Jyrki Kaitila

Bio: Jyrki Kaitila is an academic researcher from Infineon Technologies. The author has contributed to research in topics: Resonator & Reflector (antenna). The author has an hindex of 11, co-authored 25 publications receiving 509 citations. Previous affiliations of Jyrki Kaitila include Avago Technologies.

Optimization of acoustic dispersion for high performance thin film BAW resonators

Abstract: The dominant trend in mobile communication is the reduction of cost and size of the components. Bulk-Acoustic-Wave (BAW) filters are ideally suited to replace conventional RF-fil- ters for all major cell phone standards such as GSM, CDMA and WCDMA. In order to achieve excellent filter characteristics it is necessary to get rid of the so called "spurious modes". These are undesired resonances due to the finite boundaries of the device. The suppression scheme proposed by us in earlier publications only works if the layer stack fulfills some important requirements. The key issue here is to understand the concept of acoustic layer stack dispersion. It will be shown, that the overlap scheme can only work with a certain dispersion type. For a SMR (surface mounted resonator) it can be shown, that certain stack modifications can influence the dispersion in a desired way, while maintaining most of the other resonator performance parameters. Simulations and interferometrical measurements will be shown, proving this con- cept. It will be shown, that without this stack modification a clean response of a high-Q SMR-type BAW resonator is virtually impos- sible to achieve. BAW; FBAR;Spurious modes; Acoustic dispersion;

Optimization of acoustic mirrors for solidly mounted BAW resonators

Abstract: The overall performance of bulk acoustic wave (BAW) filters is dominated by the effective coupling coefficient and the quality factor of the constituting BAW resonators. Whereas the effective coupling coefficient and its dependency on the layer stack is quite accurately modeled with a simple one-dimensional acousto-electric model (e.g. Masonstransmission line model), the prediction and optimization of the resonators quality factor - particularly for solidly mounted resonators (SMR) - completely fails with this model: whereas a calculation of the acoustic reflectance of a standard quarter-wavelength mirror stack leads to theoretical Q-factors well above 10000, experimental SMR devices with this type of mirror show values of typically well below 1000. This discrepancy is commonly explained by either visco-elastic loss in the materials and/or laterally leaking waves leaving the active resonator area. However, we have found a new, far more important loss mechanism relating to shear waves generated in the device. These waves can be created by injection from the resonators border area as well as by reflection/refraction of longitudinal waves at non-perpendicular angle of incidence to a material interface. In this paper, a quantitative methodology for the optimization of the acoustic mirror layer stack will be proposed. The influence of the mirror structure on the trapping of both longitudinal and shear wave energy will be discussed based on this very simple approach. Trade-offs with respect to the other important device parameters, such as effective coupling coefficient, temperature coefficient of frequency (TCF) and purity of the electrical response, are analyzed. The usefulness of this approach for the optimization of resonator Q-values will be proven by experimental results demonstrating Q-factors of 1500 and higher.

Acoustic reflector for a BAW resonator providing specified reflection of both shear waves and longitudinal waves

Abstract: A BAW resonator includes a piezoelectric layer, a first electrode, a second electrode, a substrate, and an acoustic reflector disposed between the substrate and the second electrode The acoustic reflector has a plurality of layers A performance of the acoustic reflector is determined by its reflectivity for a longitudinal wave existing in the BAW resonator at the resonance frequency of the BAW resonator and by its reflectivity for a shear wave existing in the BAW resonator at the resonance frequency of the BAW resonator The layers of the acoustic reflector and layers disposed between the acoustic reflector and the piezoelectric layer are selected, with reference to their number, material, and thickness, such that the transmissivity for the longitudinal wave and the transmissivity for the shear wave in the area of the resonance frequency is smaller than −10 dB

Single-to-balanced filters for mobile phones using coupled resonator BAW technology

Abstract: The coupled resonator filter (CRF) is a new type of bulk-acoustic-wave (BAW) device in which two piezoresonators are stacked on top of each other in a way that a certain degree of acoustic interaction occurs. Experimental results of single-ended and mode-converting CRF for GSM applications also featuring impedance conversion, operating at 1.8 GHz and manufactured at Infineon Technologies are presented. For the balanced port, those results demonstrate excellent amplitude- and phase-imbalance, obtained by a very symmetrical design. Also, a method for suppression of spurious resonances is demonstrated. Moreover, the latest results confirm that unwanted passbands can be overcome by modification of the acoustic mirror. Furthermore, the temperature coefficient of frequency (TCF) has been measured. Due to the compensating effect of SiO/sub 2/ in the CRF stack the values obtained are exceptionally small.

