Fabrication of Meander and Spiral Type Micro Inductors

1. IntroductionThe planar type thin film inductors and transformers fabricated by semiconductor process have becomemore important with the increasing in the need forminiaturization and high frequency drive of switchingpower supplies and another high speed small magneticdevices.[1-5] To fabricate high performance inductorsand transformers, several important factors should beconsidered, such as well--designed geometrical structures, etching process for precise pattern, and the materials of each …     

A tunable magnetic inductor

For integrated radio-frequency applications, tunable magnetic inductors are expected. A tunable magnetic inductor, based on magnetoimpedance effect, is presented in this paper. The proposed inductor is constructed with a magnetic inductor body, wound by an insulated coil, inducing a longitudinal dc bias magnetic field when a dc control current is flowing through. Formed by a conductive core coated by a high-permeability magnetic layer, the magnetic inductor body can be realized by either a thin-film structure or a composite wire. The reluctance models for both thin-film and composite wire structures are studied. A prototype tunable magnetic inductor, using a composite wire element, has been characterized. The results show that by varying the dc control current, the inductance L of the magnetic inductor can be tuned. The tunable range depends on the frequency of the current flowing through the inductor. A relative variation of inductance /spl Delta/L/L/sub 0/, up to 18% at low frequency (around 5 MHz), is achieved by applying a bias current of magnitude merely up to 15 mA. The quality factor varies from 5 to 17 in the measured frequency range. The proposed tunable inductor may be further optimized for high-frequency applications and has the potential to be realized in micro-electromechanical systems technology.     

电感器用Ni-Cu-Zn铁氧体薄膜的设计与性能研究

采用丝网印刷技术制备Ni-Cu-Zn铁氧体电感器薄膜, 并对其性能进行了表征. XRD分析表明, 铁氧体薄膜具有相同的晶格结构. 研究结果表明, 在引入了铁氧体薄膜后, 电感器的电感量相对于空心电感器有30%左右的提高, 品质因数依频率不同有所改善, 共振频率有所降低. 经400℃后处理的薄膜电感器在低频时性能最好, 50 MHz时电感量提高了27%, 品质因数提高了39%.     

Monolithic double rectangular spiral thin-film inductors implemented with NiFe magnetic cores for on-chip dc-dc converter applications

This paper describes a simple, on-chip complimentary metal oxide semiconductor (CMOS) compatible thin-film inductor applied for the dc-dc converters. The double rectangular spiral types of the thin-film inductors were implemented with 15 µm-thick copper films upon 2.5 µm thick of the NiFe magnetic core. Prior to fabricating a high-voltage CMOS dc-dc converter circuit, the NiFe magnetic core was deposited on the polyimide film. Adapting a double-rectangular structure, the fabricated monolithic inductor exhibited not only high inductance of 1.6 µH but also high quality factor of 11.2 at 5 MHz. To simplify the integration process, the planarization process for the top magnetic core was eliminated. The performance of the dc-dc converter which combined with our proposed inductors was evaluated at a high power efficiency of 81% when the converter operated at a frequency of 5 MHz corresponding to input and output voltages of 3.3 V and 8.1 V, respectively.     

Radio-Frequency Planar Integrated Inductor With Permalloy-SiO$_2$Granular Films

We have designed and fabricated a radio-frequency (RF) planar integrated inductor using Permalloy-SiO$_2$granular film as the magnetic core. By controlling the composition and microstructure, we produced a granular film with excellent soft magnetic properties and high electrical resistivity. The inductance$L$of the inductor with granular Permalloy-SiO$_2$magnetic film increased 6% to 15%, compared to that of an air-core inductor, and the quality factor$Q$value was high, approaching 10 in the frequency range of 2–3 GHz. The controllable anisotropy of the granular film generated in deposition process gives the magnetic inductor a very high self-resonance frequency peak—over 6 GHz.     

In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb_0.92Sr_0.08)(Zr_0.65Ti_0.35)O₃] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350degC and 750degC for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750degC. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature activating significant grain growth for the room-temperature deposited films is about 275degC and the Curie point lies between 325 and 400degC. This relatively high Curie point makes these films suitable for wide temperature range applications.     

