Wireless communication systems appeared as a marvelous technology allowing for access to personal and other services, devices, computation and communication, wherever and whenever. Resonators and filters based on bulk acoustic waves (BAW) and surface acoustic waves (SAW) are widely used in wireless communication systems, from customer electronics to military systems, where frequency control is required. Day by day, customers are demanding higher speed and larger bandwidths, smaller in size but cheaper in price. In return, these trends necessitate the development of novel designing, structure techniques for the fabrication of devices with superior performance and higher capacity at lower manufacturing costs.
ZnO-based film bulk acoustic resonator (FBAR) process has the excellent flexibility of choosing at film and/or combination, thereby it is compatible with IC technologies.
This dissertation focuses on the designing and implementing techniques of microwave acoustic resonators for FBAR device applications. A prime choice of FBAR structure is ZnO-based solidly mounted resonator (SMR) type, which has been proved to have small size and great performance especially in power han-dling capability.
ZnO-based FBARs are made of a thin film of piezoelectric material (ZnO) sandwiched between two metal electrodes. In order to prevent propagation of energy into the substrate, they are acoustically isolated from the substrate. In the case of SMR-type, ZnO layer is isolated from the substrate by a series of acoustic reflectors (Bragg reflectors). In applications, when an electric field is applied between the two electrodes, the piezoelectric material is deformed and an acoustic wave is propagated into the material bulk.
A comprehensive manufacture process along with proposed techniques has been developed allowing the fabrication of high quality ZnO-based SMR-type FBAR device at the fundamental resonance frequency. The fabricated FBAR devices achieved very high return loss and quality factor of up to -40 dB and 7000, respectively.
On the other hand, here we have proposed a technique to realize a second-order-resonant frequency FBAR device, which operates in the range of 2.5 GHz - 3.1 GHz with high quality performance such as return loss of -45 dB and quali-ty factor of 9000.
Beside the FBAR demonstrations, we proposed two feasible studies of ZnO-based FBAR device for an ultra-mass-sensitive sensor and RF spiral inductor fabricated on multilayered Bragg reflector. The proposed mass sensor can have very high sensitivity of 0.05$\times$105 Hz.$cm^2$/ng, which is up to five-order of magnitude higher than the sensitivity (0.057 Hz.$cm^2$/ng) of the conventional 5-Mhz quartz crystal microbalance. In case of the RF spiral inductor, the proposed structure of inductor showed a better performance than conventional spiral inductor structures in terms of the return loss parameters and quality factor.
