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Challenges in magnetics for PwrSoC -
Development in high-frequency magnetics,
materials and integration
Saibal Roy
Microsystems Centre, Tyndall National Institute, Cork, Ireland.
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Overview- Integrated Magnetics
Background
Challenges
Modelling – Thin film
Integration aiming PSOC
Developed Nanomagnetic Materials
Fabricated Inductors
Test Results
2
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Market Opportunities for Miniaturised
Point of Load Power supplies
Buck Type DC-DC
Conversion
PDA
PC
Mobile Phone
GPS / Marine electronics Household Electronics fixed / portable
MP3 Camcorder
In-Store electronics
Market size billions of € !
3
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IntroductionIntroduction
Microprocessor Unit (MPU) Power Trends
Decreasing Voltage
Increasing Current
100
120
140
160
180
200
220
2008 2012 2016 2020Year
0
0.2
0.4
0.6
0.8
1
1.2
Voltage (V)
Current (I) Power (W) Voltage (V)
Power (W
), Current (A)
RIP 2=ITRS 2009 Roadmap for the power, voltage, and current
requirements of a high-performance MPU with heatsink [1]
Solution: Integrated power conversion module !
Increased current will result in
increased interconnect losses
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2 mm
1 mm
Passive Component Size Reduction with Increasing
Frequency Enables Functional Integration
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State of the ArtState of the Art
A number of different structures reported in the literature
Constraints limit the usefulness of some structures
• Out-of-plane flux
• Negative mutual inductance in turns
• Fabrication complexity
Current Applied Physics 8, 138 (2008) Microsyst. Tech. 12 , 923 (2006)
IEEE Trans. Mag. 30, 73 (1994) J. Appl. Phys. 103, 07E927 (2008)
Proc. IMAPS (2002)
International Semiconductor Conference 1, 93 (2006)
Tyndall National Institute, 2009
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Challenges – PSOC Inductor/transformers
Challenges
Modelling
Magnetic modeling for Micron scale devices
Optimisation with converter for higher efficiency
Integration
Low cost & high yield process
Non line of sight technique
CMOS compatibility
Materials
Reducing Cu winding Loss
Magnetic materials with low loss at high frequency
Eddy current loss
Hysteresis loss
Ferromagnetic resonance loss7
Optimisation with converter for higher efficiency
Reducing Cu winding Loss
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Challenge - Modelling
THIN-FILM MODELLING
Measured
Thin-Film(Unpatterned)
Scaled By
Thickness
Scaled By
Size
Desired
Geometry
Conducting
Seed Layer
It is easier to measure one film and scale the results using modelling
MODELLING
DOMAIN
Magnetic material properties differ substantially between as-deposited, wafer-
scale films and patterned structures in a micro/nano-scale device
Patterned,
Micro-magnetic
Thin-film
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ShapeShape--Dependent AnisotropyDependent Anisotropy
X
z
y
M
Ф
θ
Ф0
θ0
α
E
H
X
z
y
X
z
y
M
Ф
θ
MMM
ФФ
θθ
Ф0
θ0
Ф0Ф0
θ0θ0
ααα
E
H
H – Applied Field Vector
M – Resultant Magnetization
Vector
( ) ( )( ) HMDDDMsKE zyxf ⋅+++−−= θφθφθα 22222 cossinsincossincos
3D Demagnetizing FieldMaterial
Anisotropy
Applied
FieldK – Material Anisotropy Constant
Ms – Saturation Magnetization
Di – Shape Demagnetization factor
in i
Modelled via Stoner-Wohlfarth model of Magnetostatic Free
Energy- Particle Model
Still a good approximation of larger systems
Total free energy, Ef, along M in a system
with an induced anisotropy E in the
presence of an applied field H
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ShapeShape--Dependent AnisotropyDependent Anisotropy
*J. Aharoni, J. Appl. Phys 83, 3432 (1998)
1444
=++πππzyx DDD
( )( ) ( ) ( )
xyz
xzzyyx
xyzxxy
zzyx
xyz
zyx
xyz
zyx
zyxz
xy
xzx
xzx
y
z
yzx
yzx
x
z
yyx
yyx
z
x
xyx
xyx
z
y
yzyx
yzyx
xz
zx
xzyx
xzyx
yz
zyDx
3
3
2
3
2
arctan2ln2
ln2
ln2
ln2
ln2
ln2
23
2223
2223
22
2222222222333
22222
22
22
22
22
22
22
22
222
22222
222
22222
+++++−
++++++−+
+−+
+
+++
++
−++
++
−++
−+
+++
−+
+++
+++
−++−+
+++
−++−=π
Shape Demagnetizing Factors Extremely geometry-dependent
For a thin-film, the rectangular prism model may be used:
Total demagnetizing factor must always equal 1
