Search Results
Long-term high-temperature behavior of Ti–Al based electrodes for surface acoustic wave devices
2022, Seifert, Marietta, Leszczynska, Barbara, Menzel, Siegfried, Gemming, Thomas
The long-term high-temperature behavior of Ti–Al based electrodes for the application in surface acoustic wave (SAW) sensor devices was analyzed. The electrodes were obtained by e-beam evaporation of Ti/Al multilayers on the high-temperature stable piezoelectric Ca3TaGa3Si2O14 (CTGS) substrates and structuring via the lift-off process. AlNO (25 at.% Al; 60 at.% N and 15 at.% O) cover and barrier layers were applied as protection against oxidation from the surrounding atmosphere and to prohibit a chemical reaction with the substrate. The samples were annealed at temperatures up to 600 °C in air for a duration of up to 192 h. Scanning and transmission electron microscopy were used to evaluate the morphology and degradation of the electrodes as well as of the extended contact pads. The results revealed that the Ti–Al based electrodes remained unoxidized after annealing for 192 h at 400 and 500 °C and for 24 h at 600 °C. After the heat treatment for 192 h at 600 °C, a strong oxidation of the structured electrodes occurred, which was less pronounced within the pads. In summary, the investigation showed that Ti–Al based SAW devices are a cost efficient alternative for long-term applications up to at least 500 °C and short- and medium-term applications up to 600 °C.
Durability of TiAl based surface acoustic wave devices for sensing at intermediate high temperatures
2023, Seifert, Marietta, Leszczynska, Barbara, Weser, Robert, Menzel, Siegfried, Gemming, Thomas, Schmidt, Hagen
TiAl based surface acoustic wave (SAW) devices, which offer a promising cheap and easy to handle wireless sensor solution for intermediate high temperatures up to 600 °C, were prepared and investigated with respect to their durability. To obtain the devices, Ti/Al multilayers were deposited on high-temperature stable piezoelectric catangasite (CTGS) substrates and structured as electrodes via the lift-off technique. AlNO cover layers and barrier layers at the substrate site served as an oxidation protection. The devices were characterized regarding their electrical behavior by ex-situ measurements of their frequency characteristics after heat treatments up to 600 °C in air. In addition, long-term in situ measurements up to 570 °C were performed to analyze a possible drift of the resonant frequency in dependence on the temperature and time. Scanning electron microscopy of the surfaces of the devices and scanning transmission electron microscopy of cross sections of TiAl interdigital transducer electrode fingers and the contact pads were conducted to check the morphology of the electrode metallization and to reveal if degradation or oxidation processes occurred during the heat treatments. The results demonstrated a sufficient high-temperature stability of the TiAl based devices after a first conditioning of system. A linear dependence of the resonant frequency on the temperature of about −37 ppm/K was observed. In summary, the suitability of TiAl based SAW sensors for long-term application at intermediate temperatures was proven.