Monolithic integrated SAW filter based on AlN for high-frequency applications

Abstract

Integrated AlN/SiO 2 /Si (1 0 0) delay lines for Rayleigh surface acoustic waves (SAWs) with resonant frequencies up to 3.4 GHz were fabricated using a new CMOS compatible concept. Different thicknesses of textured AlN films with wurtzite structure were deposited on tungsten-based interdigital transducers embedded in a SiO 2 layer by reactive pulse dc-sputtering at a temperature of 200 • C. Rocking curves of the films indicate c-axis (0 0 0 1) oriented, textured piezoelectric AlN films with a full-width at half-maximum of 1.88 • . The determined propagation loss and coupling factor K 2 of these SAW devices are 0.07 dB/λ and 0.78%, respectively. Different Rayleigh modes with acoustic velocities up to 5770 m s −1 are observed. By varying the wavelength, number of fingers as well as the length (i.e., the separation between the transducers) of the delay lines, the impact of several physical parameters on the frequency responses (S 11 , S 21 ) was studied. The influence of the AlN thickness and of the orientation of the delay lines on the silicon (1 0 0) wafers was also investigated. Finite element method simulations were applied to model the resonant frequencies, giving resonant frequencies in reasonable agreement with the experimental data.

SAW Characteristics of AlN/SiO2/3C-SiC Layered Structure With Embedded Electrodes

“…Although Refs. [16] and [17] demonstrated fabrication of similar device configuration, variation of the underneath layer for the AlN growth may cause non-uniform crystal growth and/or cracks [4], [9]. To avoid this difficulty, the authors also investigate the case that SiO2 thickness is bigger (Δh=0.5%λ) than the Al electrodes, as shown in Fig.6.…”

Piezoelectric Materials in RF Applications

“…The longitudinally coupled IDT shown in Figure 8(a) is probably the most used, but it requires reflectors to improve coupling or in other cases attenuators to reduce spurious wave propa-gation on the substrate surface [16]. It is also possible to use transverse coupling [17], but this configuration is more difficult to operate (Figure 8(b)). Finally, the association of several transmission SAW structures can be done as shown in Figure 8(c) to improve filter characteristics.…”

Piezoelectric thin films for double electrode CMOS MEMS surface acoustic wave (SAW) resonator

“…Thin film piezoelectric materials play an essential role in micro-electro-mechanical system (MEMS) SAW resonators to achieve single chip transceiver implementations. Efforts have been done to realize silicon based SAW resonators that have less lossy interfacing (Kaletta et al 2013;Vellekoop et al 1994;Baca et al 1999;Neculoiu et al 2009). Non-ferroelectric piezoelectric materials such as ZnO and AlN are highly silicon compatible making them suitable for RF-MEMS applications.…”