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| Embedded passive devices require high dielectric constant hybrid
materials consisting of filled polymers to advance miniaturization
and functional performance of high-speed electronics. New metrology
methods were developed to address the needs of the electronics industry.
Two test methods, a Test Method for Dielectric Permittivity and Loss
Tangent of Embedded Passive Materials from 100 MHz to 12 GHz and a
Test Method for Dielectric Withstanding Voltage were completed and
have received wide acceptance by industry as new test methods to accelerate
the development of embedded passive device technology. |
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| Jan Obrzut |
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Introduction
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| Continuous reductions in the electrical charge required to drive
logic gates and storage cells have resulted in tremendous progress
in miniaturization and density of integrated circuits. However, enhanced
functional performance increasingly depends on passive components
such as capacitors, resistors, and inductors, where the dielectric
permittivity and impedance characteristics of the material control
spatial dimensions, time scale, speed, shapes and amplitude of electronic
signals. Passive devices have not shrunk in size as rapidly as active
devices and occupy an increasingly larger area and mass fraction of
electronic subassemblies. |
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| Significant advantages arise if passive devices are integrated directly
into the circuit board as embedded passive devices rather than discretely
attached with automated assembly. These include much thinner and sleeker
electronics such as cell phones, decreased manufacturing costs, better
electrical performance, and enhanced design flexibility. Companies
including Gould, Shipley, Ohmega, MacDermid, DuPont, Motorola, Oak-Mitsui,
3M, and Sanmia have devoted millions of dollars to advance this technology
in an effort that represents a huge transition for the electronics
industry. |
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| High dielectric constant hybrid materials consisting of filled polymers
are essential for advancing miniaturization and functional performance.
There are significant challenges in developing new thin-film materials
that require enhanced electrical performance characteristics, such
as impedance and high dielectric constant (high-k), in order to operate
at higher microwave frequencies and at increased voltage strengths.
Consequently, new metrology and test methods are needed to address
the specific behavior of thin film specimens and to better understand
the relation between functional performance and the structural attributes
of the materials. |
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| The materials and testing requirements for Embedded Passives Technology
are outlined in the National Electronics Manufacturing Initiative
(NEMI) 2004 Roadmap. A need for new standard test methods for embedded
materials was identified by the Association Connecting Electronic
Industries (IPC), Roadmap 2005 Outlook Update, IPC Embedded Passive
Device Standard Committee D-39. In partnership with industry, NIST
chaired a test methods task group to communicate and collaborate with
industrial partners. This year, two new test methods were accepted
and will be used extensively by industry to accelerate implementation
of this new technology. |
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| Figure 1: Dielectric constant of high-k polyimide based
composite films determined according to the Standard Test Method.
(HK10 is a 25 mm thick, HK11 is a 14 mm thick composite). |
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Dielectric Permittivity and Loss Tangent
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| The development of new thin-film materials that exhibit enhanced
electrical performance characteristics, such as impedance and high
dielectric constant (high-k), requires a broadband measurement technique
for measuring permittivity at microwave frequencies (100 MHz to 12
GHz). Instead of expensive, single-test microwave strip test structures,
NIST forwarded a general measurement strategy of incorporating a thin
passive film material into a device that is comprised of a capacitive
or resistive termination in a transmission line. The technique is
based on the observation and theoretical analysis of the fundamental
mode propagating at high frequencies in thin film dielectrics that
terminate a coaxial air-filled transmission line. The development
of the method involved nearly 50 active industrial partners and was
reviewed by more than 300 other parties. |
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| An example measurement of the dielectric constant for a high-k material
obtained from DuPont is shown in Fig. 1. We guided the design of the
test protocol and made arrangements with co-sponsoring member companies
for round robin evaluation of the measurement method. The work resulted
in a test document "Test Method for Dielectric Permittivity and
Loss Tangent of Embedded Passive Materials from 100 MHz to 12 GHz",
which has received wide industrial acceptance and recommendation as
a new standard test method. |
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| This new capability to measure the dielectric properties at high
frequencies for a wide range of dielectric permittivity values is
also used to quantify dispersion, alignment, and structure in hybrid
materials. For example, we demonstrated that composites of organic
polymer resins filled with ferroelectric ceramics exhibit a dominant
intrinsic high frequency relaxation behavior. Such dielectric properties
are beneficial in enhancing performance of processors and logic devices.
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Dielectric Withstanding Voltage
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| The dielectric breakdown of thin film materials is also a significant
issue in embedded passive devices. Due to a thin film configuration,
nonlinear effects may be activated at moderate bias levels and contribute
to the dielectric breakdown. A non-linear dielectric measurement methodology
was developed and applied for testing passive materials at high electric
fields and voltages. |
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| NIST-developed experimental set-up and testing procedures demonstrated
the unambiguous determination of the dielectric withstanding voltage
of embedded passive materials. In contrast to conventional procedures,
the specimen voltage and current are determined as complex quantities
from the corresponding time-resolved voltage waves. The new testing
procedure represents an extension compatible with the existing standard
test method, but is better suited for capacitive and resistive thin
film materials |
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| The specimen impedance and the loss tangent of the material can
be determined by performing complex algebra calculations. It was found
that thin-film materials for embedded passives do not exhibit a flat
impedance characteristic, as is the case for conventional dielectrics,
but the impedance sharply decreases with increasing voltage. The voltage
withstanding condition may be attributed to a voltage range where
the impedance characteristic remains insignificantly affected by the
applied voltage. An equivalent impedance comparison indicates that
high-k organic composites can withstand only a small fraction of the
conventional dielectric withstanding voltage. |
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| The NIST-developed procedure of recording and analyzing waveforms
also allows the evaluation of specific characteristics of materials
that cannot be readily evaluated with conventional techniques. This
measurement procedure is especially suitable for detecting and analyzing
non-linear dielectric effects that can result from polarization reversal
and rectifying barriers. Such effects may appear at relatively low
voltages in nano-sized interfaces, composites, and sub-micron thin
dielectric films that are of interest to emerging technologies. |
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| For More Information on This Topic |
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| A. Anopchenko, K. Kano (Polymers Division, NIST); D. McGregor (DuPont);
D. Fritz (MacDermid); T. Bergstresser (Gould Electronics); K. Fjeldsted
(Electro Scientific Industries); G. S. Cox (DuPont); J. Felten (DuPont);
R. Crosswell (Motorola); C. Vanderpan (UL); R. Whitehouse (Sanmina-SCI) |
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| J. Obrzut and A. Anopchenko, "Input Impedance of a Coaxial
Line Terminated with a Complex Gap Capacitance - Numerical and Experimental
Analysis", IEEE Transactions on Instrumentation and Measurement.
53 (4), August (2004). |
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| J. Obrzut and K. Kano, "Measurement of Complex Impedance at
High AC Voltages using Waveforms", IEEE, IMTC/2004 3, 1994-1997
(2004). |
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| J. Obrzut, A. Anopchenko, K. Kano, and H. Wang, "High Frequency
Loss Mechanism in Polymers Filled with Dielectric Modifiers",
Mat Res. Symp. Proc. 783, B3.5-8 (2003). |
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| J. Obrzut and A. Anopchenko; "High frequency input impedance
characterization of dielectric films for power-ground planes",
IEEE Transactions on Instrumentation and Measurement 52, 1120-1124
(2003). |
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