AlN Microresonator-Based Filters With Multiple Bandwidths at Low Intermediate Frequencies

Filters with various bandwidths at low intermediate frequency (IF) have been demonstrated using aluminum nitride (AlN) microresonator technology. Specifically, at 13 MHz, 6 kHz, and 25 kHz bandwidth filters were implemented using a single resonator topology, and 250 kHz and 500 kHz bandwidth filters were constructed via the parallel lattice topology using four sub-resonators and L-matching networks. The bandwidths of these filters are from 0.046% to 3.8%, and particularly the 500 kHz bandwidth filter at 13 MHz is wider than that of the resonator kt² limit (40 kHz). The 100x variations in filter percent bandwidth were realized in a 1700 nm-thick aluminum nitride film on the same wafer through CMOS-compatible fabrication processes. Changes in the filter termination for proper filter matching were implemented in the Agilent Genesys RF and microwave design simulation software using actual measured filter responses with 50 Ω termination. The great flexibility in filter bandwidths and resonant frequencies, as well as other benefits such as size, manufacturing cost, isolation, and insertion loss provided by AlN microresonators will enable next generation multi-band, multi-waveform, and cognitive radios for defense and consumer wireless applications.