Piezoelectric resonators for RF and microwave filters

IOP Conference Series Materials Science and Engineering

OPEN ACCESS

Piezoelectric resonators for RF and microwavefiltersTo cite this article M Mabrouk et al 2010 IOP Conf Ser Mater Sci Eng 13 012011

View the article online for updates and enhancements

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Piezoelectric resonators for RF and microwave filters

M Mabrouk 11 M A Boujemacirca1 F Ndagijimana2 P Benech2 and A Ghazel1 1CIRTACOM-SUPCOM-ISETCOM de Tunis Citeacute Technologique des Communications 2088 Tunisia Teacutel +216-71-857000 Fax +216-71-857555

2IMEP-LAHC UMR-5130-CNRS-INPG-UJF INPG-Minatec 3 Parvis Louis Neacuteel BP 257 38016 Grenoble France Teacutel +33-4-56529500 Fax +33-4-56529501 E-mail mohamedmabroukisetcomrnutn Abstract The interest of piezoelectric materials for Radio Frequency and Microwave applications is presented Simulation and characterization results of RF band pass filter formed by five piezoelectric Film Bulk Acoustic Resonators for UMTS wireless communication applications are carried out and showed in this work

1 Introduction In wireless communications application particularly in RF and Microwave transceivers (TXRX) the integration of filters near antennas is very difficult to be achieved One of the recent developments in MicroElectroMechanical Systems (MEMS) is concerning the Bulk Acoustic Wave (BAW) resonators and filters that have demonstrated a major interest for their good selectivity and possible above-IC integration [1-3] BAW resonators can provide better performances [4-5] than SAW especially low insertion loss temperature stability high power handling capabilities good selectivity and high Q-factor With these significant advantages BAW resonators play an interesting role in mobile communications modules

RF-BAW filters are designed with piezoelectric films called Film Bulk Acoustic Resonators (FBAR) These resonators are the main elements that provide and control the resonance frequencies and bandwidth of these filters

RF and Microwave filters must have an important role for signals filtering rejection and isolation between parts in transceivers The good selectivity of BAW filters can avoid frequency interference problems which exist in obstructed spectrum due to several wireless communication standards

2 Piezoelectric phenomena in BAW devices Nowadays Aluminum Nitride (AlN) Titano Zirconate of Lead (PZT) and Zinc Oxide (ZnO) are the three main piezoelectric materials used for the realization of RF and microwave devices Choosing this type of material is depending on its physical performances (electric and mechanical) and deposition process In Table 1 the typical values of materials characteristics used in our studied BAW filter show that AlN does not ldquoseemrdquo to be the best candidate for obtaining good electrical performances of filtering Nevertheless it remains the only piezoelectric material able to fulfill the microelectronic requirements of integration and technologies processes 1 To whom any correspondence should be addressed

JIPMA 2009 IOP PublishingIOP Conf Series Materials Science and Engineering 13 (2010) 012011 doi1010881757-899X131012011

ccopy 2010 IOP Publishing Ltd 1

Table 1 Typical values of materials characteristics used in our studied BAW filter

AlN (piezoelectric)

Mo (electrodes)

Tungsten (Bragg reflector)

SiO2 (Bragg reflector)

Silicon (Wafer)

Density p m [kgm3]

2200 10220 19300 2200 2340

Constant Stiffness c33109[Nm-2]

420 276 400 74 165

Elastic roofing stones tg (m)

10-3 34x10-3 34x10-3 34x10-3 2x10-3

Surface Sp Sm [msup2] 1156x10-10 1156x10-10 1156x10-10 1156x10-10 1156x10-10 Thickness tp tm [nm] 1460 200 600 710 Constant Dielectric

33 [pFm-1] 95

Dielectric roofing stones tg (e)

2x10-2

Piezoelectric Constant e33 [Cm2]

156

Electrodes resistance [

205

Also the SiO2 crystal quartz is the famous and known resonator The figures 1 and 2 show

respectively the electrical equivalent circuit and the response of crystal quartz resonator example

Figure 1 Electrical equivalent circuit of crystal Quartz resonator

5 501 502 503 504 505 506

x 105

101

102

103

104

105

106

107

108

109

Frequency (Hz)

Qua

rtz Im

peda

nce

Mod

ule

Figure 2 Simulated response of crystal quartz resonator


2

The module of electrical equivalent impedance of quartz is given below by equation

