Design and Fabrication of Ta $_{2}$ O $_{5}$ Stacks for Discrete Multibit Memory Application

In this paper, tantalum pentoxide (Ta₂O₅) has been investigated as the charge-storage dielectric for discrete, multibit memory applications. Two Ta₂O₅ containing dielectric stacks, Al₂O₃/Ta₂O₅/SiO₂ and Al₂O₃/Ta₂O₅/Al₂O₃/Ta₂O₅/SiO₂, have been fabricated and measured. Both structures exhibited excellent nonvolatile memory characteristics: fast program/erase speed with significant flat-band voltage shift at 1 μs, long retention, and good endurance. Interesting multiple staircase memory characteristics observed in the devices with two layers of Ta₂O₅ exhibit multiple, discrete charge-storage states. Such an integration of multibit in one cell is very attractive for developing high-density nonvolatile memory.