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Low RF Loss Radial Superlattice Via Structure Using Eddy Current Canceling Effect

Nancy (Yixuan) Zhao Mentor: Xu Chen Advisor: Prof. José E. Schutt-Ainé

Introduction Research Overview

Computational Simulation

Reference [1] Wen Huang; Xin Yu; Comberiate, T.; Cheng-Wei Qiu; Schutt-Aine, J.E.; Xiuling Li, "Miniaturized on-chip passive devices based on self-rolled-up SiNx nanomembrane inductive tube," Device Research Conference (DRC), 2013 71st Annual , vol., no., pp.227,228, 23-26 June 2013 [2] Rahimi, A.; Yong-Kyu Yk Yoon, "Low loss conductors for CMOS and through glass/silicon via (TGV/TSV) structures using eddy current cancelling superlattice structure," Electronic Components and Technology Conference (ECTC), 2014 IEEE 64th , vol., no., pp.736,741, 27-30 May 2014 [3] Clogston, A.M., “Reduction of skin effect losses by the use of laminated conductors,” The Bell System Technical Journal, vol.XXX, no.3, pp.491-529, July 1951

Cleanroom Fabrication

Application and Future Work

Theory

With an increasing demand for high-speed systems, the operation frequency of the integrated circuits has boosted in the past decade, reaching an average of 3GHz. Meanwhile, the undesirable loss at radio frequency(RF) in the conductors also grew as it suffered more from the skin effect then it was in low frequency or DC operation. •  Current is confined in the outermost surface

of the conducting material. •  Volume of the conductor is underutilized. •  Effective cross section is reduced.

•  Resistance and conductor loss are increased.

Cross section of a single strand wire under

low(left) and high(right) frequency.

In a high frequency operating environment, the ohmic loss of conductor is largely governed by the following equation, where the skin depth(δ) increases as the material’s conductivity(σ︎) and permeability(μ) decreases. *Notice that μF, the permeability for the ferromagnetic material, has a negative real part. To maximize δ, μeff has to be a value very close to zero. Thus, the thickness ratio tN/tF becomes a critical design parameter in effectively minimizing the conductor’s permeability.

The ferromagnetic layers results in a longitudinal direction eddy current opposite to the one generated by metal layers with positive permeability.

To suppress the loss at high operation frequency, a radial superlattice structure was purposed for its better performance in enlarging the skin depth and the quality factor. In the graph above, we juxtaposed multi-layers of ferromagnetic(Ni80Fe20) and non-ferromagnetic (FeCo) materials wrapping into a cylindrical shape, preventing the fringing effects using the planar structure.

To avoid unnecessary fabrication, ANSYS HFSS is used in designing and testing the schematic structure of superlattice. Parameters to be considered: •  Choice of

ferromagnetic and non-ferromagnetic material and their corresponding permeability under different ranges of frequencies.

•  Structure scale (nanoscopic or microscopic).

•  Thickness ratio

•  Number of the layers

The graphs shown above are the theoretical comparisons of current distribution between a layered CRS structure and a regular conductor made of copper only.

With no cleanroom experience, users are required to attend an extensive training before obtaining the lab access. I have completed a 20+ hours orientation and is now certified to work in the

MNTL cleanroom facilities.

Skills are gained in how to perform: •  Lithography •  Etching •  Metrology •  Deposition

Thin film deposition technique is required in superlattice fabrication to ensure the uniformity throughout the radial shape outer surface.

I would like to thank Xu Chen, Wen Huang, Prof. José E. Schutt-Ainé and Prof. Xiuling Li for their generous mentorship and assistance throughout

this fall 2014 semester.

The cylindrical shape superlattice can be manufactured based on self-rolled-up SiNx nanomembrane tubes. •  Current design for lumped passive devices

is now in a 3D plane, which allows its size to shrink more.

•  3D structures usually have smaller overlap

area with the substrate, which decreases its energy lose and increases its Q factor.

•  3D structure proves better confinement of

the EM field.