On-chip 3D air-core microinductor for high-frequency applications using deformation of sacrificial polymer

A novel on-chip 3D air core micro-inductor, utilizing deformation of sacrificial thick polymer and conformal photoresist electrodeposition techniques, is reported. The bottom conductors are formed on silicon or glass substrate by metal electroplating through SU-8 polymeric mold. A thick SJR 5740 photoresist is then spun on and patterned to be a supporting mesa. Hard curing of such polymer mesa could significantly deform it into a cross-sectional bell-shape sacrificial core with graded profile in which is used to support top conductors formation. A layer of conformal electrodeposited photoresist (PEPR 2400) is then coated along the core's surface profile, patterned by standard optical lithography and filled up by metal electroplating. Finally, all polymeric molds including significantly deformed sacrificial core and electroplating bases are removed, resulting in an on-chip solenoid-type 3D air core micro-inductor. Since this new inductor has an air core and has only two contact points per turn, the core loss and equivalent series resistance are expected to be small, and hence, to give higher quality factor at high-frequency operation. Currently, high-frequency characterization of this on-chip inductor is under way.

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