Wideband Switchable Sharp-Rejection Filter in Compact 3-D Heterogeneous Integration

A switchable bandstop filter (BSF) bank in 3-D heterogeneous integration is presented in this article for multiband applications. Compared with conventional filter banks, the proposed design features wide bandwidth, sharp skirts, compact size, and high integration. In the proposed BSF, double short-ended coupling lines are introduced to expand the operation bandwidth with sharp rejection. Moreover, to significantly reduce the size of the proposed BSFs, an in-house silicon micromachining process is developed to heterogeneously integrate two stacked BSFs with switches by through-silicon vias (TSVs). To experimentally validate the proposed configuration, a two-channel switchable BSF bank is designed, fabricated, and measured. The measured results show a tuning range of 7.95–12.3 GHz (43%), a maximum bandwidth of 30%, and a sharp stopband rejection of 50 dB. These results agree well with simulation. Moreover, the fabricated prototype is only 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 8\times $ </tex-math></inline-formula> 1 mm3, whereas a typical industrial counterpart is around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$86\times 74\times18$ </tex-math></inline-formula> mm3, i.e., the size is significantly reduced to 1‱. To the best of the authors’ knowledge, this is the first demonstration of a wideband switchable sharp-rejection BSF chip fully integrated in the TSV process.