Kuang-woo Nam

Ultra-miniature monolithic FBAR filters for wireless applications

This paper presents ultra-miniature monolithic transmit (Tx) filters for 1900 MHz PCS using thin film bulk acoustic resonators (FBAR) technology. Conventional FBAR filters often include multiple tuning inductors, which have prevented the miniaturization and the monolithic integration of the filters. However, the developed filter has a novel circuit configuration using a single integrated inductor to minimize the size. The FBAR block consists of seven FBARs electrically coupled in a ladder topology. A meander type inductor is used for simplicity of fabrication processes and is optimized to increase the receive (Rx) band rejection performance. The filters are hermetically packaged at a wafer-level, which enables us to achieve a size of 1.0 mm /spl times/ 1.0 mm /spl times/ 0.7 mm. The packaged filters showed high performance with insertion loss less than 3.3 dB and Rx band rejection over 35 dB.

MEMS BASED BULK ACOUSTIC WAVE RESONATORS FOR MOBILE APPLICATIONS

ABSTRACT A silicon based film bulk acoustic wave resonator (FBAR) composed with a filter and a duplexer is fabricated using the bulk micro-machining process. It has a simple MIM (metal-insulator-metal) membrane structure using molybdenum (Mo) for the top and bottom electrodes. The bulk acoustic wave resonances are generated by the piezoelectricity of aluminum nitride (AlN) with an air gap cavity fabricated below the membrane by silicon deep-etch process to reduce acoustic loss of FBAR. The fabricated FBAR is measured with HP 8510C vector network analyzer in wide (0.5∼10.5 GHz) and narrow (1.7∼2.1 GHz) frequency range. The measured series and parallel resonance frequencies are 1856 MHz and 1907 MHz, respectively. The minimum insertion losses are less than 0.07 dB at the series resonance frequency. With the increase of the membrane area, insertion loss decreases and effective electromechanical coefficient increases. The measured effective electromechanical coefficients are higher than 6.4%. The circuit modeling of FBAR is preformed based on the MBVD (modified Butterworth Van-Dyke) model. The above results demonstrate that the fabricated FBAR has sufficient performance to be the building block of RF filters for mobile applications.