Stopband filters built in the BAW technology [Application Notes]

This article presented the design of two band reject filters in the BAW technology. The two designs show different benefits. The ladder T topology has a better rejection bandwidth than the ladder topology because the bandwidth is controlled by resonance and antiresonance frequencies, which are selected by the loading layer. Moreover, the bandwidth is adjustable by the design. This setup presents a steeper rejection slope. The insertion loss can be reduced by increasing the bottom electrode's thickness. However, the fabrication process and the control of resonance frequency are more difficult since antiresonance frequencies of series resonators depend on the thickness of the loading layers.