Five-day-long ferroelectric memory effect in Pt∕(Bi,La)4Ti3O12∕HfO2∕Si structures

In order to form metal–ferroelectric–semiconductor–insulator–semiconductor (MFIS) structures, hafnium oxide $\left({\mathrm{HfO}}_2\right)$ films were first deposited on $\mathrm{Si}\left(100\right)$ substrates at room temperature using an electron-beam evaporation method. Then, they were annealed in an ${\mathrm{O}}_2$ atmosphere at $800°\mathrm{C}$ for $1\min$ . No hysteretic characteristics were observed in the capacitance–voltage $\left(C–V\right)$ measurement for the metal–insulator–semiconductor capacitors. On these films, lanthanum-substituted bismuth titanate $\left[{\left(\mathrm{Bi},\mathrm{La}\right)}_4{\mathrm{Ti}}_3{\mathrm{O}}_{12}:\mathrm{BLT}\right]$ films with $380\mathrm{nm}$ in thickness were deposited by a sol–gel spin-coating method and annealed in an ${\mathrm{O}}_2$ atmosphere at $750°\mathrm{C}$ for $30\min$ . The MFIS sample showed the hysteretic $C–V$ characteristics and the memory window width was about $0.9\mathrm{V}$ for the voltage sweep of $\pm 7\mathrm{V}$ . Furthermore, the high and low capacitance values biased in the hysteresis loop were clearly distinguishable for over 5 days. The origin of the excellent data retention characteristics is discussed from a viewpoint of the transient current across the film.