Microstructures and magnetic anisotropy of single-layered Fe-Pt alloy films by in-situ annealing

The single-layered Fe-Pt films with thickness of 30 nm are in-situ deposited directly on Si substrate at various substrate temperatures (Ts) of 350 to 590 degrees C. As the Fe-Pt film is sputtered at substrate temperature is 350 degrees C, it shows (111) preferred orientation and tends to in-plane magnetic anisotropy. The L1(0) Fe-Pt film with (001) texture is obtained and exhibited perpendicular magnetic anisotropy as the substrate temperature is increased to 470 degrees C. The perpendicular coercivity (Hc perpendicular), saturation magnetization (Ms) and perpendicular squareness (S perpendicular) of this film are 6.9 kOe, 674 emu/cm3 and 0.89, respectively, which reveal its significant potential as perpendicular magnetic recording media.     

Lattice Expansion by Adding Oxygen to Control Crystallographic Orientations in Chemically Ordered L10 FePt Films

We fabricated L1₀ FePt thin films by sputtering in reactive oxygen on polycrystalline glass substrates, and we investigated the magnetic properties and crystallographic orientations of the films. Oxygen addition during the FePt deposition promoted heteoroepitaxial growth by decreasing the lattice misfit with the Ag underlayer. In an oxygen/argon ratio of 1.5-3.0 vol.%, the in-plane lattice parameter of the FePt films expanded, and the lattice misfit with the Ag underlayer decreased from 6.3 to 3.9% in the as-deposited state, as determined by grazing incidence X-ray diffraction (GIXRD). Annealing at 700degC for 1 min produced a heteroepitaxially grown L1₀ (001) texture with a large out-of-plane coercivity of 8.8 kOe and a nucleation field of kOe. Transmission electron microscopy showed that average grain size in the as-deposited films was about 4-5 nm and was in the range of 10-15 nm in the annealed films, indicating that there was some grain growth.     

Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing     

Dielectric characteristics of barium strontium titanate films prepared by aerosol deposition on a Cu substrate

Polycrystalline barium strontium titanate (Ba_xSr_1-xTiO₃, BST) films were directly prepared on copper substrates using an aerosol deposition method (ADM) at room temperature. Electric properties, such as the dielectric constant and tunability, were investigated as a function of the Ba content in Ba_xSr_1-xTiO₃ (x = 1.0, 0.6, 0.4) films. At a frequency of 100 kHz, the dielectric constant of the as-deposited BST films were 100, 201, and 72 for x = 1.0, 0.6, and 0.4, respectively. After annealing in N₂ at 500degC, the dielectric constant of the films on Cu electrodes were 190, 400, and 170 at x = 1.0, 0.6, and 0.4, respectively. Moreover, the BST (x = 0.6) film showed a high tunability of 30% under an applied electric field of 300 kV cm^-1.     

圆锭电磁铸造中电磁场及液柱形状的计算机模拟

采用互感耦合模型对无负载和有负载条件下的电磁场分布及液柱形状进行了数值模拟。计算了铝合金圆锭电磁铸造的互感耦合系数。实验测定了无负载和有负载条件下的电磁场分布及液柱形状,结果表明与数值模拟结果吻合较好。得出采用斜边感应器显著削弱感应器上部的磁场强度,能获得合理的液柱形状的结论。     

A Magnetostatic Model for Square Spiral Inductors Incorporating a Magnetic Layer

Embedding magnetic layers in inductors is an attractive option for increasing inductance density, which is a critical issue for radio-frequency applications. In this letter, we develop a magnetostatic model for square spiral inductors incorporating a magnetic layer. In our model, we assume that the permeability of the magnetic layer is isotropic and infinite. The model provides a fast and effective numerical calculation of the inductance of inductors incorporating a magnetic layer. We show the derivation of the model and provide calculation results for various inductor structures.      

Fabrication of Metallic Magnetic Calorimeter X-ray Detector Arrays

Microcalorimeters with metallic magnetic sensors show great promise for use in astronomical X-ray spectroscopy. We describe the design and fabrication of a lithographically patterned magnetic microcalorimeter. A paramagnetic AuEr film is sputter-deposited as the sensor, which is coupled to a low noise SQUID via a meander superconducting pickup loop used as an inductor. This inductor also provides the magnetic field bias to the sensor. The AuEr film is deposited over this meander such that the field created by a large current flowing in the loop magnetizes the sensor material. The use of thin film techniques in the fabrication of these magnetic sensors not only allows strong magnetic coupling between the sensor and the inductor, it also is scalable for array fabrication.      

