2010 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 25, NO. 8, AUGUST 2010

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1 2010 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 25, NO. 8, AUGUST 2010 Modeling, Design, and Characterization of Multiturn Bondwire Inductors With Ferrite Epoxy Glob Cores for Power Supply System-on-Chip or System-in-Package Applications Jian Lu, Student Member, IEEE, Hongwei Jia, Student Member, IEEE, Xuexin Wang, Karthik Padmanabhan, Student Member, IEEE, William Gerard Hurley, Fellow, IEEE, and Zheng John Shen, Senior Member, IEEE Abstract The concept of coupled multiturn bondwire inductors with ferrite epoxy glob cores is investigated both experimentally and numerically to offer a cost-effective approach realizing power supply system-on-chip (PSoC) or system-in-package (PSiP). Improvement in total inductance and Q factor is demonstrated for the multiturn bondwire inductors due to the coupling effect. An empirical calculation method is developed to help determine the self and mutual inductance of the proposed bondwire inductors. The bondwire magnetic components can be easily integrated into IC packaging processes with minimal changes, and open possibilities for realizing cost-effective, high-current, and high-efficiency PSoCs or PSiPs. Index Terms Ferrite, on-chip magnetics, power supply system-on-package (PSiP), power supply system-on-chip (PsoC), wirebond. I. INTRODUCTION SYSTEM-ON-CHIP (SoC) is an emerging trend to integrate all components of an electronic system including digital, analog, mixed-signal, communication, and sensor functions, into a single IC. The SoC concept embodies what many believe to be the ultimate level of integration: an entire system on one chip. Since its emergence in the 1990s, the SoC concept has gained wide acceptance in a broad range of applications from supercomputing to embedded systems. The proliferation of the SoC concept into power management systems has also generated a great deal of interest in the electronics industry. Power management is a key enabling technology behind the digital revolution. Each year millions of power converters are Manuscript received November 13, 2009; revised February 12, Date of current version June 25, Recommended for publication by Associate Editor Y.-F. Liu. J. Lu, H. Jia, X. Wang, K. Padmanabhan, and Z. J. Shen are with the School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, FL USA ( jianlu@mail.ucf.edu; cnjhw99@yahoo.com; Karthik.Padmanabhan@petrasolar.com; wxx129@gmail.com; johnshen@mail. ucf.edu). W. G. Hurley is with the Power Electronics Research Center, Department of Electrical & Electronic Engineering, National University of Ireland, Galway, Ireland. Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /TPEL manufactured and embedded into computers, telecommunication equipment, consumer products, automobiles, and industrial control systems worldwide. Energy-related applications are a particularly strong growth area. The power management auxiliary subsystem may take up as much as 50% of the board space of the main electronic system. For this reason, power supply systems-on-chips (PSoCs) that monolithically integrate all active and passive components using low-cost semiconductor manufacturing processes will provide an extremely attractive solution with significant improvement in performance and reduction in board space, parts count, and time-to-market while reducing costs and increasing energy conversion reliability because of the inherent repeatability of the process. The power SoC concept, or in a broader sense, the power supply system-inpackage (PSiP) concept, are particularly well received in several fast-growing power management markets such as point of load dc/dc converters, LED drivers, and battery-powered mobile applications [1]. The development of PSoCs is seriously hindered by technical barriers including integration of passive magnetic components. The main challenge is to find a cost-effective means of integrating inductors and transformers onto the silicon chip, while achieving adequate performance in terms of inductance, dc and ac resistance, maximum saturation current, magnetic coupling coefficient, and Q factor. Current research work on integrated magnetics