Session: 4B THIN FILM BAW FILTERS Chair: K. Lakin TFR Technologies. 4B-1 1:30 p.m.

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1 plates of lithium niobate and potassium niobate at different values of sheet conductance of layer. These dependencies showed that hybridization appears when sheet conductance of layer (σ) exceeds some critical value σ cr ), the magnitude of which changes in wide range and depends on material and plate orientation. For example, for aforementioned hybrid pair A 0 - SH 0 in potassium niobate σ =10 3 cr S. If σ<σ cr modes are not coupled, i.e. their dispersion curves do not repulse. When σ = σ cr there appears repulsion, the degree of which increases with increase of σ and reaches maximum at σ. This conclusion was also confirmed for hybrid modes of higher order propagating in lithium niobate plates. For example, a symmetric wave S 1 and shear-horizontal wave SH 2 form hybrid mode for parameter hf 6000m/s with σ cr =10 6 S. It has been found that degree of repulsion of dispersion curves increases with increase of electromechanical coupling coefficient of waves. This work was supported by a grant from RFBR # a. Session: 4B THIN FILM BAW FILTERS Chair: K. Lakin TFR Technologies 4B-1 1:30 p.m. FBAR RX FILTERS FOR HANDSET FRONT-END MODULES WITH WAFER LEVEL PACKAGING K. WANG*, M. FRANK, P. BRADLEY, R. RUBY, W. MUELLER, A. BAR- FKNECHT, and M. GAT, Agilent Technologies, Inc. Corresponding kun wang@agilent.com To reduce handset component count, RF filters are being integrated into frontend modules (FEMs), mostly based on LTCC substrates. With this trend, size and performance of the filter over temperature become important factors compared to its discrete counterpart. AlN-based FBAR filters are attractive for FEMs applications due to its low temperature coefficient. This paper presents balanced receiver filters based on FBAR technology for GSM-based FEMs application. The balanced input/output are achieved through lattice configuration. The filter is hermetically packaged at the wafer level to reduce size and cost. The typical size of the filter is 0.7x0.8x025um. The worst close band rejection is 17 db and the worst insertion loss in the passband is 3 db. The wafer level package is realized with wafer bonding technique. No performance degradation is observed after packaging. Details of device design and performance will be discussed. The support from Agilent FBAR fabrication team is appreciated. 39

2 4B-2 1:45 p.m. FABRICATION OF 5GHZ BAND FILM BULK ACOUSTIC WAVE RESONATOR USING ZNO THIN FILM R. KUBO*, H. FUJII, H. KAWAMURA, M. TAKEUCHI, K. INOUE, Y. YOSHINO, T. MAKINO, and S. ARAI, Murata Manufacturing Co., Ltd. Corresponding We successfully fabricated a 5GHz band thin film bulk acoustic wave (BAW) resonator using ZnO thin film, in which we designed to use secondary harmonics in Al/ZnO/Al/Al 2 O 3 /SiO 2 structure to improve its performance and constructive stiffness. Membrane structure was formed by Si anisotropic etching from backside. Al thin films were prepared by electron beam evaporation as the top and the bottom electrodes. The ZnO thin film with a thickness of about 500nm adjusted to resonance frequency of 5GHz was prepared by RF magnetron sputtering. Deposition conditions of ZnO thin film were optimized for c-axis orientation, i.e. substrate temperature of 200degreeC, and gas pressure of 0.6Pa. The BAW resonator consists of both the ZnO thin film with negative temperature coefficient of sound velocity and the SiO 2 thin film with positive one, so that temperature coefficient of frequency of the BAW resonator can be controlled by the thickness ratio of ZnO and SiO 2 thin films. The Al 2 O 3 thin film that has a tensile stress about 300MPa was combined with both ZnO and SiO 2 thin films with compressive stress of about -100MPa to prevent the membrane from destruction and flexure. Through the control of total membrane stress, large sized membrane (maximum size was µm) with a thickness of 1000nm could be fabricated. In evaluation of the BAW resonators fabricated by these processes, a quality factor (Q factor) of 430 and an effective electromechanical coupling coefficient (kteff ) of 3.1% were obtained at the frequency 2 of 5.3GHz. Frequency characteristics of 5GHz band ladder type piezoelectric filter were calculated by a circuit simulator using the resonator parameters; a minimum insertion loss and a bandwidth at 3dB were estimated to be 1.8dB and 94MHz, respectively. 4B-3 2:00 p.m. HIGH C-AXIS-ORIENTED ALN FILM USING MOCVD FOR 5GHZ-BAND FBAR FILTER C. M YANG*, K. UEHARA, S. K. KIM, S. KAMEDA, H. NAKASE, and K. TSUBOUCHI, Research Institute of Electrical Communication, Tohoku University. Corresponding cmyang@riec.tohoku.ac.jp We have developed a poly-crystalline c-axis oriented aluminium nitride (AlN) film on Mo/SiO 2 /(100)Si structure for film-bulk-acoustic resonator (FBAR) filter using metal-organic-chemical-vapor deposition (MOCVD). The FBAR filter can be used as a RF band pass filter for a wireless local area network (WLAN) using 40

