Emerging quantum communication applications have advanced the rapid development of up-conversion single-photon detectors and entangled photon-pair sources, of which the core components are both based on frequency conversion in periodically poled lithium niobate (PPLN) waveguides. MgO-Doped congruent lithium niobate (Mg:LN) is known as the most promising material for the fabrication of PPLN because of its attractive properties, but the leakage current complicates the high-quality periodic poling of Mg:LN, especially regarding its use with liquid electrodes. In this paper, we demonstrated an effective approach to suppress the leakage current by using a SiO₂ dielectric layer of appropriate thickness, and high-quality periodic poling has been realized in 5 mol% Mg:LN wafers with a diameter of 76.2 mm based on the electric-field poling method using liquid electrodes. The ease of the clear removal of the liquid electrodes is beneficial for the fabrication of waveguides on the wafer surface, and the wafer-level manufacture of PPMgLN with easy operation and high rate of finished products facilitates the mass production of PPMgLN devices for quantum communication applications.