Demonstration of Substrate-Embedded Nonreciprocal Millimeter-Wave Circulators For System-In-Packaging

This work reports a strontium hexaferrite (SrM)/polydimethylsiloxane (PDMS) nanocomposite based low-temperature packaging compatible process for a millimeter-wave full-duplex circulator, which affords simultaneous transmit and receive (STAR) at 35 GHz. Salient features include: 1) low-temperature (70°C) process for compatibility with organic board packaging and back-end semiconductor processes, 2) substrate embedded circulator architecture affording low profile and thus facilitating further 3D stacking and integration, 3) yet high power handling capability with 0.25 mm thick device size, and 4) batch-fabrication and manufacturability. The measurement results show state-of-the-art RF performance including a high return loss of > 23 dB, a reasonably low insertion loss of 3.9 dB, a large isolation of 12.8 dB, and a power handling of > 29 dBm.