3 the orthogonal-frequency-division-multiplexing (OFDM) in the 5GHz band, IEEE a. The RF band pass filter for IEEE a is required with the conditions of low insertion loss at the center frequency of 5.2GHz, and the bandwidth of more than 100MHz. We have evaluated a 7th-order ladder-type filter the filter performance using Butterworth-Van Dyke (BVD) model of FBAR., it is aimed that the insertion loss depends on the area of the resonance and the frequency bandwidth depends on the electromechanical coupling constant (K 2 ) From the simulation result, the K 2 needs above 6% for more than 100MHz. According to the previous report that K 2 of 6% corresponds to FWHM of 4 degrees from Naik et al., our target full width at half maximum (FWHM) of piezoelectric thin film AlN was determined as the value of less than 4 degrees. It is difficult to realize the AlN FWHM of less than 4 degrees with sputtering method. It is expected to deposit AlN film of less than 4 degrees using MOCVD, whose mechanism is thermal chemical reaction. AlN film has been grown on Mo/SiO 2 /(100)Si substrate using MOCVD with temperature of 1050 degrees C, pressure of 20torr and V-III ratio of Before deposition, 1100 degrees C, H 2 annealing process was carried out for 20minutes. The deposited AlN film has been evaluated by X-ray diffraction (XRD). It is confirmed that the deposited film is the poly-crystalline c-oriented film. Measured FWHM is 2.98 degrees. The simulation shows that the ladder-type FBAR filter using the deposited film with (0002)AlN FWHM of 2.98 degrees can be designed with the insertion loss of 1.386dB at center frequency of 5.2GHz and the bandwidth of 146MHz. It is recognized that our AlN film is satisfied with the filter specification for IEEE a. The remarkable achievement of the deposited film with (0002)AlN FWHM of 2.98 degrees promises the success of the FBAR filter for the WLAN using the OFDM system in the 5GHz band, IEEE a. 4B-4 2:15 p.m. THIN FILM BULK ACOUSTIC WAVE DEVICES FOR APPLICATIONS AT 5.2 GHZ G. G. FATTINGER*, J. KAITILA, and R. AIGNER, Infineon Technologies AG, Munich, Germany. Corresponding gernot.fattinger@infineon.com Today s wireless communication market shows a growing demand for filter devices suitable for a frequency range well above 2 GHz. Current SAW filter technologies approach increasing difficulties when it comes to the fabrication of interdigital transducers working at considerably higher frequencies. On the other hand, the only remaining alternative to discrete filters are ceramic devices, which are in turn bulkier than potential SAW devices would be. Infineon Technologies has started volume manufacturing of Bulk Acoustic Wave (BAW) filters for GSM mobile handset applications in mid In this paper the feasibility of Wireless-LAN band filters around 5.2 GHz is discussed. Latest results from manufactured BAW resonators show a sufficient performance in order to fulfill the Wireless-LAN communication requirements. The manufactured single resonators show quality factors Q of about 900 and a piezoelectric coupling factor 41