Each axis in the rectangular prism model can be
determined by applying the cyclic permutation
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ShapeShape--Dependent AnisotropyDependent Anisotropy
( ) ( )( )( ) ( )
( )
+−−
+
−++++×
+= +
+
1
1111
1
1
2
2
δ
δ
δωαωγαωγγω
αωγγ
µdi
di
kkk
red
ei
iHiMsHiH
Ms
1+=k
siH
Mµ
Hi – Induced Anisotropy
Hmc – Magnetocrystalline Anisotropy
Hme – Magnetoelastic Anisotropy
Hd – Shape Anisotropy
memcdik HHHHH +++=
To determine the effect of shape on permeability, start with the equation for complex
permeability (Van de Riet):
At sufficiently low frequencies, the low-frequency intrinsic permeability may be
simplified as the initial permeability, inversely proportional to anisotropy
Anisotropy is made up of a number of elements
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THICKNESS-DEPENDENT
ANISOTROPY/PERMEABILITY
3D Demagnetizing Factors include
thickness
One model for anisotropy contains both
thin-film shape and thickness
X
z
y
M
Ф
θ
Ф0
θ0
α
E
H
( ) ( )( )θφθφθα 2222 cossinsincossincos2
zyxk DDDMsHm
H +++=
Thin film Modelling
(External Field)
φθ
HmDy
Dx
(Resultant Magnetization)
gggg
M
H
0
200
400
600
800
1000
1200
1400
1600
1800
90 120 150 180 210 240 270
Sample Rotation Angle, γ (Degrees)
Anisotropy, H k (A/m)
Measured Anisotropy
Calculated Anisotropy
0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4
Aspect Ratio, ARInitial Perm
eability, µ r
Measured Permeabiltiy
Calculated Permeability
12APPLIED PHYSICS LETTERS 96, 202509, 2010
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Ferromagnetic ThinFerromagnetic Thin--FilmsFilms
0
100
200
300
400
500
600
700
1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10Frequency (Hz)
Complex Perm
eability (µr' + µr")
µr' - Measured
µr" - Measured
µr' - Simulated
µr" - Simulated
0
100
200
300
400
500
600
700
1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10Frequency (Hz)
Complex Perm
eability (µr' + µr")
µr' - Measured
µr'' - Measured
µr' - Simulated
µr'' - Simulated
Measured 1 µm Co91.5P8.5 thin-film compared to a simulated
CoP thin-film without a 50 nm Cu seed layer
Measured 1 µm Co91.5P8.5 thin-film compared to a simulated
CoP thin-film with a 50 nm Cu seed layer
Complex permeability with the
modified permeability + conductivity
equation
Complex permeability with the
modified permeability equation
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NiCl2.6H2O +FeCl2.4H2O +Additives
Optimised plating current density
Mechanical agitation
Plated in magnetic field
Alloy composition- Ni45Fe55
Non-uniform deposition
Fractal/dentritic growth across film
Stressed film → limited thickness
Ni45Fe55 DC plated
14
Challenge – Integration aiming PSOC
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Pulse Reverse Plating
Iforward
Ireverse
S1S2
bath
electrodes
Control
electronics
trevtoff toff
Iforward
Ireverse
T
tforward
Voltage regulation & timer circuit
Rectangular wave at particular frequency
Milliseconds → Microseconds
15
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SEM - microfabricated inductors
Ni45Fe55 plated film
Ni45Fe55 plated film
BCB
Substrate (Si+BCB)
SU8
Top cores (over 3D topology)
Top Magnetic Core
Bottom Magnetic Core
Copper windings
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• Coercivity (Hc) < 2 Oe • Permeability (µr) - 300-1000
• Saturation Flux density (Bs) – 1.5- 2.4T• Resistivity (ρ) - 30-500 µΩcm
• Cut-off frequency for eddy current loss ( fed) – 100-500 MHz• Anisotropy field (Hk) – 10-50Oe
• Natural ferromagnetic resonance frequency (fFMR) – 1-3 GHz
17
Challenge – Next generation magnetic materials
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Advantages: (granular materials) High resistivity of nanocomposite works better than
thin film laminations for controlling eddy-current loss.
At subnanometer particle separation distances the
magnetic structure changes from dipolar coupled to
exchange coupled.
18
Granular Magnetic Materials
Ceramic (SiO2, Al2O3, etc)
Drawback: (sputtering)
Difficult to produce thicker films, hence, any reasonable power density.
Co, Ni, Fe, etc
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Grand Challenge!
To develop a next generation integratable soft
magnetic core material capable of operating at
high frequency for Power Applications
Realisation of power supply on chip (PwrSoc) !
