Preface. Microelectromechanical Systems (MEMS) and Radio Frequency MEMS. MEMS Materials and Fabrication Techniques. RF MEMS Switches and Micro Relays. MEMS Inductors and Capacitors. Micromachined RF Filters. Micromachined Phase Shifters. Micromachined Transmission Lines and Components. Micromachined Antennae. Integration and Packaging for RF MEMS Devices. Index.

RF MEMS and their applications

In this review, we discuss new developments and recent trends in both amorphous and crystalline Al2O3 oxide nanofluids related to their phase dependent characteristics in detail. Nowadays, nanofluids have gained significant attention with the enhanced energy/heat efficiency, which is highly desirable to improve the performance of any energy based devices and technology. This review article systematically describes the various chemical synthesis routes followed by bottom-up approaches, surface morphologies, and detailed microstructure characteristics, and phase dependent thermal as well as optical properties for potential use of such materials in various applications.

Phase dependent thermal and spectroscopic responses of Al2O3 nanostructures with different morphogenesis.

We present new data on the thermal conductivity of nanofluids consisting of alumina nanoparticles dispersed in water, ethylene glycol, and ethylene glycol + water mixtures. We also demonstrate that our previously published model is able to describe the temperature, particle size, and particle volume fraction dependence of these nanofluids without any adjustable parameters, irrespective of the base fluid used (water, ethylene glycol, or water + ethylene glycol mixtures). Furthermore, we demonstrate how the model may be used to check the consistency of literature data on all alumina nanofluids.

The thermal conductivity of alumina nanofluids in water, ethylene glycol, and ethylene glycol + water mixtures

GHz magnetic film inductors

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.

Integrated on-chip inductors using magnetic material (invited)

Planar-type thin film inductors were fabricated using FeTaN soft magnetic films. It was found that excellent soft magnetic properties (coercivity of 0.1–0.2 Oe, effective permeability of 4000, and saturation magnetization of 15 kG) could be obtained in the Fe78.8Ta8.5N12.7 films after anneals at 400–500 °C. The initial permeability of the films was constant up to 20 MHz. Internal-coil inductors, in which Cu coils were sandwiched by SiO2 insulator/FeTaN magnetic layers, were fabricated and their characteristics were compared with air-core inductors. The inductance was increased by a factor of 4 compared to air-core inductors. However, the high frequency characteristic was degraded due to a frequency-limited permeability of FeTaN magnetic layers.

Fabrication of thin film inductors using FeTaN soft magnetic films

We fabricated a planar-type film inductor with good high frequency characteristics using a FeTaN soft magnetic film. While FeTaN films inherently show good soft magnetic properties and high saturation magnetization, addition of Ti underlayer with a combination of magnetic field annealing leads to an increase of anisotropy field (H/sub k/), thus improving high frequency characteristics. Planar-type spiral inductors using Ti/FeTaN films exhibit an inductance of /spl sim/1 /spl mu/H, resistance of /spl sim/2 ohm, and Q factor of 2.3 at 2 MHz. We also fabricated a hybrid ZVS-CV buck converter using the film inductor. The converter shows about 80% of the conversion efficiency at 1.2 MHz, which withstands a load current up to 300 mA.

Fabrication of high frequency DC-DC converter using Ti/FeTaN film inductor

A double rectangular spiral inductor is fabricated using FeTaN films. The inductor is composed of internal coils sandwiched by magnetic layers. Characteristics of inductor performance are investigated with an emphasis on planarization of magnetic films. In the absence of the planarization process, the grating topology of upper magnetic films over the coil arrays degrades the soft magnetic properties and the inductor performance. It also induces a uniaxial magnetic anisotropy with the easy axis aligned to the magnetic flux direction. This alignment prevents the upper magnetic films from contributing to the total induction. Glass bonding is a viable method for achieving a completely planar inductor structure. The planar inductor with glass bonding shows excellent performance: inductance of 1.1 /spl mu/H, Q factor of 7 (at 5 MHz), and a DC current capability up to 100 mA.

Fabrication of double rectangular type FeTaN film inductors

Metal induced crystallization of amorphous silicon by using NiCl2 vapor

We investigated the effects of magnetic anisotropy and anisotropy alignment to the coil geometry on the performance of a thin film inductor. For this, Ti/FeTaN bilayer films with large Hk(∼10 Oe) were used as a magnetic layer. We also fabricated a double rectangular spiral inductor which gives a uniaxial coil magnetic flux. When the hard axis of magnetic film is aligned to the magnetic field direction, highest inductance values as well as best frequency response can be obtained. As misalignment angle from the hard axis alignment increases, high-frequency characteristics are substantially degraded, especially at the misalignment angle higher than 45°. Current capability of inductor is found to depend on both Hk and hard axis alignment. The hard axis alignment, in conjunction with large Hk, increases the current capability of inductor significantly.

Hyoung-June Kim

Papers

Fabrication of thin film inductors using FeTaN soft magnetic films

Fabrication of high frequency DC-DC converter using Ti/FeTaN film inductor

Fabrication of double rectangular type FeTaN film inductors

Metal induced crystallization of amorphous silicon by using NiCl2 vapor

Effect of magnetic anisotropy on the current capability of thin film inductor