Low-temperature sol–gel methods for the integration of crystalline metal oxide thin films in flexible electronics

Abstract

The development of low-temperature sol–gel (solution) processes for the fabrication of crystalline metal oxide thin films has become a key objective in the emerging Flexible Electronics. To achieve this target, crystalline oxide films need to be deposited on flexible substrates, which have degradation temperatures below 350 °C (e.g., polymers or textile). This achievement would be a step towards improving the performance of the flexible device, making feasible applications now restrained (e.g. smart-skin, flexible-displays or solar-cells) and whose performance is associated to the functional properties of the crystalline oxide (e.g., ferroelectricity, pyroelectricity or piezoelectricity). However, this is a challenge because the crystallization of these oxides usually occurs at high temperatures, over 600 °C. This paper shows an overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites (e.g., BiFeO3, PbTiO3 or Pb(Zr,Ti)O3). We have made use of UV-light as an alternative energy source to the thermal energy conventionally used to obtain the crystalline oxide. High photosensitive sol–gel solutions have been synthesized and the solution-deposited layers irradiated with UV-excimer lamps. A precise control of the photoreactions occurring during the irradiation of these layers has been carried out with the aim of advancing the formation of a high-densified, defect-free amorphous metal oxide film that easily can be converted into crystalline at temperatures compatible with the use of polymer substrates.