español
LOW-TEMPERATURE PROCESSED HIGH-PERFORMANCE OXIDE THIN FILMS FOR APPLICATION IN FLEXIBLE ELECTRONICS
Lourdes Calzada
preferably for chemists, chemical engineers, materials engineers
The electronic industry is demanding cost-efficient, soft-portable, high-tech devices that push through the integration of oxide thin layers with flexible substrates. Conventional microelectronic integration routines require processing temperatures below 500°C. Applications envisaged with flexible substrates are calling for lower thermal budgets and cheap solution-processable oxide films. Strong efforts are devoted to the low-temperature fabrication of semiconductors, the most used materials in electronics. But, there is now the need to integrate other layers in the upcoming devices to increase functionality. This is a major opportunity for ferroelectric crystalline oxides, since their intrinsic multifunctionality would permit diverse operations in the electronic device. But, integrating these oxides with flexible electronics is a challenge; they require high processing temperatures (>600°C). Solution deposition techniques seem to be nowadays the only methods available for a direct integration of crystalline oxide films with flexible substrates, with the advantage of tailoring the solution chemistry to get a reduction of the crystallization temperature.
This project addresses the low-temperature solution preparation of multifunctional complex oxide films on flexible plastic substrates. Novel synthesis strategies in solution will be used, all of them based on inducing the crystallization of the oxide layer by photochemistry as an alternative energy source to the conventional heating. The realization of the low-temperature processing will be validated for multi-metal perovskite ferroelectric oxides whose functionality is dependent on their crystal structure. Non-hazardous oxide films that fulfill the European Directives in electrical and electronic equipment will serve as model systems for the proof-of-concept of the methods developed in this work (e.g., BiFeO3 based multiferroic photovoltaic perovskites, BaTiO3 based ferroelectric compounds or (Na,K)NbO3 biocompatible piezoelectric materials). For the integration of these oxide layers with flexible plastic substrates, solution approaches will be combined with processing technologies implemented at laboratory-scale at ICMM-CSIC by the group. The properties of the materials will be characterized at the macro and nanoscale using characterization/instrumentation techniques developed in the group, thus evaluating the application of these materials for the next generation of flexible devices (e.g., energy harvesting, flexible displays or photovoltaic cells).
NEW CRYSTALLINE MATERIALS FOR FLEXIBLE ELECTRONICS: CRYSTALLIZATION MECHANISMS AND ITS EFFECTS ON PROPERTIES
Jesús Ricote
preferably for physicists, materials engineers
The electronics industry is expected to deliver ever more sophisticated embedded systems for the expansion of the internet of things, which must be foldable, stretchable and conformal to all kind of surfaces. All of this has pushed the emergence of the field of Flexible Electronics. Traditional Si-based substrates are substituted for plastics, textiles or paper. They do not allow the direct integration of materials needing high processing temperatures, so organic compounds have been the most used in Flexible Electronics up to now. However, the performance limitations and the stability deficiencies in harsh environments of the organic compounds do not make them the best choice.
The fact that high temperatures must be avoided during processing of oxides on flexible substrates, makes in general their crystallization unattainable. This restricts significantly the capabilities of flexible devices, as the wide range of excellent properties of crystalline oxides, already demonstrated in other technologies, cannot be used.
In our research group we are developing alternative processing mehtods for low temperature crystallization of oxide films on flexible plastic substrate by chemical solution methods. In this thesis project the student will study thoroughly the crystalline structure and microstructure of these films to determine, among other things, the degree of crystallinity and the average grain size obtained. As a combination of molecular design of the precursors solutions, photocatalysis, photoactivation and seeding is used, the analysis of the results will contribute to clarify the mechanisms ruling a crystallization process not based on conventional heating.
It is proposed the study of ferroelectric oxide films such as Pb(Zr1-xTix)O3 (PZT, prototypical piezoelectric), BaTiO3 (biocompatible piezoelectric) and BiFeO3 (multiferroic photovoltaic), together with the analysis of the influence of low temperature processing on their physical properties, which could be used, for example, in flexible health monitoring devices or flexible solar cells.
…