Papers by Keyword: Piezoelectric Thin Films

Abstract: In present work, we report preparation and characterization of piezoelectric films of zinc oxide (ZnO) and aluminum nitride (AlN) by RF magnetron sputtering using respective ceramic targets. The effect of ambient gas, substrate temperature, RF power and sputtering pressure has been studied to get highly c-axis oriented films for potential applications in micro-electromechanical systems. The films were characterized by X-ray diffraction technique to identify the crystallographic orientation. It was observed that the film deposited in pure Argon (Ar) ambient were amorphous or weekly crystallized with no preferred (002) orientation. On the other hand, the films prepared in Ar-O₂ for ZnO were highly c-axis oriented. Similarly AlN films were observed to be oriented along c-axis perpendicular to substrate only when deposited in mixture of Ar-N₂. To demonstrate the application of piezoelectric properties, an FBAR device (Film Bulk Acoustic Resonator) using ZnO thin film was fabricated. ZnO films are very sensitive to the chemicals used in the micro-electro-mechanical systems (MEMS) fabrication processes which include acids, bases and etchants of different material layers (e.g. SiO₂, chromium, gold etc.). A specially designed mechanical jig was used for physically protecting the film during Si anisotropic etching process in potassium hydroxide solution. The potential applications of these films in various RF MEMS devices have been discussed.

Abstract: Rapid development of wireless communication system requires high frequency and high power surface acoustic wave (SAW) filter. For SAW RF MEMS devices on diamond film, they have higher working frequency and more power endurance. A SAW RF MEMS filters on diamond film is designed. Its center frequency is 400MHz, and the line width of its Inter Digital Transducer (IDT) is 5μm. The diamond film on silicon substrate is customized by the CAEP ultra-hard material Co. 2μm thick ZnO piezoelectric film is deposited on diamond film by RF sputtering method. XRD analysis shows that the ZnO film has good C-axis orientation. IDT is fabricated by lift-off process. With delicate process control, designed delicate IDT pattern is acquired. The SAW RF MEMS filter prototype is finally packaged and tested. Its measured center frequency is about 378MHz, with insertion loss of 15.99dB.

Abstract: Thermal shock and thermal fatigue of ferroelectric (FE) thin films were investigated by the pulsed laser tests. The power density was gradually increasing in the single pulsed laser heating test which simulated a thermal shock, the part melting threshold of Pb(Zr0.52Ti0.48)O3 (PZT) thin films was found by scanning electron microscopy (SEM). After thermal shock resulted the highest temperature below Curie point at the surface of PZT thin film, X-ray diffraction (XRD), SEM and RT66A standard ferroelectrics analyzer were used to study the microstructure, crystal grain sizes, and ferroelectric failure behavior. It was found that XRD peak of PZT thin film after laser beam heating was stronger than that before laser beam heating, crystal grain sizes decreased, and the ferroelectric properties were degraded. However there was no crack observed by SEM, until PZT thin films were melted. The fined grain effects on ferroelectric properties and XRD patterns of PZT thin film, depolarization due to the single pulsed laser heating were discussed respectively. The pulsed cycles with a certain power density were gradually increasing in the repetition pulsed laser heating test. It was interesting to find that the cracks will initiate and propagate due to the thermal fatigue induced by the repetition pulsed laser. The possible origins of the thermal fatigue cracks were also discussed.