Page 1
FerroelectricsMaterial Properties, Processing, and Microwave
Applications
Spartak Gevorgian
Department of Microtechnology and NanoscienceChalmers University of Technology
Gothenburg, Sweden
Norwegian IEEE MTT/AP ChapterSINTEF, Trondheim, March, 2006
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Outline
♣Introduction
♣Materials (Bulk, Thick and thin Film)
♣Devices and Circuit Applications
♣Concluding Remarks: Problems and
Perspectives
Page 3
WiredCommunicationNew York 1921
What is this about?
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WirelessCommunicationGothenburg, Sweden 2001
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Electronics DNA: Search forcomponents with enhanced performances
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Dielectric withelectric field dependent
permttivity
Electrode
Electrode
Electrode
Electrode
Ferroelectrics: Multifunctional Dielectrics
Page 7
Ferroelectric Compositions Considered forMicrowave Applications
ABO3 Perovskites:
CaxSr1-xTiO3
KxLi1-xTaO3KxNa1-xNbO3PbxZr1-xTiO3
BaxSr1-xTiO3x=0 -1
Ferroelectric (polar) and paraelectric phases
Page 8
Polarization of Paraelectric Perovskites
O
AB
E
ε
E
P
E
Nonlinear polarization
Field dependent permittivity
)()E()(T
00ε
εε −=
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BaxSr1-xTiO3(BST) at Room Temperaturex=0.1-1.0
Smolensky & Isupov (1954)
0
2
4
6
8
10
12
14
16
50 100 150 200 250 300 350 400 450Temperature, K
Die
lect
ric c
onst
ant,
ε ×10
-3
1.0
0.9
0.8
0.70.6
0.50.40.3
0.2
0.1
b)
Page 10
Ba0.8Sr0.2TiO3+MgO. MgO: 0-10%From Doping to Composite
Su & Button (2004)
0
2000
4000
6000
8000
-80 -60 -40 -20 0 20 40 60 80
Temperature, °C
Per
mitt
ivity
0%
1%2%
1.5%
0.5%
10%4%
Doping
Com
posi
te
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Ferroelectrics- Features Attractive for Microwave Applications-1
Dielectric properties:
Permittivity ε (100-20000) - small size devices:
Size ~1/ √ε
Electric field dependent - tuneable and
nonlinear devices
Loss tangent tanδ- typically 0.0001-0.05
Tuning speed- < 1.0 ns
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Electrical properties:
Resistivity- undoped >10 8- 10 10 Ohm cm
Leakage currents- extremely lowBreakedown field- >50-100 kV/cmMetalic conductivity- if highly doped (transparent
electrode) Bandgap- Eg>3.0 eVMobility- 2D electron gas at low
temperature-15000cm2/Vs
Ferroelectrics- Features Attractive for Microwave Applications-2
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♣ Bulk- single crystal and ceramics
♣ Thick film- HTCC, LTCC
♣ Thin film- single crystal polycrystalline
Ferroelectric Material Technologies Considered for Microwave Device Fabrication
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Bulk Single Crystal (SrTiO3)
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Four Pole Tuneable Bandpass Filter Based on SrTiO3 Discs
Duroid SrTiO3 disk resonator
SrTiO3 disksDiameter: 7.0 mmThickness: 0.5 mmPlates: Cu/Ti
Deleniv et. al. Proc. EuMC’2002
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Four Pole Tuneable Bandpass Filter Based on SrTiO3 Discs
3 dB bandwidth-2.0%;Tuneability-8%; Losses-4.0 dB
-80
-70
-60
-50
-40
-30
-20
-10
0
0.4 0.45 0.5 0.55 0.6 0.65
Tra
nsm
issi
on c
oeff
icie
nt, S
21 (d
B)
Frequency, GHz
0 V300 V
500 V
T=77K
-20
-15
-10
-5
0
0.4 0.45 0.5 0.55 0.6 0.65
Ref
lect
ion
coef
ficie
nt, S
21 (d
B)
Frequency, GHz
0 V
300 V
500 V
T=77K
Deleniv et. al. Proc. EuMC’2002
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Bulk Ceramic BaxSr1-xTiO3
(Project MELODY)
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Beam Steering Lens
Tageman et. al. Proc. EuMC’2005
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Tuneable Chip Components: Resonators Capacitors and Delay Lines
9,22 mm
1,51 mm
Pd/AgPd
BST68/32 / MgO 60mol%6 layers
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LTCC and HTCC BaxSr1-xTiO3
(Project MELODY)
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HTCC Phase Shifters in Project MELODY
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• Development of tunable ferroelectric LTCC compositionsSintering temperature: <950 oC
ε=100-1000; tanδ < 0.01 at 2-50 GHz; Tunability >10%
• Development of processing routes for single and multilayer ferroelectric films with:
Thickness 5-50 μm; Area 100x100 mm2
• Development of fabrication routes for electrodes
LTCC OBJECTIVES
Page 23
LTCC BSTO Performance
140
150
160
170
180
190
200
210
0 5 10 15 20 25 30
Extracted dielectric
permittivity, ε r
Frequency, GHz
2V/μm
4V/μm
No bias
tanδ∼f; (~0.12@25GHz)
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LTCC Phase Shifters in Project MELODY
~1.5mm
~9deg/dB @25GHz
~20deg/dB @10GHz
~10deg/dB @25GHz
~50deg/dB @3.5GHzTEMEX
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Measured Phase LTCC Shifter Performance
-30
-25
-20
-15
-10
-5
0
5 10 15 20 25 30
Matching S11, dB
Frequency, GHz
No bias
4V/μm2.4V/μm
1.25V/μm
0
50
100
150
200
250
5 10 15 20 25 30Phase shift Δφ, deg
Frequency, GHz
1.25V/μm
2.4V/μm
4V/μm
Matching shows weak dependance on DC biasing!!!
