An On-Chip Fractally Chipped FBAR Filter With Ba-Zn-Fe-Sc-O Thin Film in 5G-FR2 Millimeter-Wave Band
Xin Cao, Chenyi Wang, Weiping Li, Qiang‐Ming Cai
Abstract
In this letter, an on-chip bandwidth-agile film bulk acoustic resonator (FBAR) filter employing chipped fractal structure is proposed. First, by using the high longitudinal wave velocity of the BaZn2Fe <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{16}{-}{x}}$ </tex-math></inline-formula> ScxO27 (Ba-Zn-Fe-Sc-O) functional thin film, we have realized the resonant frequency in the millimeter wave region of the 5G-FR2 communication band. Then, in order to control the bandwidth of the proposed filter, we have proposed a fractal-shaped resonator topology with chipped sides. Two resonant modes with the resonant frequencies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{s{1}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{s{2}}$ </tex-math></inline-formula> have been produced. The frequency of the second mode <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{s{2}}$ </tex-math></inline-formula> can be determined accurately by the ratio of the fractally chipped sides. Thus, the bandwidth can be controlled by changing the ratios in the design process. The proposed filter is simulated and measured. The measured results are in good agreement with the simulated ones. The proposed filter can be applied in the millimeter wave band region of modern 5G communication systems.