1
RFIC2017
RTU2B-2
Fully-Scalable 2D THz Radiating Array: A
42-Element Source in 130-nm SiGe with
80-μW Total Radiated Power at 1.01THz
Zhi Hu and Ruonan Han
MIT, Cambridge, MA, USA
RTU2B-2
Student Paper
Finalist
2
RFIC2017
Outline
• Motivation and Challenges
• Design of Oscillator
• Formation of 1-THz Oscillating-Radiating Array
• Measurement Results
• Conclusions
RTU2B-2
3
RFIC2017
Applications of high-power
high-frequency THz source
RTU2B-2
ISSCC2013
ISSCC2012
ISSCC2015
JSSC2015
JSSC2014
VLSI2015 ISSCC2016
T-MTT2015
0.2 0.4 0.6 0.8 1.0 1.2 1.4-30
-20
-10
0
10
Co
here
nt
Rad
iate
d P
ow
er
(dB
m)
Frequency (THz)
Array
Non-Array
• Building coherent radiating
array at higher frequency is
more challenging
High-Resolution Imaging
Bio-Molecule Spectroscopy
High-Precision Vibrometry
[F. Schuster et al.,
ISSCC, 2011.]
[T. Globus et al.,
Convergent Science
Physical Oncology, 2016.]
[G. Bissinger, D. Oliver,
Sound & Vibration, 2007.]
Path to high-power
1-THz radiator
Pushing Frequency and Power Limit of THz Radiator
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RFIC2017
Why Building 1-THz Radiating Array Is Difficult?
RTU2B-2
1 THz > fmax of all silicon-based
transistors (fastest: 450 GHz in IHP S13G2)
Efficient high-order harmonic
generation and radiation
Antenna array
requires λ/2 spacing
~70μm x 70μm for
each radiating unit
Very limited area to fit in
all necessary components
Array scale can
be very large
Accumulation of phase error between units due to
inter-unit injection can cause severe beam tilting
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RFIC2017
Call for Compact Multi-Functional Array Unit
RTU2B-2
Array Unit OscillatorPhase-
Synchronizing
Coupler
1-THz
Antenna
Harmonic
Filter
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RFIC2017
Our Slotline-Bound-Array Solution
RTU2B-2
• Differential oscillators plus slotlines accomplish all tasks
– Each unit oscillates at f0 = 250 GHz and radiates 4f0 = 1 THz
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RFIC2017
Outline
• Motivation and Challenges
• Design of Oscillator
• Formation of 1-THz Oscillating-Radiating Array
• Measurement Results
• Conclusions
RTU2B-2
8
RFIC2017
Multi-Functional Array Unit
RTU2B-2
Array Unit OscillatorPhase-
Synchronizing
Coupler
1-THz
Antenna
Harmonic
Filter
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RFIC2017
Oscillator Pair Capable of Efficient Harmonic Generation
RTU2B-2
• At f0 (250 GHz), two oscillators are forced to oscillate differentially
• For even-order harmonics from two oscillators, including 4f0 = 1 THz
– They are in-phase, hence repelled from slotline (feedback loop)
– No dissipation at base, more power is delivered outwards
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RFIC2017
Maximize Oscillation at f0 in Single Oscillator
RTU2B-2
2
*
21 12
1
11 12
1/ ,
arcsin Re Im( )/
opt
TL TL opt
A V V y y
Z g A y A
0 100 200 300-270
-240
-210
-180
Op
tim
um
Ph
ase S
hif
t an
g(A
op
t) (
deg
)Frequency (GHz)
Δφ = 84°
• Phase delay of V2 should be compensated
– Intrinsic delay of IC
– Undesired feed-forward current Ifeed
• Use self-feeding topology to adjust phase
[R. Spence, Linear Active Networks, 1970.]
