Integrated On-Chip Inductors Using Magnetic Material

Speaker: Dr. Donald Gardner
Friday, November 9th, 2007
1:30 PM ~ 2:30 PM
Location: Engineering II 102

ABSTRACT:

The integration of on-chip inductors with magnetic materials in silicon technology has been a major challenge in the move towards monolithic solutions for wireless microelectronics, power delivery, and EMI noise reduction. Onchip inductors with 2 levels of magnetic material have been integrated into advanced 90 nm and 120 nm CMOS process using Al and Cu metal and CoZrTa magnetic material [1, 2]. The magnetic material has to have hightemperature and long annealing-time stability, minimal hysteretic loss, high saturation magnetization, low magnetostriction, high resistivity, and compatibility with Si technology.   CoZrTa has a saturation magnetization of 1.6 Tesla, a high permeability of 850, and low coercivity of 0.015 Oe. The CoZrTa increases the inductance and quality factors (wL/Rac) by up to a factor of 27X, significantly higher than prior studies [1-4]. With such improvements, the effects of eddy currents, skin effect, and proximity effect become clearly visible. Figure 1 shows the ratio of inductance L to AC resistance Rac of a family of different inductors with the Q-factor indicated by diagonal lines. Using thicker Cu and thicker CoZrTa increases the L/ Rac ratios, but eddy currents are limiting the Qfactor.  This ratio drops sooner with inductors that have a higher ratio in part because the eddy currents are more severe [5] from the thicker magnetic film confirmed by simulations (shown as dashed lines in Fig. 1). Adding slots or laminations reduces the eddy current losses, but also reduces the inductance. Simulations and models of the permeability and eddy currents can be used to validate the results.