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Research paper
Fabrication of package embedded spiral inductors with two magneticlayers for flexible SIP point of load converters in Internet ofEverything devices
Mohamed L.F. Bellaredj ⁎, Colin A. Pardue, Paul Kohl, Madhavan SwaminathanCenter for Co-Design of Chip, Package, System (C3PS), Georgia Institute of Technology, Atlanta, GA 30332, USA
Article history:Received 17 October 2017Accepted 19 December 2017Available online 20 December 2017
Inductive DC-DC converters are key elements in power delivery units for the development of Internet of Every-thing (IoE) architecturesmade of interconnected networks of smart devices, self-powered from different energysources. The ultra-low power levels involved in IoE devices in addition to cost reduction of final products requiresthe development of new technologies for the miniaturization of all the active and passive components. In thispaper, a low temperature, cheap and simple two-steps fabrication process of embedded planar inductors withtwo magnetic layers on a very thin, flexible and lightweight FR4 organic substrate is demonstrated for flexibleSystem in package (SIP) based point of load DC-DC converters in IoE devices. The process uses standard printedwiring board (PWB) copper etching to define the square geometry of the planar inductors and trenches under-neath the inductor copper traces. Very thick top and bottommagnetic layers are deposited using stencil printingof an FR4 compatible epoxy-NiZn ferrite composite magnetic material on top of the copper traces and into thetrenches. At 30 MHz, the permittivity is 3.4 and 6.23 while the dielectric loss tangent is 0.014 and 0.009 for theepoxy and composite magnetic material respectively. The composite material has a permeability of 8.46, a losstangent value of 0.1 at a frequency of 30 MHz and saturates around 0.13 Tesla. The DC resistance varies from136 mΩ to 386 mΩ while at 30 MHz the AC resistance varies from 1.9 Ω to 10.1 Ω for an inductance valuefrom 180 nH to 715 nH, corresponding to an inductance density between 5.69 nH/mm2 and 12.47 nH/mm2
and a quality factor between 13 and 17. Flexibility and its effect on the electrical parameters of the fabricated in-ductors is demonstrated through bending tests. A variation of b3% for the DC resistance is obtained for 5 mmbend radius. At 30 MHz and for a bend radius (both upward and downward) from 3.7 mm to 5 mm, the flatstate (unbent) AC resistance and inductance values (1.9 Ω to 10.1 Ω for 180 nH to 715 nH) decrease by 6.5% to18% and by2% to 4.4% respectivelywhich increase the self-resonant frequency by 3% to 3.4% and the quality factorby 2.2% to 20%. The characterized inductors are modeled in ANSYS HFSS electromagnetic simulator and simula-tion results show a good correspondence with the measured inductances and quality factors, which allows a re-liable prediction of the inductors behavior for DC-DC converter design and implementation for IoE devices.
Keywords:Point of load DC-DC convertersInternet of EverythingEmbedded planar inductorsFlexible system in packageStencil printingComposite magnetic material
1. Introduction
The Internet of Everything concept aims at interconnecting a net-work of ultra-low-power smart objects (automotive vehicles, HomeAu-tomation,metering and Security systemsetc.) and smart sensors for realtime monitoring and/or decision-making. For an autonomous opera-tion, these devices have to be self-powered and different poweringschemes need to be implemented simultaneously such as batteries, en-ergy harvesting from surrounding environment and wireless powertransfer. The presence of different power sources at the same time in ad-dition to different power consumption levels for a given operation
.L.F. Bellaredj).
mode (standby or active mode) imply voltage levels varying over awide range. To ensure an optimal use of power for such situations, apower delivery/management system using switchingmode DC-DC con-verters is required. Among the voltage converters topologies, inductiveDC-DC converters, in which the inductor is the key power transfer ele-ment from input to the load represent the dominant architecture forhigh efficiency power delivery units [1–2]. Because of the small sizeand cost requirements for IoE applications due to the number of inter-connected devices and very low power levels involved, special careneeds to be given to the converter in terms of size reduction and cost ef-fectiveness when optimizing efficiency and integration density [3–5].However, commercially available power inductors are relatively bulkydiscrete components that preclude the downsizing of the converter[6]. By switching the converter at high frequency and using embedded
Table 1Inductance range selection for the boost converter.
