Ferromagnetic composite wire inductors

121 6 Magnetic Layer Thickness Effect on Ferromagnetic Composite Wire Based Tunable Inductors 123 6.1 Effect of the NiFe layer thickness on the magnetic properties of NiFe/Cu wires... Wi

DEPARTMENT OF MECHANICAL ENGINEERING

NATIONAL UNIVERSITY OF SINGAPORE

2010

I wish to express my utmost respect and gratitude to my supervisor, Professor

Li Xiaoping, Ph.D, of Department of Mechanical Engineering and Division ofBioengineering, National University of Singapore, for his invaluable guidance,insightful comments, strong encouragements and personal concerns both aca-demically and otherwise throughout the course of the research, without whichthe project will not be a success

I would like to extend my sincere gratitude and warmest thanks to my supervisor Associate Professor Xu Yong Ping, Ph.D, of the Department of Elec-trical and Computer Engineering, National University of Singapore, for his con-tinuous support and constructive advices throughout this work

co-I would also like to offer special thanks to Dr Zhao Zhenjie (East China NormalUniversity, Shanghai), Dr Seet Hang Li, Dr Yi Jiabao, Dr Qian Xinbo, Mr.Fan Jie, Mr Ng Wu Chun, and Mr Wu Ji, for their valuable inputs, formerfinal year project students for their important assistance and contributions Ialso acknowledges the precious support rendered by my laboratory colleagues

Dr Shen Kaiquan, Ms Shao Shiyun, and Mr Yu Ke as well as the immensetechnical support provided by the staff from Advanced Manufacturing Labo-ratory (AML) and PCB Fabrication Facility of Department of Electrical and

Computer Engineering.

I am deeply indebted to my wife, Jane, and my parents for their encouragements,moral supports and loves Also I want to thank my son, Bobby, for all the joyand happiness he has brought to me

Lastly, my regards and blessings go to all of those who supported me in anyrespect during the completion of the project

Acknowledgements i

2.2 Magnetic materials 11

2.2.1 Classification of magnetic materials 12

2.2.2 Ferromagnetic materials 14

2.2.3 Magnetization processes 19

2.2.4 Hysteresis 24

2.3 Magnetically tunable properties: magneto-impedance effect 25

2.3.1 GMI theory 26

2.3.2 Analysis of GMI phenomenology 31

2.3.2.1 Quasistatic model 32

2.3.2.2 Eddy current model 35

2.3.2.3 Domain model 37

2.3.2.4 High frequency models 38

2.4 Inductors and tunable inductors 41

2.4.1 Magnetic circuits 42

2.4.2 Inductance and quality factor 43

2.4.3 Magnetic thin-film inductors 45

2.4.3.1 Designs 49

2.4.3.2 Models 52

2.4.4 Tunable inductors 57

2.5 Material requirements and electrodeposition for inductors 58

2.5.1 Material requirements 58

2.5.2 Electrodeposition basics 62

2.5.2.1 Faraday’s laws of electrolysis 63

2.5.2.2 Deposit thickness prediction 65

2.5.2.3 Electrodeposition of Ni-Fe alloys 65

2.5.3 Electrodeposition of ferromagnetic wires 67

2.6 Concluding remarks 70

3 Methodology and Experiment Techniques 71 3.1 Proposed project methodology 71

3.2 Fabrication setups and Processes 73

3.2.1 Fabrication processes 73

3.2.2 Electrodeposition 76

3.2.3 Electroplating with a longitudinal magnetic field applied 79 3.2.4 Magnetron sputtering 81

3.3 Characterization setups 83

3.3.1 Scanning electron microscopy 83

3.3.2 Energy dispersive X-ray 84

3.3.3 X-ray diffraction 86

3.3.4 Hysteresis loops measurement by inductive techniques 88

3.3.5 Thermal stability testing setup 90

3.3.6 Impedance measurement setup 92

4 Micro Magnetic Inductors in an External Magnetic Field 94 4.1 Magnetic reluctance model 94

4.2 Ferromagnetic composite wire inductor in an external magnetic field 97

4.2.1 At different frequencies 98

4.2.2 At different angles with the applied field 102

4.3 Concluding remarks 105

5 Tunable Magnetic Inductors 107 5.1 Device model 108

5.2 Experiments, results and discussion 111

5.3 Concluding remarks 121

6 Magnetic Layer Thickness Effect on Ferromagnetic Composite Wire Based Tunable Inductors 123 6.1 Effect of the NiFe layer thickness on the magnetic properties of NiFe/Cu wires 124

