Split domain antiresonance in micromachined lithium niobate

The micromachined periodically poled LiNbO3 (PPLN) demonstrates acoustic superlattice properties. Different acoustic modes in PPLN wafer have their stop-bands with low FL and upper FU cutoff frequencies. The micromachined transducers based on such structures operate at frequencies near FL and FU; they have a strong domain resonance-antiresonance when acoustic half-wavelength is close to domain length. In this work, we investigate structures with 300- and 450-micron long domains micromachined in a 0.5-mm-thick Z-cut lithium niobate wafer. The metal electrodes are deposited onto multi-domain structures having up to 90 total inversely poled domains. Experimentally, two modes of operation are investigated: (1) acousto-electric current excitation of domain vibrations when rf current passes through the whole multidomain structure and (2) plate-waves excitation and detection at two opposite ends of domain pattern when acoustic vibration travels through the multidomain pattern. In both cases, the split antiresonances are observed, and they are characterized by two main minima coinciding with the FL and FU frequencies. The difference (FL − FU) constitutes the stop-band for propagating zero antisymmetric mode, at which PPLN transducer operates. The experimental data are in agreement with theoretical calculations. Possible application of the split antiresonance effect for micromachined ultrasonic transducers is discussed. [This work is made possible in part due to the research grant “Nonlinear vibrations of piezoelectric resonators,” UM, 2011.]