Nancy Zhao Poster
Published on: Mar 3, 2016
Transcripts - Nancy Zhao Poster
Low RF Loss Radial Superlattice Via Structure
Using Eddy Current Canceling Effect
Nancy (Yixuan) Zhao
Mentor: Xu Chen
Advisor: Prof. José E. Schutt-Ainé
 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
 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
 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
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
Cross section of a single
strand wire under
low(left) and high(right)
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
*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.
layers results in a
eddy current opposite to
the one generated by
metal layers with
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
material and their
• Structure scale
• Thickness ratio
• Number of the
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:
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
• 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.