for PSoCs has predominantly focused on utilizing microelectromechanical system (MEMS) micromachining technology as a postprocessing step after the completion of the CMOS chip containing all power switching devices and control circuitry [2] [10]. Sophisticated MEMS technology allows sequential deposition and patterning of numerous layers of conductor, insulator, permalloy, or ferrite thin films to form desirable inductor and transformer structures. However, the high dc resistance (typically Ω) and poor Q factor (typically 3 to 8) of the MEMS inductors/transformers severely limit the currenthandling capability and efficiency of the PSoC. More critically, the large increase of fabrication complexity and cost associated with the MEMS postprocessing approach raises questions about its feasibility to facilitate large-scale commercialization of the PSoC concept into the extremely cost-sensitive power supply market /$ IEEE

2 LU et al.: MODELING, DESIGN, AND CHARACTERIZATION OF MULTITURN BONDWIRE INDUCTORS 2011 Fig. 1. A packaged IC chip interconnected to metal leads through bondwires. The authors have investigated a new approach to form on-chip or in-package magnetic components utilizing existing bondwires with additional ferrite epoxy glob cores in the past few years [11] [14]. The purpose of this paper is to investigate the coupling effect of multiturn on-chip bondwire inductors, and develop a set of design guidelines to achieve high inductance and Q factor values. II. BASIC CONCEPT Wirebonding is commonly used in most power management IC packages today. Thin aluminum or gold bondwires of µm in diameter are used to provide necessary electrical interconnection between the silicon chip and the package leads as illustrated in Fig. 1. The bondwires of IC Ferrite Glob Core packages typically exhibit a parasitic inductance of a few nanohenry and a resistance of several milliomega to several tens of milliomega. On-chip bondwire inductors were first explored in RF ICs by Craninckx and Steyaert in 1995 [15]. Although bondwires behave as natural inductors, the self-inductance and coupling effect are typically insufficient for power converter applications of interest. A higher inductance in the range of several tens of nanohenry is required for PSoC applications in conjunction with higher switching frequencies. Several U.S. patents have addressed this issue by suggesting the use of multiple bondwires connected in series [16] [19], but suffer from the drawback of increased footprint. We proposed to use ferrite epoxy glob cores to increase inductance and improve coupling effect as shown in Fig. 2. Bondwire inductors can be constructed between the chip and package leads or between pads on the chip. Unlike traditional ferrite ceramics, ferrite epoxy materials are essentially ceramic magnetic powders mixed with a polymer binder, and can be dried or cured at temperatures less than 200 C [20], [21]. These materials combine appropriate magnetic properties with a high resistivity and good manufacturability, and have the additional benefit of distributed air gaps. Brandon et al. studied the use of screenprinted manganese zinc (MgZn) ferrite epoxy onto both sides of a flexible printed circuit board (PCB) [20]. Raj et al. investigated the use of two types of screen printed magnetic nanocomposite materials Co/SiO 2 mixed with benzocyclobutene and (Ni 0.5 Zn 0.5 )Fe 2 O 4 onto flame retardant 4 PCB substrate [21]. In both cases, copper traces on the PCB were used as planar metal coils which were only partially covered by the magnetic epoxy. In contrast, our proposed approach uses bondwires off Fig. 2. Conceptual sketch of on-chip multiturn (ten-turn) coupled bondwire inductor. the top surface of the silicon chip or package substrate, allowing realization of chip-level magnetic components with the wirings fully enclosed by the magnetic core. With this approach, the ferrite epoxy glob core can be formed to cover the bondwires during the SoC packaging process by brushing, squeegeeing, dipping, dripping, inking, or other viable dispensing techniques using high-precision robotic tools similar to commonly used electronic assembly equipment such as solder paste dispensers. Compared to the prior art MEMS inductor technology, the proposed approach has the following advantages. 