Research

Atomic layer deposition (ALD) thin film materials research

Atomic layer deposition (ALD) is a thin film deposition technique closely related to Chemical Vapour Deposition (CVD). Unlike CVD, ALD relies on self-limiting cyclic surface reactions that provide exquisite control over the thin film growth process. ALD is a surface chemistry driven process utilising alternating pulses of complementary precursor gases. The process involves surface exchange reactions between chemisorbed metal-containing precursors and nucleophilic co-reactants such as –OH, -NH or -SH. The reactants are separated by gas purges to suppress unwanted gas phase reactions, hence, ALD proceeds via self-limiting steps. The self limiting nature of ALD offers opportunities to accurately produce ultra thin coatings with sub-nanometre control of thickness & composition, exceptional uniformity and conformity even on high aspect ratio three dimensional microstructures. In addition, ALD processes can often be run at low temperatures allowing coatings onto temperature sensitive substrates. Although ALD has been around for almost half a century, Worldwide interest from the research community only really started to grow in the late-1990’s driven by the microelectronics industry. Over the last decade, ALD has been recognized as an enabling technology for an increasingly diverse range of research and manufacturing areas ranging from microelectronics, optoelectronics, photonics and energy storage/generation through to micro-machines (MEMS), bio-medical devices, food packaging, decorative coatings and even high energy explosives.

My key areas of interests relating to ALD:
- ALD processes: Developing new ALD processes, particularly for novel/advanced functional thin film materials.
- Precursor delivery: Developing methodologies for transport 'difficult' precursors.
- In-situ analysis techniques to probe ALD process chemistry: Gaining a fundamental insight into the surface chemistry and kinetics of different ALD process with the aim of using this knowledge to advance the field of research.
- Physico-chemical characterisation: Using techniques such as XRD, AFM, SEM, XPS, EDX, MEIS and Raman to correlate growth conditions with the resulting physico-chemical properties of the films.
- Functional characterisation: Assessing the functional (electrical, optical, biological, catalytic, etc) properties of the thin film materials.

Applications of thin film materials

ALD is a truly enabling technology with a vast range of potential applications in a diverse range of technology sectors. Much of my research is driven by the desire to exploit functional thin film coatings (produced primarily by ALD, but also by other techniques such as MOCVD & PVD) to enhance existing technology and to enable the development of new technology. Ultra-thin coatings can have a remarkable impact on the performance of existing technology, while also opening the door for the development of new technology.

In recent years, I have been involved in collaborative research spanning a number of technology sectors. For example:

- Microelectronics: High-k dielectrics for silicon microelectronics
- Microelectronics: GaN-on-Si high electron mobility transistors (HEMT)
- Microelectronics: Resistive switching memory devices
- Microelectronics: ALD of nitrides
- Microelectronics: Zn-oxide based thin-film transistors (TFTs)
- Photo-voltaics: Transparent conducting oxides
- Solar-fuels: Hematite photo anodes for active water splitting
- Battery technology: Coatings to enhance Li-ion battery lifetime
- Bio-medical: Antimicrobial silver coatings for bio-medical implants
- Optics: Coatings for advanced optical components
- Optics: High volume fabrication of laser targets using MEMS techniques

Research grants