No abstract

The bulk acoustic wave filter composed of piezoelectric thin film resonators has many features superior to those of other small filters such as a surface acoustic wave (SAW) filter and a ceramic filter. As it has no fine structure in its electrode design, it has a high Q factor that leads to low-loss and sharp-cut off characteristics and a high power durability particularly in the highfrequency range. Furthermore, it has the potentiality of integrated devices on a Si substrate. In this paper, we review the recent developments of piezoelectric thin film resonator filters in the world, including our development for mobile communication applications. After describing the feature and history of the piezoelectric thin film resonator filters, our technologies are introduced in focusing on the resonator structures, the piezoelectric thin film and electrode film materials, the cavity structures, the filter structure and its design rules and characteristics, comparing with SAW filters. The competition and coexistence between the piezoelectric thin film resonator filters and the SAW filters are also described. In this paper, we describe the development of a piezoelectric thin film resonator from the standpoint of researchers who have a long experience of SAW filter development.

No abstract

We propose a series of new compositions of AlN-based piezoelectric material based on the results of first-principles calculation. The composition is expressed by ð y ; 1Ày Þ x Al 1%x N, where the elements α and β are selected to maintain the charge neutrality of the host AlN. We found that the selection of Mg 2+ for α and Hf 4+ and Zr 4+ for β with y = 0.5 show good chemical stability with much better piezoelectric properties than pure AlN. Our results indicate broad compositional freedom for improving the piezoelectric properties of AlN by using the co-doping technique.