1) All SoC components (i.e., control circuitry, power switches, gate drivers, feedback compensation networks, etc.) except for the magnetic components can be fabricated with standard silicon processing technology, eliminating the need for costly post-cmos MEMS processing steps. 2) The on-chip bondwire inductors can be integrated into the PSoC packaging process with minimal changes. This opens possibilities for realizing cost-effective, highcurrent, and high-efficiency PSoCs with improved reliability. 3) Aluminum or gold bondwires are substantially more conductive than the thin metal films in MEMS inductors. A much lower dc resistance and higher Q factor can be expected for the bondwire inductors because aluminum or gold bondwires have large diameters than the thin films used in MEMS, and the material resistivity is also higher. Quality factor Q is the ratio of reactive impedance to equivalent series resistance, an important parameter of inductor performance. High Q leads to low power dissipation and a higher efficiency of the power converter. 4) The electromagnetic (EM) field of a bondwire inductor is mainly distributed outside the silicon substrate. The eddy current loss in the silicon substrate at high frequency, a major concern in MEMS magnetics, can, therefore, be minimized. III. MODELING OF MULTITURN INDUCTORS The experimental results for single-turn bondwire inductors with improved dc resistance and Q factor over MEMS inductors were reported in [12] [14]. However, the inductance value offered by a single-turn bondwire inductor is still too low for

3 2012 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 25, NO. 8, AUGUST 2010 Fig. 3. Multiturn versus single-turn bondwire inductors. practical PSoC applications. We address this deficiency in this paper by exploring the coupling effect of multiturn bondwires to achieve increased inductance and Q factor. As shown in Fig. 3, a set of closely placed multiple wirebonds is very similar to a solenoid, where the magnetic flux is shared by all bondwire loops. There is a strong coupling effect among those bondwire loops depending on how closely they are placed to each other. Today s automatic wirebonders can place bondwires as close as several tens of micrometers. The inductance L of a tightly wounded solenoid with N turn, a cross-sectional area A, and a length l is given by L = µ oµ r N 2 A. (1) l The proposed multiturn bondwire inductor was modeled and analyzed using the Ansoft s EM simulation tool HFSS [22]. HFSS is a high-performance full-wave electromagnetic EM finite-element simulator for arbitrary 3-D passive component modeling. The HFSS tool was used to investigate the effects of the ferrite epoxy glob core on inductance and Q factor. Furthermore, HFSS modeling was used to optimize bondwire inductor design in terms of physical dimensions of the bondwires and ferrite core, and the ferrite core material used. HFSS simulator generates a set of S parameters from the bondwire inductor structure, which are then converted to a set of Y parameters. The effective quality factor Q and inductance L can be then extracted from the Y parameters by using the following equations 1 L eff = (2) ωim(y 11 ) Q = Im(y 11) Re(y 11 ). (3) Fig. 4 shows the modeled inductance values of a single-turn (with a total bondwire length L), four-turn, and ten-turn bondwire constructions without ferrite epoxy core. Note that all the bondwire loops share the same shape and dimensions. In addition, the inductance values of two single-turn bondwire inductors with an equivalent bondwire length of 4L and 10L, respectively, are also plotted on the same graph for comparison. The 4 and 10 L single-turn inductors have the same total bondwire length as the four-turn and ten-turn inductors, respectively, but obviously do not have any coupling effect as observed in their multiturn counterparts. It is observed that the ten-turn inductor shows an inductance value of roughly 200 nh at 10 MHz as compared to 110 nh for the single-turn 10L inductor. The increase in inductance due to the coupling effect between the individual turns is desirable but far below what an ideal solenoid Fig. 4. core. HFSS simulation of single- and multiturn inductors