2Dfun aims at establishing 2D layers and heterogeneous layer stacks as basic building blocks of, and demonstrate them in functional  devices. To this end, 2Dfun will develop growth processes for 2D transition metal dichalcogenides (MX2) on graphene (with graphene coming from external resources within the Flagship) as well as high-k dielectric layers on MX2. Almost all work reported in literature in this area is based on natural MX2 material made by exfoliation, which however is not considered as a manufacturable route. An essential requirement for industrial applications is the availability of deposition techniques on large diameter (200-300mm) substrates with appropriate control over the process in terms of thickness, uniformity and material quality. Layer characterization as well as good control and understanding of the interfaces in such structures is key, and will help understanding device operation as well. Based on this high-volume manufacturing-compatible graphene/MX2/high-k platform, 2Dfun will make first functional hybrid MOSFET devices as demonstrator.

Hence, 2Dfun will work towards realizing two technological and one scientific objective:

  • Technological Objective 1: To develop a large-area deposition process for MX2 on graphene for electrical and opto-electrical applications. Atomic  Layer Deposition (ALD) is the most appropriate process choice for large area and single to few-layer scaling purposes. Device integration requires simultaneous growth of the MX2 film on patterned structures of graphene and dielectric areas, e.g. SiO2, which brings specific requirements for the nucleation step. We will work along two routes: i) ALD-grown metal or metal oxide films will be sulfurized with a low-temperature plasma-enhanced process; ii) MX2 will be grown directly with appropriate metal and chalcogen precursors.
  • Technological Objective 2: To develop a deposition process for high-k dielectrics (Al2O3, HfO2) on MX2. In this case, standard ALD processes will be our starting point. Nucleation on the MX2 surface requires also appropriate surface functionalization for which an innovative approach with self-assembled monolayers will be pioneered.

Realization of  these two Technological Objectives will allow to build a demonstrator MOSFET device, which in turn is important in realizing our 3rd, Scientific  Objective:

  • Scientific Objective: To obtain fundamental insight in the chemical structure and energy distribution or electron states at the interfaces including bandgap widths, band offsets and gap state spectrum at graphene/MX2 and MX2/dielectric interfaces which will help process optimization. These interfaces will be characterized with physico-chemical techniques on hybrid layer stacks as well as electrical characterization of test structures and MOSFET devices, and appropriate ab-initio modelling will help bringing fundamental insight.

For both of these technological objectives, nucleation on those surfaces is key and not straightforward. An important topic in the work plan will be functionalization of both graphene and MX2 surfaces to enhance nucleation during the first ALD cycles. On the other hand, this might influence the resulting interface properties. A thorough scientific study of ditto is mandatory for understanding, but moreover can allow to control this interface for tuning towards desired device parameters such as threshold voltages in MOSFETs.