This paper reviews recent progress of temperature compensated surface acoustic wave (SAW) devices for wireless communications. First, temperature compensation techniques based on the SiO 2 deposition and the wafer bonding are explained, and their implementation into real devices are discussed. Finally, we will show how high performances have been realized by the use of these technologies.
This paper presents a film transfer process to integrate barium strontium titanate (BST) metal-insulator-metal (MIM) structures with surface acoustic wave (SAW) devices on a lithium niobate (LN) substrate. A high-quality BST film grown on a Si substrate above 650 • C was patterned into the MIM structures, and transferred to a LN substrate below 130 • C by Ar-plasma-activated Au-Au bonding and the Si lost wafer process. Simple test SAW devices with the transferred BST variable capacitors (VCs) were fabricated and characterized. The resonance frequency of a one-port SAW resonator with the VC connected in series changed from 999 to 1018 MHz, when a dc bias voltage of 3 V was applied to the VC. Although the observed frequency tuning range was smaller than expected due to the degradation of BST in the process, the experimental result demonstrated that a tunable SAW filter with the transferred BST VCs was feasible.
Piezoelectric-on-silicon MEMS resonator is very well known for its compatibility with CMOS integrated circuit technology. However, its quality factor (Q) is highly affected by acoustic energy loss through the supporting structures. In this study, a resonator with butterfly-like round edge resonating plate structure and deploying properly designed PnC arrays on the tether and the anchoring boundaries are proposed to scale up the quality factor by effectively reducing the energy loss. The finite element analysis simulation results reveal that the proposed topologies can efficiently change the displacement field in the resonating plate and reduce the anchor loss. Consequently, an unloaded quality factor
Q
u
of the conventional resonator is raised from 29 899 to 51 503 (butterfly-like round edge resonating structure), 83 349 (Phononic crystal on the tether) and 83 899 (Phononic crystal on the anchor), representing 1.7 folds, 2.78 folds and 2.8 folds improvement respectively.
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