A comparison of on-chip inductors with magnetic materials from previous studies is presented and examined. Results from on-chip inductors with magnetic material integrated into a 90 nm CMOS processes are presented. The inductors use copper metallization and amorphous Co-Zr-Ta magnetic material. Inductance densities of up to 1700 nH/mm2 were obtained thanks to inductance increases of up to 31 times, significantly greater than previously published on-chip inductors. With such improvements, the effects of eddy currents, skin effect, and proximity effect become clearly visible at higher frequencies. Co-Zr-Ta was chosen for its good combination of high permeability, good stability at high temperature (> 250degC), high saturation magnetization, low magnetostriction, high resistivity, minimal hysteretic loss, and compatibility with silicon technology. The Co-Zr-Ta alloy can operate at frequencies up to 9.8 GHz, but trade-offs exist between frequency, inductance, and quality factor. Our inductors with thick copper and thicker magnetic films have dc resistances as low as 0.04 Omega, and quality factors of up to 8 at frequencies as low as 40 MHz.

Review of On-Chip Inductor Structures With Magnetic Films

This paper reviews the current state of power supply technology platforms and highlights future trends and challenges toward realizing fully monolithic power converters. This paper presents a detailed survey of relevant power converter technologies, namely power supply in package and power supply on chip (PwrSoC). The performance of different power converter solutions reported in the literature is benchmarked against existing commercial products. This paper presents a detailed review of integrated magnetics technologies, primarily microinductors, a key component in realizing a monolithic power converter. A detailed review and comparison of different microinductor structures and the magnetic materials used as inductor cores is presented. The deposition techniques for integrating the magnetic materials in the microinductor structures are discussed. This paper proposes the use of two performance metrics or figures of merit in order to compare the dc and ac performance of individual microinductor structures. Finally, the authors discuss future trends, key challenges, and potential solutions in the realization of the “holy grail” of monolithically integrated power supplies (PwrSoC).

Review of Integrated Magnetics for Power Supply on Chip (PwrSoC)

The observation of magnetic domains by magneto-optical microscopy, based on the Kerr and the Faraday effect, is one of the most prominent techniques for the visualization of distributions of magnetization within magnetic materials. The method has gained increased attention due to the possibility to visualize field and current induced phenomena in nanostructured magnetic materials on fast time-scales. Fundamental concepts and recent advances in methodology are discussed in order to provide guidance on the usage of wide-field magneto-optical microscopy in applied magnetism. Recent applications of magneto-optical microscopy in bulk and thin film materials are reviewed at the end.

https://iopscience.iop.org/article/10.1088/0022-3727/48/33/333001/pdf

Progress in magnetic domain observation by advanced magneto-optical microscopy

Integrated solenoid inductors with magnetic core were fabricated and analyzed. An inductance above 70 nH was achieved while keeping the coil resistance below 1 Omega and the device area below 1 mm2 using a solenoid design with a single magnetic layer. The inductance of the magnetic inductor was more than 30 times that of the air core inductor of the identical geometry, and the quality factor of the magnetic inductor was >5. Novel inductor designs and the scalability were also examined, and an inductance density higher than 200 nH/mm2 was obtained. The measured device properties and engineering tradeoffs were well explained by analytical models we developed.

Fabrication and Analysis of High-Performance Integrated Solenoid Inductor With Magnetic Core

This paper presents the microfabrication and measurement of high-inductance-density, moderate-Q, air-core inductors, and transformers intended for switch-mode power supplies operating in the 100-500 MHz frequency range. The inductors and transformers were fabricated on Pyrex substrates with four layers of electrodeposited copper with each layer up to 10 ?m thick. Stacked winding layers allowed for mutual coupling between layers to increase areal inductance density. Inductors of various designs exhibited inductance densities of up to 100 nH/mm 2 and quality factors approaching 20 in the frequency range of interest. Transformers were formed by interleaving primary and secondary coils and were designed with increased inductance in the secondary coil for voltage gain. A fabricated transformer, 1.5 mm × 1.5 mm in area, yielded 46 nH primary inductance and 500 nH secondary inductance with a coupling coefficient of 0.63. Measurements indicated that a maximum transformer efficiency of 78% at 125 MHz would be possible.

High-Inductance-Density, Air-Core, Power Inductors, and Transformers Designed for Operation at 100–500 MHz

On-chip inductors with magnetic material are integrated into both advanced 130 and 90 nm complementary metal-oxide semiconductor processes. The inductors use aluminum or copper metallization and amorphous CoZrTa magnetic material. Increases in inductance of up to 28 times corresponding to inductance densities of up to 1.3 μ H / mm 2 were obtained, significantly greater than prior values for on-chip inductors. 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 spectra were measured and modeled. 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 on the inductors. The inductors with thick copper and thicker magnetic films have resistances as low as 0.04 Ω , and quality factors up to 8 at frequencies as low as 40 MHz.

Roy Hallstein

Papers

Integrated on-chip inductors using magnetic material (invited)