Advanced AlN-based bulk acoustic wave filters on trap-rich/Si substrate

Abstract The thin film bulk acoustic wave resonators (FBARs) on high-resistance (HR) silicon substrates suffer from reduced electrical performance due to parasitic surface conductivity (PSC) and decrease acoustic performance from energy leakage at cavity edges. In this work, the FBARs with excellent quality factor (Q) are fabricated on trap-rich (TR) silicon substrate. For comparison, the 8-inch HR silicon and HR silicon with 1.5/2.5 μm TR layer are used to fabricate FBAR devices. The introduction of the TR layer effectively suppresses the PSC effect on the substrate surface, significantly enhancing the Qs of the device. Additionally, the TR layer reduces energy leakage into the substrate, further improving the Qp. Compared with conventional HR substrate devices, devices with TR layer substrates show an increase in Qs from 913 to 1619 and in Qp from 2183 to 2496.The calculated figure of merit (Qp×K2eff) of the FBAR with PVD AlN reaches 144. The filter based on TR substrate with a center frequency of 2.44 GHz features a minimum insertion loss (IL) of 0.74 dB. Compared to the filter on the HR substrate, it shows an improvement of about 0.5 dB in in-band IL. Overall, the FBAR devices on TR substrate show great potential for high-Q and low insertion loss application in RF fields.