Film Inductors Research Articles

Formation and characterization of Pt-containing magnetic high entropy alloy film from multilayer precursor

Pt-containing high entropy alloy films (HEAFs), FeCoNiCuxPtx (x = 0.2, 0.4, 0.6, 0.8, 1.0), have been prepared from multilayer precursors using a two-step method involving magnetron sputtering deposition and vacuum annealing. It has shown that through vacuum annealing at elevated temperatures, complete mixing of the multilayer component can be realized to form uniform high entropy alloy films. By changing their concentrations, the effects of Pt and Cu on microstructure and magnetic properties of FeCoNiCuxPtx HEAFs have been systematically investigated. The results show that FeCoNiCuxPtx HEAFs are of disordered FCC solid solution structure, exhibiting soft ferromagnetic behavior and strong in-plane magnetic anisotropy. FeCoNiCu0.2Pt0.2 HEAFs, with MS = 802 emu/cm3, HC = 52.0 Oe, HK = 2.3×104 Oe, and ρ =3.8×10−7 Ω·m, are suitable for application as the core material of high frequency thin film inductors. It is found that Pt-containing HEAFs show relatively high saturation magnetization due to the fact that Pt-containing HEAFs tend to have larger lattice parameter, which may promote the exchange interaction among the magnetic Fe, Co and Ni atoms in FeCoNiCuxPtx HEAFs. This result is further supported by DFT calculations.

Tailoring the in-plane magnetic anisotropy and permeability spectra of obliquely deposited Fe40Co40B20 films for 5G communications

Ferromagnetic films are widely used in magnetic devices owing to their high saturation magnetization, high magnetic permeability, and low coercivity. However, it is extremely challenging to apply ferromagnetic films to high-frequency communication applications due to the low resonant frequency of permeability spectra. Here, ferromagnetic Fe40Co40B20 films are prepared using oblique magnetron sputtering deposition and the static and dynamic magnetic properties are comprehensively investigated. The self-shadowing effect caused by the tilted growth of columnar grains introduces in-plane magnetic anisotropy to the films, thereby increasing the natural resonant frequency. As the sputtering angle increases from 24° to 30°, the resonant frequency increases from 4.09 to 4.87 GHz, resulting in an approximate liner tunability of 0.13 GHz/degree. Compared to the normally sputtered films, the figure of merit in regard to the microwave magnetic performance of the obliquely sputtered films is significantly enhanced by more than 50%. These results reveal the effectiveness of the oblique sputtering deposition to tailor the in-plane magnetic anisotropy and permeability spectra of ferromagnetic films for the high-frequency film inductor application of 5G communications.

The Preparation of High Saturation Magnetization and Low Coercivity Feco Soft Magnetic Thin Films via Controlling the Thickness and Deposition Temperature.

FeCo thin films with high saturation magnetization (4 πMs) can be applied in high-frequency electronic devices such as thin film inductors and microwave noise suppressors. However, due to its large magnetocrystalline anisotropy constant and magnetostrictive coefficient of FeCo, the coercivity (Hc) of FeCo films is generally high, which is detrimental to the soft magnetic properties. Meanwhile, the thickness and deposition temperature have significant effects on the coercivity and saturation magnetization of FeCo films. In this paper, FeCo thin films with different thicknesses were prepared by magnetron sputtering at different temperatures. The effects of thickness and deposition temperature on the microstructure and magnetic properties of FeCo thin films were systematically studied. When the film thickness increases from 50 nm to 800 nm, the coercivity would decrease from 309 Oe to 160 Oe. However, the saturation magnetization decreases from 22.1 kG to 15.3 kG. After that, we try to further increase the deposition temperature from room temperature (RT) to 475 °C. It is intriguing to find that the coercivity greatly decreased from 160 Oe to 3 Oe (decreased by 98%), and the saturation magnetization increased from 15.3 kG to 23.5 kG (increased by 53%) for the film with thickness of 800 nm. For the film with thickness of 50 nm, the coercivity also greatly decreased from 309 Oe to 10 Oe (decreased by 96%), but the saturation magnetization did not change significantly. It is contributed to the increase of deposition temperature, which will lead to the increase of grain size and the decrease of the number of grain boundaries. And the coercivity decreases as the number of grain boundaries decreases. Meanwhile, for the thicker films, when increasing the deposition temperature the thermal stress increases, which changes the appearance of (200) texture, and the saturation magnetization increases. Whereas, it has a negligible effect on the orientation of thin films with small thickness (50 nm). This indicates that high-temperature deposition is beneficial to the soft magnetic properties of FeCo thin films, particularly for the films with larger thickness. This FeCo thin film with high saturation magnetization and low coercivity could be an ideal candidate for high-frequency electronic devices.

