Abstract:

To investigate the effects of Al₂O₃ coating layers on the conductive stability of surface acoustic wave electrodes working at high temperature, laser molecular beam epitaxy was carried out to deposit a series of Al₂O₃/Pt/ZnO/Al₂O₃ multilayer electrodes coated with Al₂O₃ layers of different thicknesses. The real-time resistance measurements of these samples were performed in the heat treatment. It can be found that the conductive stabilities of Al₂O₃/Pt/ZnO/Al₂O₃ samples were significantly related to the thickness of the Al₂O₃ coating layers. For the sample without Al₂O₃ coating layer, its resistance began to increase when the temperature rose up to 800 ℃. However, its resistances began to increase at 900, 1100 and 1150 ℃, at the thickness of Al₂O₃ coating layers of 40, 80 and 120 nm respectively. For the samples with 160 nm and 200 nm Al₂O₃ coating layers, the resistances almost remained stable during the whole heating process. According to the surface topographies of these samples, it found that the sample without Al₂O₃ coating layer formed isolated Pt grains after high-temperature measurement. As a comparison, the samples with Al₂O₃ coating layers did not form isolated Pt grains after high-temperature resistance measurement. After high-temperature measurement, the less discontinuous Pt voids appeared at the surface of the sample with a relative thicker Al₂O₃ coating layer. XRD tests of theses samples, performed before and after high-temperature measurement, showed that Pt recrystallization at high temperature can be inhibited by the Al₂O₃ coating layer, and the thicker layer could inhibit its recrystallization more effectively. These results provide a new way to prepare SAW devices which can work stably at high temperature.

Key words: high temperature, conductivity, Al₂O₃ coating layer, La₃Ga₅SiO₁₄