D ΔIL (mA) fSW (MHz) VOUT (V) L (nH)
0.4–0.6 50 10–30 1.1–1.5 170–750
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planar power inductors with a high frequency magnetic material core,significant miniaturization of the inductor and thus of converter isachieved through size reduction and the performance is enhancedthrough higher inductance density and parasitics suppression. Also,the fabrication process is simplified compared to 3D inductors such astoroidal inductors and more design flexibility is achieved as the induc-tors can be placed as close as desired to the IC chips. Different technol-ogies have been developed for the fabrication of planar powerinductors depending on the used integration approach/substrate andmagnetic core material. Planar inductors using ferromagnetic metal al-loys (CoZrTa [7–9], FeSi [10], FeNi [11–15]) and nanogranular metal ox-ides (CoZrO [16–17], CoFeB-SiO2 [18]), built on inorganic substratessuch as semiconductor [19–22], ceramic [23–25], magnetic [26–28]and glass [29–30] wafers are not suitable for high frequency IoEpower inductors because of their low resistivity which increase eddylosses at high frequency and the heavy clean room installations andcomplicated micromachining processes involved which increase pro-cessing times and cost expensiveness [19–22].Organic substrates/pack-ages such as FR4 and polyimide [31–34] represent a valuable alternativeto inorganic technologies because they present the advantage of cheap-ness, low processing temperatures (b200 °C) and combined fabrication,connection and assembly flexibility with the IC chips on the same pack-age either in a side by side or in a stacked configuration [35–36]. Ferritematerials show high resistivity with a wide selection of permeabilityfrom moderate to high values for applications within the range of100 kHz to 100 MHz [21–22,37–38]. By mixing powders of Ferrite ma-terials with a polymer, ferrite composite magnetic materials [15,38–39] [19,34] can bedeposited using screen printing [30,15,38] for pla-nar power inductors. Screen printing requires only patterned screensfor printingwhichmakes the deposition process simple, fast and cost ef-fective compared to microfabrication processes. Very thick layers ofmagnetic material (hundreds of microns) can be deposited at a muchhigher deposition rate than sputtering or electroplating. Moreover, theprinting is generally done at room temperature and accommodates or-ganic substrates. In this work, we demonstrate a new, low temperature,simple and cheap fabrication process of planar power inductors withtwo magnetic layers deposited using a cost effective stencil printingprocess on a very thin, thus lightweight and flexible FR4 organic sub-strate for high efficiency voltage converter applications in IoE devices.The process allows the fabrication of power inductors with differentsize and inductance densities in the same batch which can be used inIoE based DC-DC converters with a multitude of switching frequencyoptions based on the inductor self-resonance frequency. The paper is or-ganized as fellows. Section 2 presents the design and modeling proce-dure of the planar inductors. In Section 3, the fabrication process ofthe planar inductors is demonstrated. The characterization results ofthe fabricated inductors are discussed in the last section of the paperand compared to the simulation results.
2. Design and modeling
2.1. Overall IoE architecture
The objective is to design spiral power inductors to be used in a SIPbased point of load DC-DC converter using energy harvesting as inputpower source for an IoE device. Because of the low power levels in-volved at the input, single or multistage boost regulators are requiredto power the different analog and digital circuits of the IoE device. As-suming the basic configuration of a boost converter given in Fig. 1, theconverter inductor L can be estimated using (1) [40]:
L ¼ VIN: VOUT−VINð ÞΔIL: f SW :VOUT
ð1Þ
where VIN is the input voltage, VOUT the desired output voltage, fSW theswitching frequency of the converter and ΔIL the estimated inductor
ripple current. By using (1) and assuming a switching frequency be-tween 10 MHz to 30 MHz, an inductor ripple current of 50 mA for aduty cycle value between 0.4 and 0.6, a wide range of inductance valuescomprised between 170 nH and 750 nH can be selected for the boostconverter depending on the output voltage as can be seen in Table 1.
2.2. Inductor geometry
The designed inductors are square planar inductors with two mag-netic layers defined on both sides of a two copper layer (35 μm copperthickness for each side) FR4 PWB. The top copper layer is used to definethe inductor traces which will be covered with the first magnetic layer.The bottom side copper is used to define trenches underneath the in-ductor which will be filled with the second magnetic layer. The bottomside copper is also used as a ground plane to reduce the EMI betweenthe inductor and its surrounding. The square shape was chosen forease of fabrication while the 35 μm copper thickness was selected forDC resistance and inductance tuning. The considered inductor geometryis shown in Fig. 2(a).