Design and fabrication of thin film inductors using closed laminated core for 20‐MHz DC–DC converters

This letter presents a feasible and cost-effective approach to realize closed laminated core, which is used to realize on silicon integrated thin film inductors. The closed laminated core is fabricated by electroplating magnetic layers with an oxide insulation layer sputtered in-between. This is compatible with the back end of line (BEOL) processes. The prototype of the thin film inductor with closed laminated core shows less degradation of AC inductance and smaller AC resistance at high frequencies than the variant with a solid core. Furthermore, it is tested in a 20-MHz DC–DC converter. The peak efficiency of 80% was achieved.

Electrodeposited Conifex Magnetic Films with Low Magnetic Losses for Power Applications

Electromagnetic induction is essential for functioning of the analog circuits used in cell phones, MEMS devices and other power related electronics. In order to meet the demand of higher efficiency and minimum magnetic losses in packaging industry, we have developed solution chemistry1 , 2 for electrodeposition of CoNiFeX (X=S,O,P,B,V) thin films (thickness=500 nm) with high magnetic moment (HMM) and >500 permeability at >500 MHz frequency; >100μΩ-cm resistivity; >1.5 T magnetic moment. The CoNiFeX alloys are fully compatible with existing manufacturing concepts in semiconductor industry. Direct current (DC) and pulse current3 (PC) deposition methods for CoNiFeX alloys is employed to demonstrate control over BCC/FCC crystal structure by tuning transport conditions during electrodeposition. The structure of CoNiFeX alloys is characterized with average grain size of 15-20 nm which consequently yields coercivity values of CoNiFeX alloy films between 8-15 Oe at 500 nm thickness. CoNiFe alloys produced by DC and PC deposition have magnetic moment of 1.8 T, which is optimized to 2.2 T with addition of X (X=S,O,P,B,V) as additives4. More than 100% increase in the resistivity of deposited CoNiFe alloys is demonstrated with controlled concentration of additives and Fe3+ ions as oxide precipitating agent5 without reduction in magnetic properties. All samples exhibit shiny surface finish and low stress. Thin film inductor devices are fabricated with CoNiFeX alloys to test magnetic properties at >500 MHz frequency, which would be discussed with testing data. Brankovic, S. R., Vasiljevic, N., Klemmer, T. J. & Johns, E. C. Influence of additive adsorption on properties of pulse deposited CoFeNi alloys. Journal of the Electrochemical Society 152, C196 (2005).Brankovic, S. R., Sendur, K. & Klemmer, T. J. Magnetic Materials, Processes, and Devices VII and Electrodeposition of Alloys. in Proceedings of the International Symposia 2002, 269 (Electrochemical Society, 2003).Puippe, J.-C. & Leaman, F. Theory and practice of pulse plating. (Amer Electroplaters Soc, 1986).Djokić, S. S. Electrodeposition of amorphous alloys based on the iron group of metals. Journal of the Electrochemical Society 146, 1824 (1999).George, J. et al. Oxide/hydroxide incorporation into electrodeposited CoFe alloys—Consequences for magnetic softness. Electrochimica Acta 110, 411–417 (2013).

Stretchable thin film inductors for wireless sensing in wearable electronic devices

The unique soft and elastic nature of stretchable electronics has potential to advance wearable devices as human-machine interfaces. The integration of wireless power and data communication technology into stretchable electronics, which could be realised by inductive coupling and oscillator circuits, is key to achieve continuous monitoring of body signals with minimally invasive devices. As one of the main components for inductive coupling and oscillator circuits, the development of stretchable inductors is therefore compelling. The most common strategy to fabricate stretchable inductors is to add periodic waves to a spiral conductor, which provides mechanical robustness but inevitably increases resistance. In this work, we introduce a method to fabricate stretchable inductors, which relies on creating a wrinkled thin film inductor on a polystyrene substrate, functionalizing the inductor surface with an adhesive layer, and then transferring the structure onto a polydimethylsiloxane (PDMS) elastomer. Contrary to inductors created through the addition of periodic wave patterns, the wrinkled inductor features low resistance while providing high stretchability. The wrinkled inductors fabricated using this approach exhibited 30% decrease in resistance compared to their flat counterparts of the same size and geometry. Resistance and inductance under uniaxial stretching remained unchanged up to 45% strain, revealing exceptional electrical and mechanical stability. The strong chemical bonding between the functionalized wrinkled inductor and the PDMS elastomer contributes to the robustness and long-term stability of the device. This method provides an added advantage of miniaturization of the stretchable inductor, as it is shrunk to 16% of its original size during the wrinkling process. This technology has potential for building high performance stretchable inductors for stretchable wireless electronic devices and can eventually benefit the design of electronics for implants, health care monitoring and wearable communication.

