A novel N79 filter using solid-mounted A1-mode resonator for 5G applications

In this paper, the authors proposed a solid-mounted (SM)-type A1-mode resonator, with acoustic mirrors under LN plate, to simplify fabrication process and improve heat dissipation and TCF. By thickening SiO2 via adding about
${{}^{1}}\!/\!_{2}\ \lambda$
length of top mirror layer, almost zero TCF (−4 ppm/K) is obtained. Piston method is applied to suppress transverse mode. We designed full-band N79 filter with simulation considering both acoustic effect and electromagnetic effect. The filter achieves a maximum insertion loss level of 1.98 dB, and the rejections in N77 band, 5G WIFI and far band frequency are close to 30 dB. The return losses are better than 12 dB, without any external matching element. The packaged device occupies compact size of
$1100^{\star}900\ \mu\mathrm{m}^{2}$
using flip-chip assembly. Under large power (31 dBm), the solid-mounted device demonstrates more uniform temperature distribution and maximum lift is 180°C, about half lower than cavity-type device, showing advantageous in high power operation.