Acoustic Filters for 5G

The complexity of the RF Front-End Module has drastically increased by switching from 3G to 4G-5G, with more frequency bands, leading to a higher number of filters, integrated in a SiP with Power Amplifiers and RF switches. The highest part of the total cost in RF FEM comes from the filters (~72%), with innovation expected to reduce their cost, their size and fulfill more and more stringent specifications. To reach Gbps capacity and beyond, new bands from 3.3–4.2GHz and 4.4–5GHz (C-band) will be crucial to support most of 5G use scenarios in a wide area. A wider bandwidth at high frequency is a difficult challenge. Can we extend BAW filters operation to higher frequency? Aluminum Nitride (AlN), deposited by PVD, has been for a long time the material of choice for high frequency acoustic resonators. Nevertheless, acoustic properties degrade in case of thinner AlN films, which is mandatory to target higher frequencies. Furthermore, Physical Vapor Deposition (PVD) AlN films do not exhibit a high electro-acoustic coupling factor, limiting the bandwidth. This paper will cover 5G requirements and propose different potential solutions, with a special focus on material engineering to increase the bandwidth, highlighting the pros and cons.