Bandwidth-tunable SAW filter based on wafer-level transfer-integration of BaSrTiO3 film for wireless LAN system using TV white space

Cognitive radio technology on TV white spaces has been promoted worldwide to solve the spectrum shortage problem due to the explosive increase in personal communication systems such as smartphones. One of the most difficult challenges to utilize TV white space for personal use is the miniaturization of frequency and bandwidth tunable filters to select vacant TV channels. We have developed a one-chip bandwidth tunable filter by wafer-level transfer-integration of BaSrTiO₃ (BST) film varactors and surface acoustic wave (SAW) resonators on a lithium tantalate wafer. The 3 dB bandwidth of the bandwidth tunable filter is tuned between 3.25 MHz and 6.25 MHz by applying 7V to the varactors, while the center frequency was constant at 1.004 GHz, as designed. These filters were installed in our developed prototype cognitive radio systems based on the IEEE802.11af draft and successfully demonstrated wireless LAN communication on TV frequency band.