L. Vergara

A model for the accurate determination of the electromechanical coupling factor of thin film SAW devices on non-insulating substrates

We propose a circuital model that simulates the frequency response of surface acoustic wave (SAW) delay lines made on piezoelectric thin films on non-insulating substrates. The model, which takes into account the parasitic elements that distort the frequency response (due to the conductive substrate, airborne coupling and mounting), allows accurate values of the piezoelectric properties of the films (k/sup 2/ and /spl nu//sub s/) to be obtained. This model has been applied to SAW delay lines made on AlN thin films deposited on different silicon substrates. We show that the values deduced for k/sup 2/ if parasitic effects are not considered can be underestimated by up to 20 times.

AlN-on-Si SAW filters: influence of film thickness, IDT geometry and substrate conductivity

In this paper we analyze the frequency response of surface acoustic wave (SAW) filters built on (00·2)-oriented AlN films deposited on silicon substrates. The experimental scattering parameters (Sij) of the filters were fitted using our own circuital model that takes into account the theoretical response of the ideal SAW along with all the external and internal parasitic effects. We discuss the relation between the different circuital elements and the physical properties of the SAW device (geometry, substrate resistivity, thickness of the piezoelectric layer, etc.) and the parasitic effects due to the packaging and the wire bonding. On the basis of this analysis, some guidelines for the design of SAW structures with an optimum frequency response are given.

SAW and BAW response of c-axis AlN thin films sputtered on platinum

We evaluate the longitudinal and transverse piezoelectric response of highly (00/spl middot/2)-oriented AlN films sputtered on platinum layers. We have observed that the existence of some defects in the films, associated with the appearance of weak diffraction peaks other than the 00/spl middot/2 reflection in the XRD patterns, annihilates the piezoelectric response, even in films with very large grain size. In the absence of these defects, the piezoelectric response of the AlN films is strongly dependent on the grain size of the microcrystals. The transverse and longitudinal electromechanical coupling factors (k/sub 31//sup 2/ and k/sub 33//sup 2/) were evaluated from the frequency response of SAW and BAW devices, respectively. Values of k/sub 31//sup 2/ = 2% and k/sub 33//sup 2/ = 4.77% were obtained for the AlN films deposited on Pt.

Assessment of the piezoelectric response of sputtered A1N films by x-ray diffraction

Thin films of sputtered AlN are usually termed as adequate for piezoelectric applications when they exhibit (00·2) texture with a narrow rocking-curve. However, in this paper we call this common belief into question by providing experimental evidence of samples with good crystal quality but very bad piezoelectric response and vice versa. According to our investigation, it is possible to assess the piezoelectric response by X-ray diffraction, but only after the sputtering chamber and the deposition system have been carefully characterized. It is necessary to correlate the crystallographic properties with the piezoelectric response in order to be able to use X-ray diffraction as a routine assessment tool.