Fabrication of a Low insertion loss intrinsically switchable BAW filter based on BST FBARs

Abstract

A Low insertion loss (IL) 1.5 stage H'-network ladder type intrinsically switchable bulk acoustic wave (BAW) filter based on barium strontium titanate (Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) thin film bulk acoustic resonators (FBARs) is presented. The filter is designed and fabricated based on switchable BST FBARs with Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> =300 and K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> =6%. When a DC bias is applied to the FBARs, the switchable filter is in its ON state and provides an insertion loss of 2.25 dB with 3-dB bandwidth of 58 MHz at 2.08 GHz center frequency. The switchable BST filter presented in this paper provides the lowest IL as compared to the previously reported BST filters.