Decoupling with Anodized Ta
Novel configurations of decoupling capacitors were formed by anodizing Ta,resulting in Ta2O5 films 2000 Å thick and k =
23,giving about 110 nF/cm2. Since the dielectric is very thin,the parasitic inductance is almost unmeasurable,and is shown
by simulation to be less than 1 pH/square. Breakdown voltages are around 30 V and leakage at 5 V is less than 0.1 µA/cm2.
The total ESR is dependent on the plate thickness,but can be less than 10 mO. Since the material is paraelectric,there is no
significant falloff of dielectric behavior at frequencies well over 10 GHz. The capacitors are formed on flex with closespaced,
alternating contacts to minimize contact inductance. The assemblies are designed to be included in a polymer-based
BGA stack to provide ultra-low inductance as close to the chip as possible. In this presentation,the reasons for using these
materials and configurations are presented from the point of view of electronic performance,reliability,and
manufacturability.