Electrical & Computer Engineering     |     Carnegie Mellon

Wednesday, October 29, 2008 11:00-12:00 p.m. HH-D210


Donald S. Gardner
Intel Corp.

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.


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.