without ferrite TABLE I MEASURED BONDWIRE INDUCTANCE WITHOUT THE FERRITE EPOXY CORE TABLE II MEASURED BONDWIRE INDUCTANCE WITH THE FERRITE EPOXY CORE offers. Instead of a factor of 10 increase based on (1) for ideal solenoids, we only observe an increase of 85% in inductance, indicating a weak coupling between the individual turns. This is due to the fact that the spacing between two adjacent bondwires is 750 µm or greater limited by the Orthodyne Model 20 manual wire bonder used, resulting in considerable leakage flux and weak coupling between the individual turns. The influence of interturn spacing on the coupling effect can also be seen later in the measurement data in Tables I and II. Detailed EM finiteelement simulation data also confirm this suspicion. Reducing the interwire spacing with automatic wire bonders can certainly solve the problem of weak coupling. In addition, introducing the ferrite epoxy core will also help reduce leakage flux and enhance the coupling effect. Fig. 5 shows the corresponding inductance simulation data when the ferrite epoxy glob core is used. A permeability of 12, 11, and 10 is assumed for the ferrite core material for the single turn, four-turn, and ten-turn inductors, respectively. The slightly reduced permeability for the multiturn inductors is to account for the increased air bubble content with the increased physical volume of the ferrite epoxy glob core for increased number of

4 LU et al.: MODELING, DESIGN, AND CHARACTERIZATION OF MULTITURN BONDWIRE INDUCTORS 2013 Fig. 5. HFSS simulation of single- and multiturn inductors with ferrite core. bondwire turns. It is recommended that the dispensing and curing of ferrite epoxy cores be performed in a vacuum chamber to minimize this effect in practice. It is observed that the inductance of the single-turn inductor increases from 10 to 55 nh. It is further observed that the ten-turn inductor shows an inductance value of roughly 1084 nh at 10 MHz as compared to 550 nh for the single-turn 10L inductor, an 97% increase in the inductance value due to the coupling effect between the turns. This also suggests that the epoxy core does not significantly improve the coupling effect between the turns. Evidently for multiturn bondwire inductors, the inductance increased by more than NL, but much less than N 2 L.Theimprovement depends on the bonding machine limit, the ferrite material, and the turn number. As shown in Figs. 4 and 5, with and without ferrite glob, we get 45% and 40% increase, respectively, for a four-turn bondwire inductor, and we get 97% and 85% increase, respectively, for a ten-turn bondwire inductor. Inductance of a single conductor wire of l in length and r in diameter can be calculated by the following empirical formula when neglecting the influence of the conducting ground plane [23] [24] [ ( ) 2l L =0.2µ core l ln r r l + µ ] wire (nh) (4) 4 where µ wire and µ core are the relative permeability of the metal wire and the media surrounding the wire respectively. µ wire is approximately 1 for aluminum or gold bondwires, while µ core is 1 if no ferrite glob core is used. The value of µ core for the ferrite epoxy glob core depends on the ferrite powder diameter, loading concentration, and the curing process, and is observed in a range of 7 15 in our experiment. Thus we have L =0.2µ core l [ ln ( ) 2l 1.0+ r ] (nh). (5) r l Since r l in most of the cases [ ( ) ] 2l L =0.2µ core l ln 1.0 (nh) =µ core L 0 (6) r Fig. 6. Comparison of the empirical formula calculation and HFSS simulation of self-inductance of bondwires. where L 0 is defined as the inductance for the bondwire without ferrite epoxy core. This empirical formula is compared to the finite-element simulation results of bondwire structures with Ansoft HFSS [22]. The results are in excellent agreement as shown in Fig. 6. The mutual inductance of two wires of l in length and separated by a distance of d can be calculated by M = µ core 0.2l ln 1+ l d + ( ) 2 l 1+ d ( d l ) 2 + d l = µ core M 0 (nh) (7) M 0 =0.2l ln l ( ) 2 ( ) 2 l 1+ d + d 1+ + d (nh) d l l where M 0 is defined as the barewire mutual inductance without the use of ferrite epoxy core. When d l, M 0 can be approximated by ( ( ) ) 2l M 0 =0.2l ln 1 (nh). (9) d This empirical formula is compared to HFSS simulation results and demonstrates excellent agreement as shown in Fig. 7. For N-turn bondwire inductor, the barewire inductance L 0,TOT can be expressed as L 0,TOT = NL 0 +2(N 1) M 0,1 +2(N 1) M 0,2 +2(N 2) M 0,3 +2(N 3) M 0,4 + +2M 0,N 1 (nh) or m =N 1 L 0,TOT = NL 0 +2 (N m) M 0,m (nh) (10) m =1 (8)

