Tuning Strain by Varying CaTiO₃ Thickness in Heteroepitaxially Grown La_2/3Sr_1/3MnO₃ Double-Clamped Resonators on...

We realize double-clamped beams made of La_2/3Sr_1/3MnO₃/CaTiO₃/SrTiO₃ [LSMO(45 nm)/CTO/STO(20 nm)] thin films grown on silicon substrates by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE). Microbridges having a width of 5 μm and length from 50 to 250 μm are released from the silicon substrate by reactive ion etching, resulting in a suspended oxide heterostructure. The thickness of the CTO buffer layer varies in the 0-14 nm range to tune the tensile stress of the microbridges. For thicker CTO, we observe an increase of the fabrication yield and a shift of the transverse curvature of the microbridges, related to the out-of-plane strain gradient, from positive to negative. The mechanical quality factors of these resonators are above 10⁵, and it is associated with a tensile stress of about 500 MPa. Our results indicate that the use of dual oxide buffer layers, with mismatched lattice parameters, is an effective route to control the epitaxial strain in oxide-based mechanical resonators integrated on silicon and to achieve high stress and a mechanical Q factor.