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Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined Antennas for Integration with Silicon Based Active Devices
Erik Öjefors
Signals and Systems, Dep.of Engineering Sciences
Uppsala University, Sweden
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
• Introduction, applications
• Challenges of on-chip antenna integration
• Design of 24 GHz on-chip antennas
• Crosstalk with on-chip circuits
• Micromachined antenna packaging
• Conclusions and future work
Outline of talk
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Introduction
ObjectiveOn-chip antenna integrated with a 24 GHz ISM bandtransceiver in SiGe HBT technology for short range RADAR and communication devices
PLL
1/8
VCO12 GHz
CrystalOscillator20 MHz
DC
IF
LO RF
RF
SHM actingas a frequencydoubler
PA
LNARFIC
Antenna
Self-contained SiGe front-end
Integration
3x3 mm large chip
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Introduction
One applicationRADAR for traffic surveillance and anti-collision warning systems
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Introduction
Advantages of integrated antenna:
• Simplified packaging (no high frequency interconnects)
• Lowered cost due to reduced number of components
• Omnidirectional radiation pattern often needed,
low gain on-chip antenna feasible
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Challenges of on-chip antenna integration
Minimum Q (quality factor) of small antennas
“a” is the radius of a sphere enclosing the antenna. “k” = 2/
High Q leads to small bandwidth and can reduce the efficiency
BWkakaQ
1113 2a
McClean, " A Re-examination of the Fundamental Limits on the Radiation Q of Electrically Small Antennas," IEEE Trans AP, May 1996.
Antenna size can NOT be reduced without consequences!
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Challenges of on-chip antenna integration
Problem:Size of antenna is an important parameter due to the high cost of the processed SiGe wafer
Solution: Chose antenna types which offer compactintegration with the active circuits
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Proposed integration with active devices
Si
Active devices
Slot antenna
Activedevices
Top metallization
3 mm
Active elements integratedwithin slot loop 3
mm
p+ channel stopper
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Challenges of on-chip antenna integration
Problem:Commercial silicon-germanium (SiGe) semiconductor uselow resisistivity (< 20 cm) substrates
Solution: Use of a low loss interface material such as BCB polymer or micromachining to reduce coupling between antenna and lossy silicon substrate
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachining – mechanical shaping of silicon wafers by semi-conductor processing techniques
Micromachining
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Post processing technique compatible with pre-processedSiGe wafers from commercial semiconductor foundaries
Si
Active circuit
Si
Si
BCB
Gold
Pre-processed wafer fromfoundary
10-20 um BCB layer appliedand cured
Top metallization evaporated anddefined using standard photolitho-graphic techniques
Micromachining – BCB process flow
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Surface micromachining of silicon
BCB, 20 um 10 um
Si 11 -15 cm
Slot
Optional micro- machining
Top metalization
Surface micromachining applied to the substrate beforeBCB-spin-on
Micromachining
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Bulk micromachining of silicon
BCB membrane, 10-20 um
Slot
Backsideetching
Top metalization
Back side of silicon substrate etched as last step in processing
Micromachining
Si
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Outline of talk
• Introduction, applications
• Challenges of on-chip antenna integration
• Design of 24 GHz on-chip antennas
• Crosstalk with on-chip circuits
• Micromachined antenna packaging
• Conclusions and future work
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
• Surface micromachined slot loop antenna• Bulk micromachined slot loop antenna• Inverted F antenna• Wire loop antenna• Meander dipole• Differential patch antenna• Comparison of designed antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Surfaced micromachined slot loop antennaC
PW
pro
be p
ad
Slot loop length corresponds to one guided wavelength at 22 GHz
2000 um
3000
um
3000 um
Si 11-15 cm
BCB 10-20 um
10, 20 um slot width
BCB, Si
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Small return loss outside the the operating frequency indicates that losses are present
Surfaced micromachined slot loop antenna
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Results – Radiation Pattern
-150 -100 -50 0 50 100 150-25
