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Donald S. Gardner
Intel Corp.
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Integrated On-Chip Inductors Using Magnetic Material
On-chip inductors with magnetic material are integrated into
both advanced 130 and 90 nm CMOS processes. The inductors
use aluminum or thick copper metallization and amorphous CoZrTa
magnetic material. Increases in inductance of up to 30 times
corresponding to an inductance density of up to 1,700 nH/mm2
were obtained, significantly greater than prior values for
on-chip inductors with magnetic material. In comparison, air-core
spiral inductors can achieve inductance densities of up to
about 200 nH/mm2. With such improvements, the effects of eddy
currents, skin effect, and proximity effect become clearly
visible at higher frequencies. The CoZrTa was chosen for its
good combination of high permeability, good high-temperature
stability (>250 °C), high saturation magnetization,
low magnetostriction, high resistivity, minimal hysteretic
loss, and compatibility with silicon technology. The CoZrTa
alloy can operate at frequencies up to 9.8 GHz, but trade-offs
exist between frequency, inductance, and quality factor. The
effects of increasing the magnetic thickness on the permeability
were measured and modeled including skin depth effects, eddy
current dampening, and the effects of the demagnetization
field. The inductors use magnetic vias and elongated structures
to take advantage of the uniaxial magnetic anisotropy. Techniques
are presented to extract a sheet inductance and examine the
effects of magnetic vias (vias that allow complete closure
in the magnetic flux) on the inductors. Comparisons of measurements
of different via width and of structures with versus without
laminations demonstrate the effectiveness of this technique
with thin cobalt oxide. Comparing inductors with maximum Q-factors
at different frequencies was accomplished by plotting the
inductance over ac resistance time constant (L/Rac) versus
frequency, then including contours representing constant quality-factor
values. Simulations of magnetic flux density and eddy current
densities and analytical models were used to gain a good understanding
of the effects of laminations. The inductors with thick copper
and thicker magnetic films were successfully demonstrated
to have L/Rac time constants about 20× higher than earlier
aluminum-based inductors with resistances as low as 0.04 W
and quality factors of up to 8 at frequencies as low as 40
MHz.
Bio
Donald S. Gardner has been with Intel Corporation since 1991
and is currently a principal engineer in Intel Research and
also is a visiting scientist at Stanford University. He received
his PhD in Electrical Engineering from Stanford University.
Donald is the inventor or co inventor of 58 patents including
for inductors using high-frequency magnetic materials, reflow
of copper metallization, layered aluminum metal for interconnections,
and embedded ground planes. He is the recipient of a 2005
Intel Achievement Award, Intel's top honor for outstanding
accomplishments that have had significant impact on a major
program. Don has published and presented over 140 electrical
engineering, materials science and computer science papers
in journals and conferences including several invited presentations.
He has received four Best Paper and Poster awards at international
conferences and over 500 authors have cited his publications.
Donald has had appointments as a visiting research scientist
at Hitachi Research Labs in Japan and as an instructor at
Stanford University. He enjoys bringing new life to old technologies
by blending them with different technologies or recent science
and new materials. His current interests include magnetic
materials for high-frequency inductors, silicon-based optoelectronic
devices, nanostructure design and devices, and process integration.
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