Ferroelectric-on-Silicon Switchable Bulk Acoustic Wave Resonators and Filters for RF Applications

Currently, multiband wireless devices such as mobile phones are based on RF transceiver configurations where each frequency band utilizes its own RF front-end components. Future wireless mobile devices are expected to operate at a larger number of frequency bands; therefore, existing transceiver configurations become large in area and costly for future mobile devices. One of the key components in wireless mobile devices is the image reject and band selection filter. Today's mobile phones often utilize bulk acoustic wave (BAW) filters for this purpose. Currently, multiband transceivers use BAW filters in conjunction with solid-state or MEMS based RF switches for selecting frequency band of operation. Ferroelectric BST, operating at their paraelectric phase, have recently been utilized in designing intrinsically switchable BAW resonators and filters due to their voltage induced piezoelectricity. The intrinsically switchable BAW filters are suitable for designing compact multiband and frequency agile transceivers.
In this thesis, we propose utilizing composite structure to improve Q of intrinsically switchable BAW resonators. Record Q values are obtained in intrinsically switchable BAW resonators by using ferroelectric-on-silicon composite structure. In addition, in this thesis, two types of intrinsically switchable BAW filters are demonstrated using ferroelectric-on-silicon composite structure: electrically connected filters and laterally coupled acoustic filters. In the first part of this thesis, the design, fabrication and measurement results for high-Q composite film bulk acoustic resonators (FBARs) are discussed. Subsequently, an intrinsically switchable electrically connected filter based on ferroelectric-on-silicon composite FBARs is presented. Finally, an intrinsically switchable laterally coupled acoustic filter with a ferroelectric-on-silicon composite structure is presented.