Modeling of a Tunable Film Bulk Acoustic Resonator and Bandpass Filter Design by using Ferroelectric Film

Abstract: Filters having smallest size, high power handling capability, high Q factor, operating frequency up to several gigahertz’s (GHz) and low cost are the demand of the market to use in front end wireless/radio communication systems. In this regard several filter technologies have been introduced and utilized commercially. The increasing demand of such type of filters has opened a new challenge for filter designers. The purpose of this thesis is to design of a Tunable Bandpass Filter based on Barium Strontium Titanate (BSTO) Ferroelectric Film. A single Film bulk acoustic resonator (FBAR) is measured. MASON and Butterworth Van-Dyke (BVD) model are studied and implemented to reproduce the measurements. Simulations are performed by using the Advance Design System (ADS) by Agilent technologies. Simulations and measured data are used to exactly extract the physical and electrical parameters of a single FBAR. FBAR filter topologies are being studied and implemented. Ladder filter topology is selected to design the bandpass filter. The extracted physical and electrical parameters are used to investigate the performance of the filter. The area and the top electrode thickness of the series and shunt resonators are optimized to achieve the bandpass response with maximum out of band rejection, minimum insertion loss and sharper roll off near the pass band. A 3rd order T-type bandpass filter for 5GHz applications is designed. The insertion loss of -2.925 dB is achieved. The filter exhibits the 3dB bandwidth of 176 MHz and out of band rejection of -10 dB. DC bias of 0-25 V is used to analyze the tuning behavior of the filter.  The electromagnetic co-simulation is also done in momentum to analyze the parasitic effects between the resonators. The results show the good agreement between the schematic and momentum simulation. Layout and masks are also designed on a 10'10 mm wafer that will be used later to fabricate the filter and further investigations.