The design parameters of the inductors are the outermost length, d,themetal trace width,w, the trace separation s and the number of turnsN. The trace separation s is set to be equal to themetal trace widthw foreach inductor design. SMA pads are included in the design for induc-tance measurements as well as a simple deembedding structure(microstrip line) with the same width and length as the inductorfeedline to eliminate the contribution of the SMA connector andfeedline to the inductor inductance.
2.3. Modeling approach
A 3D model of the planar inductor of Fig. 2(b) with two magneticlayers defined on both sides of the inductor was created in the electro-magnetic simulator ANSYS HFSS v17. A lumped port simulation wasachieved by connecting the top copper traces (port 1) to the bottom(ground) plane (port 2). A current excitation was created through thelumped port to compute the voltage reflection and the correspondingS-parameter (S11). From this S-Parameter, the Z-Parameter (Z11) wasextracted and the inductance and Q factor were calculated using(2) and (3). The considered magnetic material is a NiZn ferrite-epoxycomposite [41]. The permeability spectrum used for the simulations isshown in Fig. 12(a). The top and bottom magnetic layer thicknesseswere set to 200 μmwhile the design parameters d,w, s and Nwere var-ied to get various inductance densities for an inductance range from200to 600 nH. The modeling parameters and results are summarized inTable 2 where Lair and Qair are the inductance and the quality factorfor the air core inductor, Lmag and Qmag are the inductance and the qual-ity factor for the magnetic core inductor and fSR is the self-resonant
Fig. 2. (a) Spiral Inductor design (b) HFSS model of the spiral inductor.
Table 2Simulated parameters of the designed inductors at 30 MHz.
d (μm) w (μm) s (μm) N Lair (nH) Qair Lmag (nH) Lmag/A (nH/mm2) Qmag fSR (MHz)
The PWB designwas done in Keysight ADS v.2016.01. It includes thethree considered inductors as well as alignment marks defined sym-metrically at its edges on both sides of the board as shown in Fig. 3(a–b) so that only one stencil is used for printing the magnetic layers onboth sides of the PWB. The stencil design was done in AutoCAD 2017v N.52.0.0 and includes square openings of the same size as the squareplanar inductors for the stencil printing of the magnetic material aswell as alignment marks defined symmetrically at the edges of the lay-out for precise alignmentwith the PWB alignmentmarks as can be seenin Fig. 3(c).
3. Fabrication of the planar inductors
The fabrication process flow of the planar inductor is shown in Fig. 4.A 270 μm thick, lightweight and flexible, 2 copper layer (35 μm thick forboth layers and 200 μm thick FR4 layer) FR4 PWB was used as the
Fig. 3. (a) PWB top side square spiral inductors and alignment marks (b)
substrate. First, the planar inductor windings on the top side of the sub-strate and trenches on the backside of the substrate underneath the in-ductor windings were defined using standard PWB copper etchingprocess Fig. 4.The patterned planar inductors and trenches are shownin Fig. 5. The copper traces width and separation were measured usingan optical microscope. The copper trace width and separation were171 μm and 268 μm for both Inductor_1 and Inductor_2 and 99 μmand 194 μm for Inductor_3 as can be seen in Figs. 5(b) and 5(c). The cop-per trace thickness and trench depth were obtained using the VeecoDektak 150 surface profilometer. The copper trace thickness is around42 μm and the trench depth is 35 μm for all designed inductors asseen in Fig. 6.
Then, the top magnetic core was deposited with stencil printing(MPM SPM 7279 Semiautomatic Stencil Printer) on the top side of thePWB using a custom made FR4 compatible composite magnetic pastefabricated by mixing a silane activated magnetic powder (FP350 NiZnferrite from pptechnology) with a Bisphenol-A-Diglycidyl ether(BPADGE) based epoxy polymer binder at 85 wt% (which correspondsto 78% volume fraction) [41]. After stencil printing the top magneticlayer, the boards are cured for 1 h at 180 °C to form the top magneticcomposite core. The use of BPADGE polymermakes the compositemag-netic material FR4-compatible which allows a better adhesion of themagnetic composite to the organic substrate and reduces significantlythe built up stress that arises from the different thermal treatments ofthe boards. The resulting composite material showed no reaction tocommonly used solvents such as acetone, good electrical insolationthrough a measured very high DC resistance (beyond 30 MΩ) and
PWB backside trenches and alignment marks. (c) Stencil for printing.
Fig. 4. Fabrication process flow of the planar inductors: (a) PWB etching to define theinductor copper windings and back side trenches (b) Screen printing of NiZn ferritecomposite material on the top side of the PWB (c) Screen printing of NiZn ferritecomposite material on the back side of the PWB.
