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Three-dimensional radio-frequency transformers based on a self-rolled-up membrane platform


Radio-frequency (RF) integrated circuits are used for wireless communications and require transformers capable of transferring electrical energy at RF/microwave frequencies. Traditional on-chip RF transformer designs have complex fabrication schemes and offer limited performance scalability. Here we report on-chip RF/microwave transformers that are based on a self-rolled-up membrane platform. The monolithic nature and versatility of this platform allows us to create high-performance transformers while maintaining an ultra-compact device footprint and by using only planar processing. We also show that the performance of the three-dimensional RF transformers improves with scaling, which is in contrast to conventional planar designs. In particular, we observe a continuous rate of increase in the index of performance of our RF transformers as we scale up the turns ratio. This behaviour is attributed to the almost ideal mutual magnetic coupling inherent to the self-rolled-up membrane three-dimensional architecture.

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The authors acknowledge support from the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under award no. DEFG02-07ER46471 (materials development), and the National Science Foundation under awards EEC 1449548 (device design, model and electrical testing), ECCS 1309375 (fabrication process development) and IIP 17-01047 (yield optimization).

Author information

X.L. designed and supervised the research. W.H. led the structural designs, mechanical modelling and electromagnetic modelling. W.H. and J.Z. led the fabrication of all samples, with assistance from S.L., M.D.K., M.L. and J.A.M. W.H. and P.F. led the d.c. and RF electrical measurements, with assistance from M.L., D.J.S., J.Z. and S.G. K.W. led the mechanical measurements, with assistance from W.H. and P.F. All authors commented on the paper.

Competing interests

The authors declare no competing interests.

Correspondence to Xiuling Li.

Supplementary information

Supplementary Information

Supplementary Notes 1–9, Supplementary Figures 1–8 and Supplementary Tables 1–6

Supplementary Video 1

Simulation of self-rolling of self-rolled-up membrane transformer.

Supplementary Video 2

Magnetic field distribution around self-rolled-up membrane.

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Further reading

Fig. 1: Schematic illustration of the 3D S-RUM transformer fabrication process flow.
Fig. 2: S-RUM transformer design layout and fabrication results.
Fig. 3: Fabrication controllability, and thermal and mechanical stabilities of the S-RUM micro-transformers.
Fig. 4: Performance of S-RUM transformers before and after thermal annealing for Sample B1-C1, and the index of performance benchmarking with literature counterparts.
Fig. 5: Extended performance comparison between on-chip S-RUM air-core RF/microwave transformer tested and simulated samples and their planar on-chip counterparts in the literature.