Dual process dielectric formation for decoupling capacitors on flexible substrates

Large area, high density integrated capacitors within printed wiring boards can provide a substantial decoupling capacitance with very low parasitic inductance. Tantalum pentoxide (Ta₂O₅) is an excellent dielectric for this application due to the relatively high dielectric constant (∼22-24), however the difficulty of fabricating large, defect-free capacitors has thus far prevented the realization of practical applications. High performance capacitors with Ta₂O₅ dielectric have been developed with a two step oxidation scheme at the High Density Electronics Center (HiDEC) at the University of Arkansas. The two step oxidation scheme consists of reactive sputtering followed by anodization. Thin films of Ta₂O₅ were deposited by reactive sputtering on silicon and also on Upilex® covered glass wafers using DC magnetron sputtering with a gas flow ratio of 10/90 O₂/Ar. In the two-step oxidation scheme, anodization is performed after reactively sputtering tantalum oxide films to obtain a densified oxide structure. The electrical and physical properties of these two step oxidized sputtered/anodized tantalum oxide films are shown to be superior to those of tantalum oxide films prepared by either anodization or sputtering alone. This work has shown that Ta₂O₅ dielectric material is a potential dielectric for integrated capacitors in advanced packaging applications.