6.1.1 Effect of thickness on Fe concentration 124

6.1.2 Effect of thickness on uniformity 125

6.1.3 Effect of thickness on grain size 126

6.1.4 The combined effect on coercivity 126

6.1.5 Effect of thickness on magnetoimpedance effect 128

6.1.6 Concluding remarks 130

6.2 Effect of NiFe layer thickness on the performance of the tunable magnetic inductor 130

6.2.1 At low frequency 131

6.2.2 At high frequency 134

6.2.3 Discussion 137

6.2.4 Concluding remarks 141

7 Optimization of the Performance of Tunable Inductors 143 7.1 Plating current optimization 143

7.1.1 Concluding remarks 148

7.2 Magnetically controlled deposition 149

7.2.1 Effect on surface morphology of composite microwires 150

7.2.2 Effect on the performance of tunable magnetic inductors 150 7.2.3 Concluding remarks 153

8 Thermal Aspects of Composite Wires for Tunable Magnetic

Inductors 155

8.1 Experiments 156

8.2 Effect of thermal annealing on material properties 157

8.2.1 Effect of thermal annealing temperature 157

8.2.2 Effect of thermal annealing durations 159

8.3 Effect of thermal annealing on inductance tunability and quality factor 163

8.4 Concluding remarks 167

9 Effect of Insulation Layer on Ferromagnetic Composite Wire Based Tunable Inductors 169 9.1 The insulation layer and experiments 171

9.2 Effect of insulation layer on the magnetic properties, impedance, inductance and Q 173

9.3 Concluding remarks 182

10 Conclusions and Recommendations 184 10.1 Conclusions 184

10.2 Recommendations 192

In enabling small size light-weight portable devices and wireless electronics,miniaturization of microelectronic components has become a very importantaspect for many modern technologies As a fundamental electronic component,inductor has been extensively used in various power electronics and wireless ap-plications The performances of these circuitries are greatly dependent on thequality of the inductors, and the miniaturization and the integration of inductorwith electronic circuit are the key to realize the electronic products with highperformance, small size and light weight Therefore, it has attracted worldwideresearch interests to fabricate the high performance passive micro inductors,especially magnetic film inductors However, the available designs today havelimited inductance gain or small Q, which in turn leads to the demands of boththeoretical guidance in choosing efficient inductor design and the experimentallyverified optimizations on the various parameters On the other hand, tunableinductors have been shown promising because of their ability to optimize thecircuit performance The discrete tunable inductors available today are oftentuned manually, and are large in size Recent research efforts on miniaturetunable inductors still possess some limitations such as high fabrication cost,non-continuous tunability, or high power consumption for inductance tuning.

The objective of this thesis is to propose, develop, model, parametrically studyand optimize the high efficiency, high quality, innovative ferromagnetic compos-ite wire inductors, including non-tunable inductors and tunable inductors.

The research approach was proposed and implemented The magnetic microwire(NiFe/Cu) inductor, as a candidate miniature inductor with high efficiency,has been proposed, modeled, fabricated, and characterized in an applied mag-netic field environment With the advantages of high quality factor and lowpower consumption, novel electrically tunable magnetic inductors based on mi-cro NiFe/Cu composite wires, whose tuning effect is achieved by modulatingthe permeability of the soft magnetic layer in a magnetic film inductor, havebeen proposed, developed, tested and analyzed A theoretical model for theworking mechanism of the tunable magnetic inductor was also developed Theeffect of magnetic layer thickness, as one of the most important geometric pa-rameters of ferromagnetic composite wire, on the magnetic properties of themicrowires and the performance of the tunable magnetic inductors based onsuch composite wires, has been thoroughly investigated To optimize the tun-ability and quality factor of the tunable magnetic inductor, the effect of currentdensity and the effect of an applied longitudinal magnetic field in the electrode-position of the magnetic layer on the performance of tunable magnetic inductorhave been studied The thermal stability of ferromagnetic composite wire basedtunable inductors has also been studied Moreover, micro NiFe/insulation/Cucomposite wires have been developed and the effect of insulation layer on mag-

