Polycrystalline substrates and NAnoSHeet seed layers for low cost substrate – Polynash
In order to carry out this project, two different teams were assigned to each type of support: the nanosheets were developed at ISCR in Rennes while the polycrystalline substrates were synthesized at CRISMAT in Caen. Finally, the various films of complex oxides are deposited in the various partner laboratories: ISCR, CRISMAT and GEMaC in Versailles. Different thin layer techniques are thus made available such as pulsed laser ablation in the 3 laboratories, but also techniques to reach the largest surfaces such as chemical solution deposition in Rennes and atomic layer deposition in Versailles. Each partner laboratory have brought its skills in structural and physical characterizations at the macroscopic scale but also microscopic by near field technics for the Versailles laboratory, of which part of the equipment was financed by this project.
The project was very dynamic with good synergy between the different teams. Thus a great diversity of materials have been synthesized with the 2 approaches. It appeared that our low-cost substrates allow the synthesis of materials with properties close to thin layers deposited on a single crystal. Finally, materials such as metals (platinum) and transparent oxide conductors (see illustration in figure 1) not planned at the beginning of the project were integrated on glass and silicon. In addition, a new work package has also completed the effort to integrate complex oxides by sacrificial layers. These results has led to submission of an ANR project on TCOs and an other ANR (2021) was obtained with sacrificial layers and seed nanosheets on flexible substrates.
The initial objectives were achieved in most approaches and even exceeded.
All the polycrystalline substrates could not be produced, however the growth and studies of a single type of substrates made it possible to put a methodology in place through the synthesis parameters, the polishing process but also the different structural, microstructural and morphological characterizations which will make it possible in the future to produce other substrates with different grain sizes.
The project focused on the physical properties of polycrystalline films deposited on these substrates and currently we are focusing on grain-scale properties.
In the context of nanosheets, we have been able to show that textured films on these supports have properties close to bulk substrates. Thus we open the possibility of integrating complex oxides on low cost substrates such as silicon and glass.
With these preliminary results, we can now think of new perspectives with these nanosheets:
During the project, 4 types of nanosheets were synthesized to induce different textures but only 2 could be tested for epitaxy recovery. We must therefore carry out a systematic study of the other nanosheets in order to study the properties of the materials according to their direction of growth.
Another challenge would be to try to obtain large nanosheets larger than 500 micrometers, which would make it possible to use the nanosheets as a single crystal and avoid grain boundaries.
Moreover, we used the nanosheets for their structural property and to induce an epitaxy relationship. We could also try to functionalize these nanosheets (magnetism, ferroelectricity, metallicity, etc.) to induce new functionalities between the nanosheets and the deposited films.
Finally, new nanosheets are to be synthesized in order to modify the lattice parameters and offer a wide choice of nanosheets whose parameters would be close to bulk materials.
Finally, sacrificial layers based on SVO are an alternative to low-cost substrates with the direct transfer of functional layers onto a support. The potential is very interesting, even if the transferred layers show cracks and are not yet uniform.
15 publications were accepted during this project, including 11 common with the different partners and 4 with a single partner.
A request for invention «Synthesis of electrodes on nanosheets« was unfortunately rejected and transformed into publication.
3 publications are being written and 1 publication has been submitted.
17 orals and 13 posters were produced during this project.
The aim of the PolyNASH project is to develop the growth and study of functional oxides on low-cost substrates; and to propose a new solution for the integration of complex oxides with multifunctional properties for large surface electronics. Indeed, the miniaturization of the electronic elements arrives at a limit and new solutions are sought in order to increase the integration of new functionalities (the approach "More than Moore"). Complex oxides materials offer properties such as superconductivity, ferromagnetism, ferroelectricity, multiferroism, etc., which are not present in semiconductors and are thus very promising for the development of a new generation of materials in microelectronics, Oxide-based electronics: "oxitronics". One of the difficulty of development of oxitronic devices by start-ups or industries, is the fabrication cost from substrates to device.
In this project, we will implement two approaches to develop these low-cost substrates:
1 / Growth on Combinatorial Substrate Epitaxy (CSE)
2 / Epitaxy on 2 dimensional nanosheet seed layers (2D-NS).
These two types of substrates have the advantage of being synthesized for a wide range of functional oxides family and to offer an alternative to the relatively expensive single-crystalline substrates which offer a limited choice of materials and crystallographic orientations.
This is particularly important in order to exploit the functional properties of complex oxides, whose anisotropies (magnetism, ferroelectricity, etc.) are typically related to their crystalline orientation. In the case of CSEs, all possible orientations can be obtained in a single sample and thus make it possible to study, with a single deposition, numerous experiments carried out on single-crystalline commercial substrates. Thus, for each material, we can study and isolate the best orientation- property relationships and consequently transfer them to other types of substrates such as 2D-NS. These nanosheets are 2-dimensional materials of molecular thickness and have comparatively infinite planar dimensions.
These oxide nanosheets are exceptionally rich in structural diversity that can be used as seed layers to induce epitaxy of complex oxides. Moreover, these 2D-NS have the characteristic of being able to be deposited on all types of support without any surface limitation, such as silicon.
Thus, this project aims to demonstrate the potential of these two types of substrates on different families of complex oxides: perovskite, garnet and illmenite for their magnetism and multifunctional properties which are studied among others for spintronics. The project is organized in such a way that the two materials are optimized and studied in parallel and proposes a transfer of the CSE to the 2D-NS. This consortium encompasses the full range of skills required to carry out the project, which includes experts in the field of growth of the two types of substrates: the CRISMAT of Caen (CSE) and the ISCR of Rennes (2D-NS). Complex oxides will be deposited on CSE by pulsed laser ablation by the various partners that are experts in perovskite growth (CRISMAT) and garnet and ilmenite growth (GEMaC), respectively. The integration of complex oxides over large surfaces will be carried out by Atomique Layer Deposition at GEMaC and Chemical Solution Deposition at ISCR. The characterization of the thin films will be carried out structurally at CRISMAT and at the ISCR, and the physical characterizations macroscopically at the CRISMAT and on the local scale at the GEMaC.
The development of these substrates will enable the study of the growth of complex oxides and their integration on universal substrates with a large surface area. This will enable the development of a breakthrough technology in the field of silicon-based devices.
Monsieur Arnaud FOUCHET (Laboratoire de cristallographie et sciences des matériaux)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
ISCR Institut des Sciences Chimiques de Rennes
GEMaC Groupe d'études de la matière condensée
CRISMAT Laboratoire de cristallographie et sciences des matériaux
Help of the ANR 593,775 euros
Beginning and duration of the scientific project: November 2017 - 42 Months