5 2014 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 25, NO. 8, AUGUST 2010 Fig. 8. Fabricated ten-turn bondwire inductor on a PCB substrate. Fig. 7. Comparison of the empirical formula calculation and HFSS simulation of mutual inductance of bondwires. where [ L 0 =0.2l ln ( M 0,N 1 =0.2l ln ( 2l r ( ) ] 1.0 (nh) 2l (N 1)d 0 ) ) 1 (nh). (11) For most of the cases, the mutual inductance beyond N > 4 can be neglected, so the empirical equation can be expressed as L 0,TOT NL 0 +2(N 1) M 0,1 +2(N 1) M 0,2 +2(N 2) M 0,3 (nh) (12) L TOT = µ eff L 0,TOT µ eff (NL 0 +2(N 1) M 0,1 +2(N 1) M 0,2 +2(N 2) M 0,3 )(nh). (13) IV. EXPERIMENTAL RESULTS This section describes the experimental validation of the proposed multiturn bondwire inductor concept using the ferrite epoxy composite materials. The material is a custom-formulated magnetic epoxy comprised of MgZn ferrite powder with an average particle size of 10 µm, thermoplastic resin, and solvent from Methode Development Corporation. The MgZn ferrite loading powder is commercially available (Steward 73300). The average surface area of the powder is 1.4 m 2 /g. The saturation moment of the bulk powder is 79.4 emu/g. The cured ferrite composite (no solvent) consisted of 96% by mass ferrite with the balance consisting of polymer. The relative permeability from manufacturer s datasheet is between 12 and 16. A ten-turn aluminum bondwire inductor is made on a PCB substrate initially to verify the concept as shown in Fig. 8. The measured dc resistance of the ten-turn inductor is 130 mω.the ferrite epoxy material is manually brushed onto the bondwire to form a ferrite glob core. The ferrite epoxy core is then cured at 140 C for 30 min in atmosphere. The ferrite polymer composite displays a very high resistivity and provides sufficient Fig. 9. Measured coupling coefficient k as a function of spacing with and without ferrite epoxy core. electrical insulation between the bondwires. Table I summarizes the measured bondwire inductance values for three spacings between the turns without the ferrite epoxy core, and Table II summarizes the corresponding measured bondwire inductance values with the ferrite epoxy core. An Agilent E4980 precision LCR meter is used in the measurement. We include the equivalent inductance of ten single-turn bondwire inductors in series as a comparison. It is observed that inductance of the ten-turn bondwire inductor has increased from 74 to 340 nh after the ferrite epoxy core is used, yielding a Q factor of 28 at 5 MHz. Furthermore, the inductance of a ten-turn bondwire inductor is much greater than the equivalent inductance of ten single-turn bondwire inductors in series due to the mutual coupling effect. The coupling effect becomes more pronounced with decreasing spacing between the multiple bondwires as expected. In the case of ferrite epoxy core not being used, there is an 85% increase of inductance value due to coupling effect for a spacing of 30 mils, which is in good agreement with the modeling result in Section III. Fig. 9 shows the experimentally characterized coupling coefficient k as a function of interturn spacing for the case with

6 LU et al.: MODELING, DESIGN, AND CHARACTERIZATION OF MULTITURN BONDWIRE INDUCTORS 2015 Fig. 10. Simulated results of coupling coefficient k for different interturn spacing without ferrite epoxy core. Fig. 12. Measured switching waveform of the 10 mil bondwire inductor for core saturation characterization. Fig. 11. Bondwire inductor core saturation test circuit. and without the ferrite epoxy core. It is observed that the coupling factor k of the bondwire inductor with ferrite epoxy core is higher than the case without the ferrite core, and less dependent on the interturn spacing. Fig. 10 shows the simulated coupling coefficient k for several interturn spacing without using ferrite epoxy core. The spatial separation between the turns leads to a large leakage flux and reduced mutual