Tailoring the magnetic properties of sputtered amorphous CoZrTa/metal-oxide (MO) by interfacial oxygen migration

Modulating the soft magnetic properties of amorphous magnetic thin films is important for constructing energy-efficient and high performance thin film inductors. Here, a metal (Pt) and an oxide (Al2O3) are selected as the covering layer to investigate the effect of the interfacial microstructure on the magnetic properties of CoZrTa thin films. The results show that the magnetic dead layer thickness (tDL) and coercivity (Hc) decrease and saturation magnetization (Ms) increases with the annealing temperature for the CoZrTa/Al2O3 sample. However, tDL, Hc, and Ms of the CoZrTa/Pt sample show an opposite variation tendency with the annealing temperature. Interfacial structural results indicate that different magnetisms can be ascribed to different interfacial oxygen migration and interfacial diffusion processes. The effective interfacial oxygen migration in CoZrTa/Al2O3 reconstructs oxygen atom distribution at the interface and provides an effective way to enhance the magnetic properties of CoZrTa, whereas the intensified interfacial diffusion between CoZrTa and Pt after annealing in the CoZrTa/Pt sample caused the deterioration of the magnetism. This study will be helpful in advancing the development of magnetic thin film inductor devices.

Laser-Based Fabrication of Microstructures on Nickel Thin Films and Its Applications in On-Chip Thin Film Inductors

This work reports on the fabrication of microbump structures on nickel (Ni) films by single-pulse, localized laser irradiation. Conditions for the reproducible formation of such microstructures have been identified in terms of laser-irradiation and film parameters after systematic studies involving a relevant parameter space. Ni films deposited by vacuum evaporation were found to be better suited for reproducible laser microstructuring because they lack the typical cracks and voids morphology of sputtered films. The continuous and smooth nature of the evaporated films facilitated a radially symmetric heat flow propagation upon laser irradiation, which then resulted in a complex combination of thermal expansion, deformation, and other processes leading to a high yield of microstructures. An improvement in the inductance and the quality factor of on-chip spiral inductors, incorporating such laser-microstructured ferromagnetic nickel thin films was observed, which demonstrates the potential of such a laser-based method for fabrication or fine tuning of various micro-/nano-electric/electronic sensor and other components and systems.

Study of Thin-Film Magnetic Inductors Applied to Integrated Voltage Regulators

Intel's microprocessors are powered by high-frequency fully-integrated switching regulators implemented on die. Current products use non-magnetic inductors designed in the package substrate. This article investigates the use of magnetic thin film inductors fabricated on silicon wafers as an alternative that improves conversion efficiency while achieving higher inductance per area density. This article builds on the earlier work done on thin film inductors at Intel, and explores the feasibility of using them in a high volume product. A number of different design variations are studied to look at tradeoffs between efficiency, saturation characteristics, transient response, and voltage ripple. This is accomplished through a combination of passive measurements using a vector network analyzer (VNA) and active measurements on a fully functioning integrated voltage regulator system.

PCB Embedded Bondwire Inductors With Discrete Thin-Film Magnetic Core for Power Supply in Package

This paper details the design, assembly, and detailed characterization of printed circuit board (PCB) embedded thin magnetic film inductors for Power Supply in Package applications. Solenoidal inductors were assembled on copper tracks printed on PCB with wire bonds to complete the copper loop. Furthermore, the solenoid inductors have laminated amorphous soft magnetic thin films embedded between the two conductor layers. The devices have chemically thinned Vitrovac films laminated as core material. Three different designs of solenoid inductors with different numbers of turns are assembled and characterized. The assembled PCB inductor measured a highest quality factor of 8.5 for a three-turn device at 10 MHz.

