Formation and properties of proton-exchanged and annealed LiNbO3 waveguides for surface acoustic wave

Unveiling the Defect Structure of Lithium Niobate with Nuclear Methods

X-ray and neutron diffraction studies succeeded in the 1960s to determine the principal structural properties of congruent lithium niobate. However, the nature of the intrinsic defects related to the non-stoichiometry of this material remained an object of controversial discussion. In addition, the incorporation mechanism for dopants in the crystal lattice, showing a solubility range from about 0.1 mol% for rare earths to 9 mol% for some elements (e.g., Ti and Mg), stayed unresolved. Various different models for the formation of these defect structures were developed and required experimental verification. In this paper, we review the outstanding role of nuclear physics based methods in the process of unveiling the kind of intrinsic defects formed in congruent lithium niobate and the rules governing the incorporation of dopants. Complementary results in the isostructural compound lithium tantalate are reviewed for the case of the ferroelectric-paraelectric phase transition. We focus especially on the use of ion beam analysis under channeling conditions for the direct determination of dopant lattice sites and intrinsic defects and on Perturbed Angular Correlation measurements probing the local environment of dopants in the host lattice yielding independent and complementary information.

Proton-exchanged 36 degrees Y-X LiTaO3 waveguides for surface acoustic wave

A nontoxic proton source, octanoic acid, was adopted to fabricate proton-exchanged (PE) waveguides in 36 degrees Y-X lithium tantalate (LiTaO3) substrates. The PE ability of octanoic acid on LiTaO3, the penetration depth, was investigated by secondary-ion mass spectrometry (SIMS). The penetration depth of hydrogen ion exhibited an obviously step-like profile, which will be excellent for waveguide application. The relationship between waveguide depth (d) and exchanging time (t) was represented by d = 0.0653 X square root of t at T = 200 degrees C. To deserve to be mentioned, the octanoic acid has a slight dissociation coefficient and low activation energy, thus the accurate waveguide depth control can be obtained. For the application of acoustic wave guided acousto-optic devices, the leaky surface acoustic wave (LSAW) properties of PE 36 degrees Y-X LiTaO3 waveguides were investigated. The phase velocity slightly decreased with the increase of kd, where k was wavenumber. An indispensable parameter of acoustic wave device, the temperature coefficient of frequency (TCF), calculated from the frequency change of the output of LSAW delay line showed an increase with increased kd.