Ultrathin Calcium Titanate Capacitors
To enable further scaling for future generations of DRAM capacitors, significant efforts to replace Zirconium dioxide as high-k dielectric have been undertaken since the 1990s. In calculations, Calcium titanate has been identified as a potential replacement to allow a significant capacitance improvement. This material exhibits a significantly higher permittivity and a sufficient band gap. The scope of this thesis is therefore the preparation and detailed physical and electrical characterization of ultrathin Calcium titanate layers. The complete capacitor stacks including Calcium titanate have been prepared under ultrahigh vacuum to minimize the influence of adsorbents or contaminants at the interfaces. Various electrodes are evaluated regarding temperature stability and chemical reactance to achieve crystalline Calcium titanate. An optimal electrode was found to be a stack consisting of Pt on TiN.
Additionally, this thesis presents fundamental results on the creation, physical and electrical characterization of Calcium titanate nanocrystallites embedded in an amorphous matrix. Capacitors with these nanocrystallites exhibit an increased permittivity of 55 with low leakage currents comparable to currents in amorphous layers.