Title: Outline
1Micromachined Antennas for Integration with
Silicon Based Active Devices
Erik Öjefors Signals and Systems, Dep.of
Engineering Sciences Uppsala University, Sweden
2Outline 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
3Introduction
Objective On-chip antenna integrated with a 24
GHz ISM band transceiver in SiGe HBT technology
for short range RADAR and communication devices
Integration
Antenna
Self-contained SiGe front-end
3x3 mm large chip
4Introduction
One application RADAR for traffic surveillance
and anti-collision warning systems
5Introduction
- 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
6Challenges of on-chip antenna integration
Antenna size can NOT be reduced without
consequences!
Minimum Q (quality factor) of small
antennas a is the radius of a sphere
enclosing the antenna. k 2p/l. High Q leads
to small bandwidth and can reduce the efficiency
McClean, " A Re-examination of the Fundamental
Limits on the Radiation Q of Electrically Small
Antennas," IEEE Trans AP, May 1996.
7Challenges 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 compact integration with the active circuits
8Proposed integration with active devices
Slot antenna
Active devices
Active elements integrated within slot loop
3 mm
Top metallization
3 mm
Active devices
Si
p channel stopper
9Challenges of on-chip antenna integration
Problem Commercial silicon-germanium (SiGe)
semiconductor use low resisistivity (lt 20 Wcm)
substrates Solution Use of a low loss
interface material such as BCB polymer or
micromachining to reduce coupling between antenna
and lossy silicon substrate
10Micromachining
Micromachining mechanical shaping of silicon
wafers by semi-conductor processing techniques
11Micromachining BCB process flow
Post processing technique compatible with
pre-processed SiGe wafers from commercial
semiconductor foundaries
Active circuit
Pre-processed wafer from foundary
Si
BCB
10-20 um BCB layer applied and cured
Si
Gold
Top metallization evaporated and defined using
standard photolitho- graphic techniques
Si
12Surface micromachining of silicon
Micromachining
Top metali
zation
Slot
Optional micro
-
BCB,
machining
20 um
10 um
W
Si 11
-
15
cm
Surface micromachining applied to the substrate
before BCB-spin-on
13Bulk micromachining of silicon
Micromachining
Top metali
zation
Slot
10-20 um
BCB membrane,
Backside etching
Si
Back side of silicon substrate etched as last
step in processing
14Outline 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
15Micromachined 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
16Surfaced micromachined slot loop antenna
Micromachined 24 GHz antennas
BCB, Si
10, 20 um slot width
3000 um
CPW probe pad
BCB 10-20 um
Si 11-15 Wcm
2000 um
3000 um
Slot loop length corresponds to one guided
wavelength at 22 GHz
17Micromachined 24 GHz antennas
Surfaced micromachined slot loop antenna
Small return loss outside the the operating
frequency indicates that losses are present
18Results Radiation Pattern
Antenna on 20 um thick BCB interface layer on low
resistivity Si
H-plane
E-plane
Reasonably good agreement between simulated and
measured radiation pattern, (some shadowing in
E-plane caused by measurement setup)
19Micromachined 24 GHz antennas
Results Gain and efficiency
Reference horn antenna
- Measured gain -3.4 dBi
- Directivity (simulated) 3.2 dBi
- Calculated efficiency 20
Wafer probe station
80 cm
Foam material (low dielectric constant)
20Micromachined 24 GHz antennas
Bulk micromachining improving efficiency
Slot supported by BCB membrane
Si
200 ?m
No trenches
Trenches can be formed from the back side of the
wafer by chemical wet etching (KOH) or dry
etching (DRIE) methods
21Micromachined 24 GHz antennas
Bulk micromachining improving efficiency
Radiating slots
- DRIE
- gt100 um trench width can be etched
Radiating slots
Anisotropic etching (KOH, TMAH) Needs wafer
thinning (300 um)
22Micromachined 24 GHz antennas
- Bulk micromachining 3D-FEM simulations (HFSS)
By etching 200 um wide trenches in the silicon
wafer the simulated input impedance is increased
from 60 W to 210 W at the second resonance,