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Tuneable Power Splitters
Coplanar Plate (CPS)
Parallel Plate
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Tuneable Matching Networks
Port2Port1
V1
V2
θ1(V1)
θ2(V2)Coplanar Plate
Parallel Plate
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Thin film BaxSr1-xTiO3
(Chalmers)
D. Kuylenstierna
M. Norling
A. Vorobiev
A. Deleniv
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Growth of BST films by laser ablation
1 Hz
Rotating TargetBa0.25Sr0.75TiOx
Heater at 650°C
Laser0.4 mbar O2
PLD System -MC2 Process Lab Chalmers
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Growth of BST films by rf magnetron sputtering
Nordiko 2000 Sputter
- +magnet system
BSTO6” target
Ar ions
3” Pt/Au/Sisubstrate
halogen lamps
radiation heater
Ar/O2 (10/5)50 mTorr
200W rf
Page 31
Integration Issues
Crystalline: MgO, LaAlO3, Al2O3
Amorphous: Oxidized Silicon, Fused Silica
Substrates for ferroelectric microwave devices
Metal: Pt, Au, Cu (with diffusion stop buffer)
Polycrystalline: Al2O3
Page 32
BSTPt
nucleation center
TEM and SEM images of the BSTO filmsin Thin Film Parallel-Plate Varacotors
Bottom Pt/Au
Top Au/Pt
BSTO
TEM image by Prof. E. Olsson, Chalmers
Page 33
Pt (50 nm)
Au
Pt (200 nm)-bottom plate
SiO2 (0.43 μm)
Si substrate 0.5 mm
AuAu (0.5 μm)
-top plate
SrTiO3 (0.56 μm)
Test StructureCross Section and Top Electrode
STO or BSTO
TopPlateAu/Pt
Top ground plate, Au/Pt
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Varactor Performance at 1.0 MHz
1.2
1.4
1.6
1.8
2
2.2
2.4
100
150
200
250
300
-30 -20 -10 0 10 20 30
Cap
acita
nce
(pF)
Q-f
acto
r
Voltage (V)
BST/Pt
BST/Pt/Au
A. Vorobiev, P. Rundqvist, K. Khamchane, and S. Gevorgian, Appl. Phys. Lett. 83, 3144 (2003)
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• No dispersion in permittivity and tuneability
• Tuneability > 40 %
Microwave Performance at V=0 and 20V
0
0.01
0.02
0.03
0 10 20 30 40
tanδ
Frequency (GHz)
0 V
20 V
0.05
0.1
0.15
0.2
0.25
0.3
0 10 20 30 40
Cap
acita
nce
(pF)
Frequency (GHz)
0 V
20 V
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Technology Comparison. E=0
Shown are also:Si varactor (Metelics, MSV34,060-C12, Q=6500 @ 50 MHz, V=-4V)
GaAs HBV (Darmstadt University of Technology, fcut-off=370 GHz)
GaAs dual Schottky diode (UMS, DBES105a,fcut-off=2.4 THz)10
100
1 10
Q-f
acto
r
Frequency (GHz)
200
GaAs-HBV
Si
GaAs-Schottky
BST/Pt/Au (PLD)
BST/Pt (PLD)
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BSTO Potential for Tuneable TFBARs
Page 38
Acoustic Impedances
63.8٠106
300 nm BSTO (42.2)50 nm Pt (57.6)
Au (63.8)
150 nm Pt (57.6)
12.6
Si (19.7)0.45 μm SiO2
0.5 μm Au (63.8)
Acoustic impedance
Dis
tanc
e fr
om su
rfac
e
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0
0.005
0.01
0.015
0.02
8 8.5 9 9.5 10 10.5 11 11.5 12
Re(
Z)/5
0
Frequency, GHz
20 V
10 V
0 V
Au/Pt/STO/Pt/SiO2/Si
Real Part of Impedance (Measured)
Page 40
0.02
0.025
0.03
0.035
0.04
9 9.5 10 10.5 11Frequency, GHz
20 V
0 V
Re{
Z}/Im
{Z}
