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

We developed a plasma activation process using a gas mixture of O2/NH3/H2O for direct bonding, which realized the combination of bulk aluminum oxide (Al2O3) 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 Al2O3/SiO2 and YSZ/SiO2 heterostructures.