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very strong adhesion to the substrate assessed after N24h of high powersonication in an acetone bath. Using the same stencil screen and previ-ously prepared paste, the bottom magnetic core was stencil printed onthe backside of the PWB and the boards were cured again for 1 h at180 °C to form the bottom magnetic composite core. An example of afabricated inductor is shown in Fig. 7(a). A cross section micrograph ofInductor_3 is shown in Fig. 7(b). The measured profiles of the top andbottom side magnetic layers are shown in Fig. 8. The average thick-nesses of the top and bottom side layers are around 400 μm and 300μm respectively.
4. Experimental section
The phase identification of the NiZn ferrite powder was done usingthe Panalytical X'Pert PRO Alpha-1X ray diffraction tool. The elementalcomposition of the NiZn ferrite powder was confirmed by Energy-dispersive X-ray spectroscopy (EDS) using the LEO 1530 SEM. The elec-tromagnetic properties of the epoxy and epoxy-NiZn ferrite magneticcomposite material were measured from 1 MHz to 400 MHz usingKeysight 4291B RF Impedance/Material Analyzer, 16453A DielectricMaterial Test Fixture and 16454A Magnetic Material Test Fixture.
The magnetization curves of the magnetic composite material wasmeasured at room temperature (300K) between −150 kOe and150 kOe at a sweep rate of 25 Oe/s using a vibrating samplemagnetom-eter (VSM) from Quantum Design. The DC resistance of the fabricated
Fig. 5. (a) Inductor patterning on both sides of the PWB (b) Trace width/separati
inductors was measured using the 4-wire mode of the 3478amultimeter from HP. The RF parameters of the inductors were charac-terized between 20MHz and 400MHz using the Agilent H8363B VectorNetwork Analyzer as shown in Fig. 9(a). One port S-Parameters weremeasured and subsequently converted to Z-Parameters. The inductanceL and quality factor Q were extracted in post processing using (2) and(3). To study the effect of the mechanical loading on the DC resistanceand the RF parameters of the inductors, the inductors were bent usingan adjustable mechanical clamp up to a bend radius of 5 mm. Beyond5 mm, cracks appeared either in the bent substrate or in the compositemagnetic material. The bend radii were measured using a caliper andthe corresponding DC resistance and the RF parameters were obtainedusing the 4-wire mode of the multimeter and the network analyzer re-spectively as shown in Fig. 9(b–c).
5. Results
5.1. Characterization of the materials
The XRD diffraction spectrum of the NiZn ferrite powder is shown inFig. 10(a) where the phase is identified as (Ni0.5Zn0.5)Fe2O4. The Ni:Zn,Ni:Fe and Ni:O molar ratios are found after EDS measurements to be 1,4, 8 respectively, which corresponds to the (Ni0.5Zn0.5)Fe2O4 phase.
The dielectric properties of the epoxy and the composite magneticmaterials are shown in Fig. 11. The permittivity/dielectric loss tangentvalues for the epoxy and composite magnetic material are 3.4/0.014and 6.23/0.009 respectively at 30 MHz. The composite material showsa higher permittivity and a lower dielectric loss tangent value than theepoxy material. This indicates good electrical insulation properties ofthe composite material which allows its direct deposition on top ofthe inductorwindingswithout the need of an insulation layer. Themea-sured permeability spectrum of the epoxy-NiZn ferrite material isshown in Fig. 12. The composite has a permeability of 8.46 and a losstangent value of 0.1 at a frequency of 30MHz. Themagnetic loss tangentvalue of the composite material is ten times higher than the dielectricloss tangent value. The losses in the composite material are thus domi-nated by the magnetic losses. The magnetization curve ofFig. 12(b) shows that the composite material saturates around 0.13Tesla.
5.2. Electrical characterization of the inductors
The effective inductance of the inductors is obtained by removingthe average measured inductance of the deembedding structure(7 nH) from the measured inductance value. The measured inductanceL and quality factorQ are shown in Fig. 13, in a frequency range between20 MHz and 60 MHz where the reactance is mainly inductive. Higherfrequencies are excluded to remain far from the inductor's self-
on for Inductor_1, Inductor_2 and (c) Trace width/separation for Inductor_3.
Fig. 6. (a) Copper trace thickness-top side of PWB (b) trench depth - backside of PWB.
