부산대학교 도서관

Ferroelectric tunnel junction (FTJ) is a promising low power nonvolatile memory for beyond-CMOS applications. In this paper, Co/BaTiO 3 /SrRuO 3 FTJs are fabricated, simulated, and their electrical characteristics are measured by capacitance–voltage ( ${C}$ – ${V}$ ), current–voltage ( ${I}$ – ${V}$ ), and high-frequency S-parameter measurements. Ferroelectricity of the ultrathin BaTiO 3 (~3.2 nm) film is first verified by a butterfly shaped hysteresis ${C}$ – ${V}$ profile, from which saturation polarizations are calculated in the ON state and OFF state as ${P}_{ \mathrm{ON}}=+ {20}\,\,\mu {C} / {\text{cm}}^{ {2}}$ and ${P}_{ \mathrm{OFF}}=- {25}\,\,\mu {C}/{\text{cm}}^{ {2}}$ , respectively. The numerical simulation of the FTJ device is performed using experimental electronic band parameters of the heterostructure. The device structure was optimized for ON/OFF ratio, ${I}_{ \mathrm{ON}} / {I}_{ \mathrm{OFF}}= {75}$ for a depolarization field, ${E}_{{dpol}} < { {10}}^{ {6}}~{V} / {\text{cm}}$ . The calculated tunnel currents of $ {250}\,\,{nm}\times {250}\,\,{nm}$ FTJ in ON state ( ${I}_{ \mathrm{ON}}= {130}\times {10}^{- {9}}\,\,{A}$ ) and OFF state ( ${I}_{{OFF}}={{1.75}\times {10}}^{{-9}}\,\,{A}$ ) match with experimental values. From the S-parameters of RF measurements, the high-frequency small-signal device model of the FTJ in ON state ( ${C}_{ \mathrm{ON}}= {5}\,\,{fF},{R}_{ \mathrm{ON}}={0.8}\,\,{M}\Omega$ ) and OFF state ( ${C}_{ \mathrm{OFF}}={ {10}}\,\,{fF},{R}_{ \mathrm{OFF}}= {70}\,\,{M}\Omega$ ) is developed for a frequency range from 50 MHz to 5 GHz. The extracted capacitor model of Co/BaTiO 3 /SrRuO 3 FTJ is useful for high-frequency simulation of benchmark FTJ circuits.