BAW notch filter for WiMAX applications

Als darrers anys la necessitat de connectar-se a internet des de qualsevol lloc s'ha incrementat exponencialment sobretot de manera inalàmbrica. Degut al finit espectre radioelèctric es tendeix a aprofitar totes les franges freqüencials d'aquest convivint diferents sistemes en franges properes podent induir-se interferències mútuament. Per evitar aquestes interferències es requereix de filtres a tots els dispositius els quals aïllin un sistema del adjacent. En aquest projecte es dóna una solució al cas concret de la convivència entre els sistemes Wi-Fi y WiMAX eliminant la banda Wi-Fi interferent en sistemes WiMAX. Aquesta solució consisteix en el disseny d'un filtre banda eliminada d'ordre 3 implementat mitjançant tecnologia BAW a partir de l'estructura y especificacions d'un filtre comercial. A més també es fa un petit estudi per veure si seria interessant una millora en els processos de fabricació del filtre per part del fabricant.En los últimos años la necesidad de conectarse a internet en cualquier lugar se ha incrementado exponencialmente sobre todo de manera inalámbrica. Debido al finito espectro radioeléctrico se tiende a aprovechar cada franja frecuencial de éste conviviendo diferentes sistemas en franjas cercanas pudiendo inducirse interferencias mutuamente. Para evitar estas interferencias se requiere de filtros en todos los dispositivos los cuales aíslen un sistema de otro adyacente. En este proyecto se da una solución al caso concreto de la convivencia entre los sistemas Wi-Fi y WiMAX eliminando la banda de Wi-Fi interferente en sistemas WiMAX. Está solución consiste en el diseño de un filtro banda eliminada de orden 3 implementado mediante tecnología BAW a partir de la estructura y especificaciones de un filtro comercial. Además también se hace un pequeño estudio para ver si sería interesante una mejora en los procesos de fabricación del filtro por parte del fabricante.In the recent years the need of being connected to internet from everywhere has grown exponentially specially in a wireless way. In due to the finite radioelectric spectrum the trend is to use all the frecuencial bands of it coexisting different systems in nearby bands that might produce interferences between them. To avoid these interferences the presence of filters in every device is needed to isolate the different systems from the system nearby. This paper proposes a possible solution in the specific case of the coexistence between Wi-Fi and WiMAX systems removing the Wi-Fi band that interferes with WiMAX systems. This solution consists on the design of a stop-band filter of third order using BAW technology implementation starting from the structure and specifications of a commercial filter. A short study on the fabrication parameters is also done to watch if there is an interesting point on the improvement of the fabrication procedures

Optimization and design of radio frequency piezoelectric MEMS resonators

Radio frequency (RF) microelectromechanical system (MEMS) resonators employing Lamb waves propagating in piezoelectric thin films have recently attracted much attention since they combine the advantages of the bulk acoustic wave (BAW) and surface acoustic wave (SAW) technologies: high phase velocity and multiple frequencies on a single chip. In particular, aluminum nitride (AlN) resonators based on fundamental symmetric (S0) Lamb mode have shown great promise because they can offer high phase velocities (10,000 m/s), low dispersive phase velocity characteristic, small temperature-induced frequency drift, low motional resistance, and monolithic integration compatibility with complementary metal–oxide–semiconductor (CMOS). However, there are still a few outstanding technical challenges, including spurious modes suppression, quality factor (Q) enhancement, frequency scalability, and electromechanical coupling improvement. These issues obstruct the wide deployment and commercialization of AlN Lamb mode resonators. This dissertation presents comprehensive investigations and solutions to these issues. This thesis is organized as follows: Chapter 1 gives a brief introduction of the basics on piezoelectric MEMS resonators and their promising applications. Chapter 2 first investigates the various available Lamb wave modes in AlN and then identifies the S0 mode as the promising resonator solution to overcome several challenges associated with SOA. Chapter 2 also discusses several outstanding challenges with S0 devices, including spurious mode suppression, Q enhancement, scaling resonant frequency, and enlarging fractional bandwidth. In response, Chapters 3-7 address these outstanding challenges by developing new designs and models, resorting to new acoustic mode, and incorporating new piezoelectric material. More specifically, Chapter 3 proposes two techniques to suppress the spurious modes in the responses of S0 resonators, namely mode conversion and mode shifting. Chapter 4 address the challenge of a conventionally vague question of reflection at the interface between released and unreleased regions in S0 resonators, and then demonstrates Q enhanced resonators with defined released regions achieved by a sandbox process. Chapter 5 first characterizes the S1 Lamb mode and optimizes its resonator configuration. A high-frequency S1 resonator at 3.5 GHz with a coupling of 3.5% is fabricated and demonstrated. Chapter 6 presents a hybrid filtering topology with a mode conversion AlN S0 resonator and lumped elements for widening the bandwidths of resonator-based filters. Chapter 7 proposes lithium niobate (LiNbO3) multilayered resonators with large electromechanical coupling, structure robustness, and good temperature stability. The analysis of Bragg reflectors, resonator simulation, stress control, fabrication, and measurements are covered in this chapter