Thick-Film Multilayer Microwave Circuits for Wireless Applications

By

Kavindra krishna

Research Scholar

AMU

Department of Electronics Engineering AMU 1

CONTENTS

Introduction

Thick-film technology

Significance of line losses

Single layer microwave circuits

Multilayer microwave circuits

Summary

2

INTRODUCTON

3

Typical frequencies for wireless application :

Current mobile : 0.9GHz - 2GHz

3G systems : 2.5GHz

Bluetooth : 2.5GHz

GPS : 12.6GHz

LMDS : 24GHz and 40GHz

Automotive : 77GHz

4

LMDS (Local Multi Point Distribution Services)

5

Driving forces created by the wireless market:

lower cost

higher performance

greater functionality

increased packing density

6

Microstrip: basic microwave interconnection

structure

It provides one free surface on which solid state device can be placed.

7

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)

8

THICK-FILM TECHNOLOGY

9

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

10

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.

11

Fine lines < 25 micron with 1 micron

precision

High density, 4 micron thick conductor

High conductivity - 95% of bulk

96% Al

50m lines

Photodefined conductors 12

Losses in Thick-Film Technology

• 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.

• Effect due to loss tangent on line : - this effect is shown in figure [1] on next slide.

• Effect due to surface roughness:-the roughness on surface creates a loss,shown in figure [2]

f

1

13

Figure [1]-Effect of loss tangent on line

14

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 10 20 30 40 50

Frequency (GHz)

Lin

e lo

ss (

dB

/mm

)

RGH=0.5

RGH=0.2

RGH=0.1

RGH=0

Figure [2]-Effect of surface roughness

15

0%

20%

40%

60%

80%

100%

Line

Loss

(%)

8 20 32 44

Frequency (GHz)

Bulk Conductor Loss Loss due to Surface Roughness Dielectric Loss

16

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Line

Loss

(%)

Al LTCC

Different Material (evaluated at 2GHz)

Bulk Conductor Loss Loss due to Surface Roughness Dielectric Loss

17

LTCC TECHNOLOGY

• LTCC technology is a well-established technology

• Reliability established in the automotive market

• Advantages for high frequency applications:

• parallel processing ( reduced cost)

• precisely defined parameters

• high performance conductors

• potential for multi-layer structures

• high interconnect density

18

LTCC TECHNOLOGY

For 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 other technologies.

• Significant space savings when compared to other

technologies.

19

SINGLE-LAYER

MICROWAVE CIRCUITS

20

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 10m

21

End-coupled

filter

Directional

coupler

Examples of single-layer microstrip circuits

22

MULTI-LAYER MICROWAVE CIRCUITS

23

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

24

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

25

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

26

Directional Coupler

• Directional coupler under multi -

Layer concept and single layer concept.

27

Measured result of 2dB directional coupler under multi layer concept

28

Microstrip DC Block

29

Multi layer DC Block

30

0

0.4

0.8

1.2

1.6

2

1 2 3 4 5 6 7 8 9 10 11 12

Frequency (GHz)

Inse

rtio

n L

oss (

dB

)

Measured performance of multilayer DC block

31

Multi Layer Microwave Receiver

• All blocks processed independently.

32

Comparison

• The variation in noise figure is reduced as compare to single layer fabrication.

33

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

34