netic properties, impedance, inductance and quality factor of tunable inductorsbased on NiFe/insulation/Cu composite wire has been investigated.

The innovative ferromagnetic composite wire inductors have been successfullyproposed, developed, modeled, parametrically studied thoroughly and opti-mized The study has revealed that the applied magnetic field may have signifi-cant influence on the inductance, resistance and quality factor of ferromagneticcomposite wire inductors, depending on the frequency of the inductor, and theresult also suggests that a proper applied bias magnetic field can largely min-imized the effect of external magnetic field on such magnetic inductors Thedeveloped tunable magnetic inductor, whose inductance can be tuned by vary-ing the DC control current, showed a low DC current/power consumption forcontinuous inductance tuning A relative variation of inductance ∆L/L0, up to18% at low frequency (around 5 MHz), was achieved by applying a bias current

of magnitude up to 15 mA, and the quality factor varied from 5 to 17 in themeasured frequency range The design of the tunable inductor has the poten-tial to be realized with MEMS technology and integrated with the CMOS ICprocess The results of this thesis also show the magnetic film layer thickness

of the composite wire affects the composition, uniformity, and grain size of thedeposited material, making the coercivity in a dynamic constant state as thethickness varies There is a critical thickness for the magnetic film, below whichthe effect of a weak bias magnetic field on the L is significant and is propor-tional to the coating layer thickness tm, and above which the effect of a weak

bias magnetic field on the L is insignificant and is inversely proportional to thecoating layer thickness, tm For the optimization of the tunable magnetic in-ductor, it has been found that for the amplitude of the plating current, there

is a trade-off between maximum inductance tunability and maximum quality,which suggests that the plating current optimization should target for specificapplication It has also been found that in the electrodeposition process with

a longitudinal magnetic field applied, the variation of quality factor followsthe change of Fe% in the Ni-Fe layer, and the longitudinal field amplifies suchchange due to the effect of uniformity improvement of the plated layer Anaveraged 23% increase of quality factor was observed for specimens fabricatedwith 143 Oe imposed field, and inductance tunability was significantly higherthan previously reported results For the investigation of the thermal stability

of the studied inductors, it has been shown that when the temperature washigher than the recrystallization temperature, the degradation of the magneticproperties and inductance tunability was more pronounced, due to a decrease

in permeability that was attributed to grain growth and inter-diffusion betweenthe copper core and NiFe shell, despite the effect of stress relief by thermalannealing The study of NiFe/insulation/Cu composite wire has shown thatthe implementation of the insulation layer could lead the distinctive magneticproperties, magneto-impedance effects, inductance values and quality factors inthese ferromagnetic composite wires

multi-ˆ W.C Ng, H.L Seet, K.S Lee, N Ning, W.X Tai, M Sutedja, J.Y.H.Fuh, X.P Li, ”Micro-spike EEG sensor and the vacuum casting technologyfor mass production,” Journal of Materials Processing Technology, Vol.

209, pp 4434-4438, 2009

ˆ N Ning, X.P Li, ”Performance of tunable magnetic inductors in tion to the magnetic layer thickness and an applied longitudinal magneticfield in electrodeposition of the magnetic layer,” IEEE Transactions onMagnetics, Vol 46, No 2, pp 337-340, 2010

rela-ˆ J Fan, N Ning, J.B Yi, L.S Tan, X P Li, ”Asymmetrical impedance effect in NiFe/SiO2/Cu composite wire with a sputtered NiFeseed layer,” Physica Scripta T, Vol T139, 014076, 2010

magneto-ˆ J Fan, J Wu, N Ning, H Chiriac, X.P Li, ”Magnetic Dynamic teractive Effect in Amorphous Microwire Array,” IEEE Transactions onMagnetics, Vol 46, No 6, pp 2431 - 2434, 2010

