Bandwidth-tunable filter consisting of SAW resonators and BaSrTiO3 varactors directly fabricated on a LiTaO3 wafer

A prototyped bandwidth-tunable filter consisting of SAW resonators and BaSrTiO3 (BST) varactors is discussed in this paper. In general, the BST varactors require high deposition temperature (>600°C) in order to obtain good varactor performances. Thus special cared wafer integration process of BST varactors onto a 42°YX-LiTaO
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wafer was newly developed to prevent performance deterioration in SAW resonators. The bandwidth-tunable filter composed of ten pieces of both surface acoustic wave (SAW) resonators and BST varactors on the 42°YX-LiTaO
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substrate was successfully fabricated using the integration process. The measured center frequency of the filter is 1GHz, and the 3dB bandwidth is electrically tuned from 4.5 to 9.6MHz by adjusting a DC supply voltage from 0 to 10V.