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

Area of Science:

• Materials Science
• Electrical Engineering
• Solid State Physics

Background:

• Conventional binary oxides for dynamic random access memory (DRAM) capacitors have a limited dielectric constant (k < 100).
• Next-generation DRAM requires materials with extremely low equivalent oxide thickness (EOT).

Purpose of the Study:

• Investigate ternary oxides, strontium titanate (STO) and (Ba,Sr)TiO3 (BSTO), as alternatives for high-k DRAM capacitors.
• Optimize material properties for enhanced performance and reliability.

Main Methods:

• Epitaxial growth of STO and BSTO on SrRuO3 (SRO) using atomic layer deposition (ALD).
• In situ crystallization at low temperatures (300 °C) enabled by SRO/STO structural compatibility.
• Tuning dielectric properties of STO via Ba doping.

Main Results:

• STO on SRO maintained superior crystallinity at thicknesses down to 50 Å without film deformation.
• BSTO achieved a high dielectric constant (k_max: 527) at ~50% Ba doping.
• BSTO exhibited low leakage current (3.9 × 10^-8 A cm^-2 @ 1 V) and high reliability (10^12 cycles).

Conclusions:

• Ternary oxides STO and BSTO are promising alternatives for next-generation DRAM capacitors.
• ALD enables low-temperature, high-quality film growth with tunable properties.
• Optimized BSTO offers a viable solution for extreme EOT requirements.