-20
-15
-10
-5
0
Angle [deg]
[dB
]
E-plane
MeasuredSimulated
Antenna on 20 um thick BCB interface layer on low resistivity Si
E-planeH-plane
Reasonably good agreement between simulated and measured radiation pattern,(some shadowing in E-plane caused by measurement setup)
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
• Measured gain: -3.4 dBi
• Directivity (simulated): 3.2 dBi
• Calculated efficiency: 20 %
80 cm
Reference hornantenna
Foam material (lowdielectric constant)
AUT
Wafer probe station
Results – Gain and efficiency
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
200 m
Si
Slot supportedby BCBmembrane
Trenches can be formed from the back side of the wafer bychemical wet etching (KOH) or dry etching (DRIE) methods
No trenches
Micromachined 24 GHz antennasBulk micromachining – improving efficiency
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Bulk micromachining – improving efficiency
Anisotropic etching (KOH, TMAH) Needs wafer thinning (300 um)
DRIE>100 um trench width can be etched
Radiating slots
Radiating slots
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Bulk micromachining 3D-FEM simulations (HFSS)
freq (22.00GHz to 30.00GHz)
tren
ches
..S
(1,1
)
freq (20.00GHz to 25.00GHz)
S(1
,1)
By etching 200 um wide trenches in the silicon wafer thesimulated input impedance is increased from 60 to 210 at the second resonance, simulated efficiency increased from 20% to >50%
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Bulk Micromachining – Slot Loop Antenna
Designed antenna
• Trench width wt = 100 um
Results
• Measured gain 0-1 dBi
• Single ended feed (CPW)
• Impedance 100 Ohm
Slot
Top metallization (groundplane)
Slot
wb
lg
lg
Siwt
sa
Trench (membrane)
wt
Micromachined slot loop antenna
Silicon space for active devices
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
Inverted F Antenna
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Si
Wtr
LF
WGP
Ltr
WtrHF
LGP
Ltr
CPW feed
Membrane
Space for circuits
Inverted F antenna on membrane
• Bent quarterwave radiator formed by offset fed inverted F
• Inverted F radiator placed on 2.6 x 0.9 mm BCB membrane
• Single ended feed
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
15 20 25 30 35
-20
-15
-10
-5
0
FANT
S1
1 [
dB
]
Frequency [GHz]
SimulatedMeasured
Micromachined 24 GHz antennas
Inverted F antenna on membrane
• Measured input impedance50 at 24 GHz
• Measured gain 0 dBi
• Antenna tuning sensitive to ground plane size
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
Wire loop antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennasWire loop antenna on micromachined silicon
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas24 GHz wire loop antenna on micromachined silicon
• 3 x 3 mm wire loop• 360 um wide BCB trenches
covered with BCB membranes
• Chip size 3.6 x 3.6 mm
• Differential feed• Measured input impedance
75 at 24 GHz• Measured gain 1-2 dBi
Lc
Slot
Top metallization (ground-plane)
Trench
Wbr
Wtr
Wc
LL
Si space for active devices
SiWtr
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
Meander dipole antenna
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
Wtr
Antenna BCB
Silicon
Silicon Membrane
3.3 mm
0.9 mm
• Membrane size 3.3 x 0.9 mm
• Differential feed
• Input impedance at 24 GHz 20
• Measured antenna gain 0 dBi
Meander Dipole on BCB membrane
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Patch antennas
Micromachined 24 GHz antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Differentially fed patch antenna by University of Ulm
• Differential feed – no ground connection
• Suitable for wafer scale packaging
• Disadvantages – small bandwidth
Si
Feed point
BCB
Patch
Ground-plane30 um
3800
um
2000 um
Micromachined 24 GHz antennas
Pol
ariz
atio
n
SiGe
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Micromachined 24 GHz antennas
Modelled return loss
Differentially fed patch antenna transmission line model
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Comparison of 24 GHz AntennasSlot loop
antenna
Wire loop antenna
Meander
dipole
Inverted F
antenna
Patch
antenna
Size at 24 GHz
Trenches, die size 3.3 x 3.3 mm
Trenches, die size 3.6 x 3.6 mm
Membrane size 3.3 x 0.76 mm
Membrane size 2.6 x 0.9 mm
Thick BCB area of 3.8 x 1.9 mm
Feed type and impe-dance
Single ended 100-200
Differential
75-100 Differential 20-25
Single ended 50
Differential typically 50
Gain 0-1 dBi 1-2 dBi 0 dBi 0 dBi < 7 dBi
Remark Circuits within antenna footprint
Circuits within antenna footprint
Sensitive to size of on-chip ground
Wafer level integration
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
• Introduction, applications
• Challenges of on-chip antenna integration
• Design and results for implemented antennas
• Crosstalk with on-chip circuits