4 k 2 of about 6.0 %. The technology used is based on a solidly mounted resonator (SMR) approach incorporating a W-SiO 2 acoustic mirror. C-axis oriented aluminum nitride is used as the piezo layer. At high frequency the quality of the crystal growth becomes a more crucial issue in order to create resonators with a high coupling coefficient. Both single ended and balanced filter devices have been fabricated using ladder and lattice topology, respectively. 4B-5 2:30 p.m. SOLIDLY MOUNTED BAW FILTERS FOR 8 GHZ BASED ON ALN THIN FILMS R. LANZ* and P. MURALT, Swiss Federal Institute of Technology, Lausanne, Switzerland. Corresponding roman.lanz@epfl.ch Bulk acoustic wave resonators based on piezoelectric thin films show promising potential as silicon and GaAs compatible integrated or discrete solutions for RF bandpass filters at frequencies above 2 GHz. The acoustic isolation from the substrate is for instance achieved by a set of quarter wavelength thick layers between resonator film and substrate, thus forming a solidly mounted resonator (SMR). This paper presents the fabrication and characterization of SMR passband filters on silicon substrates based on piezoelectric AlN thin films and working near 8 GHz. Ladder filters with 3 to 14 resonators were investigated experimentally and theoretically. The SMR reflector stack consists of 5 pairs of AlN/SiO2 layers. This large number of layers guarantees a broad reflection band. The AlN thin films were deposited by pulsed dc sputtering. Simulation calculations of the transfer function yield 3 db bandwidths of 3.5 to 4.5% and insertion losses of 2 to 3 db, neglecting losses in electrodes. The fabricated versions utilize Pt or Mo bottom and Al top electrodes. The frequency tuning of the shunt resonators was performed by an additional loading, i.e. by increasing the top electrode thickness. Molybdenum based SMR are theoretically better suited than Platinum based SMR for frequencies above 5 GHz where the individual films constituting the resonator become very thin. Molybdenum electrodes offer a lower electrical resistivity than platinum and superior acoustic properties. The piezoelectric coefficient d 33 of AlN thin films deposited on Mo yields 3.1 pm/v compared with 4.0 pm/v for Pt. The highest measured coupling coefficient is thus achieved with platinum electrodes. Pt based resonators show coupling coefficients kt 2 of 5.2% and quality factors of 360, the corresponding Mo SMR exhibit coupling coefficients of 4.5% and quality factors of 440. Fabricated SMR ladder filters with the pass-band at 8 GHz exhibit -3.2dB, -5.5dB and -7.5dB insertion loss for 1, 2, respectively 3 pi-sections, and an out-of-band rejection of -13dB, -30dB and -35dB. The 3dB bandwidth is 244MHz (3.1%), 224MHz (2.8%), respectively 194MHz (2.4%). This work was supported by the European IST program (project MEDCOM) and the Swiss Office for Education and Research 42

5 4B-6 2:45 p.m. LOW-LEVEL EFFECTS IN SBARS AND THEIR APPLICATION TO DEVICE OPTIMISATION H. P. LOEBL* 1, R. F. MILSOM 2, C. METZMACHER 1, A. TUINHOUT 3,P. LOK 3, and F. VAN STRATEN 3, 1 Philips Research Laboratories, Aachen, Germany, 2 Philips Research Laboratories, Redhill, U.K., 3 Philips Discrete Semiconductors, Nijmegen, The Netherlands. Corresponding Hans-peter.loebl@philips.com RF filters based on solidly-mounted thin-film bulk acoustic wave resonators (SBARs) are of strong interest for wireless applications (1,2). The SBAR configuration comprises piezoelectric layer, top and bottom electrode layers, Braggreflector with alternate layers of high and low mechanical impedance, and substrate (typically silicon). Optimum resonator design can lead to behaviour very close to that predicted by the simple Butterworth-Van Dyke equivalent circuit model. However, understanding the many very low-level effects, which do not necessarily impinge strongly on resonator or filter performance in a given application, can be used to further improve subsequent designs. Here two approaches to understanding these small effects are presented. The first approach uses the 1D Novotny-Benes (3) model to explain three classes of weak thickness extensional (TE) mode disturbances observed in typical resonators: harmonics of the fundamental mode, fundamental and harmonics of parasitic resonators, and harmonics of the vibration of the entire structure including the substrate. The parasitic resonators are formed by a combination of interconnect metallisation, piezoelectric layer and reflector, and they are excited weakly by the stray electric fields. The substrate vibrations are strongest (but still weak) at frequencies removed from the Bragg-reflector reflection bands. It is shown here how the frequency-domain pattern of the disturbances can be used to determine more accurate values of material data including layer thickness. The second approach is mainly experimental for the moment and aimed at optimising those aspects of design, which cannot be taken into account by the above model. This experimental study addresses several layout-related issues, such as the role played by resonator area and shape including aspect ratio, corner and edge definition, and also interconnect layout. The effects of these parameters on resonator performance will be described and their implication for filter design will be discussed. (1) K.M.Lakin et. al, IEEE Trans., MTT, Vol. 43, p.2933, 1995 (2) H-P. Loebl et. al., Proc IEEE Ultrasonics Symposium, p.897, Munich 2002 (3) H. Novotny et. al., J. Acoust. Soc. Am., Vol. 82, p.513, 1987 Parts of this work was supported by the EU (Project MEDCOM IST 11511) 43