2222

2

22

q

CR)CCLC1(

)C1L(R

)j(Z

An example of typical values of that resonator characteristics (R = 10K L = 1000mH C=10pF and C=200C) gives both resonance frequencies series and parallel are respectively

KHz292503LC2

1Fs

and KHz548504FCC1FF 2sp 13 The simulated response

using Matlab program of this quartz resonator confirms the predictable resonance frequencies and the important interest for using this device in RFMicrowave applications that require stable reference frequency

The figure 3 shows an AlN-FBAR as being piezoelectric film taken ldquoin sandwichrdquo between two metallic electrodes in Mo

Figure 3 Cross section of BAW resonator

The coupling between the applied electromagnetic field between both electrodes and the elastic

field created in the bar introduces some electric terms in the equations of dynamic and mechanical terms in the Maxwells equations In order to analyze the fieldsrsquo propagation in AlN piezoelectric film the coupled equations have to be resolved simultaneously These equations are called constitutive equations [6] of piezoelectricity and are given in tonsorial form iijklm

Ejklmjk EeSCT

jEijjkijki ESeD and ijklm=123

Tjk and Sjk Tensors of the constraints and mechanical strains Di and Ei Electric field and inductions vectors eijk Piezoelectric constants tensors εij Permittivity Tensors For 1D perfect AlN resonator in case of longitudinal propagation with TE mode we have S1 = S2 = S4 = S5 = S6 = 0 S1 and S2 are the longitudinal strains S4 S5 and S6 are the shearing strains In case of

an insulator layer then D1 = D2 and 0z

D0)D(div 3

3

according to Maxwell theory The

piezoelectric constitutive equations become 3333333 EeScT and 3333333 SeED

21 Frequencies and impedance of BAW Resonator For the section of BAW resonator structure showed in figure 3 the fundamental principle of dynamic is applied for the propagation solution with the particle displacement u3 (in meters) and the density


3

of piezoelectric material (in kgm-3) The equation of motion [7] can be written using principle of

dynamic z

Tu

zT

tu

amF 33

232

32

ext

and z

uS 3

3

The electrical impedance of this BAW resonator is defined [4] as

)

2h(

)2htan(

k1Cj1

)(I)(V)(Z 2

t0

with hA

C 330

is the parallel plate capacitor of

resonator A is the surface of metallic electrode and h is the thickness of resonator D3333

2332

t ce

k

is

the piezoelectric coupling coefficient

22 Influence of the active piezoelectric layer thickness h and electrode surface A The figure 4 shows the effect of active layer thickness h on the resonance frequency For a fixed surface of electrode A=100 m2 and different values of thickness (156m Blue 146m Red and 156 m Green) the electrical equivalent impedance Z() of resonator is also simulated using Matlab program versus frequency This graphic confirms the known phenomena showing the resonance frequency has an inversely proportional behavior against the thickness h which is similar to half-wavelength ( ) in this case This can be exploited in order to design tunable filters ie filters with variable resonance frequencies and bandwidth

2 25 3 35 4 45 5 55 6 65 7

x 109

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Ii

mpe

danc

e M

odul

e

AlN Thickness increasing

Figure 4 Effect of active layer thickness h on the resonance frequency

Also the figure 5 shows the variation of resonator impedance against the surface of Mo metallic

electrode For a fixed thickness h=146m of piezoelectric active layer and different values of surface A (100m2 Red 250m2 Green and 600m2 Blue) the equivalent impedance of resonator is decreasing when the surface is increasing which is agrees with the kinematical rules


4

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600

Mo ElectrodeSurface Increasing

Figure 5 Effect of electrode surface A on resonator impedance

3 BAW Resonators used in RF and Microwave filters The crystal orientation of piezoelectric film has important influence on the quality factor of resonator In case of bad crystallographic orientation this can make a bad electromechanical coupling (lower than 6) Several important parameters such piezoelectric film or crystallographic orientation have to be taken into account when designing a piezoelectric resonator For example the metallic electrodes have to be chosen carefully for reducing electrical and mechanical losses Acoustic isolation of resonator has to be guaranteed regarding of structure The geometric forms of the electrodes have to be ldquoapodizedrdquo ie no face is parallel with another for avoiding parasitic modes of resonance The figure 6 shows these both Lattice and Ladder structures Ladder structure of BAW filter which is common mode architecture is widely used than Lattice structure which can be used only in differential mode In our work the ladder architecture was retained because of reference potential (ground for common mode)

