Fabrication and characterization of a planar interleaved micro-transformer with magnetic core

A Survey on Microtransformers

“…On the other hand, this structure usually leads to inductance values lower than those that can be achieved with other structures. The two highest L-values at the secondary windings of a coplanar microtransformer were 5 µH and 900 nH, as reported by Yamaguchi et al [24] and Kahlouche et al [25], respectively. In both cases, the microtransformers were composed by spiral-interleaved coils with magnetic films as external cores, but in the first one, the film covered both sides of the coils, while in the second the film was only present between the coils and the glass substrate.…”

“…These inductors are usually designed according to the classic modeling by Greenhouse [11], [85]- [87]. The spirals can be circular, square, elliptical or n-sided polygons, and the coils can be coplanar (interleaved or side by side) or placed in different layers (with or without magnetic layers between the coils) [6], [17]- [19], [22]- [25], [27], [31], [33]- [37], [39]. Due to their compact spiral coil assembly architecture, microtransformers having very small area and volume can be fabricated.…”

“…Since 2010 the wire bonding technique has been added to the list, although one of the first devices built with this technology appeared in an application bulletin of the Burr-Brown Corporation in 1994 [114]. One of the most versatile processes for building microtransformers with any structure and geometry, is microfabrication [2], [5], [6], [17], [22], [25], [28], [40], [49]- [51], [54], [58], [62], [63], [70], [71], [80], [81], [84], [89], [90], [92], [105], [107]- [109], [122], [128]- [130]. Of course, any of the other fabrication approaches may involve microfabrication in some of the processing steps.…”

Integrated On-Chip Transformers: Recent Progress in the Design, Layout, Modeling and Fabrication

“…A more recent effort to realize on-chip transformers with CMOS-compatible processes employed the concept of residual stresses [79] to roll-up planar membranes into a three-dimensional coil geometry [76] (Figure 6e). To improve the performance of the transformer, attempts were also made to incorporate magnetic cores to the on-chip coil [80,81,82], where the magnetic layer was built over the spiral transformer in the form of a bridge structure. The integration of magnetic core was helpful to improve the coupling coefficient of the transformer and to achieve relatively low insertion loss of 1.4 dB [80].…”

“…To improve the performance of the transformer, attempts were also made to incorporate magnetic cores to the on-chip coil [80,81,82], where the magnetic layer was built over the spiral transformer in the form of a bridge structure. The integration of magnetic core was helpful to improve the coupling coefficient of the transformer and to achieve relatively low insertion loss of 1.4 dB [80].…”