Randhir Bubber

Low-temperature (≤200 °C) plasma enhanced atomic layer deposition of dense titanium nitride thin films

Titanium nitride (TiN) has been widely used in the semiconductor industry for its diffusion barrier and seed layer properties. However, it has seen limited adoption in other industries in which low temperature (<200 °C) deposition is a requirement. Examples of applications which require low temperature deposition are seed layers for magnetic materials in the data storage (DS) industry and seed and diffusion barrier layers for through-silicon-vias (TSV) in the MEMS industry. This paper describes a low temperature TiN process with appropriate electrical, chemical, and structural properties based on plasma enhanced atomic layer deposition method that is suitable for the DS and MEMS industries. It uses tetrakis-(dimethylamino)-titanium as an organometallic precursor and hydrogen (H2) as co-reactant. This process was developed in a Veeco NEXUS™ chemical vapor deposition tool. The tool uses a substrate rf-biased configuration with a grounded gas shower head. In this paper, the complimentary and self-limiting ch...

Soft magnetic granular material Co-Fe-Hf-O for micromagnetic device applications

A granular magnetic material, Co–Fe–Hf–O, has been developed-using dc pulsed magnetron reactive sputtering. The deposition rate is as high as 1.3nm∕s. The electrical and magnetic properties of Co–Fe–Hf–O film can be tuned by changing O2 during deposition. A highly resistive, magnetically soft film has been achieved in a small range of the O2∕(Ar+O2) gas flow ratio. The origin of the dependence of magnetic and electrical properties of this material is studied and explained by monitoring the evolution of the film microstructure, using x-ray diffraction and transmission electron microscopy.

High-frequency responses of granular CoFeHfO and amorphous CoZrTa magnetic materials

High-resistivity soft magnetic materials are receiving much attention as they have relatively low core loss at high frequencies. We developed magnetically soft granular CoFeHfO material by pulsed-dc reactive magnetron sputtering and compared its electrical and magnetic properties, especially permeability spectra, with those of amorphous CoZrTa material. We also investigated the permeability spectra of patterned CoFeHfO films with different thicknesses and observed their magnetic domain structures by Kerr imaging microscopy. The granular CoFeHfO material has a better high-frequency response than the amorphous CoZrTa at thicknesses beyond ∼0.5μm, if the ratio of the real/imaginary parts of the permeability is the principal figure of merit, and is an excellent candidate for high-frequency applications such as integrated magnetic inductors.

Small-Resistance and High-Quality-Factor Magnetic Integrated Inductors on PCB

We have designed and fabricated both single-coil and parallel-coil magnetic integrated inductors with extremely small resistances and high quality factors on an 8-in-round printed circuit board (PCB) substrate for microprocessor power delivery applications. The dc resistances of these inductors are less than 12 mOmega. Soft magnetic material CoFeHfO was successfully integrated into the inductor fabrication to increase the inductance. The quality factors are more than 80 in a frequency range of 1.5-2 GHz for air-core inductors and more than 23 in a range of 200-300 MHz for magnetic inductors. The net inductance improvement of the magnetic inductor over air-core inductor is about 12%, which could be further enhanced with a thicker magnetic core, according to our theoretic calculation and HFSS simulation. We also characterized the permeability spectra of CoFeHfO material on the PCB substrate, simulated the high-frequency performance of the magnetic integrated inductor by HFSS, and, for the first time, reached a good agreement with the experimental data. The experimental and simulation results of the magnetic inductors as compared to those of the air-core inductors point out the future direction to further optimize magnetic integrated inductors.

Tensor Nature of Permeability and Its Effects in Inductive Magnetic Devices

The tensor nature of the permeability of soft magnetic materials with an in-plane anisotropy was investigated. Using tensor transformation, the measured permeability was proportional to cos2 alpha, where alpha is the angle between the external exciting magnetic field and hard axis of magnetic material, which was proven by experimental data for thin-film materials CoFeHfO and CoTaZrTb. A new type of inductor was designed and simulated by Ansoft Maxwell 3-D to study the effects of the tensor nature of the permeability in the simulation of inductors. It is important to appropriately account for the tensor nature of the permeability of soft magnetic materials in inductive device simulation to establish realistic device models. A magnetic integrated inductor with extremely low DC resistance (<9mOmega) was fabricated. Its high-frequency performance was measured and compared to HFSS simulation using appropriate tensor permeability

Optimization of high Bsat FeCo films for write pole applications

FeCo films and their lamination with ultrathin NiFe layers down to 5A were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat>2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000A. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.FeCo films and their lamination with ultrathin NiFe layers down to 5A were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat>2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000A. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.

Package compatibility and substrate dependence of granular soft magnetic material CoFeHfO developed by reactive sputtering

Integration of magnetic passive components into package has been attracting more interests recently, but efficient package-compatible magnetic materials are needed. We have developed a package-compatible granular material, CoFeHfO, on a printed circuit board by reactive sputtering and investigated the substrate dependence of its soft magnetic property. Atomic force microscopy and grazing incidence x-ray-scattering-diffraction spectra show that a rough substrate surface degrades the magnetic property of CoFeHfO thin films with almost the same crystal microstructure. With surface planarization by chemical-mechanical polishing, soft magnetic material CoFeHfO can be realized on the package substrate. This material is promising for future applications in package.

ALCVD AlO/sub x/ barrier layers for magnetic tunnel junction applications

Ultrathin AlO/sub x/ layers 5-25 /spl Aring/ thick were deposited using the atomic-layer chemical vapor deposition technique. A magnetic thickness loss of /spl sim/ 1 /spl Aring/ has been estimated at CoFe-AlO/sub x/ or NiFe-AlONiFe-AlO/sub x/ interfaces. The two-dimensional integrity of the thin AlO/sub x/ films at thickness >7 /spl Aring/ has been validated by the differential switching of two magnetic layers sandwiching a ultrathin AlO/sub x/ layer and the distinct cross-sectional transmission-electron-microscopy images. No appreciable tunnel magnetoresistance effect has been measured from the fabricated magnetic tunnel junction devices. A proper in situ treatment prior to and/or after AlO/sub x/ deposition and a proper protection of the underlying magnetic layer are expected for further improvements.

High Frequency Responses of Granular Magnetic Material CoFeHfO and Amorphous Material CoZrTa

This paper compares the permeability spectra of granular CFHO and amorphous CoZrTa (CZT) thin films with different thickness and laminated structures, and show that granular CFHO has much better high-frequency response and can be an excellent candidate for high-frequency applications.