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Study of a microwave coupled
lines filter:
from clean room realization
to measurement and backsimulation.
G.Lissorgues / Assoc. Prof.
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Outline of the presentation
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Context of the study
Description of the filter
Realisation of the filter
Measurement of the filter
Back-simulations
Conclusion
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Context of the study
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Motivations
– Illustrate the course on RF and microwave passive filters
– Introduction to simple clean room process
– Introduction to VNA RF measurement techniques
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Means available
– ADS simulation tools
• First conception of the filter
• Back-simulation after measurements
– A vector network analyser associated with a microstrip
test fixture (HP8510 up to 18GHz)
– ESIEE clean room facilities
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Description of the filter
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A parallel type coupled lines band-pass filter
– Centre frequency f0 = 12.3GHz
– Substrate characteristics
• Dimensions : 2” alumina substrate, height H = 635µm,
thickness of Gold metallizations t=12µm, s = 4.1 107S.m-1
• Dielectric permittivity @10 GHz : εr = 9.8, loss tnδ < 0.001
– Coupled lines sections
• Width W = 589µm
• Common length L1 = 2800µm, spacing S1 = 840µm
• Common length L2 = 1400µm, spacing S2 = 1680µm
Large dimensions = low cost and easy masks!
Parallel coupling
M 12
λ/2
M 23
M 34
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Description of the filter
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A parallel type coupled lines band-pass filter
– Simulations using ADS tools
• S-parameter simulation between 8 – 16 GHz
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Description of the filter
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A parallel type coupled lines band-pass filter
– Simulations using ADS-Momentum
• Calculations between 8 – 16 GHz
• Meshing @ 30 GHz
• Better consideration of the
substrate properties
= results closer to measurements!
• But these simulations can not be
performed during the ADS tutorial
on microwave filters (Momentum
more difficult to understand and
manage)
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Realisation of the filter
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Layout generated from simulations
Simple technological process
– cleaning of the alumina substate
– resist coating (with protection of the back side ground
plane)
– UV photolithography (including a short presentation of
alignment techniques)
– Gold and Chromium wet etching
– resist stripping
– a final profilometry measurement to know the exact
value of the gold thickness, as well as lateral dimensions
of the lines
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Realisation of the filter
Process flow
+
Photography of the filter
Alumina + Gold
Resist coating
UV photolithography
Gold etching
Photolithography
Resist stripping
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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Introduction to VNA measurement
– Calibration and error measurement
– VNA test set synopsis
Down conversion
a1
b1
b2
a2
Coupler
Coupler
Splitter
Splitter
Switch
Source
DUT
Attenuator
Attenuator
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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Introduction to Measurement error modelling
3 kinds of errors
– systematic errors
• due to imperfections in the analyser and test set-up
• predictable
• can be minimised through calibration process
– random errors
• due to instrument noise + switch or connector repeatability
• unpredictable
• cannot be removed with calibration
– drift errors
• due to temperature variations
• appear after calibration and can be removed with a new
calibration
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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Calibration
TRL = Thru - Reflect - Line
– used in non coaxial environments:
• waveguides, on-wafer probing, non insertable devices
– requires standards easily fabricated and characterised
– example of standards for on-wafer probing on Alumina
substrate
• thru: 50 Ω line
• reflect: total metallisation (Au)
• line: 3 types
– matched
– line1 (L1 length)
– line2 (L2 length)
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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HP8510B vector network analyser set-up
– Microstrip test fixture
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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Measurement results
– Transmission
S21 ~ -2.5dB in band
Rejection ~ 28dB out
of band
Center frequency
F0 ~ 12.4GHz
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Measurement of the filter
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Measurement results
– Reflection
S11 ~ -20dB in band
< -0.5dB out
of band
Center frequency
F0 ~ 12.4GHz
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Back-simulation
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Influence of dimensions variations
– Width of lines: W increases & F0 decreases
– Spacing between lines: change in bandwidth
– Common length of the lines: L increases & F0 decreases
1000µm<S2<2200µm
1300µm<L2<1500µm
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Back-simulation
Influence of the substrate
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–
–
–
Dielectric constant permittivity (9.6< εr < 9.9)
Dielectric losses (tanδ from 0 to 0.002)
Thickness of the substrate H
Thickness of the Gold plating layer,…
0
-20
S11 & S21
-40
dB(S(1,1))
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9.6< εr < 9.9:
Frequency shift
-60
-80
8
9
10
11
12
13
14
15
16
freq, GHz
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Back-simulation
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Influence of the substrate
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–
–
–
Dielectric constant dispersion (9.6< εr < 9.9)
Dielectric losses (tanδ from 0 to 0.002)
Thickness of the substrate H
,…
IL decreases from
-0.9dB to –1.99dB
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004
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Conclusion
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Experimentation developed to illustrate a
theoretical course on a specific RF technology =
the coupled lines filters
Possibility to offer an introduction to clean room
process + microwave measurement techniques
All could be performed during a single day:
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Tutorial on filters using ADS (3h)
Clean room realisation (2h1/2 ~ 3h)
Measurements (2h)
Additional back-simulations (student personal work)
© G. Lissorgues - ESYCOM – ESIEE - 16th April 2004