Direct bonding of high dielectric oxides for high-performance transistor applications.

We developed a plasma activation process using a gas mixture of O 2 /NH 3 /H 2 O for direct bonding, which realized the combination of bulk aluminum oxide (Al 2 O 3) and yttria-stabilized cubic zirconia (YSZ) without interlayers for the first time. The bonding could withstand multiple mechanical grinding and polishing processes and exhibited sufficient bonding strength for device micro/nanofabication. A nanoscale, sharp, and layered crystalline bonding interface with fewer grain boundaries was confirmed by transmission electron microscopy. The interfacial structure is well-suited for superior performance in high dielectric constant metal–oxide–semiconductor field-effect transistors. Moreover, this bonding method is universal for the fabrication of Al 2 O 3 /SiO 2 and YSZ/SiO 2 heterostructures. Fabrication of the Al 2 O 3 /YSZ heterogeneous structure using the O 2 /NH 3 /H 2 O plasma activation, which was also universal for the direct bonding Al 2 O 3 /SiO 2 and YSZ/SiO 2. Image, graphical abstract [ABSTRACT FROM AUTHOR]