Designer Aluminium Precursors for the Inkjet Printing of Electrical Circuits
Lead Research Organisation:
UNIVERSITY COLLEGE LONDON
Department Name: Chemistry
Abstract
Printed electronics are becoming integrated into every part of modern-day life, from light-emitting diodes, to solar cells and printed biosensors such as wearable electronics. The flexible electronics market alone is predicted to be valued at $74 billion by 2030. Whilst the technology already exists to manufacture large-scale flexible electronics, by way of the environmentally friendly, roll-to-roll industrial processes which employ inkjet printing, currently the metal inks that are employed have their limitations. The patterning of molten metals is incompatible with affordable flexible materials, including renewable eco-friendly plastics or paper, this mismatch is due to, in part, the high melting point of metals (often over a thousand degrees) and the deformation temperature of a range of plastic, paper or fabric materials being considerably lower (ca. 100 - 200 degrees Celcius). Current techniques used in the production of printed electronics are time consuming and expensive multi step-techniques that require the use of toxic chemicals. These state-of-the-art techniques require metal flakes/particles to be 'melted' together, resulting in contaminants between layers, which reduce overall conductivity of the metal.
An obvious solution to this problem is the use of specially designed inks, containing small molecules that can be printed into any desired pattern onto any material, and then be thermally 'activated' at low temperatures, in order to convert them to conductive metal. This project aims to design and synthesise new small molecules in order to improve the performance of existing printing technologies. These would provide a tuneable alternative to the current industrial nanoparticle inks based on silver or copper whose activation temperatures are too high for printing onto many materials. In addition, understanding how the structure of a small molecule can influence its ability to act as a precursor to the metal is challenging, and gaining insight will enable us to adjust thermal activation temperatures, such that after printing, it can yield highly conductive metal.
Aluminium metal is earth abundant, boasts conductivity comparable to silver and copper and yet has never been used industrially to inkjet print conductive tracks. This is because suitable precursors do not exist, despite the rich field of synthetic aluminium chemistry. To overcome this problem, we propose to adapt our small molecule design to be better compatible with modern lower temperature deposition techniques. To reap the benefits of using printing techniques for device fabrication inks that will transform at low temperatures (affording compatibility with low cost flexible materials) will be produced. This project will create a library of novel highly performing inks from aluminium which can be printed and sintered in air on low cost flexible materials for incorporation into electronic devices.
The aim of this project is to develop new small molecules containing aluminium, formulate these into metal inks and subsequently print highly conductive metal features onto low cost flexible materials for use in electronic devices.
An obvious solution to this problem is the use of specially designed inks, containing small molecules that can be printed into any desired pattern onto any material, and then be thermally 'activated' at low temperatures, in order to convert them to conductive metal. This project aims to design and synthesise new small molecules in order to improve the performance of existing printing technologies. These would provide a tuneable alternative to the current industrial nanoparticle inks based on silver or copper whose activation temperatures are too high for printing onto many materials. In addition, understanding how the structure of a small molecule can influence its ability to act as a precursor to the metal is challenging, and gaining insight will enable us to adjust thermal activation temperatures, such that after printing, it can yield highly conductive metal.
Aluminium metal is earth abundant, boasts conductivity comparable to silver and copper and yet has never been used industrially to inkjet print conductive tracks. This is because suitable precursors do not exist, despite the rich field of synthetic aluminium chemistry. To overcome this problem, we propose to adapt our small molecule design to be better compatible with modern lower temperature deposition techniques. To reap the benefits of using printing techniques for device fabrication inks that will transform at low temperatures (affording compatibility with low cost flexible materials) will be produced. This project will create a library of novel highly performing inks from aluminium which can be printed and sintered in air on low cost flexible materials for incorporation into electronic devices.
The aim of this project is to develop new small molecules containing aluminium, formulate these into metal inks and subsequently print highly conductive metal features onto low cost flexible materials for use in electronic devices.
