关键词: Aluminum doping, SrTiO₃, ultrathin, High dielectric constant, MOS capacitors

Abstract:

An ultrathin SrTiO₃ dielectric layer is optimized through Al doping to solve the problems existing in development of ultra-high-k oxide MOS capacitors. Through post-deposition annealing, Al doping induces changes in the electronic structure of SrTiO₃, thereby effectively reducing leakage current to <10^-8 A/cm² at 0.5 MV/cm but maintains good capacitance values (ε > 80) of ultrathin SrTiO₃ MOS capacitors.
Strontium titanate (SrTiO₃) is a high-k material but its bandgap is smaller than that of other oxide dielectrics (e.g., SiO₂, Al₂O₃). Consequently, an ultrathin SrTiO₃ film may have a high tunneling leakage current, which is not suitable for capacitor-based applications. To improve the performance of metal-oxide-semiconductor (MOS) capacitors using SrTiO₃, an approach based on homogenous and uniform aluminum doping to SrTiO₃ through co-sputtering is introduced. The bandgap of a pristine SrTiO₃ film showed an increase of 0.5 eV after Al doping. Furthermore, Al doping decreased the leakage current of SrTiO₃/Si-based MOS capacitors by more than five orders of magnitude (at the level of nanoampere per square centimeter). Importantly, a dielectric constant of 81.3 and equivalent oxide thickness less than 5 Å were achieved in an 8-nm-thick Al-doped SrTiO₃ film owing to changes in its crystal structure and conduction band edge electronic structure. Thus, the obtained data show the effectiveness of the proposed approach for solving the problems existing in the development of ultra-high-k oxide MOS capacitors.

Key words: Aluminum doping, SrTiO₃, ultrathin, High dielectric constant, MOS capacitors