coupling, especially when ferrite epoxy core is not used. The data shows that the coupling effect can be enhanced when the spacing between bondwires is reduced. It should be noted that automatic bonding machines currently employed in the IC packaging industry could routinely achieve a bond-to-bond pitch less than 0.2 mm or 8 mils, potentially enabling highly coupled bondwire inductors. In general, the coupling effect can be enhanced through reduction of bond pitch and use of ferrite epoxy materials with a higher permeability. The multiturn bondwire inductors are also tested in a pulsed switching circuit for core saturation characterization. Fig. 11 shows the test circuit setup. Fig. 12 shows measured switching waveforms of the inductor current. No noticeable core saturation is observed for a load current up to 30 A, most likely due to the distributed microgaps between the magnetic particles. In another Fig. 13. Measured inductance as a function of dc bias current. core saturation test, the inductance is measured with the Agilent E4980 A precise LCR meter while a HP42841 dc bias current source forces a dc current up to 20 A to the bondwire inductor. Fig. 13 shows the measured inductance as a function of the dc bias current. Less than 10% inductance decrease is observed up to a bias current of 5 A. The decrease of inductance for a current greater than 5 A may be partially caused by self-heating of the small bondwire inductor with a large dc current flowing through it. V. CONCLUSION In this paper, we reported a novel concept of coupled multiturn bondwire inductors with ferrite epoxy glob core for PSoC or PSiP applications. The concept has been validated by simulation and measurement. It has been demonstrated that its performance can be improved using ferrite polymer epoxy glob. We also developed an empirical calculation method to determine

7 2016 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 25, NO. 8, AUGUST 2010 the self- and mutual inductance of the proposed bondwire inductors. The bondwire inductors can be easily integrated into IC packaging processes with minimal changes, and open a true possibility for realizing cost-effective, high-current, and highefficiency PSoCs or PSiPs. While the permeability of available ferrite epoxy materials on the market is still relatively low, it is expected that future research in material development will make the approach even more attractive. REFERENCES [1] Market and Technology Report on Power Supply in a Package and Power Supply on a Chip, Power Sources Manufacturers Association, Mendham, NJ, Technol. Rep., [2] S. C. O. Mathuna, T. O Donnell, N. Wang, and K. Rinne, Magnetics on silicon: An enabling technology for power supply on chip, IEEE Trans. Power Electron., vol. 20, no. 3, pp , May [3] M. Wang, K. Ngo, I. Batarseh, and H. Xie, Design and fabrication of integrated power inductor based on silicon molding technology, presented at the 38th Annu. IEEE Power Electron. Spec. Conf. (PESC 2007), Orlando, FL, Jun. [4] T. Sato, K. Yamasawa, H. Tomita, T. Inoue, and T. Mizoguchi, Planar power inductor using FeCoBN magnetic film with high saturation magnetization and high electrical resistivity, in Proc. 4th International Power Electronics Conference (IPEC 2000), Tokyo, Japan, Apr., pp [5] C. H. Ahn and M. G. Allen, Micromachined planar inductors on silicon wafers for MEMS applications, IEEE Trans. Ind. Electron., vol. 45, no. 6, pp , Dec [6] Y. Fukuda, T. Inoue, T. Mizoguchi, S. Yatabe, and Y. Tachi, Planar inductor with ferrite layers for DC-DC converter, IEEE Trans. Magn., vol. 39, no. 4, pp , Jul [7] E. J. Brandon, E. Wesseling, V. White, C. Ramsey, L. Del Castillo, and U. Lieneweg, Fabrication and characterization of microinductors for distributed power converters, IEEE Trans. Magn., vol. 39, no. 4, pp , Jul [8] J. Y. Park, S. H. Han, and M. G. Allen, Batch-fabricated microinductors with electroplated magnetically anisotropic and laminated alloy cores, IEEE Trans. Magn., vol. 35, no. 5, pp , Sep [9] Y. Katayama, S. Sugahara, H. Nakazawa, and M. Edo, High powerdensity MHz-switching monolithic DC-DC converter with thin-film inductor, in Proc. 31st Annu. IEEE Power Electron. Spec. Conf. (PESC 2000), Galway, Ireland, vol. 3, Jun., pp [10] K. H. Kim, J. Kim, H. J. Kim, S. H. Han, and