SrTiO₃ and (Ba,Sr)TiO₃ Films Epitaxially Grown on SrRuO₃ Using Atomic Layer Deposition

High dielectric constant (<i>k</i>) materials have been investigated to improve the performance of dynamic random access memory (DRAM) capacitors. However, the conventional binary oxides have reached their fundamental limit of <i>k</i> < 100. In this study, we investigated alternative ternary oxides, SrTiO₃ (STO) and (Ba,Sr)TiO₃ (BSTO), which were epitaxially grown on SrRuO₃ (SRO) using atomic layer deposition (ALD). The structural compatibility between SRO and STO enables the in situ crystallization of STO during ALD at a low temperature of 300 °C. Consequently, STO on SRO exhibited no film deformation, a common issue during high temperature postdeposition annealing, and maintained superior crystallinity at a thin thickness down to 50 Å. Furthermore, the dielectric constant of STO can be adjusted by modulating its tunable ferroelectric and dielectric properties through Ba doping. BSTO, with a high dielectric constant (<i>k</i>_max:527) achieved at a Ba doping concentration of approximately 50%, displayed a low leakage current density (3.9 × 10^-8 A cm^-2 @ 1 V) and demonstrated excellent reliability of 10¹² cycles in the metal-insulator-metal capacitors. This study proposes a promising alternative to satisfy the extreme EOT required for next-generation DRAM capacitors.