Langasite Micromachining Technology Applied to Surface Acoustic Wave Sensors in Ultra-High Temperatures

This paper focuses on the micromachining technology of langasite microcavity which is mainly composed of wet etching and direct bonding procedures. The cut of the langasite wafer is (0°, 138.5°, 26.6°). The influence of external etching conditions (temperature and volume ratios of the etchant) on the etching rate has been discussed. A microcavity with a clear boundary and smooth surface is obtained, 100 μm in-depth, and 4mm in diameter, with a high etching rate of 42 μm/h. Then, the wafers are activated with the oxygen plasma to obtain high hydrophilic surfaces. They are annealed at 1000 °C 6 MPa with a duration of two hours to complete the direct bonding procedure. The high bonding strength of 3.81 MPa and well-sealing performance have been tested. Our work is of great significance to the fabrication of surface acoustic wave devices in ultra-high temperatures.