Fig. 7. (a) Pictures of the fabricated inductor (b) cross sectional view of Inductor_3.
resonant frequency. Compared to the air core inductors, the magneticcore inductors show an inductance increases by almost 100% for all in-ductors at 30 MHz as shown in Table 3. This is attributed to the twomagnetic layers applied to both sides of the substrate, and to the in-creased coupling between themagnetic layers through the reduced sep-aration resulting from the use of a thin FR4 layer in the 200 μm thickPWB. However, the use of two coupled magnetic layers affects signifi-cantly the quality factor of the inductors, which decreases significantlywith frequency (N50% decrease compared to the air core inductors At30 MHz). This is explained by the increase of the magnetic losses inthe composite material with the frequency increase as indicated bythe loss tangent spectrum shown in Fig. 12(a).
Fig. 8.Measured profiles of the magnetic layer
The measured inductance and quality factor are compared to simu-lation using updated modeling parameters based on the characteriza-tion measurements. A good match is observed between the updatedsimulation and measurement results for both inductance and qualityfactor as shown in Fig. 13. The slight difference between the simulationsand themeasured data can be attributed to the use of an averaged thick-ness value for both magnetic layers.
5.3. Bending results
It is worthmentioning that although themain objective of this paperis to demonstrate a cheap and simple fabrication process for planar
s (a) top side layer (b) bottom side layer.
Fig. 9. Experimental setups for the (a) electrical characterization of the inductors. (b) Study of the effect of mechanical loading on the inductors' DC resistance (c) study of the effect ofmechanical loading on the inductors' RF parameters.
Fig. 10. XRD diffraction spectrum of the NiZn ferrite powder.
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spiral inductors using a compositemagnetic material on a very thin FR4board, bending tests of the fabricated inductors were carried to demon-strate the flexibility achieved through the thin organic substrate despitethe FR4 nature of the substrate and the use of an FR4 compatible epoxybased magnetic composite material. Fig. 14 shows the variation of theDC resistance of the air core inductors for different bend radii up to5 mm. The mechanical loading effect is almost negligible with a varia-tion of b3% for both Inductor_1 and Inductor_3. This is an expected re-sult since no stretchable copper windings were used to build the
Fig. 11. Dielectric properties of the (a) epoxy polym
inductors. As the copper did not undergo any dimensional modification,the overall RDC value remained almost constant.
The magnetic core inductors were measured both under upwardand downward bending conditions to investigate the effect of the bend-ing direction on the RF parameters of the inductors for a givenmagneticfield orientation. When bent upward, the substrate is oriented in thesame direction as the magnetic field while when bent downward, thesubstrate is oriented in the reverse direction of the magnetic field. Toget rid of the effect of the SMA connector, the feedline and the substrate
er (b) epoxy-NiZn ferrite magnetic composite.
Fig. 12. (a) Measured spectra of the real part of the permeability and magnetic loss tangent of the composite (b) Magnetization curve of the composite material.
Fig. 13. Electrical characterization results for Inductor_1 and comparison to simulation (a) Inductance (b) Quality factor.
Table 3Measured inductance and quality factor for the air and magnetic core inductors at 30 MHz.
Inductor design RDC (Ω) Lair (nH) Qair RAC (Ω) Lmag (nH) Qmag Area (mm2) Inductance density (nH/mm2) fSR (MHz)
on the measured RF parameters under mechanical loading, thedeembeding structure used previously was also submitted to the samemechanical bending as the inductors and the measured RF parameterswere extracted from the measured inductors parameters for a givenbend radius.
Figs. 15–18 show the inductance and AC resistance variation spectraof Inductor_3 for different upward and downward bend radii respec-tively. The same trend is observed for both upward and downwardbending where the inductance and the AC resistance decrease withthe increase of the bend radius with a variation from the initial flat(unbent 0 mm) state of 2% for the inductance and 18% for the AC re-sistance at 30 MHz for a bend radius of 5 mm. Both the inductanceand AC resistance decrease can be explained by the decreased effec-tive area of the inductors resulting from the mechanical bending.Since the resulting effective area is the same for either an upwardor a downward bending, the samemagnetic field density was obtain-ed for a given effective area/vend radius and no significant induc-tance and AC resistance variations were observed. The inductancedecrease resulted in an increase of the self-resonant frequency(SRF) of the inductors with the increased bend radius. For 5 mmbending (at 30 MHz), the 2% inductance decrease resulted in a 3.4%increase of the SRF.
