Broadband Interconnect and Assembly for Sub-THz Heterogeneous Integration

This work presents three complementary broadband packaging and interconnect technologies for heterogeneous sub-terahertz (sub-THz) integration. First, an indium bump flip-chip process is implemented within a 35 nm InGaAs mHEMT technology, enabling low-parasitic assembly of monolithically integrated front-ends or standalone MMICs on interposer. The bumps exhibit uniform reflowed geometries, provide efficient thermal conduction, and achieve low DC chain resistances with shear forces within 3.6-5.6 mN per bump. Second, a spray-coated polymer process is developed for side-by-side hybrid integration of InGaAs mHEMT and SiGe BiCMOS chips or InGaAs mHEMT MMICs and fused silica interposer. The conformal dielectric coating supports chip-to-chip transitions with resistance well below 1 Ω up to at least 320 GHz. Finally, a sub-THz on-chip antenna combining a metastructured high-impedance ground, fused-silica dielectric resonator, and diamond anti-reflection layer achieves a measured 25% impedance bandwidth and directivity exceeding 10 dBi (27 dBi with a polypropylene lens). Together, these results demonstrate a scalable sub-THz packaging strategy supporting broadband radiation, low interconnect loss, and dense multi-channel integration for next-generation high-resolution radar and ultra-high data-rate communication front-ends.