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Nano-structuration of materials

 

Focalized for the last ten years or so on the development of deposits of aluminium nitride (AlN) and aluminium oxynitride (AlNO) by PVD magnetron, our research aims at confering original optical, mechanical and opto-electromechanical functionalities to the films while controlling carefully their chemistry and microstructure. The layers of the piezoelectric material are electrically insulating.

Interference fringes related to differences in the thickness of an AlN coating on silicon. The optical properties in the UV-NIR domain of films are obtained by emission spectrometry at 300 K, by spectrometric ellipsometry and transmission for sample temperatures set between 300 and 900 K.

Deposit of transparent AlN for the encapsulation of SAW micro-systems

The surface acoustic waves (SAW) are at the basis of numerous communication micro-systems and today are increasingly used to make micro-sensors. However, these piezoelectric micro-devices must be protected from the environment.

Columnar growth AlN (002) is an excellent candidate to allow the encapsulation of these micro-systems.
Our studies in this domain, which we carry out in collaboration with the Micro and nanosystems group, aim at optimizing the thickness of the AlN layers deposited by PVD magnetron at room temperature directly on IDT /ZnO, with in situ control (during the deposit) of the thickness by interferential reflectometry and at the same time control of the SAW response.

Reactively sputtered AlN film of 28 µm thickness, constituted of oriented columns (002) protecting an SAW micro-system (IDT/ZnO/Silicon).

Deposition of transparent AlN

The AlN layers are studied here for their transparency in the visible spectrum and their ability to protect against mechanical deterioration, oxidation and chemical attack.
This functionality is studied to protect equally the aesthetics of products used at high temperatures and optical systems subjected to environmental aggressions (glazing, for example).
The development of transparent piezoelectric AlN films on transparent conducting indium-tin oxide (ITO) films allows research into electro-optical functionalities.

PVD deposit at room temperature of 20 µm of AlN onto a plastic film coated with transparent ITO and printed here with the IJL logo.

Photoluminescence of AlN thin films doped with rare earth elements

 

Figure A: Green photoluminescence (538 and 557 nm) of an AlN +Er sample excited by a UV laser at 325nm.
Figure B : Visible photoluminescence spectrum of the same AlN +Er sample, showing the two peaks of Er3+ emission as well as the blue PL of the AlN matrix at 400 nm.

 

AlN is a large gap isolator (6 eV). As a result, the doping of this material with rare earth elements allows us to obtain a photoluminescence effect (PL) that is insensitive to variations in temperature.
Erbium is a rare earth that emits infra-red and visible rays, which are used in the domains of fiber optic communications and LED creation. In collaboration with the Nanomaterials group of the Institut Jean Lamour, studies are carried out to optimize deposits of AlN doped with this rare earth element.
For example, this research has revealed the influence of the size of AlN nanocristallites on the PL efficiency of the Erbium atoms.

Modelling of the PL emission of micro- and nanostructured thin films

To elaborate films that possess a specific unique optical property in photo or cathodo-luminescence, theoretical studies are necessary to model then predict the luminescence of micro- and nanostructured doped materials (columnar crystallisation, nanocrystallisation, multilayers, etc.). 
Models have already been programmed that allow specific stacking of AlN / doped AlN layers with original optical properties to be predicted. Currently, we are working to develop and characterize these stacks.

Modelling of photoluminescence as a function of thickness for AlN/ Er doped AlN multi-layers and for two different ratios of AlN /AlN+Er thicknesses.