1

Teknologioita adaptiivisiin RF-moduleihinMarkku Ylilammi

VTT Mikro- ja nanotekniikka

Teknologioita adaptiivisiin RF-moduleihin

Markku YlilammiVTT Mikro- ja nanoelektroniikka

Kännykän antennin säteilyimpedanssi vaihtelee voimakkaasti eri käyttötilanteissa. Myös laaja toimintataajuusalue ja saman antennin käyttö eri taajuusalueilla aiheuttaa impedanssi-epäsovitusta RF-elektroniikan ja antennin välillä. Säädettävän sovituspiirin avulla voidaan saavuttaa merkittävä parannus seisovan aallon suhteeseen. Tämä helpottaa tehovahvistimen vaatimuksia ja alentaa tehonkulutusta. Vastaanottopuolella adaptiivinen piiri kasvattaa LN-vahvistimeen siirtyvää signaalia. Adaptiivisia RF-moduleita voidaan valmistaa useilla tekniikoilla. Esityksessä tarkastellaan ferrosähköisten ohutkalvojen kehitystä säädettäviksi kondensaattoreiksi ja BAW-tekniikkaa, joka on korvaamassa SAW-suodattimia.

Application Example: Compensation of Handset Antenna Proximity Effects

A cellular phone next to a human body

A cellular phone on a metal table

Contact: tauno.vaha-heikkila@vtt.fi

Conventional and Reconfigurable Multi-Band Rx/Txsystem

• By using tunable and reconfigurable components and circuits• Number of components can be lowered • Performance and functionality can be increased

Contact: tauno.vaha-heikkila@vtt.fi

Analog switch

Some MEMS Components from DC to 220 GHz

• Varactors

• Switches

• Phase shifters

• Capacitor banks

• Filters

• Impedance tuners

• Matching networks

• Antennas

• Power sensors

Contact: tauno.vaha-heikkila@vtt.fi

Roadmap of passive RF components (c) WTC Arrro

Adaptiivinen RF moduli

• Integroitu RF-piiri• Sähköisesti säädettävä reaktiivinen elementti • Miniatyroisoitu RF-suodatin (BAW, SAW)• Ohjauselektroniikka

Reconfigurable Matching Networks for Power Amplifiers in Adaptive Radio Links

Multi-band matching of a 10 Ω load to 50 Ω

Matching network for 20-50 GHz applications

Contact: tauno.vaha-heikkila@vtt.fi

Electrically controlled variable capacitor (Varactor)

Adaptive antenna (impedance matching in variable environment)

Steerable antenna (adjustable phase delay lines)

Tunable filter (the pass band of a wide band filter tuned by varactors)

RF-switch (based on tunable resonance circuits)

Ferroelectric mixer (utilizes the nonlinearity of a ferroelectric material)

Tunable microwave disk (cavity) resonator

Ferroelectric thin films

The electric permittivity of a ferroelectric insulator depends on the electric field. A capacitor with this insulator can be controlled by a DC voltage.

Exemplary materials: BaSrTiO3, SrTiO3

Voltage or field

permittivity or capacitance

Q value

Temperature

Typical characteristics

Capacitance ratio 1.5 - 2.5 (STO)

Q-value at 10 GHz 100 - 200

(single crystals 1000 (STO))

Curie temp. 40 - 400 K (BSTO)

Permittivity of ferroelectric thin filmsPbMgNbO (200 nm) / LSCO / MgO heterostructure

Courtesy of University of Oulu

Perm

ittiv

ity

Bias voltage0 2 4 6

500

1000

1500ε'

UB (V)

Sähköisesti säädettävä kondensaattori voidaan tehdä käyttämällä ferrosähköistä materiaalia

GoodPoorExcellentGoodTemperature drift

2000199519901970Known since

~300°C + 750°C post-processannealing

~700°CLowNot relevantSputterTemperature

LowModerateHighHighCost

SiSapphire/SiSiGaAsSubstrate

???HermeticPackaging

ModerateModerateExcellentPoorPower handling

ModerateModerateExcellentVery poorLinearity

?µsecmsecnsecTuning Speed

<50V<30V<100V<10VDC-Bias

~200~70~200~60Q

2:13:11.5:14:1Tunability

BiZnNbOBaSrTiOMEMSGaAs

Säädettävien kondensaattoreiden kilpailevat teknologiat @ 2GHz

Source: Prof. Susanne Stemmer, UCSB, Tutorial Talk at IMS, 2005

Varactors based on ferroelectric materials

Tunable RF-circuits based on ferroelectric thin films (e.g. BaxSr1-xTiO3) offer large potential, but the technology requires development.

