A 38 GHz On-Chip Antenna in 28-nm CMOS Using

Artificial Magnetic Conductor for 5G Wireless

Systems

l2 2 2 3 4
Mahsa Keshavarz Hedayati , , Abdolali Abdipour , Reza SarrafShirazi , Matthias John , Max J. Ammann , and
l
Robert Bogdan Staszewski
Dept. of Electrical Engineering
lUniversity College Dublin, Dublin, Treland
2 Amirkabir University of Technology, Tehran, Tran

3CONNECT, Trinity College Dublin, Dublin, Ireland

4Dublin Institute of Technology, Dublin, Ireland
Mahsa.keshavarz-hedayati@ucdconnect.ie, m keshavarz@aut.ac.ir

Abstract-This paper presents the first-ever millimeter wave Several on-chip antenna (AoC) structures have been designed
on-chip antenna (AoC) in 28 nm CMOS technology. The addition and demonstrated in literature to overcome the CMOS
of artificial magnetic conductor (AMC) can increase the
integration challenges: high permittivity and low resistivity
antenna's power gain and radiation efficiency to -1.75 dBi and
CMOS substrate leading to increased losses and, therefore, to
22%, respectively, with an occupied area of 0.95 mmx4.75 mm at
reducing the AoC efficiency [4,5]. Some of the proposed
38 GHz. This structure is intended for fully integrated single-chip
nanometer CMOS transceivers for 5G communication systems.
solutions, such as micromachining, using quartz superstrate on
top of a silicon stack, and proton implantation, need post
Index Terms- on-chip antenna (AoC), artificial magnetic processing and, therefore, increase the overall costs [2,4].
conductor (AMC), 28 nm CMOS, Fifth Generation (5G) wireless. Another possible method to increase the AoC efficiency is
electromagnetic shielding between the antenna and the lossy
I. INTRODUCTION CMOS substrate by means of Artificial Magnetic Conductor
(AMC) [4]. Several AMC structures have been reported, but
The Fifth Generation (5G) of mobile communications will
mainly focusing on 60 GHz and older CMOS technologies [3-
be a flexible infrastructure capable of handling our ever­
9].
increasing demand for mobile data and providing connectivity
In this paper, a 38 GHz on-chip antenna with AMC is
for upcoming technologies, such as internet of things (ToT).
designed and verified in 28 nm CMOS. To improve the
Based on recommended frequency spectra for 5G in the
radiation efficiency, CST™ MWS software is used to optimize
millimeter-wave (mm-wave) frequencies, 38 GHz has been
the resonant frequency of a new AMC structure. Fabrication
selected in this work due to its minimum atmospheric
requirements and metal design rules are verified.
absorption [1].
Section IT describes design challenges of the on-chip
Conventional heterogeneous wireless system integration
antenna in the 28 nm CMOS technology. Section TIT presents
exploits multichip modules (MCMs) and system-in-package
the design and analysis of the AMC structure. The on-chip
(SiP). A large chip area is a major disadvantage of MCM.
antenna design using AMC is presented in Section TV.
Likewise in SiP, the antennas usually are the largest
components since they remain outside the package [2]. In II. ON-CHIP ANTENNA DESIGN CHALLENGES IN 28 NM CMOS
addition, as frequencies increase the integration gets more
The quest for on-chip antennas has triggered intense
challenging due to the interconnects becoming more lossy [2].
interest as it facilitates the monolithic integration of the
Tn comparison, a system-on-chip (SoC) approach integrates
entire RF front-end with the antenna and, therefore,
digital baseband and the complete RF front-end directly on the
noticeably reduces the losses and the total system solution
same silicon die. Therefore, it can avoid interconnections, such
expense [3]. However, there are a few challenges associated
as wire-bonds, thus eliminating their losses. In addition, in
with this concept [3,10]. The first is related to the silicon
mm-wave applications, antenna sizes can be reduced to only a
substrate with a low resistivity of 10 O-cm, which dissipates
few millimeters, which is both possible and practical for full
some of antenna's energy, thus decreasing its radiation
on-chip implementation [2]. Furthermore, joint integration of
efficiency. Second, the high dielectric constant of Er=11.9
antenna and RF front-end on the same silicon die provides
decreases the radiation efficiency due to confming the
better matching possibilities with little concern for the
energy to the lossy substrate. One solution is to utilize the
conventional 50 0 boundary [3].
lowest metal layers as a shield to isolate the antenna from
the lossy silicon substrate. However, since the distance

978-1-5090-5414-5/16/$31.00 ©2016 IEEE

29
 between top and bottom metal layers is very narrow (�10-15 minimize conduction losses. As seen in Fig. 2, the signal is fed
flm) in recent CMOS technologies, there would not be into the antenna driver through the ground-signal-ground
enough space between the antenna and ground plane, thus (GSG) on-chip probe and probing pads with the pitch of
resulting in increased losses and degraded antenna 150 flm. Figures 3 and 4 demonstrate the far-field radiation
perfonnance [2]. pattern and maximum gain of the antenna. The E-plane
In the 28 nm CMOS node, the separation between the top realized gain is -6.9 dBi. Radiation and total efficiencies of the
and bottom metal layer is narrower than previously, hence it antenna structure, before employing the AMC, are shown in
makes the AoC design more difficult. To overcome this Fig. 5, which are 7.3% and 6.9%, respectively.
problem, in the proposed structure, the ground plane is
placed at the bottom of the silicon substrate and AMC
structure has been utilized to shield the antenna from the
lossy substrate. Another major difficulty in the 28 nm
process is the emergence of extremely strict DRC rules, such
as metal width, space and area. Consequently, the antenna
and AMC structure are designed and optimized in order to
overcome these layout design rules.