Publications
Douglas SP
(2023)
Tris(ß-ketoiminate) Aluminium(III) Compounds as Aluminium Oxide Precursors.
in ChemPlusChem
Zhou Y
(2023)
Room Temperature Electronic Functionalization of Thermally Sensitive Substrates by Inkjet Printing of a Reactive Silver-Based MOD Ink
in Advanced Materials Technologies
| Description | The growing field of microelectronics is driving the search for new materials that can deposit conductive features. However, there has been limited research on aluminium in this context because it is usually deposited using highly reactive compounds. These compounds can be dangerous and unstable, making them difficult to handle. One solution to this challenge is using "ligands" - special molecules that can help stabilize these compounds while still allowing them to deposit the desired materials. In our study, we worked on developing a library of novel aluminium compounds, completing each objective of the project in turn. As a standout result, we developed a new aluminium complex that can convert to metallic aluminium without the need for highly reactive chemicals, and at a relatively low temperature of just 100°C. This was achieved by designing a multi-step process using specific compounds known as ß-ketoiminates, which acted as starting materials. These compounds were modified to create ligated aluminium hydride complexes, which are more stable and safer to handle. When we heated the molecule in a vacuum at 100°C, it decomposed to form metallic aluminium. We confirmed this transformation using several techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Additionally, we were able to successfully deposit thin films of aluminium after allowing it to react for three weeks under nitrogen at room temperature. This process does not require pyrophoric (highly reactive) chemicals, making it a safer and simpler method for producing metallic aluminium. In summary, this work represents the first known approach to producing metallic aluminium using stable, non-pyrophoric compounds at relatively low temperatures, which could have important implications for microelectronics and other industries relying on conductive materials. |
| Exploitation Route | The library of precursors have opened up new avenues for using different types of sintering (this grant was for thermal sintering), now we have expanded to look at plasma sintering with a new grant. Furthermore we have kept good connections with our industrial connections and have had several meetings to discuss the use of these precursors. |
| Sectors | Chemicals Electronics Energy Healthcare |
| Description | This study introduces a multi-step design approach that led to the creation of custom molecules, marking the first non-pyrophoric aluminium compound capable of delivering the metal at 150°C in just 1 hour. Our new molecules show significant potential as precursors for the deposition of metallic aluminium. Although optimization is still ongoing, preliminary tests suggest that conversion can also be achieved at 100°C overnight, resulting in conductive aluminium films. The expanding field of microelectronics is pushing the demand for new materials that can deposit conductive features. However, research on aluminium has been limited because it is typically deposited using highly reactive compounds, which are unstable and difficult to handle. In our study, we developed a library of novel aluminium complexes that can convert into metallic aluminium, some at a relatively low temperature of 100°C, without requiring highly reactive chemicals. This was achieved through a multi-step process involving specific compounds. We successfully deposited thin films of aluminium using a novel method, which does not require pyrophoric chemicals, and as such offers a safer and simpler approach to producing metallic aluminium. In conclusion, this work presents the first known method for producing metallic aluminium from stable, non-pyrophoric compounds at low temperatures, which could significantly impact microelectronics and other industries that rely on conductive materials. |
| First Year Of Impact | 2024 |
| Sector | Chemicals,Electronics,Energy |
| Description | PAPIER - Plasma Assisted Printing of Metal Inks with Enhanced Resistivity |
| Amount | £164,310 (GBP) |
| Funding ID | EP/Y001877/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 03/2024 |
| End | 05/2025 |
| Description | Invited plenary speaker in Leuven Belgium |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited plenary speaker in Leuven Belgium at EuroCVD 2025. Many people attended the talk that sparked much discussion afterwards |
| Year(s) Of Engagement Activity | 2023 |
| Description | Invited speaker at symposium for retirement of Prof Phil Power FRS |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Many people attended this event and the research presented being quite different to the common topics caused much discussion and many people interested in collaboration afterward. |
| Year(s) Of Engagement Activity | 2024 |
| Description | Invited speaker for department seminar at UC Irvine |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | A talk on the outcomes of the project that was highly engaging and very interactive with an hour of questions and exchanges afterwards. |
| Year(s) Of Engagement Activity | 2024 |