On-chip 3D printing of metal microinductors for radio frequency electronics.

On-chip inductors are essential components of radio-frequency integrated circuits, yet their large footprint and limited scalability constrain chip miniaturization and increase manufacturing costs. Here we show a method for integrating three-dimensional metal microinductors directly onto chip contact pads using high-precision electrodeposition. The resulting freestanding coils extend above the chip surface, decoupling their inductance from the planar silicon area they occupy. We fabricate copper microsolenoids with different geometries directly on test chips and characterize their electrical performance over a broad frequency range. The microsolenoids exhibit inductance in the nanohenry range, quality factors of up to 18, and retain inductive behaviour up to 15 GHz, in agreement with electromagnetic simulations. The process is maskless and can be applied after standard chip fabrication without modifying the underlying circuit design, providing a route towards smaller, more scalable, and potentially lower-cost radio-frequency integrated circuits.