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RFIC2017
Outline
• Motivation and Challenges
• Design of Oscillating Unit
• Formation of 1-THz Oscillating-Radiating Array
• Measurement Results
• Conclusions
RTU2B-2
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RFIC2017
RTU2B-2
• Two λ/4 @ f0 transmission lines (short open)
• E-shaped pattern composes the boundary of oscillating unit
• Resonator is implemented by slotlines
Expose Oscillation Using Branched Resonator
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RFIC2017
Reson
ato
r 1
Reson
ato
r 2
Reson
ato
r 3
Zresonator
Structure of a Complete Oscillating Unit
RTU2B-2
100 200 300 400
0
200
400
600
800
1000
1200
Res
on
ato
r Im
ped
an
ce
Ma
gn
itu
de (
Oh
m)
Frequency (GHz)
• Oscillators sealed by three resonators
– Two branched resonators
– One broadband open
• In-shunt resonators present Q = 18
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RFIC2017
Interface Adjacent Units Using Branched Resonator
RTU2B-2
…
…
…
…
……
Single Abut
Vertically
• Horizontal slotlines on the border (2x1 case) are merged
• Vertical slotlines on the border (1x2 case) run parallel
……
Abut
Horizontally
2D
Expansion
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RFIC2017
Multi-Functional Array Unit
RTU2B-2
Array Unit OscillatorPhase-
Synchronizing
Coupler
1-THz
Antenna
Harmonic
Filter
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RFIC2017
Coupling (at f0) between Horizontally Adjacent Units
RTU2B-2
Single-Node Injection vs. Distributed Phase Synchronization
[B. Razavi, JSSC, 2004.]
Phase at every
point is synced,
even if there is
mismatch of ω0
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RFIC2017
Coupling (at f0) between Vertically Adjacent Units
RTU2B-2
• Branched resonator shared phase relationship determined
• Use slotline for the purpose of array-wide in-phase radiation (discuss later)
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RFIC2017
Multi-Functional Array Unit
RTU2B-2
Array Unit OscillatorPhase-
Synchronizing
Coupler
1-THz
Antenna
Harmonic
Filter
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RFIC2017
90°
Radiation Cancellation at f0 (250 GHz): Vertical
RTU2B-2
• Vertical slotlines pairs do not radiate
– E-field in left and right slotlines balance out
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RFIC2017
Radiation Cancellation at f0 (250 GHz): Horizontal
RTU2B-2
• Horizontal slotlines pairs do not radiate
– E-field in left and right slotlines balance out
-66dBi
Antenna Gain at f0
A' B' C'ABC
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RFIC2017
Radiation Cancellation at 2f0 (500 GHz): Horizontal
RTU2B-2
• Horizontal slotlines do not radiate
– E-field in central slotlines balance out with top/bottom slotlines
A' B' C'ABC
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RFIC2017
180°
Radiation Cancellation at 2f0 (500 GHz): Vertical
RTU2B-2
• Vertical slotlines pairs do not radiate
– E-field in left and right slotlines balance out
Antenna Gain at 2f0
-12dBi
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RFIC2017
Radiation Cancellation at 3f0 (750 GHz)
RTU2B-2
• Horizontal slotlines pairs do not radiate
– E-field in left and right slotlines balance out
A' B' C'ABC
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RFIC2017
270°
Radiation Cancellation at 3f0 (750 GHz)
RTU2B-2
• Vertical slotlines pairs do not radiate
– E-field in left and right slotlines balance out
Antenna Gain at 3f0
-30dBi
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RFIC2017
Multi-Functional Array Unit
RTU2B-2
Array Unit OscillatorPhase-
Synchronizing
Coupler
1-THz
Antenna
Harmonic
Filter
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RFIC2017
Radiation at 4f0 (1 THz) from Single Unit
RTU2B-2
• All horizontal slotlines pairs radiate in-phase
• Vertical slotlines do not radiate
Antenna Gain at 4f0
