Eiju Komuro

Thin-film bulk acoustic resonators and filters using ZnO and lead-zirconium-titanate thin films

This paper presents the findings of a design, modeling, and fabrication study of ZnO and PbZr/sub 0.3/Ti/sub 0.7/O/sub 3/ thin-film bulk acoustic resonators and filters. Measurements of the high-frequency responses of ZnO resonators having different area are used to develop an acoustic model that accurately represents resonator impedance data. The models are also used to interpret S-parameter measurements on thin-film PbZr/sub 0.3/Ti/sub 0.7/O/sub 3/-based resonators and a value for the effective coupling coefficient deduced. ZnO and PbZr/sub 0.3/Ti/sub 0.7/O/sub 3/ ladder filters were designed based on measured impedance data from single resonators. Ladder filters based on PbZr/sub 0.3/Ti/sub 0.7/O/sub 3/ have been fabricated for the first time. It is shown that the high coupling coefficient in PbZr/sub 0.3/Ti/sub 0.7/O/sub 3/ leads to bandwidths in the range 100/spl sim/120 MHz at a center frequency of 1.6 GHz, larger than the bandwidths of ZnO-based filters.

Film bulk acoustic resonator filters with a coplanar waveguide

Multiple thin film bulk acoustic resonators (10, 11) configured in series (10) and parallel (11) within a coplanar waveguide line structure provides a compact ladder filter. The resonators (10, 11) are formed over an opening (28) in a substrate (20) and connected to associated circuitry by one or more transmission lines formed on the substrate (20). The arrangement of the resonators (10, 11) between the ground and signal lines of a coplanar line structure provides a means of minimising the area of the filter. Embedding a ladder filter within the coplanar transmission line structure eliminates the need for wire bonds, thus simplifying fabrication. Embodiments for 2×2, and hither order filters are described.

PZT thin film bulk acoustic wave resonators and filters

Thin Film Bulk Acoustic Wave Resonators (FBAR) using Lead Zirconate Titanate (PZT) thin films as the piezoelectric active layer are favourable for voltage controlled oscillators and wide band filters due to the large electro-mechanical coupling coefficient of PZT. This paper reports the fabrication process and results of PZT FBARs and filters. The temperature coefficient and bias voltage effect are also presented.

High frequency thin film ferroelectric acoustic resonators and filters

Abstract There is a need for more compact filters that are able to meet the needs of the next generation of mobile phone operating in the 1-2GHz frequency band. These filters are required to have low insertion loss, high Q, low sensitivity to temperature and in some cases wider bandwidths than those currently available. In this paper we review some of our recent work on the application of PZT (sol-gel PbZr0.3Ti0.7O3) as the piezoelectric layer in FBARs (thin Film Bulk Acoustic Resonators) and FBAR filters. The high electromechanical coupling coefficients in PZT offer the possibility of realising wide band-width filters. It is shown possible to incorporate PZT into a FBAR structure previously designed for piezoelectric ZnO by the simple addition of a TiO2 layer that avoids the crazing that occurs when PZT is deposited directly on SiNx. PZT FBAR filters of extremely small area (<300μ m2) can be produced. Preliminary measurements suggest that the resonance frequencies in PZT FBARs are only weakly temperature dependent. The advantages and disadvantages of using PZT in FBAR structures is discussed.

Edge supported ZnO thin film bulk acoustic wave resonators and filter design

Edge supported ZnO thin film bulk acoustic wave resonators of different areas were fabricated using both Al and Au/Cr electrodes and their high frequency response characteristic characterized by S-parameters measurement. The development of an equivalent circuit for the composite resonator leads to an understanding of the dependency on device area and electrode material. The use of varying resonator area in ladder filter design is discussed.

