Direct wafer bonding : A new fabrication method for ferroelectric-silicon heterostructures

Abstract
Ferroelectric-semiconductor heterostructures were fabricated using direct wafer bonding. Polycrystalline Bi₄Ti₃O₁₂ ferroelectric thin films were deposited on 3" silicon wafers by chemical solution deposition. The films were polished and then directly bonded to silicon wafers in a micro-cleanroom. After thermal annealing in air at 500°C for 12 hours, the bonding energy increases up to 1.5 J/m². High resolution transmission electron microscopy shows a significant difference between the bonded and reacted interfaces. A Metal-Ferroelectric-Silicon (MFS) structure containing the ferroelectric-Si bonded interface was achieved by polishing down and etching the handling wafer. Capacitance-voltage (C-V) and current-voltage (I-V) characteristics were measured for the Bi₄Ti₃O₁₂/Si heterostructures with a bonded interface.