Lanthanum-doped BiFeO₃/ZrO₂ gate stack for ferroelectric field effect transistors

A metal–ferroelectric–insulator–semiconductor (MFIS) structure was fabricated with lanthanum (La)-doped BiFeO₃ as ferroelectric and ZrO₂ as the high-k insulator layer. The BiFeO₃ film with 5 M doped La was prepared with sol–gel and ZrO₂ film was physically deposited with rf sputtering. Films structural characteristics were obtained using X-ray diffraction and scanning electron microscopy (SEM). The ferroelectric film shows the perovskite structure with orientation (110)/(104) when annealed in the range from 400 to 700 °C. The dielectric film shows an amorphous structure for the same range of annealing temperature. Electrical and ferroelectric properties were obtained by fabricating and characterizing metal/ferroelectric/silicon (MFS), metal/ferroelectric/metal (MFM), metal/insulator/silicon (MIS), metal/ferroelectric/insulator/metal (MFIM) and metal/ferroelectric/insulator/silicon (MFIS) capacitor structures with ferroelectric film of 200 nm thickness and dielectric film of various thicknesses. MFS structure shows a maximum memory window of 3.5 V and leakage current density of 1.4 × 10^–8 A/cm² with ferroelectric film annealed at 500 °C. The memory window was further improved to 6.62 V and leakage current to the order 10^–10 A/cm² with the introduction of 9 nm insulator layer between ferroelectric and silicon. The same device shows an excellent endurance property tested for 10¹² cycles and data retention tested for 5.56 h. The device shows a breakdown of 43 V, which is 9 V higher than the MFS structure. To the best of author's knowledge, this is the first report to integrate La-doped BiFeO₃ on ZrO₂ (high-k) dielectric for non-volatile memory applications.