||The surface acoustic wave and bulk acoustic wave devices are fabricated for the acoustic wave filters applications. Due to the fact that the surface acoustic wave and bulk acoustic wave devices are consisted by various structures, also their acoustic wave and propagation behaviors are different. Therefore, the various frequency response properties can be obtained when surface acoustic wave and bulk acoustic wave filters devices are constructed.|
For the purpose of overcoming the conventional photolithography, the nano-scale IDT electrodes are fabricated using E-beam lithography and dry-etching method. The photo-mask is unnecessary because the designed IDT pattern can be directly written on the photoresist by E-beam lithography system.
The positive photoresist and traditional photomask are used at the beginning to define the IDTs pattern, however, it is time-consuming. Therefore, the transparent and opaque pattern of traditional photomask is reversed to improve the process in this study. In addition, dose of E-beam lithography and etching time of dry-etching are key parameters for the assurance of IDTs line widths. This study designed four various line widths of IDTs and contributed the frequency of filters are 1339 MHz, 1801 MHz, 2422 MHz and 3745 MHz, respectively.
The ladder-type bulk acoustic wave filter consisted of solid mounted resonator with suitable serious and parallel arrangement. The solid mounted resonator is consisted of a sandwiched piezoelectric structure and a Bragg reflector. The better the characteristic of resonator, the better the bulk acoustic wave filter achieved.
In this study, the surface roughness and interface layer of the Bragg reflector consisted using Ti/Mo or SiO2/Mo are the key factor to avoid acoustic energy scattering. Therefore, the influences of Ti/Mo and SiO2/Mo structure on the frequency response have been investigated. Besides, the resonance frequency of resonator can be tuning with mass loading on it top electrode. The ladder-type filter performance is therefore controlled by serious and parallel resonators with various top electrode thicknesses.
Finally, the solid mounted resonator device fabricated with low surface roughness and clear interface layer of Bragg reflector comprised by SiO2/Mo structure shows a good frequency response. Besides, the 1.5 ladder-type filter with center frequency of 2452 MHz, 3-dB bandwidths of 84 MHz and insertion losses of -14.67 dB is obtained.