The Fabrication And Investigation Of Electrodes For Saw Devices Working At High Temperature

Surface acoustic wave?SAW?sensors have been applied in some harsh airtight environment,due to its wireless passive features.However,the stability of related SAW device working at high temperatures over 1000?is highly demanded in the special application of aerospace and weapon manufacturing.Up to now,the conventional SAW devices can only withstand the ambient temperature about 500 to 600?.In this dissertation,the multiple composite Pt-based film electrodes were deposited on La₃Ga₅SiO₁₄?LGS?substrates by laser molecular beam epitaxy?LMBE?and pulsed laser deposition?PLD?techniques.The mechanism of conductivity variation in the Pt-based film electrodes was analyzed through the conductivity measurement and the comparison of the microstructures before and after those treatments.Lastly the methods of suppressing the high temperature failure of Pt-based electrodes are proposed.These results can provide the experimental and theoretical basis for the SAW devices and other micro-size devices which are working at high temperatures.The main contents of this dissertation are organized as follows:1.The series of Pt electrodes were deposited on LGS substrates at different temperature by PLD.The influence of deposition temperature on the conductive stability was then systematically studied.It can be found that the destruction of Pt electrodes at high temperature was resulted by its agglomeration,and the higher deposition temperature resulted in the higher conductive stability at high temperature.For example,the Pt electrode deposited at 600?can maintain stable conductivity although the temperature had rose up to 1000?.Besides,the X ray diffraction?XRD?results showed that the higher deposition temperature would lead to the lager Pt grains.And the grain size of Pt was thought to be the deciding factor for its conductive stability at high temperature.2.The Pt/ZnO and Pt/ZnO/Al₂O₃ multilayer electrodes were prepared by LMBE at150?and 600?,respectively.These results showed that the insertion of the ZnO buffer layer can improve the crystal quality of Pt and obtain the larger Pt grains at a relatively lower temperature.Besides,it can be found that the Al₂O₃ can inhibit the diffusions of La?Ga?Si atoms and further improve the crystal qualities of ZnO buffer layer and Pt electrode.In this way,we can obtain the larger Pt grains and its conductive stability was significantly improved.For example,the Pt/ZnO/Al₂O₃ electrodes prepared at 600?can maintain stable conductivity at 1000?for about 30 minutes.3.AlN and Al₂O₃ coating layers with different thickness were deposited on Pt/ZnO/Al₂O₃ electrodes at 150?by LMBE.The influence of coating layer on the high-temperature stability of Pt/ZnO/Al₂O₃ electrode was investigated.For the AlN and Al₂O₃ coating layers with same thickness,it can be found that the Al₂O₃ coating layer can better inhibit the destruction of Pt at high temperature.Besides,the thicker coating layer also inhibited the destruction of Pt at high temperature more effectively.As a result,the Pt/ZnO/Al₂O₃ electrode with 160 nm Al₂O₃ coating layer can maintain stable conductivity at 1100?for at least 3 hours.4.The ITO/Pt composite film electrode was prepared at 500?by PLD.According to the measured high-temperature real-time conductivity and its microstructure before and after high-temperature process,we analyzed the relationship between its conductivity and microstructure.The results showed that the Pt holes were formed because of its agglomeration at high temperature.Then,the ITO filled up with these Pt holes and connected the Pt electrodes,providing a conductive channel.In this way,although Pt agglomerated soon,the conductivity of this ITO/Pt composite film electrode can remain stable for about 3 hours at 1000?.Besides,it can be found that the conductive stability of this ITO/Pt film electrode is closely related to conductive stability of ITO at high temperature.5.The SAW resonators were prepared by using above electrodes and their properties were measured after high-temperature annealing.It can be found that the SAW device with Al₂O₃/Pt/ZnO/Al₂O₃ electrode has the most stable property after annealing at 1100?for more than twelve circles.However,the property of SAW device with ITO/Pt electrode can only remain stable after annealing at 1100?for one cycle.Besides,the SAW device with Pt/ZnO/Al₂O₃ electrode has the poorest property after annealing at 1100?.It cannot maintain stable property after annealing at 1100?for only one time.These results showed that all the SAW devices with above electrodes can work stably above1000?for different durations,providing theoretical and experimental basis for fabricating high-temperature SAW devices.