Devices working with guided bulk acoustic waves can be used in mobile communication devices. GBAW devices (GBAW=Guided Bulk Acoustic Wave) enable manufacturing of miniaturized and low-cost micro-acoustic filter systems for RF applications.
The present trend towards miniaturization and towards lower production costs of respective devices such as filters or duplexers create a demand for cheaper components with a reduced volume.
SAW devices working with frequencies higher than 3 GHz are known from the IEEE article “4.5 GHz Lamb wave device composed of LiNbO3 thin film” by Michio Kadota, Takashi Ogami, Kansho Yamamoto, Yasuhiro Negoro, and Hikari Tochishita (IEEE, IMS 2009). A device includes z-axis orientated thin LiNbO3 (lithium niobate) films.
Boundary acoustic wave devices are known from US patent application US 2005/0057323 A1. Such boundary acoustic wave devices include a laminate of a plurality of boundary acoustic wave elements. Within the laminate different resonant structures are glued on top of each other.
U.S. Pat. No. 7,522,020 B2, discloses boundary acoustic wave devices having a single crystal piezoelectric substrate and electrode structures of a first boundary acoustic wave device on its top surface and second electrodes of a second boundary acoustic wave device on its bottom surface.
Boundary acoustic wave devices using shear horizontal boundary acoustic waves are known from United States patent application US 2006/0138902 A1. Electrode fingers are arranged on a lithium niobate single crystal substrate. The electrodes are covered by a silicon dioxide layer. The silicon dioxide layer is covered by a sound absorbing layer including a resin.
The above-mentioned boundary acoustic wave devices utilize single crystal piezoelectric substrates in which acoustic waves are excited. However, manufacturing costs of single crystal piezoelectric substrates like LiNbO3 (lithium niobate) are high. Further, the thickness of such single crystal substrates cannot be reduced according to modern demands for miniaturizing acoustic wave devices like bandpass filters or duplexers for mobile communication devices. Especially single crystals having a thickness of less than 100 μm cause problems during manufacturing when using large wafers of such crystals due to insufficient mechanical stability.