Reconfigurable SAW Resonators and Tunable Filters Using Monolithically Integrated VO₂ Switches

This article presents novel reconfigurable surface acoustic wave (SAW) resonators using switching elements based on vanadium oxide (VO2) phase change material. The switching elements are integrated monolithically with the resonators on the same chip using an in-house fabrication process, which allows the compact implementation of the proposed reconfigurable resonators. The frequency of the resonator is tuned between two different states by changing the configuration of interdigitated electrodes within the SAW resonator and by using a set of tuning electrodes and VO2 switches. Experimental results are presented for the first reconfigurable resonator with six VO2 switching elements. The resonator is tuned from 700 to 720 MHz, while the quality factor is maintained above 350 over the tuning range. A second reconfigurable resonator with a modified structure is proposed to reduce the number of required VO2 switching elements for an even more compact implementation and reduction in the required dc power consumption. The second reconfigurable resonator based on a single VO2 switching element has a tuning range from 712 to 730 MHz and a quality factor better than 514. Design, implementation, and measurement results for tunable filters based on the proposed frequency tuning method are presented. A proof-of-concept six-pole tunable filter shows center frequency tuning from 944 to 971 MHz with a 36-MHz bandwidth and an insertion loss better than 3.6 dB over the tuning range. Another three-pole filter is implemented using the proposed reconfigurable resonators with monolithically integrated VO2 switches. The filter demonstrates a measured center frequency of 713 and 733 MHz for the low and high channels, respectively, while the insertion loss is better than 2.5 dB. High power and nonlinear test results are presented for both the reconfigurable resonators and filters. The monolithic integration of the VO2 switches with SAW resonators allows the practical implementation of higher order tunable SAW filters for wireless applications without any major performance degradation or increase in the size of the filter.