Ill. DESIGN OF A NOVEL ARTIFICIAL MAGNETIC CONDUCTOR

To improve the on-chip antenna performance and to

combat the aforementioned issues of advanced CMOS
technology, an AMC structure, also designated as high
impedance surface (HIS) or perfect magnetic conductor
(PMC), is employed. The AMC structure operates with a
reflection coefficient of j=+ I at its resonance frequency, Fig. 2. AMC unit cell modeling in CST.
which means that the phase of the reflected wave is 0° Far Field Realized Gain
·90
compared to the phase of the incident wave [6-7]. As a result,
·
60 -60
at some specific frequencies, stronger radiation can be IAzimuth�O I ·10 IAzimuth�180 I
generated, since the dissipation path to the substrate is blocked.
· 20

C
_30 -30
Figure I (a) shows our proposed single AMC unit ·· 30
implemented in M8 in 28nm CMOS. This AMC structure is -4 0
designed and optimized to be able to fulfill the strict DRC rules

�
in the standard 28nm CMOS technology. CST EM-solver -6.9 dBi
1 1
software is used to accurately characterize the reflection
magnitude and phase of the wave incident on the AMC. The 30 30
CST simulation model of the proposed AMC structure is
shown in Fig. I (b). 60 60
The equivalent circuit of the AMC can be modeled simply 90
as parallel RLC resonance circuits, as shown in Fig. l(c). In the Elevation I Degree vs dB
model, the resistor represents the low-resistivity of the silicon Fig. 3. E-Plane 2-D gain radiation pattern.
substrate, the inductor represents the metal traces and the
capacitor represents the coupling between the traces of two Far Field Realized Gain
adjacent AMC cells and the fringing capacitance [7]. o

IV. ON-CHIP ANTENNA DESIGN 60 300

A. On-Chip Antenna without AMC
The proposed triangular monopole antenna is designed in the
top metal layer (AP) featuring larger metal thickness in order to 90 270

n n
250
nrl
120

----rrr 160
190
220

(a) (c) Azimuth / Degree vs dB

(b)
Fig. 1. (a) AMC unit cell, (b) AMC unit cell modeling in CST, (c) Fig. 4. H-Plane 2-D gain radiation pattern.
Equivalent circuit

30
 Figure 8 shows the input reflection coefficient of the AoC,
which is better than -10 dB from 31 GHz to 45 GHz. It results
-Radiation Efficiency
0.11 in the impedance matching bandwidth of 37%. The simulated
- Total Efficiency
realized gain is -1.75 dBi at 38 GHz, as can be seen in the
0.1
radiation patterns in Fig. 9 and Fig. 10. The radiation efficiency
>,
g 0.09 and total efficiency are 22.4% and 22.1%, respectively, as
'u
"

u::
shown in Fig. 11. As can be seen, the gain and efficiency have
& 0.08
5.15 dB and 15% improvements compared to the antenna
0.07 without AMC, respectively.
Table IT compares the performance of this antenna with
0.06
previous AoCs, which are in older CMOS technologies and
mostly in 60 GHz.
35 36 37 38 39 40 41 42 43 44
(GHz)
Frequencv
Fig. 5. Radiation efliciency versus frequency

B. On-Chip Antenna with AMC -5

Figure 6 shows the 3D view of the proposed AoC on top of

2x 10 AMC cells. The AMC cells are designed in M8. The
physical dimensions of the antenna and proposed AMC unit are
shown in Fig. 7 and Table I. The total layout area including the
RF pads is 0.95 mm x 4.75 mm.

32 34 36 38 40 42 44 46 48 50
(GHz)
Frequency
Fig. 8. Input reflection coefficient ofthe antenna with AMC.

Farfield Realized Gain

-90
-60 -60
Azimuth�O I Azimuth� 180

-30

Fig. 6. Structure ofthe AOC with AMC.

0
·'C1 -1.75 dBi 1
"0 0

J L
� ,� 30

60 60
90
� t
Elevation/Degree vs. dB

Fig. 9. 2-D E-plane radiation pattern gain of the antenna with AMC.
:t
"x:
-
I
Fig. 7. Physical dimensions of proposed AMC and antenna

TABLE I. PHYSICAL DIMENSIONS OF PROPOSED AMC AND

ANTENNA
Dimension We L Lm Wm Wp2
Value ()tm) 588 290 300 8 140
Dimension gp L, L, t X
Value ()tm) 30 436 436 12 58

31
 Far Field Realized Gain efficiency and gain of the antenna are 22% and -1.75 dBi at 38
o GHz, respectively. The total area of AoC with AMC cells and
GSG RF pads is 0.95 mm x 4.75 mm.