Adaptive RF-circuits are very advantageous for wireless applications: E.g. tunable antenna (compensation for antenna mistuning):

- improved performance: better SNR (high data rate channels), lower power consumption- reduction of parallel hardware in multiband systems- reduction of development costs (basic design adapted to several models)

Advantages of FE thin film materials:- fast (tunability up to THz-range)- low losses at high frequencies, especially above 10 GHz - high relative permittivity (typically εr > 100 …500) <=> compact devices- thin films allow low tuning voltages, also compact structures

Current disadvantages / limitations: - small tuning range ε (0)/ε (Umax) ~ 2 due to low breakdown fields - large temperature-coefficient. T-compensation by adaptive tuning restricted due to small available tuning range.- nonlinear effects- hysteresis, thin-film nonidealities

Ferroelectric varactors vs. competing technologies:-diode varactors: larger tunabilities available Cmax/Cmin = 5 .. 10, but losses and tunability worsen above 10 GHz.- MEMS varactors: typically excellent performance, but plagued by size, integration issues, price.

Design of an integrated adaptive matching circuit with adjustable BST-capacitors, a coil with thick Cu metal, bias resistors. (c) Tomi Mattila, VTT

top view

ACin

ACout

GND

GND

side view inductor Cu

BSTPt

Pb/Sn

SiO2

R

GND ACin ACoutDC1

R

GNDDC2L

DC1

DC2

LQ_L

C2Q_C2

C1Q_C1

Z_a = R_a + j X_a

Zin

Design parameters:f0 = 1 GHz, Za = 20 ... 100 + j -100 ... 100 OhmL = 5 nH, QL = 50 QC1 = QC2 = 50

Optimization strategy (preliminary):Adjust C1 and C2 to minimize|Γ|2 at f0, f0 - ∆f, f0 +∆f, ∆f = 10 MHz

0.620.600.380.00300.4644.98.812.7100100

0.890.720.110.00090.2947.18.710.50100

0.620.620.380.00300.4144.87.112.8-100100

0.500.560.500.00410.5444.09.013.410050

1.000.800.000.00020.1748.79.48.5050

0.500.590.500.00410.4444.06.413.7-10050

0.270.410.730.00980.7541.08.716.010020

0.820.900.180.00000.0449.87.15.7020

0.270.450.730.00970.641.05.616.6-10020

Pout no ΠPout|Γ|^2 no Π|Γ|^2Xin (Ω)Rin (Ω)C2 (pF)C1 (pF)X_a (Ω)R_a (Ω)

• sacrifice 1dB power at Za=50Ω <=> significant reduction in |Γ|2

Tunable π-network

AntennaMatching net Zin Pout

2.20.41.80.7

-1.00.50.0

-0.9-0.1

dB

Physical Properties of Ferroelectric Materials

TcT

εr

FERROelectric• spontaneous

polarization• piezo• hysteresis

(high RF-losses)

PARAelectric

• tunable, low-loss materialfor RF-applications

21)0(

)(E

E r

r αε

ε+

≈

!!))0((:Note 3rεαα =

E

εr

electric field

BaxSr1-xTiO3

O.G. Vendik, E.K. Hollmann, A.B. Kozyrev , and A. M. Prudan,"Ferroelectric tuning of planar and bulk microwave devices ",

J. Supercond. 12, 325 (1999).

Q

1000

100

10

Nonlinearity

-20.000 -10.000 0.000 10.000 20.000-60.00

-35.00

-10.00

15.00

40.00APLAC 7.90 User: VTT Microsensing Nov 29 2005

DCbiasf1 2f13f1 4f15f1

-20.000 -10.000 0.000 10.000 20.00030.00

37.50

45.00

52.50

60.00APLAC 7.90 User: VTT Microsensing Nov 29 2005

DCbiasPIIP3

DCbias

Udc = 0..20 V

PIIP

3[d

Bm

]

[V]

[V]

GSM spec.

ω

3ω

Pω = +33 dBm

P3ω = -22 dBm

Goal: ∆f/f = 5% for 1 GHz Q=10 antenna

Application analysis: Antenna tuning

U1/2 = 20 VAntenna eq. circuit

Q = 10

50

Ohm

spec. 65 dBm

Utilize inversely biased varactors topology:- no even-order nonlinearities- convenient DC-blocking

-20.000 -10.000 0.000 10.000 20.0002.80

3.80

4.80

5.80

6.80APLAC 7.90 User: VTT Microsensing Nov 28 2005

DCbiasC

C [p

F]

DC

RFin RFout

APLAC-model forFE capacitor

FE non-idealities: history effects

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

-5 0 5 10 15 20

Udc (V)

C(U

dc)

/ C

(0)

4.7pF series

7.5pF series

5 min

10 min

1 sec

1 sec

=> typical offset ∆C/C0 ~ 10 % after 1 sec!!!