• Micromachined antenna packaging
• Conclusions and future work
Outline
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Crosstalk with active circuits
BCB
Si 11 -15 cm
Slot mode E-field
Parallel-plate mode
p+ layer, active device area
Parallel plate modes can be excited between the antenna groundplane and conductive active device area
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Crosstalk with active circuits
Slot mode E-field
BCB
Si 11 -15 cm
BCB substrate contact
p+ layer, active circuit ground
Parallel plate modes short circuited by BCB via to substrate, crosstalk improvement of 30 dB possible insome cases
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Outline of talk
• Introduction, applications
• Challenges of on-chip antenna integration
• Design and results for implemented antennas
• Crosstalk with on-chip circuits
• Micromachined antenna packaging
• Conclusions and future work
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Si
Glob top
Active devices
LTCC carrier
• LTCC (Low Termperature Co-fired Ceramic) used as a carrier for
flip-chip or wire-bonded device
• Glob-top encapsulation obviates the need for a packaging lid
Packaging of Micromachined Antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging of Micromachined Antennas
Glob-top Type Loss tangent
Dielectric constant
Amicon S 7503 Silicone 0.0005 / 1 kHz
3.1
Semicosil 900LT Silicone 0.005 / 50 Hz
3.0
Lord CircuitSaf TM ME-455
Epoxy cavity fill
0.006 / 1 MHz
3.37
Lord CircuitSaf TM ME-430
Epoxy glob top
0.006 / 1 MHz
3.7
Namics XV6841-0209
Side fill 0.008 / 1 MHz
3.5
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging - Evaluated Glob-tops
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging – glob top characterization
22 22.5 23 23.5 24 24.5 25 25.5 26
-80
-70
-60
-50
-40
-30
-20
f [GHz]
S2
1 [
dB
]
AirAmicon siliconeSemicosil siliconeNamics side-fillME430 epoxyME455 epoxy
Measured resonator insertion loss – single tape (100 um dielectric)
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging – glob top characterization
Glob-top Single layer fr
[GHz]
Double layer fr
[GHz]
Single layer Q0
Double layer Q0
No glob-top / Air 24.67 24.85 95 75
Amicon S 7503 23.14 23.44 75 50
Semicosil 900LT 23.41 23.98 67 65
Lord CircuitSaf ME-455
22.84 23.26 95 72
Lord CircuitSaf ME-430
22.66 22.87 95 67
Namics XV6841-0209
22.78 22.96 87 71
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging - Summary
• A low cost packaging method for 24 GHz MMIC’s is proposed
• Ferro A6-S ceramic LTCC evaluated at 24 GHz
• Glob-top, cavity fill and side fill polymers characterized - epoxy based materials better than silicone ones
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Packaging – future and ongoing work
Membrane / glob-top compatibilityPreliminary results promising – no membrane breakage for > 10 mm2 membranes covered with BCB glob tops
Glob-top covered antennas – electrical performanceGlop-top covered loop and dipole antennas mounted on standard FR4 printed circuit boards – characterization pending
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
• Introduction, applications
• Challenges of on-chip antenna integration
• Design and results for implemented antennas
• Crosstalk with on-chip circuits
• Micromachined antenna packaging
• Conclusions and future work
Outline
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Conclusions
• Integration of an on-chip antenna with a 24 GHz circuits in SiGe technology has been proposed
• 24 GHz on-chip antennas, suitable for integration, have been manufactured and evaluated
• Micromachining of the silicon substrate yields antennaswith reasonable efficiency
• Simple glob-top packaging for micromachinedantennas has been evaluated
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Future and ongoing work
• Characterization and modeling of the manufactured antennas
• Improve antenna measurement techniques
• Integrate the antenna with SiGe receiver/transmitter
• Demonstrate packaging of micromachined antennas
• Integrate opto-electronic devices with antennas
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Ring slot antenna integrated with 24 GHz receiver* being manufactured
3 mm
3 mm
Receiver
Transistor test structures
Slot in metal 3
Micromachined trenches
to be inserted in silicon
Substrate contacts
*Receiver is designed by University of Ulm
Future and ongoing work
Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices
Acknowledgements
• The entire ARTEMIS consortium: Staff at University of Ulm, CNRS/LAAS Toulouse, Atmel GmbH, Sensys Traffic, VTT Electronics
• Klas Hjort and Mikael Lindeberg at Ångström Laboratory
This work was financially supported by the European Commision through the IST-program