Demonstration of Ultra-thin Tantalum Capacitors on Silicon Substrates for High-frequency and High-efficiency Power Applications

This paper describes an innovative scheme for integrating thinfilm tantalum (Ta) capacitors on active silicon substrates, an approach that can serve as a roadmap for the potential integration of ultra-thin high density capacitors in near future. The paper describes a new 3D concept for ultra-miniaturized, multi-functional and relatively low-cost power converter modules. The scheme consists of planar tantalum (Ta) capacitors by forming Ta2O5 (30-120 nm thick) dielectric and attaching directly to active or passive Si substrates using ultra-loss dielectrics (Zeon, ZS-100). Capacitors attached directly on Si allow for shorter interconnection length (< 10 mu m) yielding lower parasitics in loop inductance and planar resistance. Reducing these parasitics results in higher switching frequency (>100 MHz) with fewer Ta capacitors on active Si. The paper focuses on capacitor fabrication of ultra-thin Ta foils (< 5 mu m) and their integration on ultra-thin active Si for lowering the parasitics. Consequently, electrical characterization of the above capacitors demonstrates the fundamental electrical superiority of the 3D integrated Ta capacitors.