H. J. Kim, A megahertz switching DC/DC converter using FeBN thin film inductor, IEEE Trans. Magn., vol. 38, no. 5, pp , Sep [11] Z. J. Shen, A method of manufacturing low cost on-chip magnetic components, U.S. Provisional Patent Serial No. 11/835,144, Aug. 7, [12] Z. J. Shen, J. Lu, X. Cheng, H. Jia, and X. Gong, On-chip bondwire inductor with ferrite-epoxy coating: a cost-effective approach to realize power systems on chip, in Proc. 38th Annu. IEEE Power Electron. Spec. Conf. (PESC 2007), Orlando, FL, Jun., pp [13] J. Lu, H. Jia, A. Arias, X. Gong, and Z. J. Shen, On-chip bondwire transformers for power SOC applications, in Proc. 23rd Annu. IEEE Appl. Power Electron. Conf. Expo. (APEC 2008), Austin, TX, Feb., pp [14] J. Lu, H. Jia, A. Arias, X. Gong, and Z. J. Shen, On-chip bondwire magnetics with ferrite-epoxy glob coating for power systems on chip, Int. J. Power Manage. Electron., vol. 2008, 2008 Article ID , 9 pp. [15] J. Craninckx and M. S. J. Steyaert, A 1.8-GHz CMOS low phase-noise voltage-controlled oscillator with prescaler, IEEE J. Solid-State Circuits, vol. 30, no. 12, pp , Dec [16] K. S. Yeo, H. P. Ian, J. Ma, M. A. Do, and J. K. W. Chew, High performance RF inductors and transformers using bonding technique, U.S. Patent , Feb [17] D.-B. Cheon, Inductor including bonding wires, U.S. Patent , Feb [18] R. B. Merrill and I. Singh, Bonding wire inductor for use in an integrated circuit package and method, U.S. Patent , Mar [19] M. A. Imam and S. Yoganathan, Inductor formed at least partially in a substrate, U.S. Patent , Jun [20] E. J. Brandon, E. E. Wesseling, V. Chang, and W. B. Kuhn, Printed microinductors on flexible substrates for power applications, IEEE Trans. Compon. Packag. Technol., vol. 26, no. 3, pp , Sep [21] P. M. Raj, P. Muthana, T. D. Xiao et al., Magnetic nanocomposites for organic compatible miniaturized antennas and inductors, in Proc. 10th Int. Symp. Adv. Packag. Mater., Process., Properties Interfaces, Irvine, CA, Mar. 2005, pp [22] Ansoft Corporation. (2007). [Online]. Available: [23] W. G. Hurley and S. J. Croall, Electromagnetic voltage induction and mitigation on passive conductors from overhead transmission lines, IEEE Trans. Power App. Syst., vol. PAS-102, no. 7, pp , Jul [24] H. M. Greenhouse, Design of planar rectangular microelectronic inductor, IEEE Trans. Parts, Hybrids, Package, vol. PHP-10, no. 2, pp , Jun Jian Lu (S 06) received the B.S. degree in electronics science & technology from Nanjing University of Science & Technology (NUST), Nanjing, China, in 2003, and the M.S. and Ph.D. degrees in electrical engineering from the University of Central Florida, Orlando, in 2007 and 2009, respectively. His research interests include power semiconductor devices and ICs, power system on-chip or inpackage, and RFIC and microwave devices. Hongwei Jia (S 06) received the B.S. degree from Xi an Jiao Tong University, Shaanxi, China, in 1996, and the M.S. degree from the University of Electronic Science and Technology of China, Chengdu, Sichuan, China, in He is currently working toward the Ph.D. degree in the School of Electrical Engineering and Computer Science, University of Central Florida, Orlando. He was with STMicroelectronics as an IC Design Engineer during His research interests include power management IC design, power electronics, and power system-on-chip or in-package. Xuexin Wang received the B.S. degree in electrical engineering from Tsinghua University, Beijing, China, in She is currently working toward the Ph.D. degree in the School of Electrical Engineering and Computer Science, University of Central Florida, Orlando. Her research interests include IC design for power electronics and power system-on-chip or in-package. Karthik Padmanabhan (S 06) received the B.S. degree in electrical engineering from Birla Institute of Technology Science Pilani, Dubai, UAE, in 2005 and the M.S. degree in electrical engineering from the University of Florida, Gainesville, in He is currently working toward a Ph.D. degree in the School of Electrical Engineering and Computer Science, University of Central Florida, Orlando. His research interests include analog IC design, photovoltaic microinverters, power electronics, and power system-on-chip or in-package.

