IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 16, NO. 4, JULY 2017 695
Electrical Modeling and Analysis of Cu-CNT
Heterogeneous Coaxial Through-Silicon Vias
Qijun Lu, Zhangming Zhu, Yintang Yang, Ruixue Ding, and Yuejin Li
Abstract—An equivalent-circuit model of Cu-carbon nanotube
heterogeneous coaxial through-silicon vias (HCTSVs) in 3-D inte-
grated circuits (3-D ICs) is proposed in this paper. Based on the
complex effective conductivity method, the resistances and induc-
tances of Cu-single walled carbon nanotube (SWCNT) HCTSVs
and Cu-multi walled carbon nanotube (MWCNT) HCTSVs are
compared with that of Cu coaxial through-silicon vias (CTSVs).
Furthermore, using the proposed model, the magnitudes of their
insertion losses are compared. It is shown that the transmission
performance of Cu-SWCNT HCTSVs with higher metallic frac-
tion and Cu-MWCNT HCTSVs is better than that of Cu CTSVs,
and the improvement of Cu-MWCNT HCTSVs is more obvious at
high frequencies. Finally, the transmission characteristics of Cu-
MWCNT HCTSVs are analyzed deeply to provide helpful design
guidelines for them in future high-speed 3-D ICs.
Index Terms—3-D integrated circuits (3-D ICs), carbon nan-
otube (CNT), equivalent-circuit model, heterogeneous coaxial
through-silicon vias (HCTSVs), transmission characteristics.
I. INTRODUCTION
S
INCE the scaling limits of physics, technology, and econ-
omy encountered in planar integrated circuits become in-
creasingly prominent, and to meet the continuous demand
for miniaturized, high performance, and high-speed microelec-
tronic systems, three-dimensional integrated circuits (3-D ICs)
have attracted great interest of researchers [ 1]–[3]. Through sil-
icon vias (TSVs), which are high aspect ratio vertical intercon-
nects providing connectivity between active layers, constitute a
key component of 3-D ICs [4]–[6]. They have the potential ben-
efits of improving the electrical performance including speed,
bandwidth, and functionality, and reducing power consumption
by shortening the interconnection path in 3-D ICs [7], [8].
Coaxial through-silicon vias (CTSVs), which use an outer
shell both as the return path of the inner signal wire and as the
shielding layer, can effectively reduce signal loss and coupling
noise, and their characteristic impedance is easy to be controlled.
Manuscript received August 27, 2016; revised January 19, 2017 and March 27,
2017; accepted May 21, 2017. Date of publication May 26, 2017; date of current
version July 7, 2017. This work was supported in part by the National Basic Re-
search Program of China (973 Program) under Grant 2014 CB339900 and in part
by the National Natural Science Foundation of China under Grant 61604113,
Grant 61625403, Grant 61334003, Grant 61376039, Grant 61574104, and Grant
61474088. (Corresponding author: Zhangming Zhu.)
The authors are with the School of Microelectronics, Xidian Univer-
sity, Xi’an 710071, China (e-mail: luqijun2000@126.com; zmyh@263.net;
yangyt@xidian.edu.cn; rxding@mail.xidian.edu.cn; yjli@mail.xidian.edu.cn).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TNANO.2017.2708509
Therefore, the fabrication of Cu CTSVs was implemented
[9], [10], and their frequency- and temperature-dependent
equivalent-circuit model [11] and wideband impedance model
were proposed [12]. Furthermore, the latency, power, insertion
loss, and crosstalk of Cu CTSVs were evaluated and compared
with that of Cu signal-ground TSV pairs, respectively, showing
that Cu CTSVs have better electrical performance [13]. On the
other hand, due to their extremely desirable properties of high
mechanical and thermal stability, high thermal and electrical
conductivity, and large current carrying capacity, carbon
nanotube (CNT) bundles have been identified as a promising
candidate for next generation high-speed interconnect systems
even if at present the fabricating cost is much higher [14]–[16].
Recently, CNT bundle TSV arrays were fabricated successfully
using various methods [17]–[21], and the equivalent-circuit
model of single walled carbon nanotube (SWCNT) bundle
signal-ground TSV pairs was established [22]. Then, the
stacking of silicon chips with CNT TSVs was experimentally
demonstrated [23]. Furthermore, the equivalent-circuit model
[24] and the electrothermal cosimulation [25] of carbon
heterogeneous interconnects consisting of horizontal multilayer
graphene transmission lines and vertical CNT TSVs were also
reported. In addition, the CNT-Cu composite can also be used as
the conducting material of TSVs, and the mechanical integrity
[26] and the thermo-mechanical stresses and reliability analysis
[27] of Cu-CNT hybrid TSVs were investigated deeply.
The objectives of this paper are t o propose an equivalent-
circuit model of Cu-CNT heterogeneous coaxial through-silicon
vias (HCTSVs), which use CNT bundle and Cu as their inner
signal wire and shielding layer conducting materials, respec-
tively, and study their transmission characteristics. Its organi-
zation is as follows. In Section II, an equivalent-circuit model
of Cu-CNT HCTSVs is proposed and simplified. Using the
proposed model, the resistances, inductances, and transmission
performance of Cu-CNT HCTSVs are compared with that of
Cu CTSVs, respectively, in Section III. Furthermore, a deep
analysis of transmission characteristics of Cu-multi walled car-
bon nanotube (MWCNT) HCTSVs is carried out in Section IV.
Finally, some conclusions are drawn in Section V.
II. E
QUIVALENT-CIRCUIT MODEL OF CU-CNT HCTSVS
The 3-D and cross-sectional views of a Cu-CNT HCTSV
configuration are shown in Fig. 1, where H and r
i
(i =
1 − 6) are the height and the radii, respectively. In this pa-
per, the equivalent-circuit model of Cu-CNT HCTSVs is de-
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