Effect of short annealing times on the magnetoelectronic properties of Co/Pd-based pseudo-spin-valves

We investigated the effects of short annealing times on the magnetoelectronic properties of pseudo-spin-valves (PSV) with perpendicular magnetic anisotropy based on Co/Pd multilayers using a contact hot plate. In order to study the time scale at which the degradation of film properties occurs for possible application in perpendicular MgO-based magnetic tunnel junctions (MTJ), the results were compared against our previous study of Co/Pd PSV based on vacuum annealing. With contact annealing for up to 90 s, no significant changes to the current-in-plane giant magnetoresistance (CIP-GMR), interlayer coupling, sheet resistance and layer coercivities were observed for up to 200 degrees C. At 350 degrees C, a 39 to 46% decrease in CIP-GMR was observed for annealing times of 30 to 90 s, respectively, slightly lower than that observed for vacuum annealing at 230 degrees C for 1 h. Similar results were also obtained for interlayer coupling, sheet resistance and layer coercivities, indicating that short annealing times allow for reduced interlayer diffusion at higher temperatures. However, it is clear that significant degradation of GMR performance occurs at 350 degrees C and above even for annealing times as short as 30 s, indicating the potential difficulty of realizing Co/Pd-based perpendicular MgO-MTJ.     

Low temperature ordering of FePt films by in-situ heating deposition plus post deposition annealing

FePt thin films with 40 nm thickness were prepared on thermally oxidized Si (001) substrates by dc magnetron sputtering at the nominal growth temperature 375 °C. The effects of annealing on microstructure and magnetic properties of FePt thin films were investigated. The as-deposited FePt thin films show soft magnetic properties. After the as-deposited FePt thin films were annealed at various temperatures and furnace cooled, it is found that the ordering temperature of L1₀ FePt phase could be reduced to 350 °C. For FePt thin films annealed at 350 °C, the in-plane and out-of-plane coercivities of the films increased to 510 and 543 kA/m, respectively, and the films had hard magnetic properties. A highly (001) orientation was obtained, when FePt thin films were annealed at 600 °C. And the hysteresis loops of FePt thin films annealed at 600 °C show out-of-plane magnetic anisotropy.     

Room temperature ferromagnetism in Co-incorporated TiO2 thin films

Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.     

Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

The Inductance Enhancement Study of Spiral Inductor Using Ni–AAO Nanocomposite Core

The letter presents the fabrication and characterization of on-chip spiral inductors with Ni–anodic alumina oxide (Ni–AAO) nanocomposite core. Ni nanorods with 70 nm diameter are deposited and isolated in an AAO matrix to form a layer of nanocomposite on silicon substrate. About 3% inductance enhancement to the inductor with the nanocomposite core has been observed and the enhancement can be kept up more than 6 GHz. Because the proposed inductance enhancement scheme using ferromagnetic–AAO-based nanocomposite as inductor core employs a CMOS-compatible fabrication process with the characteristics that can be further improved, it is our belief that the scheme has a great potential application for future radio frequency integrated circuitry (RFIC) manufacture.      

Exchange-Coupled IrMn/CoFe Mulitlayers for RF-Integrated Inductors

The high-frequency characteristics of the RF integrated inductors with antiferromagnetic/ferromagnetic (AF/F) multilayers (MLs) are studied. Each AF layer is 8-nm IrMn and F is Co₅₀Fe₅₀ with a 200-nm splitting into N = 1 to 5 repeats of MLs. This exchange coupled {IrMn/CoFe(d nm)}_N MLs are deposited on top of the two-port inductors with five-turn square spiral coils, a dimension of 100 mum times 100 mum and line/space of 5 mum/2 mum. The inductor surface and magnetic layer is separated by 1-mum-thick SiO₂. The enhancement of inductance (DeltaL) is 20% compared to an air-core of the same coil size. The resonance peak gradually shifted to a higher frequency with increasing N, and reached at a maximum of 4.3 GHz when N = 5. This is in good agreement with our magnetic data which revealed that the anisotropy field (H_k) and ferromagnetic resonance frequency (f_FMR) of {IrMn/CoFe(d nm)}_N MLs are increased with increasing N. The quality factor, Q is improved by 6.8% at 1.5 GHz for the {IrMn/CoFe(40 nm)}_N=5 integrated inductors compared to air-core inductors.     

Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.