Figure 6 Structure of Lattice filter (6a) and Ladder filter (6b)

The two curves depicted in figure 7 show the series and parallel resonators impedances obtained

with the help of ADScopy simulator The low resonance frequency of parallel resonator is the low cutoff frequency of filter the high resonance frequency of series resonator is the high cutoff frequency of filter These two frequencies control the bandwidth of filter


5

Figure 7 Impedances of series and parallel resonators

4 Simulation and measurement of our filter BAW The figure 8 shows our studied band pass filter that was designed by the assembly of five piezoelectric resonators on silicon substrate All of the five resonators are composed of Aluminum Nitride (AlN) thin film placed between two metallic Molybdenum (Mo) electrodes (figure 3)

Figure 8 Structure of our ladder filter with five FBAR

41 Calibration for RF high power measurement BAW filters have to operate at high power levels up 2W and more in several applications so non-linearity intermodulation distortion and inter-channel interferences become major limitations [8-10] Ddedicated bench setup for characterizing output power at 1dB compression and 3rd order IMD of BAW filters has been developed [11] So some BAW filters samples were characterized for output power compression and inter-modulation products measurements

42 Response calibration and verification of validity There are several calibration techniques but in the power measurements we have to take cautions because all of them cannot be used because many limitations exist We used response calibration which has a middle level complexity [12] allowing us to measure S21 and S22 only We have measured the output return loss (S22 parameter) of the calibration ldquoshortrdquo standard which is confirming the good validity level of response calibration showed in figure 9


6

Figure 9 On-wafer S22 measurement of the calibration ldquoshortrdquo standard

43 RF high power characterization of our BAW filter The figure 10 shows simulated and measured S21 of the BAW filter Figure 12 shows the top view of on-wafer station RF Probes and measured filter [11]

Theoretical result was obtained on ADS and measured S21 was carried out using 8720ES-VNA (Vectorial Network Analyzer) of Agilent Technologies connected to on-Wafer RF probes station (Infinity) of Cascade Microtech We used the response calibration procedure for calibrating the VNA allowing us to make power measurements of filter on this characterization bench In our case this power is of 10W ie 400dBm at the input of the filter

Figure 10 Simulated and measured S21 of our BAW filter

The figure 10b shows measured bandwidth is about 615 MHz the and equals UMTS uplink and

downlink frequency bands the filter is designed for The zoom of figure 10a showed in figure 11 shows the simulated bandwidth is about 560 MHz The both simulated and experimental results are closely correlated


7

Figure 11 Zoom on simulated S21 of our BAW filter

Figure 12 Top view of on-wafer station RF Probes and measured filter [11]

44 RF Measurement of 3rd order distortion of our BAW filter Figure 13 shows the measured 3rd output intermodulation products (OIMP3) of the filter Two microwave synthesized sources (Agilent 83711B and Anritsu 68367C) are used for providing two tones at F1 = 20 and F2 = 1999 GHz with interval of 10 MHz Two isolators are used to prevent any interference phenomena between both sources Spectrum analyzer MS2668C of Anritsu is used for measuring and displaying tones One of the two OIMP3 is the ratio Δ1dB of fundamental power at F1 to the power of lower adjacent band distortion at F = 2F1-F2 The second OIMP3 is the one of the ratio Δ2dB of fundamental power at F2 to the power of upper adjacent band distorsion at F = 2F2-F1 We can observe an obvious slight difference of 10dBc between Δ1dB (520 dBc) and Δ2dB (530 dBc) distortion levels since the two sources come from two different manufacturers so they canrsquot guarantee identical power levels


8

Figure 13 Measured 3rd Inter Modulation Products (IMP)

5 Conclusion In this work we have presented the excellent acoustic properties of piezoelectric materials such AlN ZnO PZT or Quartz These materials are used in FBAR resonators manufacturing The simulation results of impedance resonace frequencies and bandwidth of resonators are carried out and reported These theoritical results show and confirm the potential use of these resonators in many applications like RF and Microwave tunable devices such oscillator or filter

To give prominence to these applications a band pass BAW filter intended for 3G wireless applications was designed by the assembly of five piezoelectric resonators measured and simulated at 20 GHz A complete on-Wafer characterization setup is developed and used for measuring the S21 power response and 3rd output intermodulation products of the filter The theoritical and experimental results are closely correlated