19
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Nanocrystalline grain
structure (grains <10nm)
NiNi4545FeFe5555
Nano-structured NiFe
20
Create nano-crystalline structure
Magnetic film for high frequency
Higher resistivity
Reduction in Anisotropy dispersion
Pinning of domain wall in the film
No Domain wall motion
Only Domain wall rotation
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Magnetic characterization of Ni45Fe55
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-3000 -2000 -1000 0 1000 2000 3000
H (A/m)
B (T)
Ni45Fe55- 1 µm thickNi45Fe55- 1 µm thick
“Electrodeposited anisotropic NiFe 45/55 thin films for high-frequency micro-inductor applications”, T. O’Donnell, N. Wang, S. Kulkarni, R. Meere, F. M.F. Rhen, S. Roy, S.C. O’Mathuna, Journal of Magnetism and Magnetic Materials 322, pp. 1690–1693, (2010). 21
Electroplated Ni45Fe55
Saturation, Bsat 1.5 T
Coercivity, Hc 80 A/m
Resistivity, ρ 48 µΩ cm
Anisotropy, Ηk 800 A/m
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CoNiFe – beyond 100 MHz
Hc = Hc morph + Hc anis
22
J. Appl. Phys 103, 103901, (2008). Editorially selected for republication in virtual J. of Nanoscience and Nanotechnology.
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Electroplated CoNiFeP
Saturation, Bsat 1.6 -1.8 T
Coercivity, Hc 95 A/m
Resistivity, ρ 24-85 µΩcm
Anisotropy, Ηk 2500 A/m
CoNiFeP – 10 µm
“Dependence of magnetic properties on micro to nanostructure of CoNiFe films”, Fernando Rhen, Saibal Roy; J. Appl. Phys
103, 103901, (2008)
“Soft-magnetic CoNiFeP alloy films for high frequency applications”, Fernando Rhen and Saibal Roy; IEEE Trans. Magn. 44,
No 11, 3917-3920, (2008)
CoNiFeP – 10 µm
CoNiFeP – 28 µmCoNiFeP – 28 µm
23
Magnetic characterization of CoNiFeP alloys
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High resistivity >100 µΩ.cm → Increased skin
depth → Increased operational frequency
DC plated films have perpendicular anisotropy
& low permeability
Use of Pulse Reverse plating to achieve in-
plane anisotropy
To produce multi-nano layer structures
Pulse Reverse plating;
- Composition of M layer Co74P26, thickness-
30 nm
- Composition of NM layer Co66P34, thickness-
2-5 nm
24
Nanostructured CoP
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0
100
200
300
400
500
600
700
800
1 10 100 1000
Frequency (Mhz)
Relative Perm
eability
200 nm Cu seed
50 nm Cu Seed
No seed
Magnetic characterization of CoP
-40
-30
-20
-10
0
10
20
30
40
-25 -20 -15 -10 -5 0 5 10 15 20 25
Oersteds
nWb Easy
Hard
Electroplated CoP
Saturation, Bsat 1.2 T
Coercivity, Hc 8 A/m
Resistivity, ρ 130 µΩ cm
Anisotropy, Ηk 1500 A/m
“High Frequency Nanostructured Magnetic Materials for Integrated Inductors”, P. McCloskey, B. Jamieson, T. O’Donnell,
D. Gardner, M.Morris, S. Roy, Journal of Magn. Magn. Mater., Vol. 320, Issue 20, Pages 2509-2512 (2008)25
0
50
100
150
200
250
300
350
400
450
500
10 100 1000 10000
Frequency, f (MHz)
Complex Perm
eability, µr', µr"
ur'
ur"
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Nanostructured CoPRe
• Addition of Re to CoP thin films for increased thermal stability
• Co100-x-y, Px, Rey where; 9.7 at%<x<17.5at% and 0.4at%<y<7.6at%
Hard axis measurement for CoP Hard axis measurement for CoPRe
Magnetic moment (nWb)
Magnetic moment (nWb)
Applied field (A/m) Applied field (A/m)
Electrodeposited amorphous Co-P based alloy with improved thermal stability; P McCloskey, B Jamieson, T O’Donnell, D Gardner, M A Morris, S Roy; J. Magn & Mag Mat, 322, 1536-1539, (2010)
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Fabrication- Inductor/Transformer
Anisotropy induced in
material during deposition
L: 2 mm
W: 1.1 mm
Typical Fabricated inductor
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Micro-inductor: Structure
• 5 Mask Layers
Core Core
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• Electroplated copper windings.
• Thin-film, electroplated magnetic core.
• Design optimisation process
– Focus on efficiency and footprint.
– Coupled to validated models.
• Race-track shape to achieve:
– good frequency response
– high inductance density
– Low DC resistance
• CMOS-compatible process:
– Copper coils deposited by electroplating
– Core consists of thin film of NiFe alloy
deposited by electroplating
Cross section of a micro-inductor
Micro-inductors fabricated on 4 inch Si wafer
Tyndall Fabricated Microinductors
29
www.tyndall.ieInductor Current handling performance
Inductor Electrical performance
30
Electrical Characterisation of Microinductors
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Thank you for your attention
Acknowledgement
Tyndall- Brice Jamieson, Jeffrey Godsell, Paul McCloskey*,
Fernando Rhen+, Ningning Wang, Santosh Kulkarni, Shunpu Li,
Terence O’Donnell*, Cian O’Mathuna
INTEL – Donald Gardner
*Currently with Enterprise Ireland+Currently with University of Limerick
