High-Precision Flip-Chip Process Yields E-Band Harmonic Mixers with Potential Sub-10-dB Conversion Loss

A process in which discrete semiconductor chips are flip-attached by thermocompression bonding to 30-micron-diameter gold bumps on fine-featured passive integrated circuits was employed in the fabrication of diode subharmonic mixers for use over the 71-76 GHz and 81-86 GHz ranges. Incorporated in the substrate were high-precision grounded heat sinks, semi-lumped filters, and matching networks in low-loss microstrip format. Measurements show conversion loss minima of 12 dB, but the frequency response was impaired by inaccuracies in the filter design. Parasitics characteristic of flip-chip technology were not an impediment, and a mixer technology with high performance and low materials cost appears feasible