References [1] Aigner R 2003 ldquoMEMS in RF Filter Applications Thin-Film Bulk Acoustic Wave

Technologyrdquo Sensors applications 12 175-210 [2] Carpentier J F and al 2005 A SiGe BiCMOS WCDMA Zero-IF RF Front-End using an

above-IC BAW Filter ISSCC-2005 IEEE International Solid-State Circuits Conference San Francisco USA 394-395

[3] Lakin K M Belsick J R McDonald J P McCarron K T and Andrus C W 2002 ldquoBulk Acoustic Wave Resonators and Filters for Applications above 2GHz rdquoIEEE-MTT-S Dig TH1D-6 1487-1490 Seattle WA USA

[4] Frank Z Bi and Barber B P 2008 ldquoBulk acoustic wave RF technologyrdquo IEEE Microwave Magazine 9 no 5 65-80

[5] Mourot L Bar P Parat G Ancey P Bila S and Carpentier J F 2008 ldquoStopband Filters Built in the BAW Technologyrdquo Application Notes IEEE Microwave Magazine 9 no 5 104-116

[6] Tadigadapa S and Mateti K 2009 ldquoPiezoelectric MEMS sensors state-of-the-art and perspectivesrdquo Measurement Science and Technology 20 IOP Publishing Ltd

[7] Kaajakari V 2009 ldquoClosed form expressions fro RF MEMS switch actuation and release timerdquo Electronics Letters 45 no 3 149-150 29

[8] Girbau D Otegi N Pradell L and Lazaro A 2006 Study of Intermodulation in RF MEMS Variable Capacitors IEEE-MTT 54 No 3 1120-1130


9

[9] Abubakar M Velichko A V Lancaster M J Xiong X and Porch A 2003 Temperature and Magnetic Field Effects on Microwave Intermodulation in YBCO Films IEEE Tarnsactions on Applied Superconductivity 13 No 2 3581-3584

[10] Girbau D Laacutezaro A and Pradell L 2004 ldquoCharacterization of dynamics in on-wafer RF MEMS variable capacitors using RF measurement techniquesrdquo in 63rd ARFTG Microwave Measurement Conf Tech Dig 117ndash123

[11] Mabrouk M Ndagijimana F Corrao N Benech Ph and Ghazel A 2007 ldquoOn-Wafer Power Measurements of BAW Filters Non-Linearitiesrdquo 70th ARFTG Microwave Measurement Conference Tempe AZ USA

[12] Using a Network Analyzer to Characterize High-Power Components Agilent Application Note 1287-6 literature number 5966-3319E


10

Piezoelectric resonators for RF and microwave filters

M Mabrouk 11 M A Boujemacirca1 F Ndagijimana2 P Benech2 and A Ghazel1 1CIRTACOM-SUPCOM-ISETCOM de Tunis Citeacute Technologique des Communications 2088 Tunisia Teacutel +216-71-857000 Fax +216-71-857555

2IMEP-LAHC UMR-5130-CNRS-INPG-UJF INPG-Minatec 3 Parvis Louis Neacuteel BP 257 38016 Grenoble France Teacutel +33-4-56529500 Fax +33-4-56529501 E-mail mohamedmabroukisetcomrnutn Abstract The interest of piezoelectric materials for Radio Frequency and Microwave applications is presented Simulation and characterization results of RF band pass filter formed by five piezoelectric Film Bulk Acoustic Resonators for UMTS wireless communication applications are carried out and showed in this work

1 Introduction In wireless communications application particularly in RF and Microwave transceivers (TXRX) the integration of filters near antennas is very difficult to be achieved One of the recent developments in MicroElectroMechanical Systems (MEMS) is concerning the Bulk Acoustic Wave (BAW) resonators and filters that have demonstrated a major interest for their good selectivity and possible above-IC integration [1-3] BAW resonators can provide better performances [4-5] than SAW especially low insertion loss temperature stability high power handling capabilities good selectivity and high Q-factor With these significant advantages BAW resonators play an interesting role in mobile communications modules

RF-BAW filters are designed with piezoelectric films called Film Bulk Acoustic Resonators (FBAR) These resonators are the main elements that provide and control the resonance frequencies and bandwidth of these filters