Since the AC resistance variation is muchmore important than the in-ductance variation for a given bend radius, the Q factor of the bent induc-tor increased with the bent radius increase for both upward and
Fig. 15. Inductance variation of Inductor_3 for different upward bend radii (a) full spectrum (b) around 30 MHz (c) around SRF.
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downward bendings. For a 5 mm bend radius, a 20% variation increase ofthe quality factor was observed at 30 MHz as seen in Fig. 19 and Fig. 20.
Compared to Inductor_3, Inductor_1which has smaller area showedsomehow a similar decrease ratio of both the inductance and the AC re-sistance (and consequently a less pronounced increase in the qualityfactor) due to applied mechanical bending as can be seen in Fig. 21. At30MHz and a 3.8mmbend radius, the inductance and the AC resistancedecreased by 4.4% and 6.5% respectivelywhich resulted in an increase ofthe self-resonant frequency and the quality factor of 3% and 2.2%respectively.
6. Conclusion
In this work, we demonstrated a new easy and cheap process for thefabrication of embedded planar power inductors with two magneticlayers on a very thin, flexible and lightweight two copper layers organicsubstrate. The top copper layer was patterned to define the inductorstracks while the bottom copper layer was used to etch trenches under-neath the inductors tracks and as a ground plane. The top and bottommagnetic layers were deposited by stencil printing an FR4 compatibleNiZn ferrite-epoxy magnetic composite material on top of the inductor
Fig. 16. Inductance variation of Inductor_3 for different downward b
Fig. 17. AC resistance variation of Inductor_3 for different upward b
tracks and into the trenches to increase the coupling between the twomagnetic layers through the very thin 200 μm separation layerrepresenting the substrates FR4 dielectric thickness. Bendability testsof the inductorswere carried out to demonstrate theflexibility achievedthrough a 270 μm thick FR4 organic substrate despite the use of a curedepoxy basedmagneticmaterial. The process allows the batch fabricationof inductors with different inductance densities, quality factors and self-resonance frequencies, which can be reliably characterized andmodeled. Stretchability and more flexibility can be obtained by replac-ing both the FR4 thin substrate material and the epoxy polymer forthe magnetic composite material with a stretchable elastomer such aspolydimethylsiloxane (PDMS), styrene-butadiene rubber (SBR), andpolyurethane (PU). The embedded planar inductors will be used inthe design and fabrication of a high frequency flexible System in Pack-age (SIP) DC-DC converter in an IoE device.
Acknowledgment
This work was supported by the Power Delivery for Electronic Sys-tems (PDES) consortium at Georgia Tech and performed in part at theGeorgia Tech Institute for Electronics and Nanotechnology, a member
end radii (a) full spectrum (b) around 30 MHz (c) around SRF.
end radii (a) full spectrum (b) around 30 MHz (c) around SRF.
Fig. 18. AC resistance variation of Inductor_3 for different downward bend radii (a) full spectrum (b) around 30 MHz (c) around SRF.
Fig. 19. Quality factor variation of Inductor_3 for different upward bend radii (a) full spectrum (b) around 30 MHz.
Fig. 20. Quality factor variation of Inductor_3 for different downward bend radii (a) full spectrum (b) around 30 MHz.
Fig. 21. RF parameters variation of Inductor_1 for different upward bend radii (a) inductance (b) AC resistance (c) quality factor Q.
27M.L.F. Bellaredj et al. / Microelectronic Engineering 189 (2018) 18–27
of the National Nanotechnology Coordinated Infrastructure, which issupported by the National Science Foundation (Grant ECCS-1542174).
References
[1] R.W. Erickson, D. Maksimovic, Fundamentals of Power Electronics, Springer,London, U.K., Jan. 2001
[2] S. Chunlei, B.C. Walker, E. Zeisel, B. Hu, G.H. McAllister, A highly integrated powermanagement IC for advanced mobile applications, IEEE J. Solid State Circuits 42(8) (Aug. 2007) 1723–1731.
[3] S. Li, S. Smaili, Y. Massoud, Parasitic-aware design of integrated DC–DC converterswith spiral inductors, IEEE Transactions on Very Large Scale Integration (VLSI) Sys-tems, vol. 23, Dec. 2015, pp. 3076–3084 (12).
[4] T.M. Andersen, C.M. Zingerli, F. Krismer, J.W. Kolar, C. O'Mathuna, Inductor optimi-zation procedure for Power Supply in Package and Power Supply on Chip, 2011IEEE Energy Conversion Congress and Exposition, Phoenix, AZ 2011, pp. 1320–1327.
