Paragraf develops graphene at commercial grade

Materials World magazine
,
7 Aug 2019

Discs up to 20cm in diameter are being produced by former IOM3 president Colin Humphreys FIMMM.

In 2004, University of Manchester, UK, Researchers Andre Geim and Konstantin Novoselov discovered a carbon monolayer flake produced from graphite using sticky tape. The product, name graphene, was more conductive than copper, flexible, had a tensile strength greater than steel, was 97% transparent and thermally stable. But scale-up has been seemingly elusive – contamination during processing and working with such a small material have posed challenges to product manufacturers. Through a novel method, UK company Paragraf has been able to develop sheets of graphene at up to 20cm, and has attracted interest from investors based in China and Singapore.

High expectations

Billions of US dollars have been invested in the past 10 years to scale-up graphene production. Intel invested a reported US$750mln, Samsung US$2.2bln and IBM US$3bln, all attempting to bring the laboratory results using graphene flakes to the market. Additionally, the UK government funded major centres at several universities to research and develop graphene.

However, despite investment, industry has been unable to find a method to scale-up the flakes into large-area graphene suitable for manufacturing. For example, Bosch claimed its Hall effect magnetic sensor made from graphene flakes was 100 times more sensitive than one made from silicon. But on the back of its release in 2015, Bosch Researcher Robert Roelver said, ‘Graphene-based sensor applications will require 5-10 years before they can compete with established technologies because of the current lack of large-scale, wafer-based and transfer-free synthesis techniques’.

Industry hurdles

There are three main types of graphene that can be purchased commercially. One is small exfoliated graphene flakes, less than 5mm² in area, obtained from graphite using sticky tape or other exfoliation methods. These are high-quality monolayer graphene layers that are excellent for laboratory-scale experiments. Another is dispersions and solutions of graphene powders and flakes. These have been found to improve the performance of composite materials, car tyres, running shoes and paint.

The third is large area, up to 12cm diameter, sheets of graphene produced by chemical vapour deposition (CVD). The CVD process uses a metal substrate, usually copper, as a catalyst to decompose the growth gases used, and place the graphene onto the desired substrate, for example silicon. Unfortunately, this results in copper atoms being incorporated in the graphene. It then needs to be removed from the metal substrate using, for example, iron chloride, resulting in further contamination with iron as well as copper. This contamination is highly undesirable in electronic device manufacturing.

Problem solving

In 2004, I ran the Cambridge Centre for Gallium Nitride (GaN), researching materials and devices based on GaN at the University of Cambridge, UK, Department of Materials Science and Metallurgy. The centre avoided working on graphene because of the hype and large number of scientists researching graphene worldwide.

In 2015, a centre project began on a graphene-GaN tunnel transistor, in partnership with Novoselov. The project failed because of the difficulty in making a transistor by hand using small and invisible graphene flakes. In the same year, Post Doctoral Research Assistant Simon Thomas joined the GaN research group to work on GaN electronic devices, funded by an Engineering and Physical Sciences Research Council (EPSRC) grant. He thought of a new way to make large-area graphene, which did not involve metal catalysts and was transfer free, being produced directly on substrates such as sapphire and silicon. Thomas and the centre’s Post Doctoral Research Assistant Ivor Guiney worked in the university’s Materials Science Department to develop the new graphene method.

Introducing Paragraf

Patents were filed on the new growth method and its applications, and Thomas, Guiney and I founded spin-out company Paragraf. The venture received seed funding of £2.9mln in October 2017 and moved to Somersham, UK, in February 2018. Paragraf employs 21 people. The company has developed capabilities to make graphene electronic devices at commercial scale. Currently, most silicon (Si) and GaN electronic devices are manufactured on wafers having diameters between 15–30cm. Paragraf has made graphene devices on wafers of diameter up to 20cm, limited by the equipment currently used, but 30cm or more is possible.

Theoretically, the wafer sheets could be made of infinite size using the same methodology if the machines could be made bigger. It is not thought the material will fray as the sheets get larger, but the process may be more difficult to control, increasing the risk of defects. The graphene can be doped during production and therefore have its properties tuned.

The production of Paragraf materials is different from that of conventional CVD graphene production. The company’s graphene is produced directly onto the chosen substrate, so the bonding on silicon, for example, is different. This has a significant beneficial impact on the graphene which is yet to be fully understood, so there is much research to be done.

Paragraf’s first product is a graphene Hall-effect sensor for measuring magnetic fields. The packaged device operates at temperatures as low as -270°C – the lowest tested – and up to 300°C, but it can operate at up to 800°C unpackaged. By comparison, semiconductor-based Hall sensors do not operate at low temperatures because the carriers are not then thermally activated, and have a maximum operating temperature of about 250°C. The magnetic sensor operates in a wide range of magnetic fields, has a low power consumption and is radiation resistant. 

Growth opportunities

The business plan is to develop graphene-based devices and to form partnerships with other companies to market them, or to licence the technology to other companies. Parties based in China and Singapore have expressed interest in manufacturing large quantities of graphene-based products in collaboration with Paragraf.

In July 2019, the company was able to announce the close of a £12.8mln funding round led by Parkwalk. The round also included investment from IQ Capital Partners, Amadeus Capital Partners and Cambridge Enterprise, the commercialisation arm of the University of Cambridge, as well as several angel investors. The funding will help Paragraf’s first graphene-based electronics products reach the market.

In February 2018 I moved to a professorship at Queen Mary University of London, UK. Paragraf now has a collaboration agreement with that university, which performs research to study a range of graphene devices. Paragraf and Queen Mary were awarded £500,000 by Innovate UK in January 2019 to explore using graphene as a contact layer on semiconductor devices.

Proven efficiency

Single layer sheets of graphene can be made by depositing graphene directly onto the chosen substrate, without risk of contamination. It offers a more efficient way of producing the material and increased opportunities for applications where conductivity is highly prized. Commercial scaling of the product – which is production ready – would only enable further opportunities for this wonder material to realise its full potential.