Technological process and resonator design optimization of Ir/LGS high temperature SAW devices
Photolithography together with ion beam etching was used for fabrication of high temperature SAW devices. Ir thin film of 0.3 μm thick was deposited by magnetron sputtering without additional adhesion layers and than Ir film was annealed after electrode patterning in different conditions. The resistivity of magnetron sputtered thick Ir films drops noticeably after annealing. However, this process requires special care in order to avoid delaminating of the film due to developing high stress during such procedures. We have annealed the substrates with Ir films in different regimes and in different gas/vacuum conditions. The results of these studies have shown that annealing in air up to about 500 °C decreases the Ir film resistivity 1.5-2 times. Vacuum annealing did not show much improvement in comparison to open air annealing. Magnetron sputtered thin Ir films have somewhat porous structure allowing oxygen to diffuse from the substrate surface through Ir films. Resonator structures with thick Ir electrodes were prepared and tested. Examples of the resonator structures show very promising properties, such as high conductance and high Q-factor.
High-Temperature Conductive Stability of ITO/Pt Bilayer-Film Electrode for Applications in High-Temperature SAW Devices
Surface-acoustic-wave (SAW) devices have been widely investigated over many years as demand has grown for information sensing above 1000°C. At such high temperatures, metal electrode creep occurs, thereby causing the transformation of an electrode from a continuous uniform film to a discontinuous film with hollows or isolated grains. In this study, 100 nm thick ITO conductive oxide film is deposited on 100 nm thick Pt film to form an ITO/Pt bilayer-film composite electrode for high-temperature SAW devices. According to this way, the conductive stability of the Pt film electrode at high temperature can be greatly improved. Compared with the initial value, the electrical conductivity of single-layer 100 nm thick Pt film decreases to 65.4% with the area fraction of Pt at 64.1%. Meanwhile, the electrical conductivity of ITO/Pt bilayer-film decreases to only 95% with the area fraction of Pt at 63.1%. Then, the enhancement of high-temperature conductive stability can be attributed to the added ITO conduction channels. These findings demonstrate a potential route to design multilayer electrodes that can operate above 1000°C with promising applications in SAW devices needing to operate at high temperatures.
Stability results for the solutions of some third and fourth order differential equations
SummaryThe paper investigates conditions under which solutions of the equations (1) and (2) of § 1.1 tend to zero as t → ∞.