Effect of electrodes on GHZ ZnO thin film bulk-acoustic-wave resonator

Abstract Thin film bulk acoustic resonators (FBARs) were prepared with ZnO films using Al and Cr/Au electrodes. ZnO films were deposited by RF sputtering. Al and Cr/Au electrodes were prepared by DC sputtering and thermal evaporation respectively. S parameters were measured with a network analyzer. From TEM images, it is apparent that there are some defects on ZnO with Al electrode while no defects are detected on ZnO with Cr/Au. Also, an intermediate layer is observed between ZnO and Al but nothing between ZnO and Au. As a result of those differences, the resonant frequency, the width between series and parallel frequency and the value of S11 between peak and valley, are different between the FBAR samples with Al or Cr/Au even though both FB AR samples have the same thickness of ZnO.

Nonstoichiometric Properties of Bi-Substituted Yttrium Iron Garnet Sputtered Films

Structural, magnetic and magnetooptical properties of nonstoichiometric Bi-substituted yttrium iron garnet (Bi-YIG) films have been studied in terms of Fe concentration. The garnet films were prepared by rf sputtering using targets which had various Fe contents. In the wide range of Fe content from about 3.9 to 5.4, garnet phases were obtained at an annealing temperature of 650° C. For the Fe contents ranging from 1.9 to 5.1, saturation magnetization increased linearly, and beyond the Fe content of 5.1, it dropped sharply. By considering the magnitude of Faraday rotation of the garnet phase formed in the films (θ F/M s) and Curie temperature, it is expected that the Bi concentration in the garnet-phase crystallites in the prepared films increases as Fe content increases. It was observed, in energy dispersive X-ray spectrometry (EDX) and secondary ion mass spectrometry (SIMS) analyses, that the excess Bi ions in low-Fe-content films concentrated at the surface, near the film-substrate interface, at the edge of the films and at grain boundaries.

High Frequency Thin Film Acoustic Ferroelectric Resonators

Both ZnO and PZT Thin Film Bulk Acoustic Resonator filters were fabricated, tested and modeled in this study. The development of an accurate Mason model allows the effect of particular parasitic components on the microwave s-parameters in the region of the series and parallel resonances to be identified. The parasitic components that limit the performance of our ZnO and PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filters are analysed. From an analysis of PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator measurements values for the longitudinal acoustic velocity and electromechanical coupling coefficient can be derived. Measured PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filter responses confirm that the larger electromechanical coupling coefficients in this material compared to ZnO give wider filter band-widths. INTRODUCTION: There is a great commercial interest in decreasing the size of microwave 1-3 GHz filters to allow more functions to be incorporated in future mobile phones [1]. Presently there are two types of filters being developed to meet this need, ceramic filters based on electromagnetic modes and acoustic filters. The typical dimensions of both types of microwave filters are similar to the wavelength at the operating frequency. By using the piezoelectric effect to generate acoustic modes wavelengths and dimensions can be reduced by about four orders of magnitude compared to electromagnetic modes. There are two types of acoustic filters considered contenders for future generations of mobile phones, both based on piezoelectric materials: surface acoustic wave (SAW) devices and Thin Film Bulk Acoustic Resonators (FBAR). The piezoelectric effect has been widely used in bulk acoustic resonators, such as single crystal quartz for many years. Recently by careful thinning or etching the quartz plate operation up to 200 MHz can be achieved but the low acoustic velocity of quartz and the resulting fragility of thinned substrates means that this technology cannot progress to higher frequencies. In SAW devices that direction of propagation is in the plane of the wafer while for FBAR it is perpendicular to a substrate surface. For FBAR operation the piezoelectric film thickness must be of the order of the acoustic wavelength at the desired operating frequency. In this paper we compare two candidate thin film piezoelectric materials, ZnO and PbZr0.3Ti0.7O3 (PZT) that have different acoustic properties. Although there has been considerable previous work on ZnO FBAR [2] and ZnO FBAR filters [3] there has only been a few reports on PZT FBARs [4]. In particular, the electromechanical coupling coefficients Mat. Res. Soc. Symp. Proc. Vol. 655