60 300
ACKNOWLEDGMENT

The authors acknowledge Science Foundation Ireland (SFI)

90 270 grant 14/RP/I2921 for fmancial support, MCCI for hardware
support, and TSMC for chip fabrication.

120 240
REFERENCES

[1] T. S. Rappaport, S. Sun, and R. Mayzus, "Millimeter Wave

ISO 210
Mobile Communications for 5G Cellular: It Will Work." IEEE
180
Access. vol. I, May 2013.
Azimuth / Degree vs dB
[2] Hammad M. Cheema and Atif Shamim, "The last Barrier" IEEE
Fig. 10. 2-D H-plane radiation pattern gain of the antenna with AMC. Microw. Mag. 2013.

[3] D. Gang, HU Ming-Yang, and Y. Tang, "Wideband 60 GHz On­

Chip Triangular Monopole Antenna in CMOS Technology," 3rd
0.24
i-----,----t=:=::::"l'----
:: -;==
===.:::
= ::.:::=:::;l
- Radiation Efficiency
IEEE Asia-Pacific Con! on Antenna and Propagation, 2014.
- To!al Efllciency [4] A. Barakat, A. Allam, R. K. Pokharel, et al. "Compact Size High
0.22
Gain AoC Using Rectangular AMC in CMOS for 60 GHz
Millimeter Wave Applications" IEEE MTT-S International
0.2 Microwave Sympoium Digest, 2013.
c [5] B.-B. Adela, P. Zeijl, U. Johannsen, and B. Smolders, "On-Chip
"
'G 0.18 Antenna Integration for Millimeter-Wave Single-Chip FMCW
�
"" Radar, Providing High Efficiency and Isolation," IEEE Trans.
W
0.16
Antennas Propag., vol. 64, no. 8, August 2016.

[6] Hsin-Chih Kuo, Han-LinYue, et all, "A 60-GHz CMOS Sub­

0.14
Harmonic RF Receiver With Integrated On-Chip Artificial­
Magnetic-Conductor Vagi Antenna and Balun Bandpass Filter
for Very-Short Range Gigabit Communications" IEEE Trans.
0.12 "------'---'---�
34 36 38 40 42 44 Microw. Theory Techn., vol. 61, no. 4, April 2013.
Frequency (GHz) [7] Xiao-Yue Bao, Yong-Xin Guo, and Yong-Zhong Xiong, "60-
Fig. II. Radiation efficiency versus frequency of the antenna with AMC. GHz AMC-Based Circularly Polarized On-Chip Antenna Using
Standard 0.18- m CMOS Technology" IEEE Trans. Antennas
Propag., vol. 60, no. 5, May 2012.
TABLE II. PERFORMANCE COMPARISON WITH PREVIOUSLY
REPORTED WORKS [8] Y. Huo, X. Dong, and J. Bornemann, "A Wideband Artificial
Magnetic Conductor Vagi Antenna For 60 GHz Standard 0.13
Type of CMOS Process Frequency Gain Efficiency flm CMOS Application," IEEE International Conference on
Antenna Solid-State and Integrated Circuit Technology, 2014.
AMC loop Standard 0.18 65 GHz -4.4 dBi N.A.
[9] X. Y. Bao et aI., "60-GHz AMC-based circularly polarized on­
[9] �m
chip antenna using standard 0.18-l1m CMOS technology,"
2-element N.A. 60 GHz -3. 5 dBi 15.8%
Vagi [11] IEEE Trans. Antennas Propag., pp. 2234-2241, May 2012.
AMC [8] Standard 0.13 60 GHz -0.2 dBi 19.6% [10] S. Pan, and F. Capolino, "Design of a CMOS On-Chip Slot
�m Antenna With Extremely Flat Cavity at 140 GHz," IEEE
AMC [12] Standard 0.18 60 GHz OdBi 39% Antennas Wireless Propag. Lett., vol. 10, 2011.
�m
[11] F. Gutierrez et aI., "On-chip integrated antenna structures in
AMC [13] Standard 0.18 60 GHz -2.2 dBi -
CMOS for 60 GHz WPAN systems," IEEE J. Sel. Areas
�m
This work Standard 28 nm 38 GHz -1.75 dBi 22.4% Commun., pp. 1367-1368, Oct. 2009.

[12] A. Barakat et aI., "Performance Optimization of a 60 GHz

Antenna-on-Chip over an Artiticial Magnetic Conductor," IEEE
V. CONCLUSIONS Proceedings of Japan-Egypt Conferece on Electronics,
Communication and Computers, March 2012.
A 38 GHz triangular monopole antenna-on-chip (AoC)
employing a new AMC structure to improve the performance is [13] H. Chu, L. Qingyuan, and Y.-X. Guo, "60-GHz Broadband
CMOS On-Chip Antenna with an Artiticial Magnetic
introduced in 28 nm CMOS technology for 5G communication
Conductor," IEEE MTT-S IMWS-AMP, July 2016.
applications. The AoC performance improved by optimizing
the structure over several configurations of AMC cells. The

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