9dBi
A' B' C'
ABC
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RFIC2017
1-THz Radiating Array
RTU2B-2
λ/2 @ 1 THz
λ/2 @ 1 THz
Radiating Slotline
• In-phase radiation from all units is
achieved by CPW and slotline coupling
• 1-THz antennas are spaced by λ/2 in both
horizontal and vertical directions
• Equivalently, the array is like an “active
planar wave front” with big aperture
underpinned by transistors
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RFIC2017
Outline
• Motivation and Challenges
• Design of Oscillator
• Formation of 1-THz Oscillating-Radiating Array
• Measurement Results
• Conclusions
RTU2B-2
29
RFIC2017
RTU2B-2
SiGe Chip Prototype
Dummy
Cut for the
Symmetry
of the Cell
1mm
• Technology: IHP S13G2 SiGe BiCMOS
– fmax = 450 GHz
• Area: 1 mm2
• Array scale
– 42 units
– 91 antennas
• DC Power: 1.1 W
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RFIC2017
Measurement of Spectrum of Leaked Fundamental
RTU2B-2
• Chip is attached to a half-ball silicon lens and radiates into backside
• Due to device mismatch, there will be little of f0 wave leaking out, with
which we can confirm f0 and hence 4f0
1.0 1.1 1.2 1.3252
253
254
Me
as
ure
d fOSC,fund (
GH
z)
VB (V)
f0 = 16fLO + foffset
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RFIC2017
Measurement of Total Radiated Power
RTU2B-2
Measurement using VDI WR-1.0 zero-bias diode detector
• Total radiated power of 1 THz (from ZBD): 80μW (-11dBm)
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RFIC2017
Measurement of Total Radiated Power
RTU2B-2
• Total radiated power of 1 THz (from ZBD): 80μW (-11dBm)
• Total radiated power of all harmonics (from TK): 100μW
Measurement using large-aperture Thomas Keating photo-acoustic powermeter
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RFIC2017
Measurement of Radiation Pattern
RTU2B-2
E-PlaneSimulation
Measurement
-90 -60 -30 0 30 60 90
-40
-30
-20
-10
0
Theta (degree)No
rmalized
Re
ce
ive
d P
ow
er
(dB
)
Simulation
Measurement
H-Plane
-90 -60 -30 0 30 60 90
-40
-30
-20
-10
0
Phi (degree)No
rmalized
Re
ce
ive
d P
ow
er
(dB
)
• Measured using zero-bias diode detector
• Peak directivity: 24dBi
• EIRP: 13dBm
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RFIC2017
Performance Comparison
RTU2B-2
• Highest total radiated power
• Highest EIRP
Reference This Work MTT2015 ISSCC2011 ISSCC2016 VLSI 2015
Circuit TypeOscillator
Array (4f0)
Active
Multiplier (6f0)
Active
Multiplier (5f0)
Passive
Multiplier (10f0)
Passive
Multiplier (5f0)
Output Frequency (THz) 1.01 0.99 0.82 1.33 0.73
Radiated Power (dBm) -10.9 N/A N/A -22.7 -21.3
EIRP (dBm) 13.1 -37 -17 -13 -22.2
Input RF Power (dBm) N/A 8 14 18 13.8
DC Power (W) 1.1 4 3.7 0 0
Chip Area (mm2) 1.00 3.28 3.22 0.36 0.26
Technology 0.13μm SiGe 0.25μm SiGe 0.25μm SiGe 65nm CMOS 65nm CMOS
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RFIC2017
Conclusions
RTU2B-2
• A high-power 1-THz radiator featuring 2D-coupled array architecture
– Large array scale
– Directive radiated beam
• Compact multi-functional structure will be an important component
in future THz circuits
This Work
ISSCC2013
ISSCC2012
ISSCC2015
JSSC2015
JSSC2014
VLSI2015 ISSCC2016
T-MTT2015
0.2 0.4 0.6 0.8 1.0 1.2 1.4-30
-20
-10
0
10
Co
he
ren
t R
ad
iate
d P
ow
er
(dB
m)
Frequency (THz)
36
RFIC2017
Acknowledgements
• Analog Devices Inc.
• MIT/MTL GaN Energy Initiative
• MIT Center for Integrated Circuits and Systems (CICS)
• Singapore-MIT Alliance for Research and Technology (SMART)
• Prof. Qing Hu at MIT for chip testing support
• Dr. Mehmet Kaynak at Leibniz-Institut für innovative Mikroelektronik
(IHP) for chip fabrication support
RTU2B-2
37
RFIC2017
RTU2B-2
Fully-Scalable 2D THz Radiating Array: A
42-Element Source in 130-nm SiGe with
80-μW Total Radiated Power at 1.01THz
Zhi Hu and Ruonan Han
MIT, Cambridge, MA, USA
RTU2B-2
Student Paper
Finalist