Ultra-miniature coupled resonator filter with single-layer acoustic coupler
Tiberiu Jamneala, Uli B. Koelle, A. Shirakawa, Stephen R. Gilbert, Phil Nikkel, C. Feng, Rich Ruby · IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control · 2009
Coupled resonator filters designed using a single-layer coupler require coupling materials with an acoustic impedance less than 5.0 MRayl. Carbon-doped oxide, with an acoustic impedance of 4.8 MRayl and an acoustic attenuation of 200 to 600 dB/cm at 1 GHz, can be used as a single-layer coupler to produce a competitive 2-stage coupled resonator filter for cellular handset applications in the gigahertz frequency range. The electrical response of our filter is superior to that of coupled resonator filters using a traditional acoustic mirror as the coupling element. We present an ultra-miniature 0.58 mm x 0.38 mm coupled resonator filter operating at a frequency of 2.15 GHz.