Wire bonder made on-chip microtransformers for very high frequency (VHF) regime applications

Abstract:
We present a novel wafer-level fabrication method for 3D solenoidal microtransformers using an automatic wire bonder for chip-scale, very high frequency (VHF) regime applications. Using standard MEMS fabrication processes for the manufacturing of supporting structures, together with ultra-fast wire bonding for the fabrication of solenoids, enables the flexible fabrication of high performance air core microtransformers at high throughput. The primary and secondary sole-noids are wound one on top of the other in the lateral direction, using a 25 µm thick insulated gold wire. A simulation model based on the solenoids’ wire bonding trajectories has been defined using FastHenry to accurately predict and optimize the transformers inductive properties. The transformer chips are encapsulated in PDMS in order to protect the coils from environmental factors and mechanical damage. A fabricated transformer with 20 windings in both the primary and the secondary coils, yields an inductance of 490 nH, a maximum efficiency of 68 %, and a coupling factor of 94 % at a footprint of only 1 mm².