Reducing leakage current during periodic poling of ion-sliced x-cut MgO doped lithium niobate thin films

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Ion-sliced lithium niobate thin films offer high optical confinement over their bulk counter parts, enabling compact and efficient nonlinear optics. Quasi-phase matching by periodic poling of thin film lithium niobate remains challenging, however, due to large leakage currents, especially in magnesium oxide doped lithium niobate, which is used in bulk to reduce photorefractive damage. Here we present fabrication and poling details of 700 nm thick x-cut magnesium oxide doped lithium niobate thin films using electric field poling. We introduce a silicon dioxide insulation layer under co-planar electrodes to reduce leakage current. Rounded tips are utilized to encourage nucleation at the center of the electrodes. Uniform domains with 7.5 µm period and 50% duty cycle are achieved. The poling characteristics are compared to bulk lithium niobate, with and without the silicon dioxide insulation layer. The domains are characterized by piezoresponse force microscopy, hydrofluoric etching, and waveguide second harmonic generation at 1550 nm wavelength in a thin film lithium niobate waveguide loaded with a silicon nitride strip.