In this paper, the development of piezoelectric transducers based on periodically poled ferroelectric domains is investigated. Optical quality Z-cut LiNbO3 wafers have been used for the fabrication of test devices operating in the range of 10–100 MHz. The fabrication process is detailed and the characterization results are reported. A very good agreement between theoretical predictions achieved by periodic finite element analysis and experiments is observed, allowing for a precise identification of the excited modes. Elliptically polarized modes as well as quasipure longitudinal waves are pointed out. The robustness of the devices to lapping and polishing operations has also been tested. The possible utilizations of such transducers are discussed to conclude the paper. ©2007 American Institute of Physic

International audienceThe demand for highly coupled high quality acoustic wave devices for radio-frequency (RF) signal processing based on passive devices has generated a strong innovative activity, yielding the investigation of new excitation principles and waveguide structures. Periodically poled transducers (PPTs) have been recently investigated [E. Courjon et al., J. Appl. Phys. 102, 114107 (2007)], as an alternative to classical interdigital transducers (IDTs) for the excitation and detection of guided acoustic waves. PPTs have two principal advantages compared to IDTs: the robustness of the excitation versus defects or surface contamination and the possibility to excite waves exhibiting a wavelength equal to the poling period. Here a new acoustic resonator concept is suggested, allowing high frequency operation with a simplified package. The idea consists of using a waveguide based on a PPT fabricated on a ferroelectric single-crystal substrate such as lithium niobate or tantalate inserted between two single-crystal substrates allowing the guidance of elastic waves without losses. The concept analysis points out optimum configurations of the structure allowing the excitation of elastic waves compatible with RF applications

1% I ',I 1 I -. r( d.td%,fi(i r I-"[I 1 ' r -1. \/t' Abstract-The development of piezoelectric transducers based on periodically poled ferroelectrics domains is investigated.Optical quality Z-cut LiNb03 wafers have been used for the fabrication of test devices operating in the range 7 -70 MHz The fabrication process is detailed and characterization results are reported. A very good agreement between theoretical predictions achieved by periodic finite element analysis and experiments is observed, allowing for a precise identification of the excited modes.

In this paper, we present new results on the development of piezoelectric transducers based on periodically poled ferroelectrics domains. The fabrication of test devices operating in the range 50 -500 MHz has been achieved. Pure longitudinal modes are excited, yielding high frequency operation of test devices with easily achievable lithography process (20 and 10 µm periods). The dispersion analysis of our devices is reported and the capability of the proposed waveguide to support pure longitudinal modes along the plate radial dimension is emphasized

Passive radiofrequency filters and resonators exploited for telecommunication applications are generally based on surface or bulk acoustic wave (SAW or BAW) devices. However, these devices present some technological limits as short-circuits between the electrodes of the interdigital transducers (for SAW devices) or an accurate control of the resonator dimension (plate or film thickness for BAW devices). An alternative concept based on periodically poled transducers (PPT) implemented on ferroelectric substrates (LiNbO3 or LiTaO3) embedded between two guiding substrates yielding advanced packaging opportunities has been developed. An oscillator stabilized by such a PPT-based resonator operating at 131 MHz has been successfully fabricated. A phase noise of −165 dBc/Hz at 60 kHz from the carrier has been measured with an input power of 2 mW and a relative short term frequency stability of 10−9 per second. Other resonators built on waveguides exploiting thinned PPTs (around thirty microns) have allowed the excitation of only one contribution with a thermal sensibility equal to the one of the guiding materials (−30 ppm/K for silicon).

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