ThickFilm Multilayer Microwave Circuits for Wireless Applications

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Thick-Film Multilayer Microwave Circuits for
Wireless Applications

• Charles Free
• Advanced Technology Institute
• University of Surrey, UK
• and
• Zhengrong Tian
• Formely with Middlesex University
• Now with NPL

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University of Surrey ? Located in Guildford ?
30km south of London ? Approx. 5000 students ?
Single campus - lot of student accommodation
on-site ? Technological university ? Research-led
university ? Top of UK research ratings in
Electronic Engineering
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School of Electronics Research Groups ? Surrey
Space Centre Small satellites design
construction control ? Advanced Technology
Institute Semiconductors ion beam applications
microwave systems ? Centre for Communication
Systems Research Mobile satellite
communications ? Centre for Vision, Speech and
Signal Processing Medical Multimedia
Robotics
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Advanced Technology Institute Microwave
Systems - MMIC design - RF and Microwave
MCMs - Microwave circuits and antennas -
thick-film (including photoimageable)
processing - access to clean rooms (class 1000
and class 100) - measurement capability to
220GHz
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Thick-Film Multilayer Microwave Circuits for
Wireless Applications
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CONTENTS ? Introduction ? Thick-film
technology ? Significance of line losses ?
Single layer microwave circuits ? Multilayer
microwave circuits ? Summary
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INTRODUCTON
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Typical frequencies for wireless
applications Current mobile 0.9GHz -
2GHz 3G systems 2.5GHz Bluetooth
2.5GHz GPS 12.6GHz LMDS 24GHz and
40GHz Automotive 77GHz
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Driving forces created by the wireless
market ? lower cost ? higher
performance ? greater functionality ?
increased packing density
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Microstrip basic microwave interconnection
structure
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Summary of key material requirements at
RF Conductors - low bulk resistivity - good
surface finish (low surface roughness) - high
line/space resolution - good temperature
stability Dielectrics - low loss tangent
(lt10-2) - good surface finish - precisely
defined ??r (stable with frequency) - isotropic
??r - consistent substrate thickness - low
Tf (lt 50 ppm/oC)
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RF Transceiver Architecture
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Features of an RF MCM
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THICK-FILM TECHNOLOGY
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Thick-Film Technology Advantages Low
Cost Feasibility for mass production Adequate
quality at microwave frequencies Potential for
multi-layer circuit structures Difficulty Fabri
cation of fine line and gaps limited quality
by direct screen printing
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Standard range of materials is
used CONDUCTORS - gold - silver -
copper DIELECTRICS - ceramic (alumina) -
green tape (LTCC) - thick-film pastes -
laminates Plus photoimageable conductors and
dielectrics
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Fine lines lt 25 micron with 1 micron
precision High density, 4 micron thick
conductor High conductivity - 95 of bulk
96 Al
50?m lines
Photodefined conductors
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MICROSTRIP RESONANT RING TEST STRUCTURE
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Microstrip Resonant Ring
can be used to measure total line loss and vp
(measure Q ? loss, measure fo ? vp ) does not
separate conductor and dielectric loss ring is
loaded by input and output ports - source of
measurement error
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Meander-line test structure
can be used to measure total line loss and vp
(measure Q ? loss, measure fo ? vp ) does not
separate conductor and dielectric loss ring is
loaded by input and output ports - source of
measurement error
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Chamfering of the corners is a necessary
precaution in microstrip to avoid reflections
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Comparison of measured and simulated loss in a
50? line fabricated on 99.6 alumina. substrate
thickness 254?m and line width 255?m
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Measured line loss 50? thick-film microstrip line
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Typical microstrip line losses
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Skin effect at RF and microwave frequencies
current tends to flow only in the surface of a
conductor Skin depth (?) depth of penetration
at which the magnitude of the current has
decreased to 1/e of the surface value
Significance surface of conductors must be
smooth and the edges well defined to minimise
losses
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Effect of surface roughness on the loss in a
microstrip line
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Effect of loss tangent on line loss
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• LTCC TECHNOLOGY
• LTCC technology is a well-established
  technology
• Reliability established in the automotive
  market
• Advantages for high frequency applications
• parallel processing (? high yield, fast
  turnaround, reduced cost)
• precisely defined parameters
• high performance conductors
• potential for multi-layer structures
• high interconnect density

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• LTCC TECHNOLOGY
• Microwave applications
• ?? LTCC can meet the physical and electrical
  performance demanded at frequencies above 1GHz
• ? Increases in material and circuit production
  are reflected in lower costs LTCC is now
  comparable to FR4
• ? Significant space savings when compared to
  other technologies, such as FR4

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SIGNIFICANCE OF LINE LOSSES
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MICROWAVE RECEIVER
LNA
Feeder
BPF1
BPF2
Mixer
Schematic of front-end of a microwave receiver
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RECEIVER NOISE PERFORMANCE
Feeder
BPF1
BPF2
LNA
Mixer
System noise temperature (Tsys)
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RECEIVER NOISE PERFORMANCE

• Significance of expression for Tsys
• noise performance dominated by first stage
• a lossy first stage introduces noise
• Tfeeder (L -1) 290
• a lossy first stage magnified noise from
• succeeding stages Gfeeder lt 1

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Dielectric Properties _at_ 9GHz Material ?r Tan ? x
10-3 99.5 AL 9.98 0.1 LTCC1 7.33 3.0 LTCC2 6.
27 0.4 LTCC3 7.2 0.6 LTCC4 7.44 1.2 LTCC5 6.
84 1.3 LTCC6 8.89 1.4
Published material data
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CALCULATED RESULTS Noise figure variation
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SINGLE-LAYER MICROWAVE CIRCUITS
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Single-layer microstrip circuits ? all
conductors in a single layer ? coupling between
conductors achieved through edge or end
proximity (across narrow gaps) Problem ?
difficult to fabricate (cheaply in production)
fine gaps, possibly ? 10?m
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End-coupled filter
Directional coupler
Examples of single-layer microstrip circuits
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DC break
Edge-coupled filter
Examples of single-layer microstrip circuits
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MULTI-LAYER MICROWAVE CIRCUITS
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Multilayer microwave circuits ? conductors
stacked on different layers ? conductors
separated by dielectric layers ? allows for
(strong) broadside coupling ? eliminated need for
fine gaps ? registration between layers not as
difficult to achieve as narrow gaps ?
technique well-suited to thick-film print
technology ? also suitable for LTCC technology
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Multilayer configuration
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Thick-film technology is particularly suitable
for the implementation of multilayer circuits ?
higher packing density ? integration of
antenna ? close coupling between
conductors Circuit examples ? DC
block ? Directional coupler
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Directional Coupler
Multilayer Concept
Single Layer Structure
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2dB Directional Coupler - Measured Results
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3dB Directional Coupler - Measured Results
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?/4
Microstrip DC block
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Multilayer DC block
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Measured performance of multilayer DC block
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Measured performance of multilayer DC block
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SUMMARY
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SUMMARY ?? Thick-film technology provides a
viable fabrication process for wireless
circuits at microwave frequencies ? Multilayer
microwave circuits can offer enhanced
performance for coupled-line circuits ? Photoima
geable thick-film materials extend the usable
frequency range to mm-wavelengths
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C.Free_at_surrey.ac.uk www.ee.surrey.ac.uk www.ee.s
urrey.ac.uk/ati