In-ˆ N Ning,J Fan, J Wu, H Chiriac, X.P Li, ”NiFe/Insulator/Cu ite Wires and Their Giant Magneto-Impedance Effects,” Surface Reviewand Letters, Vol 17, No 3, pp 369-373, 2010

Compos-Conference Papers

ˆ N Ning, X.P Li, H.L Seet, ”The effect of external magnetic field onmagnetic film inductors,” Technical Digests of IEEE International Mag-

netics Conference (INTERMAG 2006), pp 58-59, 2006

ˆ H.L Seet, X.P Li, N Ning, ”On the non-uniqueness of optimum ness for the magnetic coating layer of NiFe/Cu composite wires,” TechnicalDigests of IEEE International Magnetics Conference (INTERMAG 2006),

thick-pp 52-53, 2006

ˆ X.P Li, N Ning, K.Q Shen, H Zhen, W.C Ng, X.B Qian, E.P.V.Wilder-Smith, ”A Pilot Mental Fatigue Screening System for Flight Safety,”The 5 th Asia-Pacific Conference on Aerospace Technology and Science(APCATS’2006), Guilin, China, 30 October - 03 November 2006

ˆ S Marlin, H.L Seet, W.X Tai, W.C Ng, N Ning, K.S Lee, J.Y H Fuhand X.P Li, ”Micro-Spike EEG Sensor and the Vacuum Casting Technol-ogy for Mass Production,” Proceedings of the 8th Asia-Pacific Conference

on Materials Processing, Guilin-Guangzhou, China, 16 - 20 Jun 2008

ˆ X.P Li, J Fan, X Qian, H.L Seet, J Yi, J Ding, N Ning and W.C Ng,

”A Novel Micro Magnetic Sensor,” Proceedings of DTA 2008, Singapore,

22 - 23 May 2008

ˆ N Ning , X.P Li , W.C Ng, ”The Effect of External Magnetic Field onMagnetic Inductors of Composite Wire Structure,” Proceedings of IFSM

2007, Taiwan, December 2007

ˆ N Ning, J Fan, J.B Yi, X.P Li, ”Giant magneto-impedance effect

of electrodeposited NiFe/Au/SiO/Cu composite wires,” Proceeding of the

3rd International Symposium of Functional Materials (ISFM 2009), gaigou, China, May 2009

Jiuz-ˆ N Ning, J Fan, J Wu, X.P Li, ”Development and characterization ofNiFe/insulation/Cu composite wires for magnetic sensing and their giantmagneto-impedance effect,” Proceeding of INTERMAG 2009, Sacramento,California, USA, 2009

ˆ J Fan, N Ning, J Wu, X.P Li, ”Noise Study of the Multi-core thogonal Fluxgate Sensors Based on NiFe/Cu Composite Micro-wires,”Proceeding of INTERMAG 2009, Sacramento, California, USA, 2009

Or-ˆ N Ning, X.P Li, ”The influence of soft magnetic layer thickness on theinductance and resistance of NiFe/Cu composite wires,” Proceeding of 19thSoft magnetic Materials Conference (SMM19), Torino, Italy, September2009

2.1 Curie temperatures of selected ferromagnetic materials 19

3.1 Concentration of the Ni-Fe electrolyte 77

3.2 Calculated maximum centerline magnetic field strengths 81

2.1 Magnetization curves for different types of magnetic materials 15

2.2 Orientation of domain magnetic moments in the structure of un-magnetized iron 16

2.3 Domain walls 17

2.4 Coherent Rotation 23

2.5 Magnetic hysteresis loop 24

2.6 GMI ratio (∆Z/Z(%)) change as a function of external magnetic field (Hext) and frequency (f ) for a Ni80Fe20/Cu microwire 26

