Gain-Enhanced On-Chip Antenna Utilizing Artificial Magnetic Conductor Reflecting Surface at 94 ...

101 Pages·2015·8.7 MB·English

Gain-Enhanced On-Chip Antenna Utilizing
Artificial Magnetic Conductor Reflecting Surface
at 94 GHz
Thesis by
Mahmoud Nafe
In Partial Fulfillment of the Requirements
For the Degree of
Masters of Science
King Abdullah University of Science and Technology, Thuwal,
Kingdom of Saudi Arabia
July, 2015
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The thesis of Mahmoud Nafe is approved by the examination committee
Committee Chairperson: Assist. Prof. Dr. Atif Shamim
Committee Member: Assoc. Prof. Dr. Hakan Bagci
Committee Member: Assoc. Prof. Dr. Khaled Salama
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Copyright 2015
Mahmoud Nafe
All Rights Reserved
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ABSTRACT
Gain-Enhanced On-Chip Antenna Utilizing Artificial
Magnetic Conductor Reflecting Surface at 94 GHz
Mahmoud Nafe
Nowadays, there is a growing demand for high frequency-bandwidth mm-wave
(30-300 GHz) electronic wireless transceiver systems to support applications such as
high data-rate wireless communication and high resolution imaging. Such mm-wave
systems are becoming more feasible due to the extreme transistor downscaling in
silicon-based integrated circuits, which enabled densely-integrated high-speed elec-
tronics operating up to more than 100 GHz with low fabrication cost. To further
enhance system integrability, it is required to implement all wireless system compo-
nents on the chip. Presently, the last major barrier to true System-on-Chip (SoC)
realization is the antenna implementation on the silicon chip.
Although at mm-wave frequencies the antenna size becomes small enough to fit on
chip, the antenna performance is greatly deteriorated due the high conductivity and
high relative permittivity of the silicon substrate. The negative e↵ects of the silicon
substrate could be avoided by using a metallic reflecting surface on top of silicon,
which e↵ectively isolates the antenna from the silicon. However, this approach has
the shortcoming of having to implement the antenna on the usually very thin silicon
oxide layer of a typical CMOS fabrication process (10’s of µm). This forces the
antenna to be in a very close proximity (less than one hundredth of a wavelength)
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to the reflecting surface. In this regime, the use of conventional metallic reflecting
surfaceforsiliconshieldinghasseveree↵ectsontheantennaperformanceasittendsto
reducetheantennaradiationresistanceresultinginmostoftheenergybeingabsorbed
rather than radiated.
In this work, the use of specially patterned reflecting surfaces for improving on-
chip antenna performance is investigated. By using a periodic metallic surface on
top of a grounded substrate, the structure can mimic the behavior of a perfect mag-
netic conductor, hence called Artificial Magnetic Conductor (AMC) surface. Unlike
conventional ground plane reflecting surfaces, AMC surfaces generally enhance the
radiation and impedance characteristics of close-by antennas. Based on this property,
a ring-based AMC reflecting surface has been designed in the oxide layer for on-chip
antennas operating at 94 GHz. Furthermore, a folded dipole antenna with its associ-
ated planar feeding structures has been optimized and integrated with the developed
ring-based AMC surface. The proposed design is then fabricated at KAUST clean-
room facilities. Prototype characterization showed very promising results with good
correlation to simulations, with the antenna exhibiting an impedance bandwidth of
10% (90-100 GHz) and peak gain of -1.4 dBi, which is the highest gain reported
for on-chip antennas at this frequency band without the use of any external o↵-chip
components or post-fabrication steps.
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ACKNOWLEDGEMENTS
IthasbeenanhonorandprivilegetoworkundersupervisionofProfessorAtifShamim
towhomIwouldliketoexpressmysincereappreciationandgratitudeforthegenerous
support, guidance and encouragement prior to and during the course of this thesis
work.
Also, I would like to thank my loving family for their continuous moral support
and for always believing in me. My father: Dr. Ali Nafe, thank you for keeping me
a top priority above your needs. My mother: Dr. Ola El-amrawi, thank you for your
overwhelming love and care. My brother Ahmed Nafe: thank you for always being a
friend at need.
