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

High dielectric constant (k) 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 k < 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 (k_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.