2.7 Domain structure of a uniaxial film with the easy direction along y-axis θ1 and θ2 are the magnetization orientations in domain 1 and 2, 2d is the period of domain structure and u is the displace-ment of domain walls from their equilibrium positions 33

2.8 Transverse susceptibility calculated for a uniaxial film: (a) Hext⊥ easy axis - domain wall movement, (b) Hext⊥ easy axis - magne-tization rotation, (c) Hextk easy axis 34

2.9 Exploded view of a sandwiched spiral 50

2.10 Schematic of a magnetic stripe inductor: (a) a trilayer without

flanges; (b) an enclosed stripe inductor; (c) a magnetic stripe

inductor with gaps 52

2.11 Geometry of the electromagnetic model for a magnetic sandwich

inductor 56

3.1 Flowchart showing the fabrication, characterization and

evalua-tion methods for the ferromagnetic composite wire based micro

tunable inductors 72

3.2 Flowchart of the fabrication processes for NiFe/Cu and NiFe

/in-sulation/Cu composite wires 74

3.3 SEM photo of the copper wire 75

3.4 Schematics and picture of the glass coated copper wire fabrication

setup 75

3.5 Schematic diagram of the electrodeposition setup 78

3.6 The longitudinal magnetic field imposed electrodeposition setup 79

3.7 Diagram of a solenoid for the calculation of the magnetic field

strength 81

3.8 Photograph of the Denton Discovery 18 system 82

3.9 Photo and schematics of a SEM machine 83

3.10 Photos showing: (a) Philips 7000 diffractometer; (b)

measure-ment stages in the diffractometer 86

3.11 Bragg’s Law 87

3.12 XRD data of NiFe/Cu composite thin film 88

3.13 Schematic diagram of the AC hysteresis loop tracer 89

3.14 An example of hysteresis loops measured by the inductive tech-niques 91

3.15 Schematics of the furnace setup 92

3.16 Testing setup for magneto-impedance effect 93

3.17 A photo of testing setup 93

4.1 The magnetic inductor of thin film structure 95

4.2 The magnetic inductor of composite wire structure 95

4.3 Inductance versus Hext at different frequencies 99

4.4 Resistance versus Hext at different frequencies 100

4.5 Quality factor versus Hext at different frequencies 100

4.6 Variation of the normalized inductance Ln at 100 kHz 102

4.7 Variation of the normalized inductance Ln at 100 MHz 103

4.8 Variation of the normalized quality factor Qn at 100 kHz 103

4.9 Variation of the normalized quality factor Qn at 100 MHz 104

5.1 Schematic diagram of the tunable magnetic inductor 108

5.2 Testing setup of the fabricated tunable magnetic inductor 112

5.3 Variation of inductance versus control current 114

5.4 Quality factor versus control current at different frequencies 114

5.5 Model for the rotational magnetization 116

5.6 Simulation results of the field dependence of transverse

suscepti-bility 118

5.7 Inductance versus frequency for different control current (0 -15

mA) 119

6.1 Surface Fe% variations with coating thickness 125

6.2 SEM photos of composite wires of coating thickness (a) 1 µm;

(b) 1.5 µm; (c) 4.45 µm; (d) 10.2 µm 126

6.3 Calculated plating current density with coating layer thickness

The inset shows the effect of current density on average grain size.127

6.4 Variation of coercivity Hc with coating thickness Inset shows

hysteresis loop of specimen with tm at 1.5 µm 128

6.5 Variation of maximum MI% with coating thickness at 1 MHz

testing frequency Inset graph shows the MI% variation with

ex-ternal field for specimen with tm of 2.3 µm for different frequencies.129

6.6 A 3D model of the tunable magnetic inductor of composite wire

structure, with different thickness of magnetic coating layer 131

