Gallium orthophosphate device manufacturing by chemical etching

This paper presents a study of gallium orthophosphate chemical etching as a method to design high frequency AT resonators. The dissolution reaction was studied in phosphoric acid solutions and the equation of the dissolution kinetics was determined. The apparent dissolution rate depends both on the solvent and the solute concentrations at the solid-liquid interface and follows an Arrhenius type law in terms of temperature. In order to completely determine the kinetics at this interface, the rates of dissolution and nucleation processes were both established. The geometry and the density of etch figures appearing on the surface of the plates were observed using optical microscopy photographs. During the chemical dissolution, the surface quality was evaluated essentially through the measurement of the roughness average Ra parameter. The best surface state was obtained with solutions containing dissolved GaPO₄. Finally, resonators manufactured by the chemical etching process are characterized piezoelectrically by the air-gap method. These first results show that the Q factor (Q*F=1 to 1.5E+11) is not affected by the chemical etching process.