Work Packages
The main objectives of the HYCOAT research programme translate into five research Work Packages (WPs). The envisioned ESR projects are included in the schematic diagram below as orange labels numbered 1-15. WP1 (inner pentagon) aims at introducing innovative processing, modelling, characterization and reactor concepts to the MLD field. The ESRs in WP1 will exchange information with tool manufacturers on reactor design and process know-how. WP2-5 target specific developments of MLD in four application domains (inner and outer rings). MLD process development will be mainly taking place at the HYCOAT academic institutions (TNO, nanoGUNE, UiO, UHel, Aalto, IMEC and UGent) (inner ring), while functional testing of the deposited layers will be performed at either industrial labs or at research institutes (outer ring). To support the process development in the application-oriented WPs, secondments are planned to the academic partners that are involved in WP1 (UHel, UGent, Tyndall, KUL, RUB and TNO), i.e. from the inner ring to the inner pentagon. Secondly, secondments are planned from the inner ring to the outer ring on the diagram in a ‘follow-the-sample’ strategy, allowing a close collaboration with industrial partners. This approach will enhance industrial adoption of the developed ideas, as well as creating opportunities for ESRs to build professional networks with these industrial labs.
Overall, the number of precursors explored so far in MLD is very limited and little understanding of the detailed growth mechanisms has been gained to date. Organic precursors are most often homo-bifunctional molecules with –OH, –COOH, –NHx or –halide functional groups. Inorganic precursors are simple metal alkyl, halide or alkoxide complexes. A key challenge in MLD is that the volatility of organics drops rapidly with an increase in molecular weight or chemical functionality. WP1 mainly focuses on the advancement of the MLD field by increasing the library of MLD precursors and introducing innovative processing, modelling, characterization and reactor concepts. It includes the following tasks:
- Exploring novel precursor chemistries (ESR1 & ESR2)
- MLD of thin films with intrinsic porosity (ESR3)
- Exploring plasma-based concepts for MLD (ESR4)
- Developing dedicated tools for molecular modelling of MLD process chemistries (ESR5)
- Developing dedicated tools for in situ characterization during MLD (ESR6)
- Exploring spatial reactor concepts for MLD (ESR7)
Many applications require some form of encapsulation with permeation barriers, from food packaging to solar cells or OLED displays. However, each application has different requirements regarding barrier properties, fabrication throughput and costs. For example, for flexible electronics, such as OLEDs, the barrier requirements are very stringent, as exposure to moisture will reduce efficiency and lifetime. On the other hand, food packaging allows water vapour transmission rate values many orders of magnitude higher, but has to be produced in large volumes and at very low cost while maintaining mechanical flexibility. Barriers made by combining ALD, MLD and vapour phase infiltration have the potential to be tunable in performance and cost and could therefore be used on both ends of the application spectrum. WP2 specifically targets:
- Electronic functionalization of packaging materials (ESR8)
- Biofunctionalized gas permeation barriers through vapour phase infiltration and spatial MLD (ESR9)
Ex vivo cell growth, e.g. for regenerative medicine, requires exquisite control over the surface properties of culture vessels. Suitable surfaces are usually prepared by plasma treatments (e.g. of polystyrene) or by polymer grafting (e.g. poly-D-lysine) through wet chemical techniques to control surface wetting properties and charge. Further fine-tuning is possible by structuring the surface to resemble the in vivo environment of the cell culture, e.g. through topographies with features of the order of 100 nm in a complex three-dimensional patterns. Conformal coating through MLD holds great potential for practical improvements of such cell cultures. WP3 aims at:
- Bioactive surface for cell growth through MLD (ESR10)
- Hybrid coatings for enhancing bone compatibility (ESR11)
- Low-k coatings by MLD (ESR12): As electronic devices are further down-scaled, interconnect resistance capacitance (RC) delay may dominate the overall device speed. To minimize RC delay, the traditional dielectric material SiO2 (κ = 4.2) has been replaced with low-κ materials. Porosity is often introduced as a strategy to lower the κ-value. For the next generation of electronic devices, dielectrics with ultra-low κ (< 2.5) are needed. Additionally, there is an increasing demand for 3D deposition of low-κ materials. WP4 will explore the potential of MLD for the conformal deposition of low-κ materials consisting of stacks of inorganic and polymeric materials.
- Thermoelectric coatings by MLD (ESR13): Thermoelectric (TE) materials show high potential for sustainable energy generation by converting waste heat into electricity (Seebeck effect). Conversely, TE materials can also be used for cooling (Peltier effect). To achieve high TE efficiency, a material must simultaneously be a good electrical conductor and a poor heat conductor. The difficulty lies in tuning these contradictory material properties independently. In multilayers of materials with dissimilar electronic and vibrational properties, material interfaces are anticipated to efficiently reduce heat transport by phonon-boundary-scattering and/or reduced transmission of thermal energy. The MLD approach can offer control of the structural and chemical properties of these interfaces as well as their position within a material stack (i.e. superlattice period), providing an exciting means to tailor thermal conductivity independently of electrical conductivity.
Thin inorganic ALD coatings have been shown to improve the cycle life of Li-ion batteries. However, as these dense films are mechanically rigid, they quickly degrade upon repeated shrinking and swelling of the electrodes during successive charging and discharging. WP5 targets mechanically flexible MLD-based coatings instead with following two functionalities:
- Solid composite electrolyte coatings allowing good ionic but no electronic exchange between the active electrode and the wet organic electrolyte (ESR14)
- Dual conductor coatings facilitating both ionic and electronic conduction desirable for all-solid-state Li-ion batteries (ESR15)