Nanoscale electrode and dielectric materials, processes and interfaces to form thin-film tantalum capacitors for high-frequency applications
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Today’s thin-film passive components such as capacitors and inductors are limited to low volumetric density and large form-factors that pose as major roadblock to miniaturization of the power modules. These components are also placed far away from the IC’s leading to large interconnect parasitics and lower operating frequencies. Novel thin-film technologies with high densities and small form-factors are, therefore, required to enable miniaturization and performance at high frequencies. Glass- and silicon- based interposer technologies that utilize vertical through-via interconnections have shown way to improve power distribution network (PDN) performance with thin power-ground planes. However, integration of ultra-high density capacitors in such substrates has not yet been demonstrated. This thesis addresses these challenges with tantalum-based, silicon-integrated, ultrathin, high-density capacitors at higher operating frequencies with lower leakage properties (<0.01µA/µF). The anodization kinetics of tantalum pentoxide and the underlying leakage current mechanisms are investigated to provide optimal process guidelines. The thin-film Ta capacitors demonstrated capacitance density of 0.1 µF/mm2 at 1-10 MHz in form-factors of 50 µm, which corresponds to 6X higher volumetric density relative to commercial tantalum capacitors. An innovative approach to address incompatibility of tantalum electrodes with substrates is pursued by prefabricating the electrodes on a free-standing foil, which are then transferred onto the active wafer to form the capacitors on Si. The integration approach is designed to embed these thin tantalum capacitors on alternative substrates such as organic, glass or silicon, with copper via interconnections for lower parasitics. The thesis also explores titanium-based high-density capacitors with high-permittivity titania dielectric as a potential alternate high-density capacitor technology.