Bandpass filters for 8 GHz using solidly mounted bulk acoustic wave resonators

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 52; no. 6; pp. 936 - 946
• Main Authors: Lanz, R., Muralt, P.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.06.2005; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustics; Aluminum; Aluminum nitride; Bandpass filters; Bandwidth; Bypasses; Channels; Exact sciences and technology; Fundamental areas of phenomenology (including applications); General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Noise levels; Physics; Resonators; Thin films; Transducers; Ultrasonics, quantum acoustics, and physical effects of sound; Acoustic wave device; Acoustic wave resonator; Thin film device; Texturation; Aluminium nitride; Bulk wave; Bragg grating; Modeling; Tuning; Thin film; Antiresonance; Ladder circuit; Frequency shift; Silicon oxides; Resonance frequency; Insertion loss; Band pass filter; Series resistance; Group delay
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2005.1504014

Frequency shift, design, and fabrication issues have been investigated for the realization of 8 GHz bandpass filters based on AlN thin film bulk acoustic wave resonators. Fabrication includes well-textured AlN thin films on Pt (111) electrodes and SiO/sub 2//AlN Bragg gratings for the solidly mounted resonators. The chosen ladder filter design requires the tuning of the shunt resonators with respect to the series one. For this purpose, mass loading of the shunt resonators with aluminum (Al) and SiO/sub 2/ were studied. Design simulations showed that the channel bandwidth can be doubled by shifting more than the difference of resonance and antiresonance frequency. Bandpass filters at 8 GHz were successfully fabricated with -5.5 dB insertion loss, -26 dB out-of-band rejection, 99 MHz (1.2%) /spl plusmn/0.2 dB channel bandwidth, and 224 MHz (2.8%) 3 dB bandwidth. The group delay variations within any 30 MHz channel inside the channel bandwidth amounts to <0.2 ns. Comparisons with simulation calculations and single resonator characteristics show that each /spl pi/-section includes a parasitic series resistance and inductance.