Fabrication of double sided YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on 2 inch diameter LaAlO/sub 3/ wafers by direct wafer bonding

We have demonstrated a novel fabrication process for double-sided YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) thin films on 2 inch diameter (100) LaAlO/sub 3/ wafers by direct wafer bonding. YBCO thin films were deposited on one side of two LaAlO/sub 3/ wafers by a 90/spl deg/ off-axis sputtering technique. These two LaAlO/sub 3/ wafers were then polished on the opposite side and directly bonded at room temperature. We have also developed and optimized the process of LaAlO/sub 3/ wafer bonding. The effect of annealing on the roughness, twin structure and bonding strength of bonded LaAlO/sub 3/ wafers has been investigated. After annealing at 120/spl deg/C for 100 hours, the bonded LaAlO/sub 3/ pairs remained intact even after immersion in deionized water for 20 hours. This process can be used for fabricating double sided high temperature superconducting thin films on heterostructure substrates, which have important applications in high frequency devices.