DC Field Dependent Resonance (Measured)
Page 41
Device Applications
Page 42
Main Device Fabrication Steps(Prepatterning of bottom electrode)
Deposition prepatterning of Pt/Au/Pt (50/500/100nm) bottom electrode
Growth of BST film (300nm) by PLD650 °C, 0.4 mbar
Top electrode formation by lift-off process
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Typical Varactor Structures
Page 44
Tuneable Delay Lines
Type2
Page 45
15 20 2510 30
7.0E-11
7.5E-11
8.0E-11
6.5E-11
8.5E-11
freq, GHz
time
(s)
0V
30V
)V(LC=τ
15 20 25 3010 35
-4.5
-4.0
-3.5
-3.0
-5.0
-2.5
-25
-20
-15
-10
-30
-5
freq, GHz
dB(S
(1,1))dB(S
(1,2
))
S-parameters (0V)
Tuneable Delay Line Performance
D. Kuylenstierna et. al, EuMC’2004
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Lumped Element Tunable Resonators and Filters
(a) (b)
(c) (d)
CC CC
CS1
CS2
LS2
LS1
CC CC
CS1/2
CS2/2
4LS1
LS2
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20 40 600 80
-60
-40
-20
-80
0
freq, GHz
dB(S
21)
20 40 600 80
-30
-20
-10
-40
0
freq, GHz
dB(S
(1,1
))Two-Pole Lumped Element Tunable Filter
(simulated)
D. Kuylenstierna et. al,Si RFIC’2006
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20 30 40 50 6010 70
-8
-6
-4
-2
-10
0
-40
-30
-20
-10
-50
0
freq, GHz
dB(S
11) dB(S21)
35 40 4530 50
-5
-4
-3
-2
-6
-1
freq, GHz
dB(S
11)
Single –Pole Lumped Element Filter(measured)
D. Kuylenstierna et. al,Si RFIC’2006
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Tuneable Phase Shifters
3.6 mm
DC bias
DC bias
D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters
Page 50
15 20 2510 30
-50
-40
-30
-20
-10
-60
0
-20
-15
-10
-5
-25
0
freq, GHz
dB(S11)dB(S
21)
Tuneable Phase ShiftersMesured S-parameters
Relatively high losses due to steps and surface conductivity of Si
D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters
15 V
0 V
15 V
0 V
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15 20 2510 30
20
40
60
0
80
freq, GHz
Phas
e sh
ift [d
B]
Tuneable Phase ShiftersMesured Phase Shift Under 15 V
D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters
Expected phase shift under 25 V: ~90o
Page 52
Problems and Perspectives
Page 53
Ferr
oele
ctri
c Paraelectric
Bax1Sr1-x1TiO3Bax2Sr1-x2TiO3
tanδ
Perm
ittiv
ity, ε
T2T1
Los
ses,
tanδ
ε
Temperature Stabilization (Materials/design based)
Page 54
MgO substrate
2g
Ba0.75Sr0.25O3
Au
Ba0.25Sr0.75O3
Au
105
110
115
120
125
130
26
28
30
32
34
36
38
0 50 100 150 200 250 300 350
Cap
acita
nce,
fF
Q-f
acto
r
Temperature, K
C
Q
Temperature Dependence (Materials/Design Based- Measured)
Page 55
Temperature Stabilization (Circuit Topology Based)
VDC
Vv
VCVaractor C
VTCTL
DC bias network
Page 56
0
0.05
0 .1
0.15
0 .2
0.25
0 .3
0.35
0 50 100 150 200 250 300
Cap
acita
nce,
pF
T em pera ture , K
E =50 kV /cm
100
100
50
N ot s tab ilised
S tab ilised
Temperature Stabilization (Circuit Topology Based-Summation)
Page 57
Perspective applications :
Project HiMission (EUREKA/MEDEA+/VINNOVA )
Phase shiftersTuneable delay LinesTuneable filtersVCO
Project Nanostar (FP6, EU) VaractorsTuneable TFBARsVCOs