6.7 Variations of the inductance L versus the bias magnetic field Hext

for the ferromagnetic composite wire inductors of different

coat-ing thickness, at 100 kHz 132

6.8 Variations of the resistance Rs versus the bias magnetic field Hext

for the ferromagnetic composite wire inductors of different

coat-ing thickness, at 100 kHz 133

6.9 Variations of the quality factor Q versus the bias magnetic field

Hext for the ferromagnetic composite wire inductors of different

coating thickness, at 100 kHz 134

6.10 Variations of the inductance L versus the bias magnetic field Hext

for the ferromagnetic composite wire inductors of different

coat-ing thickness, at 100 MHz 135

6.11 Variations of the resistance Rs versus the bias magnetic field Hext

for the ferromagnetic composite wire inductors of different

coat-ing thickness, at 100 MHz 136

6.12 Variations of the quality factor Q versus the bias magnetic field

Hext for the ferromagnetic composite wire inductors of different

coating thickness, at 100 MHz 137

6.13 The relative variation of inductance, ∆L/L0, versus the bias

mag-netic field, Hext, for the ferromagnetic composite wire inductors

of different coating layer thickness tm ranging from 2.3 µm to 6.2

µm, at a low frequency of 100 kHz Inset graphs show ∆L/L0 as

a function of the coating layer thickness, tm , under a weak bias

magnetic field ranging from 0.9 Oe to 2.6 Oe 138

6.14 The relative variation of inductance, ∆L/L0, versus the bias

mag-netic field, Hext, for the ferromagnetic composite wire inductors

of different coating layer thickness tm ranging from 2.3 µm to 6.2

µm, at a high frequency of 100 MHz Inset graphs show ∆L/L0

as a function of the coating layer thickness, tm , under a weak

bias magnetic field ranging from 0.9 Oe to 2.6 Oe 139

7.1 FeSO4 concentration required to achieve the Ni/Fe ratio of 80:20

and 2 µm thickness under different current density 145

7.2 Deposition time required to achieve the Ni/Fe ratio of 80:20 and

2 µm thickness under different current density 145

7.3 The effect of plating current amplitude on the maximum

induc-tance tunablity |∆L/L0| at 100 kHz 146

7.4 The effect of plating current amplitude on the maximum Q 148

7.5 SEM pictures of electrodeposited microwires: (a) without a

mag-netic field imposed in the deposition, (b) with 573 Oe field applied

in the deposition process 150

7.6 Fe% and total diameter of the plated wire in relation to the

mag-netic field imposed during the electrodeposition process 151

7.7 Quality factor measured at 10 MHz under different Hext, in

rela-tion to the magnetic field imposed during the electrodeposirela-tion

process 152

7.8 Inductance value versus the bias magnetic field at different

fre-quencies, for the tunable inductor body electrodeposited with 143

Oe imposed longitudinal magnetic field 153

8.1 SEM pictures at 4000 magnifications of specimens before and

after thermal annealing at different temperatures 158

8.2 Percentage change in grain size with annealing temperature 159

8.3 Zoom-in of hysteresis loops at different annealing temperatures 160

8.4 Percentage change in coercivity with annealing temperature 160

8.5 SEM pictures of specimens before and after annealing at different

thermal annealing duration 161

8.6 Percentage change in grain size with thermal annealing duration

at (a) Ta= 210◦C, and (b) Ta= 750◦C 162

8.7 Percentage change in coercivity with annealing duration at 210 ◦C163

8.8 Inductance tunability, ∆L/L0, versus applied magnetic field Hext

at different operating frequencies: (a) before 210◦C annealing, (b)

