Uniform coverage with porous layers over extended surfaces is beneficial for many purposes. Depending on the nature/composition, thickness and interfaces of the layer, this kind of special coverage can assure pivotal properties such as transparency, bendability, high surface reactivity, intermixing capability. In the long list of desired porous materials, transparent oxides find application in the fields of Photovoltaics, Sensing, Photocatalysis, Water Purification and Splitting, Lithium Batteries and many more.
We indeed developed a method to cover large surfaces with porous materials, oxides (e.g. TiO2, Al2O3 etc) and potentially also nitrides, using a modified reactive sputtering approach called gig-lox. The method is clean since it does not require solvents, reactants or catalytic species. The porous material, that we call sponge, can be confined on small areas or extended on large substrates. Moreover, it can be deposited at any desired thickness, from tens of nanometers to several microns, with properties that can be tuned by eventually doping or heating or modulating the stoichiometry during their growth. The high performances of oxides deposited with our method were already demonstrated by scientific publications wherein the material is integrated in Solar Cells and Sensing Devices. The method can be implemented into production flow-charts on roll-to-roll substrates or bent surfaces of any extension.
Porous materials can be hardly deposited by conventional physical deposition methods, that are instead extensively used to grow compact layers with high reproducibility and reliability. Chemical methods are usually preferred to the purpose since they are more versatile and more appropriate to generate sponges. Reliability and reproducibility on large area with chemical growth are, on the other hand, critical issues.
To level the disparity, we developed a new physical method called gig-lox based on a modified reactive sputtering concept to allow large area deposition of porous materials (namely oxides and potentially nitrides) that are contamination-free for high production throughput of devices or to cover extended area of any nature and shape.
The innovation resides in:
- compositional tunability of the sponge
- double-scale porosity, in the nanometer scale, through the whole layer thickness
- thickness tunability, typically in the of thickness 20-1000nm; to be further extended
- covered area tunability, uniformity over 4 inches wafer assured; to be further extended
- conformal step coverage
- use of any kind of substrate
- multi-parameters conditions: temperature, power loading, anode-cathode distance, gas flow, gas mixture etc.
- large area production and reliability of the process
- up-scalable, contamination-free production
- large surface area availability for functionalization, blending with other materials, small molecules infiltration etc.