3-Dimensional Integration of Epitaxial Magnetic Tunnel Junctions with New Materials for Future MRAM

We fabricated novel epitaxial magnetic tunnel junction (MTJ) films with single-crystal spinel MgAl
2
O
4
(001) tunnel barrier on ϕ300 mm Si(001) wafers by sputtering deposition and demonstrated 3-dimensional (3D) integration of the epitaxial MTJ nano-pillars in STT-MRAM by using direct bonding of the epitaxial MTJ wafer and CMOS wafer. The epitaxial MTJs exhibit smaller bit-to-bit variations of magnetic and transport properties compared with poly-crystalline CoFeB/MgO/CoFeB MTJs due to the absence of crystal grains. The 3D integration of epitaxial MTJs allows us to replace conventional MTJ materials (MgO and CoFeB) with new dielectric and ferromagnetic materials, giving great flexibilities and scalability to future MRAM technology. The developed technologies will be applicable also to other kinds of tunnel junction devices such as the Josephson junctions in superconducting qubit for quantum computing.