after 210◦C annealing, and (c) before 750◦C annealing, (d) after

750◦C annealing 164

8.9 Percentage change in maximum inductance tunability and quality

factor with thermal annealing temperature 166

8.10 Percentage change in maximum inductance tunability and quality

factor with thermal annealing duration 166

9.1 Schematics of NiFe/seed layer/SiO2/Cu wire, where rc is the

ra-dius of copper core, tins is the thickness of the SiO2 layer, and tm

is the thickness of the NiFe layer 172

9.2 Fabrication processes of NiFe/insulation/Cu composites wires 172

9.3 SEM photos for NiFe/insulation/Cu composites wires: (a)

com-posite wire CW-GC ; (b) comcom-posite wire CW-SP 174

9.4 Hysteresis loops of NiFe/Cu composite wire and NiFe/insulation/Cucomposite wires ( CW-GC and CW-SP ) 175

9.5 Magneto-impedance testing result of specimens of (a) NiFe/Cu

composite wire, (b) composite wire CW-GC, and (c) composite

wire CW-SP 176

9.6 Measured inductance of specimens of (a) NiFe/Cu composite

wire, (b) composite wire GC, and (c) composite wire

CW-SP, under an applied magnetic field up to 43 Oe 178

9.7 Simulated and measured values of maximum inductance for

com-posite wires with insulation layer 179

9.8 Measured quality factor of specimens of (a) NiFe/Cu composite

wire, (b) composite wire GC, and (c) composite wire

CW-SP, under an applied magnetic field up to 43 Oe 181

A interatomic exchange

exchange stiffness constant

a radius of the wire or half thickness of the thin film

radius of the solenoid

Bd broadening of diffraction line measured at half its

maxi-mum intensity

b number of layers of a solenoid

space between the planes in the atomic latticehalf period of domain structure

δm penetration depth in a magnetic medium

δ0 wall-width parameter

non-magnetic skin depth

δmin minimum value of skin depth

∆L/L0 relative variation of inductance

∆Q/Q0 relative variation of quality factor

Ean magnetocrystalline anisotropy energy

Emag magnetostatic interaction energy

Emag magnetostatic interaction energy

Ez longitudinal component of electric field

h magnetic field

Hd magneticstatic self-interaction

HCtr magnetic controlling field during the electrodeposition

Hext longitudinal external magnetic field

Hmax maximum external magnetic field

Ht transverse magnetic field

Hef f effective magnetic field

Hef f,0 equilibrium DC component of effective field

hef f ac component of effective field

hz axial components of the AC magnetic field

hφ circumferential components of the AC magnetic field

Iac amplitude of sinusoidal current

J electrical current density

jz longitudinal component of current density

J0, J1 Bessel function of the first kind

K1 second-order uniaxial anisotropy

L0 inductance of the tunable magnetic inductor without a

bias magnetic field

Lint internal inductance

molar mass of the substance

Ms spontaneous magnetization within a domain

nt turn density of a solenoid

θ angle between the magnetization and the easy axis

angle between the incident ray and the scattering planes

θk angle between the easy axis and circumferential direction

ϕ angle between the uniaxial anisotropy and the easy axis

Qn normalized quality factor

Qe total electric charge

tan annealing duration

tc thickness of the conductor layer

tins thickness of insulation layer

tm thickness of the soft magnetic layer

µ0 permeability of free space

µr relative permeability of the magnetic material

wdw relaxation frequency of domain wall movement

wrot relaxation frequency of spin rotation

χm magnetic susceptibility

χt transverse susceptibility

χt dw transverse susceptibility due to domain wall movement

χt rot rotational susceptibility

b

z valency number of ions of the substance

horizontal distance along the centerline of the solenoid

AC alternative current

BE backscattered electrons

CMOS Complementary Metal-Oxide-Semiconductor

CVP Chemical Vapor Deposition

CW-GC composite wire fabricated by glass-coated melt spinningCW-SP composite wire fabricated with sputtered SiO2

EDX Energy Dispersive X-Ray

emf Electromotive Force

FMR Ferromagnetic resonance

GMI Giant Magneto-impedance

IPD Integrated Passive Devices

MED Magneto-electrolytic Deposition

MEMS Micro electro mechanical system

MI Magneto-impedance

NEMS Nano electro mechanical system

PCB Printed Circuit Board

PDA Personal digital assitant

SEM Scanning Electron Microscopy

UHF Ultra high frequency

VCO Voltage-Controlled Oscillator

VLSI Very Large Scale Integrated circuit

VSM Vibrating Specimen Magnetometer

Portable devices such as mobile phones, personal digital assistants (PDA), andlaptop computers became pervasive over the past decades In recent years,portable devices and consumer electronics tend to be increasingly smaller in sizeand lighter in weight Especially for today’s wireless communication systemsand personal medical devices, there is a growing trend towards miniaturized andultra-portable products, which bring a lot of convenience in people’s everydaylives

