Dr. Don Gardner
Intel Corporation
March 15, 2011 | 12:00 to 01:00 | 540 Cory Hall, DOP Center Conference Room
Host: Liwei Lin
On-chip inductors with magnetic material are integrated into both advanced 130 and 90 nm CMOS processes. Increases in inductance of up to 30 times corresponding to an inductance density of up to 1,700 nH/mm2 were demonstrated, significantly greater than air-core and other on-chip inductors with magnetic material. 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 film thickness on the permeability were measured and modeled including skin depth effects, eddy current dampening, and the effects of the demagnetization field. 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. 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. The DC resistance is also important for voltage converters and was 0.04 ohms with a peak quality factor of 8 when using thick copper metallization and thick CoZrTa.
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