Micro/Nanostructure Engineering of Epitaxial Piezoelectric α-quartz Thin Films on Silicon.

The monolithic integration of sub-micron quartz structures on silicon substrates is a key issue for the future development of piezoelectric devices as prospective sensors with applications based on the operation in the high frequency range. However, to date it has not been possible to make existing quartz manufacturing methods compatible with integration on silicon and structuration by top down lithographic techniques. Here we report unprecedented large-scale fabrication of ordered arrays of piezoelectric epitaxial quartz nanostructures on silicon substrates by the combination of soft-chemistry and three lithographic techniques: (i) laser transfer lithography, (ii) soft nanoimprint lithography on Sr-doped SiO2 sol-gel thin films and (iii) self-assembled SrCO3 nanoparticles reactive nanomasks. Epitaxial α-quartz nanopillars with different diameters (from 1 µm down to 50 nm) and heights (up to 2000 nm) were obtained. This work demonstrates the complementarity of soft-chemistry and top-down lithographic techniques for the patterning of epitaxial quartz thin films on silicon while preserving its epitaxial crystallinity and piezoelectric properties. These results open up the opportunity to develop a cost-effective on-chip integration of nanostructured piezoelectric α-quartz MEMS with enhanced sensing properties of relevance in different fields of application.