High-Performance N79 Band AlScN BAW Resonator and Filter With the Consideration of Area Effect

With the increase of operating frequency above 4 GHz, the required resonator size is reduced to hundreds of mu m(2), which is proportional to 1/f(2). In traditional, the size reduction of the resonator will induce its parallel resonant frequency decrease, thus resulting in the decrease of its effective coupling coefficient (k(t)(2)). Besides the parallel resonant frequency, we found that the serial resonant frequency of resonators working above 3 GHz also varies with its area size. However, this effect is not taken into account in conventional circuit models, leading to the failure of high-performance filter design. To address this issue, a modified Mason model of bulk acoustic wave (BAW) resonators was proposed in this work. Using the modified model, a high-performance N79 band (4.8-4.96 GHz) filter based on Al0.904Sc0.096N piezoelectric film was designed and fabricated, which achieved a minimum insertion loss of -0.93 dB and a bandwidth of 240 MHz. The power capacity and wire-bond package of BAW filters were further studied. The whole process of the Mason model modification, filter design, and fabrication pave the road for high-frequency filter applications.