My sincere appreciation goes to my colleges at the IMPACT Lab for their fruitful
discussions and beneficial exchange of opinions during the weekly group meetings.
Finally, I would like to thank Eng. Ahad syad for time and help in understanding
essential nano-fabrication concepts and technicalities and in teaching me to carry out
independently fabrication of my proposed on-chip antennas modules using KAUST
nano-fabrication cleanroom.
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TABLE OF CONTENTS
Examination Committee Approval 2
Copyright 3
Abstract 4
Acknowledgements 6
List of Figures 9
List of Tables 13
1 Introduction 14
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.3 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2 System-on-Chip Overview 20
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2 Challenges related to On-Chip Antennas’ Low Gain . . . . . . . . . . 22
2.3 Gain Enhancement Techniques . . . . . . . . . . . . . . . . . . . . . . 26
2.3.1 Silicon Hemispherical Lens . . . . . . . . . . . . . . . . . . . . 27
2.3.2 Micro-Electro-Mechanical Systems in CMOS . . . . . . . . . . 28
2.3.3 Micromachining and Proton Implantation . . . . . . . . . . . 30
2.3.4 Shielding Silicon Substrate . . . . . . . . . . . . . . . . . . . . 30
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Artificial Magnetic Conductor Surfaces: Theory, Design, and Simu-
lations 36
3.1 Antenna-Reflecting Surfaces . . . . . . . . . . . . . . . . . . . . . . . 36
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3.2 Surface Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.1 Surface Impedance as a Boundary Condition . . . . . . . . . . 38
3.2.2 Reflection from Surface Impedance . . . . . . . . . . . . . . . 39
3.3 AMC Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3.1 AMC Implementations . . . . . . . . . . . . . . . . . . . . . . 41
3.4 AMC Design, Simulation, and Optimization at 94 GHz . . . . . . . . 45
3.4.1 Floquet Theorem . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.4.2 Unit-Cell Simulation Model . . . . . . . . . . . . . . . . . . . 46
3.4.3 Investigated AMC Unit-Cell Designs . . . . . . . . . . . . . . 48
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4 Antenna on Chip 55
4.1 Investigations on 94 GHz Dipole Antennas . . . . . . . . . . . . . . . 55
4.1.1 Dipole on Silicon Substrate . . . . . . . . . . . . . . . . . . . 55
4.1.2 Dipole on AMC Surface . . . . . . . . . . . . . . . . . . . . . 59
4.2 Folded Dipole Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2.1 Principal of Operation . . . . . . . . . . . . . . . . . . . . . . 64
4.2.2 Folded Antenna Simulations . . . . . . . . . . . . . . . . . . . 66
4.3 Integrated AMC-Backed Folded Dipole Antenna . . . . . . . . . . . . 68
4.3.1 Planar Feeding Network . . . . . . . . . . . . . . . . . . . . . 68
4.3.2 End-to-End Structure . . . . . . . . . . . . . . . . . . . . . . 71
4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5 Fabrication and Measurement 75
5.1 Fabrication Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.2 Metrology of the fabricated prototype . . . . . . . . . . . . . . . . . . 80
5.3 On-Chip Antenna Measurements . . . . . . . . . . . . . . . . . . . . 82
5.4 Post-Measurement Analysis . . . . . . . . . . . . . . . . . . . . . . . 88
5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6 Conclusions and Future Work 95
References 97
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LIST OF FIGURES
1.1 Millimeter wave frequencies are more attractive for wireless communi-
cation applications: (a) available bandwidth [1] and (b) atmospheric
attenuation [2] for the di↵erent frequency bands. . . . . . . . . . . . . 15
2.1 The di↵erent integration techniques of a wireless communication sys-
tem: (a) multi-chip-module, (b) system-in-package, (c) system-on-
package and (d) system-on-chip [3, 4]. . . . . . . . . . . . . . . . . . . 21
2.2 Typical silicon based CMOS stack-up. . . . . . . . . . . . . . . . . . 23
