Impact of process parameters on the structural and electrical properties of metal/PZT/Al2O3/silicon gate stack for non-volatile memory applications

In this paper, we present the structural and electrical properties of the Al2O3 buffer layer on non-volatile memory behavior using Metal/PZT/Al2O3/Silicon structures. Metal/PZT/Silicon and Metal/Al2O3/Silicon structures were also fabricated and characterized to obtain capacitance and leakage current parameters. Lead zirconate titanate (PZT:: 35: 65) and Al2O3 films were deposited by sputtering on the silicon substrate. Memory window, PUND, endurance, breakdown voltage, effective charges, flat- band voltage and leakage current density parameters were measured and the effects of process parameters on the structural and electrical characteristics were investigated. X-ray data show dominant (110) tetragonal phase of the PZT film, which crystallizes at 500 degrees C. The sputtered Al2O3 film annealed at different temperatures show dominant (312) orientation and amorphous nature at 425 degrees C. Multiple angle laser ellipsometric analysis reveals the temperature dependence of PZT film refractive index and extinction coefficient. Electrical characterization shows the maximum memory window of 3.9 V and breakdown voltage of 25 V for the Metal/Ferroelectric/Silicon (MFeS) structures annealed at 500 degrees C. With 10 nm Al2O3 layer in the Metal/Ferroelectric/Insulator/Silicon (MFeIS) structure, the memory window and breakdown voltage was improved to 7.21 and 35 V, respectively. Such structures show high endurance with no significant reduction polarization charge for upto 2.2 x 10(9) iteration cycles.