RF and Microwave filters must have an important role for signals filtering rejection and isolation between parts in transceivers The good selectivity of BAW filters can avoid frequency interference problems which exist in obstructed spectrum due to several wireless communication standards

2 Piezoelectric phenomena in BAW devices Nowadays Aluminum Nitride (AlN) Titano Zirconate of Lead (PZT) and Zinc Oxide (ZnO) are the three main piezoelectric materials used for the realization of RF and microwave devices Choosing this type of material is depending on its physical performances (electric and mechanical) and deposition process In Table 1 the typical values of materials characteristics used in our studied BAW filter show that AlN does not ldquoseemrdquo to be the best candidate for obtaining good electrical performances of filtering Nevertheless it remains the only piezoelectric material able to fulfill the microelectronic requirements of integration and technologies processes 1 To whom any correspondence should be addressed


ccopy 2010 IOP Publishing Ltd 1


AlN (piezoelectric)

Mo (electrodes)



Silicon (Wafer)

Density p m [kgm3]

2200 10220 19300 2200 2340


420 276 400 74 165


10-3 34x10-3 34x10-3 34x10-3 2x10-3


33 [pFm-1] 95


2x10-2


156


205




5 501 502 503 504 505 506

x 105

101

102

103

104

105

106

107

108

109

Frequency (Hz)

Qua

rtz Im

peda

nce

Mod

ule



2


2222

2

22

q

CR)CCLC1(

)C1L(R

)j(Z


KHz292503LC2

1Fs







Ejklmjk EeSCT




D0)D(div 3

3





3


dynamic z

Tu

zT

tu

amF 33

232

32

ext

and z

uS 3

3


)

2h(

)2htan(

k1Cj1

)(I)(V)(Z 2

t0

with hA

C 330



2332

t ce

k

is



2 25 3 35 4 45 5 55 6 65 7

x 109

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Ii

mpe

danc

e M

odul

e






4

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600








5







6








7





8














9






10


AlN (piezoelectric)

Mo (electrodes)



Silicon (Wafer)

Density p m [kgm3]

2200 10220 19300 2200 2340


420 276 400 74 165


10-3 34x10-3 34x10-3 34x10-3 2x10-3


33 [pFm-1] 95


2x10-2


156


205




5 501 502 503 504 505 506

x 105

101

102

103

104

105

106

107

108

109

Frequency (Hz)

Qua

rtz Im

peda

nce

Mod

ule



2


2222

2

22

q

CR)CCLC1(

)C1L(R

)j(Z


KHz292503LC2

1Fs







Ejklmjk EeSCT




D0)D(div 3

3





3


dynamic z

Tu

zT

tu

amF 33

232

32

ext

and z

uS 3

3


)

2h(

)2htan(

k1Cj1

)(I)(V)(Z 2

t0

with hA

C 330



2332

t ce

k

is



2 25 3 35 4 45 5 55 6 65 7

x 109

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Ii

mpe

danc

e M

odul

e






4

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600








5







6








7





8














9






10


2222

2

22

q

CR)CCLC1(

)C1L(R

)j(Z


KHz292503LC2

1Fs







Ejklmjk EeSCT




D0)D(div 3

3





3


dynamic z

Tu

zT

tu

amF 33

232

32

ext

and z

uS 3

3


)

2h(

)2htan(

k1Cj1

)(I)(V)(Z 2

t0

with hA

C 330



2332

t ce

k

is



2 25 3 35 4 45 5 55 6 65 7

x 109

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Ii

mpe

danc

e M

odul

e






4

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600








5







6








7





8














9






10


dynamic z

Tu

zT

tu

amF 33

232

32

ext

and z

uS 3

3


)

2h(

)2htan(

k1Cj1

)(I)(V)(Z 2

t0

with hA

C 330



2332

t ce

k

is



2 25 3 35 4 45 5 55 6 65 7

x 109

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Ii

mpe

danc

e M

odul

e






4

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600








5







6








7





8














9






10

2 25 3 35 4 45 5 55 6 65 7

x 109

10-2

10-1

100

101

102

103

104

105

106

Frequency (Hz)

Res

onat

or Im

peda

nce

Mod

ule

A=100 A=250 A=600








5







6








7





8














9






10







6








7





8














9






10








7





8














9






10





8














9






10














9






10






10

Piezoelectric resonators for RF and microwave filters

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Transcript of Piezoelectric resonators for RF and microwave filters