2.3 Illustration showing that most of the radiated power of on-chip anten-
nas is coupled into the substrate[3]. . . . . . . . . . . . . . . . . . . . 24
2.4 Curving the backside of silicon into a hemispherical lens to convert
surface waves into useful radiation [5]. . . . . . . . . . . . . . . . . . 27
2.5 Photos of the fabricated MEMS based on-chip antenna [6]. . . . . . . 28
2.6 The fabrication steps proposed by [6] to realize the BCP, in order to
lift the antenna of the lossy silicon. . . . . . . . . . . . . . . . . . . . 29
2.7 Electromagneticallycoupledmicrostrippatchantennadesignedonquartz
substrate, which is placed on top of a silicon chip [7]. . . . . . . . . . 31
2.8 Perfect Magnetic Conductor (PMC) is artificially engineered by the
periodic arrangement of shaped metals on top of grounded substrate:
(a) square patches [8] and (b) Uniplanar Compact Photonic Bandgap
(UC-PBC) [9]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.9 AMC ground plane locations in a typical CMOS stack-up: (a) under-
neath the silicon substrate and (b) on top of silicon using the metal
layers embedded in the oxide. . . . . . . . . . . . . . . . . . . . . . . 34
3.1 Mushroom-like AMC surface proposed by Dan Sievenpiper [10]. . . . 41
3.2 Cross-sectionalviewofthemushroom-basedAMCalongwiththeequiv-
alent parallel LC circuit [11]. . . . . . . . . . . . . . . . . . . . . . . . 42
3.3 Mushroom-based AMC: (a) surface impedance and (b) reflection phase
[11]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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3.4 Examples of partially reflective surfaces: (a) square patches and (b)
wire grids [11]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.5 Optical ray model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.6 CST-MWS AMC unit cell simulation model . . . . . . . . . . . . . . 47
3.7 Simulation model of the square patch based AMC unit cell. . . . . . . 49
3.8 Simulated reflection phase response of square patch based AMC unit
cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.9 Square-patch sensitivity study (a) f is plotted against the gap for
AMC
di↵erent values of periodicity for a fixed oxide thickness of S=100 µm
and (b) f is plotted against the oxide thickness for di↵erent values
AMC
of periodicity and a fixed gap of G=5 µm. . . . . . . . . . . . . . . . 51
3.10 Ring-based AMC: (a) f decreases with the increase in slot width
AMC
and (b) AMC bandwidth decreases with the increase in slot width. . . 52
3.11 Reflection phase of the optimized ring based AMC . . . . . . . . . . . 53
4.1 Dipole antenna in air: (a) simulation model and (b) input impedance
at 94GHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.2 Radiation pattern of a dipole antenna in air at 94 GHz: (a) 3D pattern
and (b) principal planes: E-plane (XZ plane) and H-plane (YZ plane). 57
4.3 Dipole on silicon: (a) simulation model, (b) input impedance at 94 GHz. 57
4.4 Dipole on silicon: (a) 3D pattern and (b) principal planes: E-plane
(XZ plane) and H-plane (YZ plane) at 94GHz for substrate size of
2.4mm 2.4mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
⇥
4.5 Dipole on silicon: (a) 3D pattern and (b) principal planes: E-plane
(XZ plane) and H-plane (YZ plane) at 94GHz for substrate size of
2mm 2mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
⇥
4.6 Dipole antenna with a PEC/PMC/AMC underneath as a reflector . . 59
4.7 Maximum gain versus the number of unit cells. . . . . . . . . . . . . 61
4.8 Radiation pattern at 94GHz for dipole antenna on the di↵erent reflec-
tors: (a) PEC, (b) PMC and (C) ring-based AMC. . . . . . . . . . . 62
4.9 Foldedantenna: (a)model, (b)transmissionlinemodeand(c)antenna
mode [12]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.10 Folded dipole in air: (a) model and (b) input resistance. . . . . . . . 66
4.11 Folded dipole on a 4 4 ring-based AMC: (a) model and (b) input
⇥
resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67