Extraction of COM parameters on langasite substrates and the application to design of a SAW filter

Pus paper presents new results on extracted COM parameters of the langasite (LGS) crystal cuts yxlt/48.5°/26.6° and SAW filters implemented on this cut. Test structures were made to measure relevant parameters like velocity, reflectivity, transduction coefficient and capacity. Variations of terms for velocity and reflectivity due to mass and electrical loading are such, that for a certain range of Al film thickness, the sensitivity to process parameters on the investigated crystal cut is reduced. The analysis of the test structures, as well as the SAW filters implemented, showed low bulk wave excitation. Advantages of LGS wafers for possible SAW device applications are discussed. In order to demonstrate a practical filter application on LGS, a SAW filter at the center frequency of 114.99 MHz was designed and realised. The chip fits into a 3.8×3.8 mm² SMD package. Measured performance is in excellent agreement with the predicted response and the chip size was dramatically reduced compared to the state-of-the-art for this kind of filters