Agilent 4294A LCR-bridgefac ~ 5 MHz, Vac ~ 50 mV

Bulk Acoustic Wave FiltersBulk Acoustic Wave Filters

EGSM (Enhanced Global System for Mobiles) Widely spread standard

Receiver Rx band 925-960 MHz (3.71%)Transmitter Tx band 880-915 MHz (3.90%)PCN band around 2 GHz

Very demanding application from filter design &Very demanding application from filter design &manufacturing point of view!manufacturing point of view!

Coils have very low Q value in this frequency range LC filters are not feasible.

Electromagnetic resonators' size about wavelength (30 cm).Traditional solution is SAW (Surface Acoustic Wave) filter:- requires single crystal piezoelectric substrate LiTaO3- lithography too expensive above 2 GHz- very low maximum power;

not suitable for Tx

Infineon CDMA RF front end

Operation principle of BAW

Piezolayer

Sound velocity 10000 m/s

Top metal electrode

Bottom metal electrode

Acoustic wave (stress distribution)

Electric field generates an acoustic wave inside the piezolayer. This wave resonates between the air interfaces.

Resonance frequency = ½ velocity of sound / thickness.

The sound wave may be either longitudinal or shear.

RF

BAW Approaches

Air

Piezolayer

Air

AirSupportElectrode

Electrode

Substrate

Substrate

Electrode

Piezolayer

Electrode

Low-Z

High-Z

Low-Z

High-Z

λ/4

BRIDGE FBAR MIRROR SMR SEM cross section image

Cross-section of a complete resonator, 3 Mo / SiO2 layer pairs in the mirror

Piezo

Bottom contact

Frequency tuning layer

In a mirror resonator there is an acoustic interference mirror which reflects sound back to the piezolayer. The structure is also called SMR Solidly Mounted Resonator

Infineon, Epcos (Ger.), NXP (formerly Philips, Netherl.)

BAW Mirror Resonator

One segement of a ladder filter

0

5

10

15

20

25

30900 950 1000 1050Frequency (MHz)

Tra

nsm

issi

on (d

B)

Serial resonance frequencyof the shunt (L) resonator

Parallel resonance frequencyof the series (H) resonator

Pass band

H

L

The width of the pass band is limited by the coupling keff.

One segment of a ladder filter

2eff

center

kfBW

<

BAW filters on a test waferH resonators

L resonators

Test resonators1 mm

Example of a commercial product on market

Courtesy Infineon AG

Size 2 x 1.6 x 0.6 mm

2W#69 D4G6o11 b

0

5

10

15

20

25

30800 850 900 950 1000 1050

Frequency (MHz)

Ref

lect

ion

S11,

Ins

ertio

n lo

ss S

21 (d

B)

S21

S11EGSM

VSWR

S21925 MHz 2.95 dB960 MHz 2.33 dB3.5 dB BW 38.2 MHzILmin 1.26 dBRipple 1.69 dBVSWR 2.17Stopband 23.38 dB

Ladder filter with six resonators.

Properties of resonator D41o11:fs 944.7 MHz, fp 971.6 MHzQs 460, Qp 890, Radius 0.943keff 0.234, FoM 48.5Nonc. 0.37 %, RL 53 kOhmCo 3.70 pF Cm 213.7 fF Lm 132.8 nHRm 0.91 Ohm Rx 0.82 Ohm

VTT Measured EGSM ladder filter with three segments or six resonators

Potential of BAW technology in RF filters

Performance estimates expected in commercial devices:

• Operating frequency 1 - 10 GHz, probably higher

• Q-value 2000 at 2 GHz, higher in more distant future

• Coupling coefficient 0.24 (6.5%, AlN), decreases with frequency

• Power handling capacity in filter 4 W, probably higher

• New filter structures (SCR, CRF) in near future

Industrial playersInfineon AG, GermanyAvago, USA, (Agilent)Epcos AG, GermanySkyworks, USA, (Agere)Triquint, USA, (TFR

Technologies)Fujitsu, JapanNXP, Netherland (Philips)STM, FranceLG, KoreaSamsung, Korea

Main products FiltersDuplexersDevelopment goalsHigher frequencies (above 2 GHz)Lower temperature coefficient (< 20 ppm/K)Higher power (several watts)Integration of BAW in IC chipsNew device structures

Markets

Main competitor still SAW filters.

Fierce competition in prices.

New manufacturers enter production.

In mass production

In development phase

Entering the market

Infineon AG, Munich, is the largest manufacturer and technically the most advanced.

BAW filters

• Resonators: coupling K2 up to 10.4% (keff = 0.282, ZnO), quality factor Q > 1200• Theory developed sufficiently to predict measurements

• Filters meeting EGSM specifications can be made without any external components

• No need for hermetic package (unpacked wirebonded VTT filter worked years in a Nokia mobile phone)

• Technology is compatible with integration on silicon chips

• Future:

• Filters for mobile phones have been commercialized

⇒ R&D directed to improve performance

and to create new device structures.

BAW ladder filters on 100 mm glass wafer (VTT)