Abstract
Solutions for the development of compact RF passive transducers as an alternative to standard surface or bulk acoustic wave devices are receiving increasing interest. This article presents results on the development of an acoustic band-pass filter based on periodically poled ferroelectric domains in lithium niobate. The fabrication of periodically poled transducers (PPTs) operating in the range of 20 to 650 MHz has been achieved on 3-in (76.2-mm) 500-μm-thick wafers. This kind of transducer is able to excite elliptical as well as longitudinal modes, yielding phase velocities of about 3800 and 6500 ms(-1), respectively. A new type of acoustic band-pass filter is proposed, based on the use of PPTs instead of the SAWs excited by classical interdigital transducers. The design and the fabrication of such a filter are presented, as well as experimental measurements of its electrical response and transfer function. The feasibility of such a PPT-based filter is thereby demonstrated and the limitations of this method are discussed.
Highlights
Solutions for the development of compact RF passive transducers as an alternative to standard surface or bulk acoustic wave devices are receiving increasing interest
Its fabrication is performed by locally forcing the LiNbO3 ferroelectric polarization using a poling bench [3]
periodically poled transducers (PPTs) allow for the excitation of symmetrical Lamb modes [2] with operating frequencies twice as high as the operating frequencies obtained using SAWs excited by standard interdigital transducers (IDTs)
Summary
A PPT is based on a periodically poled piezoelectric substrate metalized on its both sides to obtain a capacitive dipole in which an elastic wave can be excited by phase construction [2]. The second feature is the possibility of exciting waves exhibiting a wavelength equal to the poling period, contrary to standard IDTs, for which the wavelength is twice the mechanical period of the grating (the Bragg condition). This characteristic, implies that the device operates in a second-harmonic regime, yielding the superimposition of progressive direct and backward modes. For this situation, one may expect some operational differences compared with standard IDTs. For this situation, one may expect some operational differences compared with standard IDTs This point will be discussed in the sections devoted to filter design and manufacture
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