Process Characterization: Characterizing Dielectric
Materials
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Introduction
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In collaboration with Electronic and Electrical Engineering
Laboratory (EEEL) staff, Statistical Engineering Division (SED)
staff are developing statistical methods for the design and
analysis of experiments in which the permittivity and loss tangent
of dielectric materials are estimated.
Background/Impetus
Customers
Goals
Impact
SED Milestones
R&D Team
Achievements
Publications
Related Work
Additional technical information on the dielectric materials project
is included in the 2000
Yellowbook.
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Background/
Impetus
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Dielectric materials have many applications throughout the
electronics, microwave, communication, and aerospace inductries.
NIST is developing new measurement methods for characterizing
permittivity and loss tangent of dielectric materials for the
purpose of producing Standard Reference Materials.
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Customers
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The customers for the dielectric materials project are the
electronic, microwave, communication, and aerospace industries.
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Goals
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The goals for the dielectric materials project are:
- Develop a high-accuracy measurement system for determining
dielectric properties of materials (permittivity and loss
tangent).
- Characterize the resulting measurement process and develop
standard reference materials.
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Impact
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The impact of this work is that it improves the development of
printed circuit boards, substrates, electronic and microwave
components, sensor windows, antenna radomes and lenses, and
microwave absorbers, through more accurate measurement of
dielectric constants.
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Milestones for the dielectric materials project are:
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FY02 Milestones
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- Identify and quantify all systematic errors associated
with the measurement system.
- Develop an uncertainty statement.
- Develop a measurement assurance program.
- Complete certification of SRM and document results.
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FY01 Milestones
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- Develop a method for estimating the electrical length and
diameter of the cavity in which measurements are completed.
Also determine the uncertainty of the estimates.
- Design experiments and analze the resulting data to establish
the stability of the measurement process and to quantify
random error.
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FY00 Milestones
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- Develop a method for estimating two quantities, the
quality factor and resonant frequency, and their
associated uncertainties.
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FY99 Milestones
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- Develop a method for estimating the thickness of the SRM
samples and the associated uncertainty.
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R&D Team
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Kevin
Coakley, Statistical Engineering Division, ITL
Jolene
Splett, Statistical Engineering Division, ITL
Mike Janezic, Radio Frequency Technology Division, EEEL
Raian Kaiser, Radio Frequency Technology Division, EEEL
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Achievements
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Achievements of the dielectric materials project include:
- A procedure for estimating sample thickness and its
uncertainty was developed. Analyzed data needed to quantify
systematic sources of uncertainty.
- A non-linear fitting technique was used to estimate the quality
factor and resonant frequency based on the observed resonance
curve. Developed a model to describe the frequency-dependent
noise present in the resonance curve and used this information
to determine the random error in the quality factor and
resonant frequency. Developed a procedure for determining
the optimal frequency spacing of the resonance curve to minimize
the random error in the quality factor. Quantified the bias
in the quality factor due to frequency drift as a source of
systematic error.
- Developed an estimation procedure for computing the electrical
length and diameter of the microwave cavity in which measurements
are completed. Investigated the possibility of using a skin-depth
correction, using three versus five data points, and using a
weighted versus an unweighted model. Analyzed data needed to
quantify the systematic error due to modeling.
- Developed a Monte Carlo simulation program that estimates
permittivity and loss tangent. Based on this code, we identified
the experimental sources of uncertainty that have the most
influence on the uncertainty of the estimated permittivity and
loss tangent. Used the code to generate uncertainties associated
with several sources of systematic error including: cavity
endplate surface resistance, cavity length and diameter, sample
thickness template orientation, error in the quality factor due to
frequency drift, and sample thickness probe error.
- Designed a repeatability experiment to quantify the random
variability in the measurement system and to establish a measurement
assurance program. Analyzed the repeatability study data.
- Provided software to perform the estimation algorithms.
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Publications
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Publications resulting from the dielectric materials project
include:
- K. Coakley, J. Splett, M. Janezic, and R. Kaiser,
"Estimation of Q-factors and resonant frequencies," to be
submitted to IEEE Transactions on Microwave Theory and
Techniques.
- M. Janezic, J. Splett, K. Coakley, and R. Kaiser,
"Complex permittivity measurement using the NIST 60 mm
cylindrical cavity," for the NIST Journal of Research.
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Related Work
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Plans for related work include:
- Extend the quality factor and resonant frequency estimation
methods to other quality factor regimes.
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