[5] M. Fioretto, P. Ladoux, P. Marino, G. Raimondo, L. Rubino, N. Serbia, Considerationson boost inductor design in back-to-back converters for renewable energy, 2011 In-ternational Conference on Clean Electrical Power (ICCEP), Ischia 2011, pp. 46–50.
[6] Y. Yan, C. Ding, K.D.T. Ngo, Y. Mei, G. Lu, Additive manufacturing of planar inductorfor power electronics applications, 2016 International Symposium on 3D PowerElectronics Integration and Manufacturing (3D-PEIM), Raleigh, NC, USA, 2016.
[7] A.M. Crawford, D. Gardner, S.X. Wang, High-frequency microinductors with amor-phous magnetic ground planes, IEEE Trans. Magn. 38 (2002) 3168–3170.
[8] D.W. Lee, S.X. Wang, Multiple magnetic resonances in permeability spectra of thickCoTaZr films, J. Appl. Phys. 99 (2002) 08F109.
[9] D.S. Gardner, G. Schrom, F. Paillet, B. Jamieson, T. Karnik, S. Borkar, Review of on-chip inductor structures with magnetic films, IEEE Trans. Magn. 45 (10) (2009)4760–4766.
[10] S.T. Lim, H.J. Kim, I.B. Jeong, T.K. Lee, H. Hwang, An integrated inductor for high cur-rent with using Fe-Si metal alloy composite films, J. Appl. Phys. 113 (2013), 17A302.
[11] D. Flynn, M.P.Y. Desmulliez, Design, fabrication, and characterization of flip-chipbonded microinductors, IEEE Trans. Magn. 45 (8) (2009) 3055–3063.
[12] T. O'donnell, N. Wang, S. Kulkarni, R. Meere, F.M.F. Rhen, S. Roy, S.C. O'mathuna,Electrodeposited anisotropic NiFe 45/55 thin films for high-frequency micro-inductor applications, J. Magn. Magn. Mater. 322 (2010) 9–12.
[13] N. Wang, T. O'donnell, S. Roy, P. Mccloskey, C. O'mathuna, Micro-inductors integrat-ed on silicon for power supply on chip, J. Magn. Magn. Mater. 316 (2) (2007)E233–E237.
[14] R. Meere, T. O'donnell, N. Wang, N. Achotte, S. Kulkarni, S.C. O'mathuna, Size andperformance tradeoffs in micro-inductors for high frequency DC-DC conversion,IEEE Trans. Magn. 45 (10) (2009) 4234–4237.
[15] J.Y. Park, M.G. Allen, Development of magnetic materials and processing techniquesapplicable to integrated micromagnetic devices, J. Micromech. Microeng. 8 (4)(1998).
[16] D.V. Harburg, G.R. Khan, F. Herrault, J. Kim, C.G. Levey, C.R. Sullivan, On-chip RFpower inductors with nanogranular magnetic cores using prism-assisted UV-LED li-thography, 17th Transducers & Eurosensors Conference 2013, pp. 701–704.
[17] S. Ohnuma, H.J. Lee, N. Kobayashi, H. Fujimori, T. Masumoto, Co-Zr-O nano-granularthin films with improved high frequency soft magnetic properties, IEEE Trans.Magn. 37 (4) (2001) 2251–2254.
[18] M.Munakata, M.Motoyama, M. Yagi, T. Ito, Y. Shimada, M. Yamaguchi, K.I. Arai, Veryhigh electrical resistivity and heteroamorphous structure of soft magnetic(Co35.6Fe50B14.4)-(SiO2) thin films, IEEE Trans. Magn. 38 (5) (2002) 3147–3149.
[19] M.Wang, J. Li, K.D.T. Ngo, H. Xie, A surface-mountable microfabricated power induc-tor in silicon for ultracompact power supplies, IEEE Trans. Power Electron. 26 (2011)1310–1315.
[20] C.D. Meyer, S.S. Bedair, B.C. Morgan, D.P. Arnold, Influence of layer thickness on theperformance of stacked thick-film copper air-core power inductors, IEEE Trans.Magn. 48 (11) (2012) 4436–4439.
[21] J. Lee, Y.-K. Hong, S. Bae, J. Jalli, J. Park, G.S. Abo, G.W. Donohoe, B.-C. Choi, Integratedferrite film inductor for power system-on-chip (PowerSoC) smart phone applica-tions, IEEE Trans. Magn. 47 (2) (2011).
