight, high-frequency antenna components for satellite systems. Here, the team has been exploring different methods of creating antenna assemblies using readily accessible stereolithographic resin printing, and plating the finished parts with non-toxic silver and copper processes.

If successful, this process will reduce the production lead time and environmental impact of these critical components, while making them light enough to be launched from low-cost CubeSat platforms. The initial results are extremely promising, with waveguides in the 18–26 GHz frequency range achieving electrical performance comparable to their brass extrusion counterparts.