브래그 반사층 구조의 체적 탄성파 공진기와 필터의 이론적 분석

초록

Two configurations of FBAR with reflector layers and without reflector layers are theoretically analyzed using equivalent circuit and their characteristics discussed. It is assumed that ZnO is used for piezoelectric film, W and SiO2 are used for the reflector layer and Al is used for the electrode. Each layer is considered to have a acoustic propagation loss. ABCD parameters was picked out and input impedance was calculated by converting 3-port to 2-port of equivalent circuit. From the variation of resonance properties, Keff and electrical Q with the number of layer, Keff is not much affected by the number of layers but electrical Q increases with the number of layers when the number of layers is less than seven. The electrical Q is saturated when the numvber of layers become seven. Both Ladder filter and SCF (Stack Crystal Filter) show insertion loss decreases with the numver of layers but the bandwidth is not much affected by the number of layers. Ladder filter shows better skirt-selectivity characteristics in bandwidth but SCF show better characteristics in insertion. Characteristics S21 of SCF with SMR in spurious mode bandwidth in insertion shows increase over 40dB.