simulated efficiency increased from 20 to gt50
23Bulk Micromachining Slot Loop Antenna
Micromachined slot loop antenna
sa
Si
wt
Trench (membrane)
Slot
- Designed antenna
- Trench width wt 100 um
- Results
- Measured gain 0-1 dBi
- Single ended feed (CPW)
- Impedance 100 Ohm
Silicon space for active devices
wb
lg
wt
Slot
Top metallization (groundplane)
lg
24Micromachined 24 GHz antennas
Inverted F Antenna
25Micromachined 24 GHz antennas
Inverted F antenna on membrane
Ltr
LF
Ltr
Wtr
- 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
HF
Membrane
CPW feed
Space for circuits
LGP
WGP
26Micromachined 24 GHz antennas
Inverted F antenna on membrane
- Measured input impedance
- 50 W at 24 GHz
- Measured gain 0 dBi
- Antenna tuning sensitive to ground plane size
27Micromachined 24 GHz antennas
Wire loop antennas
28Micromachined 24 GHz antennas
Wire loop antenna on micromachined silicon
29Micromachined 24 GHz antennas
24 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 W at 24 GHz
- Measured gain 1-2 dBi
Lc
Si
Wtr
30Micromachined 24 GHz antennas
Meander dipole antenna
31Micromachined 24 GHz antennas
Meander Dipole on BCB membrane
3.3 mm
0.9 mm
Membrane
Silicon
- Membrane size 3.3 x 0.9 mm
- Differential feed
- Input impedance at 24 GHz 20W
- Measured antenna gain 0 dBi
-
Antenna
BCB
Silicon
Wtr
32Micromachined 24 GHz antennas
Patch antennas
33Micromachined 24 GHz antennas
Differentially fed patch antenna by University of
Ulm
Patch
3800 um
BCB
30 um
Polarization
Si
Ground-plane
SiGe
- Differential feed no ground connection
- Suitable for wafer scale packaging
- Disadvantages small bandwidth
Feed point
2000 um
34Micromachined 24 GHz antennas
Differentially fed patch antenna transmission
line model
Modelled return loss
35Comparison of 24 GHz Antennas
Slot 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 W Differential 75-100 W Differential 20-25 W Single ended 50 W Differential typically 50 W
Gain 0-1 dBi 1-2 dBi 0 dBi 0 dBi lt 7 dBi
Remark Circuits within antenna footprint Circuits within antenna footprint Sensitive to size of on-chip ground Wafer level integration
36Outline
- 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
37Crosstalk with active circuits
Slot mode E
-
field
Parallel
-
plate
BCB
mode
p layer, active
device area
W
Si 11
-
15
cm
Parallel plate modes can be excited between the
antenna groundplane and conductive active device
area
38Crosstalk with active circuits
BCB substrate
Slot mode E
-
field
contact
BCB
p layer, active
W
Si 11
-
15
cm
circuit ground
Parallel plate modes short circuited by BCB via
to substrate, crosstalk improvement of 30 dB
possible in some cases
39Outline 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
40Packaging of Micromachined Antennas
- 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
41Packaging of Micromachined Antennas
42Packaging - Evaluated Glob-tops
43Packaging glob top characterization
Measured resonator insertion loss single tape
(100 um dielectric)
44Packaging glob top characterization
45Packaging - Summary
- A low cost packaging method for 24 GHz MMICs 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
46Packaging future and ongoing work
Membrane / glob-top compatibility Preliminary
results promising no membrane breakage for gt 10
mm2 membranes covered with BCB glob
tops Glob-top covered antennas electrical
performance Glop-top covered loop and dipole
antennas mounted on standard FR4 printed circuit
boards characterization pending
47Outline
- 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
48Conclusions
- 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
antennas - with reasonable efficiency
- Simple glob-top packaging for micromachined
- antennas has been evaluated
49Future 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
50Future and ongoing work
Ring slot antenna integrated with 24 GHz
receiver being manufactured
Micromachined trenches to be inserted in silicon
Slot in metal 3
3 mm
Receiver
Substrate contacts
Transistor test structures
Receiver is designed by University of Ulm
3 mm
51Acknowledgements
- 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