Reconfigurable Radios Employing Ferroelectrics: Recent Progress on Reconfigurable RF Acoustic Devices Based on Thin-Film Ferroelectric Barium Strontium Titanate

Wireless communication has become an integral part of our lives, continuously improving the quality of our everyday activities. A multitude of functionalities are offered by recent generations of mobile phones, resulting in a significant adoption of wireless devices and a growth in data traffic, as reported by Ericsson [1] in Figure 1. To accommodate consumers' continuous demands for high data rates, the number of frequency bands allocated for communication by governments across the world has also steadily increased. Furthermore, new technologies, such as carrier aggregation and multiple-input/multiple-output have been developed. Today's mobile devices are capable of supporting numerous wireless technologies (i.e., Wi-Fi, Bluetooth, GPS, 3G, 4G, and others), each having its own designated frequency bands of operation. Bandpass filters, multiplexers, and switchplexers in RF transceivers are essential for the coexistence of different wireless technologies and play a vital role in efficient spectrum usage. Current mobile devices contain many bandpass filters and switches to select the frequency band of interest, based on the desired mode of operation, as shown in Figure 2. This figure presents a schematic of a generic RF front end for a typical mobile device, where a separate module is allocated for the filters. Each generation of mobile devices demands a larger number of RF filters and switches, and, with the transition toward 5G and its corresponding frequency bands, the larger number of required filters will only add to the challenges associated with cell-phone RF front-end design.