RF inductors with sputtered nanomagnetic films on glass substrates

Inductors utilize spiral or helical designs to enhance magnetic flux and inductance. Spiral inductors require large footprint while solenoid inductors require thick substrates to achieve adequate flux coupling. As such, both these designs impose trade offs in inductance density, Q, and frequency stability. Nanomagnetic films with stable and high permeability can enhance inductance density and correspondingly the Q factor. However, nanomagnetic films suffer from two disadvantages. They have high losses beyond 1.0 GHz. They are also sputter-deposited as thin films that are less than five microns. Therefore, the benefits of nanomagnetic films in RF inductors are not clear. Performance improvements and trade-offs in RF inductors with nanomagnetic films are analyzed through material and component-level modeling. In the first part of the paper, nanomagnetic films and properties are modeled. The inductance density and Q trade-offs with nanomagnetic films are simulated after imposing their constraints: frequency dependence and thickness of five microns. Both helical and spiral inductors are considered with and without the nanomagnetic films. The simulations show enhancement in inductance by 5× with mild degradation in Q for spiral inductors. However, the Q degraded more with solenoid inductors. Higher resistivity and ferromagnetic resonance frequency are critical to improve the performance of nanomagnetic film inductors.

Soft Magnetic Properties of High-Entropy Fe-Co-Ni-Cr-Al-Si Thin Films

Soft magnetic properties of Fe-Co-Ni-Al-Cr-Si thin films were studied. As-deposited Fe-Co-Ni-Al-Cr-Si nano-grained thin films showing no magnetic anisotropy were subjected to field-annealing at different temperatures to induce magnetic anisotropy. Optimized magnetic and electrical properties of Fe-Co-Ni-Al-Cr-Si films annealed at 200 °C are saturation magnetization 9.13 × 105 A/m, coercivity 79.6 A/m, out-of-plane uniaxial anisotropy field 1.59 × 103 A/m, and electrical resistivity 3.75 μΩ·m. Based on these excellent properties, we employed such films to fabricate magnetic thin film inductor. The performance of the high entropy alloy thin film inductors is superior to that of air core inductor.

Improvement in inductance and Q-factor by laser microstructuring of ferromagnetic on-chip thin film inductors

In this work, we examine the potential improvement in inductance (L) and quality factor (Q) of on-chip ferromagnetic thin film inductors through the formation of conical microstructures by localized ultraviolet laser irradiation on ferromagnetic thin film. Parameters affecting L and Q, and arising from the surface modification upon laser irradiation include thickness of the film, size, and density of the structures. The thickness of the film is optimized to 0.2 μm, and at least 18% increase in inductance and 25% increase in Q-factor for NiFe thin film in comparison to the conventional spiral inductor is expected. L and Q values of NiFe films with and without microstructuring are compared, and a 7% increase is predicted for the microstrucired film. The proposed fabrication process, including the laser microstructuring technique, is likely to provide a significant flexibility, cost effectiveness and even better parameters, if other material systems are considered.

集積回路上へのBST薄膜可変容量とAuめっき厚膜インダクタのモノリシック集積化

集積回路上へのBST薄膜可変容量とAuめっき厚膜インダクタのモノリシック集積化

Design of Magnetic Transceivers for 3-D Integrated Circuits

Use of magnetic film inductors as transceiver elements for wireless transfer of power and signal communication between vertically stacked silicon integrated circuits is discussed. Two characteristic designs are compared-a vertical magnetic core with high-aspect-ratio laminations and a planar magnetic core where flux closure is achieved by a suitable design of the interchip air gap. The latter design is argued to hold a promise for 3-D circuit integration.

Micromagnetic simulation on the dynamic permeability spectrum of micrometer sized magnetic elements

The inductance of a thin film inductor with magnetic core is much less than μ׳(magnetic core׳s permeability) times that of inductor without magnetic core due to the complicated magnetic structure in the scaled-down magnetic elements. Therefore, it is very important to optimize the micro-scale magnetic structure for improving the inductance value of the thin film inductor with magnetic core. In this paper, the magnetization dynamics and magnetic structure have been investigated using micromagnetic simulation method, in which the additional internal boundaries are considered. The simulated results show that the permeability of structured micromagnetic core is promoted 32.5% than that of magnetic element without slits. It opens a new way to improve the dynamic high frequency characteristics of micro-scale magnetic element, which can be used in a thin film inductor.

Formation of particulate Fe-Al films by selective oxidation of aluminum

Fe-5wt%Al films were RF-sputtered and annealed in an atmosphere of hydrogen and water vapor mixture at 1173 K for up to 200 min in order to selectively oxidize aluminum. As the annealing time increased, the morphology of the films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. Thermodynamics simulation was performed to determine the ideal conditions for this process. Temperatures exceeding 1073 K are necessary to prevent iron from oxidation confirmed by both the depth profile in XPS and magnetic moment increment in VSM. Annealing the films in an atmosphere with a very low dew point of 77 K did not make the films become particulate. New findings are expected to be applied to the thin film inductors for GHz application as well as to manufacturing process of nanoparticles.