8 LU et al.: MODELING, DESIGN, AND CHARACTERIZATION OF MULTITURN BONDWIRE INDUCTORS 2017 William Gerard Hurley (M 83 F 07) was born in Cork, Ireland. He received the B.E. degree in electrical engineering from National University of Ireland, Cork, in 1974, the M.S. degree in electrical engineering from the Massachusetts Institute of Technology, Cambridge, in 1976, and the Ph.D. degree from the National University of Ireland, Galway, Ireland, in He was a Product Engineer at Honeywell Controls, Canada during He was a Development Engineer in transmission lines at Ontario Hydro during He was a Lecture in electronic engineering at the University of Limerick, Ireland during He is currently a Professor of electrical engineering at the National University of Ireland, Galway, Ireland, where he is also the Director of the Power Electronics Research Center. He was a Visiting Professor of electrical engineering in the Faculty at the Massachusetts Institute of Technology during His research interests include high-frequency magnetics, power quality, and renewable energy systems. Prof. Hurley has delivered invited presentations in Mexico, Japan, Singapore, Spain, Czech Republic, Hong Kong, China, and USA. He received the Best PaperPrizefortheIEEETRANSACTIONS ON POWER ELECTRONICS in He is a Fellow of the Institution of Engineers of Ireland and a member of Sigma Xi. He was a member of the Administrative Committee of the Power Electronics Society of the IEEE and was the General Chair of the Power Electronics Specialists Conference in Zheng John Shen (S 09 M 94 SM 01) received the B.S.E.E. degree from Tsinghua University, Beijing, China, in 1987, and the M.S. and Ph.D. degrees in electrical engineering from Rensselaer Polytechnic Institute, Troy, NY, in 1991 and 1994, respectively. His research interests include power semiconductor devices and ICs, power electronics, automotive electronics, and renewable energy systems. He was a Senior Principal Staff Scientist at Motorola Inc. during , and a Faculty of the University of Michigan, Dearborn during He was also a Consulting Engineer at Ford Motor Company during He joined the University of Central Florida (UCF), Orlando in 2004, where he is currently a Professor in the School of Electrical Engineering and Computer Science. He is the Director of the Power Semiconductor Research Laboratory and the Associate Director of Florida Power Electronics Center (FPEC), UCF. He has authored or coauthored more than 90 papers published in various international journals and conferences. He holds 11 issued patents and numerous pending or provisional patents in these areas. He is the Inventor of the world s first commercial sub-mω power MOSFET. Dr. Shen is the Vice President of Products of the IEEE Power Electronics Society, where he is in charge of publications, digital media products, and publicity activities. He is a recipient of the 2003 National Science Foundation CAREER Award, the 2006IEEE TRANSACTION ONPOWER ELECTRONICSPrize Paper Award, the 2003 IEEE Best Automotive Electronics Paper Award from IEEE TRANSACTION ON VEHICULAR TECHNOLOGY. He was an Associate Editor of IEEE TRANSACTIONS ON POWER ELECTRONICS during , and has served as the Technical Program Chair for the 2nd IEEE Energy Conversion Congress and Expo (ECCE 2010) in 2010, the 38th IEEE Power Electronics Specialists Conference (PESC 2007) in 2007, and the 1st IEEE Vehicle Power and Propulsion Conference (VPPC 2005) in 2005.