3D Heterogenous Integrated Wideband Switchable Bandpass Filter Bank for Millimeter Wave Applications

Abstract

This article proposes a three-dimensional heterogenous-integrated (3DHI) switchable bandpass filter bank with two independent wideband filter channels that cover 26–40 GHz and 32.5–40 GHz, respectively. An accurate wafer-level process with a high hollowed ratio of the applied 8-inch high-resistivity-silicon (HR-Si) interposer wafers is presented to form both compact filter channels. Above the interdigital filter patterns fabricated on the bottom interposer wafer, deep cavities are etched in the cap interposer wafer to improve the quality factor of the filter bank. Besides the cavities, the cap interposer wafer is 35% hollow inside, which two bare dies of GaAs single-pole double-throw (SPDT) switches and two thin film resistors are attached to the bottom interposer after the wafer-to-wafer (W2W) bonding. To ensure good out-of-band performance, a 3D EM co-simulation of the switch layout at the chip level and filter patterns at the package level is applied. Measurement results show that the switchable filter bank achieves a high isolation of 50 dB and a competitive shape factor (BW30dB/BW3dB) of about 1.3. In addition, the size of the switchable filter bank is only 7.0 mm × 3.5 mm × 0.6 mm, and the weight is only 0.1 g.