1. 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 1
RF Multi-chip Modules (c) UniS 2002

2. University of Surrey  Located in Guildford  30km south of London
 Approx students
 Single campus - lot of student accommodation on-site
 Technological university
 Research-led university
 Top of UK research ratings in Electronic Engineering

3. 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

4. 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

5. Thick-Film Multilayer for Wireless Applications
Microwave Circuits
for Wireless Applications

6.  Thick-film technology  Significance of line losses
CONTENTS
 Introduction
 Thick-film technology
 Significance of line losses
 Single layer microwave circuits
 Multilayer microwave circuits
 Summary 3

7. INTRODUCTON

8. 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

9. Driving forces created by the wireless market:
 lower cost
 higher performance
 greater functionality
 increased packing density

10. Microstrip: basic microwave interconnection structure

11. 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 (<10-2)
- good surface finish
- precisely defined r (stable with frequency)
- isotropic r
- consistent substrate thickness
- low Tf (< 50 ppm/oC) 28

12. RF Transceiver Architecture

13. Features of an RF MCM 9

14. THICK-FILM TECHNOLOGY

15. Thick-Film Technology
Advantages:
Low Cost
Feasibility for mass production
Adequate quality at microwave frequencies
Potential for multi-layer circuit structures
Difficulty:
Fabrication of fine line and gaps: limited
quality by direct screen printing

16. 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 23

17. Photodefined conductors
Fine lines < 25 micron with 1 micron
precision
High density, 4 micron thick conductor
High conductivity - 95% of bulk
96% Al
50m lines
Photodefined conductors

18. MICROSTRIP RESONANT RING
TEST STRUCTURE W S r1 r2

19. 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

20. 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

21. Chamfering of the corners is a necessary precaution in microstrip to avoid reflections

22. [substrate thickness = 254m and line width = 255m]
Comparison of measured and simulated loss in a 50 line fabricated on 99.6% alumina.
[substrate thickness = 254m and line width = 255m]

23. Measured line loss: 50 thick-film microstrip line

24. Typical microstrip line lossesII
III
Typical microstrip line losses 29

25. 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 27

26. Effect of surface roughness on the loss
in a microstrip line 30

27. Effect of loss tangent on line loss31

28. 32

29. 33

30. LTCC TECHNOLOGY Advantages for high frequency applications:
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

31. 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

32. SIGNIFICANCE OF LINE LOSSES

33. MICROWAVE RECEIVER Schematic of front-end of a microwave receiver LNA
Feeder
BPF1
BPF2
Mixer
Schematic of front-end of a microwave receiver

34. RECEIVER NOISE PERFORMANCE
Feeder
BPF1
LNA
BPF2
Mixer
System noise temperature (Tsys)

35. 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 < 1

36. Dielectric Properties @ 9GHz
Material r Tan  x 10-3
99.5% AL
LTCC
LTCC
LTCC
LTCC
LTCC
LTCC
Published material data

37. CALCULATED RESULTS Noise figure variation
Feeder
BPF1
BPF2
LNA
Mixer

38. SINGLE-LAYER MICROWAVE CIRCUITS

39. 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

40. Examples of single-layer microstrip circuits
End-coupled
filter
Directional
coupler
Examples of single-layer microstrip circuits

41. Examples of single-layer microstrip circuits
DC break
Edge-coupled
filter
Examples of single-layer microstrip circuits

42. MULTI-LAYER MICROWAVE CIRCUITS

43. 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

44. Multilayer configuration
3 Isolated port
Direct port 4
Ground plane H h1 εr W1 W2
εr1 1
2 Coupled port l S
Main substrate
Thick-film dielectric layer
Input port
Multilayer configuration

45. 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

46. Directional Coupler
Multilayer Concept
Single Layer
Structure

47. 2dB Directional Coupler - Measured Results

48. 3dB Directional Coupler - Measured Results

49. /4
Microstrip DC block

50. Multilayer DC block
300um
380um
Alumina
r = 3.9
180um

51. Measured performance of multilayer DC block

52. Measured performance of multilayer DC block

53. SUMMARY

54. 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
 Photoimageable thick-film materials extend the usable
frequency range to mm-wavelengths