In enabling small size light-weight products, miniaturization of microelectroniccomponents has become a very important aspect for many modern technologies

In addition, the consumer market has placed strict constrains on the tronic components and subsystems for low cost, low power and high volumeproduction In response to these requirements, an integrated system is one ofthe most promising solutions

microelec-In the last few decades, complementary metal-oxide-semiconductor (CMOS)technology has dominated microelectronics fabrication for integrated circuits(ICs) The minimum feature size has continued to decrease with increasing

integration density as predicted by semiconductor roadmaps, as described byMoore’s Law However, many passive components, microsensors and microac-tuators, and biological function modules do not scale down with Moore’s Law,and these components or modules may not be compatible with standard CMOSprocess or the performances of these on-chip components far lag behind their off-chip counterparts In many of these cases, non-CMOS solutions are employed.

It becomes increasingly important to integrated CMOS and non-CMOS basedtechnologies into a single package, or system-in-package (SiP), which is char-acterized by any combination of more than one active electronic component ofdifferent functionality plus optionally passives and other devices like microelec-tromechanical system (MEMS) or optical components assembled preferred into

a single standard package that provides multiple functions associated with asystem or sub-system

In either on-chip integration or system-in-package solution, the high qualitypassive elements such as capacitor, inductor and resistor remain critical to thesystem performance for many applications In wireless communication systems,the performance of many radio frequency (RF) and analog/mixed signal (AMS)circuits are mainly determined by the performance of passive elements

The fundamental electronic component least compatible with silicon integration

changing current The changing current produces a time-varying magnetic fieldwhich induces an electromotive force (emf) that acts to oppose this change incurrent.

Inductors have been extensively used in various power electronics and less applications, such as voltage regulation, DC-DC converter, power harmonicfiltering, inverter current wave shaping in power applications [1], and voltage-controlled oscillators (VCO), low-noise amplifiers (LNA), filters, matching net-works in wireless applications The performances of these circuitries are greatlydependent on the quality of the inductors, and the miniaturization and the in-tegration of inductor with electronic circuit are the key to realize the electronicproducts with high performance, small size and light weight Especially, mi-cro DC-DC converters constructed by magnetic thin film micro inductor will

wire-be extensively applied in all kinds of portable electronic products With thedevelopment of VLSI (Very Large Scale Integrated circuit), system integration,and high density of surface mounted PCB (Printed Circuit Board) component,there has been a great demand for micro inductor in the market of power appli-cations and communication systems with an emphasis on RF and mixed-signalICs, and system on chip (SoC) applications

For these reasons, it has attracted great attentions for researchers all over theworld to fabricate the high performance passive micro inductors

The miniature inductors of particular interest are magnetic film inductors Someprogress has been made in the past in fabricating planar inductors based on

magnetic films (discussed in detail in Chapter2, Section2.4.3, page 45), which,however, did not result in favorable characteristics of high efficient inductors.Either poor design or lossy magnetic materials made the gain in inductance and

Q unacceptably small This, in turn, leads to the demands of both theoreticalguidance in choosing efficient inductor design and the experimentally verifiedoptimization on the various geometrical and other parameters Design consid-erations in many cases substantially limit the range of magnetic materials thatcan be used in a practical device, thus the materials’ development efforts can

be closely focused

Besides the coveted miniaturization, the tunability of the passive components ishighly desirable in many circuit applications such as impedance matching net-works, LC -tanks, filters, and other RF circuitries, as it gives the circuit designerthe possibility to arrange for an adjustment to the optimum circuit operation

at all termination conditions [2] In the development of RF circuits, there aretwo types of tuning: wide range tuning for channeling on wireless communica-tion equipment and narrow range tuning for precise impedance matching Inboth types of tuning, not only tunable capacitors but also tunable inductorsare required in order to realize a larger tuning range or more precise matching[3] In addition, tunable inductors can also improve the reliability of a system

by overcoming the tolerances introduced by manufacturing limitations Recentadvancements in the area of power electronics have also resulted in a greaterdemand for high quality tunable inductors [1]