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A surface micro-machining process is described to realize planar inductors on ferrite (Ni 0.49 Zn 0.33 Cu 0.18 Fe 2 O 4 ) for high-frequency applications (<30 MHz). The highly resistive nature (~10 8 Ω m) of the Ni–Cu–Zn substrate allows direct conductor patterning by electroplating of Cu windings through a photoresist mold on a sputtered seed layer and eliminates the need for a dielectric layer to isolate the windings from the bottom magnetic core. Measured inductances~367 nH (DC resistance~1.16 Ω and Q-value>14 at 30 MHz) and ~244 nH (DC resistance~0.86 Ω and Q-value~18 at 30 MHz) at 1 MHz for elongated racetrack (10.75 nH/mm 2 ) and racetrack inductors (12.5 nH/mm 2 ), respectively show good agreement with simulated finite element method analysis. This device can be integrated with power management ICs PMICs for cost-effective, high-performance realization of power-supply in package (PSiP) or on-chip (PSoC). This simple process lays the foundation for fabricating closed core ferrite nano-crystalline core micro-inductors. [ABSTRACT FROM AUTHOR]

Abstract: Micro-inductors, with an electrodeposited nickel–iron core have been fabricated on silicon substrates, and have been characterized in the frequency range up to 100MHz. The core consists of a nickel iron, 45:55 alloy which is deposited using pulse-reverse electroplating in the presence of a magnetic field to control anisotropy. The operation of the inductors with low loss at high-frequency critically depends on core thickness, which is used to control eddy-current loss as the frequency is increased. However, it is shown that the permeability of NiFe 45/55 has a dependency on thickness, and decreases with increasing thickness. For example, the permeability is measured to be approximately 1000 for a 1-μm-thick film, decreasing to approximately 400 for a 5-μm-thick film. In order to correctly design micro-inductors for operation up to 100MHz, it is important that this characteristic of the material is taken into account. [Copyright &y& Elsevier]

• Microscopic characteristics of a magnetorheological fluid (MRF) are investigated. • A new simulation model is developed and validated by experimental data. • Length of particle chain increased sharply with the magnetic field. With the aim of studying the microscopic characteristics of a magnetorheological fluid (MRF) in a magnetic field, the theoretical analyses of the particles dynamics in a magnetic field are presented, and a model for the particle motion is proposed. Based on these analyses, a three-dimensional numerical simulation of the microstructure of MRFs in different magnetic fields is performed. Furthermore, the microstructures of the MRFs are investigated using industrial computed tomography (CT) imaging. The numerical simulation and industrial CT results indicate that the chain structure of the same MRF becomes more apparent as the magnetic field strength increases, and in the same external magnetic field, this chain structure also becomes more apparent with an increase in the particle volume fraction. The lengths of particle chains in different magnetic fields are also captured in the industrial CT experiments. When the magnetic field strength is 12 mT, the particle chains of the MRF with a particle volume fraction of 30% reach more than 10 mm in length, which bridge the inner diameter of the container, and the dense clusters-like structure is formed, the clusters-like structure becomes denser with an increase in magnetic field. Moreover, the particle chain lengths of MRF with high particle volume fractions increase sharply with the magnetic field. The experiments demonstrated that the industrial CT is an efficient method to study the microstructures of MRFs by providing particle distributions of MRFs more clearly and intuitively. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the technologies required to produce magnetics on silicon for power supply on chip. Prototypes of micro-inductors have been fabricated using techniques such as thick copper coil deposition and improved magnetic materials. The measured maximum Q factor and inductance value are 5 at 2.5MHz and 38nH/mm2, respectively. The impact of seed layers and core overlap has been identified to be significant at high frequencies. Using the validated analytical model, the electrical performance of micro-inductors in a buck converter can be predicted and efficiency of 85.9 with a power density of 15.8W/cm2 can be achieved. [Copyright &y& Elsevier]

• The SOT efficiency and field-free switching are enhanced by the presence of the in-situ field, in perpendicularly coupled Pt/Co and CoFeB bilayers sandwiched by an ultrathin PtMn/Ta layer. • Quantitative characterization indicates that the damping-like field, H DL , is boosted by an amount of up to 45%. • The tilted spin texture at the Co/PtMn interface caused by the presence of the in-situ field may play a role on the enhancement of SOT efficiency and field-free switching. Field-free switching of perpendicular magnetization and improvement of spin-orbit torque (SOT) efficiency are the keys for SOT-based devices towards ultrafast and low-power memory and computing applications. In this letter, we investigated pulse current induced magnetization switching and its efficiency in perpendicularly coupled Pt/Co and CoFeB bilayers sandwiched by an ultrathin PtMn/Ta layer, prepared in the presence/absence of an in-plane in-situ field. It is found that both the SOT efficiency and field-free switching are enhanced by the presence of the in-situ field. Quantitative characterization indicates that the damping-like field, H DL , is boosted by an amount of up to 45%. The tilted spin texture at the Co/PtMn interface caused by the presence of the in-situ field may play a role on the enhancement of SOT efficiency and field-free switching. Our findings not only provide a promising approach for SOT efficiency enhancement but also offer a possible layer stack for the integration of a full magnetic tunnel junction (MTJ) for low power memory and computing. [ABSTRACT FROM AUTHOR]

• A micro-inductor has been fabricated using a MEMS process. • The device has a single layer copper winding sandwiched between two layers of core. • The micro-inductor has a footprint area of 2.9 mm2. • The measured inductance is 204 nH at 21.7 MHz and DC resistance is 470 m Ω. • The peak quality factor of the micro-inductor is 9.23 at 9.2 MHz. • The micro-inductor has been applied in a buck converter. • The achieved maximum converter efficiency is 81.74% at 20 MHz. • The micro-inductor has also been compared with an air core inductor embedded in PCB. • The 220 nH air core inductor has a large footprint area of 32 mm2. • The maximum converter efficiency is 85.47% when the air core inductor is applied. A micro-inductor has been fabricated on silicon substrate using a Micro-Electromechanical Systems (MEMS) process. The micro-inductor has a single layer copper winding sandwiched between two layers of electroplated NiFe core. It has a footprint area of 2.9 mm2, an inductance of 204 nH at 21.7 MHz, a DC resistance of 470 m Ω , and a peak quality factor of 9.23 at 9.2 MHz. The micro-inductor has been applied in a buck converter and achieved a maximum converter efficiency of 81.74% at 20 MHz. The performance of the micro-inductor has also been compared with an air-core inductor embedded in PCB. The air core inductor has a similar inductance of 220 nH, but with a large footprint area of 32 mm2. The maximum buck converter efficiency is 85.47% when the air core inductor is applied. [ABSTRACT FROM AUTHOR]