Langasite based miniaturized functional structures: Preparation, high-temperature properties and applications

Langasite single crystals show piezoelectrically excited bulk acoustic waves up to 1470 °C and are, therefore, used to prepare high‐temperature functional components such as membranes, cantilevers and field emission tips. The underlying concept includes monolithic structures to avoid thermal stress at elevated temperatures. In order to control the preparation processes, wet chemical etch rates, the transport of dopants and their impact on the materials properties of langasite are determined. Heavily Sr‐doped langasite shows a strong increase in conductivity which is used to realize monolithic electrodes by local doping. Further, the stability of small langasite structures is confirmed up to 1350 °C. Biconvex membranes could be operated in the fundamental and 3rd resonance mode up to 700 °C. The fundamental modes of those 16.3 MHz resonators show quality factors of 500 at the above‐mentioned temperature. Further, field emitter tips of 27 nm in radius are prepared and demonstrated to be operational up to at least 600 °C. The mechanical displacement and the electrical response of vibrating cantilevers is characterized simultaneously and found to be consistent. Finally, the feasibility of sensor film coated membrane arrays to distinguish between CO and H2 at 600 °C is demonstrated.