Wafer-to-wafer transfer process of barium strontium titanate metal-insulator-metal structures by laser pre-irradiation and gold-gold bonding for frequency tuning applications

This is the first report on successful direct transfer of barium strontium titanate (BST) grown on a sapphire substrate at high temperature (~650 °C) to a target substrate at low temperature. The key point of the transfer process is the pre-irradiation of frequency-tripled Nd:YVO₄ laser to a laser adsorption layer beneath the BST layer through the transparent substrate, which weakens BST/Pt adhesion by thermal effect. The bonded substrates separated at BST/Pt interface near sapphire by slight impact to sapphire. After forming an upper Pt electrode on the transferred BST, voltage tuning of the dielectric constant was confirmed.