[22] S. Bae, Y.K. Hong, J.-J. Lee, J. Jalli, G.S. Abo, A. Lyle, B.C. Choi, G.W. Donohoe, High Q Ni-Zn-Cu ferrite inductor for on-chip power module, IEEE Trans. Magn. 45 (10) (2009)4773–4776.
[23] M.H. Lim, J.D. Van Wyk, F.C. Lee, K.D.T. Ngo, A class of ceramic-based chip inductorsfor hybrid integration in power supplies, IEEE Trans. Power Electron. 23 (2008)1556–1564.
[24] T. Mikura, K. Nakahara, K. Ikeda, K. Furukuwa, K. Onitsuka, New substrate for microDC-DC converter, 56th Electronic Components and Technology Conf 2006, p. 5.
[25] R. Hahn, S. Krumbholz, H. Reichl, Low profile power inductors based on ferromag-netic LTCC technology, 56th Electronic Components and Technology Conf 2006, p. 6.
[26] R. Anthony, N. Wang, D.P. Casey, C.Ó. Mathúna, J.F. Rohan, MEMS based fabricationof high-frequency integrated inductors on Ni–Cu–Zn ferrite substrates, J. Magn.Magn. Mater. 406 (2016) 89–94.
[27] E. Haddad, C. Martin, C. Joubert, B. Allard, C. Buttay, et al., Planar, double-layer mag-netic inductors for low power, high frequency DC-DC converters, CIPS 1-5 (Feb2014) 2014 (Nuremberg, Germany).
[28] S. Bharadwaj, et al., Fabrication of microinductor using nanocrystalline NiCuZn fer-rites, J. Electroceram. 31 (1–2) (2013) 81–87.
[29] Y. Sugawa, K. Ishidate, M. Sonehara, T. Sato, Carbonyl-iron/epoxy composite mag-netic core for planar power inductor used in package-level power grid, IEEE Trans.Magn. 49 (7) (2013) 4172–4175.
[30] I. Kowase, T. Sato, K. Yamasawa, Y. Miura, A planar inductor usingMn-Zn ferrite/pol-yimide composite thick film for low-voltage and large-current DC-DC converter,IEEE Trans. Magn. 41 (2005) 3991–3993.
[31] E. Waffenschmidt, et al., Design method and material technologies for passives inprinted circuit Board Embedded circuits, IEEE Trans. Power Electron. 20 (2005)576–584.
[32] E. Waffenschmidt, et al., Embedded passives integrated circuits for power con-verters, IEEE 33rd Annu. Power Electronics Specialists Conf. (pesc 02), vol. 1,2002, pp. 12–17.
[33] M. Ludwig, M. Duffy, T. O'Donnell, P. McCloskey, S.C.O. Mathuna, PCB integrated in-ductors for low power DC/DC converter, IEEE Trans. Power Electron. 18 (2003)937–945.
[34] D.H. Bang, J.Y. Park, Ni-Zn ferrite screen printed power inductors for compact DC-DCpower converter applications, IEEE Trans. Magn. 45 (6) (2009) 2762–2765.
[35] M. Conner, IC-like modules simplify DC/DC power design, EDN 56 (2011) 29–34.[36] M. Wens, M. Steyaert, A fully-integrated 0.18 μm CMOS DC-DC step-down convert-
er, using a bondwire spiral inductor, IEEE Custom Integrated Circuits Conf. (CICC2008) 2008, pp. 17–20.
[37] W. Zhang, M. Mu, D. Hou, Y. Su, Q. Li, F.C. Lee, Characterization of low temperaturesintered ferrite laminates for high frequency point-of-load (POL) converters, IEEETrans. Magn. 49 (11) (2013) 5454–5463.
[38] Y. Fukuda, T. Inoue, T. Mizoguchi, S. Yatabe, Y. Tachi, Planar inductor with ferritelayers for DC-DC converter, IEEE Trans. Magn. 39 (4) (2003).
[40] Texas Instruments, “Basic Calculation of a Boost Converter's Power Stage,” Applica-tion Report, Nov. 2009 (Revised Jan. 2014).
[41] M.L.F. BELLAREDJ, S. Mueller, A. Davis, P. Kohl, M. Swaminathan, Y. Mano, Fabrica-tion, characterization and comparison of FR4-compatible composite magnetic mate-rials for high efficiency integrated voltage regulators with embedded magnetic coremicro-inductors, 2017 IEEE 67th Electronic Components and Technology Confer-ence (ECTC), May 2017.