Improved High Frequency Response and Quality Factor of On-Chip Ferromagnetic Thin Film Inductors by Laminating and Patterning Co-Zr-Ta-B Films

In this work, we report the improvement of high frequency response and quality factor of on-chip inductors by integrating ferromagnetic thin films (Co-Zr-Ta-B) including two different combinations of laminations and 500 nm thick non-laminated film. Up to 4.2X increase in inductance and 5X increase in quality factor (Q) was obtained from 4-turn spiral inductors incorporated with 50 nm by 10 laminated films with a peak Q at 500 MHz. Effects of patterning magnetic film have also been investigated by changing magnetic thin film aspect ratio. It was demonstrated that the peak Q can be pushed towards using higher frequencies as high as 1 GHz by a combination of patterning magnetic films into fine bars and laminations.

Increase of $Q$-Factor of RF Magnetic Thin Film Inductor by Introducing Slit-Patterned Magnetic Thin Film and Multiline-Conductor Spiral Coil

In order to increase Q -factor of radio-frequency (RF) magnetic thin film inductor integrated in chip-size-package RF-ICs, two schemes have been investigated experimentally. For suppressing the in-plane eddy current of the magnetic thin film, a slit-patterned structure was introduced, and it was found that the slit-patterned magnetic thin film is very effective for increasing Q-factor. On the other hand, for suppressing alternating current (ac) copper loss, a multiline-conductor spiral coil was introduced, and it was found that the multiline coil is effective for improving decrease of inductance at high frequencies. By introducing the two schemes, a maximum Q-factor of 18 at 1.5 GHz was obtained in a spiral inductor with a bottom slit-patterned CoFeSiO/SiO2 granular multilayer film and triple-line-conductor spiral coil.

Si(100) wafer와 SiO2/Si(100) 기판에 동시 스퍼터링법으로 증착된 NiFe 합금 박막의 상변화 및 자기적 특성

Si(100) wafer와 <TEX>$SiO_2$</TEX>/Si(100) 웨이퍼에 증착된 NiFe 합금 박막의 결정상과 자기적 특성을 비교하고자 동시 스퍼터링법을 이용하여 두 기판 위에 150 nm의 박막을 제조하여 그의 상변화와 자기적 특성을 XRD, FE-SEM, VSM으로 비교하였다. 두 기판 위에 증착된 NiFe 박막은 BCC상으로 증착되었으나 <TEX>$400^{\circ}C$</TEX>에서 2시간 열처리를 한 결과 BCC에서 FCC로의 상전이가 일어나는 것을 관찰 할 수 있었으며 Si(100) wafer위에 증착된 박막에서는 <TEX>$500^{\circ}C$</TEX>에서 열처리 후에도 BCC와 FCC가 혼재하여 나타나는 것을 알 수 있었다. <TEX>$450^{\circ}C$</TEX>에서 열처리 하였을 때 각형비가 가장 높았으며 포화자화는 0.0118 emu로 나타나고 있었다. <TEX>$500^{\circ}C$</TEX> 이상의 온도에서는 상전이로 인해 포화자화가 급격히 감소하는 것을 볼 수 있었다. Ni-Fe alloys have various applications such as thin film inductor, thin film transformer, magnetic head's shield case, etc. Magnetic properties of Ni-Fe thin films depend on the process parameters such as thickness, contents, deposition rate, substrates, etc. In this study, NiFe films with a thickness of about 150nm were deposited on Si(100) wafer and <TEX>$SiO_2$</TEX>/Si(100) substrate at room temperature by a DC magnetron co-sputtering using Fe and Ni targets. Their phase formation and magnetic properties as a function of annealing temperature were investigated with XRD, FE-SEM and VSM. The assputtered films have BCC structure. With increasing annealing temperature, NiFe thin film for <TEX>$SiO_2$</TEX>/Si(100) substrate transformed completely from BCC to FCC phase above <TEX>$500^{\circ}C$</TEX>, but some BCC phase remained above <TEX>$500^{\circ}C$</TEX> on Si(100) wafer. For samples annealed at <TEX>$450^{\circ}C$</TEX>, squareness ratio of NiFe thin film shows peak value and its saturation magnetization is around 0.0118 emu, which means that the optimum annealing temperature of NiFe thin film seems to be <TEX>$450^{\circ}C$</TEX>. The saturation magnetization of films decreased rapidly above the annealing temperature of <TEX>$500^{\circ}C$</TEX> due to phase transformation from BCC to FCC phase.