Thin-film BAW filter, and a method for production of a thin-film BAW filter

Abstract: A thin-film BAW filter has at least one CRF section and at least one ladder or grating filter section, with the CRF section having at least two coupled resonators, with the CRF section and the ladder or grating filter section being integrated on a common substrate, in order to produce a thin-film BAW filter. In a method for production of a thin-film BAW filter, having at least one CRF section and at least one ladder or grating filter section, the CRF section has at least two coupled resonators and the CRF section and the ladder or grating filter section are integrated on a common substrate.

Recent Progress in Materials Issues for Piezoelectric MEMS

Abstract: Piezoelectric materials play a crucial role in a large number of devices and applications modern society would not like to miss. Mobile phones and ultrasonic imaging are just the most prominent ones. Since two decades, miniaturization of mechanical devices in silicon technology is a major research direction in engineering known under name of MEMS, which stands for micro-electro-mechanical systems. Piezoelectricity fits very well into this concept and was expected right from the beginning to play its role in MEMS. The breakthrough was made with RF filters in mobile phones working on the principle of standing thickness waves in AlN films. What counts here is acoustic quality and stability. The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3 gave more problems in processing, and requires more patience to meet requirements and needs for a mass applications. It seems, however, that the breakthrough is imminent. This article attempts to give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications.

11E-2 Review and Comparison of Bulk Acoustic Wave FBAR, SMR Technology

Abstract: Since FBAR (free-standing bulk acoustic resonator) and solidly mounted resonator SMR-BAW devices came onto the scene as serious competition to the entrenched SAW technology (for cell phone applications), there has been much speculation and discussion as to which of these two "disruptive" technologies is the superior one. The one fundamental difference between SMR-BAWs and FBARs, is the means by which the acoustic energy is trapped. For FBAR the air/crystal interface on both faces of the resonator ensures that the main mode of interest (the thickness extensional mode, TE1) is appropriately trapped In the SMR-BAW, Bragg reflectors underneath the resonator, effectively trap this mode. This addition of a Bragg reflector will degrade the effective coupling coefficient as well as creating additional Q loss mechanisms. The science of improving Q must focus on the edges of the resonator for FBAR, while for SMR devices, both the edges and the vertical design of the Bragg reflector must be optimized. That said, compared to conventional SAW technology, both BAW and FBAR provide temperature stability, power handling capability, good ESD (electro-static discharge), and -most important-high Q's. One of the key drivers for the success (in terms of high Q and coupling coefficients) of both BAW and FBAR was the exploitation of AlN as the piezoelectric material and high acoustic impedance, electrode materials such as molybdenum, tungsten or ruthenium. These are the technology differentiators that create the inherent superiority of BAW/FBAR over both the conventional SAW technology and the newer and enhanced flavors of SAW. The need for large coupling coefficients and high Q's becomes an important value proposition as one considers the proliferation of new bands and services.

Acoustic Wave Filter Technology–A Review

Abstract: Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

RF bulk acoustic wave filters for communications

Abstract: Background and History. Resonator and Filter Topologies. Baw Device Basics. Design and Fabrication of BAW Devices. FBAR Resonators and Filters. Comparison with SAW Devices. Films Deposition for BAW Devices. Characterization of BAW Devices. Monolithic Integration. System-in-Package (SiP) Integration. Index.

Bulk acoustic wave RF technology

Abstract: In this article, we will provide an overview of BAW filter technology by discussing comparison between BAW and SAW RF filter technologies, working principles of BAW resonator and filter, BAW resonator key performance parameters, comparison between free-standing bulk acoustic resonator (FBAR) and solidly mounted resonator (SMR) technologies, status of BAW resonator design and models, BAW filter manufacturing challenges, and future BAW technology improvement directions.