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

Outline

♣Introduction

♣Materials (Bulk, Thick and thin Film)

♣Devices and Circuit Applications

♣Concluding Remarks: Problems and

Perspectives

WiredCommunicationNew York 1921

What is this about?

WirelessCommunicationGothenburg, Sweden 2001

Electronics DNA: Search forcomponents with enhanced performances

Dielectric withelectric field dependent

permttivity

Electrode

Electrode

Electrode

Electrode

Ferroelectrics: Multifunctional Dielectrics

Ferroelectric Compositions Considered forMicrowave Applications

ABO3 Perovskites:

CaxSr1-xTiO3

KxLi1-xTaO3KxNa1-xNbO3PbxZr1-xTiO3

BaxSr1-xTiO3x=0 -1

Ferroelectric (polar) and paraelectric phases

Polarization of Paraelectric Perovskites

O

AB

E

ε

E

P

E

Nonlinear polarization

Field dependent permittivity

)()E()(T

00ε

εε −=

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)

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

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

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

♣ Bulk- single crystal and ceramics

♣ Thick film- HTCC, LTCC

♣ Thin film- single crystal polycrystalline

Ferroelectric Material Technologies Considered for Microwave Device Fabrication

Bulk Single Crystal (SrTiO3)

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

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

Bulk Ceramic BaxSr1-xTiO3

(Project MELODY)

Beam Steering Lens

Tageman et. al. Proc. EuMC’2005

Tuneable Chip Components: Resonators Capacitors and Delay Lines

9,22 mm

1,51 mm

Pd/AgPd

BST68/32 / MgO 60mol%6 layers

LTCC and HTCC BaxSr1-xTiO3

(Project MELODY)

HTCC Phase Shifters in Project MELODY

• 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

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)

LTCC Phase Shifters in Project MELODY

~1.5mm

~9deg/dB @25GHz

~20deg/dB @10GHz

~10deg/dB @25GHz

~50deg/dB @3.5GHzTEMEX

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!!!

Tuneable Power Splitters

Coplanar Plate (CPS)

Parallel Plate

Tuneable Matching Networks

Port2Port1

V1

V2

θ1(V1)

θ2(V2)Coplanar Plate

Parallel Plate

Thin film BaxSr1-xTiO3

(Chalmers)

D. Kuylenstierna

M. Norling

A. Vorobiev

A. Deleniv

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

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

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

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

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

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)

• 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

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)

BSTO Potential for Tuneable TFBARs

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

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)

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)

Device Applications

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

Typical Varactor Structures

Tuneable Delay Lines

Type2

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

Lumped Element Tunable Resonators and Filters

(a) (b)

(c) (d)

CC CC

CS1

CS2

LS2

LS1

CC CC

CS1/2

CS2/2

4LS1

LS2

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

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

Tuneable Phase Shifters

3.6 mm

DC bias

DC bias

D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters

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

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

Problems and Perspectives

Ferr

oele

ctri

c Paraelectric

Bax1Sr1-x1TiO3Bax2Sr1-x2TiO3

tanδ

Perm

ittiv

ity, ε

T2T1

Los

ses,

tanδ

ε

Temperature Stabilization (Materials/design based)

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)

Temperature Stabilization (Circuit Topology Based)

VDC

Vv

VCVaractor C

VTCTL

DC bias network

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)

Perspective applications :

Project HiMission (EUREKA/MEDEA+/VINNOVA )

Phase shiftersTuneable delay LinesTuneable filtersVCO

Project Nanostar (FP6, EU) VaractorsTuneable TFBARsVCOs

End