Al2O3 Coating Layer on the High Temperature Conductive Stability of Pt/ZnO/Al2O3 Film Electrode

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 degrees C. However, its resistances began to increase at 900, 1100 and 1150 degrees C, 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.